ASTM C1720-21

Standard Test Methods for Determining Liquidus Temperature of Waste Glasses and Simulated Waste Glasses

SIGNIFICANCE AND USE
5.1 This procedure can be used for (but is not limited to) the following applications:
(1) support glass formulation development to make sure that processing criteria are met,
(2) support production (for example, processing or troubleshooting), and
(3) support model validation.
SCOPE
1.1 These test methods cover procedures for determining the liquidus temperature (TL) of nuclear waste, mixed nuclear waste, simulated nuclear waste, or hazardous waste glass in the temperature range from 600 °C to 1600 °C. This test method differs from Practice C829 in that it employs additional methods to determine TL. TL is useful in waste glass plant operation, glass formulation, and melter design to determine the minimum temperature that must be maintained in a waste glass melt to make sure that crystallization does not occur or is below a particular constraint, for example, 1 volume % crystallinity or T1%. As of now, many institutions studying waste and simulated waste vitrification are not in agreement regarding this constraint (1).2  
1.2 Three methods are included, differing in (1) the type of equipment available to the analyst (that is, type of furnace and characterization equipment), (2) the quantity of glass available to the analyst, (3) the precision and accuracy desired for the measurement, and (4) candidate glass properties. The glass properties, for example, glass volatility and estimated TL, will dictate the required method for making the most precise measurement. The three different approaches to measuring TL described here include the following: Gradient Temperature Furnace Method (GT), Uniform Temperature Furnace Method (UT), and Crystal Fraction Extrapolation Method (CF). This procedure is intended to provide specific work processes, but may be supplemented by test instructions as deemed appropriate by the project manager or principle investigator. The methods defined here are not applicable to glasses that form multiple immiscible liquid phases. Immiscibility may be detected in the initial examination of glass during sample preparation (see 9.3). However, immiscibility may not become apparent until after testing is underway.  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 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.  
1.5 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: 30-Sep-2021
• ICS: 81.040.10 - Raw materials and raw glass
• Technical Committee: C26 - Nuclear Fuel Cycle
• Drafting Committee: C26.13 - Spent Fuel and High Level Waste

Relations

• Refers: ASTM C859-24 - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-Jan-2024
• Refers: ASTM E2282-23 - Standard Guide for Defining the Test Result of a Test Method
• Effective Date: 01-Nov-2023
• Refers: ASTM C162-23 - Standard Terminology of Glass and Glass Products
• Effective Date: 01-Oct-2023
• Refers: ASTM C162-05(2015) - Standard Terminology of<brk type="line"/> Glass and Glass Products
• Effective Date: 01-Nov-2015
• Refers: ASTM E2282-14 - Standard Guide for Defining the Test Result of a Test Method
• Effective Date: 01-Oct-2014
• Refers: ASTM C859-14a - Standard Terminology Relating to Nuclear Materials
• Effective Date: 15-Jun-2014
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM C859-14 - Standard Terminology Relating to Nuclear Materials
• Effective Date: 15-Jan-2014
• Refers: ASTM E2282-13 - Standard Guide for Defining the Test Result of a Test Method
• Effective Date: 01-Aug-2013
• Refers: ASTM C859-13a - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-Jun-2013
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM C859-13 - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-May-2013
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM C859-10b - Standard Terminology Relating to Nuclear Materials
• Effective Date: 01-Nov-2010

Overview

ASTM C1720-21, "Standard Test Methods for Determining Liquidus Temperature of Waste Glasses and Simulated Waste Glasses," defines standardized procedures to determine the liquidus temperature (TL) of nuclear waste glass, mixed nuclear waste glass, simulated nuclear waste, and hazardous waste glasses. The standard covers crucial testing within a temperature range of 600 °C to 1600 °C. Determining the liquidus temperature is essential for effective glass formulation, melter design, and process optimization in vitrification and disposal of radioactive and hazardous materials.

Key Topics

• Liquidus Temperature (TL): The maximum temperature at which thermodynamic equilibrium exists between molten glass and its primary crystalline phase.
• Test Methods Covered:
  • Gradient Temperature Furnace Method (GT): Employs a temperature gradient across the test sample to identify the crystallization front. Particularly used for glasses with lower TL or low volatility near TL.
  • Uniform Temperature Furnace Method (UT): Uses a consistent temperature to heat samples for precise measurement, reducing volatility effects and applicable up to high TL values.
  • Crystal Fraction Extrapolation Method (CF): Relies on quantifying the crystalline fraction via XRD or microscopy, extrapolating TL as crystals approach zero.
• Types of Glasses Addressed:
  • Nuclear waste glass
  • Mixed nuclear waste glass
  • Simulated nuclear waste glass
  • Hazardous waste glass
• Exclusions: Not applicable to glasses forming multiple immiscible liquid phases.

Applications

ASTM C1720-21 supports several critical applications in the waste management and glass manufacturing sectors:

• Glass Formulation Development: Ensures glass compositions maintain processing criteria regarding crystallization, supporting the development of stable glass matrices for waste immobilization.
• Production and Process Support: Validates melter temperatures to avoid unwanted crystallization, assists in troubleshooting, and ensures robust operating conditions for glass production plants.
• Model Validation: Provides benchmark data for validating computational models predicting glass behavior and liquidus temperatures.
• Quality Assurance: Establishes reliable methods to assess and maintain the quality and performance standards in vitrified waste products.

Related Standards

This standard references and complements several key documents relevant to waste glass testing and quality:

• ASTM C829 - Practices for Measurement of Liquidus Temperature of Glass by the Gradient Furnace Method
• ASTM C162 - Terminology of Glass and Glass Products
• ASTM D1193 - Specification for Reagent Water
• ASTM E177, E691, E2282 - Practices and guides related to measurement precision, bias, and defining test results
• ISO/IEC 17025 - General requirements for competence of testing and calibration laboratories
• NIST Standard Reference Materials such as SRM-773, SRM-1416, and SRM-674b, provide calibration and quality checks.

Practical Value

Implementing ASTM C1720-21 enables organizations to:

• Promote safety and regulatory compliance in nuclear waste handling.
• Achieve consistency and reproducibility in glass processing operations.
• Mitigate risks associated with unpredictable crystallization in waste glass, thereby enhancing the durability and reliability of waste storage forms.
• Support international trade and acceptance of waste glass products through adherence to globally recognized test procedures.

Using these test methods ensures that glass products for immobilizing radioactive and hazardous waste meet rigorous industry expectations for stability, safety, and performance.

