Application requirements for α-alumina for polishing

Definition and classification of polishing

Definition: Polishing refers to the processing method that uses mechanical, chemical or electrochemical action to reduce the surface roughness of the workpiece to obtain a bright and flat surface. It is a finishing process using polishing tools and abrasive particles or other polishing media on the surface of the workpiece.

Classification: Polishing methods are divided into: mechanical polishing, chemical polishing, electrolytic polishing, ultrasonic polishing, fluid polishing, etc. Polishing media are divided into: diamond polishing liquid (polycrystalline diamond polishing liquid, single crystal diamond polishing liquid and nano diamond polishing liquid), silicon oxide polishing liquid, cerium oxide polishing liquid, alumina polishing liquid and silicon carbide polishing liquid and other categories.

The polishing liquid should meet the requirements of fast polishing rate, good polishing uniformity and easy cleaning after polishing. The hardness of the abrasive particles should not be too high to ensure that the mechanical damage to the surface of the film layer is relatively light.

In the field of fine alumina, alumina as a grinding and polishing material is roughly divided into two categories, namely molten corundum (such as white corundum, brown corundum, etc.) and sintered corundum. The so-called sintered corundum refers to a type of alumina in which aluminum hydroxide and alumina are calcined at high temperature to convert them into α phase. It is called α-alumina in China, and is also called high-temperature alumina by industry insiders.

Molten corundum: It has the characteristics of white color, high hardness, slightly lower toughness, high purity, excellent self-sharpening, strong grinding force, low calorific value, high efficiency, acid and alkali corrosion resistance, high temperature resistance, and good thermal stability.

Sintered corundum: It has good volume stability and chemical stability at high temperature, is not eroded by reducing atmosphere, molten glass and molten metal, and has good mechanical strength and wear resistance at room temperature and high temperature.

In China, the application of α-alumina in the field of grinding and polishing began in the late 1980s. With China's reform and opening up, labor-intensive manufacturing was gradually transferred to China, which also brought α-alumina polishing to China. Grinding materials, China has the concept of α-alumina grinding and polishing.

Traditional fine polishing raw materials: quicklime, feldspar powder, iron oxide red, chromium oxide green, etc. Traditional rough polishing raw materials: feldspar powder, quartz powder, white corundum, brown corundum powder.

Compared with the traditional polishing materials, the process is complicated and the work efficiency is low. The advantages of α-alumina as grinding and polishing are more obvious. The Mohs hardness is as high as 9, second only to diamond and silicon carbide, which is very helpful for improving the polishing efficiency. The control of the original crystal form and crystal appearance in the phase inversion process can achieve the effect of both cutting force and high gloss brightness at the same time, which not only improves the efficiency, but also reduces the polishing process.

Due to the late start of polishing and grinding α-alumina in China, there is little grasp of the technology and application in this field. At first, I did not understand the contradictory relationship between the cutting force and brightness of polished alumina, so that the product either has high cutting force, but the luminosity is very poor, or the luminosity is very good, the cutting force is very poor, and it is impossible to produce α-alumina with both high cutting force and brightness. At that time, the production technology was monopolized by several alumina producers in developed countries, such as Japan's Showa Denko, Sumitomo Chemical, Japan Light Metals, Germany's Anmai, etc. China's alpha-alumina industry has just started, and can only produce some primary alpha-alumina for industrial ceramics and refractories. Limited to the technical resources at that time, there was no personalized and specialized product design for downstream customers, and the product quality was poor, which brought a lot of difficulties and troubles to customers.

Foreign countries: The morphology of the original crystal of the polished powder is relatively uniform, there are no abnormally large particles, the particle size distribution is concentrated, and the phase inversion temperature is moderately controlled. The powder has both cutting force and the brightness of the surface of the polished device.

Domestic: The morphology of the original crystal is irregular, there are many abnormally large grains, the particle size distribution is wide, the content of α phase is not controlled in place, and the cutting force and brightness cannot be well guaranteed at the same time.

Through decades of continuous research and development, application and production, domestic polishing α-alumina has emerged in the world's polishing alumina field, gradually catching up with the pace of foreign polishing alumina development, so that the market share of foreign products in China continues to shrink. The application field covers hardware (stainless steel, copper alloy, zinc alloy), inorganic non-metallic materials (glass, granite, crystal, marble, inorganic material jewelry), polymer materials (automotive lacquer mirror polishing, polymer material jewelry) and other serialized products, targeted development of rough, medium and fine polishing products, customized professional products according to customer needs.

According to the above problems, our company has optimized the precursor decomposition process, prepared homogeneous and dispersed nano-aluminum hydroxide in the original crystal, and used nano-aluminum hydroxide as the raw material for high-temperature calcination under a uniform and stable temperature field. The prepared nano-alumina has high purity, concentrated particle size distribution, good dispersion, and uniform original crystal. It has good performance in fine polishing, diaphragm ceramic coating, special ceramics, etc.