Cerium-based rare earth polishing powder is one of the more important rare earth products. Because it has the advantages of strong cutting ability, short polishing time, high polishing accuracy and clean operating environment, it is better than other polishing powders (such as Fe2O3 red powder) and is called "the king of polishing powders". This product has developed rapidly in China and its application is increasing day by day. Its output has soared and its development prospect is promising.
Development process of 1. 1
Red powder (iron oxide) is the earliest polishing material in history, but its polishing speed is slow and it can't eliminate rust pollution. With the development of rare earth industry, in 1930s, rare earth oxides were used as polishing powder for polishing glass for the first time in Europe. In World War II, an employee of WF and Banister Company in Rockford, Illinois, put forward a rare earth oxide polishing powder called Banister in 1943, which soon successfully polished precision optical instruments. Rare earth polishing powder has the advantages of high polishing efficiency, good quality and little pollution, which has attracted research in the United States and other countries. In this way, the trend of rare earth polishing powder replacing traditional polishing powder has developed rapidly.
Foreign countries began to produce rare earth polishing powder 60 years ago, and in the 1990s, various standardized and serialized products reached more than 30 specifications.
There are mainly 15 overseas producers of rare earth polishing powder (with an annual production capacity of more than 200 tons). Among them, the annual production capacity of France Rhodia Company is more than 2,200 tons. Is currently the world's largest manufacturer of rare earth polishing powder. The annual production capacity of polishing powder in the United States exceeds 65,438+0,500 tons. The raw materials for producing rare earth polishing powder in Japan are bastnasite, crude cerium chloride and rare earth chloride, and the processes are different. The production of rare earth polishing powder in Japan has its own characteristics in sintering equipment and technology. 1968, China successfully developed rare earth polishing powder for the first time in Shanghai Yuelong Chemical Plant. Subsequently, Northwest Optical Instrument Factory and Yunnan Optical Instrument Factory successively developed different types of rare earth polishing powder with monazite as raw material. Beijing Institute of Nonferrous Metals and Beijing Institute of Technology developed and popularized 739 rare earth polishing powder in 1976, and successfully developed 77 1 rare earth polishing powder in 1977. 1979 Gansu rare earth company successfully developed 797 rare earth polishing powder. At present, there are 14 rare earth polishing powder manufacturers in China (with an annual production capacity of over 30 tons), and the largest one has an annual production capacity of 2,220 tons (Baotou Tianjiao Mei Qing Rare Earth Polishing Powder Co., Ltd.). However, compared with foreign countries, there is still a big gap, mainly due to the unstable quality of rare earth polishing powder products, failure to achieve standardization and serialization, and failure to fully meet the polishing requirements of various industrial fields, so we must catch up.
1.2 component classification
1.2. 1 divided by the amount of CeO2 in the rare earth polishing powder:
The main component of rare earth polishing powder is CEO _ 2. According to the amount of CEO _ 2, cerium polishing powder can be divided into two categories: one is high-priced and high-quality cerium polishing powder with high CEO _ 2 content, and the CEO _ 2/Treo ratio is generally ≥ 80%; The other is cheap low cerium polishing powder, with low CEO _ 2 content, less than 50% cerium content, and the rest are La2O3, Nd2O3 and PR6O60.
For high cerium polishing powder, the higher the grade of cerium oxide, the greater the polishing ability and the longer the service life, especially when polishing hard glass (timely, optical lenses, etc.) for a long time. ), it is advisable to use high-grade cerium polishing powder.
Low cerium polishing powder generally contains about 50% CeO2, and the remaining 50% is La2O3? SO3，Nd2O3？ SO3，Pr6O 1 1？ Alkaline anhydrous sulfate such as SO3 or alkaline fluoride such as LaOF, NdOF, PrOF, etc. This kind of polishing powder is characterized by low cost, and its initial polishing ability is almost the same as that of cerium oxide polishing powder, so it is widely used for glass polishing of flat glass, kinescope glass, spectacle lens and so on. But its service life must be lower than that of cerium oxide polishing powder.
