六氨氯化镁热分解的TG-DTA,DSC研究

Investigation of Thermal Decomposition of Hexammoniate Magnesium Chloride by TG-DTA and DSC

对水氯镁石合成的六氨氯化镁,用化学分析和XRD进行表征,采用热重(TG-DTA)和示差扫描量热(DSC)等热分析方法,研究了六氨氯化镁热分解的特性,获得了分解热和非等温动力学参数。(1)TG-DTA显示六氨氯化镁热分解过程表现为四个脱氨反应阶段,采用Ozawa法,等转化率计算得到各反应阶段表观活化能分别为:92.25 kJ/mol,100.069kJ/mol,139.23 kJ/mol、157.07 kJ/mol;等温计算指前因子分别为0.129×1011/S,2.714×1011/S,56.27×1011/S,46.78×1011/S。(2)DSC显示六氨氯化镁的热分解过程有四个吸热阶段,吸热量分别为0.685 kJ/g,0.285 kJ/g,0.072 kJ/g,0.036 5 kJ/g,总吸热量为1.408 kJ/g。(3)综合TG-DTA和DSC结果,认为TG-DTA的第二三个峰是中温阶段的两个过程,而DSC的第三四个峰是高温阶段的两个过程,这样六氨氯化镁热分解过程可粗分三个阶段,每个阶段吸收热量和释放氨的个数分别为:低温阶段0.685 kJ/g,3.5个氨;中温阶段0.285 kJ/g,1个氨;高温阶段0.437 kJ/g,1.5个氨。按释放每摩尔氨所需热计,三个阶段吸热分别为了38.64 kJ/mol,56.37 kJ/mol,57.41 kJ/mol。

The hexammoniate magnesium chloride （MgCl2·6NH3 ） , which was synthesized by bischofite, was characterized by chemical analysis and X - ray powder diffraction. Thermal decomposition and non-isothermal kinetic evaluation were studied with thermogravmetry（TG）, differencial thermal analysis （DTA） and differential scanning calorimeter （ DSC ）. TG - DTA results showed that the thermal decomposition of MgCl2·6NH3 was divided into four stages. Based on Ozawa method the calculated activation energy at each thermal decomposition stage were 92.25 kJ/mol, 100.069 kJ/mol , 139.23 kJ/mol and 157.07 kJ/mol respectively. The corresponding pre - exponential factors were 0.129 ×10^11/S, 2.714×10^11/S, 56.27×10^11/S, 46.78 ×10^11/S respectively. DSC results showed that the thermal decomposition of MgCl2·6NH3 have four endothermic stages. The heat of endothermic were 0. 685 kJ/g, 0.285 kJ/g, 0. 072 kJ/g, 0. 036 5 kJ/g for each stage respectively and 1. 408 kJ/g total process. Compared with TG - DTA and DSC results, it was considered that the second and third peaks in TG - DTA are the two parts of the middle temperature stage and the third and fourth peaks in DSC are the two parts of the high temperature stage. Thus, the thermal decomposition of MgCl2·6NH3 were briefly divided into three stages, the heat and the number of ammonia molecule losed were 0. 685 kJ/g and 3.5 in lower temperature stage, 0.285 kJ/ g and 1 in middle temperature stage, 0. 437 kJ/g and 1.5 in high temperature stage. Based on the losed ammonia molecule, the heat of endothermie were 38.64 kJ/mol, 56.37 kJ/mol, 57.41 kJ/ mol for each stage respectively.