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Mullite is an excellent material due to its high temperature stability, strength and creep resistance. It is similar to Cordierite, although it is not as good an insulator and has a higher coefficient of thermal expansion. It is commonly used in heater exchange parts and electrical insulators.

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PropertyASTM MethodUnitsMullite
Color--Gray - Tan
Gas Permeability-atms-cc/sec-
Water AbsorptionC 20-97%0

PropertyASTM MethodUnitsMullite
DensityC 20-97g/cc3.00
HardnessVickers 500 gmGPa (kg/mm2)10 (1000)
Fracture ToughnessNotched BeamMPam1/23
Flexural Strength (MOR) (3 point) @ RTºF417-87MPa (psi x 103)206 (30)
Tensile Strength @ RTº-MPa (psi x 103)138 (20)
Compressive Strength @ RTº-MPa (psi x 103)1034 (150)
Elastic ModulusC848GPa (psi x 106)179 (26)
Shear ModulusC848psi x10610
Poisson's RatioC848-0.24

PropertyASTM MethodUnitsMullite
C.T.E., 25 - 100°CC 372-96x10-6/°C3.6
C.T.E., 25 - 300°CC 372-96x10-6/°C4.1
C.T.E., 25 - 600°CC 372-96x10-6/°C4.8
Thermal Conductivity @ RTºC 408W/m-K4
Max Use Temperature (Non-Loading)
(at high strength)
-Fahrenheit (°F)3100
Max Use Temperature (Non-Loading) 
(at high strength)
-Celsius (°C)1700

PropertyASTM MethodUnitsMullite
Dielectric Strength
(.125" Thick)
D 149-97AV/mil250
Dielectric Constant
@ 1MHz
D 150-98-6.7
Dielectric ConstantD 2520-95-6.7
@GHzD 2520-95-11.4
Dielectric Loss @ 1MHZD 150-98-0.003
Dielectric LossD 2520-95-0.003
@GHzD 2520-95-11.4
Volume Resistivity,
D 257ohms-cm> 1 x 1014
Volume Resistivity,
D 1829ohms-cm1 x 1010
Volume Resistivity,
D 1829ohms-cm1 x 109
Volume Resistivity,
D 1829ohms-cm-
Volume Resistivity,
D 1829ohms-cm-

Note: The information in this data sheet is for design guidance only. STC does not warrant this data as absolute values. Forming methods and specific geometry could affect properties. Slight adjustments can be made to some of the properties to accommodate specific customer requirements. Most of the dense materials in the table are resistant to mechanical erosion and chemical attack. STC has performed ASTM testing qualification for certain compositions, in accordance with ASTM D2442. Please consult our technical staff for appropriate material and specifc test results.

Note: In addition to the above compositions, STC offers a wide range of alternative materials. Please contact one of our applications engineers for material requirements that may not be shown above.

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