1.2.2 divided by the particle size and particle size distribution of rare earth polishing powder:
The particle size and particle size distribution of rare earth polishing powder have an important influence on the properties of polishing powder. For polishing powder with certain composition and processing technology, the larger the average particle size, the greater the glass grinding speed and surface roughness. In most cases, the polishing powder with a particle size of about 4μm has the highest grinding speed. On the contrary, if the average particle size of polishing powder is small, the grinding amount will be reduced, the grinding speed will be reduced, and the smoothness of glass surface will be improved. Generally, the particle size distribution of standard polishing powder is narrow, and there are few particles that are too fine and too coarse. Polishing powder without large particles can polish high-quality surface, while polishing powder with less fine particles can improve grinding speed. In addition, rare earth polishing powder can also be classified according to different kinds of additives. The production technology of rare earth polishing powder belongs to micropowder engineering technology, and rare earth polishing powder belongs to ultrafine powder. There are generally three kinds of ultrafine powders in the world: nano (1nm ~100 nm); Submicron scale (100 nm ~ 1 micron); Micron-scale (1 micron ~ 100 micron). According to this classification method, rare earth polishing powder can be divided into three categories: nano-scale rare earth polishing powder, sub-micron rare earth polishing powder and micron-scale rare earth polishing powder. Usually, the rare earth polishing powder we use is micron, and its particle size distribution is between 1 micron and10μ m. According to its physical and chemical properties, rare earth polishing powder is generally used for fine grinding in the last process of glass polishing, so its particle size distribution is generally not greater than10μ m. Polishing powder with particle size larger than 10μm (including rare earth polishing powder) is mostly used in the initial stage of glass processing. Sub-micron rare earth polishing powder with coarse grinding smaller than 1μm has been paid more and more attention because of its application in the field of liquid crystal display and computer CD, and its output has increased year by year.
Nano rare earth polishing powder came out. With the development of modern science and technology, its application prospect is unpredictable, but its market share is still very small, belonging to the research and development stage.
1.3 raw materials for production
The raw materials for producing cerium rare earth polishing powder in China are:
(1) cerium oxide (CeO2), which is obtained by separating mixed rare earth salts (W (CeO2) = 99%);
(2) Mixed rare earth hydroxide (RE(OH)3) is an intermediate raw material (w(REO)=65%, W (CEO 2) ≥ 48%) after chemical treatment of rare earth concentrate (w(REO)≥50%);
(3) mixing rare earth chloride (RECl3), and extracting and separating rare earth chloride with less europium content (mainly containing La, Ce, Pr and nd, w(REO)≥45%, w (CEO 2) ≥ 50%) from the mixed rare earth chloride;
(4) High-grade rare earth concentrates (w(REO)≥60%, w(CeO2)≥48%), including mixed rare earth concentrates in Baotou, Inner Mongolia, and bastnaesite concentrates in Weishan, Shandong and Mianning, Sichuan.
Except 1, No.2, No.3 and No.4 raw materials all contain light rare earth (w(REO)≈98%), with CeO2 as the main component and w(CeO2) accounting for 48% ~ 50%. China is rich in cerium resources. According to the calculation, its industrial reserve is about180,000 tons (calculated by CeO2), which lays a solid foundation for the sustainable development of rare earth polishing powder in China in the future, and is also a unique advantage in China, which can promote the rapid development of rare earth industry in China.
1.4 main production technologies and equipment
1.4. 1 production of high cerium rare earth polishing powder
Using cerium oxide separated from rare earth mixture as raw material, powder products with high hardness, uniform and fine particle size and face-centered cubic crystals were processed by physical and chemical methods. The main technological process is as follows: raw materials → high temperature → calcination → water quenching → hydraulic classification → filtration → drying → advanced cerium rare earth polishing powder products.
The main equipment includes: calciner, water quenching tank, classifier, filter and drying box.
Main indicators: w(REO)=99% and W (CEO 2) = 99% in the product; The recovery rate of rare earth is about 95%; The average particle size is 1 μ m ~ 6 μ m (or 200 ~ 300 mesh), and the crystal form is complete. This product is suitable for high-speed polishing. This high cerium polishing powder replaced the classic polished iron oxide powder (red powder) for the first time.
1.4.2 preparation of cerium-based rare earth polishing powder
Using mixed rare earth hydroxide (w(REO)=65%, w(CeO2)≥48%) as raw material, rare earth salt solution was obtained through chemical pretreatment, and intermediate (precipitant) was added to convert it into intermediate cerium rare earth polishing powder with w (CEO 2) = 80% ~ 85%. The main process flow is as follows:
Raw materials → oxidation → excellent dissolution → filtration → acid dissolution → precipitation → washing and filtration → high temperature calcination → fine grinding and screening → intermediate cerium rare earth polishing powder products.
Main equipment: oxidation tank, optimal solution tank, acid solution tank, precipitation tank, filter, calciner, fine grinding and screening machine and packaging machine.
Main indicators: w(REO)=90% and w (w(CEO 2)= 80% ~ 85%；% in the product; The recovery rate of rare earth is about 95%; The average particle size is 0.4 μ m ~1.3 μ m. This product is suitable for high-speed polishing and its performance is better than that of high-grade cerium rare earth polishing powder.
1.4.3 preparation of low cerium rare earth polishing powder
Low-grade cerium-based rare earth polishing powder can be prepared by using rare earth chloride with less europium (w(REO)≥45% and w(CeO2)≥48%) as raw materials and precipitating with synthetic intermediate (precipitant). The main process flow is as follows:
Raw materials → dissolution → double salt precipitation → filtration and washing → high temperature calcination → crushing → fine grinding and screening → low-grade cerium rare earth polishing powder products.
