ASTM E1652-21

Standard Specification for Magnesium Oxide and Aluminum Oxide Powder and Crushable Insulators Used in the Manufacture of Base Metal Thermocouples, Metal-Sheathed Platinum Resistance Thermometers, and Noble Metal Thermocouples

ABSTRACT
This specification covers the requirements for magnesium oxide (MgO) and aluminum oxide (Al2O3) powders and crushable insulators used to manufacture metal-sheathed platinum resistance thermometers (PRTs), noble metal thermocouples, base metal thermocouples, and their respective cables. The following test shall be performed to meet the requirements specified: breaking force test; wet chemical analysis; fusion calorimetric analysis; quantitative analysis; and density determination.
SCOPE
1.1 This specification covers the requirements for magnesium oxide (MgO) and aluminum oxide (Al2O3) powders and crushable insulators used to manufacture base metal thermocouples, metal-sheathed platinum resistance thermometers (PRTs), noble metal thermocouples, and their respective cables.  
1.2 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
1.3 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.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Oct-2021
• ICS: 17.200.20 - Temperature-measuring instruments
• ICS: 29.035.30 - Glass and ceramic insulating materials
• Technical Committee: E20 - Temperature Measurement
• Drafting Committee: E20.13 - Thermocouples - Materials and Accessories Specifications

Relations

• Refers: ASTM E344-23 - Terminology Relating to Thermometry and Hydrometry
• Effective Date: 01-Dec-2023
• Refers: ASTM B329-20 - Standard Test Method for Apparent Density of Metal Powders and Compounds Using the Scott Volumeter
• Effective Date: 01-May-2020
• Refers: ASTM E344-19 - Terminology Relating to Thermometry and Hydrometry
• Effective Date: 01-Sep-2019
• Refers: ASTM C809-19 - Standard Test Methods for Chemical, Mass Spectrometric, and Spectrochemical Analysis of Nuclear-Grade Aluminum Oxide and Aluminum<brk/>Oxide-Boron Carbide Composite Pellets
• Effective Date: 01-Feb-2019
• Refers: ASTM B329-18 - Standard Test Method for Apparent Density of Metal Powders and Compounds Using the Scott Volumeter
• Effective Date: 01-Oct-2018
• Refers: ASTM E344-18 - Terminology Relating to Thermometry and Hydrometry
• Effective Date: 01-Apr-2018
• Refers: ASTM E344-16 - Terminology Relating to Thermometry and Hydrometry
• Effective Date: 01-Nov-2016
• Refers: ASTM E228-11(2016) - Standard Test Method for Linear Thermal Expansion of Solid Materials With a Push-Rod Dilatometer
• Effective Date: 01-Sep-2016
• Refers: ASTM B329-14 - Standard Test Method for<brk type="line"/> Apparent Density of Metal Powders and Compounds Using the Scott Volumeter
• Effective Date: 01-Dec-2014
• Refers: ASTM E344-13 - Terminology Relating to Thermometry and Hydrometry
• Effective Date: 01-May-2013
• Refers: ASTM C809-13 - Standard Test Methods for Chemical, Mass Spectrometric, and Spectrochemical Analysis of Nuclear-Grade Aluminum Oxide and Aluminum<brk/>Oxide-Boron Carbide Composite Pellets
• Effective Date: 01-Jan-2013
• Refers: ASTM B329-06(2012) - Standard Test Method for<brk type="line"/> Apparent Density of Metal Powders and Compounds Using the Scott Volumeter
• Effective Date: 01-Oct-2012
• Refers: ASTM E585/E585M-12 - Standard Specification for Compacted Mineral-Insulated, Metal-Sheathed, Base Metal Thermocouple Cable
• Effective Date: 01-May-2012
• Refers: ASTM E344-12 - Terminology Relating to Thermometry and Hydrometry
• Effective Date: 01-May-2012
• Refers: ASTM E2181/E2181M-11 - Standard Specification for Compacted Mineral-Insulated, Metal-Sheathed, Noble Metal Thermocouples and Thermocouple Cable
• Effective Date: 01-Nov-2011

Overview

ASTM E1652-21 is the standard specification developed by ASTM International for magnesium oxide (MgO) and aluminum oxide (Al₂O₃) powder and crushable insulators. These materials are essential components in the manufacturing of base metal thermocouples, metal-sheathed platinum resistance thermometers (PRTs), noble metal thermocouples, and their respective mineral-insulated cables. The standard outlines the requirements, classification, testing methods, and handling practices to ensure the insulators' performance and reliability in demanding temperature measurement applications.

Key Topics

• Material Requirements: Specifies purity levels and permissible impurity limits for both magnesium oxide and aluminum oxide materials to ensure electrical isolation and mechanical support within thermometric devices.
• Product Classification: Provides types for MgO and Al₂O₃, each with specific chemical requirements suitable for different application temperatures and environments.
• Physical and Dimensional Properties:
  • Density and modulus of rupture (crushability) of powder and insulators.
  • Tolerances for insulator outside and hole diameters.
  • Requirements for wall and web thickness, length, camber, and hole pattern.
• Testing Methods:
  • Chemical analysis (using wet chemistry, fusion calorimetry, X-ray fluorescence, ICP).
  • Density determination (using Scott Volumeter and displacement methods).
  • Modulus of rupture (breaking force test for crushability).
  • Thermal properties tests (specific heat, conductivity, expansion).

