ASTM C1470-20

Standard Guide for Testing the Thermal Properties of Advanced Ceramics

SIGNIFICANCE AND USE
5.1 The high-temperature capabilities of advanced ceramics are a key performance benefit for many demanding engineering applications. In many of those applications, advanced ceramics will have to perform across a broad temperature range. The thermal expansion, thermal diffusivity/conductivity, specific heat, and emittance/emissivity are crucial engineering factors in integrating ceramic components into aerospace, automotive, and industrial systems.  
5.2 This guide is intended to serve as a reference and information source for testing the thermal properties of advanced ceramics, based on an understanding of the relationships between the composition and microstructure of these materials and their thermal properties.  
5.3 The use of this guide assists the testing community in correctly applying the ASTM thermal test methods to advanced ceramics to ensure that the thermal test results are properly measured, interpreted, and understood. This guide also assists the user in selecting the appropriate thermal test method to evaluate the particular thermal properties of the advanced ceramic of interest.  
5.4 The thermal properties of advanced ceramics are critical data in the development of ceramic components for aerospace, automotive, and industrial applications. In addition, the effect of environmental exposure on thermal properties of the advanced ceramics must also be assessed.
SCOPE
1.1 This guide covers the thermal property testing of advanced ceramics, to include monolithic ceramics, particulate/ whisker-reinforced ceramics, and continuous fiber-reinforced ceramic composites. It is intended to provide guidance and information to users on the special considerations involved in determining the thermal properties of these ceramic materials.  
1.2 Five thermal properties (specific heat capacity, thermal conductivity, thermal diffusivity, thermal expansion, and emittance/emissivity) are presented in terms of their definitions and general test methods. The relationship between thermal properties and the composition, microstructure, and processing of advanced ceramics (monolithic and composite) is briefly outlined, providing guidance on which material and specimen characteristics have to be considered in evaluating the thermal properties of advanced ceramics. Additional sections describe sampling considerations, test specimen preparation, and reporting requirements.  
1.3 Current ASTM test methods for thermal properties are tabulated in terms of test method concept, testing range, specimen requirements, standards/reference materials, capabilities, limitations, precision, and special instructions for monolithic and composite ceramics.  
1.4 This guide is based on the use of current ASTM standards for thermal properties, where appropriate, and on the development of new test standards, where necessary. It is not the intent of this guide to rigidly specify particular thermal test methods for advanced ceramics. Guidance is provided on how to utilize the most commonly available ASTM thermal test methods, considering their capabilities and limitations.  
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. See IEEE/ASTM SI 10.  
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Dec-2019
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: C28 - Advanced Ceramics
• Drafting Committee: C28.03 - Physical Properties and Non-Destructive Evaluation

Relations

• Replaces: ASTM C1470-06(2013) - Standard Guide for Testing the Thermal Properties of Advanced Ceramics
• Effective Date: 01-Jan-2020
• Refers: ASTM C168-24 - Standard Terminology Relating to Thermal Insulation
• Effective Date: 15-Apr-2024
• Refers: ASTM C1130-24 - Standard Practice for Calibration of Thin Heat Flux Transducers
• Effective Date: 15-Mar-2024
• Refers: ASTM C1044-24 - Standard Practice for Using a Guarded-Hot-Plate Apparatus or Thin-Heater Apparatus in the Single-Sided Mode
• Effective Date: 01-Mar-2024
• Refers: ASTM E1142-23b - Standard Terminology Relating to Thermophysical Properties
• Effective Date: 01-Oct-2023
• Refers: ASTM E473-23b - Standard Terminology Relating to Thermal Analysis and Rheology
• Effective Date: 01-Oct-2023
• Refers: ASTM C714-23 - Standard Guide for Thermal Diffusivity of Carbon and Graphite by Thermal Pulse Method
• Effective Date: 01-Oct-2023
• Refers: ASTM C767-20 - Standard Test Method for Thermal Conductivity of Carbon Refractories
• Effective Date: 01-Apr-2020
• Refers: ASTM E423-71(2019) - Standard Test Method for Normal Spectral Emittance at Elevated Temperatures of Nonconducting Specimens
• Effective Date: 01-Oct-2019
• Refers: ASTM E408-13(2019) - Standard Test Methods for Total Normal Emittance of Surfaces Using Inspection-Meter Techniques
• Effective Date: 01-Oct-2019
• Refers: ASTM C1145-19 - Standard Terminology of Advanced Ceramics
• Effective Date: 01-Jul-2019
• Refers: ASTM E831-19 - Standard Test Method for Linear Thermal Expansion of Solid Materials by Thermomechanical Analysis
• Effective Date: 01-Apr-2019
• Refers: ASTM C202-19 - Standard Test Method for Thermal Conductivity of Refractory Brick
• Effective Date: 01-Apr-2019
• Refers: ASTM C182-19 - Standard Test Method for Thermal Conductivity of Insulating Firebrick
• Effective Date: 01-Apr-2019
• Refers: ASTM C1045-19 - Standard Practice for Calculating Thermal Transmission Properties Under Steady-State Conditions
• Effective Date: 01-Apr-2019

Overview

ASTM C1470-20: Standard Guide for Testing the Thermal Properties of Advanced Ceramics provides a comprehensive framework for assessing the thermal behavior of advanced ceramics in engineering applications. Published by ASTM International, this standard offers guidelines for evaluating five key thermal properties: specific heat capacity, thermal conductivity, thermal diffusivity, thermal expansion, and emittance/emissivity. It applies to monolithic ceramics, particulate/whisker-reinforced ceramics, and continuous fiber-reinforced ceramic composites. This document is vital for industries such as aerospace, automotive, and industrial manufacturing, where advanced ceramics must withstand wide temperature ranges and environmental exposure.

Key Topics

• Thermal Property Definitions and Test Methods

  • Specific heat capacity: Measurement of energy required to raise temperature per unit mass.
  • Thermal conductivity: Rate of heat flow through materials, important for thermal insulation or conduction.
  • Thermal diffusivity: Rate of temperature change under transient conditions.
  • Thermal expansion: Change in material dimension with temperature fluctuations.
  • Emittance/emissivity: Radiative properties affecting heat transfer at high temperatures.

• Material Characterization

  • Importance of detailed documentation of composition, microstructure, processing history, and environmental exposure.
  • Assessment of anisotropy and spatial variations, especially in composites.
  • Effects of porosity, grain structure, phase changes, and impurities on thermal properties.

• Guide for Test Method Selection

  • Utilizes current ASTM methods where applicable.
  • Offers strategies for selecting the appropriate method based on material and property of interest.
  • Considers precision, limitations, specimen requirements, and capabilities for both monolithic and composite ceramics.

• Practical Considerations in Testing

  • Guidance on sampling, specimen preparation, and reporting.
  • Emphasis on test conditions such as temperature range, heating/cooling rates, and atmosphere to ensure valid and reproducible results.

Applications

ASTM C1470-20 enhances thermal property evaluation for advanced ceramics used in:

• Aerospace: High-temperature components, thermal protection systems, and insulating elements.
• Automotive: Engine components, heat shields, and exhaust systems benefiting from controlled thermal expansion and high thermal conductivity.
• Industrial Manufacturing: Furnace linings, cutting tools, and insulation requiring reliable measurement and prediction of ceramic performance under varying thermal conditions.
• Research and Development: Material scientists and engineers designing advanced ceramic materials for next-generation applications benefit from standardized, repeatable testing procedures.

Correct thermal property data is essential for integrating advanced ceramics in systems requiring stability, performance, and longevity in harsh environments. The guide ensures results are valid, reducing risk of component failure due to inaccurate data and supporting effective material selection and system design.

Related Standards

ASTM C1470-20 references and aligns with key ASTM standards for thermal properties of ceramics and related materials, including:

• Specific Heat Capacity

  • ASTM E1269: Differential Scanning Calorimetry
  • ASTM E2716: Sinusoidal Modulated Temperature Differential Scanning Calorimetry

• Thermal Conductivity

  • ASTM C177: Guarded-Hot-Plate Apparatus
  • ASTM C201: Thermal Conductivity of Refractories
  • ASTM E1225: Guarded-Comparative-Longitudinal Heat Flow

• Thermal Expansion

  • ASTM C372: Dilatometer Method
  • ASTM E228: Push-Rod Dilatometer

• Thermal Diffusivity

  • ASTM E1461: Flash Method
  • ASTM E2585: Flash Method Procedures

• Emittance/Emissivity

  • ASTM E408: Inspection-Meter Techniques
  • ASTM E423: Spectral Emittance at Elevated Temperatures

Referencing these standards gives laboratories and manufacturers a reliable, internationally recognized foundation for accurate thermal testing of advanced ceramics.

