How to process alumina ceramics

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Alumina ceramic is an advanced ceramic material with high hardness, high wear resistance, high temperature resistance, corrosion resistance, and excellent electrical insulation properties, widely used in fields such as electronics, aerospace, machinery, and medical care. Its processing technology is complex and involves multiple links, including raw material preparation, molding, sintering, precision machining, etc.

1、 Raw material preparation
The performance of alumina ceramics largely depends on the purity and particle size distribution of the raw materials. Common purity grades of alumina powder include:
-Ordinary industrial grade: Al ₂ O Ⅲ content is 90% -95%, suitable for wear-resistant parts and refractory materials.
-High purity grade: Al ₂ O3 content of over 99.5%, used for electronic devices and bioceramics.

Powder processing usually includes the following steps:

1. Ball milling: By wet ball milling (using alcohol or water as a medium), the powder particles are refined to the sub micron level (0.5-1 μ m) to improve sintering activity.
2. spray drying: atomize and dry the slurry after ball milling to produce granulating powder with good fluidity for subsequent molding.

2、 Forming process
Forming is the process of shaping alumina powder into a predetermined shape according to design requirements. Common molding methods include:

1. Dry pressing molding: suitable for simple shaped components (such as sheet and column). By applying a pressure of 100-300 MPa through a uniaxial press, the density of the formed billet is about 50% -60% of the theoretical density.
2. Isostatic pressure forming: By uniformly applying pressure (200-400 MPa) through liquid or gas media, a denser and more uniform billet is obtained, which is suitable for complex structures.
3. Grouting molding: Inject alumina slurry into porous gypsum molds and dehydrate them through capillary action, suitable for thin-walled or irregular parts.
4. Casting molding: used for preparing thin films (thickness 0.1-1mm), commonly used for multi-layer ceramic substrates such as electronic packaging.
5. 3D printing: including photopolymerization (DLP/SLA) and adhesive spraying technologies, suitable for customizing complex structures.

3、 Sintering process
Sintering is the core step in the processing of alumina ceramics, which enhances the strength and properties of the ceramics by densifying the particles through high temperature bonding. The sintering process mainly includes the following steps:

1. Glue removal (degreasing): Remove the adhesive (such as PVA, paraffin) at a heating rate of 1-5 ° C/min at a temperature of 400-600 ° C.
2. Sintering method:
   -Atmospheric pressure sintering: Sintering at 1600-1800 ° C and holding for 1-4 hours, the density can reach 95% -99% of the theoretical density.
   -Hot pressing sintering: sintering under a pressure of 10-40 MPa, at a temperature of 1400-1600 ° C, with a density exceeding 99.5%.
   -Spark plasma sintering (SPS): rapid heating (several hundred ° C/min), densification is completed within 5-20 minutes, and the grain size is fine.
3. Post processing: The sintered embryo can be treated by hot isostatic pressing (HIP), applying high pressure and temperature of 100-200 MPa to eliminate internal pores and further improve mechanical properties.

4、 Precision machining
Alumina ceramics have high hardness (Mohs hardness level 9) and require the use of superhard tools and precision machining techniques for subsequent processing to meet high-precision application requirements.

1. Diamond tool cutting: Use a ceramic engraving and milling machine equipped with cubic boron nitride (CBN) or diamond tools, and achieve micrometer level accuracy by optimizing cutting parameters (speed>3000rpm, feed rate 0.01mm/time).
2. Grinding and polishing:
   -Rough grinding: Use silicon carbide (SiC) or boron carbide (B ₄ C) abrasives to remove surface defects.
   -Precision polishing: Using<1 μ m Al ₂ O3 micro powder or diamond abrasive paste, combined with ultrasonic polishing technology, to achieve mirror level smoothness (Ra<0.1 μ m).
3. Laser/EDM: Suitable for ultra-fine structures such as micro holes and irregular grooves, with an accuracy of up to ± 0.005mm.

5、 Quality Inspection and Control
The processed alumina ceramic components require strict testing and quality control to ensure their performance and dimensional accuracy. Common detection methods include:
-Dimensional measurement: Use high-precision measuring tools such as coordinate measuring instruments.
-Hardness testing: Measuring the hardness of materials through a hardness tester.
-Thermal stability testing: testing the performance of materials in high temperature environments.
-Internal defect detection: X-ray or ultrasonic testing is used to detect internal cracks or pores.

6、 Application Fields
Alumina ceramics play an important role in multiple fields due to their excellent performance:
-In the field of electronics: used for integrated circuit packaging, high-power electronic device heat sinks, etc.
-Aerospace: Used for high value-added products such as aviation bearings and nuclear fuel components.
-In the medical field, such as artificial bones, dental implants, etc., high surface smoothness is required.
-Mechanical field: used for wear-resistant parts, seals, etc.

The processing technology of alumina ceramics is complex and involves multiple links, from raw material preparation to precision machining, each step has a significant impact on the performance and quality of the final product. By optimizing the process parameters of each stage, high-performance and high-precision alumina ceramic components can be prepared to meet the application needs of different fields.