Applications

• Base Metal Thermocouples: Used extensively in industrial temperature monitoring, process control, and power generation. The specified MgO and Al₂O₃ insulators provide electrical insulation and mechanical integrity at high temperatures.
• Noble Metal Thermocouples: Critical for high-temperature processes such as furnace monitoring and laboratory research, requiring insulators of the highest purity to avoid sensor degradation.
• Metal-Sheathed Platinum Resistance Thermometers (PRTs): Widely used for accurate temperature measurement in scientific and industrial settings. The mineral insulators ensure long-term stability and prevent contamination between conductors.
• Mineral-Insulated Cable Assemblies: The standard provides guidance for the manufacture of cables that require robust, reliable insulation for harsh or critical environments, including chemical plants, nuclear facilities, and aerospace applications.
• Quality Assurance in Sensor Manufacturing: Adoption of ASTM E1652-21 ensures that suppliers and manufacturers can consistently procure and use insulation materials suited to their end-use requirements, supporting traceability and compliance in regulated industries.

Related Standards

• ASTM E235: Specification for mineral-insulated, metal-sheathed thermocouples for nuclear and high-reliability applications.
• ASTM E585/E585M: Specification for compacted mineral-insulated, metal-sheathed, base metal thermocouple cable.
• ASTM E2181/E2181M: Specification for compacted mineral-insulated, metal-sheathed, noble metal thermocouples and cable.
• ASTM E1137/E1137M: Specification for industrial platinum resistance thermometers.
• ASTM B329: Test method for apparent density of metal powders.
• ASTM C809, C832, E228, E1225: Test methods related to chemical analysis, thermal expansion, and conductivity of insulating materials.
• ASTM E344: Standard terminology relating to thermometry and hydrometry.

Practical Value

By following ASTM E1652-21, manufacturers, suppliers, and end-users ensure the consistent quality and performance of MgO and Al₂O₃ powders and insulators in temperature sensors. This standard directly supports:

• Reliable high-temperature measurement by mitigating insulation breakdown or contamination.
• Consistency in manufacturing through standardized material and dimensional specifications.
• Regulatory compliance for products and processes in critical sectors such as energy, aerospace, and industrial automation.
• Informed procurement through clearly defined material types, tolerances, and test procedures.

Keywords: ASTM E1652-21, magnesium oxide powder, aluminum oxide powder, crushable insulator, thermocouple insulation, platinum resistance thermometer, mineral-insulated cable, temperature sensor manufacturing.

