碳酸镨的结晶活性、外观形貌及结晶生长机制

采用原位pH值测定法确定了碳酸镨的结晶活性区域,并用扫描电镜观测了不同结晶区域结晶碳酸镨的外观形貌.结果表明在低配比区域(NH4HCO3/PrCl3的摩尔比小于3)为碳酸镨的易结晶区域,结晶产物为交叉层叠的花瓣形颗粒;在高配比区域(NH4HCO3/PrCl3的摩尔比大于3)为碳酸镨的可结晶区域,延长陈化时间可以得到鱼鳞片状的亮晶产物;所有结晶碳酸镨都具有镧石型结构,其基本构筑单元为片状结晶,这与镧石的层状结构相关.影响结晶的主要因素是加料比,其它因素象温度,加料方式和搅拌强度等对结晶过程也有影响.     

碳酸氢铵与氯化钇反应及结晶产物的组成和晶相类型

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 tempera-ture, 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.     

水菱钇型碳酸钕的形成及聚甘油脂肪酸酯对结晶的影响

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 n_(NH4HCO3)/n_(NdCl3 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.     

镧石型碳酸钕的形成及晶种对结晶的促进作用

The characteristics of pH value variation during aging process of amorphous neodymium carbonate formed by three different feeding manners have been investigated. The promotion action of seeding on the crystallization of neodymium carbonate is discussed. X-ray diffraction pattern and the elemental analysis results show that neodymium carbonate can transfer from amorphous to crystalline normal neodymium carbonate Nd₂(CO₃)₃·8H₂O with lanthanide structure at room temperature. Its crystallization activity zone lies in lower feeding ratio area expressed by n_NH4HCO3/n_NdCl3 between 2～3. The existing of seeds can shorten crystalline time, from more than 15 h without seed to 2 h with seeds under normal feeding manner. And the spontaneity nucleation time can be shortened further when feeding with multi-steps normal manner. However, whether multi-steps normal or synchronously and continuously feeding manner, the precipitate formed can transfer to crystalline neodymium carbonate directly under seeding. At the same time, it is observed that the variation of pH value reduces with the decrease of feeding amount and the shortening of aging period, indicating that with synchronously and continuously feeding manner can not only realize fast crystallization, but also control pH value within a narrow range, which is beneficial for the producing of neodymium carbonate crystal with narrow-distributed particle size and monitoring of its crystallization process.     

碳酸钇铵复盐结晶的形成及影响因素

对碳酸氢铵沉淀钇时碳酸钇铵复盐结晶的形成条件与ｐＨ变化特征进行了研究,发现其结晶过程与平衡溶液ｐＨ有对应关系。溶液ｐＨ由碳酸钇铵结晶化反应和碳酸氢铵的水解反应所控制。根据溶液ｐＨ的变化可以判断结晶反应是否发生或完成,以及结晶速度的快慢和结晶的程度。Ｘ－射线衍射及差热－热重分析结果表明,产物为复盐结晶２,加料方式对结晶的形成有很大影响。     

稀土Tb3+,Eu3+对N-苯基邻氨基苯甲酸及邻菲咯啉间能量传递与蓝色发射的强化作用

合成了一种由稀土离子与N—苯基邻氨基苯甲酸(N—HPA)和邻菲咯啉(phen)形成的蓝色发光配合物。该配合物是典型的配体发光配合物，其发射峰位于444nm，激发波长为334nm和407nm。元素分析、红外光谱、紫外—可见光谱和差热—热重的分析结果表明：配合物中含有大量的N—HPA和相对较少的稀土离子和phen，其中稀土离子与N—PA中的羧酸根配位，而N—PA中的氨基通过氢键与phen的氯原子结合，形成了有利于配体之间的能量传递和电子转移的通道。稀土离子Tb^3 ，Eu^3 的共同存在促进了这一能量转移通道的形成，进而强化了配体的蓝色发射。