Fused Mullite - Properties and Applications of Duramul

Fused mullite is produced by the electric furnace fusion of Bayer process alumina and high purity silica. The result is a needle-like alumina-silica grain that has low conductivity, excellent thermal shock resistance, and excellent resistance to deformation under load. Fused mullite is used in applications such as refractories for glass and steel industries, as kiln furniture, in investment casting as shell building materials, in spark plug bodies, and many other applications.

Description

Duramul is a fused, high purity mullite produced by the electric furnace fusion of Bayer process alumina and high purity silica. There is an excess of aluminum oxide above the normal mullite ratio (3 Al2O3 : 2 SiO2) to ensure that all of the SiO2 is contained within the mullite phase and is not present in the glass phase. Duramul receives high intensity magnetic treatment to remove virtually all of the magnetic iron present. Each lot is sampled and test fired to insure against contamination.

Applications of Fused Mullite

Duramul is utilized in the manufacture of refractory products where hot strength, resistance to spalling and low thermal conductivity are important factors. Such applications include setters and saggers for firing electronic substrates, spark plug bodies, and laboratory ware.

Typical Chemical Analysis of Fused Mullite

Typical chemical analysis of fused mullite is described in the table below.

TYPICAL CHEMICAL ANALYSIS
Chemical Composition
Al2O3 (by difference) 75.00%
SiO2 24.70%
Na2O 0.30%

Typical Physical Properties of Fused Mullite

Typical physical properties of fused mullite are descibed in the table below.

TYPICAL PHYSICAL PROPERTIES
Physical Property Specification
Crystallography Fragments of columnar joining crystals in the Orthorhombic system with trace quantities of hexagonal aluminum oxide crystals.
Color Brilliant White
Specific Gravity 3.15
Melting Point 1830º C

Typical Thermal Properties of Fused Mullite

Typical thermal properties of fused mullite are descibed in the table below.

TYPICAL THERMAL PROPERTIES
Thermal Property Specification
Useful Temperature Ranges 1800ºC in Air; 1500º - 1700ºC in Vacuum
Thermal Conductivity
(0% porosity)
(cal / sec · cm · ºC)
0.0145 at 100ºC ; 0.013 at 200ºC
0.011 at 400ºC ; 0.010 at 600ºC
0.0095 at 800ºC ; 0.009 at 1000ºC
0.008 at 1200ºC ; 0.009 at 1400ºC
Coefficient of Linear Expansion 4.63 x 10-6 per ºC: 25-500ºC
5.13 x 10-6 per ºC: 25-1000ºC
5.62 x 10-6 per ºC: 25-1500ºC

Sizes Available

Duramul fused mullite is available in the following sizes:

10/F, 20/F, and 100/F
Other splits are available upon request

This information has been sourced, reviewed and adapted from materials provided by Washington Mills.

For more information on this source, please visit Washington Mills.

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Comments

  1. Shanmugam P Shanmugam P India says:

    Specific gravity, apparent specific gravity and true specific gravity difference

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