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: C1720 − 21
Standard Test Methods for
Determining Liquidus Temperature of Waste Glasses and
Simulated Waste Glasses
This standard is issued under the fixed designation C1720; 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 1.3 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
1.1 These test methods cover procedures for determining
standard.
the liquidus temperature (T ) of nuclear waste, mixed nuclear
L
1.4 This standard does not purport to address all of the
waste,simulatednuclearwaste,orhazardouswasteglassinthe
safety concerns, if any, associated with its use. It is the
temperature range from 600°C to 1600°C. This test method
responsibility of the user of this standard to establish appro-
differs from Practice C829 in that it employs additional
priate safety, health, and environmental practices and deter-
methods to determine T . T is useful in waste glass plant
L L
mine the applicability of regulatory limitations prior to use.
operation, glass formulation, and melter design to determine
1.5 This international standard was developed in accor-
the minimum temperature that must be maintained in a waste
dance with internationally recognized principles on standard-
glassmelttomakesurethatcrystallizationdoesnotoccuroris
ization established in the Decision on Principles for the
below a particular constraint, for example, 1 volume %
Development of International Standards, Guides and Recom-
crystallinity or T . As of now, many institutions studying
1%
mendations issued by the World Trade Organization Technical
waste and simulated waste vitrification are not in agreement
Barriers to Trade (TBT) Committee.
regarding this constraint (1).
2. Referenced Documents
1.2 Three methods are included, differing in (1) the type of
equipment available to the analyst (that is, type of furnace and 3
2.1 ASTM Standards:
characterization equipment), (2) the quantity of glass available
C162Terminology of Glass and Glass Products
to the analyst, (3) the precision and accuracy desired for the
C829PracticesforMeasurementofLiquidusTemperatureof
measurement, and (4) candidate glass properties. The glass
Glass by the Gradient Furnace Method
properties, for example, glass volatility and estimated T , will
L
C859Terminology Relating to Nuclear Materials
dictate the required method for making the most precise
E177Practice for Use of the Terms Precision and Bias in
measurement. The three different approaches to measuring T
L
ASTM Test Methods
described here include the following: Gradient Temperature
E691Practice for Conducting an Interlaboratory Study to
Furnace Method (GT), Uniform Temperature Furnace Method
Determine the Precision of a Test Method
(UT), and Crystal Fraction Extrapolation Method (CF). This
E2282Guide for Defining the Test Result of a Test Method
procedure is intended to provide specific work processes, but 4
2.2 NIST Standards:
may be supplemented by test instructions as deemed appropri-
SRM-773 National Institute for Standards and Technology
ate by the project manager or principle investigator. The
(NIST) Liquidus Temperature Standard
methods defined here are not applicable to glasses that form
SRM-674bNIST X-Ray Powder Diffraction Intensity Set
multiple immiscible liquid phases. Immiscibility may be de-
for Quantitative Analysis by X-Ray Diffraction (XRD)
tected in the initial examination of glass during sample
SRM-1416Aluminosilicate Glass for Liquidus Temperature
preparation (see 9.3). However, immiscibility may not become
SRM-1976aNISTInstrument Response Standard for X-Ray
apparent until after testing is underway.
Powder Diffraction
SRM-1976cInstrument Response Standard for X-Ray Pow-
der Diffraction
These test methods are under the jurisdiction of ASTM Committee C26 on
Nuclear Fuel Cycle and is the direct responsibility of Subcommittee C26.13 on
Spent Fuel and High Level Waste. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2021. Published December 2021. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
ɛ1
approved in 2011. Last previous edition approved in 2017 as C1720–17 . DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/C1720-21. the ASTM website.
2 4
The boldface numbers in parentheses refer to a list of references at the end of Available from National Institute of Standards and Technology (NIST), 100
this standard. Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
C1720 − 21
2.3 Other Standard: 3.2.14 inhomogeneous glass—a glass that is not a single
ISO/IEC 17025:2017 American National Standards amorphous phase; a glass that is either phase separated into
Institute/National Conference of Standards Laboratories multiple amorphous phases or is crystallized.
(ANSI/NCSL) General Requirements for the Competence
3.2.15 liquidus temperature (T )—the maximum tempera-
L
of Testing and Calibration Laboratories
ture at which thermodynamic equilibrium exists between the
molten glass and its primary crystalline phase.
3. Terminology
3.2.15.1 Discussion—T is the maximum temperature at
L
which a glass melt crystallizes.
3.1 Fortermsnotdefinedherein,refertoTerminologyC859
and C162.
3.2.16 melt insoluble—a crystalline, amorphous, or mixed
phase material that is not appreciably soluble in molten glass,
3.2 Definitions:
for example, noble metals, noble metal oxides.
3.2.1 air quenching—to pour or place a molten glass speci-
men on a surface, for example, a steel plate, and cool it to the 3.2.17 mixed waste—waste containing both radioactive and
hazardous components regulated by the Atomic Energy Act
solid state.
(AEA) (3) and the Resource Conservation and Recovery Act
3.2.2 anneal—to prevent or remove processing stresses in
(RCRA) (4), respectively.
glass by controlled cooling from a suitable temperature, for
3.2.17.1 Discussion—Theterm“radioactivecomponent”re-
example, the glass transition temperature (T ) (modified from
g
fers to the actual radionuclides dispersed or suspended in the
Terminology C162).
waste substance (5).
3.2.3 annealing—a controlled cooling process for glass
3.2.18 mold—a pattern, hollow form, or matrix for giving a
designed to reduce thermal residual stress to an acceptable
certain shape or form to something in a plastic or molten state.
level and, in some cases, modify structure (modified from
Webster’s Dictionary
Terminology C162).
3.2.19 nuclear waste glass—a glass composed of glass-
3.2.4 cleaning glass—glass or flux used to remove high
forming additives and radioactive waste.
viscosity glass, melt insolubles, or other contamination from
3.2.20 observation—the process of obtaining information
platinum-ware.
regarding the presence or absence of an attribute of a test
3.2.5 crystallize—to form and/or grow crystals from a glass
specimen or of making a reading on a characteristic or
melt during heat-treatment or cooling.
dimension of a test specimen (see Terminology E2282).
3.2.6 crystallization—the progression in which crystals are
3.2.21 preferred orientation—when there is a stronger ten-
first nucleated and then grown within a host medium.
dencyforthecrystallitesinapowderoratexturetobeoriented
3.2.6.1 Discussion—Generally, the host may be a gas,
more one way, or one set of ways, than all others.
liquid, or another crystalline form. However, in this context, it
3.2.21.1 Discussion—This is typically due to the crystal
is assumed that the medium is a glass melt. 7
structure. IUCr
3.2.7 crystallization front—the boundary between the crys-
3.2.22 primary phase—the crystalline phase at equilibrium
talline and crystal-free regions in a test specimen that was
with a glass melt at its liquidus temperature.
subjected to a temperature gradient heat-treatment.
3.2.23 radioactive—of or exhibiting radioactivity; a mate-
3.2.8 furnace profiling—the process of determining the
rial giving or capable of giving off radiant energy in the form
8 6
actual temperature inside of a furnace at a given location; this
of particles or rays. American Heritage Webster’s
involves different steps for different types of furnaces.
3.2.23.1 Discussion—Example of particles or rays formed
by the disintegration of atomic nuclei are α, β, and γ; said of
3.2.9 glass—an inorganic product of fusion that has cooled
to a rigid condition without crystallizing (see Terminology certain elements, such as radium, thorium, and uranium and
their products.
C162); a noncrystalline solid or an amorphous solid (2).
3.2.24 Round-Robin—aninterlaboratoryandintralaboratory
3.2.10 glass sample—the material to be heat-treated or
testing process to develop the precision and bias of a proce-
tested by other means.
dure.
3.2.11 glass specimen—the material resulting from a spe-
3.2.25 section—a part separated or removed by cutting; a
cific heat treatment.
slice, for example, representative thin section of the glass
3.2.12 glass transition temperature (T )—on heating, the
g 6
specimen. Webster’s
temperatureatwhichaglasstransformsfromasolidtoaliquid
3.2.26 simulated nuclear waste glass—a glass composed of
material,characterizedbytheonsetofarapidchangeinseveral
glass forming additives with simulants of, or actual chemical
properties, such as thermal expansivity.
species, or both, in radioactive wastes or in mixed nuclear
3.2.13 gradient furnace—a furnace in which a known tem-
wastes, or both.
perature gradient is maintained between the two ends.
Merriam-webster.com.
5 7
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St., IUCr Online Dictionary of Crystallography, 2011.
4th Floor, New York, NY 10036, http://www.ansi.org. American Heritage Dictionary, 1973.
C1720 − 21
3.2.27 surface tension—a property, due to molecular forces, 3.4.18 OM—optical microscope or optical microscopy
by which the surface film of all liquids tends to bring the
3.4.19 PDF—powder diffraction file
contained volume into a form having the least possible area.
3.4.20 RCRA—Resource Conservation and Recovery Act
3.2.28 test determination—the value of a characteristic or
3.4.21 RIR—relative intensity ratio
dimension of a single test specimen derived from one or more
3.4.22 RLM—reflected light microscopy
observed values (see Terminology E2282).
3.4.23 SD—standard deviation
3.2.29 test method—a definitive procedure that produces a
test result (see Terminology E2282). 3.4.24 SEM—scanning electron microscope or scanning
electron microscopy
3.2.30 test observation—see observation.
3.4.25 SRM—Standard Reference Material
3.2.31 uniform temperature furnace—afurnaceinwhichthe
temperature is invariant over some defined volume and within
3.4.26 SSE—sum of squared errors
some defined variance.
3.4.27 T —temperature where glass contains 1 volume%
1%
3.2.32 vitrification—the process of fusing waste with glass
of a crystalline phase
making chemicals at elevated temperatures to form a waste
3.4.28 T —primary UT measurement above T
a L
glass (see Terminology C162).
3.4.29 T —primary UT measurement below T
c L