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:E1652 −21 An American National Standard
Standard Specification for
Magnesium Oxide and Aluminum Oxide Powder and
Crushable Insulators Used in the Manufacture of Base Metal
Thermocouples, Metal-Sheathed Platinum Resistance
Thermometers, and Noble Metal Thermocouples
This standard is issued under the fixed designation E1652; 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 C832Test Method for Measuring Thermal Expansion and
Creep of Refractories Under Load
1.1 This specification covers the requirements for magne-
D2766Test Method for Specific Heat of Liquids and Solids
sium oxide (MgO) and aluminum oxide (Al O ) powders and
2 3
(Withdrawn 2018)
crushable insulators used to manufacture base metal
E228Test Method for Linear Thermal Expansion of Solid
thermocouples, metal-sheathed platinum resistance thermom-
Materials With a Push-Rod Dilatometer
eters (PRTs), noble metal thermocouples, and their respective
E235 Specification for Type K and Type N Mineral-
cables.
Insulated, Metal-Sheathed Thermocouples for Nuclear or
1.2 The values stated in SI units are to be regarded as
for Other High-Reliability Applications
standard. The values given in parentheses after SI units are
E344Terminology Relating to Thermometry and Hydrom-
providedforinformationonlyandarenotconsideredstandard.
etry
1.3 This standard does not purport to address all of the E585/E585M Specification for Compacted Mineral-
safety concerns, if any, associated with its use. It is the
Insulated, Metal-Sheathed, Base Metal Thermocouple
responsibility of the user of this standard to establish appro- Cable
priate safety, health, and environmental practices and deter-
E1137/E1137MSpecification for Industrial Platinum Resis-
mine the applicability of regulatory limitations prior to use. tance Thermometers
1.4 This international standard was developed in accor-
E1225Test Method for Thermal Conductivity of Solids
dance with internationally recognized principles on standard- Using the Guarded-Comparative-Longitudinal Heat Flow
ization established in the Decision on Principles for the Technique
Development of International Standards, Guides and Recom-
E2181/E2181M Specification for Compacted Mineral-
mendations issued by the World Trade Organization Technical Insulated, Metal-Sheathed, Noble Metal Thermocouples
Barriers to Trade (TBT) Committee.
and Thermocouple Cable
2. Referenced Documents
3. Terminology
2.1 ASTM Standards:
3.1 The definitions given in Terminology E344 shall apply
B329Test Method for Apparent Density of Metal Powders
to this specification.
and Compounds Using the Scott Volumeter
C809Test Methods for Chemical, Mass Spectrometric, and
4. Significance and Use
Spectrochemical Analysis of Nuclear-Grade Aluminum
4.1 Magnesium oxide and aluminum oxide are used to
Oxide and AluminumOxide-Boron Carbide Composite
electrically isolate and mechanically support the thermoele-
Pellets
ments of a thermocouple (see Specifications E235, E585/
E585M, and E2181/E2181M) and the connecting wires of a
This specification is under the jurisdiction of ASTM Committee E20 on
PRT(see Specification E1137/E1137M) within a metal sheath.
Temperature Measurement and is the direct responsibility of Subcommittee E20.13
The metal sheath is typically reduced in diameter to compact
on Thermocouples - Materials and Accessories Specifications.
Current edition approved Nov. 1, 2021. Published November 2021. Originally the oxide powder or crushable oxide insulators around the
approved in 1995. Last previous edition approved in 2015 as E1652–15. DOI:
thermoelements or wires.
10.1520/E1652-21.
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 last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1652−21
TABLE 2 Chemical Requirements for Al O Type 1P
4.2 In order to be suitable for this purpose, the materials
2 3
A
and MgO Type 1P
shall meet certain criteria for purity and for mechanical and
Aluminum Oxide (Al O ) 99.65 % Magnesium Oxide (MgO) 99.40 %
2 3
dimensional characteristics. Material that does not meet the
(mass) min (mass) min
purity criteria may cause premature failure of the sensor.
Concentration, Concentration,
Impurity % (mass) Impurity % (mass)
4.3 Use of this specification for the procurement of powder
CaO 0.08 max CaO 0.35 max
and crushable insulators will help to ensure that the product
SiO 0.08 max SiO 0.13 max
2 2
obtained is suitable for the intended purpose.
MgO 0.08 max Al O 0.15 max
2 3
Fe O 0.04 max Fe O 0.04 max
2 3 2 3
4.4 Usefulinformationaboutaluminaandmagnesiaisgiven
ZrO 0.08 max
in the appendixes.
Na O 0.06 max
C 0.01 max C 0.02 max
S 0.005 max S 0.0025 max
5. Classification
B 0.001 max B 0.0035 max
5.1 ThepurchasershallspecifytheappropriateMaterialand Cd 0.001 max Cd 0.001 max
B+Cd 0.004 max
Type from 5.2 through 5.6 below.
A
Platinum thermoelements and noble Metal thermocouples for use below 650 °C
5.2 MgO Type 1 in accordance with Table 1.
may optionally specify Type 1 composition according to Table 1.
5.3 Al O Type 1 in accordance with Table 1.
2 3
5.4 MgO Type 1P in accordance with Table 2.
TABLE 3 Chemical Requirements for MgO Type 2
5.5 Al O Type 1P in accordance with Table 2.
Magnesium Oxide (MgO) 97.00 % (mass) min
2 3
Impurity Concentration, % (mass)
5.6 MgO Type 2 in accordance with Table 3.
CaO 1.50 max
NOTE 1—There is no corresponding Al O Type 2 designation at this
2 3
Al O 1.00 max
2 3
time.
SiO 3.00 max
5.7 The final product shall be chemically analyzed using Fe O 0.15 max
2 3
C 0.02 max
appropriate methods listed in 9.1. Major impurities shall not
S 0.0025 max
exceed the limits indicated in Table 1 through Table 3 for the
B 0.0050 max
