Al₂O₃ (Sapphire) Single Crystal

Advantages

• Exceptional hardness: Mohs hardness of 9, Knoop hardness of ~2000–2200 kg/mm² (orientation-dependent).
• Broad optical transmission: Useful transmission from 0.17–5.5 μm.
• Excellent chemical stability: Resistant to acids, alkalis, and plasmas under normal and elevated-temperature conditions.
• High thermal conductivity: ~23–27 W/(m·K) at 300 K, enabling good thermal management in high-power applications.
• High melting point: 2040–2050°C, suitable for high-temperature environments.
• Birefringent (negative uniaxial): Δn ≈ 0.008 at visible wavelengths; birefringence eliminated along the C-axis.

Typical Specifications

• Crystal structure: Hexagonal system; lattice constants a = 4.785 Å, c = 12.991 Å.
• Optical transmission range: 0.17–5.5 μm (transmittance >80% over much of this range).
• Refractive indices: nₒ = 1.768, nₑ = 1.760 at ~0.55 μm; nₒ = 1.75449, nₑ = 1.74663 at 1.06 μm.
• Birefringence: 0.008 (nₒ − nₑ).
• Density: 3.97–3.98 g/cm³.
• Melting point: 2040–2050°C.
• Thermal conductivity: ~23–27 W/(m·K) at 300 K.
• Thermal expansion coefficient: ~5.0 × 10⁻⁶/K (perpendicular to C-axis), ~6.7 × 10⁻⁶/K (parallel to C-axis).
• Young‘s modulus: ~335–390 GPa.
• Poisson’s ratio: ~0.25–0.30.
• Water absorption: nil.
• Dielectric constant: 9.4 (perpendicular) to 11.5 (parallel) at 1 MHz.

Main Applications

• Optical windows and viewports: UV, visible, and near-IR applications, including high-vacuum systems, furnaces, deep-sea cameras, and fire alarm systems.
• Laser systems: High-power laser windows, laser mirrors, and laser hosts (UV/VIS/IR) due to high damage threshold and thermal shock resistance.
• Aerospace and defense: Reconnaissance windows, domes, transparent armor, sensor windows.
• Semiconductor and LED: Wafer carriers, plasma tubes, and high-purity processing components.
• Precision mechanical components: Bearings, nozzles, blades, and wear-resistant parts.
• Medical and dental: Endoscope lens covers, dental tool tips, and surgical instrument windows.