---

By following the guidelines in ASTM C1470-20, organizations ensure consistency, accuracy, and reliability in measuring and interpreting the thermal properties of advanced ceramics, supporting innovation and safety in high-performance applications.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1470 − 20
Standard Guide for
Testing the Thermal Properties of Advanced Ceramics
This standard is issued under the fixed designation C1470; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.1 This guide covers the thermal property testing of ad-
1.7 This international standard was developed in accor-
vanced ceramics, to include monolithic ceramics, particulate/
dance with internationally recognized principles on standard-
whisker-reinforced ceramics, and continuous fiber-reinforced
ization established in the Decision on Principles for the
ceramic composites. It is intended to provide guidance and
Development of International Standards, Guides and Recom-
information to users on the special considerations involved in
mendations issued by the World Trade Organization Technical
determining the thermal properties of these ceramic materials.
Barriers to Trade (TBT) Committee.
1.2 Five thermal properties (specific heat capacity, thermal
conductivity, thermal diffusivity, thermal expansion, and 2. Referenced Documents
emittance/emissivity)arepresentedintermsoftheirdefinitions 2
2.1 ASTM Standards:
and general test methods. The relationship between thermal
2.1.1 Specific Heat:
propertiesandthecomposition,microstructure,andprocessing
C351Test Method for Mean Specific Heat of Thermal
of advanced ceramics (monolithic and composite) is briefly
Insulation (Withdrawn 2008)
outlined, providing guidance on which material and specimen
D2766Test Method for Specific Heat of Liquids and Solids
characteristics have to be considered in evaluating the thermal
(Withdrawn 2018)
properties of advanced ceramics. Additional sections describe
E1269Test Method for Determining Specific Heat Capacity
samplingconsiderations,testspecimenpreparation,andreport-
by Differential Scanning Calorimetry
ing requirements.
E2716Test Method for Determining Specific Heat Capacity
1.3 Current ASTM test methods for thermal properties are by Sinusoidal Modulated Temperature Differential Scan-
tabulated in terms of test method concept, testing range, ning Calorimetry
specimen requirements, standards/reference materials, 2.1.2 Thermal Conductivity:
capabilities, limitations, precision, and special instructions for C177Test Method for Steady-State Heat Flux Measure-
monolithic and composite ceramics. ments and Thermal Transmission Properties by Means of
the Guarded-Hot-Plate Apparatus
1.4 This guide is based on the use of current ASTM
C182Test Method for Thermal Conductivity of Insulating
standardsforthermalproperties,whereappropriate,andonthe
Firebrick
development of new test standards, where necessary. It is not
C201Test Method forThermal Conductivity of Refractories
theintentofthisguidetorigidlyspecifyparticularthermaltest
C202Test Method for Thermal Conductivity of Refractory
methods for advanced ceramics. Guidance is provided on how
Brick
to utilize the most commonly available ASTM thermal test
C408Test Method for Thermal Conductivity of Whiteware
methods, considering their capabilities and limitations.
Ceramics
1.5 The values stated in SI units are to be regarded as
C518Test Method for Steady-State Thermal Transmission
standard. No other units of measurement are included in this
Properties by Means of the Heat Flow Meter Apparatus
standard. See IEEE/ASTM SI10.
C767Test Method for Thermal Conductivity of Carbon
1.6 This standard does not purport to address all of the Refractories
safety concerns, if any, associated with its use. It is the
C1044Practice for Using a Guarded-Hot-PlateApparatus or
responsibility of the user of this standard to establish appro- Thin-Heater Apparatus in the Single-Sided Mode
1 2
This guide is under the jurisdiction of ASTM Committee C28 on Advanced For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Ceramics and is the direct responsibility of Subcommittee C28.03 on Physical contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Properties and Non-Destructive Evaluation. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Jan. 1, 2020. Published January 2020. Originally the ASTM website.
approved in 2000. Last previous edition approved in 2013 as C1470–06 (2013). The last approved version of this historical standard is referenced on
DOI: 10.1520/C1470-20. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1470 − 20
C1045Practice for Calculating Thermal Transmission Prop- IEEE/ASTM SI10American National Standard for Metric
erties Under Steady-State Conditions Practice
C1113/C1113MTest Method for Thermal Conductivity of
3. Terminology
RefractoriesbyHotWire(PlatinumResistanceThermom-
eter Technique)
3.1 Definitions:
C1114Test Method for Steady-State Thermal Transmission
3.1.1 advanced ceramic, n—a highly engineered, high-
Properties by Means of the Thin-Heater Apparatus
performance, predominantly nonmetallic, inorganic, ceramic
C1130Practice for Calibration of Thin Heat Flux Transduc-
material having specific functional attributes. (C1145)
ers
3.1.2 ceramic matrix composite, n—a material consisting of
E1225Test Method for Thermal Conductivity of Solids
two or more materials (insoluble in one another), in which the
Using the Guarded-Comparative-Longitudinal Heat Flow
majorcontinuouscomponent(matrixcomponent)isaceramic,
Technique
whilethesecondarycomponent/s(reinforcingcomponent)may
E1530Test Method for Evaluating the Resistance to Ther-
be ceramic, glass-ceramic, glass, metal, or organic in nature.
mal Transmission by the Guarded Heat Flow Meter
These components are combined on a macroscale to form a
Technique
useful engineering material possessing certain properties or
2.1.3 Thermal Expansion:
behavior not possessed by the individual constituents. (C1145)
C372Test Method for Linear Thermal Expansion of Porce-
–1
3.1.3 coeffıcient of linear thermal expansion,α[T ],n—the
lainEnamelandGlazeFritsandFiredCeramicWhiteware
change in length, relative to the length of the specimen,
Products by the Dilatometer Method
accompanying a unit change of temperature, at a specified
C1300Test Method for Linear Thermal Expansion of Glaze
temperature. (This property can also be considered the instan-
Frits and Ceramic Whiteware Materials by the Interfero-
taneous expansion coefficient or the slope of the tangent to the
metric Method
∆L/L versus T curve at a given temperature.) (E1142)
E228Test Method for Linear Thermal Expansion of Solid
3.1.4 continuous fiber-reinforced ceramic composite
Materials With a Push-Rod Dilatometer
(CFCC), n—aceramicmatrixcompositeinwhichthereinforc-
E289Test Method for Linear Thermal Expansion of Rigid
ing phase(s) consists of continuous filaments, fibers, yarns, or
Solids with Interferometry
knitted or woven fabric. (C1145)
E831Test Method for Linear Thermal Expansion of Solid
3.1.5 differential scanning calorimetry (DSC), n—a tech-
Materials by Thermomechanical Analysis
nique in which the difference in energy inputs into a test
2.1.4 Thermal Diffusivity:
specimen and a reference material is measured as a function of
C714Test Method for Thermal Diffusivity of Carbon and
temperature while the test specimen and reference material are
Graphite by Thermal Pulse Method
subjected to a controlled temperature program. (E1269)
D4612Test Method for Calculating Thermal Diffusivity of
Rock and Soil
3.1.6 discontinuous fiber-reinforced ceramic composite,
E1461Test Method for Thermal Diffusivity by the Flash n—a ceramic matrix composite reinforced by chopped fibers.
Method (C1145)
E2585PracticeforThermalDiffusivitybytheFlashMethod
3.1.7 emittance (emissivity), ε (nd), n—the ratio of the
2.1.5 Emittance/Emissivity:
radiant flux emitted by a specimen per unit area to the radiant
E408Test Methods for Total Normal Emittance of Surfaces
flux emitted by a black body radiator at the same temperature
Using Inspection-Meter Techniques
and under the same conditions. Emittance ranges from 0 to 1,
E423Test Method for Normal Spectral Emittance at El-
with a blackbody having an emittance of 1.00. (E423)
evated Temperatures of Nonconducting Specimens
3.1.8 linear thermal expansion, [nd],n—the change in
2.1.6 General Standards:
length per unit length resulting from a temperature change.
C168Terminology Relating to Thermal Insulation
Linear thermal expansion is symbolically represented by ∆L/
C373Test Methods for Determination of Water Absorption
L , where ∆L is the observed change in length ∆L=L – L ,
0 2 1
andAssociated Properties byVacuum Method for Pressed
and L , L , and L are the lengths of the specimen at reference
0 1 2
Ceramic Tiles and Glass Tiles and Boil Method for
temperature T and test temperatures T and T . (E228)
0 1 2
Extruded Ceramic Tiles and Non-tile Fired Ceramic
–1
3.1.9 mean coeffıcient of linear thermal expansion, α [T ],
L
Whiteware Products
n—the change in length, relative to the length of the specimen,
C1045Practice for Calculating Thermal Transmission Prop-
accompanying a unit change of temperature measured across a
erties Under Steady-State Conditions
specified temperature range (T to T ). (C372)
1 2
C1145Terminology of Advanced Ceramics
3.1.10 particulate-reinforced ceramic matrix composite,
E122PracticeforCalculatingSampleSizetoEstimate,With
n—a ceramic matrix composite reinforced by ceramic
Specified Precision, the Average for a Characteristic of a
particulates. (C1145)
Lot or Process
–1 –2 –1
E473Terminology Relating to Thermal Analysis and Rhe- 3.1.11 specific heat (specific heat capacity), C[mL T θ ],
ology
n—the quantity of heat required to provide a unit temperature
E1142Terminology Relating to Thermophysical Properties increase to a unit mass of material. (E1142)
C1470 − 20
–1 –1
3.1.12 thermal conductivity, λ [mLT θ ],n—the time rate 5.4 Thethermalpropertiesofadvancedceramicsarecritical
of heat flow, under steady conditions, through unit area, per data in the development of ceramic components for aerospace,
unit temperature gradient in the direction perpendicular to the automotive, and industrial applications. In addition, the effect
area. (C168) of environmental exposure on thermal properties of the ad-
2 –1
vanced ceramics must also be assessed.
3.1.13 thermal diffusivity, [L T ],n—the property given by
the thermal conductivity divided by the product of the bulk
6. Procedure
density and heat capacity per unit mass. (C168)
3.1.14 thermodilatometry, n—atechniqueinwhichadimen- 6.1 ReviewSections7–10tobecomefamiliarwiththermal
property concepts and thermal testing issues for advanced
sion of a test specimen under negligible applied force is
ceramics, specimen preparation guidance, and reporting rec-
measured as a function of temperature while the test specimen
is subjected to a controlled temperature program in a specified ommendations.
atmosphere. (E473)
6.2 Review the test method text and tables in Section 11 for
3.2 Units for Thermal Properties: the property you need to determine. Use the text and tables to
help select the most appropriate ASTM test method for
Property SI Units Abbreviation
Specific heat capacity joules/(gram-kelvin) J/(g·K)
evaluating the thermal property of interest for the specific
Thermal Conductivity watts/(metre-kelvin) W/(m·K)
advanced ceramic.
2 2
Thermal diffusivity metre/second m/s
–1
Coefficient of Thermal metre/(metre-kelvin) K
6.3 Performthethermalpropertytestinaccordancewiththe
Expansion
selected ASTM test method, but refer back to the guide for
Emittance/emissivity no dimensions —
directions and recommendations on material characterization,
4. Summary of Guide
sampling procedures, test specimen preparation, and reporting
4.1 Five thermal properties (specific heat capacity, thermal
results.
conductivity, thermal diffusivity, thermal expansion, and
emittance/emissivity)arepresentedintermsoftheirdefinitions
7. Thermal Properties and Their Measurement
and general test methods. The relationship between thermal
7.1 Specific Heat Capacity:
propertiesandthecomposition,microstructure,andprocessing
7.1.1 Specificheatcapacityistheamountofenergyrequired
of advanced ceramics is briefly outlined, providing guidance
to increase the temperature by one unit for a unit mass of
on which material characteristics have to be considered in