Cd 0.001 max
appropriate grade.Any detected impurity with a concentration
B + Cd 0.0050 max
greater than 0.001% (mass) shall be reported to the purchaser.
MgO + CaO + Al O +SiO 99.50 min
2 3 2
6. Ordering Information
6.1 The purchaser shall specify the following when order-
ing:
6.2 The purchaser may specify the following additional
6.1.1 Material and Type in accordance with Section 5.
information when ordering:
6.1.2 Insulator Outside Diameter. 6.2.1 Minimum Inside Diameter (at Maximum Material
6.1.3 Hole Diameter.
Condition (MMC)) of the Tubing,(intowhichinsulatorswillbe
6.1.4 Number of Holes. inserted, see 8.3).
6.1.5 Hole Pattern.
6.2.2 Maximum Outside Diameter of Wire which will be
6.1.6 Length. inserted into the insulators, (see 8.3).
6.1.7 Particle Size (if supplied as powder).
6.3 Consult the insulator manufacturer for limitations of
relationships between outside diameter, hole diameters, hole
patterns, and length.
TABLE 1 Chemical Requirements for Al O Type 1
2 3
A, B
and MgO Type 1
7. Physical Properties
Aluminum Oxide (Al O ) Magnesium Oxide (MgO)
2 3
7.1 Density—The density of crushable magnesium oxide
99.65 % (mass) min 99.40 % (mass) min
and aluminum oxide insulators typically ranges from 2060
Concentration, Concentration,
Impurity Impurity
3 3 3 3
% (mass) % (mass)
kg/m (0.074 lbm/in. ) to 3060 kg/m (0.111 lbm/in. ).
CaO 0.08 max CaO 0.35 max
Specific density requirements, as well as the test method to be
SiO 0.08 max SiO 0.35 max
2 2
used to determine density, shall be negotiated between the
MgO 0.08 max Al O 0.15 max
2 3
purchaser and manufacturer. See Appendix X3 for suggested
Fe O 0.04 max Fe O 0.07 max
2 3 2 3
ZrO 0.08 max
2 test methods.
Na O 0.06 max
C 0.01 max C 0.02 max
7.2 Modulus of Rupture (MOR)—In the past, a breaking
S 0.005 max S 0.0025 max
force test that is based on a relative modulus of rupture and is
B 0.001 max B 0.0035 max
relatedtocrushabilityhasbeenused.However,withvariations
Cd 0.001 max Cd 0.001 max
B+Cd 0.004 max
in modulus from 21 to 83 MPa (3000 to 12000 lb/in. )
A
Platinum thermoelements and Noble Metal thermocouples for use above 650 °C influenced by insulator configuration, number of holes, and
shall specify Type 1P composition according to Table 2.
cross-sectional dimensions, specific modulus requirements
B
Base metal thermocouples for nuclear environments in accordance with Speci-
cannotbelistedforeachconfiguration.Themodulusofrupture
fication E235 shall specify Type 1P composition according to Table 2.
is best used for lot-to-lot comparison of a given insulator size
E1652−21
A
TABLE 5 Hole Diameter Tolerance
and configuration. See Appendix X4 for a suggested test
Nominal Insulator Hole Diameter Hole Diameter Tolerance
method and X2.4 for recommended tolerances.
Over 0.18 to 1.00 mm (0.007 to 0.039 in.), ±0.05 mm (±0.002 in.)
inclusive
8. Dimensional Requirements
Over 1.00 to 2.00 mm (0.040 to 0.079 in.), ±0.08 mm (±0.003 in.)
8.1 Outside diameter and hole diameter tolerances for insu- inclusive
Over 2.00 to 2.50 mm (0.079 to 0.098 in.), ±0.10 mm (±0.004 in.)
latorsshallbeasspecifiedinTable4andTable5,respectively,
inclusive
unless otherwise agreed to between the purchaser and manu-
Over 2.50 mm (0.098 in.) and larger, ±05 %
facturer. inclusive
A
See X2.3 for recommended inspection procedure.
8.2 Thewallandwebthicknesses(seeFig.1)shallbeequal
withinoutsidethetotalallowableoutsidediametertoleranceas
specified in Table 5 and the minimum measured web or wall
shall be no smaller than 75% of the maximum measured web
or wall, unless otherwise agreed to between the purchaser and
manufacturer.
8.3 The camber shall not exceed 0.3% of the length. The
insulator shall be capable of passing through a rigid straight
tube longer than the insulator and with an inside diameter as
specified in 6.2.1. Local camber defects caused by "knees" or
"doglegs" shall not impede the insertion of wire.
8.4 Thehelicaltwistofholesshallnotexceed2°percm(5°
per in.) of the length.
8.5 Thelengthshallbeasspecifiedin6.1.6withatolerance
of+6⁄−0.00 mm (+0.25⁄−0.00 in.).
8.6 The ends of each insulator should be cut square and
shall be essentially chip-free as agreed upon between the
FIG. 1 Wall and Web Thicknesses
supplier and purchaser.
9.1.2 Test Method C809 can be used for quantitative analy-
9. Test Methods
sis of elemental impurities.
9.1.3 Any method used for quantitative determination of
9.1 Chemical Composition:
MgO, Al O , CaO, SiO , and ZrO should have a detection
9.1.1 Wet chemical analysis, X-ray florescence, inductively
2 3 2 2
sensitivity of at least 0.01% (mass).Test methods used for the
coupled plasma spectrometry (ICP), or a combination of test
quantitative analysis of boron, cadmium, sulfur, carbon and
methods, can be used for quantitative determination of silicon
iron oxide should have a detection sensitivity of 0.0001%
dioxide (SiO ), iron oxide (Fe O ), and zirconium oxide
2 2 3
(mass).
(ZrO ) with gravimetric determination for SiO and Fe O .
2 2 2 3
The SiO filtrate can be used for further calcium oxide (CaO)
2 9.2 Density (Powder)—Test Method B329 can be used for
determination.BoronandcadmiumcanbemeasuredusingICP
determining the density of Al O and MgO powders.
2 3
and other minor components. Sulfur and carbon can be
9.3 Appendix X5 lists other optional test methods.
measured using infrared spectrometry.
10. Handling and Storage Precautions
TABLE 4 Outside Diameter (O.D.) Tolerances
10.1 Powders and crushable insulators shall be shipped and
Nominal Insulator O.D. O.D. Tolerance
stored in containers that prevent contamination and breakage.
Over 0.25 to 1.00 mm (0.010 to 0.039 in.), ±0.05 mm (±0.002 in.)
Powders and crushable insulators should be stored in sealed