3.2.33 volatility—the act of one or more constituents of a
3.4.30 T —glass transition temperature
g
solid or liquid mixture to pass into the vapor state.
3.4.31 T —liquidus temperature
L
3.2.34 waste glass —a glass developed or used for immo-
3.4.32 TLM—transmitted light microscopy
bilizing radioactive, mixed, or hazardous wastes.
3.4.33 T —melting temperature for glass preparations
M
3.3 Definitions of Terms Specific to This Standard:
3.4.34 UF—uniform temperature furnace
3.3.1 ASTM Type I water—purified water with a maximum
total matter content including soluble silica of 0.1 g/m,a
3.4.35 UT—uniform temperature furnace method
-1
maximum electrical conductivity of 0.056 µΩ /cm at 25 °C,
3.4.36 WC—tungsten carbide
and a minimum electrical resistivity of 18 MΩ×cmat25°C.
3.4.37 XRD—X-ray diffraction
3.3.2 set of samples—samples tested simultaneously in the
same oven. 4. Summary of Test Method
3.3.3 standard—to have the quality of a model, gauge, 4.1 These test methods describe methods for determining
pattern, or type. Webster’s
the T ofwasteorsimulatedwasteglasses.Fig.1illustratesan
L
example T for a simple two-component liquid on an arbitrary
3.3.4 standardize—to make, cause, adjust, or adapt to fit a L
binary phase diagram.
standard (5); to cause to conform to a given standard, for
4.1.1 Gradient Temperature Furnace Method (GT)—This
example, to make standard or uniform. Webster’s
method is similar to Practice C829, “Standard Practices for
3.4 Abbreviations:
Measurement of Liquidus Temperature of Glass by the Gradi-
3.4.1 AEA—Atomic Energy Act
ent Furnace Method,” although it has been modified to meet
3.4.2 ANSI—American National Standards Institute
thespecificneedsofwasteandsimulatedwasteglassmeasure-
ments. The most pronounced differences between this method
3.4.3 ASTM—American Society for Testing and Materials
and the Practice C829 “boat method” are the sample prepara-
3.4.4 CF—crystal extrapolation method
tion and examination procedures.
3.4.5 C —crystal fraction in a sample or specimen
F
4.1.1.1 Samples are loaded into a boat, for example, plati-
3.4.6 EDS—energy dispersive spectrometry
num alloy (Fig. 2) with a tight-fitting lid, and exposed to a
linear temperature gradient in a gradient furnace (Fig. 3) for a
3.4.7 η—viscosity
fixedperiodoftime.Thetemperature,asafunctionofdistance,
3.4.8 FWHM—full width of a peak at half maximum
d, along the sample, is determined by the location within the
3.4.9 GF—gradient temperature furnace
gradient furnace, and the T is then related to the location of
L
3.4.10 GT—gradient temperature furnace method the crystallization front in the heat-treated specimen (Fig. 4).
4.1.1.2 Following the heat-treatment, the specimen should
3.4.11 HF—hydrofluoric acid
be annealed at, or near, the glass transition temperature, T,of
g
3.4.12 HLW—high-level waste
the glass (this should be previously measured or estimated) to
3.4.13 ID—identification
reduce specimen cracking during cutting and polishing.
4.1.1.3 The specimen should then be scored or marked to
3.4.14 MSE—mean squared error
signifythelocationsonthespecimenlocatedatdifferentdepths
3.4.15 NBS—National Bureau of Standards
into the gradient furnace, that is, locations heat-treated at
3.4.16 NCSL—National Conference of Standards Laborato-
specific temperatures.
ries
4.1.1.4 If the specimen is optically transparent, it can be
3.4.17 NIST—National Institute for Standards and Technol- observedwithtransmittedlightmicroscopy(TLM)orreflected
ogy (formerly NBS) light microscopy (RLM) to look for bulk or surface
C1720 − 21
FIG. 1 Binary Phase Diagram of Components A and B with T of Composition C Highlighted
L
FIG. 2 GF Boat Diagram: (A) Single Chamber Crucible Design (B) Single Chamber Design Loaded with a Set of Samples (that is,
Smaller Crucibles)
FIG. 3 Photograph of Typical Gradient Temperature Furnace
crystallization, respectively. If the specimen is not optically the crystallization front is likely not constant at a given
transparent or is barely optically transparent (for example, in temperature (see Fig. 4)).
glasses with high quantities of Fe O ), a cut or fractured 4.1.1.5 The temperature gradient and increased volatility at
2 3
section of the glass can be polished very thin (that is, a thin higher temperatures cause gradients in surface tension, which
section can be made) to allow for observation.Another option in turn cause convective flow. This method is ideal for glasses
for surface observations is scanning electron microscopy with a T less than roughly 1000 °C or glasses with a low
L
(SEM). This method provides a quick measurement of T in volatility near the T . If the temperature range spanned by the
L L
theabsenceofconvectiveflowofglassinthegradiantfurnace, crystallizationfrontistoohighforthedesiredtolerance, UTor
which distorts the location of the crystallization front (that is, CF should be used for a more precise T measurement. GT is
L
C1720 − 21
FIG. 4 OM Micrograph of the Crystallization Front in a GT Specimen
not easily used to measure the T on radioactive glasses is more easily applied to radioactive glasses, and can be used
L
becauseofthesizeofthegradientfurnaceandthecomplicated
to measure T values as high as 1600 °C with typical
L
sampleanalysisrequired.Thismethodisnotrecommendedfor
high-temperature furnaces (for example, furnaces with MoSi
glasses with a T in a temperature range of very low glass
heatingelements),andevenhigherwithspecializedequipment
L
viscosity (that is, η < 50 Pa·s).
and high-temperature crucibles. This method may be used for
4.1.2 Uniform Temperature Furnace Method (UT)—This
glasses with a high volatility near T under certain circum-
L
method is similar to the methods used in phase diagram
stances.
determination and can be used for making more precise
4.1.3 Crystal Fraction Extrapolation Method (CF)—This
measurements than those determined with GT.
method is an alternate method that uses a UT specimen to
4.1.2.1 In this method, a glass sample is loaded into a
measure the crystal fraction, C (in mass% or volume%), of
F
crucible (for example, platinum alloy, see Fig. 5) with a
a crystalline phase or phases in a sample heat-treated at
tight-fittinglidandsubjectedtotemperaturesforafixedperiod
multiple temperatures,T< L F
of time (for example, 24h 6 2 h). Following heat-treatment,
measured with XRD, RLM, TLM, SEM, or combinations
the specimen can be observed by optical microscopy (OM) for
thereof, by mass and/or volume%, and then T is achieved by
L
the appearance or absence of crystalline or other undissolved
extrapolating C as a function of temperature to zero crystals.
F
materials with methods similar to those previously described
This method is more suited for glasses with a higher volatility
(4.1.1). Crystalline material present in the meniscus (that is, in
near the T than the previous methods. When multiple crystal-
L
the upper corners of the heat-treated specimen) can be an
line phases are present, XRD is an effective method for
artifact of this process and should be reported separately. The
quantifying C as a function of temperature and is very
locations of the crystals within the heat-treated specimen need F
effective at determining the T of each phase independently;
to be reported (that is, the melt-crucible interface, meniscus, L
this would be more difficult by GT and UT. CF yields the
melt-airinterface,orthebulk)ontheliquidustemperaturedata
additional benefit of equilibrium crystal fractions as a function
sheet (see Appendix X1). The crystal locations used to define
T shouldbeclearlydocumentedwhenreporting T .Typically, of temperature, which can sometimes tend to be non-linear at
L L
crystals in any location except for the meniscus (where C > 5 mass % to 10 mass% crystallinity for most crystalline
F
composition can be affected by volatility) are used. In some
phases. Different techniques for CF are described below.
circumstances, surface crystallization can be excluded from T
L 4.1.3.1 Volume Fraction of Crystal(s) in the Specimen
determination.
(12.4.2)—WithTLM, RLM, or SEM as well as image analysis
4.1.2.2 The T is then given by the temperature range
L
software, it is possible to measure the area fraction of crystals
between the highest temperature at which a specimen contains
in an image or micrograph of the specimen. The area fraction
crystals (T ) and the lowest temperature without crystals in the
c
is then equivalent to the volume fraction if the image is
specimen(T );theT isthentypicallydefinedastheaverageof
a L
representative of the bulk of the specimen, and the effective
T and T .
a c
depth of the image is insignificant. If this process is done at
4.1.2.3 This method is more time consuming as it requires
differenttemperatures,the T canbeextrapolatedasafunction
L
more heat-treatments than GT, although it minimizes the
of temperature.
effects of volatility and eliminates the convection-driven un-
certainty in crystallization front measurements.This method is
NOTE1—Themassfractionofcrystalsinthespecimencanbeestimated
usedforhighprecisionmeasurements(ontheorderof 65°C), if the densities of the glass and the crystal(s) are known.
C1720 − 21
FIG. 5UT andCF Crucible Schematic
4.1.3.2 Number Fraction of Crystal(s) in the Specimen 4.1.3.4 Mass Fraction of Crystal(s) in the Specimen by
(12.4.3)—Inthesamefashionasdescribedin4.1.3.1,countthe Comparing it to the Calibration Curve (12.4.5)—In this
number of crystals in an image or micrograph of the specimen
method, samples with known concentrations of the crystalline
at different temperatures. If this process is done at different
phasesbeinganalyzedarepreparedandtestedusingXRD.The
temperatures, the T can be extrapolated as a function of
peak area’s (full width at half maximum or FWHM, total
L
temperature.
crystal peak area, or highest peak area) and known crystal
4.1.3.3 Mass Fraction of Crystal(s) in the Specimen by
fractionsareusedtogenerateacalibrationcurve.Thepeakarea
Adding a Known Crystalline Phase(12.4.4)—Addingaknown
of the unknown specimen is then used in the calibration
mass fraction of a known, standard crystalline material (for
equation to determine a quantitative (if interpolated) or semi-
example, NIST SRM-674b) allows the standardization of the
quantitative (if extrapolated) crystal fraction.
XRDpattern.Thestandardsandtheunknownspecimenshould
4.1.3.5 Volume Fraction of Crystal(s) in the Specimen With
be run independently before mixing to verify that there is not
C Data From XRD Analysis—Commonly, melter constraints
F
overlap between the peaks of the standard and the peaks in the
are in terms of a volume% of crystallinity, for example, T .
1%
unknown specimen because this will make quantification
Once C data are obtained in mass% by XRD, the remaining
F
difficultandlessaccurate.Thestandardizedpatterncanthenbe
mass of glass, m , is calculated as a difference given by
g
used to generate quantitative (if the crystal structure has been
N