material.Itisafundamentalthermalpropertyforengineersand
evaluating the thermal properties.Additional sections describe
scientists in determining the temperature response of materials
samplingconsiderations,testspecimenpreparation,andreport-
tochangesinheatfluxandthermalconditions.TheSIunitsfor
ing requirements.
specific heat capacity are joules/(gram·K). Since the specific
4.2 Current ASTM test methods for thermal properties are
heat capacity changes with temperature, a specific heat capac-
tabulated in terms of test method concept, testing range,
ity value must always be associated with a specific test
specimen requirements, standards/reference materials,
temperature or temperature range.
capabilities, limitations, precision, and special instructions for
7.1.2 Specific heat capacity is commonly measured by
monoliths and composites.
calorimetry in which changes in thermal energy are measured
against changes in temperature. The two common calorimetry
5. Significance and Use
methods are differential scanning calorimetry and drop calo-
5.1 The high-temperature capabilities of advanced ceramics
rimetry.
areakeyperformancebenefitformanydemandingengineering
7.1.3 Differential scanning calorimetry heats the test mate-
applications.Inmanyofthoseapplications,advancedceramics
rial at a controlled rate in a controlled atmosphere through the
will have to perform across a broad temperature range. The
temperature region of interest. The heat flow into the test
thermal expansion, thermal diffusivity/conductivity, specific
material is compared to the heat flow into a reference material
heat, and emittance/emissivity are crucial engineering factors
to determine the energy changes in the test material as a
in integrating ceramic components into aerospace, automotive,
function of temperature.
and industrial systems.
7.1.4 In drop calorimetry, the test sample is heated to the
5.2 This guide is intended to serve as a reference and
desired temperature and then immersed in an instrumented,
information source for testing the thermal properties of ad-
liquid-filled container (calorimeter), which reaches thermal
vanced ceramics, based on an understanding of the relation-
equilibrium. The increase in temperature of the calorimeter
ships between the composition and microstructure of these
liquid/container is a measure of the amount of heat in the test
materials and their thermal properties.
specimen.
5.3 The use of this guide assists the testing community in 7.1.5 In any calorimetry test, the experimenter must recog-
correctlyapplyingtheASTMthermaltestmethodstoadvanced nize that phase changes and other thermo-physical transforma-
ceramics to ensure that the thermal test results are properly tions in the material will produce exothermic and endothermic
measured, interpreted, and understood. This guide also assists events which will be captured in the test data. The thermal
the user in selecting the appropriate thermal test method to events must be properly identified and understood within the
evaluate the particular thermal properties of the advanced context of the material properties, chemistry, and phase com-
ceramic of interest. position across the temperature range of interest.
C1470 − 20
7.2 Thermal Conductivity: the thermal expansion is different along the different crystal
7.2.1 Thermal conductivity is a measurement of the rate of axes.(Thisisofparticularconcernforsinglecrystalspecimens
heat flow through a material for a given temperature gradient. and for specimens with oriented grain structures.) For some
It is normalized for thickness and cross-sectional area to give specificceramics(cordierite,aluminumtitanate,andzirconium
a material-specific value. The thermal conductivity of a ce- phosphate), the thermal expansion may be zero or negative in
ramic is used in determining the effectiveness of a ceramic certain crystal axes in specific temperature regimes.
either as a thermal insulator or as a thermal conductor. The SI
7.3.3 The quantitative determination of the change in di-
unitsforthermalconductivityarewatts/(metre·kelvin).Aswith
mension as a function of temperature is defined as the mean
other thermal properties, thermal conductivity changes with
coefficient of linear thermal expansion – the ratio of a given
temperature, so that a specific thermal conductivity value for a
change in length per unit length for a specimen for a specific
material must be associated with a specific test temperature.
change in temperature as follows:
7.2.2 In electrically nonconductive ceramics, thermal con-
α 5 @~L 2 L !/~T 2 T !#/L (3)
2 1 2 1 1
ductivity occurs by lattice vibration (phonon) conductivity and
where:
by radiation (photon) at higher temperatures (>500°C). Ther-
mal conductivity decreases when the mean free path of the
L and L = lengths of the test specimen at test temperatures
1 2
phonons and photons decreases. Lattice imperfections, differ-
T and T , respectively, where T > T .
1 2 2 1
ences in atomic weight between anions and cations, non-
7.3.4 The units for mean coefficient of linear thermal
stoichiometric compositions, solid solutions, amorphous
expansion are metres/(metre·K).The mean coefficient of linear
atomic structures, porosity, and grain boundaries all act as
thermal expansion for a material has to be defined for a given
scattering sites for phonons and reduce the thermal conductiv-
–6
temperature range, for example,7×10 m/(m·K) for 25 to
ity of the material.
500°C.
7.2.3 Thermal conductivity is commonly measured by
7.3.5 The mean coefficient of linear thermal expansion
steady-state methods, that is, cut bar comparative techniques,
across a temperature range is different than the instantaneous
heat flow meter techniques, guarded hot-plate/heater/hot-wire
coefficient of thermal expansion, which is the tangent slope at
techniques, and calorimetry techniques. It can also be deter-
a specific temperature for the expansion-temperature curve of
mined by transient techniques (hot wire and flash diffusivity).
the sample.
7.2.4 In cut bar comparative heat flow techniques, the test
7.3.6 Thermal expansion is commonly measured by
specimen is subjected to a known heat flow and the tempera-
thermodilatometry,atechniqueinwhichaknowndimensionof
ture differential/s are measured across the dimension/s of
a test specimen under negligible applied force is measured as
interest. The entire test system with the test specimen is
a function of temperature while the specimen is subjected to a
configured with insulation and heaters to minimize heat flow
controlled-temperatureprograminaspecifiedatmosphere.The
perpendicular to the direction of interest. In the heat flowmeter
measurement of the dimensional change can be done by direct
technique, the heat flow in the test is measured by a calibrated
mechanical measurement or by optical techniques (interferom-
heat flux transducer without the use of direct reference mate-
etry and optical lever).
rials in the test system. In both techniques, the thermal
conductivity of the material is then calculated as follows: 7.3.7 Different crystalline phases in ceramics have different
thermal expansion characteristics. Major phase changes in
λ 5 q ∆ L/~∆ T! (1)
ceramicscangiveabruptorprogressivechangesinlengthwith
where:
increasing or decreasing temperature and may cause confusion
λ = thermal conductivity, whenincludedinoverallexpansionmeasurements.Inasimilar
q = heat flow/unit area,
manner, crystallization and changes in amorphous, glassy
∆L = distance across which the temperature difference is
phasesinceramicscanproducemarkedchangesinthethermal
measured, and
expansion over specific temperature regimes.
∆T = measured temperature difference.
7.3.8 Thermal expansion measurements for ceramics often
Thermal conductivity (λ) can be calculated from thermal show heating/cooling hysteresis when microcracking or minor
diffusivity measurements, using the specific heat capacity and
phase changes occur. There are also irreversible thermal
the material density as follows: expansion effects, based on annealing, heating rate, creep,
crystallization, or microcracking. Thermal expansion tests
λ 5thermaldiffusivity 3specificheatcapacity 3density (2)
doneonlyonheatingcanbemisleading,andthermalexpansion
7.3 Thermal Expansion (Thermodilatometry):
measurements should be done under both heating and cooling
7.3.1 All materials expand or contract with changes in
conditions.
temperature, with most materials expanding with increasing
7.4 Thermal Diffusivity:
temperature. Thermal expansion is often very important in
engineering applications, because differences in thermal ex-
7.4.1 Thermal diffusivity is a measurement of the rate of
pansion between fitted or bonded components can produce temperature change in a material measured under transient
thermal stresses, leading to component failure.
conditions.Itisdefinedastheratioofthethermalconductivity
7.3.2 The thermal expansion for a given ceramic composi- to the “specific heat capacity per unit volume” (which is the
tion and phase is a function of crystal structure and of atomic specific heat capacity multipled by the bulk density), as
bond strength. In ceramics with anisotropic crystal structures, follows:
C1470 − 20
Thermal Diffusivity 5λ / C 3ρ (4) (>600°C)whereradiationisamajormodeofheattransfer,the
~ !
p
emittance properties of the ceramic are necessary to model the
where:
thermal conditions and to determine the heat transfer rates
λ = thermal conductivity,
under heating and cooling conditions.
C = specific heat capacity, and
p
7.5.3 The measurement of emittance has a directional com-
ρ = the bulk density, all at the specific temperature of
ponent based on the observation angle to the plane of the
measurement.
sample. Directional emittance is measured at a specific obser-
The units of thermal diffusivity are metre/second .
vation angle. Normal emittance is a special case of directional
7.4.2 Thermal diffusivity is important in characterizing the
emittance, measured normal to the plane of the sample.
transient thermal response of ceramics that are used in heat
Hemispherical emittance is measured by integration over the
transfer applications, either as insulators or as thermal conduc-
entire range of solid observation angles.
tion paths. As with the other thermal properties that change
7.5.4 Emittancecanalsobecharacterizedaseither“total”or
with temperature, a specific thermal diffusivity value must be
“spectral.” Total emittance is a measurement of the radiant
defined for a specific temperature or a temperature range.
energy across the entire range of thermal wavelengths and is
7.4.3 Thermal diffusivity is experimentally determined by
commonly utilized for total radiation pyrometry and radiant
measuring the temperature-time response of a material to a
thermalevent.Thecurrentmethodofchoiceisflashdiffusivity, heat transfer analysis. Spectral emittance is a measurement of
in which one side of a specimen of known thickness and the radiant energy at/across a particular portion of the
temperature is subjected to a short-duration thermal pulse.The wavelength/frequency spectrum. The emittance at a particular
energy of the pulse is absorbed on the front surface of the frequency is important in temperature-measuring equipment,
specimen and the resulting rear face temperature rise is
such as optical pyrometers.
measured. Thermal diffusivity is calculated from the specimen
7.5.5 Most materials are not perfect emitters. The emission
thicknessandthetimerequiredfortherearfacetemperatureto
of radiation from a surface depends on many factors:
reach a specified percentage of its maximum value.
temperature, bulk composition, surface composition
7.4.4 All of the microstructural variables that have an
(impurities, coatings, and oxidation), optical transparency,
impactonthermalconductivitywillhaveasimilareffectonthe
surface profile/roughness, radiation wavelength, and observa-
thermal diffusivity.
tion angle. The relative radiant flux of a given material can be
7.5 Emittance/Emissivity: characterized by the term emittance (also called emissivity).
7.5.1 Allobjectsradiateenergydependingontheirtempera-
Emittanceistheratiooftheradiantfluxemittedbyaspecimen
ture and their radiative characteristics. This radiation is called
per unit area to the radiant flux emitted by blackbody radiator
thermalradiation,becauseitisstronglydependentontempera-
at the same temperature and under the same conditions.
