Development history
With the development of rare-earth industry, in twentieth Century 30 time, first appeared in Europe by rare earth oxide polishing powder for polishing glass. In the Second World War, rare earth polishing powder quickly in the polishing precision optical instrument to succeed. Because of the rare earth polishing powder with high polishing efficiency, good quality, less pollution, stimulated western research enthusiasm. Thus, rare earth polishing powder to replace the traditional trend of rapid development of polishing powder. Foreign 60 years ago to begin production of rare earth polishing powder, in twentieth Century 90 time already formed a variety of standardized, serialized products amounted to 30 a variety of. At present, foreign rare-earth polishing powder manufacturers mainly has 15 ( annual production capacity of 200 tons. Among them, the French Rhodia Inc annual production capacity of 2200 tons, is currently the world's largest rare earth polishing powder manufacturer. The United States of America polishing powder with an annual output of 1500 tons or more. Japanese production of rare earth polishing powder raw material using bastnaesite, coarse cerium chloride and rare earth chloride three, technology each are not identical. Japan rare-earth polishing powder on sintering equipment and technology are most characteristic. In 1968, China in Shanghai chemical plant Yuelong first successful preparation of rare earth polishing powder.
Composition and structure of
Cerium oxide polishing powder is defined by a group composed of cerium oxide polishing powder, cerium oxide polishing powder as main component in two cerium oxide ( CeO2 ), followed by lanthanum oxide, praseodymium oxide ( La2O3 ) ( Pr2O3 ), also contains trace amounts of silica, alumina and calcium oxide, and some types of polishing powder for polishing performance to join 3-7% fluoride.
Under electron microscopy of cerium oxide polishing powder crystal structure
Cerium oxide polishing powder and the use of
1, in addition to cerium oxide polishing powder, polishing powder and other materials: polishing powder usually consists of cerium oxide, alumina, silicon oxide, iron oxide, zirconium oxide, chromium oxide and other components, different materials of different hardness, in the water chemical properties are also different, therefore the use of occasions each not same. Alumina and chromium oxide Mohs hardness 9, cerium oxide and zirconium oxide is 7 lower, iron oxide. Cerium oxide and silicate glass with high chemical active, hardness is also quite, it is widely used in glass polishing.
2, cerium oxide particle size: size bigger cerium oxide, grinding force increases, more suitable for harder materials, ZF glass should be used fine polishing powder. Note that, all of the cerium oxide particles have an average particle size distribution, or median diameter of D50 size determining only the polishing speed, while the maximum size Dmax determines the polishing precision. Therefore, in order to obtain high accuracy requirement, must control the maximum particle polishing powder.
3, The polishing powder real hardness: hardness associated with the material, such as cerium oxide hardness is hardness of about 7, all sorts of cerium oxide are almost. But different cerium oxide body give people the feeling of different hardness, is because of cerium oxide polishing powder usually aggregate, drawings for a polishing powder dimerization electron microscope photos. As a result of firing temperature different, aggregate strength is not the same, so use will have a hardness of not the same feeling. Of course, some polishing powder adding alumina and other hard materials, demonstrated the grinding rate and the wear resistance are improved.
4, In a polishing slurry concentration: polishing slurry in the process of concentration determines the speed of polishing, the polishing speed higher concentration. The use of small particles of polishing powder, slurry concentration by appropriate reduction.
5, cerium oxide polishing powder, polishing mold choice: polishing die should use soft point. It should be pointed out that, a lot of polyurethane polishing disc adding cerium oxide polishing powder. The maximum particle size of polishing powder also determines the final polishing precision. In my, preferably using without polishing powder, polishing mould.
Effect of cerium oxide polishing powder properties
1, powder particle size: determines the polishing precision and speed, commonly used the number of heads and powder average particle size. Sift sieve mesh can grasp the powder relative granularity value, average particle size of polishing powder particle size determines the overall level.
2, powder: hardness Mohs hardness of relatively large powder has the advantages of high cutting efficiency, while adding some auxiliary grinding agent, also can improve the cutting effect; different applications will have very big discrepancy, including its processing technology.
3, powder suspension: good powder for polishing powder have better suspension, shape of the powder and particle size on the suspension performance has a certain impact, sheet and fine particle size of polishing powder suspension relative to be friends with some, but not for the. Polishing powder suspension performance enhancement can also be added to improve the suspension ( agent ).
4, powder: powder crystal polymorphs is together single crystal particles, determines the powder cutting performance, wear resistance and fluidity. Powder agglomeration together in a single crystal particles in the polishing process separation (broken ), so that its cutting resistance, abrasion resistance decreased gradually, irregular hexagonal crystal particles having excellent cutting performance, wear resistance and fluidity.
5, color: raw materials and the content of Pr and calcination temperature and other factors, praseodymium content is higher, the powder was red brown. Low polishing powder contains large amounts of praseodymium ( cerium praseodymium material ), it was red brown. Polishing powder, ignition temperature is high, its significant partial white pink, low temperature ( about 900 degrees ), it was a pale yellow.
To sum up, in order to increase the cerium oxide polishing powder, polishing speed, usually in cerium oxide polishing powder adding fluoride to increase grinding efficiency. The lower cerium content of mixed rare earth polishing powder often combined with 3 - 8 fluorine; pure cerium oxide polishing powder is usually not doped with fluorine. On ZF or F series of glass, because of their lower hardness, but also the material itself is a high fluoride content, therefore because of choosing a fluoride-free polishing powder as well.