refined) or semi-quantitative (if the crystal structure has not
m 5 m 2 m (1)
g t ( c,i
been refined) C analysis with Rietveld (6-8) refinement
F i51
software or the relative intensity ratio (RIR) method (12.4.5). where:
C1720 − 21
6.1.3 Resistance furnace and controller used for annealing
m = the total mass (that is, the value is normalized to one
t
(capableofmaintainingconstanttemperaturesbetween400°C
and thus component values are mass fractions), and
and ~900 °C) with a temperature accuracy of 10 °C.
m = themassfractionofthei-thcrystallinephaseobserved
c,i
6.1.4 Specimen boat made of material inert to the sample
and quantified by XRD.
(for example, platinum alloy) with approximate dimensions of
By converting the mass fractions of the i-th component
0.5 cm × 1 cm × 10 cm to 30 cm (width × height × length),
additives, m, into mole fractions, M, the density of glass, ρ ,
i i g
respectively; an example specimen boat is shown in Fig. 2.If
can be computed with the following expression:
the test glass viscosity is below 5 Pa·s at the measurement
N
M m temperature, it is recommended that a round-based crucible be
(i51 i m,i
ρ 5 (2)
g N
used. A separate option with Method A is to fill the long boat
M V
(i51 i M,i
with several small individual boats with individual lids (Fig.
where:
2-B).
m = the molecular mass of the i-th oxide, and
6.1.5 Diamond cutoff saw.
m,i
V = the molar volume of the i-th component additive
M,i 6.1.6 Variable speed polisher.
explained elsewhere (9).
6.1.7 Silicone rubber mold for mounting of GT glass
specimen in epoxy.
The total volume of each heat treatment, V , is calculated
HT
6.1.8 OM for TLM and/or RLM.
with
6.1.9 SEM/EDS.
N
m
m
(i51 c,i
g 6.1.10 XRD.
V 5 1 (3)
HT
ρ ρ
g c,i
6.2 Equipment Needed for UT:
where:
6.2.1 Resistance furnace capable of maintaining constant
ρ = the density of the i-th crystalline component. temperatures T ~550°C to 1600 °C (that is, MoSi heating
c,i 2
elements) or furnace capable of T ≤ 1200 °C for glasses with
The volume% of the i-th crystalline component, V ,inthe
c,i
T ≤ 1150 °C.
L
heat-treated specimen is denoted by
6.2.2 Calibrated thermocouple and temperature readout de-
m
c,i
vice appropriate for the estimated temperature range that will
V 5100 3 (4)
c,i
~ρ 3V !
c,i HT
be used for testing (6.1.2).
6.2.3 Specimen boat (or crucible) and tight fitting lid made
The values of V can then be plotted as a function of
c,i
of material compatible with the sample (for example, platinum
temperature and a linear correlation fit to the data with
alloy) with suggested dimensions of 1.2 cm × 1.2 cm × 1.2 cm
V 5 m 3T1b (5)
c,i
(width × height × length, respectively) (Fig. 5-1A). Another
where:
option is a round-bottom, thimble-shaped crucible (Fig. 5-1B).
6.2.4 Diamond cutoff saw.
T =(V –b)/m when V =1(T )
1% c,i c,i 1%
6.2.5 Variable speed polisher.
6.2.6 OM for TLM and/or RLM.
5. Significance and Use
6.2.7 SEM/EDS.
5.1 Thisprocedurecanbeusedfor(butisnotlimitedto)the
6.2.8 XRD.
following applications:
6.3 Equipment Needed for CF:
(1)support glass formulation development to make sure
6.3.1 This includes the same equipment as described previ-
that processing criteria are met,
ously in 6.2 because a UT specimen is required for the
(2) support production (for example, processing or
measurement technique, although additional materials are also
troubleshooting), and
required.
(3)support model validation.
6.3.2 Image analysis software for measuring the C present
F
in a micrograph collected with OM, SEM, etc.
6. Apparatus
6.3.3 Crystal structure/unit cell refinement software for
6.1 Equipment for GT:
quantifying crystal fractions by spiking in a known mass% of
6.1.1 Resistance-heated tubular gradient furnace capable of a known crystalline material.
achieving temperatures of 550°C to 1150 °C with gradients in 6.3.4 Known crystalline material (for example, SRM-674b)
the range of roughly 1 °C/mm (Fig. 3). For glasses with an that does not overlap with crystalline peaks in unknown
estimated T > 1150 °C, furnaces with elements capable of specimen.
L
high temperatures need be used, for example, MoSi .
7. Reagents and Materials
6.1.2 Calibrated thermocouple and temperature readout de-
vice appropriate for the estimated temperature range that will 7.1 Reagents and materials used in conjunction with the
be used for testing. Type K thermocouples can be used within various methods outlined in this procedure.
95°C to 1260 °C, Type R thermocouples can be used within 7.1.1 Reagents:
870°C to 1450 °C, and Type S thermocouples can be used 7.1.1.1 ASTM Type 1 water.
within 980°C to 1450 °C without special calibrations or 7.1.1.2 Cleaning solvents, for example, ethanol,
qualifications. isopropanol, acetone.
C1720 − 21
7.1.1.3 Abrasive media for polishing (such as SiC or dia- range (based on model predictions), heat treatment time, and
mond). data recording requirements.
7.1.1.4 Glass microscope slides.
9.2 GF Preparation:
7.1.1.5 Glass cover slides.
9.2.1 A gradient furnace is constructed of two or more
7.1.1.6 Meltable adhesive (such as wax).
independent heating zones, and thus the gradient can be
7.1.1.7 Solvent-soluble adhesives (such as methyl
adjusted as needed to obtain a low-pitched (∆T/∆d is low,
methacrylate-based adhesives).
where Tistemperatureand disdistancefromareferencepoint
7.1.1.8 Non-temperature sensitive adhesives (such as cya-
inside the furnace) or sharp gradient (∆T/∆d is high), a
noacrylate or other epoxy).
parameterthatshouldbeoptimizedwithinthegradientfurnace
7.1.2 Materials:
accordinglydependingupontheexpectedcrystallizationrateof
7.1.2.1 Furnace appropriate to method being used, for
the sample (∆C /∆T). If ∆C /∆T is low (for example, ≤ 1
F F
example, GF, UF (required heating elements dependent on
mass% ∆C increase over ≥ 100 °C is considered low), the
F
temperature needs).
gradient can be low-pitched, and in cases where ∆C /∆T is
F
7.1.2.2 Material for making crucibles or boats, for example,
high (for example, ≥ 1 mass% ∆C increase over ≤ 10 °C is
F
sheets of platinum alloy or pre-formed crucible(s).
considered extremely high), the gradient can be high-pitched.
7.1.3 Calibrated Thermocouples—Type K thermocouples
9.3 Sample Preparation for GF, UT and CF:
can be used within 95°C to 1260 °C, Type R thermocouples
9.3.1 Glass samples for T analysis are typically melted,
can be used within 870°C to 1450 °C, and Type S thermo- L
groundtoapowderandmixed,remelted,andthenquenchedon
couples can be used within 980°C to 1450 °C without special
a steel plate. Once quenched, analyze the glass sample with
calibrations or qualifications.
OM, SEM, and/or XRD to make sure that the sample is free of
7.1.3.1 Standard reference material for calibrating furnace,
crystalline and/or immiscible phases. Melt insolubles (for
for example, SRM-773 or SRM-1416.
example, noble metal oxides) are acceptable, but should be
7.1.3.2 OM or SEM for making visual observations of
reported. If the sample is crystal free and homogeneous, then
heat-treated specimens.
follow 9.3.2 – 9.3.4. However, if the glass is crystallized or
7.1.3.3 XRD for making C measurements.
F
otherwise inhomogeneous, then skip to step 9.3.5.
7.1.3.4 XRD standard reference material for peak location
9.3.2 According to Practice C829, the particle sizes recom-
and C calibration (for example, SRM-1976a or 1976c).
F
mended for T determination of the SRM-773 or SRM-1416
L
8. Hazards glasswith GFMethod(boatmethod)is<0.85mm(–20mesh)
and with UT Method (perforated plate) is between 1.70mm
8.1 The hazards associated with this procedure should be
and 2.36 mm (+12/-8 mesh). However, in practice, glass
evaluated by each institution before conducting work.
particles that are too small (that is, ≤ 0.100 mm) when
8.2 The primary hazards encountered when following this
heat-treated can introduce a significant degree of bubbles into
procedure are sharp objects (for example, metal foil for
the melt, especially in moderate and high viscosity glasses (η
crucibles, glass shards, and saws), high-temperature surfaces
> 10 Pa·s), which can dramatically affect heat transfer as well
(for example, furnace surfaces, heat-treated specimens fresh
as visibility through a heat-treated glass specimen. Also, it is
out of a furnace, tongs used to remove specimens from a
difficult to clean glass particles that are too small (that is,
furnace), electrical hazards (for example, exposed heating
≤0.100mm).Glassparticlesthataretoolarge(thatis,>4mm)
elements such as MoSi ), and radiation hazards (for example,
2 will not fit in the previously described crucibles. Thus, the
if working with radioactive glasses). When handling a glass
recommended particle size for these measurements is between
specimen, protective gloves should be worn to prevent injury.
0.422mmand4mmor(+40/-5mesh);thustheglassshouldbe
The furnaces used for heat-treatment of the glass samples
sievedandthissizeretained.Thesesizesareusedbecausesizes
outlined in this procedure are at temperatures of 600°C to
<<0.422 mm will promote crystal nucleation and growth
1600°C;thus,temperature-resistantorinsulatedglovesshould
during heat treatments, and sizes >>4.0 mm pose a issues
be worn when putting samples into the furnace or when
when attempting to load glass into the crucible because the
removing specimens from the furnace. Electrically insulating
packing density is reduced significantly. Carefully crush the
gloves could also be used in conjunction with (that is,
glass,beingcautiousnottointroducecontamination(thatis,no
underneath) the leather gloves to electrically isolate the user’s
direct contact with steel). Use a mill or mortar and pestle
hands from potential contact of the tongs or tweezers with
composed of material harder than the glass (for example, SiC,
exposed electrical elements when removing heat-treated speci-
WC, or equivalent) to crush the sample to the desired size.
mens.ItispertinentthattheoperatoroftheXRDiscautiousof
9.3.3 Wash the sample by ultrasonic cleaning for 2 min in a
the hazards associated with the technique and is trained to the
cleanglassbeakerorequivalentcontainerbysubmergingglass
institution’s safety procedures for operating the equipment.
particles in ASTM Type 1 water, which fills the container
abovetheglassbyanequivalentvolume.Decantthewaterand
9. Sampling, Test Specimens, and Test Units
repeattheultrasoniccleaningtwicemore(2mineachcleaning)
9.1 Specific test instructions will contain all or part of the withfreshASTMType1water.Ultrasonicallycleanthesample
following information: preferred T measurement method, a fourth time for 2 min with ethanol. Decant the ethanol and
L
tolerance goals, estimated T (needed for the gradient tem- drythesampleat ≥90°Cfor ≥1hinanopenbeakerinanoven
g
perature furnace method only), an estimated T or temperature designed for drying combustibles. The washing steps can be
L
C1720 − 21
performed using alternative, non-polar solvents (for example, every six months during active projects. Profiling of the
