Raw materials used in the production of refractory and insulation products are the essential foundation of the entire refractory industry. While most of these materials originate from naturally occurring minerals—such as fireclay, bauxite, silica, chromite, magnesite, dolomite, olivine, zircon, kyanite group minerals—they are increasingly complemented by industrial and synthetic alternatives to meet modern performance demands. Examples include industrial alumina, synthetic mullite, man-made refractory fibers, and bubble alumina bricks.
Material selection directly impacts both the quality and cost of refractory products. From a mineralogical perspective, raw materials must possess sufficiently high refractoriness; from a processing standpoint, they must support essential manufacturing techniques; and from a functional view, they must ensure reliable high-temperature performance during service.
Raw materials can be classified by chemical nature (acidic, basic, or neutral), source (natural vs synthetic), and function (main or auxiliary). They are generally grouped into four categories: alumino-silicate raw materials, basic raw materials, insulating raw materials, and other specialty types. Below is a breakdown of the six foundational raw materials used across the refractory industry.
Silica bricks are made directly from siliceous stones—vein quartz, quartzite, flint, and sandstone—all of which contain high SiO₂ content with minimal impurities. Siliceous raw materials are divided into crystalline and cemented types. Firebird offers silica refractory bricks made from carefully selected high-grade sources, featuring low impurity levels and stable composition. These bricks are widely used in glass furnaces, coke ovens, and other high-temperature industrial settings.
Fireclay is the core ingredient for alumino-silicate refractories and includes hard clays, soft clays, and clay shales with a refractoriness above 1580°C. These are primarily composed of kaolinite (Al₂O₃ • 2SiO₂ • 2H₂O), free silica, pyrite, rutile, and organic matter.
Fireclays are classified as primary (residual) or secondary (sedimentary). Primary clays remain at the site of formation, while secondary clays are transported and redeposited, typically exhibiting finer particles, higher plasticity, and greater dispersion.
Hard clays are dense and fine-grained with low plasticity and are commonly grey or off-white in appearance. Firebird’s hard clays feature high refractoriness and low iron content, making them ideal for high-grade fireclay bricks and monolithic refractories.
Soft or semi-soft clays are more plastic, loosely packed, and vary widely in color from grey to purple or red, depending on their impurity levels. They are often used in unshaped refractory materials and applications requiring formability.
Bauxite is the key raw material for producing fused alumina and sintered high-alumina clinker. It mainly consists of diaspore, boehmite, and gibbsite. China has abundant reserves, particularly in Shanxi, Henan, and Guizhou, and it is classified into DK, BK, and DP types. Firebird sources high-quality bauxite with stable Al₂O₃ content and low impurities for use in high alumina bricks and fused alumina products.
Fused alumina is produced by melting industrial alumina or bauxite in electric arc furnaces. Sintered alumina involves high-temperature calcination, grinding, pelletizing, and firing—yielding high-strength, erosion-resistant materials. “Semi-white” fused alumina, with Al₂O₃ > 98% and porosity < 4%, is a dense form made in reducing atmospheres from bauxite.
Synthetic mullite (3Al₂O₃•2SiO₂) offers excellent thermal and mechanical stability. It is resistant to hydrofluoric acid, has low thermal expansion, and high resistance to thermal shock and chemical attack. Firebird’s mullite insulation bricks are manufactured with precision and used in high-performance refractory applications and kiln furniture.
Kyanite, andalusite, and sillimanite all convert into mullite and amorphous silica upon heating, with volumetric expansion. Andalusite expands the least and is commonly used in raw form, while kyanite and sillimanite are calcined before use. These minerals are suitable for dense bricks and also serve as expansion agents in unshaped refractories.
China’s magnesite deposits—crystalline and amorphous—are mainly found in Liaoning and Shandong. The primary impurities include talc and dolomite. High-purity magnesia is produced using two-step flotation and calcination methods. It is crucial for developing high-performance refractory products for steelmaking and non-ferrous metallurgy.
Dolomite (CaMg(CO₃)₂) contains both CaO and MgO. It is widespread and pure in China, particularly in Dashiqiao, Shandong, and other regions. Used for basic linings, dolomite offers good slag resistance and compatibility with converter linings and cement kilns.
Zircon (ZrSiO₄) is the main source of zirconia for refractory and ceramic applications. Rich deposits are found in Hainan and other provinces. It is valued for its low thermal conductivity, chemical inertness, and resistance to glass melts and acids. Due to trace TiO₂ and rare earth elements, safety measures must be in place during use.
Natural baddeleyite is rare in China. Industrial zirconia is obtained through chemical processing of zircon and is available in monoclinic, tetragonal, and cubic forms. Partially stabilized zirconia offers better thermal shock resistance and is used to toughen ceramics and refractory bodies.
Used in electrofused AZS refractories, desilicated zircon stabilizes formulations and enhances product properties.
Made from alumina, kaolin, and zircon, zirconia-mullite is sintered at 1300–1700°C. Increasing zircon content improves sintering behavior, reduces shrinkage, and enhances thermal shock resistance and density.
Chromite, a mixture of minerals rich in Cr₂O₃, Fe₂O₃, and MgO, is used in chrome bricks, magnesia-chrome bricks, and chrome-magnesia refractories. Associated with silicates like serpentine and olivine, it has variable composition and structure. Its corrosion resistance makes it valuable for non-ferrous metallurgy and incinerator linings.
The advancement of refractory technologies is driving the development of cleaner, high-performance raw materials. Alongside traditional minerals, synthetic and recycled materials like silicon nitride-iron and ceramsite are being explored. At Firebird, we continuously monitor industry trends to innovate new products and ensure top quality—helping our partners build the future of high-temperature industries.
