The method of polishing alumina ceramics

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Ceramica di allumina are widely used in high-end industrial and technological fields due to their high hardness, wear resistance, corrosion resistance, and excellent electrical insulation properties. However, the surface of sintered alumina ceramics is usually rough and has microcracks, which seriously affect their performance and reliability. Therefore, precision polishing treatment has become a key post-processing step to enhance its value.

The necessity of polishing alumina ceramics: the core problem to be solved
The unpolished surface of alumina ceramics has many problems, which limit its application in high-precision and cutting-edge fields. Polishing treatment aims to address the following core issues:

1. Surface roughness issue: The surface of the sintered body is composed of micron or submicron sized particles, and the inherent roughness can lead to high friction coefficient, poor sealing performance, and severe optical scattering.
2. Surface and subsurface damage: Microcracks, pores, and residual stresses are prone to occur during the processing and sintering of green bodies, which are the root causes of reduced mechanical strength and premature failure of components.
3. Biocompatibility and Cleanliness Issues: In the medical and food fields, rough surfaces are prone to bacterial growth and difficult to thoroughly clean. Polishing can obtain a smooth and sterile surface.
4. Electrical performance and signal integrity: For electronic substrates and insulation components, rough surfaces can affect current distribution, increase signal transmission losses, and may cause partial discharge.
5. Aesthetics and Touch: For consumer electronics and luxury components, the high gloss mirror effect can greatly enhance the texture and value of the product.

Mainstream polishing methods and their technical analysis
The polishing methods of alumina ceramics can be divided into three categories based on their principles: mechanical polishing, chemical polishing, and composite polishing.

1. Lucidatura meccanica
   Mechanical polishing is a method of using fine abrasives for physical cutting and plastic flow on ceramic surfaces to achieve a smooth effect.
   Principle: Diamond, boron carbide, aluminum oxide and other micro abrasive powders are added to the polishing solution. Through tools such as polishing wheels and polishing cloths, they undergo relative motion with the surface of the workpiece under pressure, and the material is removed through the “micro cutting” effect of the abrasive.
   Common processes:
   Rough polishing: Use larger diamond grinding wheels or grinding paste (such as W40-W10) to quickly remove machining allowances and larger defects.
   Fine polishing: Use finer abrasives (such as W7-W1.5), even nanoscale abrasives, to gradually reduce surface roughness.
   Mirror polishing: Use soft polishing discs such as velvet cloth with diamond or silicon dioxide polishing solution to achieve a mirror effect with nanoscale roughness.
   Product Application:
   Ceramic cutting tools: Polish the surface of the tool holder to reduce chip adhesion and improve durability.
   Mechanical seal ring: Ensure a flat and smooth end face to achieve zero leakage sealing.
   Textile porcelain parts: such as wire guides, high smoothness can effectively prevent fiber scratches.
   Vantaggi del prodotto:
   Mature technology with relatively low equipment costs.
   Strong adaptability to workpiece shape, capable of handling various geometric shapes such as flat and curved surfaces.
   High material removal rate and high processing efficiency.
   Limitations:
   Easy to introduce sub surface damage and residual stress.
   The dependence on operator experience is high, and consistency control is challenging.
2. Chemical mechanical polishing
   Chemical mechanical polishing is a composite polishing technique that combines mechanical grinding with chemical corrosion, and is currently the most mainstream method for achieving global planarization.
   Principle: During the polishing process, the chemical components in the polishing solution (such as acid, alkali, or oxidant) react with the surface of alumina to form a softer modified layer (such as hydrated alumina), which is then removed by the mechanical action of the polishing pad and abrasive (usually nano silica or ceria). This’ soft grinding hard ‘mode greatly reduces the damage caused by pure mechanical polishing.
   Product Application:
   Integrated circuit manufacturing: used for polishing alumina ceramic substrates to provide atomic level flat surfaces for chip mounting.
   LED substrate: polished sapphire (Al ₂ O ∝ single crystal) substrate to ensure epitaxial growth quality.
   Medical implants, such as artificial joint ball heads, achieve high smoothness while avoiding microcracks and extending fatigue life.
   Vantaggi del prodotto:
   It can achieve extremely low surface roughness (Ra<1 nm) and extremely high flatness.
   Effectively eliminate subsurface damage and obtain a perfect crystal surface.
   Good processing consistency, suitable for large-scale, automated industrial production.
   Limitations:
   The formula for polishing solution is complex and the cost is high.
   The process parameters (pressure, speed, pH value, flow rate) need to be precisely controlled.
3. Laser polishing
   Laser polishing is an advanced non-contact and high-precision polishing technology.
   Principle: Using a high-energy density laser beam to scan the surface of ceramics, the extremely thin material on the surface is instantly melted or vaporized. Under the action of surface tension, molten material will flow towards the valleys on the surface, achieving a smooth effect of “peak shaving and valley filling”, and then rapidly condense to form a smooth surface.
   Product Application:
   Complex three-dimensional structural components, such as microreactor flow channels and polished inner walls of complex cavities of engine turbine blades, are difficult to access using traditional methods.
   Medical devices: Selective area polishing of surgical tools or implants with fine structures.
   Vantaggi del prodotto:
   Non contact processing, no tool wear, no mechanical stress.
   High processing accuracy, good controllability, and easy implementation of automation.
   Can handle complex geometric shapes that are difficult to process using traditional methods.
   Limitations:
   The equipment investment is huge.
   Possible microstructural changes or thermal stress may occur due to the heat affected zone.
   The processing efficiency is relatively low.
4. Plasma polishing
   Plasma polishing is a dry polishing method based on physical and chemical interactions.
   Principle: In a vacuum environment, plasma is generated by exciting process gases (such as CF ₄, Ar) through a high-frequency power source. Active ions in plasma react chemically with ceramic surface atoms to generate volatile products, or through high-energy ion bombardment to achieve physical sputtering, thereby uniformly removing surface materials.
   Product Application:
   High purity electronic components, such as vacuum tube shells and RF windows, have a pollution-free polishing process and can maintain the high purity of materials.
   Components that require extremely high chemical stability: The entire process is carried out in a controlled environment with no liquid residue.
   Vantaggi del prodotto:
   The entire processing environment is clean and there is no discharge of chemical waste liquid.
   It can achieve isotropic polishing and uniformly process complex shapes.
   No mechanical damage to the material.
   Limitations:
   The equipment and operating costs are high.
   The material removal rate is usually low.

The polishing of alumina ceramics is a multidisciplinary technical field, and the choice of method depends on a comprehensive consideration of surface quality, processing efficiency, cost control, and workpiece geometry.
When pursuing high efficiency and economy, mechanical polishing is still the first choice for many industrial applications.
Chemical mechanical polishing is an irreplaceable gold standard when it comes to achieving atomically flat and undamaged surfaces.
When facing complex three-dimensional structures, laser polishing and plasma polishing demonstrate their unique advantages.

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