室温固相法合成ZnCO_3及其自晶化特征

Synthesis of ZnCO_3 via Solid State Reaction at Room Temperature and the Characteristics of Its Spontaneous Crystallization

以ZnSO4-7H2O与NH4HCO3为原料,聚乙二醇-400为模板剂,经室温固相反应合成得到了ZnCO3纳米晶体,其粒径为25nm左右.实验结果表明,在始终保持NH4HCO3过量的条件下可抑制杂质的形成,得到结晶完好的ZnCO3纳米晶体;在研磨反应的20min内,产物ZnCO3已自动晶化成为完好的晶体,无需静置晶化,长时间的静置晶化反而会导致副产物碱式碳酸锌的生成;模板剂对产物组成具有重要的调控作用,有模板剂时得到的是ZnCO3纳米晶体,无模板剂时得到的是含有碱式碳酸锌与ZnCO3的混合物,但以碱式碳酸锌为主.与文献报道的微乳液法相比,可知模板剂是通过与反应物释放出来的结晶水在研磨搅拌作用下形成微乳液体系,从而对产物组成进行调控.

The nano-crystals of ZnCO3 were synthesized via solid state reaction at room temperature, when ZnSO4.7H20 reacted with NH4HCO3 containing PEG-400 as template, the average particle size of the crystals was about 25 nm. The experimental results showed that the crystals with ideal crystallization were obtained, while keeping NH4HCO3 excessive all the time to keep from impurity forming under optimal mixing of reactants. It was not necessary to let the reaction mixtures deposit for crystallization, for the product of zinc carbonate had spontaneously crystallized into ideal crystals within 20 mm grinding time. On the contrary, the byproduct would form in long depositing time, resulting in formation of basic zinc carbonate. The template reagent played a key role for controlling composition of the product. The product was nano-crystals of zinc carbonate with the template, and leaving the rest mixture without the template, which contained basic zinc carbonate in majority and zinc carbonate. Comparing the product with that from microemulsion synthesis method reported in the literature, it was supposed that the controlling role of the template was played via forming microemulsion with water releasing from crystallized water in the reactants during the grinding process.