Oxide Bonded SIC Products

Silicon carbide (SiC) products are made of industrial SiC as raw material by firing, which is a kind of advanced refractory with SiC as the main component. It has high strength at room temperature and high temperature, high thermal conductivity, small linear expansion coefficient, good thermal shock resistance, high temperature wear resistance, strong resistance to chemical erosion and a series of excellent properties, has been widely used in steel, nonferrous metallurgy, chemistry, electric power, ceramics and aerospace and other industrial fields. With the development of the research on the application of SiC refractory and the improvement of the production level, the demand is increasing year by year and the application field is expanding.
SiC products can be classified according to SiC content, binder type and addition amount. The properties of materials largely depend on the bonding status of SiC particles in materials. Therefore, SiC products are usually classified according to the type of bonding phase.
(1) oxide binding SiC: al2o3-sio2 silicate as the combination phase, including clay binding, mullite binding and SiO2 binding SiO2.
(2) nitride binding SiC: the binding phase is Si3N4, Si2N2O, Sialon and other covalent bonding compounds.
(3) self-bonded SiC: including bl-sic bonded SiC and recrystallized SiC.
(4) siliconizing reaction sintering SiC: a SiC engineering ceramic material composed of SiC and free Si.
In addition, refractory products with SiC content less than 50% are usually referred to as semi-sic products. Semi-sic products include clinker SiC products, high-alumina SiC products, zircon SiC products, mullite SiC products and corundum SiC products.
The mineral composition of oxide bonded silicon carbide products is mainly quartz, mullite and silicate glass. According to the difference in the composition of the bonded phase, oxide bonded SiC products are classified as SiO2 bonded, mullite bonded and clay bonded respectively. The production process of such silicon carbide products is shown in figure 14-16.

This kind of products appeared in the 1940s to 1950s, the content of SiC is generally 50%~90%. The raw materials for the combination phase are mainly bonded clay, usually adding silica, andalusite, bluestar and other mineral powder raw materials. The firing temperature is 1350~1450℃, which can be fired together with clay refractory materials. The type and content of the combined materials will affect the properties of the products. With the increase of clay content, the oxidation resistance of the materials increases, but the thermal conductivity, deformation temperature under load, thermal shock resistance and high temperature strength decrease. The physical phase analysis shows that the combination of clay and SiC material consists of quartz, mullite and silicoaluminate glass. In clay and aluminum silicate mineral raw materials, impurities such as R2O, RO, Fe2O3 exist to varying degrees, which will enter the glass phase during the high-temperature sintering process, which will seriously affect the high-temperature properties of the materials. Because the content of glass phase is more, the high temperature performance of this kind of products is worse.
Clay combined with SiC products are mainly used for various industrial kiln flame shield, ceramic kiln tools (shed boards, pillars, saggers, etc.). Foreign countries began to use this kind of kiln from the 1940s to 1950s, and China began to develop and research in the 1960s. In clay combined with SiC kiln furniture material, due to the excellent properties of SiC materials have been clay in combination with the destruction of the phase, high temperature performance is poorer, kiln furniture itself thickness and weight is big, the product loading ratio is low, high energy consumption of the burning, the SiC waste of resources and energy caused by now has been basically no production and use of this kind of refractory products.
Mullite combined with silicon carbide products
This kind of product is a kind of higher SiC products developed on the basis of clay and SiC. The raw materials for the combination phase are usually Al2O3 and SiO2 micro powder or fine powder with high purity. Sometimes, a small amount of silliferous stone, andalusite and bluestar fine powder is added. The combination phase is mainly composed of mullite with low content of glass phase. In mullite bonded SiC, the content of SiC is generally 65%~85%, and the sintering temperature is usually 1350~1500℃. Mullite bonded SiC products have better performance than clay bonded SiC, and are still used in ceramic, nonferrous metallurgy, machinery and other industries.
The sio2-bonded SiC phase is composed of si-scale quartz, si-square quartz and a small amount of silicon-rich glass phase. The raw materials for the combination phase are SiO2 micro powder or fine powder with high purity, and a small amount of MnO2, V2O5 and other mineralizers are usually added into the ingredients, and the sintering temperature is 1350~1500℃. SiO2 bonded SiC material has higher high-temperature performance than clay bonded SiC, and its high-temperature flexural strength is higher than mullite bonded SiC. Such products are mainly used in kiln furniture products.
China began to study SiO2 combined with SiC kiln tools around 1987 and put them into mass production, but the effect was not ideal. SiO2 combined with SiC products from Taiwan has been at the international advanced level for many years, and the products are widely used in China, Europe, Japan and other places. Now, Chinese and Taiwanese manufacturers have invested and set up factories in mainland China. In recent years, domestic SiO2 combined with SiC kiln furniture products have made a great breakthrough in production technology, and some manufacturers' products have reached or approached the products of Taiwan, China, and have products exported.
The performance of various oxide bonded SiC products is shown in table 14-110. Among oxide bonded SiC, SiO2 bonded SiC kiln furniture products, especially the thin shed board with large area, have the highest usage and technical difficulty. At present, SiO2 combined with SiC products is the most used in SiC kiln furniture.

At present, China is the world's largest producer of SiO2 combined with SiC products, and also the country with the largest consumption of this product. With people's attention to energy and production cost, clay binding and low grade mullite bonded SiC products will gradually be phased out, while high quality oxide bonded SiC, especially high quality SiO2 bonded SiC products will still have a good development prospect.