The main application fields of high-purity mullite ceramics
Mullite has many excellent properties that make it widely used. In addition to the traditional application of making refractory materials, it is also widely used in high-temperature materials, electronics, optics and other fields.
① High temperature material
Mullite ceramics have the characteristics of high melting point, creep resistance, low expansion coefficient, thermal shock resistance and corrosion resistance. Mullite refractory bricks can be used as linings for various high-temperature kilns, including furnace kilns and blast furnaces. , Lining materials such as hot iron pouring troughs and continuous casting furnaces.
The traditional application of mullite is to make refractory materials. As a refractory material, mullite has many excellent properties: (1) high melting point; (2) excellent creep resistance; (3) low thermal expansion coefficient, excellent anti-corrosion Thermal shock resistance; (4) Excellent corrosion resistance; (5) High shear modulus.
High temperature engineering materials
The Al2O3 content of pure mullite is 62wt%~100wt%. It is a high-alumina material. The [AlO6] octahedron in its structure acts as a stable support, making it have stable energy, so mullite is very stable. The refractoriness is as high as 1850℃, chemical corrosion resistance and high temperature creep resistance. At high temperature, mullite products have very low thermal expansion coefficient and thermal conductivity, so they have excellent thermal shock resistance.
② Electronic materials
a. The thermal expansion coefficient of mullite (4.0╳10-6/℃, 20～200℃) is very close to that of silicon, and the matching can be further improved by combining with glass and low expansion ceramics (such as cordierite or spodumene) performance.
b. The dielectric constant of mullite (ε=6.7) is very low, which can ensure the rapid transmission of signals, and the conduction lag time is about 17% lower than that of corundum (ε=9.8). If mullite is combined with glass and cordierite, The delivery speed will be further accelerated.
c. The sintering temperature of mullite is very high (>1500°C), so that it is limited on the packaging substrate, but by combining with glass or cordierite, the sintering temperature is greatly reduced, and the composite phase prepared by sol-gel method Micropowder can be sintered at 1250°C, and can be co-fired with copper.
d. High-performance electronic equipment also has high requirements for heat conduction. Mullite has excellent thermal conductivity. AlN can be used as a substrate for electronic equipment, and mullite can be used as a packaging material for it.
e. After mullite is combined with glass and cordierite, it can be co-fired with copper. The electrical conductivity and electromigration resistance of copper are good, thereby increasing the wiring density.
In recent years, research on the optical properties of mullite has mainly focused on using it to make window materials, because mullite has excellent thermal shock resistance, dielectric properties, high-temperature strength, and good light transmission.
Mullite material has good transmittance to light in the infrared band with a wavelength between 3 and 5 μm. The light transmittance is very good until 5 μm, but the transmittance suddenly decreases near 5 μm. This is due to the silicon in the matrix. caused by the presence of oxygen bonds.
As an excellent infrared light-transmitting material, mullite is potentially used in high chemical aggressive environments and high temperature, high mechanical stress occasions.
Mullite-containing ceramic alloys - brake pads for aviation and high-speed rail systems, and can also be used for linings in automotive clutches
Porous mullite-based ceramic material - the porous ceramics prepared by the former method can be used as the support of the reactor
Fused mullite can also be used to prepare mullite granules - used as cast iron sand, filler sand, and can also be used as filter material
Far-infrared-emitting ceramics prepared from mullite ceramics—could be used to purify and excite water
Mullite fiber - used as a heat-resistant filling material for automobile engines and a heat-resistant sealing material