inclusive
containers to prevent contamination by moisture absorption.
Over 1.00 to 1.50 mm (0.039 to 0.059 in.), ±0.08 mm (±0.003 in.)
inclusive
(See Appendix X2.)
Over 1.50 to 5.00 mm (0.059 to 0.197 in.), ±0.10 mm (±0.004 in.)
inclusive
11. Keywords
Over 5.00 to 8.00 mm (0.197 to 0.315 in.), ±0.13 mm (±0.005 in.)
inclusive 11.1 aluminum oxide; crushable; insulator; magnesium ox-
Over 8.00 to 10.00 mm (0.315 to 0.394 in.), ±0.15 mm (±0.006 in.)
ide; mineral-insulated, metal-sheathed cable; platinum resis-
inclusive
tance thermometer; thermocouple, base metal; thermocouple,
Over 10.0 mm (0.394 in.) ±1.75%
noble metal
E1652−21
APPENDIXES
(Nonmandatory Information)
X1. MATERIALS AND MANUFACTURE
X1.1 Alumina (Al O ) X1.1.2.2 Crystal Shape— Hexagonal.
2 3
3 3
X1.1.2.3 Maximum Theoretical Density—3.98×10 kg/m
X1.1.1 Sources:
(0.144 lbm/in ).
X1.1.1.1 Bauxite is the principal source of alumina.
X1.1.2.4 Dielectric Strength—5600 kV/m (142000 V/in).
, is the most stable phase. Boehmite,
Gibbsite, Al(OH)
X1.1.2.5 Hardness (MOHS)—9.
AlO(OH), also occurs in nature. High grade bauxite is low in
X1.1.2.6 Softening Temperature—1750°C (3182°F).
iron and silica content.The major use of purified alumina is in
X1.1.2.7 Melting Temperature—2050°C (3722°F).
the production of aluminum metal.
X1.1.2.8 Molecular Weight—101.94.
X1.1.1.2 Depending upon the application, the economics,
X1.1.2.9 Typical Electrical Resistivity—See Table X1.1.
and the purity of the bauxite, the purification process could be
X1.1.2.10 Specific Heat—8.8×10 J/kg·K@ 20°C (0.21
wet alkaline, wet acid, alkaline furnace, carbothermic furnace,
Btu/lbm °F @ 68°F). 1.2×10 J/kg·K @ 1000°C (0.28
or electrolytic processes.
Btu/lbm °F @ 1832°F).
X1.1.1.3 The wet alkaline processes are the most economi-
X1.1.2.11 Typical Thermal Conductivity—See Table X1.2.
cal. Gibbsite bauxite is easier to dissolve. It is digested in
X1.1.2.12 Macroscopic Thermal Neutron Absorption Cross
sodiumhydroxide(NaOH)solutionatabout150°C(302°F)at
−1 −1
Section—1.0 m (0.03 in ).
345kPa (50 lb/in. ). Boehmitic bauxite, AlO(OH), is more
difficulttodissolve.ItrequiresahigherconcentrationofNaOH
X1.2 Magnesia (MgO)
solution, a pressure of 1930 to 4826 kPa (280 to 700 lb/in. ),
X1.2.1 Sources:
and a temperature of about 238°C (545°F).
X1.2.1.1 Magnesia can be made by the oxidation of mag-
X1.1.1.4 When digested, the slurry is cooled to about
nesiummetalorbyheatingeasilydecomposedoxy-compounds
100°C (212°F) by releasing pressure to atmospheric, and the
of magnesium, such as the hydroxide, Mg(OH) , the oxalate,
undissolved “mud” is sedimented or filtered off. When cooled
MgC O , or the naturally occurring carbonate (magnesite),
2 4
to about 50°C (122°F) and seeded with alumina-trihydrate,
MgCO . Mg(OH) exists as the mineral brucite in small
3 2
precipitation occurs. The precipitated trihydrate is washed and
amounts; however the principal commercial source of magne-
then calcinated. The trihydrate dehydrates slowly. At atmo-
siaismagnesite,whichoccursinarelativelypurestateinmany
spheric pressures, the dehydration process involves two steps.
parts of the world. Another source of magnesia is dolomite (a
X1.1.1.5 The trihydrate dehydrates first to a composition
more abundant substance), a double carbonate of magnesium
close to boehmite (Al O ·H O). Even at 200°C (392°F) the
2 3 2
and calcium. With dolomite, the calcium must be removed.
rate of dehydration is very slow. Dehydration is essentially
X1.2.1.2 When magnesite is heated, the change to MgO is
complete at 400°C (752°F) in an oven at below atmospheric
completed at about 620°C (1148°F). The MgO remains as
pressure or at 500°C (932°F) at atmospheric pressure. In one
submicroscopic crystals up to about 1000°C (1832°F). At
study, the heating at 538°C (1000°F) for 7 h still resulted in
1200°C(2192°F)thecrystalsgrowtoabout1µm(39.37µin.).
0.1 moles of H O per mole Al O , that is, about 2%.
2 2 3
With additives, such as sodium chloride, the crystals could be
Differential thermal analysis (DTA) studies show endothermic
3 to 4 µm (120 to 160 µin.) in size at 1200°C (2192°F). The
effects at 225, 300, and 550°C (437, 572, and 1022°F,
crystal size increases with increases in the temperature of
respectively). The peak at 550°C (1022°F) represents the
sintering. The calcination and sintering of magnesite is carried
dehydration of boehmite.
out in rotating kilns at 1600 to 1700°C (2912 to 3092°F). For
X1.1.1.6 Activatedaluminaisadesiccantandismoreeasily
requirements of purest quality, the MgO is fused in an electric
rehydrated when activated in vacuum. Alumina activated in
furnace where many of the impurities are removed by volatil-
vacuumat180to200°C(356to392°F)andthenheatedinair
ization. The fused MgO is crushed to the required size.
at about 350 to 450°C (662 to 842°F) does not rehydrate as
X1.2.1.3 Magnesia prepared by heating magnesite can vary
easily. No rehydration was found with alpha alumina of low
widely in purity and in the composition of the impurities,
surfacearea.Toachievelowsurfaceareathealuminashouldbe
dependinguponthesourceofthemagnesite.Theimpuritiesare
heated to at least 1700°C (3092°F). Alumina is sintered at
about 1700 to 2000°C (3092 to 3632°F). It melts around
2050°C (3722°F). The maximum temperature is impacted by
TABLE X1.1 Typical Electrical Resistivity of Alumina
the presence of certain metals and atmospheres where the
(Theoretical, 100% Density)
phase change diagram can be lower than predicted by pure
Temperature Typical Resistivity
metal materials.
°C °F ohm-cm ohm-in.
14 13
X1.1.2 Typical Crystal Properties:
20 68 >1 × 10 >4×10
11 10
400 752 1 × 10 4×10
X1.1.2.1 Coeffıcien
