Chemical Composition: The primary component is Al₂O₃, with purity typically ranging from 75% to 99.9% (adjusted according to application requirements).
Crystal Structure: The high-temperature stable phase is α-Al₂O₃ (corundum structure), exhibiting high hardness and a high melting point.
Color: Typically white or ivory-colored; becomes translucent at high purity levels.
Key Properties
High Hardness: Mohs hardness of 9, second only to diamond and cubic boron nitride.
High Melting Point: Approximately 2050°C, offering outstanding high-temperature resistance.
Wear Resistance: Exceptional abrasion resistance, suitable for friction-intensive environments.
Electrical Insulation: High resistivity at room temperature, making it an ideal insulating material.
Chemical Stability: Resistant to acid and alkali corrosion (except hydrofluoric acid and strong alkalis).
Mechanical Strength: High compressive strength, but relatively brittle.
Alumina ceramic is a high-performance ceramic material primarily composed of α-alumina (α-Al₂O₃) as its main crystalline phase. Due to its outstanding physical, chemical, and mechanical properties, it is widely used in industrial, electronic, medical, and other fields.
Preparation Process
1. Raw Material Preparation: Purification of bauxite or chemical synthesis to produce high-purity alumina powder.
2. Forming:
Dry pressing (simple shapes)
Slip casting (complex shapes)
Isostatic pressing (high-performance components)
3. Sintering: High-temperature densification (1600°C–1800°C) via atmospheric or hot-press sintering.
4. Post-processing: Precision grinding and polishing (high processing costs due to extreme hardness).
Classification (by Al₂O₃ content)
Standard alumina ceramics: 75%–95% Al₂O₃, used for general corrosion-resistant and wear-resistant components.
High-purity alumina ceramics (≥99%): Applied in electronics and biomedicine, e.g., insulating substrates, artificial joints.
Transparent alumina ceramics: >99.9% purity, used in high-pressure sodium lamps and infrared windows.
Advantages and Disadvantages
Advantages:
Balanced overall properties (hardness, temperature resistance, insulation).
Abundant raw material sources and relatively low cost (compared to silicon nitride, silicon carbide, etc.).
Disadvantages:
High brittleness and poor thermal shock resistance (can be improved through composite modification).
Difficult to achieve high-precision machining.Alumina ceramics, offering a balanced combination of cost-effectiveness and performance, rank among the most widely used structural ceramics. They continue to hold significant growth potential in emerging fields such as new energy and semiconductors.
Parameter
Typical Value
Unit
Remarks
Purity
92%, 95%, 96%, 99%, 99.5%, 99.9%
%
Higher purity generally yields superior performance
Densité
3.6 3.98
g/cm³
99% purity is achieved
Flexural Strength
300 400 (96%) / 350 450 (99%)
MPa
Affected by the sintering process
Compressive Strength
2000 3000
MPa
High-hardness material
Young's Modulus
300 380
GPa
High rigidity
Vickers Hardness (HV)
1500 1800
kgf/mm²
High wear resistance
Fracture Toughness (KIC)
3.5 4.5
MPa·m¹/²
Relatively low, brittle material
Coefficient of Thermal Expansion
7 8 (20-1000°C)
×10⁻⁶/K
Temperature-dependent
Thermal Conductivity
20 30 (25°C)
W/(m·K)
Superior to most ceramics
Maximum operating temperature
1500 1700
°C
Under no-load conditions
Dielectric constant (1MHz)
9 10
-
Commonly used in electronic packaging
Volume resistivity (20°C)
>10¹⁴
Ω·cm
Excellent insulation properties
Dielectric strength
10 15
kV/mm
High-voltage insulation applications
Application
Electronics Industry: Integrated circuit substrates, insulators, sensors.
Machinery Industry: Cutting tools, bearings, wear-resistant liners.
Medical Devices: Artificial hip joints, dental implants (excellent biocompatibility).
Chemical Industry: Corrosion-resistant pumps and valves, catalyst carriers.
Energy Sector: Sodium lamp tubes, lithium battery separator coatings.
Military/Aerospace: Ballistic armor, rocket nozzles.
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