ture. A perfect emitter (a blackbody) emits radiation across a
7.5.6 Emittance is determined by measuring the emitted
range of wavelengths according to its surface temperature
thermal radiation at a given temperature and then comparing it
through the Planck radiation equation. The amount of hemi-
to a reference standard of known emittance or by direct
spherical radiated energy per unit surface area at a given
comparison to an experimental “blackbody” at the same
temperature for a blackbody is calculated through the Stefan-
temperature.
Boltzmann’s law as follows:
28 4 2 4
E 55.670 310 3T W/ m ·K (5)
@ ~ !#
b,total 8. Test Specimen Characterization
where:
8.1 Introduction:
T = specimen temperature for hemispherical emittance.
8.1.1 Advanced ceramics, both monolithic and composite,
7.5.2 At high temperatures, the emittance of radiation by a offer a wide range of thermal properties, from thermal insula-
tors to thermal conductors. Nominal thermal property values
material has significant impact on its thermal condition, based
on how the thermal radiation is emitted, absorbed, and re- forarangeofadvancedmonolithicceramicsaregiveninTable
flected. For advanced ceramics operating at high temperatures 1. Note the range of thermal properties listed in the table.
TABLE 1 Nominal Thermal Properties for Monolithic Ceramics at Room Temperature
NOTE 1—Thermal property data obtained from reference books and producer specifications. Values are approximate for a given class of material and
are provided for the sake of general comparison.Actual values in specific test specimens will depend on composition, microstructure, porosity, and other
factors. Emittance/emissivity data from Thermal Radiative Properties: Nonmetallic Solids, Touloukian, Y. S. and DeWitt, D. P., IFI/Plenum, 1972.
Alumina, Silicon Silicon Aluminum Boron
Property at Room Temperature Zirconia Mullite Beryllia Cordierite
99.5 % Nitride Carbide Nitride Nitride
Density, g/cm 3.85 3.31 3.10 3.25 2.10 6.02 2.80 2.90 2.30
Specific heat capacity, [J/(g·K)] 0.92 0.69 0.67 0.78 0.79 0.45 0.77 1.04 0.74
Thermal conductivity, [W/(m·K)] 35.6 15 110 115 32.8 2.2 3.5 250 3.0
2 –6
Thermal diffusivity, m /s×10 10.0 6.6 53.0 45.4 19.8 0.8 1.6 82.9 1.8
Coefficient of linear thermal 8.0 3.0 4,4 5.7 10 10.3 5.3 8.7 1.7
–6
expansion, 10 /K (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C)
Emittance/Emissivity, 1000 °C 0.1–0.3 0.7–0.9 0.7–0.9 0.7–0.9 0.7–0.9 0.1–0.3 0.4 '0.3 NA
C1470 − 20
Advancedceramicssuchasaluminumnitrideandberylliawith fiber-reinforced composites. The degree of characterization
their high thermal conductivity are often used as thermal required depends on the variation in the thermal properties
conductors. produced by changes in composition, constituents, and micro-
8.1.2 Table 2 provides nominal thermal properties for dif- structure.Spatialvariationsmustbeconsideredandadequately
ferent types of ceramic fibers used in continuous fiber- evaluated, particularly for whisker- and particle-reinforced
reinforced ceramic matrix composites. When these different composites, in which reinforcement concentrations may vary
ceramic fibers are combined with different ceramic matrices, spatially through the test specimen.
the resulting composites can contain constituents whose ther- 8.2.4 For advanced ceramic composites (whisker, chopped-
mal properties are widely different. fiber,andcontinuous-fiberreinforced)andformonolithicswith
8.1.3 Therangeofthermalpropertiesforadvancedceramics oriented or textured grain growth, anisotropy effects must be
and the complexity inherent in ceramic composites require a carefully evaluated and characterized. Directional effects are
detailed understanding of the relationships between pronounced in thermal conductivity/diffusivity and thermal
composition, processing, microstructure, and thermal proper- expansion measurements. The character and degree of anisot-
ties in those ceramics. With that understanding, test operators ropy in such composites must be adequately characterized and
will ensure that thermal test results for advanced ceramics are understood.
valid, useful, and reproducible. 8.2.5 In a similar manner, the exposure history of a compo-
nent can also affect the thermal properties through oxidation,
8.2 Material Characteristics and Thermal Properties:
phase changes, grain growth, high-temperature reactions,
8.2.1 Advanced ceramics cover a broad range of
corrosion, and slow crack growth. Exposure history (time,
compositions,microstructures,andphysicalproperties.Itisnot
temperature,andatmosphere)fortestspecimenshastobewell
possible to give specific guidance for every current or future
documented.
advanced ceramic material, but general guidelines and infor-
8.2.6 Exposureandthermaleffectscanalsooccurduringthe
mation are provided on the effects of composition,
thermal testing, changing the composition and microstructure.
microstructure, and processing on the thermal properties of
It is imperative that the test operator be aware of potential
advanced ceramics and on thermal property measurement.
reactions, oxidation, phase changes, and other thermal events
8.2.2 The thermal properties of an advanced ceramic
that could occur across the test temperature range. This can
(monolithic or composite) are a function of the material
occur if the test temperature exceeds the maximum processing
compositionandconstituents,itsmicrostructure,itsprocessing
temperature or if oxidation reactions (surface or bulk) occur at
history, and its environmental exposure. For example, porosity
elevated temperatures. Oxidation-sensitive materials should be
hasaverystrongeffectonthermalconductivityanddiffusivity.
tested in inert atmospheres.Accelerated heating rates can also
In a similar manner, composites containing high thermal
produce test anomalies, because of nonuniform temperatures
conductivity components can be tailored to specific thermal
within a test specimen. Thermal tests should always be done
propertytargetsbychangingtheamountandthearchitectureof
with the test specimen in relative steady-state thermal
the reinforcing component. The advanced ceramic must be
equilibrium,unlesstransientpropertiesarespecificallydesired.
adequatelycharacterizedintermsofcomposition,constituents,
microstructure, processing methods, and exposure history. 8.3 Monolithic Ceramics—Material Variables:
8.2.3 Thesensitivityofthethermalpropertiesofceramicsto 8.3.1 For monolithic ceramics, the following material char-
such variations requires that the composition and constituents acteristics should be carefully considered in terms of their
in advanced ceramics be sufficiently determined and docu- expected and actual effect on the thermal properties. Evalua-
mented to avoid misinterpretation of results and to permit tionofthematerialcharacteristicsmayberecommended,ifthe
adequate characterization of the test material. This character- thermal properties are sufficiently impacted by the pertinent
ization may be simple and straightforward for monolithic characteristics.
ceramics, but may require extensive microstructural, chemical, 8.3.2 Porosity has a major effect on thermal conductivity/
and physical analysis for complex systems such as whisker or diffusivity. From one viewpoint, porosity can be considered an
TABLE 2 Nominal Thermal Properties of Ceramic Fibers at Room Temperature
NOTE 1—Thermal property data obtained from reference books and producer specifications. Values are approximate and are provided for the sake of
general comparison. Actual values in specific test specimens will depend on composition, microstructure, porosity, architecture, and other factors.
T-300 P-120
A A A A B B B
Property at Room Temperature Nicalon CG Hi-Nicalon Hi-Nicalon S Sylramic SiC Nextel 312 Nextel 610 Nextel 720
C C
Carbon Carbon
Nominal composition Silicon Silicon Silicon Silicon Alumino- Alumina Alumina- Carbon Graphite
Carbide Carbide Carbide Carbide borosilicate Mullite
Density, g/cm 2.55 2.74 3.10 3.20 2.70 3.88 3.40 1.76 2.17
Specific Heat, [J/(g·K)] 1.14 .067 NA 0.61 '0.7 '0.9 '0.85 '0.70 '0.70
Thermal conductivity, [W/(m·K)] 2.97 7.77 18.4 40-45 '3(est) '30 (est) '10 (est) 8.5 640
Coefficient of Linear Thermal 4.0 3.5 NA 5.4 3.0 7.9 6.0 –1.4 at –1.45 at
–6
Expansion, 10 /K (0–900 °C) (0–500 °C) (20–1320 °C) (100–1100 °C)(100–1100 °C)(100–1100 °C) (23 °C) (23 °C)
A
CDI Ceramics, Inc., San Diego, CA.
B
3M Corp., St. Paul, MN.
C
Amoco Performance Products, Alpharetta, GA.
C1470 − 20
additional, low thermal conductivity/capacity phase in the test late packing factor is high enough to produce significant
specimen in which the pore volume fraction, the porosity size particle-to-particle contact.
(mean and distribution), and its geometric distribution can all 8.4.3 If there is a large difference in thermal expansion
have variable effects on the thermal properties, especially the between the reinforcement and the matrix in the composite,
residual stresses or microcracks, or both, can develop during
thermaltransportproperties.Theporosityinthetestspecimens
should be adequately defined and characterized with regard to processing. Such residual stresses and microcracks can pro-
duce anomalies in thermal expansion measurements. Microc-
its effect on thermal conductivity/diffusivity.
racking can also have a direct effect on thermal conductivity/
8.3.3 Variations in stoichiometry, impurities, grain size, and
diffusivity.
grain boundary phases can have a large effect on the thermal
conductivity and thermal diffusivity for ceramics with high
8.5 Continuous Fiber-Reinforced Ceramic Composites—
intrinsic thermal conductivity (aluminum nitride, beryllia,
Material Variables:
silicon carbide, and so forth). The effect of such composition
8.5.1 The use of continuous fiber reinforcement in ceramic
variations and phase distributions should be carefully consid-
compositesprovidestheceramicengineerthegreatestrangeof
eredandevaluated(iffeasible)inthermaltestsofhighthermal
property control and tailoring, but also introduces the highest
conductivity ceramics.
level of complexity into the composition and microstructure of
advanced ceramics.
8.3.4 Phase changes and devitrification of amorphous
8.5.2 It is essential that the composition and architecture of
phasesmayoccurduringthermaltests,producinganomaliesin
the fiber reinforcement in the composite be adequately char-
the various thermal properties. Test operators should be in-
acterized and documented to include the following:
formed of the potential for such transformations in specimens
8.5.2.1 Fiber composition, filament morphology (diameter
submitted for testing.
and length), and fiber volume fraction.
8.3.5 Thermal expansion measurements for ceramics often
8.5.2.2 Filament counts in tows, comprehensive description
show heating/cooling hysteresis when microcracking or minor
of the reinforcement architecture (one-dimensional (tows),
phase changes occur. Irreversible thermal expansion effects
two-dimensional (woven fabrics), and three-dimensional
may also occur in certain materials, based on annealing, rapid
(weaves and braid)) to include tow count and repeat units.
heating rates, creep, crystallization, or microcracking.Thermal
8.5.2.3 The composition and morphology of any interface
expansion tests done only on heating can be misleading, and
coatings on the fibers, used for process protection of the fibers
thermal expansion measurements should be done under both
orfordevelopmentofcrackdeflectionmodesinthecomposite.
heating and cooling conditions.
8.5.2.4 The composition and morphology (thickness,
8.3.6 Oriented or textured grain structures in monolithic
porosity, and grain structure) of any surface coatings on the
ceramics can introduce anisotropic effects in the thermal
composite component, used for surface sealing, oxidation/
properties. Such grain structures are commonly developed
corrosionprotection,orwear/abrasionresistance.Surfacecoat-
during processing. If the thermal effects of such anisotropy are
ings may be considered as monolithic layers on the surface of
significant, the grain structure should be characterized by
the composite.
optical or SEM microscopy or by X-ray diffraction.
8.5.3 The matrix in the composite must also be adequately
characterized in terms of composition, constituents,
8.4 Particulate and Whisker-Reinforced Ceramic
morphology, and grain structure. Porosity in the composite
Composite—Material Variables:
shouldalsobecharacterized,consideringvolumefraction,pore
8.4.1 Particulate and whisker reinforcement of advanced
size, shape factors, and distribution of porosity.
ceramics adds an additional degree of complexity to the
8.5.4 Fiber-reinforcedceramiccompositesoftenhavestrong
composition and microstructure of the test specimen. It is
anisotropic properties, determined by the reinforcement archi-
critical that the particulate or whisker additions be adequately
tecturewithhigherfibervolumeloadingsinspecificdirections.
characterized in terms of composition, phase and crystal
It is essential that the geometry and orientation of the rein-
structure,particle/whiskermorphology,andsizedistribution.It
forcement are fully documented and correlated with the ther-
is also useful to have nominal thermal properties, that is,
mal test results.
specific heat, thermal conductivity, and thermal expansion, for
8.5.5 In many thermal tests (such as thermal dilatometery,
the reinforcement across the temperature range of interest.
diffusivity, and specific heat), the test specimens may have one
Those thermal property data will assist in interpreting the
or more dimensions which are small in comparison to the
composite thermal test results.
weave repeat elements. Experimenters should carefully con-
8.4.2 As part of the composite specimen, the particulate/
sider the size of the test specimens for a specific test to ensure
whisker reinforcement must be adequately defined in terms of
thatanadequatenumberofweaverepeatelementsareincluded
the volume fraction, spatial distribution, and orientation/
in the specimen. Specimens of insufficient size may not be
anisotropy/texture. For example, reinforcements with high
representative of the properties of the larger piece or may have
thermal conductivity relative to the matrix will have markedly
exaggerated end or edge effects.
different effects on the composite thermal properties, depend-
ingonhowthereinforcementsaredistributedandoriented.For
9. Test Specimen Sampling and Preparation
example, whiskers in a laminated, planar orientation will
produceanisotropicthermalconductivityinthecomposite.The 9.1 Test Specimen Sources—Test specimens for thermal
bulk thermal conductivity will markedly change if the particu- evaluation can be taken from engineering components or
C1470 − 20
fabricated test panels/billets. The selection of a particular flash. Surface finish measurements may be advisable to ensure
sourcedependsontherequiredtestspecimengeometryandthe reproducibility and proper interpretation of specific thermal
suitability of the test component for test specimen preparation. test results.
The primary objective is to select test specimens that are
9.7 Test Specimen Preparation:
representativeofthecomposition,processing,andpropertiesof
9.7.1 Careful machining of specimens is critical in all
the final functional part.
thermal measurements, primarily for accurate measurement of
9.2 Specimen Sampling to Assess Variability:
critical dimensions and for accurate fit of specimens into
9.2.1 Depending on the degree of process control, variabil-
fixtures. Machining procedures should be sufficiently docu-
ity may occur among test specimens within a batch and
mented for reproducibility.
betweendifferentbatchesoftestspecimens.Thevariationmay
9.7.2 Per Test Method C372, test specimens for mechanical
occur in the composition, microstructure, and porosity of
dilatometry should have ends that are cut/ground flat and
advanced ceramics.The degree of variation will depend on the
perpendicular to the specimen axis. Dilatometer fixtures are
homogeneity within the batch and on reproducibility between
commonly designed to provide point contact with specimens
batches from the producer. The test operator should select/
and to prevent sideways levering. For thermal expansion
prepare sufficient test specimens to provide a representative
measurements using optical test methods, specimen ends need
sample of the entire batch of specimens submitted for testing.
to be flat and parallel to a quite high precision to ensure
In addition, batch/lot identification should be carefully noted
stability and to define light paths.
for documentation purposes.
9.7.3 There is no standard method for machining and
9.2.2 Practice E122 provides guidance on calculating the
finishing ceramic specimens for thermal testing. There are
number of units required for testing to obtain an estimate of
three general categories of machining which can be applied
certain precision for a given property.
both to monolithic and composites ceramics.
9.3 Orientation and Anisotropy Effects—If the test material
9.7.3.1 Application-Matched Machining—The machined
hassignificantanisotropyororientationeffects,itisimperative
surfaces of the thermal test specimen will have the same
that test specimens be selected to adequately sample the
surface/edge preparation as that given to a service component.
anisotropy in the major directions of interest. A minimum of
9.7.3.2 Customary Practices—In instances where a custom-
two directions should be selected for test specimens. The
arymachiningprocedurehasbeendevelopedthatiscompletely
orientations should be selected to produce the maximum and
satisfactory for a class of materials (that is, it induces no
minimum material properties. Each test specimen should be
unwanted surface/subsurface damage or residual stresses), this
marked and identified so that its orientation in the original
procedure may be used to produce the thermal specimens.
part/test piece can be identified.
9.7.3.3 Recommended Procedure—In instances where
9.4 Location and Identification:
application-matched machining and customary practices are
not pertinent, the following machining procedures are recom-
9.4.1 Giventhevariabilitywhichmayoccurindevelopmen-
mended as a method commonly used for ceramic test speci-
tal advanced ceramics and the anisotropy which may be an
mens for mechanical testing.
engineered characteristic of composite components, test speci-
(1)Perform all grinding or cutting with ample supply of
men locations should be documented by drawing or photo-
appropriate filtered coolant to keep the specimen and grinding
graph.Testspecimensshouldbeidentifiedsothattheirlocation
wheelconstantlyfloodedandparticlesflushed.Grindingcanbe
can be traced on the original part. Special identification should
doneintwostages,rangingfromcoarsetofineratesofmaterial
beusedfortestspecimenstakenfromplateedgesorfromareas
removal. All cutting can be done in one stage appropriate for
with local anomalies.
the depth of cut.
9.4.2 Nondestructive evaluation (NDE) methods may be of
(2)The stock removal rate shall not exceed 0.03 mm per
value in characterizing test plates prior to specimen
pass to the last 0.06 mm of material removed. Final finishing
preparation, particularly for fiber-rein
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C1470 − 06 (Reapproved 2013) C1470 − 20
Standard Guide for
Testing the Thermal Properties of Advanced Ceramics
This standard is issued under the fixed designation C1470; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This guide covers the thermal property testing of advanced ceramics, to include monolithic ceramics, particulate/
whisker-reinforced ceramics, and continuous fiber-reinforced ceramic composites. It is intended to provide guidance and
information to users on the special considerations involved in determining the thermal properties of these ceramic materials.
1.2 Five thermal properties (specific heat capacity, thermal conductivity, thermal diffusivity, thermal expansion, and
emittance/emissivity) are presented in terms of their definitions and general test methods. The relationship between thermal
properties and the composition, microstructure, and processing of advanced ceramics (monolithic and composite) is briefly
outlined, providing guidance on which material and specimen characteristics have to be considered in evaluating the thermal
properties of advanced ceramics. Additional sections describe sampling considerations, test specimen preparation, and reporting
requirements.
1.3 Current ASTM test methods for thermal properties are tabulated in terms of test method concept, testing range, specimen
requirements, standards/reference materials, capabilities, limitations, precision, and special instructions for monolithic and
composite ceramics.
1.4 This guide is based on the use of current ASTM standards for thermal properties, where appropriate, and on the development
of new test standards, where necessary. It is not the intent of this guide to rigidly specify particular thermal test methods for
advanced ceramics. Guidance is provided on how to utilize the most commonly available ASTM thermal test methods, considering
their capabilities and limitations.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
See IEEE/ASTM SI 10.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
2.1.1 Specific Heat:
C351 Test Method for Mean Specific Heat of Thermal Insulation (Withdrawn 2008)
D2766 Test Method for Specific Heat of Liquids and Solids (Withdrawn 2018)
E1269 Test Method for Determining Specific Heat Capacity by Differential Scanning Calorimetry
E2716 Test Method for Determining Specific Heat Capacity by Sinusoidal Modulated Temperature Differential Scanning
Calorimetry
2.1.2 Thermal Conductivity:
This guide is under the jurisdiction of ASTM Committee C28 on Advanced Ceramics and is the direct responsibility of Subcommittee C28.03 on Physical Properties
and Non-Destructive Evaluation.
Current edition approved Feb. 1, 2013Jan. 1, 2020. Published March 2013January 2020. Originally approved in 2000. Last previous edition approved in 20062013 as
C1470 – 06.C1470 – 06 (2013). DOI: 10.1520/C1470-06R13.10.1520/C1470-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1470 − 20
C177 Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the
Guarded-Hot-Plate Apparatus
C182 Test Method for Thermal Conductivity of Insulating Firebrick
C201 Test Method for Thermal Conductivity of Refractories
C202 Test Method for Thermal Conductivity of Refractory Brick
C408 Test Method for Thermal Conductivity of Whiteware Ceramics
C518 Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus
C767 Test Method for Thermal Conductivity of Carbon Refractories
C1044 Practice for Using a Guarded-Hot-Plate Apparatus or Thin-Heater Apparatus in the Single-Sided Mode
C1045 Practice for Calculating Thermal Transmission Properties Under Steady-State Conditions
C1113C1113/C1113M Test Method for Thermal Conductivity of Refractories by Hot Wire (Platinum Resistance Thermometer
Technique)
C1114 Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus
C1130 Practice for Calibration of Thin Heat Flux Transducers
E1225 Test Method for Thermal Conductivity of Solids Using the Guarded-Comparative-Longitudinal Heat Flow Technique
E1530 Test Method for Evaluating the Resistance to Thermal Transmission by the Guarded Heat Flow Meter Technique
2.1.3 Thermal Expansion:
C372 Test Method for Linear Thermal Expansion of Porcelain Enamel and Glaze Frits and Fired Ceramic Whiteware Products
by the Dilatometer Method
C1300 Test Method for Linear Thermal Expansion of Glaze Frits and Ceramic Whiteware Materials by the Interferometric
Method
E228 Test Method for Linear Thermal Expansion of Solid Materials With a Push-Rod Dilatometer
E289 Test Method for Linear Thermal Expansion of Rigid Solids with Interferometry
E831 Test Method for Linear Thermal Expansion of Solid Materials by Thermomechanical Analysis
2.1.4 Thermal Diffusivity:
C714 Test Method for Thermal Diffusivity of Carbon and Graphite by Thermal Pulse Method
D4612 Test Method for Calculating Thermal Diffusivity of Rock and Soil
E1461 Test Method for Thermal Diffusivity by the Flash Method
E2585 Practice for Thermal Diffusivity by the Flash Method
2.1.5 Emittance/Emissivity:
E408 Test Methods for Total Normal Emittance of Surfaces Using Inspection-Meter Techniques
E423 Test Method for Normal Spectral Emittance at Elevated Temperatures of Nonconducting Specimens
2.1.6 General Standards:
C168 Terminology Relating to Thermal Insulation
C373 Test Methods for Determination of Water Absorption and Associated Properties by Vacuum Method for Pressed Ceramic
Tiles and Glass Tiles and Boil Method for Extruded Ceramic Tiles and Non-tile Fired Ceramic Whiteware Products
C1045 Practice for Calculating Thermal Transmission Properties Under Steady-State Conditions
