Detailed Explanation of the Grain Size Analysis Method for White Corundum Crystal Structure

　　White corundum produced by melting production technology has uneven chemical composition and structure in different parts of the crystal block due to the uneven refining of the aluminum oxide solution. This unevenness is clearly visible in the fractured white corundum crystal blocks, which can be divided into the following parts based on appearance, structure, and mineral composition: the so-called upper part, lower part, center, edge, and bottom.

　　The crystal structure of white corundum is dense and porous in the upper part, with colors ranging from light gray to dark gray, and various types of contamination. Some surfaces appear reddish-brown, while the lower part shows a sponge-like granular structure, with colors of rose, blue, and a few purple-brown. The overall structure of the lower part of white corundum is a porous and dense granular structure with fine crystallization. The center of the white corundum crystal block is an overall dense mass, mostly medium and fine crystallization, with a greasy luster. The color ranges from purple-brown to rose-brown. There are iron alloy inclusions in the block, with light yellow in the silver cross-section. The edge structure of the white corundum crystal block is dense, mostly with fine crystallization, some areas are medium, and occasionally there are coarse crystallizations. The structure is not uniform, the cross-section is relatively rough, non-lustrous, occasionally greasy, and the color ranges from dark brown to blue-black. The bottom of the white corundum crystal block is overall dense, with a structure ranging from fine to coarse crystallization, mostly coarse crystallization, and a large number of iron alloy inclusions of different sizes.

　　The structure of white corundum crystal blocks is very complex, divided into 5 parts, each with different structures, colors, and particle sizes. Studying the crystal structure of white corundum helps people better understand the wear resistance, self-sharpening, toughness, and other properties of white corundum abrasives, thus laying the foundation for the research and development of new types of white corundum tools.

　　White corundum particle size analysis methods

　　1. Screening method

　　Advantages: Simple, intuitive, low equipment cost, commonly used for samples larger than 40um.

　　Disadvantages: Results are greatly affected by human factors and sieve hole deformation.

　　2. Microscope (image) method

　　Advantages: Simple, intuitive, can perform morphology analysis, suitable for samples with narrow distribution (and small particle size ratio less than 10:1).

　　Disadvantages: Poor representativeness, analysis of samples with wide distribution range is more troublesome, cannot analyze samples smaller than 1um.

　　3. Sedimentation method (including gravitational sedimentation and Li Xin sedimentation)

　　Advantages: Gradual operation, instruments can run continuously, low price, good accuracy and repeatability, wide testing range.

　　Disadvantages: Longer testing time, more complicated operation.

　　4. Resistance method.

　　Advantages: Gradual operation can measure particle count, clear concept, fast speed, good accuracy.

　　Disadvantages: Not suitable for measuring particle samples smaller than 0.1um, changing to small hole tubes for samples with wide particle size distribution is more troublesome.

　　5. Laser method.

　　Advantages: Simple operation, fast testing speed, wide testing range, good repeatability and accuracy, can perform online measurement and dry measurement.

　　Disadvantages: Results are greatly affected by the distribution model, high equipment cost, low resolution.

　　6. Electron microscope method.

　　Advantages: Suitable for testing ultra-fine particles or even nanoparticles, high resolution, can perform morphology and structure analysis.

　　Disadvantages: Small sample size, poor representativeness, measurements are easily affected by human factors, expensive equipment.

　　7. Optical obstruction method.

　　Advantages: Convenient and fast testing, can measure particle count in liquids or gases, high resolution.

　　Disadvantages: Not suitable for samples with particle size smaller than 1um, systematic comparison is required, only suitable for measuring dust, pollutants, or well-diluted drugs, not commonly used for general powders.

　　8. Permeability method.

　　Advantages: Low equipment cost. No need to disperse samples, can measure the powder of measurable materials.

　　Disadvantages: Can only obtain average particle size value, cannot measure particle size distribution; cannot measure fine powder smaller than 5um.

　　9. Small-angle X-ray scattering method

　　Used for measuring the particle size of nanoparticles.

　　10. Photon correlation spectroscopy (dynamic light scattering method)

　　Used for measuring the particle size of nanoparticles.