Alumina (Al₂O₃): Types, Properties & Industrial Applications
Alumina (Al₂O₃) — crystalline forms (α-alumina/corundum, γ, θ, δ, κ, η), properties (hardness 9 Mohs, MP 2050°C, high thermal/electrical insulation), and applications — abrasives, refractories, electrical insulators, biomedical implants, catalyst supports, armor, wear parts. Grades: smelter, calcined, tabular, fused, reactive.
Aluminum oxide (Al₂O₃), or alumina, is the most widely used oxide ceramic. Its α-phase (corundum) has 9 Mohs hardness, 2050°C melting point, high thermal conductivity, excellent electrical insulation, and chemical inertness — making it indispensable across industries.
Crystalline Phases of Alumina
| Phase | Structure | Stability | Key Properties |
|---|---|---|---|
| α-Al₂O₃ (Corundum) | Trigonal | Thermodynamically stable >1000°C | Hardest (9 Mohs), highest thermal conductivity, best insulation |
| γ-Al₂O₃ | Defect spinel | Metastable, <1000°C | High surface area, catalytic activity |
| θ, δ, κ, η | Transitional | Metastable | Intermediate properties |
α-Alumina (corundum) dominates industrial use due to superior properties.
Key Properties
| Property | Value |
|---|---|
| Hardness | 9 Mohs (2nd only to diamond) |
| Melting point | ~2050°C |
| Density | 3.95–4.0 g/cm³ |
| Thermal conductivity | 30–35 W/m·K (high for ceramic) |
| Electrical resistivity | >10¹⁴ Ω·cm (excellent insulator) |
| Compressive strength | 2000–3000 MPa |
| Chemical resistance | Inert to most acids/bases at RT |
Industrial Grades
| Grade | Purity | Production | Applications |
|---|---|---|---|
| Smelter Grade | 99.5%+ | Bayer process | Aluminum metal production |
| Calcined Alumina | 99.5–99.9% | Rotary kiln calcination | Refractories, ceramics, polishing |
| Tabular Alumina | 99.5%+ | High-temp sintering | High-temp refractories, thermal shock resistance |
| Fused Alumina | 99%+ | Electric arc furnace | Abrasives, refractory bricks |
| Reactive Alumina | 99.9%+ | Controlled calcination | Advanced ceramics, electronic substrates |
| High-Purity (4N/5N) | 99.99%+ | Specialized | Semiconductors, phosphors, single crystals |
Applications
| Sector | Applications |
|---|---|
| Refractories | Kiln furniture, furnace linings, crucibles |
| Abrasives | Grinding wheels, sandpaper, lapping compounds |
| Electrical | Insulators, substrates, spark plug bodies |
| Biomedical | Hip/knee implants, dental implants (high purity) |
| Catalysts | γ-Al₂O₃ catalyst support (hydrotreating, reforming) |
| Armor | Lightweight vehicle/body armor (Al₂O₃/SiC composites) |
| Wear Parts | Nozzles, seals, bearings, pump components |
| Electronics | IC substrates, LED heat sinks, IC packages |
Khat Group Alumina Capabilities
- Custom alumina ceramics — 99.5–99.99% purity, custom shapes
- Advanced forming — CIM, dry pressing, CIP, slip casting
- Precision machining — Diamond grinding, lapping, polishing
- Quality assurance — Density, hardness, strength, purity certification
Contact Khat Group for custom alumina components, grade selection, or project feasibility.
Khat Group — Engineered alumina solutions for demanding applications.
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