Alumina ceramic, also known as aluminum oxide (Al₂O₃) ceramic, is made through a series of processes that involve the following steps:
1. Raw Material Preparation:
Source and Purity: High-purity alumina powder is the primary raw material. The purity of the alumina can vary depending on the desired properties of the final product, typically ranging from 85% to over 99.9%.
Additives: Small amounts of additives, such as binders, plasticizers, and lubricants, may be mixed with the alumina powder to aid in processing.
2. Powder Processing:
Mixing: The alumina powder and additives are thoroughly mixed to achieve a homogeneous composition.
Granulation: The mixture may be granulated to improve flow properties and ensure uniformity in the forming process.
3. Forming:
Pressing: The most common method is uniaxial pressing, where the powder is compacted in a mold under high pressure to form a green body, which is a pre-sintered ceramic part.
Isostatic Pressing: For more complex shapes, isostatic pressing may be used, where pressure is applied uniformly from all directions.
Extrusion and Injection Molding: These methods are used for creating more intricate shapes or thin-walled components.
4. Drying:
The green body is dried to remove any residual moisture and solvents, which helps prevent defects during sintering.
High-Temperature Firing: The dried green body is then fired in a high-temperature kiln, typically at temperatures between 1500°C and 1800°C. This process densifies the material, causing the alumina particles to bond together.
Controlled Atmosphere: The sintering process may take place in a controlled atmosphere to prevent contamination and to achieve specific material properties.
6. Post-Sintering Processing:
Machining: If needed, the sintered ceramic may be machined to achieve the final dimensions and surface finish. Alumina ceramics are very hard, so diamond tools are often required.
Glazing or Coating: Some alumina ceramics are glazed or coated to enhance their surface properties, such as wear resistance or chemical stability.
7. Quality Control and Inspection:
The final product undergoes rigorous quality control to ensure it meets the required specifications, including density, hardness, and dimensional accuracy.
This manufacturing process results in alumina ceramics with excellent mechanical properties, high hardness, wear resistance, and good electrical insulation, making them suitable for a wide range of industrial applications.
