The production of mullite raw materials in Mullite Suppliers can generally be directly synthesized using kaolinite, sillimanite group minerals, aluminum hydroxide or alumina and silica. Clay substances react with alumina or sillimanite group minerals and industrial alumina under heating conditions to form primary and secondary mullite. In Mullite Suppliers ,The primary mullite is formed in the range of 1000~1200℃, and further increasing the temperature only increases the crystallinity. The formation of secondary mullite in Mullite Suppliers usually completes at 1650°C. In order to obtain dense mullite products, a two-step sintering method is commonly used.
Mullite in Mullite Suppliers comes in two crystalline forms: acicular and prismatic. The acicular mullite strengthens the glass phase, and when the chemical composition of the material is the same, the refractoriness of the acicular mullite material is higher than that of the prismatic mullite material. Kaolinite is rapidly heated to above 1400°C to form acicular mullite. Otherwise, slow heating to lower temperatures forms prismatic mullite in Mullite Suppliers. There are also reports of tubular morphology and spherical mullite in Mullite Suppliers, the former is presumed to be caused by the tension caused by the uncoordinated size of silicon-oxygen and aluminum-oxygen tetrahedra, and the latter is the so-called nitrogen-containing mullite. In Mullite Suppliers,The anisotropy of thermal expansion of mullite makes it have good thermal stability. When high-grade mullite material is used as feeder accessories, it can be directly replaced on the running feeder without preheating.
What is mullite?
Mullite is a refractory raw material with 3Al₂O₃·2SiO₂ crystal phase as the main component. Mullite in Mullite Suppliers is divided into two categories: natural mullite and synthetic mullite. There are very few natural mullites in Mullite Suppliers, and synthetic ones are generally used.
The chemical composition of mullite is Al₂O₃71.8% and SiO₂ 28.2%. The mineral structure is orthorhombic, and the crystals are arranged in long column, needle and chain shape. The needle-shaped mullite is interspersed in the product to form a solid skeleton. Mullitein Mullite Suppliers is divided into 3 types: α-mullite, equivalent to pure 3Al₂O₃·2SiO₂, referred to as 3:2 type; β-mullite, with excess aluminum oxide in solid solution, slightly expanded lattice, referred to as 2 : 1 type; γ-mullite, with a small amount of titanium oxide and ferric oxide in solid solution. Mullite is chemically stable and insoluble in hydrofluoric acid. Its density is 3.03g/cm3, Mohs hardness is 6-7, melting point is 1870℃, thermal conductivity (1000℃) is 13.8W/(m.K), and linear expansion coefficient (20-1000℃) is 5.3*10⁻⁶/ ℃, elastic modulus 1.47*10¹ºPa.
Because mullite in Mullite Suppliers has good high-temperature mechanical and high-temperature thermal properties, synthetic mullite and its products have high density and purity, high high-temperature structural strength, low high-temperature creep rate, low thermal expansion rate, and strong chemical resistance. , thermal shock resistance, etc.
The key indicators for evaluating the quality level of mullite are the phase composition and density of mullite in Mullite Suppliers.
