制备纳米氧化锌前驱体碱式碳酸锌的热解动力学

Research on mechanism and kinetics of the thermal decomposition of precursor basic zinc carbonate in the preparation of nanometer zinc oxide

采用碳酸氢铵法由粗氧化锌制备纳米氧化锌。研究了碳酸氢铵法制备纳米氧化锌前驱体碱式碳酸锌的组成、热解温度、纳米氧化锌晶型,以及前驱体热解动力学。研究表明:前驱体碱式碳酸锌的组成为Zn5(CO3)2(OH)6,它在222℃左右开始分解,在250℃左右强烈分解为氧化锌、水和二氧化碳,温度高于265℃后分解接近完全。前驱体在600℃下热解1h得属于六方晶系的纳米氧化锌,空间群为C46V%DP63mc。Zn5(CO3)2(OH)6热解反应的表观活化能Ea为184.59kJ/mol,表观频率因子A为4.98×1018s-1,动力学机理就是随机核化机理,遵从Aurami方程Ⅱf(α)=3(1-α)[-ln(1-α)]2/3。

The nanometer zinc oxide is prepared from coarse zinc oxide by ammonium bicarbonate method.The composition of basic zinc carbonate which is the precursor of nanometer zinc oxide preparation,thermal-decomposition temperature,crystal form of nanometer zinc oxide and kinetics of thermal-decomposition of the precursor are studied.The results indicate that the composition of basic zinc carbonate is Zn_5(CO_3)_2(OH)_6,it begins decomposition at 222 ℃ and decomposes into zinc oxide,water and carbon dioxide at about 250 ℃ and decomposes completely above 265 ℃.The hexagonal crystal nanometer zinc oxide can be obtained when the precursor is heated at 600 ℃ for 1 h.,the space group is C^4_(6v)-P6_3 mc.The apparent activation energy Ea of precursor thermal-decomposition reaction is 184.59 kJ/mol,its apparent frequency factor A is 4.98×10^(18) s^(-1).Its kinetics mechanism belongs random nucleation mechanism and obeys the equation of AuramiⅡ,e.g.f(α)=3(1-α)\^(2/3).