With the development of rare earth industry, in the 1930s, rare earth oxide was first used as polishing powder to polish glass in Europe. In the Second World War, rare earth polishing powder was very successful in polishing precision optical instruments. Due to the advantages of high polishing efficiency, good quality and less pollution, rare earth polishing powder has aroused the research enthusiasm of western countries. In this way, rare earth polishing powder is developing rapidly to replace the traditional polishing powder. Rare earth polishing powder was produced in foreign countries 60 years ago. In the 1990s, more than 30 kinds of standardized and serialized products have been produced. At present, the main foreign manufacturers of rare earth polishing powder are Rhodia of France, Solvay of Belgium, universal photonics of the United States, Showa chemical and Xunzi of Japan, rcmpa of India. In 1968, China successfully developed rare earth polishing powder for the first time in Shanghai Yuelong chemical plant. Now China is the main producer of polishing powder in the world, and its annual output accounts for more than 80% of the world.
Rare earth polishing powder, also known as ceria polishing powder, refers to the polishing powder mainly composed of ceria. The main component of ceria polishing powder is ceria (CeO2), followed by lanthanum oxide (La2O3), praseodymium oxide (Pr2O3), in addition to a small amount of silicon oxide, alumina and calcium oxide, In addition, some types of polishing powder add 3-7% fluorine to provide polishing performance. It is usually made from lanthanum, cerium, rare earth chloride or cerium rich rare earth carbonate by chemical treatment, burning, crushing and screening.
Application of ceria polishing powder
1. In addition to ceria polishing powder, other polishing powder materials: polishing powder is usually composed of ceria, alumina, silicon oxide, iron oxide, zirconia, chromium oxide and other components. Different materials have different hardness and chemical properties in water, so the application occasions are different. The Mohs hardness of alumina and chromium oxide is 9, that of ceria and zirconia is 7, and that of iron oxide is lower. Ceria and silicate glass have high chemical activity and similar hardness, so they are widely used in glass polishing.
2. Particle size of cerium oxide: the larger the particle size of cerium oxide, the greater the grinding force, the more suitable for harder materials, ZF glass should use finer polishing powder. It should be noted that all ceria particles have a distribution problem. The average particle size or median diameter D50 only determines the polishing speed, while the maximum particle size Dmax determines the polishing accuracy. Therefore, it is necessary to control the maximum particle size of polishing powder in order to achieve high precision.
3. Hardness of polishing powder: the real hardness of polishing powder is related to materials. For example, the hardness of ceria is about Mohs hardness 7, and all kinds of ceria are similar. But the hardness of different ceria is different, because ceria polishing powder is usually aggregate. The attached picture is an electron microscope picture of a polishing powder aggregate. Due to the different firing temperature, the strength of the aggregate is also different, so there will be a feeling of different hardness when using. Of course, some polishing powder with alumina and other hard materials will improve the grinding rate and wear resistance.
4. Concentration of polishing slurry: the concentration of slurry determines the polishing speed in the polishing process. The higher the concentration is, the higher the polishing speed is. When using small particle polishing powder, the slurry concentration should be adjusted properly.
5. Selection of polishing die for ceria polishing powder: the polishing die should be softer. It should be pointed out that ceria powder is added to many polyurethane polishing wafers. The maximum particle size of these powders also determines the final polishing accuracy. According to me, it's better to use the polishing die without polishing powder.
The indexes affecting the properties of ceria polishing powder
1. Particle size of powder: determines the polishing accuracy and speed, commonly used to determine the number of mesh and average particle size of powder. The mesh number of the screen can grasp the relative particle size of the powder, and the average particle size determines the overall level of the particle size of the polishing powder.
2. Mohs hardness of powder: the powder with relatively high hardness has faster cutting effect, and the addition of some grinding aids can also improve the cutting effect; there will be great differences in different application fields, including its own processing technology.
3. Suspension property of powder: good powder requires better suspension property of polishing powder. The shape and particle size of powder have certain influence on the suspension property. The suspension property of polishing powder with sheet shape and finer particle size is relatively better, but it is not absolutely right. The suspension property of polishing powder can also be improved by adding suspension.
4. Crystal form of powder: the crystal form of powder is agglomerated single crystal particles, which determines the machinability, wear resistance and fluidity of powder. The single crystal particles agglomerated with powders are separated (broken) in the polishing process, which makes the machinability and wear resistance gradually decrease. The irregular hexagonal crystal particles have good machinability, wear resistance and fluidity.
5. Appearance color: the content of PR in the raw material is related to the ignition temperature and other factors. The higher the content of PR, the brownish red powder will appear. Low cerium polishing powder contains a lot of praseodymium (cerium praseodymium material), which makes it brown red. The higher the calcination temperature is, the whiter the high cerium polishing powder is. The lower the calcination temperature is (about 900 ℃), the lighter the color is.
In conclusion, in order to increase the polishing speed of ceria polishing powder, fluorine is usually added to ceria polishing powder to increase the grinding rate. The mixed rare earth polishing powder with low cerium content is usually doped with 3-8 fluorine, and the pure ceria polishing powder is usually not doped with fluorine. For ZF or F series glass, because of its low hardness and high fluorine content in the material itself, it is better to choose polishing powder without fluorine.
1. Raw materials
At present, the raw materials for producing cerium series rare earth polishing powder in China are as follows: (1) ceria (CeO2), which is obtained by separating mixed rare earth salts (w (CeO2) = 99%); (2) mixed rare earth hydroxide (re (OH) 3) (w (REO) = 65%, w (CeO2) ≥ 65%); (3) rare earth chloride (RECl3), which is extracted from mixed rare earth chloride, and obtained lanthanum cerium chloride (mainly containing La, CE and PR (w (REO) ≥ 45%) (4) lanthanum cerium carbonate (w (REO) ≥ 45%, w (CeO2) ≥ 60%)
2. Production process
Polishing powder production process: raw material preparation → mixing → high temperature calcination → grinding → grading → adding suspending agent → packaging
The classification is divided into hydraulic classification and air flow grinding classification
Cerium based rare earth polishing powder has been widely used in industrial products polishing because of its excellent chemical and physical properties.
It is mainly used for polishing flat glass, surface covered glass and process glass. Ordinary optical glass, glasses, glass mold polishing. Precision optical glass, TN, STN, liquid crystal glass substrate, precision optical lens polishing. Polishing of prism, lens and projector lens. LCD liquid crystal glass, TFT, ITO conductive glass, IC mask and other high-precision polishing, also suitable for metal polishing, process jewelry, lamps and other industries parts of the rough polishing.
Cerium based rare earth polishing powder is mainly used for high speed polishing of precision optical lens. The polishing powder has excellent performance, good polishing effect and high price. Compared with high cerium powder, this kind of polishing powder can reduce the liquid concentration of polishing powder by 11%, increase the polishing speed by 35%, improve the finish of products by one grade, and increase the service life of polishing powder by 30%. Low cerium rare earth polishing powder is suitable for polishing TV picture tube, spectacle lens and flat glass.
