非团聚二钼酸铵热分解机理及热力学分析

Thermal Decomposition Mechanism and Thermodynamic Analysis of Non-agglomerated Ammonium Dimolybdate

通过DSC-TGA研究了非团聚二钼酸铵在室温至800℃温度范围内的热分解过程。结果表明:非团聚二钼酸铵在室温至800℃温度范围内的失重过程包含了4个连续阶段,各阶段反应温度区间为196.79~206.63℃、227.55~235.15℃、278.06~305.68℃和735.97~800℃。经分析,非团聚热分解实际只包括前3阶段,第4阶段的失重是由于前3阶段热分解产物的升华而引起的。XRD和SEM表征显示:非团聚二钼酸铵热分解产物为纯相MoO_(3),其形貌遗传了母体二钼酸铵的形貌,并对MoO_(3)形貌的形成机理进行了探讨。提出了非团聚二钼酸铵的热分解机理并进行理论验证,在热分解的前3个阶段均失去摩尔比为2∶1的NH_(3)和H_(2)O。通过各阶段的热反应焓变值,计算了实验室条件下非团聚二钼酸铵及热分解中间产物(NH_(4))_(2)Mo_(3)O 10(s)、(NH_(4))_(4)Mo_(8)O_(26)(s)和(NH_(4))_(2)Mo_(2)O_(7)(s)的标准摩尔生成焓以及非团聚二钼酸铵热分解反应的标准摩尔焓变。

The thermal decomposition process of non-agglomerated ammonium dimolybdate in the temperature range of room temperature to 800℃was studied by DSC-TGA.The results show that the weight loss process of non-agglomerated ammonium dimolybdate in the temperature range of room temperature to 800℃includes four continuous stages,and the reaction temperature ranges of each stage are 196.79~206.63℃,227.55~235.15℃,278.06~305.68℃and 735.97~800℃.After analysis,the actual decomposition of non-agglomerate thermal decomposition only includes the first three stages,and the weight loss in the fourth stage is caused by the sublimation of the products in the first three stages.XRD and SEM characterization showed that the thermal decomposition product of non-agglomerated ammonium dimolybdate was pure phase MoO_(3),and its morphology inherited the morphology of parent ammonium dimolybdate.The formation mechanism of MoO_(3) morphology was discussed.The mechanism of thermal decomposition of non-agglomerated ammonium dimolybdate was proposed and verified theoretically.NH_(3) and H_(2)O with molar ratio of 2∶1 were lost in the first three stages of thermal decomposition.The standard molar enthalpies of formation and thermal decomposition of non-agglomerated ammonium dimolybdate and its intermediate products(NH_(4))_(2)Mo_(3)O_(10)(s)、(NH_(4))_(4)Mo_(8)O_(26)(s)and(NH_(4))_(2)Mo_(2)O_(7)(s)were calculated by the enthalpy changes of thermal reaction in each stage.