The relationships of crystal type, crystallization speed, purity, grain size and shape of rare earth carbonate with precipitation and crystallization conditions are very important for the production of rare earth carb...The relationships of crystal type, crystallization speed, purity, grain size and shape of rare earth carbonate with precipitation and crystallization conditions are very important for the production of rare earth carbonate with high efficiency, high quality and low cost. It is necessary for us for further understand the crystallization process mechanism and the factors effect on the crystallization. In the present paper, the crystallization characteristic, composition and crystal phase type of yttrium carbonates or ammonium yttrium carbonates precipitated from yttrium chloride solution using ammonium bicarbonate as precipitant were determined by chemical analysis, X ray powder diffraction and the pH situ determination. It was found that the crystal phase type was dominated by the feed molar ratio of ammonium bicarbonate to yttrium chloride, and the crystallization speed and the crystal composition were also influenced by temperature, feed manner and aging period etc. When precipitating and aging under lower temperature, crystallization is easy to take place in the high feed molar ratio zone, and when increasing temperature, crystallization will take place both in lower and higher feed molar ratio zones. The results show that spherical yttrium carbonate with tengerite type crystal phase can be formed within the temperature 30～70℃ when feed molar ratio of ammonium bicarbonate to yttrium chloride is less than 4, and that a rhombus flake crystal, which possesses the composition of ammonium yttrium quasi double carbonate and a new XRD pattern, is formed when the feed molar ratio is over 4. Their compositions can be represented as (NH4)aY(CO3)b(OH)c·nH2O, a< 1, 1< b< 2, c=3+a-2b. A fine crystal of ammonium yttrium double carbonate with the formula of (NH4)Y(CO3)2·H2O can also be obtained as using an enough amount of ammonium bicarbonate and aging enough time.展开更多
Ultra fine ceria was prepared by calcining hydrate cerium acetate. The effects of pyrolysis temperature on the particle size, morphology, specific surface area and loose packing density of ceria were investigated, and...Ultra fine ceria was prepared by calcining hydrate cerium acetate. The effects of pyrolysis temperature on the particle size, morphology, specific surface area and loose packing density of ceria were investigated, and the removal rate of optical glasses polishing by ceria was determined. The results show that with the increase of pyrolysis temperature, the loose deposit density and crystallinity increases and the specific surface area decreases, however, the particle size decreases firstly and then increases, the minimum medium particle size D50 is 0.47 μm at pyrolysis temperature of 1 000 ℃. The SEM images of ceria prepared by the decomposition at 800 ℃ or at 1 100 ℃ show porous powders or quasi-sphere small particles with loosely agglomeration, respectively. It was found that the removal rate varied with pyrolysis temperature in preparation of ceria and the property of glass polished. The removal rate for three kinds of glasses was in the order of ZF7> F1> K9, and the maximum value appeared at around 1 000 ℃ for ZF7 and F1, and at around 1 100 ℃ for K9.展开更多
Amorphous Neodymium carbonate was prepared by the precipitation reaction of neodymium chloride with ammonium bicarbonate in solution, and then aged at 60 ℃ to form crystalline neodymium carbonate. The feed molar rati...Amorphous Neodymium carbonate was prepared by the precipitation reaction of neodymium chloride with ammonium bicarbonate in solution, and then aged at 60 ℃ to form crystalline neodymium carbonate. The feed molar ratio of nNH4HCO3/nNdCl3 was 2.5, and the precipitation was carried out with or without addition of polyglyceryl fatty acid ester (PGFAE). The phase type and morphology of crystalline neodymium carbonates were examined by XRD and SEM, and the effect of PGFAE on the crystallization speed was investigated by volume change in deposit layer and in situ pH determination. The content of neodymium and chloride in crystals was analyzed, and the crystallization reaction or crystal growth characteristics were discussed. It was found that all the crystalline neodymium carbonates were tengerite type, and contained less crystalline water and chloride than that of lanthanite type neodymium carbonate crystallized at room temperature, which is beneficial to the production of neodymium carbonate with higher neodymium and lower chloride content. The addition of PGFAE not only could eliminate the foam formed during precipitation, but also could shorten crystallization time, and form large radiative-like shape conglomeration by the irregulative linkage of one dimension needle crystals. It is also suggested that the morphology and the chloride content of neodymium carbonate were dependent on the structure and crystal growth characteristics.展开更多