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1652 − 15 E1652 − 21 An American National Standard
Standard Specification for
Magnesium Oxide and Aluminum Oxide Powder and
Crushable Insulators Used in the Manufacture of Base Metal
Thermocouples, Metal-Sheathed Platinum Resistance
Thermometers, and Noble Metal Thermocouples
This standard is issued under the fixed designation E1652; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This specification covers the requirements for magnesium oxide (MgO) and aluminum oxide (Al O ) powders and crushable
2 3
insulators used to manufacture base metal thermocouples, metal-sheathed platinum resistance thermometers (PRTs), noble metal
thermocouples, and their respective cables.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. after
SI units are provided for information only and are not considered standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 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:
B329 Test Method for Apparent Density of Metal Powders and Compounds Using the Scott Volumeter
C809 Test Methods for Chemical, Mass Spectrometric, and Spectrochemical Analysis of Nuclear-Grade Aluminum Oxide and
AluminumOxide-Boron Carbide Composite Pellets
C832 Test Method for Measuring Thermal Expansion and Creep of Refractories Under Load
D2766 Test Method for Specific Heat of Liquids and Solids (Withdrawn 2018)
E228 Test Method for Linear Thermal Expansion of Solid Materials With a Push-Rod Dilatometer
E235 Specification for Type K and Type N Mineral-Insulated, Metal-Sheathed Thermocouples for Nuclear or for Other
High-Reliability Applications
E344 Terminology Relating to Thermometry and Hydrometry
E585/E585M Specification for Compacted Mineral-Insulated, Metal-Sheathed, Base Metal Thermocouple Cable
This specification is under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.13 on
Thermocouples - Materials and Accessories Specifications.
Current edition approved Nov. 1, 2015Nov. 1, 2021. Published November 2015November 2021. Originally approved in 1995. Last previous edition approved in 20142015
as E1652 – 14a.E1652 – 15. DOI: 10.1520/E1652-15.10.1520/E1652-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1652 − 21
E1137/E1137M Specification for Industrial Platinum Resistance Thermometers
E1225 Test Method for Thermal Conductivity of Solids Using the Guarded-Comparative-Longitudinal Heat Flow Technique
E2181/E2181M Specification for Compacted Mineral-Insulated, Metal-Sheathed, Noble Metal Thermocouples and Thermo-
couple Cable
3. Terminology
3.1 The definitions given in Terminology E344 shall apply to this specification.
4. Significance and Use
4.1 Magnesium oxide and aluminum oxide are used to electrically isolate and mechanically support the thermoelements of a
thermocouple (see Specifications E235, E585/E585M, and E2181/E2181M) and the connecting wires of a PRT (see Specification
E1137/E1137M) within a metal sheath. The metal sheath is typically reduced in diameter to compact the oxide powder or crushable
oxide insulators around the thermoelements or wires.
4.2 In order to be suitable for this purpose, the materials shall meet certain criteria for purity and for mechanical and dimensional
characteristics. Material that does not meet the purity criteria may cause premature failure of the sensor.
4.3 Use of this specification for the procurement of powder and crushable insulators will help to ensure that the product obtained
is suitable for the intended purpose.
4.4 Useful information about alumina and magnesia is given in the appendixes.
5. Classification
5.1 The purchaser shall specify the appropriate Material and Type from 5.2 through 5.6 below.
5.2 MgO Type 1 in accordance with Table 1.
5.3 Al O Type 1 in accordance with Table 1.
2 3
5.4 MgO Type 1P in accordance with Table 2.
5.5 Al O Type 1P in accordance with Table 2.
2 3
TABLE 1 Chemical Requirements for Al O Type 1
2 3
A, B
and MgO Type 1
Aluminum Oxide (Al O ) Magnesium Oxide (MgO)
2 3
99.65 % (mass) min 99.40 % (mass) min
Concentration, Concentration,
Impurity Impurity
% (mass) % (mass)
Al O 99.65 % min MgO 99.40 % min
2 3
CaO 0.08 max CaO 0.35 max
B B
SiO 0.08 max SiO 0.35 max
2 2
SiO 0.08 max SiO 0.35 max
2 2
MgO 0.08 max Al O 0.15 max
2 3
Fe O 0.04 max Fe O 0.07 max
2 3 2 3
ZrO 0.08 max
Na O 0.06 max
C 0.01 max C 0.02 max
S 0.005 max S 0.0025 max
B 0.001 max B 0.0035 max
Cd 0.001 max Cd 0.001 max
B+Cd 0.004 max
A
Platinum thermoelements and Noble Metal thermocouples for use above
650°C650 °C shall specify Type 1P composition according to Table 2.
B
Base metal thermocouples for nuclear environments in accordance with Speci-
fication E235 shall specify Type 1P composition according to Table 2.
E1652 − 21
TABLE 2 Chemical Requirements for Al O Type 1P
2 3
A
and MgO Type 1P
Aluminum Oxide (Al O ) 99.65 % Magnesium Oxide (MgO) 99.40 %
2 3
(mass) min (mass) min
Concentration, Concentration,
Impurity % (mass) Impurity % (mass)
Al O 99.65 % min MgO 99.40 % min
2 3
CaO 0.08 max CaO 0.35 max
SiO 0.08 max SiO 0.13 max
2 2
MgO 0.08 max Al O 0.15 max
2 3
Fe O 0.04 max Fe O 0.04 max
2 3 2 3
ZrO 0.08 max
Na O 0.06 max
C 0.01 max C 0.02 max
S 0.005 max S 0.0025 max
B 0.08 max B 0.0035 max
B 0.001 max B 0.0035 max
Cd 0.08 max Cd 0.001 max
Cd 0.001 max Cd 0.001 max
B+Cd 0.004 max
A
Platinum thermoelements and noble Metal thermocouples for use below
650°C650 °C may optionally specify Type 1 composition according to Table 1.
5.6 MgO Type 2 in accordance with Table 3.
NOTE 1—There is no corresponding Al O Type 2 designation at this time.
2 3
5.7 The final product shall be chemically analyzed using appropriate methods listed in 9.1. Major impurities shall not exceed the
