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Study on the Preparation of Ceria-based Polishing Powder by Rare Earth Carbonate

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Tutor: TuGanFeng WuWenYuan
School: Northeastern University
Course: Non-ferrous metallurgy
Keywords: ceria-based polishing powder,rare earth carbonate,process of calcination,crystal
CLC: TB383.3
Type: PhD thesis
Year:  2008
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Abstract:
The ceria-based polishing powder is a kind of outstanding polishing material. With its unique polishing performance and quality, it is extensively applied to High-tech fields, such as the optical glass, electronic product, etc. The polishing performance of ceria-based polishing powder is determined by its special physical and chemical property. And how to prepare the polishing powder of excellent performance, already become a hot subject for research.In this paper, using cerium carbonate and lanthanum-cerium carbonate as raw materials, four kinds of ceria-based rare earth polishing powders were prepared by the processes of ball milling grinding, fluorine-doping, drying and calcination.Their crystal structure were analysized, and the polishing performance were also tested.The relation between crystal structure and polishing performance were studied.This paper consists four parts:In part¢ñ,the phase composition and the chemical reaction during the processes of ball milling grinding, fluorine-doping, drying and calcination were studied by XRD and DTA.And the dynamics of flu-oxide intermediate compound generating during C and LC calcinating process were studied first time.The results showed, the corresponding dynamics equation were y1=-4.4x102x+0.45,y2=-3.4¡Á103x+0.69 respectively, and the apparent activation energy were 8425 kJ¡¤mol-1,65104kJ¡¤mol-1 respevtively, and the reaction order were 0.45,0.69 respevtively.In part¢ò,the particle pattern and crystal structure(consists of grain size, lattice constant and distortion of lattice) were studied by XRD,SEM and HRTEM.The results showed that: firstly, the particle patterns of WFC and WFLC ceria-based polishing powders appeared flaky and needlelike, while those of C and LC ceria-based polishing powders appeared spherical aggregate; the particle of four ceria-based polishing powders all consisted of spherical crystal grain, among which the WFC crystal grain aggregate closely, the crystal grain closeness of WFLC only was less than that of WFC, the C crystal grain aggregate incompact relatively, the crystal grain closeness of LC was higher than that of C. The above results indicated that the particle pattern and coherent condition were influenced obviously by F. Secondly, La solutionized into CeO2 crystal lattice, while in the condition that contains F simultaneously, one part of La solutionized into CeO2 crystal lattice, and the other part of La generated new phase CeLa2O3F3 with F. Thirdly, the crystal size of four ceria-based polishing powders increased with the prolonging sintering time.The effect of F on crystal size was grater than that of La. The phase CeLa2O3F3 in the ceria-based polishing powder doping La and F simultaneously fixed large quantity of F, which caused that F existed mainly as fluoxide, so the CeO2 crystal growth tendency of C and LC basically in correspondence. The general tendency of CeO2 lattice constant of four ceria-based polishing powders gradually decreased and drived to stabilization. The CeO2 lattice constant of four ceria-based polishing powders was LC>WFLC>C>WFC.The distortion of lattice gradually decreased with the prolonging time. The effect of F on the lattice distortion was grater than that of La.In part¢ó, the relation between polishing performance and many factors such as different sintering condition, size distribution,particle pattern,crystal structure(consists of grain size and crystallizing shape)were studied. The results showed that:the polishing performance of four ceria-based polishing powders was LC>WFLC>C>WFC;the polishing performance, fishtail, smooth finish of LC ceria-based polishing powder calcined under 950¡æwere better than others; too low L111/L200 caused tertiary edge angle to be very sharp, and work surface were easily fishtailed, while too high L111/L200 caused tertiary edge angle not to be obvious, and the polishing performance decreased, which indicated that the polishing ability was the best as the value of L111/L200 approached 1.In part¢ô, the relationship between ceria-based polishing powder¡¯s color and the polishing performance was studied using Hunter¡¯s Lab theory of color space. The results showed that, with the increasing calcination temperature and time, the value of L and b increased, the value of a decreased, the color became dark.The viration between the ceria-based polishing powder¡¯s color and the polishing performance appeared regularity, so it was possible to use the color parameters to control ceria-based polishing powder¡¯s preparing condition and evaluate the product quality.
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