Fe^(3+)掺杂对硝酸羟胺热稳定性的影响及其机理

Effects of Doping of Fe^(3+) on the Thermal Stability of Hydroxylamine Nitrate and Its Mechanism

为研究Fe^(3+)掺杂对硝酸羟胺(HAN)热稳定性的影响,在升温速率分别为3、4、5K/min下对无Fe^(3+)以及Fe^(3+)掺杂的HAN水溶液进行热分析。借助非等温DSC曲线的参数值,应用Kissinger和Ozaw方法分别计算热分解反应动力学参数。采用密度泛函方法对影响机理进行研究,优化得到NH2OH及其与Fe^(3+)形成配位化合物Fe(NH2OH)3+6的稳定构型,计算了N-H和O-H键的键长、Wiberg键级以及分子的前线轨道分布。结果表明,Fe^(3+)掺杂使得硝酸羟胺的热稳定性降低,使HAN的起始分解温度平均降低约16℃,表观活化能略有升高,指前因子大幅增加,热分解反应速率提高;NH2OH与Fe^(3+)形成配位化合物Fe(NH2OH)3+6后,N-H和O-H键的键长增加,伸缩振动频率减弱,Wiberg键级减小,键周围的电子云密度减小,键的强度减弱,加快了HAN的热分解。

To investigate the effect of doping of Fe^(3+)on the thermal stability of hydroxylamine nitrate(HAN),the thermal analysis of HAN aqueous solution with and without Fe^(3+)doped was carried out at heating rates of 3,4and5K/min.With the help of parameter values from the non-isothermal DSC curves,the kinetic parameters of the thermal decomposition reaction were obtained by Kissinger′s method and Ozawa′s method.Density functional theoretical method was used to study the influence mechanism.The optimized geometries of NH2 OH and coordination compound Fe(NH2OH)3+6formed by NH2 OH and Fe^(3+)were obtained.The bond length of N-H and O-H,Wiberg bond order and molecular frontier orbital distribution were calculated.The results show that Fe^(3+)doping makes the thermal stability of HAN decrease and the initial decomposition temperature decrease by 16℃,the activation energy increase and pre-exponential factor increase greatly,and the reaction rate of thermal decomposition increase.After coordination compound Fe(NH2OH)3+6formed by NH2 OH and Fe^(3+),the bond length of N-H and O-H increases,the stretching frequency,Wiberg bond order and electron cloud density around bonds decrease.The bond strength decreases,which lead to the acceleration of the thermal decomposition of HAN.