C1145 Terminology of Advanced Ceramics
E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or
Process
E473 Terminology Relating to Thermal Analysis and Rheology
E1142 Terminology Relating to Thermophysical Properties
C1045 Practice for Calculating Thermal Transmission Properties Under Steady-State Conditions
IEEE/ASTM SI 10 Standard for Use of the International System of Units (SI) (The Modern Metric System)American National
Standard for Metric Practice
3. Terminology
3.1 Definitions:
3.1.1 advanced ceramic, n—a highly engineered, high-performance, predominantly nonmetallic, inorganic, ceramic material
having specific functional attributes. (C1145)
3.1.2 ceramic matrix composite, n—a material consisting of two or more materials (insoluble in one another), in which the major
continuous component (matrix component) is a ceramic, while the secondary component/s (reinforcing component) may be
ceramic, glass-ceramic, glass, metal, or organic in nature. These components are combined on a macroscale to form a useful
engineering material possessing certain properties or behavior not possessed by the individual constituents. (C1145)
-1–1
3.1.3 coeffıcient of linear thermal expansion, α[T ],n—the change in length, relative to the length of the specimen,
accompanying a unit change of temperature, at a specified temperature. [This(This property can also be considered the
instantaneous expansion coefficient or the slope of the tangent to the ΔL/L versus T curve at a given temperature.]temperature.)
(E1142)
C1470 − 20
3.1.4 continuous fiber-reinforced ceramic composite (CFCC), n—a ceramic matrix composite in which the reinforcing phase(s)
consists of continuous filaments, fibers, yarns, or knitted or woven fabric. (C1145)
3.1.5 differential scanning calorimetry (DSC), n—a technique in which the difference in energy inputs into a test specimen and
a reference material is measured as a function of temperature while the test specimen and reference material are subjected to a
controlled temperature program. (E1269)
3.1.6 discontinuous fiber-reinforced ceramic composite, n—a ceramic matrix composite reinforced by chopped fibers. (C1145)
3.1.7 emittance (emissivity), ε (nd), n—the ratio of the radiant flux emitted by a specimen per unit area to the radiant flux emitted
by a black body radiator at the same temperature and under the same conditions. Emittance ranges from 0 to 1, with a blackbody
having an emittance of 1.00. (E423)
3.1.8 linear thermal expansion, [nd],n—the change in length per unit length resulting from a temperature change. Linear thermal
expansion is symbolically represented by ΔL/L , where ΔL is the observed change in length ΔL = L – L , and L , L , and L are
0 2 1 0 1 2
the lengths of the specimen at reference temperature T and test temperatures T and T . (E228)
0 1 2
-1–1
3.1.9 mean coeffıcient of linear thermal expansion, α [T ],n—the change in length, relative to the length of the specimen,
L
accompanying a unit change of temperature measured across a specified temperature range (T to T ). (C372)
1 2
3.1.10 particulate reinforced particulate-reinforced ceramic matrix composite, n—a ceramic matrix composite reinforced by
ceramic particulates. (C1145)
–1 –2 –1
3.1.11 specific heat (specific heat capacity), C [mL T θ ],n—the quantity of heat required to provide a unit temperature
increase to a unit mass of material. (E1142)
–1 –1
3.1.12 thermal conductivity, λ [mLT θ ],n—the time rate of heat flow, under steady conditions, through unit area, per unit
temperature gradient in the direction perpendicular to the area. (E1142C168)
2 –1
3.1.13 thermal diffusivity, [L T ],n—the property given by the thermal conductivity divided by the product of the bulk density
and heat capacity per unit mass. (E1461C168)
3.1.14 thermodilatometry, n—a technique in which a dimension of a test specimen under negligible applied force is measured
as a function of temperature while the test specimen is subjected to a controlled temperature program in a specified atmosphere.
(E473)
3.2 Units for Thermal Properties:
Property SI Units Abbreviation
Specific heat capacity joules/(gram-kelvin) J/(g·K)
Thermal Conductivity watts/(metre-kelvin) W/(m·K)
2 2
Thermal diffusivity metre/second m/s
–1
Coefficient of Thermal metre/(metre-kelvin) K
Expansion
Emittance/emissivity no dimensions —
4. Summary of Guide
4.1 Five thermal properties (specific heat capacity, thermal conductivity, thermal diffusivity, thermal expansion, and
emittance/emissivity) are presented in terms of their definitions and general test methods. The relationship between thermal
properties and the composition, microstructure, and processing of advanced ceramics is briefly outlined, providing guidance on
which material characteristics have to be considered in evaluating the thermal properties. Additional sections describe sampling
considerations, test specimen preparation, and reporting requirements.
4.2 Current ASTM test methods for thermal properties are tabulated in terms of test method concept, testing range, specimen
requirements, standards/reference materials, capabilities, limitations, precision, and special instructions for monoliths and
composites.
5. Significance and Use
5.1 The high-temperature capabilities of advanced ceramics are a key performance benefit for many demanding engineering
applications. In many of those applications, advanced ceramics will have to perform across a broad temperature range. The thermal
expansion, thermal diffusivity/conductivity, specific heat, and emittance/emissivity are crucial engineering factors in integrating
ceramic components into aerospace, automotive, and industrial systems.
5.2 This guide is intended to serve as a reference and information source for testing the thermal properties of advanced ceramics,
based on an understanding of the relationships between the composition and microstructure of these materials and their thermal
properties.
5.3 The use of this guide assists the testing community in correctly applying the ASTM thermal test methods to advanced
ceramics to ensure that the thermal test results are properly measured, interpreted, and understood. This guide also assists the user
in selecting the appropriate thermal test method to evaluate the particular thermal properties of the advanced ceramic of interest.
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5.4 The thermal properties of advanced ceramics are critical data in the development of ceramic components for aerospace,
automotive, and industrial applications. In addition, the effect of environmental exposure on thermal properties of the advanced
ceramics must also be assessed.
6. Procedure
6.1 Review Sections 7 – 10 to become familiar with thermal property concepts and thermal testing issues for advanced ceramics,
specimen preparation guidance, and reporting recommendations.
6.2 Review the test method text and tables in Section 11 for the property you need to determine. Use the text and tables to help
select the most appropriate ASTM test method for evaluating the thermal property of interest for the specific advanced ceramic.
6.3 Perform the thermal property test in accordance with the selected ASTM test method, but refer back to the guide for
directions and recommendations on material characterization, sampling procedures, test specimen preparation, and reporting
results.
7. Thermal Properties and Their Measurement
7.1 Specific Heat Capacity:
7.1.1 Specific heat capacity is the amount of energy required to increase the temperature by one unit for a unit mass of material.
It is a fundamental thermal property for engineers and scientists in determining the temperature response of materials to changes
in heat flux and thermal conditions. The SI units for specific heat capacity are joules/(gram·K). Since the specific heat capacity
changes with temperature, a specific heat capacity value must always be associated with a specific test temperature or temperature
range.
7.1.2 Specific heat capacity is commonly measured by calorimetry in which changes in thermal energy are measured against
changes in temperature. The two common calorimetry methods are differential scanning calorimetry and drop calorimetry.
7.1.3 Differential scanning calorimetry heats the test material at a controlled rate in a controlled atmosphere through the
temperature region of interest. The heat flow into the test material is compared to the heat flow into a reference material to
determine the energy changes in the test material as a function of temperature.
7.1.4 In drop calorimetry, the test sample is heated to the desired temperature and then immersed in an instrumented,
liquid-filled container (calorimeter), which reaches thermal equilibrium. The increase in temperature of the calorimeter
liquid/container is a measure of the amount of heat in the test specimen.
7.1.5 In any calorimetry test, the experimenter must recognize that phase changes and other thermo-physical transformations
in the material will produce exothermic and endothermic events which will be captured in the test data. The thermal events must
be properly identified and understood within the context of the material properties, chemistry, and phase composition across the
temperature range of interest.
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7.2 Thermal Conductivity:
7.2.1 Thermal conductivity is a measurement of the rate of heat flow through a material for a given temperature gradient. It is
normalized for thickness and cross-sectional area to give a material specific material-specific value. The thermal conductivity of
a ceramic is used in determining the effectiveness of a ceramic either as a thermal insulator or as a thermal conductor. The SI units
for thermal conductivity are watts/(metre·kelvin). As with other thermal properties, thermal conductivity changes with temperature,
so that a specific thermal conductivity value for a material must be associated with a specific test temperature.
7.2.2 In electrically nonconductive ceramics, thermal conductivity occurs by lattice vibration (phonon) conductivity and by
radiation (photon) at higher temperatures (>500°C).(>500 °C). Thermal conductivity decreases when the mean free path of the
phonons and photons decreases. Lattice imperfections, differences in atomic weight between anions and cations, non-
stoichiometric compositions, solid solutions, amorphous atomic structures, porosity, and grain boundaries all act as scattering sites
for phonons and reduce the thermal conductivity of the material.
7.2.3 Thermal conductivity is commonly measured by steady-state methods, that is, cut bar comparative techniques, heat flow
meter techniques, guarded hot-plate/heater/hot-wire techniques, and calorimetry techniques. It can also be determined by transient
techniques (hot wire and flash diffusivity).
7.2.4 In cut bar comparative heat flow techniques, the test specimen is subjected to a known heat flow and the temperature
differential/s are measured across the dimension/s of interest. The entire test system with the test specimen is configured with
insulation and heaters to minimize heat flow perpendicular to the direction of interest. In the heat flowmeter technique, the heat
flow in the test is measured by a calibrated heat flux transducer without the use of direct reference materials in the test system.
In both techniques, the thermal conductivity of the material is then calculated as follows:
λ5 q Δ L/~Δ T! (1)
where:
λ = thermal conductivity,
q = heat flow/unit area,
ΔL = distance across which the temperature difference is measured, and
ΔT = measured temperature difference.
Thermal conductivity (λ) can be calculated from thermal diffusivity measurements, using the specific heat capacity and the
material density as follows:
λ5 thermal diffusivity*specific heat capacity*density (2)
λ5 thermal diffusivity 3specific heat capacity 3density (2)
7.3 Thermal Expansion (Thermodilatometry):
7.3.1 All materials expand or contract with changes in temperature, with most materials expanding with increasing temperature.
Thermal expansion is often very important in engineering applications, because differences in thermal expansion between fitted
or bonded components can produce thermal stresses, leading to component failure.
7.3.2 The thermal expansion for a given ceramic composition and phase is a function of crystal structure and of atomic bond