pentane, hexane) if a reaction with water or between the gradientfurnaceshallbeperformedaccordingtoPracticeC829
cleaning solvent and the glass is suspected. (see 11.1.1.1).
9.3.4 Transfer the cleaned and dried glass sample into a
11.1.1.1 The gradient furnace can be profiled by inserting a
clean, marked container or bag while being careful not to
calibrated thermocouple into the furnace, while empty, and
contaminate the glass with dust, dirt, oils, or salts or cross-
measuringtheequilibriumtemperatureatdifferentdistances,d,
contaminate the sample with other samples. Seal the container
from a location (typically, a stopper inserted at the back end).
or bag and store in a clean, dry environment until ready for
Use the gradient furnace temperature profile to determine the
testing.
length of the specimen boat and the position where the boat is
9.3.5 Glassesthatarecrystallized,inhomogeneous,orphase
placed in the gradient furnace. If the gradient is non-linear, the
separated should be prepared by grinding the entire batch to a
different heating zones can be adjusted accordingly until the
very fine powder. The grinding and mixing will best homog-
desiredgradientandgradientshapeareachieved.Thetempera-
enize the sample. It is essential to reduce the effects of sample
ture gradient in the GF should be close to linear (61 °C over
inhomogeneity when making T measurements.
the temperature range of interest) with a gradient of no more
L
than1.2°C/mm.Then,thegradientfurnaceshouldbeoperated
10. Preparation of Apparatus with standard reference materials for temperature calibration,
for example, SRM-773 or SRM-1416.
10.1 Furnace Setup—The furnace should be capable of
11.1.1.2 To profile a uniform temperature furnace, tempera-
sustaining temperatures that will be used for heat treatments
ture uniformity among the locations where the sample crucible
with ≥ 50 °C between the furnace’s maximum operating
shall be located inside the furnace must be verified. If a
temperature and the heat-treatment temperature. The furnace
temperature value at a specific location on the sample stage at
should have a calibrated temperature monitoring capability.
a given temperature is 62°C different from the average
The furnace should have an over-temperature control to pre-
temperature over the other profiling locations, then data col-
vent damage to the furnace by potential heating past the
lected at that location and temperature should not be used for
maximum safe operating temperature of the furnace. See 6.1
the T /T values used to determine T .
and 6.2 for further information.
c a L
An example of uniform temperature furnace profiling is
10.2 Specimen Preparation for Analysis—See 12.2.4 for
given by using a calibrated thermocouple. The first profiling
instructions on preparing specimens for GT , 12.3.2 for
step is to create a sample stage inside of the furnace in the
instructions on preparing specimens for UT, and the 12.4
middle of the hot zone of the furnace. Then, make sure that
subsections for instructions on preparing specimens for the
there are an adequate number of holes through the top of the
different CF methods.
furnacethatarelargeenoughtofitthewidthofathermocouple
10.3 Analysis Equipment:
(~0.6 cm) directly above the positions labeled on the sample
10.3.1 OM—OM can be used to observe heat-treated speci-
stage. Holes not in use should be plugged to prevent heat loss
mens in TLM and/or RLM mode (depending on specimen
that could potentially lead to undesirable temperature gradi-
opticaltransparencyandmorphology).Forimageanalysiswith
ents. If using the example in Table1, then nine holes must be
CF, the microscope should be equipped with a micrograph
made in the top of the furnace directly above the locations
acquisition system such as a digital camera.
being profiled.
10.3.2 SEM—SpecimenpreparationforgeneralSEMobser-
11.1.1.3 The furnace is to be profiled through a temperature
vations typically requires that the specimen be coated with an
range of a given test. For instance, if the furnace is going to be
electrically-conductivecoating(forexample,C,Au,Pd)unless
usedtotestsamplesintherangeof810°Cto1290°C,thenthe
the SEM can analyze low-conductivity specimens. For high-
furnace should be profiled at 800 °C, 1300 °C, and a regular
resolution SEM micrograph acquisition, specimens can either
temperature increment in between (for example, every 100 °C
be polished (best if done to optical quality) to expose the
from 800°C to 1300 °C). Note that not all types of thermo-
features of interest on a surface of the specimen, or they can
couplecanbecalibratedthroughthisentirerange,somakesure
remain unpolished.
that a calibration curve is used for each type of thermocouple
10.3.3 XRD—Typical specimen preparation for XRD in-
to extrapolate the actual temperature value from the voltage
volves grinding a heat-treated specimen to a powder.To verify
reading on the thermocouple readout if a specific type of
peak locations, the powdered specimen should be doped with
thermocouple is being used outside of the recommended
an approved XRD standard, for example SRM-1976a or
temperature validity range (for example, Type R/S at T ≥
SRM-674b.
1450°C).
11.1.1.4 At each temperature, place the calibrated thermo-
11. Calibration and Standardization
couple through the hole in the top of the furnace and rest the
11.1 Calibration—The test equipment, including thermo-
end of the thermocouple at the location where the sample
couplesandthermocouplereadouts,mustbecalibrated,atleast crucible shall be located on the sample stage. Note that
annually, in accordance with a consensus standard, for
electrical safety procedures must be followed when working
example, ANSI/NCSL 17025:2017. near electrical hazards. Let the temperature come to thermal
11.1.1 Furnaces must be profiled for temperature at least equilibrium(forexample,5minto20min)ateachlocationand
once every six months and checked for accuracy at least once record the reading from the thermocouple in the profiling table
C1720 − 21
NOTE1—Thisisshownasanexampleforasquaresamplestage.Thetabulateddatatotherightofthediagramsshowshowthethermocouplereadouts
are entered at each reported temperature for each position on the sample stage. Locations at temperatures that are more than 62 °C from the average
temperatures collected at a specific temperature are to be omitted from use for T or T values—these values are to be labeled as red, bold, or underlined,
a c
or combinations thereof.
(see example in Table 1). If a temperature value at a given 12.2.1 Place test glass sample in a boat (6.1) and slide into
specific location on the sample stage at a given temperature is apreheatedandprofiledgradientfurnace(11.1.1.1)throughthe
62 °C different from the average temperature collected at a
coolerendofthefurnace.Positiontheboatinthefurnaceatthe
specific temperature over all the profiling locations, then data
desired test temperature range. Let the glass sample soak for
collected at that location and temperature should not be used
the time specified in the test instruction. The typical heat
for the T /T values used to determine T . When measuring T
c a L c treatment time is 24h 6 2 h, although this is dictated by the
and T values used to determine T , it is ideal to run these
a L time required to reach thermodynamic equilibrium.
heat-treatments at locations on the stage that are within the
12.2.2 At the completion of the heat treatment, remove the
required tolerance.
boat with the specimen from the gradient furnace and place
11.1.2 TheXRDshouldbecalibratedeverysixmonthsorat
into a preheated annealing furnace with the temperature near
the completion of any maintenance. To do this, perform an
themeasuredorestimated T for ≥2handthenslowlycoolthe
g
XRD scan on a 2θ calibration standard (for example, SRM-
furnace to room temperature.
1976a or SRM-1976c) and verify that the diffraction peak
12.2.3 Remove the boat from the annealing furnace and
locations (that is, degrees, 2θ) and intensities match those of
mark the specimen in a way to correlate locations on the
the standard. If peaks are not in the correct locations, then the
specimen with d and T values (4.1.1). Remove the test
instrument must be realigned.
specimen from the boat, attempting to keep the specimen
11.2 Accuracy Check—At least one standard glass with T
L
intact.Dependingonthecrystallizationrateoftheglasstested,
traceable to a round robin study or NIST standard (such as
the low-temperature end of the heat-treated specimen might
SRM-773orSRM-1416)shallbetestedwitheachnewbatchof
appear to be a heavily crystallized glass ceramic. Place the
T measurements or on a regular frequency to determine the
L
specimeninamold,forexample,siliconerubber,largeenough
accuracy of each furnace over time. The minimum frequency
to fit the entire specimen or, at the very least, the region of
shall be once annually or with each change of furnace profile
intended interest (estimated T 6 5 cm). Cover the specimen
L
or gradient, whichever comes first. The measured value must
entirely with a single batch of epoxy.Allow the epoxy to cure
be within the tolerance expected for the standard glass, or the
and harden. Remove the specimen from the mold.The process
furnace must be re-configured and the standard re-measured.
of mounting the specimen in resin will improve the ability to
The data from these tests should be maintained, plotted, and
keep the specimen intact during cutting and polishing.
analyzedtocheckfortrends,biases,orincreasesinvariationas
part of a defined measurement control program. This can
12.2.4 Use a saw equipped with a diamond cut-off blade to
provide continuous validation of the test method and basis for
cut the specimen in half longitudinally, along the temperature
bias adjustments.
gradient, and polish the cut side of one of the halves. Adhere
the polished side to a single or to multiple glass microscope
12. Procedure
slides (for example, with cyanoacrylate or CrystalBond); it is
12.1 Liquidus temperature measurements of a glass speci-
typicallyeasiertopolishmultiplesmallsections(≤5cm,each)
men shall be determined by one of three methods: Gradient
versus one large section. Cut the remainder of the specimen
Temperature Furnace Method (GT), Uniform Temperature
parallel to the slide, leaving ~2 mm thick of specimen adhered
Furnace Method (UT),or Crystal Fraction Extrapolation
to the slide, and polish a thin section of the specimen with a
Method (CF). The appropriate method for the samples to be
variable speed polisher. Make sure to permanently mark the
tested shall be specified in the applicable test instructions. For
identification of the specimen, the gradient profile, and the
GT specimens, proceed to 12.2; for UT specimens, proceed to
profile measurement increments on the glass slide. Fig. 6
12.3; for CF specimens, proceed to 12.4.
shows examples
...