Production of raw materials
At present, China's production of cerium rare earth polishing powder raw materials are the following: ( 1) the cerium oxide ( CeO2 ), made from a mixture of rare-earth salts after separation of income ( w ( CeO2 ) =99% );
( 2) mixed rare-earth hydroxide ( RE ( OH ) 3), is a rare earth concentrate ( w ( REO )≥50%) after chemical treatment of intermediate raw materials ( w ( REO ) =65%, w ( CeO2 )≥ 48% );
( 3) the mixed rare earth chloride ( RECl3 ), from mixed rare earth chloride extraction separation of the rare earth chloride without europium (mainly including La, Ce, Pr and Nd, w ( REO )≥ 45%, w ( CeO2 )≥ 50% );
( 4) high grade rare earth concentrate ( w ( REO )≥ 60%, w ( CeO2 )≥ 48% ), Inner Mongolia Baotou rare earth concentrate, the Weishan in Shandong and Sichuan Mianning bastnaesite concentrate.
Production process
( 1) high CE rare-earth polishing powder
In the rare earth mixture after the separation of cerium oxide as raw materials, physical and chemical method in processing high hardness, uniform particle size, small, a face-centered cubic crystal powder products.
The main process is: raw material, high temperature calcining→→→water quenching hydraulic classification, filtering, drying and high cerium rare earth polishing powder products. The main equipment are: calcination furnace, water quenching tank, classification, filter, drying box. Main measures: products w (REO ) =99%, w ( CeO2 ) =99%; rare earth recovery rate of about 95%. The product is suitable for high speed polishing. This polishing powder first instead of the classical polishing iron oxide powder ( pink ).
( 2) in cerium rare earth polishing powder preparation
Mixed rare earth hydroxide ( w ( REO ) =65%, w ( CeO2 )≥ 48% ) as raw material, in the process of chemical pretreatment of rare earth salt solution, adding intermediates ( agent ) that is transformed into w ( CeO2 ) =80% ～ 85% intermediate cerium rare earth polishing powder products. The technological process for:
Raw material, oxidation, and dissolving and filtering to acid dissolution, precipitation, washing filter high temperature calcination, grinding and screening, intermediate cerium rare earth polishing powder products.
The main equipment are: oxidation tank, and melting trough, acid dissolving tank, precipitation tank, filter, calcining furnace, fine grinding and sieving machine and a packing machine.
Main measures: products w (REO ) =90%, w ( CeO2 ) =80% ~ 85%; rare earth recovery rate of about 95%; the average particle size of 0.4 microns to 1.3 microns. The product is suitable for high speed polishing, than high cerium rare earth polishing powder high-speed polishing performance more excellent.
( 3) low cerium rare earth polishing powder preparation
With little europium rare earth chloride ( w ( REO )≥ 45%, w ( CeO2 )≥ 48% ) as raw materials, to synthesis intermediates ( precipitation ) of salt precipitation process, can process for preparing low cerium rare earth polishing powder products.
The main process is: raw material, dissolving, salt precipitation, filtration and washing, high temperature calcination, crushing, screening, grinding low cerium rare earth polishing powder products.
The main equipment are: dissolving tank, precipitation tank, filter, calcining furnace, mill, fine grinding and sieving machine.
Main measures: products w ( REO ) =85% ～ 90%, w ( CeO2 ) =48% ~ 50%; rare earth recovery rate of about 95%; the average particle size of 0.5 microns to 1.5 microns.
At present, the domestic production of low-grade cerium rare earth polishing powder amount is maximum, the total yield of more than 90%.
Application fields
As a result of cerium rare earth polishing powder has excellent chemical and physical properties, so in the industrial products polishing has obtained the widespread application.
And is mainly used for flat glass, sheet glass, craft glass polishing. Optical glass, glasses, glass mold polishing. Precision optical glass, TN, STN, LCD glass substrate, precision optical lens polishing. Prism, lens, projector lens polishing. LCD LCD glass, TFT, ITO, IC conductive glass photomask and other high precision polishing, can also be applied to metal polishing, jewelry, lighting and other industries parts rough polishing.
·the high cerium rare earth polishing powder, mainly used in precision optical lens polishing. The polishing powder of excellent performance, good polishing effect, high price. Cerium in rare earth polishing powder, mainly applied to optical instruments of small spherical lens with medium precision high speed polishing, the polishing powder and high cerium powder, can make the polishing liquid concentration decreased by 11%, the polishing rate increases by 35%, products can improve smoothness level, polishing powder using life can be raised 30%. Low cerium rare earth polishing powder, suitable for the television picture tubes, glasses and flat glass polishing.
Selection of cerium oxide polishing powder
Selection of polishing powder according to the polishing material, as well as the polishing precision requirements, selecting appropriate models of polishing powder.
According to the hardness of similar phase polishing principle, for different materials hardness of glass to use the corresponding models of polishing powder. There is also based on the polishing precision requirements, selection of different size range of polishing powder, particle size index are the main center of grain size D50, and D10, D90 etc.. Particle size distribution test report peak range of smaller, more focused. The center than the small size particles on the polishing of no effect, than in the center of big diameter particles on the polishing surface scratches, so the particle size distribution is a important index.
In addition, the content of cerium oxide polishing powder on polishing performance have certain effect, but have different polishing material to use to adapt the content of cerium oxide polishing powder, polishing its effect will be better.
Polishing powder using process generally is water or other media as a carrier, but in the solution, so the suspension in water is also very important, the suspension of poor polishing powder into the bottom of the container cannot follow solution circulation use, so the cerium oxide polishing powder suspension on polishing performance also has a great influence on.
There is a polishing powder pH indicator is to ensure that the polishing process on human security.