strength. In ceramics with anisotropic crystal structures, the thermal expansion is different along the different crystal axes. (This
is of particular concern for single crystal specimens and for specimens with oriented grain structures).structures.) For some specific
ceramics (cordierite, aluminum titanate, and zirconium phosphate), the thermal expansion may be zero or negative in certain crystal
axes in specific temperature regimes.
7.3.3 The quantitative determination of the change in dimension as a function of temperature is defined as the mean coefficient
of linear thermal expansion – the ratio of a given change in length per unit length for a specimen for a specific change in
temperature as follows:
α5 L 2 L / T 2 T /L (3)
@~ ! ~ !#
2 1 2 1 1
where:
L and L = lengths of the test specimen at test temperatures T and T , respectively, where T > T .
1 2 1 2 2 1
7.3.4 The units for mean coefficient of linear thermal expansion are metres/(metre · K). metres/(metre·K). The mean coefficient
–6
of linear thermal expansion for a material has to be defined for a given temperature range, for example, 7 × 10 m/(m·K) for 25
to 500°C.500 °C.
7.3.5 The mean coefficient of linear thermal expansion across a temperature range is different than the instantaneous coefficient
of thermal expansion, which is the tangent slope at a specific temperature for the expansion-temperature curve of the sample.
7.3.6 Thermal expansion is commonly measured by thermodilatometry, a technique in which a known dimension of a test
specimen under negligible applied force is measured as a function of temperature while the specimen is subjected to a
controlled-temperature program in a specified atmosphere. The measurement of the dimensional change can be done by direct
mechanical measurement or by optical techniques (interferometry and optical lever).
7.3.7 Different crystalline phases in ceramics have different thermal expansion characteristics. Major phase changes in ceramics
can give abrupt or progressive changes in length with increasing or decreasing temperature and may cause confusion when
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included in overall expansion measurements. In a similar manner, crystallization and changes in amorphous, glassy phases in
ceramics can produce marked changes in the thermal expansion over specific temperature regimes.
7.3.8 Thermal expansion measurements for ceramics often show heating/cooling hysteresis when microcracking or minor phase
changes occur. There are also irreversible thermal expansion effects, based on annealing, heating rate, creep, crystallization, or
microcracking. Thermal expansion tests done only on heating can be misleading, and thermal expansion measurements should be
done under both heating and cooling conditions.
7.4 Thermal Diffusivity:
7.4.1 Thermal diffusivity is a measurement of the rate of temperature change in a material measured under transient conditions.
It is defined as the ratio of the thermal conductivity to the “specific heat capacity per unit volume” (which is the specific heat
capacity dividedmultipled by the bulk density), as follows:
Diffusivity 5 λ/~C /ρ! (4)
p
Thermal Diffusivity 5 λ / ~C 3ρ! (4)
p
where:
λ = thermal conductivity,
C = specific heat capacity, and
p
ρ = the bulk density,
all at the specific temperature of measurement.
The units of thermal diffusivity are metre/second .
7.4.2 Thermal diffusivity is important in characterizing the transient thermal response of ceramics that are used in heat transfer
applications, either as insulators or as thermal conduction paths. As with the other thermal properties that change with temperature,
a specific thermal diffusivity value must be defined for a specific temperature or a temperature range.
7.4.3 Thermal diffusivity is experimentally determined by measuring the temperature-time response of a material to a thermal
event. The current method of choice is flash diffusivity, in which one side of a specimen of known thickness and temperature is
subjected to a short duration short-duration thermal pulse. The energy of the pulse is absorbed on the front surface of the specimen
and the resulting rear face temperature rise is measured. Thermal diffusivity is calculated from the specimen thickness and the time
required for the rear face temperature to reach a specified percentage of its maximum value.
7.4.4 All of the microstructural variables that have an impact on thermal conductivity will have a similar effect on the thermal
diffusivity.
7.5 Emittance/Emissivity:
7.5.1 All objects radiate energy depending on their temperature and their radiative characteristics. This radiation is called
thermal radiation, because it is strongly dependent on temperature. A perfect emitter (a blackbody) emits radiation across a range
of wavelengths according to its surface temperature through the Planck radiation equation. The amount of hemispherical radiated
energy per unit surface area at a given temperature for a blackbody is calculated through the Stefan-Boltzmann’s law as follows:
28 4 2 4
E 5 5.670 310 *T @W/~m ·K !# (5)
b,total
28 4 2 4
E 5 5.670 310 3T @W/~m ·K !# (5)
b,total
where:
T = specimen temperature for hemispherical emittance
T = specimen temperature for hemispherical emittance.
7.5.2 At high temperatures, the emittance of radiation by a material has significant impact on its thermal condition, based on
how the thermal radiation is emitted, absorbed, and reflected. For advanced ceramics operating at high temperatures
(>600°C)(>600 °C) where radiation is a major mode of heat transfer, the emittance properties of the ceramic are necessary to model
the thermal conditions and to determine the heat transfer rates under heating and cooling conditions.
7.5.3 The measurement of emittance has a directional component based on the observation angle to the plane of the sample.
Directional emittance is measured at a specific observation angle. Normal emittance is a special case of directional emittance,
measured normal to the plane of the sample. Hemispherical emittance is measured by integration over the entire range of solid
observation angles.
7.5.4 Emittance can also be characterized as either “total” or “spectral.” Total emittance is a measurement of the radiant energy
across the entire range of thermal wavelengths and is commonly utilized for total radiation pyrometry and radiant heat transfer
analysis. Spectral emittance is a measurement of the radiant energy at/across a particular portion of the wavelength/frequency
spectrum. The emittance at a particular frequency is important in temperature measuring temperature-measuring equipment, such
as optical pyrometers.
7.5.5 Most materials are not perfect emitters. The emission of radiation from a surface depends on many factors: temperature,
bulk composition, surface composition (impurities, coatings, and oxidation), optical transparency, surface profile/roughness,
radiation wavelength, and observation angle. The relative radiant flux of a given material can be characterized by the term
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emittance (also called emissivity). Emittance is the ratio of the radiant flux emitted by a specimen per unit area to the radiant flux
emitted by blackbody radiator at the same temperature and under the same conditions.
7.5.6 Emittance is determined by measuring the emitted thermal radiation at a given temperature and then comparing it to a
reference standard of known emittance or by direct comparison to an experimental “blackbody” at the same temperature.
8. Test Specimen Characterization
8.1 Introduction:
8.1.1 Advanced ceramics, both monolithic and composite, offer a wide range of thermal properties, from thermal insulators to
thermal conductors. Nominal thermal property values for a range of advanced monolithic ceramics are given in Table 1. Note the
range of thermal properties listed in the table. Advanced ceramics such as aluminum nitride and beryllia with their high thermal
conductivity are often used as thermal conductors.
8.1.2 Table 2 provides nominal thermal properties for different types of ceramic fibers used in continuous fiber-reinforced
ceramic matrix composites. When these different ceramic fibers are combined with different ceramic matrices, the resulting
composites can contain constituents whose thermal properties are widely different.
8.1.3 The range of thermal properties for advanced ceramics and the complexity inherent in ceramic composites require a
detailed understanding of the relationships between composition, processing, microstructure, and thermal properties in those
ceramics. With that understanding, test operators will ensure that thermal test results for advanced ceramics are valid, useful, and
reproducible.
8.2 Material Characteristics and Thermal Properties:
8.2.1 Advanced ceramics cover a broad range of compositions, microstructures, and physical properties. It is not possible to give
specific guidance for every current or future advanced ceramic material, but general guidelines and information are provided on
the effects of composition, microstructure, and processing on the thermal properties of advanced ceramics and on thermal property
measurement.
8.2.2 The thermal properties of an advanced ceramic (monolithic or composite) are a function of the material composition and
constituents, its microstructure, its processing history, and its environmental exposure. For example, porosity has a very strong
effect on thermal conductivity and diffusivity. In a similar manner, composites containing high thermal conductivity components
can be tailored to specific thermal property targets by changing the amount and the architecture of the reinforcing component. The
advanced ceramic must be adequately characterized in terms of composition, constituents, microstructure, processing methods, and
exposure history.
8.2.3 The sensitivity of the thermal properties of ceramics to such variations requires that the composition and constituents in
advanced ceramics be sufficiently determined and documented to avoid misinterpretation of results and to permit adequate
characterization of the test material. This characterization may be simple and straightforward for monolithic ceramics, but may
require extensive microstructural, chemical, and physical analysis for complex systems such as whisker or fiber-reinforced
composites. The degree of characterization required depends on the variation in the thermal properties produced by changes in
composition, constituents, and microstructure. Spatial variations must be considered and adequately evaluated, particularly for
whisker- and particle-reinforced composites, in which reinforcement concentrations may vary spatially through the test specimen.
8.2.4 For advanced ceramic composites (whisker, chopped-fiber, and continuous-fiber reinforced) and for monolithics with
oriented or textured grain growth, anisotropy effects must be carefully evaluated and characterized. Directional effects are
pronounced in thermal conductivity/diffusivity and thermal expansion measurements. The character and degree of anisotropy in
such composites must be adequately characterized and understood.
TABLE 1 Nominal Thermal Properties for Monolithic Ceramics at Room Temperature
NOTE 1—Thermal property data obtained from reference books and producer specifications. Values are approximate for a given class of material and
are provided for the sake of general comparison. Actual values in specific test specimens will depend on composition, microstructure, porosity, and other
factors. Emittance/emissivity data from—Thermalfrom Thermal Radiative Properties,Properties: Nonmetallic Solids, Touloukian, Y. S. and DeWitt, D.P.,
I.F. I. Plenum, D. P., IFI/Plenum, 1972.
Alumina, Silicon Silicon Aluminum Boron
Property at Room Temperature Zirconia Mullite Beryllia Cordierite
99.5 % Nitride Carbide Nitride Nitride
Density, g/cm 3.85 3.31 3.10 3.25 2.10 6.02 2.80 2.90 2.30
Specific heat capacity, [J/(g·K)] 0.92 0.69 0.67 0.78 0.79 0.45 0.77 1.04 0.74
Thermal conductivity, [W/(m·K)] 35.6 15 110 115 32.8 2.2 3.5 250 3.0
2 -6
Thermal diffusivity, m /s × 10 10.0 6.6 53.0 45.4 19.8 0.8 1.6 82.9 1.8
2 –6
Thermal diffusivity, m /s × 10 10.0 6.6 53.0 45.4 19.8 0.8 1.6 82.9 1.8
Coefficient of linear thermal 8.0 3.0 4,4 5.7 10 10.3 5.3 8.7 1.7
-6