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.
´1
Designation: C1720 − 17 C1720 − 21
Standard Test MethodMethods for
Determining Liquidus Temperature of Waste Glasses and
Simulated Waste Glasses
This standard is issued under the fixed designation C1720; 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.
ε NOTE—Editorially corrected Fig. 9 title and 15.1.5 in January 2018.
1. Scope
1.1 These practices test methods cover procedures for determining the liquidus temperature (T ) of nuclear waste, mixed nuclear
L
waste, simulated nuclear waste, or hazardous waste glass in the temperature range from 600°C600 °C to 1600°C.1600 °C. This test
method differs from Practice C829 in that it employs additional methods to determine T . T is useful in waste glass plant
L L
operation, glass formulation, and melter design to determine the minimum temperature that must be maintained in a waste glass
melt to make sure that crystallization does not occur or is below a particular constraint, for example, 1 volume % crystallinity or
T . As of now, many institutions studying waste and simulated waste vitrification are not in agreement regarding this constraint
1%
(1).
1.2 Three methods are included, differing in (1) the type of equipment available to the analyst (that is, type of furnace and
characterization equipment), (2) the quantity of glass available to the analyst, (3) the precision and accuracy desired for the
measurement, and (4) candidate glass properties. The glass properties, for example, glass volatility and estimated T , will dictate
L
the required method for making the most precise measurement. The three different approaches to measuring T described here
L
include the following: (A) Gradient Temperature Furnace Method (GT),(BGT)), Uniform Temperature Furnace Method (UT), and
(CUT)), and Crystal Fraction Extrapolation Method (CF).(CF). This procedure is intended to provide specific work processes, but
may be supplemented by test instructions as deemed appropriate by the project manager or principle investigator. The methods
defined here are not applicable to glasses that form multiple immiscible liquid phases. Immiscibility may be detected in the initial
examination of glass during sample preparation (see 9.3). However, immiscibility may not become apparent until after testing is
underway.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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 and health practices and determine the applicability of regulatory
limitations prior to use.
1.4 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.
ThisThese test method ismethods are under the jurisdiction of ASTM Committee C26 on Nuclear Fuel Cycle and is the direct responsibility of Subcommittee C26.13
on Spent Fuel and High Level Waste.
Current edition approved Nov. 1, 2017Oct. 1, 2021. Published December 2017December 2021. Originally approved in 2011. Last previous edition approved in 20112017
ɛ1
as C1720 – 11C1720 – 17 . DOI: 10.1520/C1720-17E01.10.1520/C1720-21.
The boldface numbers in parentheses refer to a list of references at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1720 − 21
1.5 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:
C162 Terminology of Glass and Glass Products
C829 Practices for Measurement of Liquidus Temperature of Glass by the Gradient Furnace Method
C859 Terminology Relating to Nuclear Materials
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E2282 Guide for Defining the Test Result of a Test Method
2.2 Other Documents:NIST Standards:
SRM-773 National Institute for Standards and Technology (NIST) Liquidus Temperature Standard
SRM-674b NIST X-Ray Powder Diffraction Intensity Set for Quantitative Analysis by X-Ray Diffraction (XRD)
SRM-1416 Aluminosilicate Glass for Liquidus Temperature
SRM-1976a NIST Instrument Response Standard for X-Ray Powder Diffraction
Z540.3SRM-1976c American National Standards Institute/National Conference of Standards Laboratories (ANSI/NCSL)
Requirements for the Calibration of Measuring and Test EquipmentInstrument Response Standard for X-Ray Powder
Diffraction
2.3 Other Standard:
ISO/IEC 17025:2017 American National Standards Institute/National Conference of Standards Laboratories (ANSI/NCSL)
General Requirements for the Competence of Testing and Calibration Laboratories
3. Terminology
3.1 For terms not defined herein, refer to Terminology C859 and C162.
3.2 Definitions: (refer to Terminology C859)
3.2.1 air quenching—to pour or place a molten glass specimen on a surface, for example, a steel plate, and cool it to the solid state.
3.2.2 anneal—to prevent or remove processing stresses in glass by controlled cooling from a suitable temperature, for example,
the glass transition temperature (T ) (modified from Terminology C162).
g
3.2.3 annealing—a controlled cooling process for glass designed to reduce thermal residual stress to an acceptable level and, in
some cases, modify structure (modified from Terminology C162).
3.1.4 ASTM Type I water—purified water with a maximum total matter content including soluble silica of 0.1 g/m , a maximum
electrical conductivity of 0.056 μΩ/cm at 25°C and a minimum electrical resistivity of 18 MΩ × cm at 25°C (see Specification
D1193 and Terminology D1129).
3.2.4 cleaning glass—glass or flux used to remove high viscosity glass, melt insolubles, or other contamination from
platinum-ware.
3.2.5 crystallize—to form and/or grow crystals from a glass melt during heat-treatment or cooling.
3.2.6 crystallization—the progression in which crystals are first nucleated and then grown within a host medium. Generally, the
host may be a gas, liquid, or another crystalline form. However, in this context, it is assumed that the medium is a glass melt.
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 boldface numbers in parentheses refer to a list of references at the end of this standard.Available from National Institute of Standards and Technology (NIST), 100
Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
Webster’s New Universal Unabridged Dictionary, 1979.Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036,
http://www.ansi.org.
C1720 − 21
3.2.6.1 Discussion—
Generally, the host may be a gas, liquid, or another crystalline form. However, in this context, it is assumed that the medium is
a glass melt.
3.2.7 crystallization front—the boundary between the crystalline and crystal-free regions in a test specimen that was subjected to
a temperature gradient heat-treatment.
3.2.8 furnace profiling—the process of determining the actual temperature inside of a furnace at a given location; this involves
different processessteps for different types of furnaces.
3.2.9 glass—an inorganic product of fusion that has cooled to a rigid condition without crystallizing (see Terminology C162); a
noncrystalline solid or an amorphous solid (2).
3.2.10 glass sample—the material to be heat-treated or tested by other means.
3.2.11 glass specimen—the material resulting from a specific heat treatment.
3.2.12 glass transition temperature (T )—on heating, the temperature at which a glass transforms from a solid to a liquid material,
g
characterized by the onset of a rapid change in several properties, such as thermal expansivity.
3.2.13 gradient furnace—a furnace in which a known temperature gradient is maintained between the two ends.
3.2.14 inhomogeneous glass—a glass that is not a single amorphous phase; a glass that is either phase separated into multiple
amorphous phases or is crystallized.
3.2.15 liquidus temperature—temperature (T )—the maximum temperature at which thermodynamic equilibrium exists between
L
the molten glass and its primary crystalline phase.
3.2.15.1 Discussion—
T is the maximum temperature at which a glass melt crystallizes.
L
3.2.16 melt insoluble—a crystalline, amorphous, or mixed phase material that is not appreciably soluble in molten glass, for
example, noble metals, noble metal oxides.
3.2.17 mixed waste—waste containing both radioactive and hazardous components regulated by the Atomic Energy Act (AEA) (3)
and the Resource Conservation and Recovery Act (RCRA) (4), respectively; the term “radioactive component” refers to the actual
radionuclides dispersed or suspended in the waste substance respectively.(5).
3.2.17.1 Discussion—
The term “radioactive component” refers to the actual radionuclides dispersed or suspended in the waste substance (5).
3.2.18 mold—a pattern, hollow form, or matrix for giving a certain shape or form to something in a plastic or molten state.
Webster’s Dictionary
3.2.19 nuclear waste glass—a glass composed of glass-forming additives and radioactive waste.
3.2.20 observation—the process of obtaining information regarding the presence or absence of an attribute of a test specimen or
of making a reading on a characteristic or dimension of a test specimen (see Terminology E2282).
3.2.21 preferred orientation—when there is a stronger tendency for the crystallites in a powder or a texture to be oriented more
one way, or one set of ways, than all others. This is typically due to the crystal structure.
3.2.21.1 Discussion—
This is typically due to the crystal structure. IUCr
Merriam-webster.com.
IUCr Online Dictionary of Crystallography, 2011.
C1720 − 21
3.2.22 primary phase—the crystalline phase at equilibrium with a glass melt at its liquidus temperature.
3.2.23 radioactive—of or exhibiting radioactivity; a material giving or capable of giving off radiant energy in the form of particles
or rays, for example, α, β, and γ, by the disintegration of atomic nuclei; said of certain elements, such as radium, thorium, and
8 6
uranium and their products.rays. American Heritage Webster’s
3.2.23.1 Discussion—
Example of particles or rays formed by the disintegration of atomic nuclei are α, β, and γ; said of certain elements, such as radium,
thorium, and uranium and their products.
3.2.24 Round-Robin—an interlaboratory and intralaboratory testing process to develop the precision and bias of a procedure.
3.2.25 section—a part separated or removed by cutting; a slice, for example, representative thin section of the glass specimen.
Webster’s
3.1.27 set of samples—samples tested simultaneously in the same oven.
3.2.26 simulated nuclear waste glass—a glass composed of glass forming additives with simulants of, or actual chemical species,
or both, in radioactive wastes or in mixed nuclear wastes, or both.
3.1.29 standard—to have the quality of a model, gage, pattern, or type. Webster’s
3.1.30 standardize—to make, cause, adjust, or adapt to fit a standard (5); to cause to conform to a given standard, for example,
to make standard or uniform. Webster’s
3.2.27 surface tension—a property, due to molecular forces, by which the surface film of all liquids tends to bring the contained
volume into a form having the least possible area.
3.2.28 test determination—the value of a characteristic or dimension of a single test specimen derived from one or more observed
values (see Terminology E2282).
3.2.29 test method—a definitive procedure that produces a test result (see Terminology E2282).
3.2.30 test observation—see observation.
3.2.31 uniform temperature furnace—a furnace in which the temperature is invariant over some defined volume and within some
defined variance.
3.2.32 vitrification—the process of fusing waste with glass making chemicals at elevated temperatures to form a waste glass (see
Terminology C162).
3.2.33 volatility—the act of one or more constituents of a solid or liquid mixture to pass into the vapor state.
3.2.34 waste glass—glass —a glass developed or used for immobilizing radioactive, mixed, or hazardous wastes.
3.3 Definitions of Terms Specific to This Standard:
3.3.1 ASTM Type I water—purified water with a maximum total matter content including soluble silica of 0.1 g/m , a maximum
-1
electrical conductivity of 0.056 μΩ /cm at 25 °C, and a minimum electrical resistivity of 18 MΩ × cm at 25 °C.
3.3.2 set of samples—samples tested simultaneously in the same oven.
American Heritage Dictionary, 1973.
C1720 − 21
3.3.3 standard—to have the quality of a model, gauge, pattern, or type. Webster’s
3.3.4 standardize—to make, cause, adjust, or adapt to fit a standard (5); to cause to conform to a given standard, for example, to
make standard or uniform. Webster’s
3.4 Abbreviations:
3.4.1 AEA—Atomic Energy Act
3.4.2 ANSI—American National Standards Institute
3.4.3 ASTM—American Society for Testing and Materials
3.4.4 CF—crystal fraction extrapolationextrapolation method
3.4.5 C —crystal fraction in a sample or specimen
F
3.4.6 EDS—energy dispersive spectrometry
3.4.7 η—viscosity
3.4.8 FWHM—full width of a peak at half maximum
3.4.9 GF—gradient temperature furnace
3.4.10 GT—gradient temperature furnace method
3.4.11 HF—hydrofluoric acid
3.4.12 HLW—high-level waste
3.4.13 ID—identification
3.4.14 MSE—mean squared error
3.4.15 NBS—National Bureau of Standards
3.4.16 NCSL—National Conference of Standards Laboratories
3.4.17 NIST—National Institute for Standards and Technology (formerly NBS)
3.4.18 OM—optical microscope or optical microscopy
3.4.19 PDF—powder diffraction file
3.4.20 RCRA—Resource Conservation and Recovery Act
3.4.21 RIR—relative intensity ratio
3.4.22 RLM—reflected light microscopy
3.4.23 SD—standard deviation
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3.4.24 SEM—scanning electron microscope or scanning electron microscopy
3.4.25 SRM—Standard Reference Material
3.4.26 SSE—sum of squared errors
3.4.27 T —temperature where glass contains 1 volume % of a crystalline phase
1%
3.4.28 T —primary UT measurement above T
a L
3.4.29 T —primary UT measurement below T
c L
3.4.30 T —glass transition temperature
g
3.4.31 T —liquidus temperature
L
3.4.32 TLM—transmitted light microscopy
3.4.33 T —melting temperature for glass preparations
M
3.4.34 UF—uniform temperature furnace
3.4.35 UT—uniform temperature furnace method
3.4.36 WC—tungsten carbide
3.4.37 XRD—X-ray diffraction
4. Summary of Test Method
4.1 This procedure describes methods These test methods describe methods for determining the T of waste or simulated waste
L
glasses. Temperature is defined as the maximum temperature at which equilibrium exists between the molten glass and its primary
