Mullite

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Mullite consists of aluminium oxide (Al2O3) and silicon dioxide (SiO2) with the nominal composition of 3 Al2O3, 2 SiO2. It offers numerous advantages, including:

Oxidation resistance
Good wear resistance
Low creep
Low thermal expansion coefficient
Good thermal shock resistance
Low-cost refractory compared to high-purity alumina, zirconia, and magnesia

Typical Applications

High-temperature protection tubes
Kiln furniture
Electrical insulators/substrates
Engineering ceramics in turbine engine parts
Infrared-transmitting windows

Material properties

Please note that the information set forth herein is offered for comparison only, and is not to be construed as absolute engineering data or constituting a warranty or representation for which we assume legal responsibility.

	SI/Metric	Imperial
Coefficient of Expansion CTE -100°C->25°C	81 x 10-7 /°C	45x10-7 /°F
Coefficient of Expansion CTE 25°C->300°C	90 x 10-7 /°C	50x10-7 /°F
Coefficient of Expansion CTE 25°C->600°C	112 x 10-7 /°C	62 x 10-7 /°F
Coefficient of Expansion CTE 25°C->800°C	123 x 10-7 /°C	68 x 10-7 /°F
Specific Heat, 25°C	0,79 kJ/kg°C	0.19 Btu/lb°F
Thermal Conductivity, 25°C	1,46 W/m°C	10.16 Btu.in/hr.ft2/hr
Thermal Diffusivity, 25°C	7,3 x 10-7 m2/s	0.028 ft2/hr
Continuous Operating Temperature	800°C	1472°F
Maximum No Load Temperature	1000°C	1832°F

	SI/Metric	Imperial
Density	2,9 g/cm3	157 lbs/ft3
Porosity	0%	0%
Young's Modulus, 25°C (Modulus of Elasticity)	66,9 GPa	9.7x10(6) PSI
Poisson's Ratio	0,29	0.29
Shear Modulus, 25°C	25,5 GPa	3.7x10(6) PSI
Knoop Hardness, 100g	250 kg/mm2	-
Modulus of Rupture, 25°C (Flexural Strength)	94 MPa (minimum specified average value)	13600 PSI
Compressive Strength (After polishing)	345 MPa (up to 900 MPa)	49900 PSI (130000 PSI)

	SI/Metric	Imperial
Dielectric Constant, 25°C - 1 kHz	6,01	6.01
Dielectric Constant, 25°C - 8,5 GHz	5,64	5.64
Loss Tangent, 25°C - 1 kHz	0,0040	0.0040
Loss Tangent, 25°C - 8,5 GHz	0,0025	0.0025
Dielectric Strength (AC) avg. 25°C, under 0,3 mm thickness	45 kV/mm	1143 V/mil
Dielectric Strength (DC) avg. 25°C, under 0,3 mm thickness	129 kV/mm	3277 V/mil
DC Volume Resistivity, 25°C	10(17)Ohm.cm	10(17)Ohm.cm

Solution	pH	Time	Temp	Weight Loss (mg/cm2)
5% HCl (Hydrochloric Acid)	0,1	24 Hrs	95°C	~100
0,002 N HNO(3) (Nitric Acid)	2,8	24 Hrs	95°C	~0,6
0,1 N NaHCO(3) (Sodium Bicarbonate)	8,4	24 Hrs	95°C	~0,3
0,02 N Na(2)CO(3) (Sodium Carbonate)	10,9	6 Hrs	95°C	~0,1
5% NaOH (Sodium Hydroxide)	13,2	6 Hrs	95°C	~10

Chemical Durability		Class
DIN 12111 / NFISO 719	Water	HGB2
DIN 12116	Acid	4
DIN 52322 / ISO 695	Alkali	A3

DATA MEASUREMENTS – All data measurements are typical and made at room temperature unless otherwise noted
THERMAL SHOCK RESISTANCE – Tests are run by quenching samples into water from various elevated temperatures. The change in temperature where a sharp decrease in flexural strength is observed is listed as ‘delta Tc’
CHEMICAL RESISTANCE – Although all alumina and zirconia ceramics are highly resistant to chemical attack, it is recommended that specific applications are discussed with Almath Crucibles to ensure optimum ceramic selection

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Almath Crucibles Ltd.

Epsom Building,
The Running Horse,
Burrough Green,
Newmarket, Suffolk
CB8 9NE

ISO 9001:2015 registered
(CQS Cert #GB2001792)

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