limits indicated in Table 1 through Table 3 for the appropriate grade. Any detected impurity with a concentration greater than
0.001 % (mass) shall be reported to the purchaser.
6. Ordering Information
6.1 The purchaser shall specify the following when ordering:
6.1.1 Material and Type in accordance with Section 5.
6.1.2 Insulator Outside Diameter.
6.1.3 Hole Diameter.
6.1.4 Number of Holes.
6.1.5 Hole Pattern.
6.1.6 Length.
TABLE 3 Chemical Requirements for MgO Type 2
Magnesium Oxide (MgO) 97.00 % (mass) min
Impurity Concentration, % (mass)
MgO 97.00 % min
CaO 1.50 max
Al O 1.00 max
2 3
SiO 3.00 max
Fe O 0.15 max
2 3
C 0.02 max
S 0.0025 max
B 0.0050 max
Cd 0.001 max
B + Cd 0.0050 max
MgO + CaO + Al O + SiO 99.50 min
2 3 2
E1652 − 21
6.1.7 Particle Size (if supplied as powder).
6.2 The purchaser may specify the following additional information when ordering:
6.2.1 Minimum Inside Diameter (at Maximum Material Condition (MMC)) of the Tubing, (into which insulators will be inserted,
see 8.3).
6.2.2 Maximum Outside Diameter of Wire which will be inserted into the insulators, (see 8.3).
6.3 Consult the insulator manufacturer for limitations of relationships between outside diameter, hole diameters, hole patterns, and
length.
7. Physical Properties
7.1 Density—The density of crushable magnesium oxide and aluminum oxide insulators typically ranges from 2060 kg/m (0.074
3 3 3
lbm/in. ) to 3060 kg/m (0.111 lbm/in. ). Specific density requirements, as well as the test method to be used to determine density,
shall be negotiated between the purchaser and manufacturer. See Appendix X3 for suggested test methods.
7.2 Modulus of Rupture (MOR)—In the past, a breaking force test that is based on a relative modulus of rupture and is related to
crushability has been used. However, with variations in modulus from 21 to 83 MPa (3000 to 12 000 lb/in. ) influenced by insulator
configuration, number of holes, and cross-sectional dimensions, specific modulus requirements cannot be listed for each
configuration. The modulus of rupture is best used for lot-to-lot comparison of a given insulator size and configuration. See
Appendix X4 for a suggested test method and X2.4 for recommended tolerances.
8. Dimensional Requirements
8.1 Outside diameter and hole diameter tolerances for insulators shall be as specified in Table 4 and Table 5, respectively, unless
otherwise agreed to between the purchaser and manufacturer.
8.2 The wall and web thicknesses (see Fig. 1) shall be equal within outside the total allowable outside diameter tolerance as
specified in Table 5 and the minimum measured web or wall shall be no smaller than 75 % of the maximum measured web or wall,
unless otherwise agreed to between the purchaser and manufacturer.
8.3 The camber shall not exceed 0.3 % of the length. The insulator shall be capable of passing through a rigid straight tube longer
than the insulator and with an inside diameter as specified in 6.2.1. Local camber defects caused by "knees" or "doglegs" shall not
impede the insertion of wire.
8.4 The helical twist of holes shall not exceed 2° per cm (5° per in.) of the length.
8.5 The length shall be as specified in 6.1.6 with a tolerance of +6 ⁄−0.00 mm ( +0.25 ⁄−0.00 in.).
8.6 The ends of each insulator should be cut square and shall be essentially chip-free as agreed upon between the supplier and
purchaser.
TABLE 4 Outside Diameter (O.D.) Tolerances
Nominal Insulator O.D. O.D. Tolerance
Over 0.25 to 1.00 mm (0.010 to 0.039 in.), ±0.05 mm (±0.002 in.)
inclusive
Over 1.00 to 1.50 mm (0.039 to 0.059 in.), ±0.08 mm (±0.003 in.)
inclusive
Over 1.50 to 5.00 mm (0.059 to 0.197 in.), ±0.10 mm (±0.004 in.)
inclusive
Over 5.00 to 8.00 mm (0.197 to 0.315 in.), ±0.13 mm (±0.005 in.)
inclusive
Over 8.00 to 10.00 mm (0.315 to 0.394 in.), ±0.15 mm (±0.006 in.)
inclusive
Over 10.0 mm (0.394 in.) ±1.75%
E1652 − 21
A
TABLE 5 Hole Diameter Tolerance
Nominal Insulator Hole Diameter Hole Diameter Tolerance
Over 0.18 to 1.00 mm (0.007 to 0.039 in.), ±0.05 mm (±0.002 in.)
inclusive
Over 1.00 to 2.00 mm (0.040 to 0.079 in.), ±0.08 mm (±0.003 in.)
inclusive
Over 2.00 to 2.50 mm (0.079 to 0.098 in.), ±0.10 mm (±0.004 in.)
inclusive
Over 2.50 mm (0.098 in.) and larger, ±05 %
inclusive
A
See X2.3 for recommended inspection procedure.
FIG. 1 Wall and Web Thicknesses
9. Test Methods
9.1 Chemical Composition:
9.1.1 Wet chemical analysis, or fusion calorimetric analysis, or both,X-ray florescence, inductively coupled plasma spectrometry
(ICP), or a combination of test methods, can be used for quantitative determination of silicon dioxide (SiO ), iron oxide (Fe O ),
2 2 3
and zirconium oxide (ZrO ) with gravimetric determination for SiO and Fe O . The SiO filtrate can be used for further calcium
2 2 2 3 2
oxide (CaO) determination. Boron and cadmium can be measured using ICP and other minor components. Sulfur and carbon can
be measured using infrared spectrometry.
9.1.2 Test Method C809 can be used for quantitative analysis of elemental impurities.
9.1.3 Any method used for quantitative determination of MgO, Al O , CaO, SiO , and ZrO should have a detection sensitivity
2 3 2 2
of at least 0.001 % (mass).0.01 % (mass). Test methods used for the quantitative analysis of boron, cadmium, sulfur, carbon and
iron oxide should have a detection sensitivity of 0.0001 % (mass).
9.2 Density (Powder)—Test Method B329 can be used for determining the density of Al O and MgO powders.
2 3
9.3 Appendix X5 lists other optional test methods.
10. Handling and Storage Precautions
10.1 Powders and crushable insulators shall be shipped and stored in containers that prevent contamination and breakage. Powders
