Chemistry Laboratory, Department of Science Education, Graduate School of Education, Hiroshima University, 1-1-1 Kagamiyama, Higashi-Hiroshima 739-8524, Japan.
J Phys Chem A. 2013 Mar 7;117(9):1880-9. doi: 10.1021/jp3123924. Epub 2013 Feb 26.
The reaction mechanism and overall kinetics of the thermal decomposition of sodium percarbonate crystals were investigated by thermoanalytical measurements and morphological observations. The reaction proceeds via a surface reaction and subsequent advancement of the as-produced reaction interface toward the center of the crystals, where the seemingly smooth mass-loss behavior can be described by the apparent activation energy Ea of ca. 100 kJ mol(-1). However, considering the rate behavior, as the reaction advances, it is expected that the secondary reaction step characterized by an autocatalytic rate behavior takes part in the overall reaction. The hindrance of the diffusional removal of the evolved gases by the surface product layer, Na2CO3, is the most probable reason for the change in the reaction mechanism. In the deceleration part of the first reaction step, the second reaction step is accelerated due to an increase in the water vapor pressure at the reaction interface inside the reacting particles. We also expect the self-generated reaction condition of the high water vapor pressure and the existence of liquid phase due to the formation of Na2CO3 whiskers as the solid product and the insensitive rate behavior of the second reaction step to a higher atmospheric water vapor pressure. A relevant reaction model for the thermal decomposition of SPC crystals are discussed by focusing on the role of the surface product layer.
通过热分析测量和形态观察研究了过碳酸钠晶体热分解的反应机理和总动力学。该反应通过表面反应进行，随后生成的反应界面向晶体中心推进，在晶体中心，看似光滑的质量损失行为可以用约 100 kJ/mol 的表观活化能 Ea 来描述。然而，考虑到反应速率，随着反应的进行，预计以自催化速率行为为特征的二次反应步骤会参与到总反应中。表面产物层（Na2CO3）阻碍了释放气体的扩散去除，这是反应机理发生变化的最可能原因。在第一步反应的减速阶段，由于反应颗粒内部反应界面处水蒸气压力的增加，第二步反应会加速。我们还期望由于 Na2CO3 晶须的形成作为固体产物而产生的高水蒸气压力和液相的自生成反应条件，以及由于高大气水蒸气压力和第二反应步骤的不敏感速率行为而存在的液相，对 SPC 晶体的热分解有相关的反应模型进行讨论。
