Overview
Calcined alumina is produced through thermal decomposition of aluminum hydroxide or aluminum salts at temperatures between 1000-1500°C. This process drives off chemically combined water and transforms the material into stable crystalline forms of aluminum oxide. The industrial product typically contains 99%+ Al₂O₃, with properties tailored through controlled calcination parameters. The material exists in several transitional phases (gamma, theta) before converting to the thermodynamically stable alpha phase at highest temperatures. Phase composition significantly impacts properties—gamma alumina offers higher surface area for catalytic applications, while alpha alumina provides maximum hardness and thermal stability for refractory uses.
Physical and Chemical Properties
High-purity calcined alumina demonstrates exceptional hardness (9 on Mohs scale), second only to diamond. Its ionic/covalent bonding structure grants outstanding compressive strength (2-3 GPa) and thermal conductivity (30 W/m·K), with low thermal expansion (8×10⁻⁶/°C) that prevents thermal shock damage. Chemically, it resists attack from most acids and alkalis except hydrofluoric acid and concentrated sulfuric acid. Surface area ranges from 5-200 m²/g depending on calcination conditions, while particle sizes span 0.1-100 microns. Electrical resistivity exceeds 10¹⁴ Ω·cm at room temperature, making it valuable for insulating applications.
Main Applications
In refractory industries, calcined alumina serves as the primary raw material for high-alumina bricks (70-99% Al₂O₃ content) used in steelmaking furnaces, cement kilns, and glass tanks. Ceramic applications include substrates for electronic components, wear-resistant tiles, and high-strength porcelain. The abrasives industry utilizes its hardness for grinding wheels and sandpaper. Petroleum refining employs gamma-phase alumina as catalyst support due to its porous structure. Emerging uses include lithium-ion battery separators and advanced ceramic armor systems, where its combination of lightness and impact resistance proves valuable.
Safety and Storage
While chemically inert, alumina powder requires careful handling to prevent dust inhalation. OSHA recommends a TWA limit of 15 mg/m³ for total dust and 5 mg/m³ for respirable fraction. Facilities should employ local exhaust ventilation and provide NIOSH-approved N95 respirators for workers. Storage should avoid contamination from moisture or foreign particles. Bulk storage silos should feature vibration-assisted discharge due to the material's tendency to compact. For small quantities, moisture-proof bags with polyethylene liners are recommended, stacked no more than 10 layers high to prevent caking.
B2B Procurement Guide
Industrial buyers should specify: phase composition (alpha content ≥90% for refractory grades), median particle size (D50), and impurity limits (particularly SiO₂, Fe₂O₃, and Na₂O). Technical alumina (99.5% purity) commands 20-30% premium over metallurgical grade (98.5% purity). Major global suppliers include Almatis, Alteo, and Sumitomo Chemical. Asian markets typically offer competitive pricing but may vary in quality consistency. For large-volume contracts (500+ tons), consider securing multiple qualified suppliers to mitigate supply chain risks. Just-in-time delivery requires careful planning due to potential shipping delays for bulk shipments.
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