Classification of alumina powder

The main component of aluminum oxide powder is alumina, with the chemical formula Al2O32. The purity of alumina powder may vary depending on different applications and manufacturing processes, but generally speaking, higher purity alumina powder can have an alumina content of over 99%. In certain specific products, such as flat alumina powder, its purity can even reach over 99.99%.

Alpha alumina

Alpha Al2O3, also known as high-temperature alumina or calcined alumina, has a cubic crystal structure with a relative molecular weight of 101.96. The physical and chemical properties of α - Al2O3 are stable. It is a white powder with a melting point of 2050 ℃ and a boiling point of 2980 ℃. The coefficient of linear expansion is 8.6 × 10-8K-1, and the thermal conductivity is 0.2888W/(cm · K). α - Al2O3 has excellent properties such as small specific surface area, uniform particle size, easy dispersion, high hardness (Mohs hardness of 9.0), low water absorption (≤ 2.5%), good insulation performance, high mechanical strength, strong wear resistance and thermal shock resistance, as well as insolubility in water, slight solubility in acid and alkali, easy sintering and corrosion resistance.

β - alumina

Na β - alumina is a compound Na2O · 11Al2O3 composed of 5% (mass fraction) Na2O and 95% (mass fraction) Al2O3. Its grain size is small and evenly distributed, with a melting point of about 2000 ℃, a refractive index ε of 1.635-1.650, a bulk density of 3.25g/cm3, low porosity (sintering degree>97%), high mechanical strength, good heat shock resistance, low grain boundary resistance [α - axis expansion coefficient of about 5.7 × 10-6, c-axis expansion coefficient of about 7.7 × 10-6], and high ion conductivity (resistivity of 35 Ω· cm at 300 ℃).

Activated alumina

Activated alumina mainly exists in γ, ρ and other crystal forms, and is a highly dispersed and porous solid material Has a large specific surface area and pore capacity. Good adsorption performance, with an acidic surface. And it has excellent thermal stability, high mechanical strength and heat resistance, strong sintering resistance, and a specific surface area of 250-350 m2/g.

Plate shaped alumina

Plate shaped alumina, also known as plate shaped corundum in China, is a pure sintered alumina that undergoes thorough shrinkage without the addition of any additives such as MgO or B2O3. It has a coarse-grained and well-developed α - Al2O3 crystal structure. Plate shaped alumina has the following special properties: ① high melting point, about 2040 ℃; ② The grain hardness is high, with a Mohs hardness of 9 and a Knoop hardness of 2000; ③ Resistant to chemical corrosion, except for hydrofluoric acid and phosphoric acid, most alkalis and mineral acids have no effect on plate-like alumina; ④ Due to the absence of microcracks and large internal pores, its strength is relatively high; At the same time, its strength does not decrease much when subjected to thermal shock, so its thermal shock stability is good; ⑤ High thermal conductivity and high electrical resistivity, with excellent electrical performance at high frequencies and temperatures.