How to process high-purity alumina ceramic structural components

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High purity alumina ceramic structural components are widely used in semiconductor, aerospace, medical equipment, new energy and other fields due to their excellent performance, such as high hardness, high temperature resistance, corrosion resistance, good electrical insulation, and low thermal expansion coefficient. However, due to its high hardness and brittleness, it is difficult to process and requires the use of special processes and equipment.

1、 Raw material preparation
The starting point for high-purity alumina ceramics is high-purity alumina powder (with Al ₂ O3 content ≥ 99.9%). By using ultrafine grinding technology, the particle size of the powder is controlled below 1 μ m to ensure the uniformity and density of the material. In addition, it is usually necessary to add a small amount of sintering aids (such as MgO, SiO ₂, etc.) to improve sintering performance. The spray granulation process is often used to optimize the fluidity of particles. Polyvinyl alcohol (PVA) or water-soluble paraffin is added as the binder to make the powder spherical, loose in density and less than 30 ° in fluidity angle.

2、 Forming process
Select the appropriate molding method based on the shape and precision requirements of the structural components. Common molding processes include:

-Dry pressing molding: suitable for simple geometric shapes (such as parts with a length to diameter ratio of ≤ 4:1), it can be rapidly molded at a pressure of 200MPa through hydraulic or mechanical presses, with a molding efficiency of 15-50 pieces/minute.
-Grouting molding: suitable for complex and irregular parts, using gypsum molds to absorb the moisture of the slurry and solidify it into shape. A demulsifier (such as polyacrylamide) and a binder (such as methyl cellulose) need to be added to the slurry to stabilize the suspension system.
-Casting molding+pre embedding technology: For complex structural components containing micropores or channels, alumina slurry is cast into sheets and pre embedded with polyvinyl butyral (PVB) filling material, which is then formed by temperature isostatic pressing (75-100 ℃, 100-200MPa). After sintering, the filling material evaporates to form precise pore channels.
-Isostatic pressure forming: By uniformly applying pressure (200-400 MPa) through liquid or gas media, the density of the billet is higher and more uniform, suitable for complex structures.

3、 Sintering process
Sintering is the core step that determines the properties of ceramics, which densifies the particles through high temperature bonding. Common sintering processes include:

-Atmospheric pressure sintering: carried out at high temperatures above 1600 ℃, suitable for conventional structural components.
-Hot isostatic pressing (HIP): Uniform pressure in high-temperature and high-pressure gas media can increase the density by 30-50%, suitable for high value-added products such as aviation bearings and nuclear fuel components.
-Hot pressing sintering: sintering under pressure (10-40 MPa), the sintering temperature can be reduced to 1400-1600 ℃, and the density is greater than 99.5%.
-Spark plasma sintering (SPS): rapid heating (several hundred ° C/min), short time (5-20 minutes) to complete densification, fine grain size.

The sintered embryo needs to undergo X-ray inspection to ensure that there are no internal cracks or porosity defects, laying the foundation for subsequent precision machining.

4、 Precision machining
The hardness of high-purity alumina ceramics is second only to diamond (Mohs hardness level 9), so it requires the use of superhard tools and CNC technology for precision machining. Common processing methods include:

-Diamond tool cutting: Ceramic engraving and milling machines are equipped with cubic boron nitride (CBN) or diamond tools, achieving micrometer level accuracy by optimizing cutting parameters (speed>3000rpm, feed rate 0.01mm/time).
-Grinding and polishing: Diamond grinding wheels (particle size # 200- # 2000) are used for grinding, with a surface roughness Ra of up to 0.1 μ m. Step by step polishing, from coarse grinding to fine grinding, and finally using submicron grade alumina powder or diamond gypsum polishing, can achieve a mirror effect.
-Laser processing: Femtosecond or picosecond lasers can be used for drilling and cutting, with an accuracy of ± 5 μ m, suitable for ultra-thin or complex microstructures.
-Electric discharge machining: Suitable for slotting and cutting high hardness ceramics by etching materials through discharge.
-Ultrasonic machining: using high-frequency vibration to grind thin-walled or complex workpieces, reducing the risk of edge breakage.

5、 Surface treatment
In order to further improve the performance of ceramic structural components, surface treatment is an indispensable step. Common surface treatment methods include:

-Polishing: Chemical mechanical polishing (CMP) can reduce surface roughness to Ra<1nm, suitable for optical windows and semiconductor components.
-Coating: Depending on the requirements, corrosion-resistant coatings can be applied to ceramic surfaces.

6、 Quality inspection
After processing, a comprehensive quality inspection of high-purity alumina ceramic structural components is required, including dimensional accuracy, surface smoothness, internal defects, etc. Technologies such as X-ray testing and ultrasonic testing are commonly used to detect internal defects.

The processing technology of high-purity alumina ceramic structural components is complex and precise, from raw material preparation to final surface treatment, each step has a significant impact on the performance of the final product.