In general and special refractory materials, the commonly used varieties mainly have the following kinds:
Acid: The larger amount of silica bricks and clay bricks. Silica brick is containing more than 93% SiO2 of silicon products, the use of raw materials are silica, waste silica bricks. Silica brick resistance to acid slag erosion, but susceptible to alkaline slag erosion, its load softening temperature is very high, close to its fire resistance, repeated calcination volume does not shrink, or even slightly expanded, but the thermal shock resistance is poor. Silica brick is mainly used in coke oven, glass melting kiln, acid steelmaking furnace and other thermal equipment.
The clay brick contains 30%~46% alumina, it takes the refractory clay as the main raw material, the fireproof degree 1580~1770℃, the thermal shock resistance is good, belongs to the weak acidic refractory, has the corrosion resistance to the acid slag, the use is widespread, is the production quantity biggest kind of refractory material.
Neutral: The main crystal phase in high alumina products is mullite and corundum, the content of corundum increases with the increase of alumina content, and the corundum products containing more than 95% alumina are a kind of high quality refractory. Chrome bricks are mainly made of chrome ore, the main crystal phase is chromite. The corrosion resistance of the steel slag is good, but the thermal shock resistance is poor, and the temperature of the load deformation is low.
Chrome-Magnesia bricks made of chromium ore and magnesia are of good thermal shock resistance and are mainly used as Sheping top bricks. Carbon products are another kind of neutral refractory, according to the composition of carbon-containing raw materials and products of mineral composition, divided into carbon bricks, graphite products and SIC products three categories. The carbon brick is uses the high grade petroleum coke as the raw material, adds the tar, the bitumen as the adhesive, under 1300 ℃ isolates the air condition to burn. Graphite Products (in addition to natural graphite) with carbon materials in the electric furnace by 2500~2800℃ graphite treatment system. SIC products with SIC as raw material, add clay, silica and other binders in 1350~1400℃ sintering.
Silicon carbide and silicon carbide powders can also be made in the nitrogen atmosphere of the furnace. The thermal expansion coefficient of carbon products is very low, high thermal conductivity, good thermal shock performance and high temperature strength. In the high temperature long-term use also does not soften, is not subjected to any acid-base erosion, has the good salt-resisting performance, also is not affected by the metal and the molten slag wetting, the light weight, is the high temperature high-temperature material. The disadvantage is that it is easy to oxidize at high temperature, it is unfavorable to use in oxidizing atmosphere. Carbon products are widely used in high-temperature furnace lining (furnace bottom, furnace cylinder, lower hearth, etc.), smelting non-ferrous metal furnace lining. Graphite products can be used as reaction tanks and petrochemical autoclave lining.
SIC and graphite products can also be made into crucible for smelting copper and light alloys.
Alkaline: Magnesium products for the representative. It contains Magnesia 80%~85% above, with square magnesite as the main crystalline phase. Magnesia brick production of the main raw materials are magnesite, seawater magnesia from seawater extracted from magnesium hydroxide by High-temperature calcination and so on. Very good resistance to alkaline slag and iron slag. The melting point of pure magnesia is as high as 2,800 ℃, so the fire resistance of magnesia bricks is higher than that of clay bricks and silica bricks. Since the mid 1950s, the production of alkaline refractories has gradually increased due to the use of oxygen-blowing converter steelmaking and the use of Sheping roof, and the manufacturing of clay bricks and silica bricks is decreasing.
Alkaline refractory is mainly used in open hearth, oxygen blowing converter, electric furnace, non-ferrous metal smelting and some high-temperature thermal equipment.