expansion, 10 /K (25–1000°C) (25–1000°C) (25–1000°C) (25–1000°C) (25–1000°C) (25–1000°C) (25–1000°C) (25–1000°C) (25–1000°C)
Coefficient of linear thermal 8.0 3.0 4,4 5.7 10 10.3 5.3 8.7 1.7
–6
expansion, 10 /K (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C) (25–1000 °C)
Emittance/Emissivity, 1000°C 0.1-0.3 0.7-0.9 0.7-0.9 0.7-0.9 0.7-0.9 0.1-0.3 0.4 '0.3 NA
Emittance/Emissivity, 1000 °C 0.1–0.3 0.7–0.9 0.7–0.9 0.7–0.9 0.7–0.9 0.1–0.3 0.4 '0.3 NA
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TABLE 2 Nominal Thermal Properties of Ceramic Fibers at Room Temperature
NOTE 1—Thermal property data obtained from reference books and producer specifications. Values are approximate and are provided for the sake of
general comparison. Actual values in specific test specimens will depend on composition, microstructure, porosity, architecture, and other factors.
T-300 P-120
A A A A B B B
Property at Room Temperature Nicalon CG Hi-Nicalon Hi-Nicalon S Sylramic SiC Nextel 312 Nextel 610 Nextel 720
C C
Carbon Carbon
Nominal composition Silicon Silicon Silicon Silicon Alumino- Alumina Alumina- Carbon Graphite
Carbide Carbide Carbide Carbide borosilicate Mullite
Density, g/cm 2.55 2.74 3.10 3.20 2.70 3.88 3.40 1.76 2.17
Specific Heat, [J/(g·K)] 1.14 .067 NA 0.61 '0.7 '0.9 '0.85 '0.70 '0.70
Thermal conductivity, [W/(m·K)] 2.97 7.77 18.4 40-45 '3(est) '30 (est) '10 (est) 8.5 640
Coefficient of Linear Thermal 4.0 3.5 NA 5.4 3.0 7.9 6.0 –1.4 at –1.45 at
–6
Expansion, 10 /K (0–900°C) (0–500°C) (20–1320°C) (100–1100°C) (100–1100°C) (100–1100°C) (23°C) (23°C)
Coefficient of Linear Thermal 4.0 3.5 NA 5.4 3.0 7.9 6.0 –1.4 at –1.45 at
–6
Expansion, 10 /K (0–900 °C) (0–500 °C) (20–1320 °C) (100–1100 °C)(100–1100 °C)(100–1100 °C) (23 °C) (23 °C)
A
CDI Ceramics, Inc., San Diego, CA.
B
3M Corp., St. Paul, MN.
C
Amoco Performance Products, Alpharetta, GA.
8.2.5 In a similar manner, the exposure history of a component can also affect the thermal properties through oxidation, phase
changes, grain growth, high-temperature reactions, corrosion, and slow crack growth. Exposure history (time, temperature, and
atmosphere) for test specimens has to be well-documented.well documented.
8.2.6 Exposure and thermal effects can also occur during the thermal testing, changing the composition and microstructure. It
is imperative that the test operator be aware of potential reactions, oxidation, phase changes, and other thermal events that could
occur across the test temperature range. This can occur if the test temperature exceeds the maximum processing temperature or
if oxidation reactions (surface or bulk) occur at elevated temperatures. Oxidation-sensitive materials should be tested in inert
atmospheres. Accelerated heating rates can also produce test anomalies, because of nonuniform temperatures within a test
specimen. Thermal tests should always be done with the test specimen in relative steady-state thermal equilibrium, unless transient
properties are specifically desired.
8.3 Monolithic Ceramics—Material Variables:
8.3.1 For monolithic ceramics, the following material characteristics should be carefully considered in terms of their expected
and actual effect on the thermal properties. Evaluation of the material characteristics may be recommended, if the thermal
properties are sufficiently impacted by the pertinent characteristics.
8.3.2 Porosity has a major effect on thermal conductivity/diffusivity. From one viewpoint, porosity can be considered an
additional, low thermal conductivity/capacity phase in the test specimen in which the pore volume fraction, the porosity size (mean
and distribution), and its geometric distribution can all have variable effects on the thermal properties, especially the thermal
transport properties. The porosity in the test specimens should be adequately defined and characterized with regard to its effect on
thermal conductivity/diffusivity.
8.3.3 Variations in stoichiometry, impurities, grain size, and grain boundary phases can have a large effect on the thermal
conductivity and thermal diffusivity for ceramics with high intrinsic thermal conductivity (aluminum nitride, beryllia, silicon
carbide, and so forth). The effect of such composition variations and phase distributions should be carefully considered and
evaluated (if feasible) in thermal tests of high thermal conductivity ceramics.
8.3.4 Phase changes and devitrification of amorphous phases may occur during thermal tests, producing anomalies in the various
thermal properties. Test operators should be informed of the potential for such transformations in specimens submitted for testing.
8.3.5 Thermal expansion measurements for ceramics often show heating/cooling hysteresis when microcracking or minor phase
changes occur. Irreversible thermal expansion effects may also occur in certain materials, based on annealing, rapid heating rates,
creep, crystallization, or microcracking. Thermal expansion tests done only on heating can be misleading, and thermal expansion
measurements should be done under both heating and cooling conditions.
8.3.6 Oriented or textured grain structures in monolithic ceramics can introduce anisotropic effects in the thermal properties.
Such grain structures are commonly developed during processing. If the thermal effects of such anisotropy are significant, the grain
structure should be characterized by optical or SEM microscopy or by X-ray diffraction.
8.4 Particulate and Whisker-Reinforced Ceramic Composite—Material Variables:
8.4.1 Particulate and whisker reinforcement of advanced ceramics adds an additional degree of complexity to the composition
and microstructure of the test specimen. It is critical that the particulate or whisker additions be adequately characterized in terms
of composition, phase and crystal structure, particle/whisker morphology, and size distribution. It is also useful to have nominal
thermal properties, that is, specific heat, thermal conductivity, and thermal expansion, for the reinforcement across the temperature
range of interest. Those thermal property data will assist in interpreting the composite thermal test results.
8.4.2 As part of the composite specimen, the particulate/whisker reinforcement must be adequately defined in terms of the
volume fraction, spatial distribution, and orientation/anisotropy/texture. For example, reinforcements with high thermal
conductivity relative to the matrix will have markedly different effects on the composite thermal properties, depending on how the
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reinforcements are distributed and oriented. For example, whiskers in a laminated, planar orientation will produce anisotropic
thermal conductivity in the composite. The bulk thermal conductivity will markedly change if the particulate packing factor is high
enough to produce significant particle-to-particle contact.
8.4.3 If there is a large difference in thermal expansion between the reinforcement and the matrix in the composite, residual
stresses or microcracks, or both, can develop during processing. Such residual stresses and microcracks can produce anomalies in
thermal expansion measurements. Microcracking can also have a direct effect on thermal conductivity/diffusivity.
8.5 Continuous Fiber-Reinforced Ceramic Composites—Material Variables:
8.5.1 The use of continuous fiber reinforcement in ceramic composites provides the ceramic engineer the greatest range of
property control and tailoring, but also introduces the highest level of complexity into the composition and microstructure of
advanced ceramics.
8.5.2 It is essential that the composition and architecture of the fiber reinforcement in the composite be adequately characterized
and documented,documented to include the following:
8.5.2.1 Fiber composition, filament morphology (diameter and length), and fiber volume fraction.
8.5.2.2 Filament counts in tows, comprehensive description of the reinforcement architecture [one-dimensional(one-
dimensional (tows), two-dimensional (woven fabrics), and three-dimensional (weaves and braid)]braid)) to include tow count and
repeat units.
8.5.2.3 The composition and morphology of any interface coatings on the fibers, used for process protection of the fibers or for
development of crack deflection modes in the composite.
8.5.2.4 The composition and morphology (thickness, porosity, and grain structure) of any surface coatings on the composite
component, used for surface sealing, oxidation/corrosion protection, or wear/abrasion resistance. Surface coatings may be
considered as monolithic layers on the surface of the composite.
8.5.3 The matrix in the composite must also be adequately characterized in terms of composition, constituents, morphology, and
grain structure. Porosity in the composite should also be characterized, considering volume fraction, pore size, shape factors, and
distribution of porosity.
8.5.4 Fiber-reinforced ceramic composites often have strong anisotropic properties, determined by the reinforcement
architecture with higher fiber volume loadings in specific directions. It is essential that the geometry and orientation of the
reinforcement are fully documented and correlated with the thermal test results.
8.5.5 In many thermal tests (such as thermal dilatometery, diffusivity, and specific heat), the test specimens may have one or
more dimensions which are small in comparison to the weave repeat elements. Experimenters should carefully consider the size
of the test specimens for a specific test to ensure that an adequate number of weave repeat elements are included in the specimen.
Specimens of insufficient size may not be representative of the properties of the larger piece or may have exaggerated end or edge
effects.
9. Test Specimen Sampling and Preparation
9.1 Test Specimen Sources—Test specimens for thermal evaluation can be taken from engineering components or fabricated test
panels/billets. The selection of a particular source depends on the required test specimen geometry and the suitability of the test
component for test specimen preparation. The primary objective is to select test specimens that are representative of the
composition, processing, and properties of the final functional part.
9.2 Specimen Sampling to Assess Variability:
9.2.1 Depending on the degree of process control, variability may occur among test specimens within a batch and between
different batches of test specimens. The variation may occur in the composition, microstructure, and porosity of advanced ceramics.
The degree of variation will depend on the homogeneity within the batch and on reproducibility between batches from the
producer. The test operator should select/prepare sufficient test specimens to provide a representative sample of the entire batch
of specimens submitted for testing. In addition, batch/lot identification should be carefully noted for documentation purposes.
9.2.2 Practice E122 provides guidance on calculating the number of units required for testing to obtain an estimate of certain
precision for a given property.
9.3 Orientation and Anisotropy Effects—If the test material has significant anisotropy or orientation effects, it is imperative that
test specimens be selected to adequately sample the anisotropy in the major directions of interest. A minimum of two directions
should be selected for test specimens. The orientations should be selected to produce the maximum and minimum material
properties. Each test specimen should be marked and identified so that its orientation in the original part/test piece can be identified.
9.4 Location and Identification:
9.4.1 Given the variability which may occur in developmental advanced ceramics and the anisotropy which may be an
engineered characteristic of composite components, test specimen locations should be documented by drawing or photograph. Test
specimens should be identified so that their location can be traced on the original part. Special identification should be used for
test specimens taken from plate edges or from areas with local anomalies.
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9.4.2 Nondestructive evaluation (NDE) methods may be of value in characterizing test plates prior to specimen preparation,
particularly for fiber-reinforced ceramic composites. The NDE results will assist in locating material anomalies, such as excessive
porosity or delaminations.
9.5 Specimen Count and Repeat Tests—Follow
...