稀土氧化物对高氯酸铵热分解的作用及机制

Role and Mechanism of Rare Earth Oxides in Decomposition of Ammonium Perchlorate

采用草酸沉淀法、碳酸氢铵沉淀法和乙二醇溶胶凝胶法制备了多种稀土氧化物,用差热分析技术比较了不同稀土氧化物对高氯酸铵热分解的催化作用。结果表明:所有稀土氧化物均能使高氯酸铵的第一放热峰滞后,而第二放热分解峰提前;随着稀土添加量的增加,两分解峰逐渐靠近,最终合并为一个分解放热峰,分解热也大大提高。不同稀土氧化物种类对高氯酸铵热分解的催化作用有一定的差异,轻稀土镨和钕的氧化物使分解峰表现为前弱后强的两个相连的峰,中稀土钐和钆的氧化物表现为单一的强峰,而重稀土铒和镱的氧化物表现为前强后弱的两个分立的放热峰。对于同一种稀土氧化物,制备方法的不同对催化高氯酸铵的热分解也有差异,这与产物的比表面积有关,随着产物比表面积的增加,催化效果越明显。用能带理论解释了氧化稀土对AP热分解过程的影响,把氧化稀土作为半导体来考虑,正是由于它们储存和释放电子的功能性质导致了AP第一分解峰的滞后和第二分解峰的提前。

Various rare earth oxides were synthesized respectively by precipitation with oxalate acid,ammonium bicarbonate as well as glycol sol-gel methods.Their catalytic effects on the decomposition of ammonium perchlorate（AP）were studied using differential thermal analysis（DTA）techniques.It can be seen from their DTA curves that the addition of rare earth oxides could make the first exothermal peak of ammonium perchlorate hysteresised and the second exothermal peak advanced.With the addition amount of rare earth oxide increasing,the two exothermal peaks of AP came closer and finally merge into one strong peak with a great increase of decomposition heat.The catalyzing action caused by different rare earth oxides was different.Two adjacent exothermal peaks with former weak and later strong were observed in the DTA curves of AP mixed with 5% lighter rare earth oxides Pr6O11 or Nd2O3,one strong peak for middle rare earth oxides Sm2O3 or Gd2O3,and two separated peaks with former strong and later weak for heavier rare earth oxides Er2O3 or Yb2O3.Difference also existed among the Gd2O3 powders prepared by different methods,which was attributed to the difference of their specific surface area.The catalytic activity of oxides increased with their specific surface area increasing.The effect of rare earth oxides on the thermal decomposition of AP was explained by energy band theory.Rare earth oxides can be considered as typical semiconductors.It was their functional property of storing and releasing electron that resulted in the hysteresising of first exothermal peak or advancing of the second exothermal peak.