crystalline phase. In other words, T is the maximum temperature at which a glass melt crystallizes. Fig. 1 illustrates an example
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T for a simple two-component liquid on an arbitrary binary phase diagram.
L
4.1.1 (A) Gradient Temperature Furnace Method (GT)—This method is similar to Practice C829, “Standard Practices for
Measurement of Liquidus Temperature of Glass by the Gradient Furnace Method,” although it has been modified to meet the
FIG. 1 Binary Phase Diagram of Components A and B with T of Composition C Highlighted
L
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specific needs of waste and simulated waste glass measurements. The most pronounced differences between this method and the
Practice C829 “boat method” are the sample preparation and examination procedures.
4.1.1.1 Samples are loaded into a boat, for example, platinum alloy (Fig. 2) with a tight-fitting lid, and exposed to a linear
temperature gradient in a gradient furnace (Fig. 3) for a fixed period of time. The temperature, as a function of distance, d, along
the sample, is determined by the location within the GF, gradient furnace, and the T is then related to the location of the
L
crystallization front in the heat-treated specimen (Fig. 4).
4.1.1.2 Following the heat-treatment, the specimen should be annealed at, or near, the glass transition, transition temperature, T ,
g
of the glass (this should be previously measured or estimated) to reduce specimen cracking during cutting and polishing.
4.1.1.3 The specimen should then be scored or marked to signify the locations on the specimen located at different depths into
the gradient furnace, that is, locations heat-treated at specific temperatures.
4.1.1.4 If the specimen is optically transparent, it can be observed with transmitted light microscopy (TLM) or reflected light
microscopy (RLM) to look for bulk or surface crystallization, respectively. If the specimen is not optically transparent or is barely
optically transparent (for example, in glasses with high quantities of Fe O ), a cut or fractured section of the glass can be polished
2 3
very thin (that is, a thin section can be made) to allow for observation. Another option for surface observations is scanning electron
microscopy (SEM). This method provides a quick measurement of T in the absence of convective flow of glass in the GF, gradiant
L
furnace, which distorts the location of the crystallization front (that is, the crystallization front is likely not constant at a given
temperature (see Fig. 4)).
4.1.1.5 The temperature gradient and increased volatility at higher temperatures cause gradients in surface tension, which in turn
cause convective flow. This method is ideal for glasses with a T less than roughly 1000°C 1000 °C or glasses with a low volatility
L
near the T . If the temperature range spanned by the crystallization front is too high for the desired tolerance, theUT or CF methods
L
(Method B or C) should be used for a more precise T measurement. MethodGT A is not easily used to measure the T on
L L
radioactive glasses because of the size of the GF gradient furnace and the complicated sample analysis required. This method is
not recommended for glasses with a T in a temperature range of very low glass viscosity (that is, η < 50 Pa·s).
L
4.1.2 (B) Uniform Temperature Furnace Method (UT)—This method is similar to the methods used in phase diagram
determination and can be used for making more precise measurements than those determined with (A) Gradient Temperature
Furnace Method (GT).GT.
4.1.2.1 In this method, a glass sample is loaded into a crucible (for example, platinum alloy, see Fig. 5) with a tight-fitting lid and
subjected to temperatures for a fixed period of time (for example, 2424 h 6 2 hrs).h). Following heat-treatment, the specimen can
be observed by optical microscopy (OM) for the appearance or absence of crystalline or other undissolved materials with methods
similar to those previously described (4.1.1). Crystalline material present in the meniscus (that is, in the upper corners of the
heat-treated specimen) can be an artifact of this process and should be reported separately. The locations of the crystals within the
heat-treated specimen need to be reported (that is, the melt-crucible interface, meniscus, melt-air interface, or the bulk) on the
liquidus temperature data sheet (see Appendix X1). The crystal locations used to define T should be clearly documented when
L
reporting T . Typically, crystals in any location except for the meniscus (where composition can be effectedaffected by volatility)
L
are used. In some circumstances, surface crystallization can be excluded from T determination.
L
FIG. 2 GF Boat Diagram: (A) Single Chamber Crucible Design (B) Single Chamber Design Loaded with a Set of Samples (that is,
Smaller Crucibles)
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FIG. 3 Photograph of Typical Gradient Temperature Furnace
FIG. 4 OM Micrograph of the Crystallization Front in a GT Specimen
4.1.2.2 The T is then given by the temperature range between the highest temperature at which a specimen contains crystals (T )
L c
and the lowest temperature without crystals in the specimen (T ); the T is then typically defined as the average of T and T .
a L a c
4.1.2.3 This method is more time consuming as it requires more heat-treatments than theGT, GT method, although it minimizes
the effects of volatility and eliminates the convection-driven uncertainty in crystallization front measurements. This method is used
for high precision measurements (on the order of 65°C), 65 °C), is more easily applied to radioactive glasses, and can be used
to measure T values as high as 1600°C 1600 °C with typical high-temperature furnaces (for example, furnaces with MoSi heating
L 2
elements), and even higher with specialized equipment and high-temperature crucibles. This method may be used for glasses with
a high volatility near T under certain circumstances.
L
4.1.3 (C) Crystal Fraction Extrapolation Method (CF)—This method is an alternate method that uses a UT specimen to measure
the crystal fraction, C (in mass % or volume %), of a crystalline phase or phases in a sample heat-treated at multiple temperatures,
F
T << T . The C at each temperature is measured with XRD, RLM, TLM, SEM, or combinations thereof, by mass and/or
L F
volume %, and then T is achieved by extrapolating C as a function of temperature to zero crystals. This method is more suited
L F
for glasses with a higher volatility near the T than the previous methods. When multiple crystalline phases are present, XRD is
L
an effective method for quantifying C as a function of temperature and is very effective at determining the T of each phase
F L
independently; this would be more difficult withby MethodsGT Aand orUT.CF B. The C method yields the additional benefit of
F
equilibrium crystal fractions as a function of temperature, which can sometimes tend to be non-linear at C > 5 mass % to 10
F
mass % crystallinity for most crystalline phases. Different techniques for the CCF method are described below.
F
C1720 − 21
FIG. 5 UFUT and CF Crucible Schematic
4.1.3.1 Volume Fraction of Crystal(s) in the Specimen (12.4.2)—With TLM, RLM, or SEM as well as image analysis software,
it is possible to measure the area fraction of crystals in an image or micrograph of the specimen. The area fraction is then equivalent
to the volume fraction if the image is representative of the bulk of the specimen, and the effective depth of the image is
insignificant. If this process is done at different temperatures, the T can be extrapolated as a function of temperature.
L
NOTE 1—The mass fraction of crystals in the specimen can be estimated if the densities of the glass and the crystal(s) are known.
4.1.3.2 Number Fraction of Crystal(s) in the Specimen (12.4.3)—In the same fashion as described in 4.1.3.1, count the number
of crystals in an image or micrograph of the specimen at different temperatures. If this process is done at different temperatures,
the T can be extrapolated as a function of temperature.
L
4.1.3.3 Mass Fraction of Crystal(s) in the Specimen by Adding a Known Crystalline Phase (12.4.4)—Adding a known mass
fraction of a known, standard crystalline material (for example, NIST SRM-674b) allows the standardization of the XRD pattern.
The standards and the unknown specimen should be run in independently before mixing to verify that there is not overlap between
the peaks of the standard and the peaks in the unknown specimen because this will make quantification difficult and less accurate.
The standardized pattern can then be used to generate quantitative (if the crystal structure has been refined) or semi-quantitative
(if the crystal structure has not been refined) C analysis with Rietveld (6-8) refinement software or the relative intensity ratio (RIR)
F
method (12.4.5).
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4.1.3.4 Mass Fraction of Crystal(s) in the Specimen by Comparing it to the Calibration Curve (12.4.5)—In this method, samples
with known concentrations of the crystalline phases being analyzed are prepared and tested using XRD. The peak area’s (full width
at half maximum or FWHM, total crystal peak area, or highest peak area) and known crystal fractions are used to generate a
calibration curve. The peak area of the unknown specimen is then used in the calibration equation to determine a quantitative (if
interpolated) or semiquantitative (if extrapolated) crystal fraction.
4.1.3.5 Volume Fraction of Crystal(s) in the Specimen With C Data From XRD Analysis—Commonly, melter constraints are in
F
terms of a volume % of crystallinity, for example, T . Once C data are obtained in mass % by XRD, the remaining mass of glass,
1% F
m , is calculated as a difference given by
g
N
m 5 m 2 m (1)
g t c,i
(
i51
where:
m = the total mass (that is, the value is normalized to one and thus component values are mass fractions), and
t
m = the mass fraction of the i-th crystalline phase observed and quantified by XRD.
c,i
By converting the mass fractions of the i-th component additives, m , into mole fractions, M , the density of glass, ρ , can be
i i g
computed with the following expression:
N
M m
(i51 i m,i
ρ 5 (2)
N
g
M V
i M,i
(i51
where:
m = the molecular mass of the i-th oxide, and
m,i
V = the molar volume of the i-th component additive explained elsewhere (9).
M,i
The total volume of each heat treatment, V , is calculated with
HT
N
m
m c,i
(i51
g
V 5 1 (3)
HT
ρ ρ
g c,i
where:
ρ = the density of the i-th crystalline component.
c,i
The volume % of the i-th crystalline component, V , in the heat-treated specimen is denoted by
c,i
m
c,i
V 5 100 3 (4)
c,i
ρ 3V
~ !
c,i HT
The values of V can then be plotted as a function of temperature and a linear correlation fit to the data with
c,i
V 5 m 3T1b (5)
c,i
where:
T = (V – b)/m when V = 1 (T )
1% c,i c,i 1%
5. Significance and Use
5.1 This procedure can be used for (but is not limited to) the following applications:
(1) support glass formulation development to make sure that processing criteria are met,
(2) support production (for example, processing or troubleshooting), and
(3) support model validation.
6. Apparatus
6.1 Equipment for the GT Method: GT:
6.1.1 Resistance-heated tubular gradient furnace capable of achieving temperatures of 550550 °C to 1150°C 1150 °C with
gradients in the range of roughly 1°C/mm 1 °C/mm (Fig. 3). For glasses with an estimated T > 1150°C, 1150 °C, furnaces with
L
elements capable of high temperatures need be used, for example, MoSi .
C1720 − 21
6.1.2 Calibrated thermocouple and temperature readout device appropriate for the estimated temperature range that will be used
for testing. Type K thermocouples can be used within 9595 °C to 1260°C, 1260 °C, Type R thermocouples can be used within
870870 °C to 1450°C, 1450 °C, and Type S thermocouples can be used within 980980 °C to 1450°C 1450 °C without special
calibrations or qualifications.
6.1.3 Resistance furnace and controller used for annealing (capable of maintaining constant temperatures between 400400 °C and
~900°C) ~900 °C) with a temperature accuracy of 10°C.10 °C.
6.1.4 Specimen boat made of material inert to the sample (for example, platinum alloy) with approximate dimensions of 0.5 cm
× 1 cm × 10 cm to 30 cm (width × height × length), respectively; an example specimen boat is shown in Fig. 2. If the test glass
viscosity is below 5 Pa·s at the measurement temperature, it is recommended that a round-based crucible be used. A separate option
with Method A is to fill the long boat with several small individual boats with individual lids (Fig. 2-B)-B).
6.1.5 Diamond cutoff saw.
6.1.6 Variable speed polisher.
6.1.7 Silicone rubber mold for mounting of GT glass specimen in epoxy.
6.1.8 OM for TLM and/or RLM.
6.1.9 SEM/EDS.
6.1.10 XRD.
6.2 Equipment Needed for the UT Method: UT:
6.2.1 Resistance furnace capable of maintaining constant temperatures T ~550~550 °C to 1600°C 1600 °C (that is, MoSi heating
elements) or furnace capable of T ≤ 1200°C 1200 °C for glasses with T ≤ 1150°C. 1150 °C.
L
6.2.2 Calibrated thermocouple and temperature readout device appropriate for the estimated temperature range that will be used
for testing (6.1.2).
6.2.3 Specimen boat (or crucible) and tight fitting lid made of material compatible with the sample (for example, platinum alloy)
with suggested dimensions of 1.2 cm × 1.2 cm × 1.2 cm (width × height × length, respectively) (Fig. 5-1A). Another option is a
round-bottom, thimble-shaped crucible (Fig. 5-1B).
6.2.4 Diamond cutoff saw.
6.2.5 Variable speed polisher.
6.2.6 OM for TLM and/or RLM.
6.2.7 SEM/EDS.
6.2.8 XRD.
6.3 Equipment needed for the CF method includes the same equipment as described previously in 6.2 because a UT specimen
is required for the measurement technique, although additional materials are also required.Equipment Needed for CF:
6.3.1 This includes the same equipment as described previously in 6.2 because a UT specimen is required for the measurement
technique, although additional materials are also required.
6.3.2 Image analysis software for measuring the C present in a micrograph collected with OM, SEM, etc.