文摘The relationships of crystal type, crystallization speed, purity, grain size and shape of rare earth carbonate with precipitation and crystallization conditions are very important for the production of rare earth carbonate with high efficiency, high quality and low cost. It is necessary for us for further understand the crystallization process mechanism and the factors effect on the crystallization. In the present paper, the crystallization characteristic, composition and crystal phase type of yttrium carbonates or ammonium yttrium carbonates precipitated from yttrium chloride solution using ammonium bicarbonate as precipitant were determined by chemical analysis, X ray powder diffraction and the pH situ determination. It was found that the crystal phase type was dominated by the feed molar ratio of ammonium bicarbonate to yttrium chloride, and the crystallization speed and the crystal composition were also influenced by temperature, feed manner and aging period etc. When precipitating and aging under lower temperature, crystallization is easy to take place in the high feed molar ratio zone, and when increasing temperature, crystallization will take place both in lower and higher feed molar ratio zones. The results show that spherical yttrium carbonate with tengerite type crystal phase can be formed within the temperature 30～70℃ when feed molar ratio of ammonium bicarbonate to yttrium chloride is less than 4, and that a rhombus flake crystal, which possesses the composition of ammonium yttrium quasi double carbonate and a new XRD pattern, is formed when the feed molar ratio is over 4. Their compositions can be represented as (NH4)aY(CO3)b(OH)c·nH2O, a< 1, 1< b< 2, c=3+a-2b. A fine crystal of ammonium yttrium double carbonate with the formula of (NH4)Y(CO3)2·H2O can also be obtained as using an enough amount of ammonium bicarbonate and aging enough time.
文摘Ultra fine ceria was prepared by calcining hydrate cerium acetate. The effects of pyrolysis temperature on the particle size, morphology, specific surface area and loose packing density of ceria were investigated, and the removal rate of optical glasses polishing by ceria was determined. The results show that with the increase of pyrolysis temperature, the loose deposit density and crystallinity increases and the specific surface area decreases, however, the particle size decreases firstly and then increases, the minimum medium particle size D50 is 0.47 μm at pyrolysis temperature of 1 000 ℃. The SEM images of ceria prepared by the decomposition at 800 ℃ or at 1 100 ℃ show porous powders or quasi-sphere small particles with loosely agglomeration, respectively. It was found that the removal rate varied with pyrolysis temperature in preparation of ceria and the property of glass polished. The removal rate for three kinds of glasses was in the order of ZF7> F1> K9, and the maximum value appeared at around 1 000 ℃ for ZF7 and F1, and at around 1 100 ℃ for K9.
文摘Amorphous Neodymium carbonate was prepared by the precipitation reaction of neodymium chloride with ammonium bicarbonate in solution, and then aged at 60 ℃ to form crystalline neodymium carbonate. The feed molar ratio of nNH4HCO3/nNdCl3 was 2.5, and the precipitation was carried out with or without addition of polyglyceryl fatty acid ester (PGFAE). The phase type and morphology of crystalline neodymium carbonates were examined by XRD and SEM, and the effect of PGFAE on the crystallization speed was investigated by volume change in deposit layer and in situ pH determination. The content of neodymium and chloride in crystals was analyzed, and the crystallization reaction or crystal growth characteristics were discussed. It was found that all the crystalline neodymium carbonates were tengerite type, and contained less crystalline water and chloride than that of lanthanite type neodymium carbonate crystallized at room temperature, which is beneficial to the production of neodymium carbonate with higher neodymium and lower chloride content. The addition of PGFAE not only could eliminate the foam formed during precipitation, but also could shorten crystallization time, and form large radiative-like shape conglomeration by the irregulative linkage of one dimension needle crystals. It is also suggested that the morphology and the chloride content of neodymium carbonate were dependent on the structure and crystal growth characteristics.
