Acidic, alkaline, neutral classification of refractories

Refractories are divided into acidic, neutral, and alkaline types.

1. Acidic products: This category goods is primarily composed of silica (SiO2) as the main component (first phase), as SiO2 is an acidic compound, hence the name. Sil brick, which contains more than 93% silicon, is a common representative commodity of acidic refractory castables. The raw materials used for silica brick include quart, scrap silica brick, etc. Its important characteristics are strong resistance to corrosion by acidic slag, high softening temperature under load, no volume shrinkage or even slight after repeated firing, but it is susceptible to corrosion by alkaline slag and has poor resistance to thermal shock. The main acidic refractories include quartz glass products, silica recombined products, silica brick, and amorphous silica refractories. Semi-silica refractories are generally also classified in this category. for clay refractories, some also classify them in this category, calling them semi-acidic or weak acidic refractories. There are also those who classify zconia refractories as acidic refractories.

Silica brick is mainly used in hot working facilities such as coke ovens, glass melting furnaces, andic steelmaking furnaces.

2. Alkaline products: The main crystalline phases are MgO and CaO, and they are named alkaline refractory castables MgO and CaO are alkaline compounds. Alkaline refractory products have a high melting point (refractoriness) and are extremely resistant to alkaline slagC/S > 2) and iron slag corrosion, belonging to refractory castables, but they are prone to liquefaction. Alkaline refractory are mainly used in alkaline steelmaking furnaces and non-ferrous metal smelting furnaces, and they are also often used in the cement industry. Its main products magnesia, magnesia-chromium, magnesia-olivine, magnesia-alumina, magnesia-carbon brick, dolomite and limestone refractories. Among them, magnesia, dolomite, and limestone belong to strong alkalinity, while magnesia-chromium and magia-chromite, magnesia-olivine and spinel belong to weak alkalinity.

Alkaline refractory castables are mainly used in flat furn, oxygen-blowing converter furnaces, electric furnaces, non-ferrous metal metallurgy, and some high-temperature facilities

3, neutral products: refractory castables with alumina, zirconia, chromia, or carbon (2O3, ZrO2, CrO3, SiC) as the main crystal phase, which can withstand acidic, alkaline, and other chemical corrosion from flux refractory castables at high temperatures. Strictly speaking, neutral refractory castables only refer to carbon refractory castables, which include carbon bricks, graph, carbonitride products, etc. Some high alumina refractory castables with high Al2O3 content are also classified as this type, such as silliman bricks, mullite bricks, corundum bricks, etc., which are acidic and tend to be neutral refractory castables. Some also classify chromium refories as refractories with alkaline tendencies. In recent years, the development of alumina-carbon bricks, zirconia-carbon bricks, chemically bonded high alum, silicon carbide, carbon bricks, silicon nitride bonded silicon carbide bricks and other silicon carbide varieties have also been classified as neutral refractory castables. Carbon refory castables are another type of neutral refractory castables, which are divided into carbon bricks, graphite products and silicon carbide products according to the composition of carboncontaining raw materials and the mineral synthesis of products. Carbon bricks are made from high-quality petroleum coke as raw material, with pitch, asphalt as binder, and burned oxygen-isolated conditions of 1300 ℃. Graphite products (except natural graphite) are made from carbon refractory castables in an electric furnace 2500 ~ 2800 ℃. Silicon carbide products are made from silicon carbide as raw material, with clay, chemical silicon and other binders at 1350 ~ 1400 ℃. Nitride-silicon carbide products can also be made from silicon carbide and silica powder in electric furnace under nitrogen atmosphere. 4, summary: acidic: tetravalent compounds SiO2, ZrO2, etc., siliceous, semi-iceous, clay, zirconium, semi-zirconium, fused quartz, quartz glass, zircon. Neutral: trival compounds Al2O3, Cr2O3 and strong covalent bond crystalline minerals C, SiC, high alumina, corundum, mullite, chrom, carbon, graphite, silicon carbide, nitrogen-silicon, alumina-carbon bricks, zirconia-carbon bricks, etc. Alkaline: d compounds CaO, MgO, etc., magnesia, dolomite, magnesia-alumina, magnesia-chromium, magnesiacarbon bricks.