Main equipment: dissolving tank, settling tank, filter, calciner, pulverizer, fine grinding and screening machine.
Main indicators: w (reo) = 85% ~ 90% and w (w(CEO 2)= 48% ~ 50%；% in the product; The recovery rate of rare earth is about 95%; The average particle size is 0.5 micron ~ 1.5 micron (or 320 ~ 400 mesh). This product is suitable for high-speed polishing of optical glass.
Using bastnasite mixed with high-grade rare earth concentrate (w(REO)≥60%, w(CeO2)≥48%) as raw materials, low-grade rare earth polishing powder can be directly produced by chemical and physical methods such as grinding, calcination and screening.
The main process flow is as follows:
Raw materials → dry and fine grinding → batching → powder mixing → roasting → grinding and screening → low-grade cerium rare earth polishing powder products.
Main equipment: ball mill, mixer, roaster, screening machine, etc. Main indicators: w(REO)≥95% and W (CEO 2) ≥ 50% in the product; The recovery rate of rare earth is ≥ 95%; The product granularity is 65438±0.5 μm ~ 2.5 μm m. This product is suitable for high-speed polishing of spectacle lenses and TV picture tubes.
The amount of low-grade cerium rare earth polishing powder produced in China is the largest, accounting for more than 90% of the total output.
1.5 application
Because of its excellent chemical and physical properties, cerium-based rare earth polishing powder has been widely used in polishing industrial products, such as various optical glass devices, TV picture tubes, optical glass, oscilloscopes, flat glass, semiconductor wafers, metal precision products and so on.
1.6 market
Among the consumption of rare earth polishing powder, Japan is the largest consumer, producing about 3,550-4,000 tons of polishing powder every year, with an output value of 3.5-4 billion yen, and also importing some polishing powder from France, the United States and China. Among them, the biggest consumption market of polishing powder is color TV cathode ray tube. In the mid-1990s, the production of cathode ray tubes in Japan turned overseas, and the output of flat panel display products increased rapidly, so did the demand for cerium-based polishing powder. The polishing powder consumed by flat panel displays for liquid crystal displays in Japan accounts for about 50% of its market. Since 1990s, Japan has transferred the production technology and equipment of polishing powder for cathode ray tubes overseas. For example, since 1989, Mei Qing Chemical Company has been producing cerium-based polishing powder for cathode ray tubes overseas. 1989 established a wholly-owned enterprise in Taiwan Province province. 1990 was put into operation, with an annual production capacity of 1000 tons. 1997 a joint venture with China Baotou iron and steel company was established in Baotou, specializing in the production of polishing powder for color TV cathode ray tubes, electron tubes and flat glass polishing. The design capacity is 1200 tons/year, and the raw materials used are high-grade bastnaesite and cerium-rich rare earth carbonate. Therefore, the polishing powder for cathode ray tube of Japanese Metal Chemical Company is also interested in producing high-performance polishing powder for LCD due to the impact of a large number of low-priced polishing powders in Chinese mainland and Taiwan Province Province. Northeast Metal Chemical Company plans to engage in the production of polishing powder for optical lenses and liquid crystal displays.
High cerium rare earth polishing powder is mainly suitable for high-speed polishing of precision optical lenses. The practice shows that the polishing powder has excellent performance and good polishing effect. Because of its high price, it is seldom used in China.
Medium cerium rare earth polishing powder is mainly suitable for high-speed polishing of precision small spherical lenses in optical instruments. Compared with cerium oxide powder, polishing powder can reduce the liquid concentration of polishing powder 1 1%, increase the polishing rate by 35%, improve the product smoothness by one grade, and prolong the service life of polishing powder by 30%. At present, the use of this polishing powder in China is still very small, and it needs to continue to develop new uses in the future.
Low cerium rare earth polishing powder, such as 77 1, is suitable for high-speed polishing of optical glass and metal products; Models 797 and C- 1 are suitable for polishing TV picture tubes, glass and flat glass. H-500 and 877 are suitable for polishing TV picture tubes. In addition, other polishing powders are also used to polish optical instruments, cameras and camera lenses. This kind of polishing powder is most used in China, accounting for more than 85% of the total domestic consumption.
1.7, conclusion
China's rare earth polishing powder industry has gone through nearly 50 years of history. At present, China has made great achievements and development in production, application, market, technology and equipment, and is in a leading position in the same industry in the world, becoming the main producer and supplier of rare earth polishing powder in the world. In the future, we should speed up the innovation of technology and equipment and improve the production level. It is necessary to speed up the process of product standardization and serialization, increase new varieties, improve product quality, and strive to increase product exports and occupy the international market.