and crushable insulators should be stored in sealed containers to prevent contamination by moisture absorption. (See Appendix
X2.)
11. Keywords
11.1 aluminum oxide; crushable; insulator; magnesium oxide; mineral-insulated, metal-sheathed cable; platinum resistance
thermometer; thermocouple, base metal; thermocouple, noble metal
E1652 − 21
APPENDIXES
(Nonmandatory Information)
X1. MATERIALS AND MANUFACTURE
X1.1 Alumina (Al O )
2 3
X1.1.1 Sources:
X1.1.1.1 Bauxite is the principal source of alumina. Gibbsite, Al(OH) , is the most stable phase. Boehmite, AlO(OH), also occurs
in nature. High grade bauxite is low in iron and silica content. The major use of purified alumina is in the production of aluminum
metal.
X1.1.1.2 Depending upon the application, the economics, and the purity of the bauxite, the purification process could be wet
alkaline, wet acid, alkaline furnace, carbothermic furnace, or electrolytic processes.
X1.1.1.3 The wet alkaline processes are the most economical. Gibbsite bauxite is easier to dissolve. It is digested in sodium
hydroxide (NaOH) solution at about 150°C (302°F) at 345 kPa 150 °C (302 °F) at 345 kPa (50 lb/in. ). Boehmitic bauxite,
AlO(OH), is more difficult to dissolve. It requires a higher concentration of NaOH solution, a pressure of 1930 to 4826 kPa (280
to 700 lb/in. ), and a temperature of about 238°C (545°F).238 °C (545 °F).
X1.1.1.4 When digested, the slurry is cooled to about 100°C (212°F)100 °C (212 °F) by releasing pressure to atmospheric, and
the undissolved “mud” is sedimented or filtered off. When cooled to about 50°C (122°F)50 °C (122 °F) and seeded with
alumina-trihydrate, precipitation occurs. The precipitated trihydrate is washed and then calcinated. The trihydrate dehydrates
slowly. At atmospheric pressures, the dehydration process involves two steps.
X1.1.1.5 The trihydrate dehydrates first to a composition close to boehmite (Al O ·H O). Even at 200°C (392°F)200 °C (392 °F)
2 3 2
the rate of dehydration is very slow. Dehydration is essentially complete at 400°C (752°F)400 °C (752 °F) in an oven at below
atmospheric pressure or at 500°C (932°F)500 °C (932 °F) at atmospheric pressure. In one study, the heating at 538°C
(1000°F)538 °C (1000 °F) for 7 h still resulted in 0.1 moles of H O per mole Al O , that is, about 2 %. Differential thermal analysis
2 2 3
(DTA) studies show endothermic effects at 225, 300, and 550°C550 °C (437, 572, and 1022°F,1022 °F, respectively). The peak at
550°C (1022°F)550 °C (1022 °F) represents the dehydration of boehmite.
X1.1.1.6 Activated alumina is a desiccant and is more easily rehydrated when activated in vacuum. Alumina activated in vacuum
at 180 to 200°C200 °C (356 to 392°F)392 °F) and then heated in air at about 350 to 450°C450 °C (662 to 842°F)842 °F) does not
rehydrate as easily. No rehydration was found with alpha alumina of low surface area. To achieve low surface area the alumina
should be heated to at least 1700°C (3092°F).1700 °C (3092 °F). Alumina is sintered at about 1700 to 2000°C2000 °C (3092 to
3632°F).3632 °F). It melts around 2050°C (3722°F).2050 °C (3722 °F). The maximum temperature is impacted by the presence
of certain metals and atmospheres where the phase change diagram can be lower than predicted by pure metal materials.
X1.1.2 Typical Crystal Properties : Properties:
−6 −6
X1.1.2.1 Coeffıcient of Thermal Expansion—6 to 9 × 10 /K (3.3 to 5 × 10 /°F) between 20 and 1000°C1000 °C (68 and
1832°F).1832 °F).
E1652 − 21
X1.1.2.2 Crystal Shape— Hexagonal.
3 3 3
X1.1.2.3 Maximum Theoretical Density—3.98 × 10 kg/m (0.144 lbm/in ).
X1.1.2.4 Dielectric Strength—5600 kV/m (142 000 V/in).
X1.1.2.5 Hardness (MOHS)—9.
X1.1.2.6 Softening Temperature—1750°C (3182°F).1750 °C (3182 °F).
X1.1.2.7 Melting Temperature—2050°C (3722°F).2050 °C (3722 °F).
X1.1.2.8 Molecular Weight—101.94.
X1.1.2.9 Typical Electrical Resistivity—See Table X1.1.
2 3
X1.1.2.10 Specific Heat—8.8 × 10 J/kg·K@ 20°C20 °C (0.21 Btu/lbm °F @ 68°F).68 °F). 1.2 × 10 J/kg·K @ 1000°C1000 °C
(0.28 Btu/lbm °F @ 1832°F).1832 °F).
X1.1.2.11 Typical Thermal Conductivity —Conductivity—See Table X1.2.
−1 −1
X1.1.2.12 Macroscopic Thermal Neutron Absorption Cross Section—1.0 m (0.03 in ).
X1.2 Magnesia (MgO)
X1.2.1 Sources:
X1.2.1.1 Magnesia can be made by the oxidation of magnesium metal or by heating easily decomposed oxy-compounds of
magnesium, such as the hydroxide, Mg(OH) , the oxalate, MgC O , or the naturally occurring carbonate (magnesite), MgCO .
2 2 4 3
Mg(OH) exists as the mineral brucite in small amounts; however the principal commercial source of magnesia is magnesite, which
occurs in a relatively pure state in many parts of the world. Another source of magnesia is dolomite (a more abundant substance),
a double carbonate of magnesium and calcium. With dolomite, the calcium must be removed.
TABLE X1.1 Typical Electrical Resistivity of Alumina
(Theoretical, 100 % Density)
Temperature Typical Resistivity
°C °F ohm-cm ohm-in.
14 13
20 68 >1 × 10 >4 × 10
11 10
400 752 1 × 10 4 × 10
9 8
800 1472 1 × 10 4 × 10
6 5
1300 2372 1 × 10 4 × 10
E1652 − 21
TABLE X1.2 Typical Thermal Conductivity of Alumina
Temperature Typical Thermal Conductivity
°C °F W/(m·K) Btu·in./(h·ft ·°F)
20 68 33 227
500 932 11.4 41
1200 2192 6.7 28
TABLE X1.3 Typical Electrical Resistivity of Magnesia
(Theoretical, 100 % Density)
Temperature Typical Electrical Resistivity
°C °F ohm-cm ohm-in.
16 15
0 32 >1 × 10 >4 × 10
13 12
400 752 1 × 10 4 × 10
9 8
800 1472 1 × 10 4 × 10
5 4
1200 2192 1 × 10 4 × 10
TABLE X1.4 Typical Thermal Conductivity of Magnesia
Temperature Typical Thermal Conductivity
°C °F W/(m·K) Btu·in./(h·ft ·°F)
100 212 29.4 202
600 1112 12.3 67
1000 1832 8.1 36
X1.2.1.2 When ma
...