F
6.3.3 Crystal structure/unit cell refinement software for quantifying crystal fractions by spiking in a known mass% of a known
crystalline material.
C1720 − 21
6.3.4 Known crystalline material (for example, SRM-674b) that does not overlap with crystalline peaks in unknown specimen.
7. Reagents and Materials
7.1 Reagents and materials used in conjunction with the various methods outlined in this procedure.
7.1.1 Reagents:
7.1.1.1 ASTM Type 1 water.
7.1.1.2 Cleaning solvents, for example, ethanol, isopropanol, acetone.
7.1.1.3 Abrasive media for polishing (such as SiC or diamond).
7.1.1.4 Glass microscope slides.
7.1.1.5 Glass cover slides.
7.1.1.6 Meltable adhesive (such as wax).
7.1.1.7 Solvent-soluble adhesives (such as methyl methacrylate-based adhesives).
7.1.1.8 Non-temperature sensitive adhesives (such as cyanoacrylate or other epoxy).
7.1.2 Materials:
7.1.2.1 Furnace appropriate to method being used, for example, GF, UF (required heating elements dependent on temperature
needs).
7.1.2.2 Material for making crucibles or boats, for example, sheets of platinum alloy or pre-formed crucible(s).
7.1.3 Calibrated Thermocouples—Type K thermocouples can be used within 9595 °C to 1260°C, 1260 °C, Type R thermocouples
can be used within 870870 °C to 1450°C, 1450 °C, and Type S thermocouples can be used within 980980 °C to 1450°C 1450 °C
without special calibrations or qualifications.
7.1.3.1 Standard reference material for calibrating furnace, for example, SRM-773.SRM-773 or SRM-1416.
7.1.3.2 OM or SEM for making visual observations of heat-treated specimens.
7.1.3.3 XRD for making C measurements.
F
7.1.3.4 XRD standard reference material for peak location and C calibration (for example, SRM-1976a).SRM-1976a or 1976c).
F
8. Hazards
8.1 The hazards associated with this procedure should be evaluated by each institution before conducting work.
8.2 The primary hazards encountered when following this procedure are sharp objects (for example, metal foil for crucibles, glass
shards, and saws), high-temperature surfaces (for example, furnace surfaces, heat-treated specimens fresh out of a furnace, tongs
used to remove specimens from a furnace), electrical hazards (for example, exposed heating elements such as MoSi ), and radiation
hazards (for example, if working with radioactive glasses). When handling a glass specimen, protective gloves should be worn to
prevent injury. The furnaces used for heat-treatment of the glass samples outlined in this procedure are at temperatures of
600600 °C to 1600°C; 1600 °C; thus, temperature-resistant or insulated gloves should be worn when putting samples into the
furnace or when removing specimens from the furnace. Electrically insulating gloves shouldcould also be used in conjunction with
(that is, underneath) the leather gloves to electrically isolate the user’s hands from potential contact of the tongs or tweezers with
exposed electrical elements when removing heat-treated specimens. It is pertinent that the operator of the XRD is cautious of the
hazards associated with the technique and is trained to the institution’s safety procedures for operating the equipment.
C1720 − 21
9. Sampling, Test Specimens, and Test Units
9.1 Specific test instructions will contain all or part of the following information: preferred T measurement method, tolerance
L
goals, estimated T (needed for Method A the gradient temperature furnace method only), an estimated T or temperature range
g L
(based on model predictions), heat treatment time, and data recording requirements.
9.2 GF Preparation:
9.2.1 A gradient furnace is constructed of two or more independent heating zones, and thus the gradient can be adjusted as needed
to obtain a low-pitched (ΔT/Δd is low, where T is temperature and d is distance from a reference point inside the furnace) or sharp
gradient (ΔT/Δd is high), a parameter that should be optimized within the GF gradient furnace accordingly depending upon the
expected crystallization rate of the sample (ΔC /ΔT). If ΔC /ΔT is low (for example, ≤1 ≤ 1 mass % ΔC increase over ≥100°C
F F F
≥ 100 °C is considered low), the gradient can be low-pitched, and in cases where ΔC /ΔT is high (for example, ≥1 ≥ 1 mass %
F
ΔC increase over ≤10°C ≤ 10 °C is considered extremely high), the gradient can be high-pitched.
F
9.3 Sample Preparation for Methods A, B, and C:GF, UT and CF:
9.3.1 Glass samples for T analysis are typically melted, ground to a powder and mixed, remelted, and then quenched on a steel
L
plate. Once quenched, analyze the glass sample with OM, SEM, and/or XRD to make sure that the sample is free of crystalline
and/or immiscible phases. Melt insolubles (for example, noble metal oxides) are acceptable, but should be reported. If the sample
is crystal free and homogeneous, then follow 9.3.2 – 9.3.4. However, if the glass is crystallized or otherwise inhomogeneous, then
skip to step 9.3.5.
9.3.2 According to Practice C829, the particle sizes recommended for T determination of the SRM-773 or SRM-1416 glass with
L
GF Method A (boat method) is <0.85 < 0.85 mm (-20(–20 mesh) and with UT Method B (perforated plate) is between 1.701.70 mm
and 2.36 mm (+12/-8 mesh). However, in practice, glass particles that are too small (that is, ≤0.100 ≤ 0.100 mm) when heat-treated
can introduce a significant degree of bubbles into the melt, especially in moderate and high viscosity glasses (η > 10 Pa·s), which
can dramatically affect heat transfer as well as visibility through a heat-treated glass specimen. Also, it is difficult to clean glass
particles that are too small (that is, ≤0.100≤ 0.100 mm). Glass particles that are too large (that is, >4> 4 mm) will not fit in the
previously described crucibles. Thus, the recommended particle size for these measurements is between 0.422 mm and 4 mm or
(+40/-5 mesh); thus the glass should be sieved and this size retained. These sizes are used because sizes <<0.422<< 0.422 mm will
promote crystal nucleation and growth during heat treatments, and sizes >>4.0>> 4.0 mm pose a issues when attempting to load
glass into the crucible because the packing density is reduced significantly. Carefully crush the glass, being cautious not to
introduce contamination (that is, no direct contact with steel). Use a mill or mortar and pestle composed of material harder than
the glass (for example, SiC, WC, or equivalent) to crush the sample to the desired size.
9.3.3 Wash the sample by ultrasonic cleaning for 2 min in a clean glass beaker or equivalent container by submerging glass
particles in ASTM Type 1 water, which fills the container above the glass by an equivalent volume. Decant the water and repeat
the ultrasonic cleaning twice more (2 min each cleaning) with fresh ASTM Type 1 water. Ultrasonically clean the sample a fourth
time for 2 min with ethanol. Decant the ethanol and dry the sample at ≥90°C for ≥1 hr ≥ 90 °C for ≥ 1 h in an open beaker in an
oven designed for drying combustibles. The washing steps can be performed using alternative, non-polar solvents (for example,
pentane, hexane) if a reaction with water or between the cleaning solvent and the glass is suspected.
9.3.4 Transfer the cleaned and dried glass sample into a clean, marked container or bag while being careful not to contaminate
the glass with dust, dirt, oils, or salts or cross-contaminate the sample with other samples. Seal the container or bag and store in
a clean, dry environment until ready for testing.
9.3.5 Glasses that are crystallized, inhomogeneous, or phase separated should be prepared by grinding the entire batch to a very
fine powder. The grinding and mixing will best homogenize the sample. It is essential to reduce the effects of sample
inhomogeneity when making T measurements.
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10. Preparation of Apparatus
10.1 Furnace Setup—The furnace should be capable of sustaining temperatures that will be used for heat treatments with ≥50°C
≥ 50 °C between the furnace’s maximum operating temperature and the heat-treatment temperature. The furnace should have a
calibrated temperature monitoring capability. The furnace should have an over-temperature control to prevent damage to the
furnace by potential heating past the maximum safe operating temperature of the furnace. See 6.1 and 6.2 for further information.
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10.2 Specimen Preparation for Analysis—See 12.2.4 for instructions on preparing specimens for theGT method,, 12.3.2 for
instructions on preparing specimens for theUT, UT method, and the 12.4 subsections for instructions on preparing specimens for
the different CF methods.
10.3 Analysis Equipment:
10.3.1 OM—OM can be used to observe heat-treated specimens in TLM and/or RLM mode (depending on specimen optical
transparency and morphology). For image analysis with MethodCF, C, the microscope should be equipped with a micrograph
acquisition system such as a digital camera.
10.3.2 SEM—Specimen preparation for general SEM observations typically requires that the specimen be coated with an
electrically-conductive coating (for example, C, Au, Pd) unless the SEM can analyze low-conductivity specimens. For
high-resolution SEM micrograph acquisition, specimens can either be polished (best if done to optical quality) to expose the
features of interest on a surface of the specimen, or they can remain unpolished.
10.3.3 XRD—Typical specimen preparation for XRD involves grinding a heat-treated specimen to a powder. To verify peak
locations, the powdered specimen should be doped with an approved XRD standard, for example SRM-1976a or SRM-674b.
11. Calibration and Standardization
11.1 Calibration—The test equipment, including thermocouples and thermocouple readouts, must be calibrated, at least annually,
in accordance with a consensus standard, for example, ANSI/NCSL Z540.3.17025:2017.
11.1.1 Furnaces must be profiled for temperature at least once every six months and checked for accuracy at least once every six
months during active projects. Profiling of the GF gradient furnace shall be performed according to Practice C829 (see 11.1.1.1).
11.1.1.1 The GF gradient furnace can be profiled by inserting a calibrated thermocouple into the furnace, while empty, and
measuring the equilibrium temperature at different distances, d, from a location (typically, a stopper inserted at the back end). Use
the gradient furnace temperature profile to determine the length of the specimen boat and the position where the boat is placed in
the gradient furnace. If the gradient is non-linear, the different heating zones can be adjusted accordingly until the desired gradient
and gradient shape are achieved. The temperature gradient in the GF should be close to linear (61°C (61 °C over the temperature
range of interest) with a gradient of no more than 1.2°C/mm. 1.2 °C/mm. Then, the gradient furnace should be operated with
standard reference materials for temperature calibration, for example, SRM-773.SRM-773 or SRM-1416.
11.1.1.2 To profile a uniform temperature furnace, temperature uniformity among the locations where the sample crucible shall
be located inside the furnace must be verified. If a temperature value at a specific location on the sample stage at a given
temperature is 62 °C different from the average temperature over the other profiling locations, then data collected at that location
and temperature should not be used for the T /T values used to determine T .
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To profile a UF, An example of uniform temperature furnace profiling is given by using a calibrated thermocouple. The first
profiling step is to create a sample stage inside of the furnace in the middle of the hot zone of the furnace. Then, make sure that
there are an adequate number of holes through the top of the furnace that are large enough to fit the width of a thermocouple (~0.6
cm) directly above the positions labeled on the sample stage. Holes not in use should be plugged to prevent heat loss that could
potentially lead to undesirable temperature gradients. If using the example in Table 1Table 1Table, then nine holes must be made
in the top of the furnace directly above the locations being profiled.
11.1.1.3 The furnace is to be profiled through a temperature range of a given test. For instance, if the furnace is going to be used
to test samples in the range of 810810 °C to 1290°C, 1290 °C, then the furnace should be profiled at 800°C, 1300°C, 800 °C, 1300
°C, and a regular temperature increment in between (for example, every 100°C 100 °C from 800800 °C to 1300°C). 1300 °C). Note
that not all types of thermocouple can be calibrated through this entire range, so make sure that a calibration curve is used for each
type of thermocouple to extrapolate the actual temperature value from the voltage reading on the thermocouple readout if a specific
type of thermocouple is being used outside of the recommended temperature validity range (for example, Type R/S at T ≥
1450°C).1450 °C).
11.1.1.4 At each temperature, place the calibrated thermocouple through the hole in the top of the furnace and rest the end of the
thermocouple at the location where the sample crucible shall be located on the sample stage. Note that electrical safety procedures
must be followed when working near electrical hazards. Let the temperature come to thermal equilibrium (for example, 55 min
to 20 min) at each location and record the reading from the thermocouple in the profiling table (see example in Table 1). If a
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NOTE 1—This is shown as an example for a square sample stage. The tabulated data to the right of the diagrams shows how the thermocouple readouts
are entered at each reported temperature for each position on the sample stage. Locations at temperatures that are more than 62°C 62 °C from the
reportedaverage temperatures collected at a specific temperature are to be omitted from use for T or T values—these values are to be labeled as red,
a c
bold, or underlined, or combinations thereof.
temperature value at a given specific location on the sample st
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