Technical Breakthroughs and Application Prospects of High-Purity Alumina Powder and Slurry in Precision Polishing

Properties of Alumina Materials and Current Industry Development

Alumina (Al₂O₃) is a significant inorganic non-metallic material that plays a crucial role across various industrial sectors due to its unique physicochemical properties. From a crystallographic perspective, alumina exists in multiple polymorphic forms, with α-Al₂O₃ (corundum type) and γ-Al₂O₃ being the most industrially valuable variants. α-Al₂O₃ exhibits characteristics close to that of atomic crystals, with a Mohs hardness of 9 and a melting point exceeding 2000°C, along with exceptional chemical stability. In contrast, γ-Al₂O₃ possesses a larger specific surface area and enhanced catalytic activity.

As the world's largest producer of alumina, China boasts abundant bauxite resources and a well-established industrial chain. Statistics indicate that the domestic alumina annual production capacity has exceeded 43.5 million tons, representing a significant share of global output. With the rapid development of high-tech industries such as semiconductors and renewable energy, the demand for high-purity alumina continues to grow, particularly for high-end products with a purity of over 99.99%, which have become critical materials for industrial upgrades.

Core Technical Advantages of Alumina in Precision Polishing

In surface treatment applications, alumina has become an irreplaceable polishing material due to its excellent physical characteristics. Compared to other abrasives, alumina demonstrates three core advantages in precision polishing:

Perfect Balance of Hardness and Wear Resistance: The hardness of α-Al₂O₃ is second only to that of diamond and silicon carbide, effectively removing material without causing excessive damage to the substrate. This trait makes it particularly suitable for polishing precision components such as optical glass and semiconductor wafers.

Chemical Stability: Alumina remains stable in most acidic and alkaline environments, avoiding reactions with other components in the polishing slurry, thus ensuring stability and repeatability in the polishing process.

Morphology Control: Advanced preparation techniques allow for the production of alumina particles in various shapes, including spherical and polyhedral, to meet the diverse needs of different polishing scenarios.

In Chemical Mechanical Polishing (CMP) processes, the performance of alumina abrasives directly affects polishing quality. Research has shown that using sub-micron spherical alumina powder in polishing slurries can achieve higher Material Removal Rates (MRR) and lower surface roughness (Ra). For instance, in silicon wafer polishing, optimized alumina slurries can maintain surface roughness below 0.1 nm, fully meeting the processing requirements for sub-7 nm fabrication.

Technological Breakthroughs in High-End Application Fields

Optical Component Processing

In the processing of high-end optical components such as optical lenses and sapphire substrates, alumina polishing technology exhibits distinct advantages:

Sapphire Substrate Polishing

Widely used in the LED industry, sapphire substrates (α-Al₂O₃ single crystals) require extremely high surface quality. Utilizing high-purity alumina slurry with a narrow particle size distribution (D50 ≈ 150 nm) can control surface roughness below 0.2 nm, significantly enhancing the quality of the epitaxial layers.

Optical Glass Polishing: Compared to traditional cerium oxide polishing slurries, alumina slurries offer advantages in environmental sustainability and cost-effectiveness, making them particularly suitable for high-volume production scenarios such as smartphone lens modules.

Emerging Application Fields

With technological advancements, alumina polishing materials are showing new application potential in the following areas:

Processing of Third-Generation Semiconductor Materials: The processing of wide bandgap semiconductor materials like silicon carbide (SiC) and gallium nitride (GaN) is challenging, and traditional polishing methods are inefficient. Specially treated alumina slurries can improve the polishing efficiency of these hard materials by 3-5 times.

Polishing of Flexible Display Substrates: For flexible substrates like polyimide (PI), low-hardness alumina composite abrasives have been developed to ensure effective polishing while preventing substrate damage.

Technical Innovation and Process Optimization

To meet the demands of high-end applications, the preparation technologies for alumina powders and slurries are continuously innovating:

Powder Preparation Technologies: These include high-purity processes, morphology control techniques, and surface modification technologies to regulate the purity and characteristics of alumina powders.

Slurry Formulation Optimization

Stable Dispersion Systems: By combining anionic and non-ionic dispersants, a dual stabilization mechanism is established, extending slurry shelf life to over six months.

pH Regulation Technology: Slurry systems have been developed with adjustable pH values ranging from 2 to 11, where acidic systems are suitable for metal polishing, while alkaline systems are better for oxide

Additive Compatibility: Specific functional additives such as oxidants and corrosion inhibitors are introduced to achieve precise control over polishing rates and surface quality.

Quality Control and Performance Evaluation
To ensure the reliability of alumina polishing materials, a comprehensive quality evaluation system has been established:

Physical Performance Testing: Includes analysis of particle size distribution (laser particle size analyzer), specific surface area (BET), morphology (SEM/TEM), etc.

Chemical Performance Testing: Impurity content detected by ICP-MS; surface charge characteristics determined by potentiometric titration.

Application Performance Testing: Key indicators such as material removal rate, surface roughness, and defect density are evaluated through simulated actual polishing processes.

For semiconductor-grade alumina slurry, typical technical specifications include:

Purity: ≥99.99%

Particle Size: D50=100±10nm

Metallic Impurities: <10ppm

Zeta Potential: >+30mV or <-30mV

Particle Agglomeration Degree: <5%

Industry Trends and Outlook
With the advancement of downstream industries, alumina polishing materials exhibit the following development trends:

Large-Scale Production: Development of high-volume slurry preparation technologies with improved uniformity to accommodate 12-inch and larger wafer production.

Green and Eco-Friendly: R&D of water-based, low-COD environmentally friendly polishing fluids to reduce wastewater treatment complexity.

Intelligentization: Real-time monitoring and intelligent adjustment of polishing processes through IoT technology.

Multifunctionalization: Development of composite abrasive systems with additional functions such as self-lubrication and self-repair.

Looking ahead, the market demand for high-purity alumina powders and slurries will continue to grow alongside the rapid development of 5G communications, artificial intelligence, and new energy vehicles. Particularly in emerging fields like third-generation semiconductors and Micro LED, higher requirements for alumina polishing materials will drive continuous technological innovation and breakthroughs.