用Flash DSC研究硝酸铵的相变特征与规律

采用闪速差示扫描量热法(Flash DSC)对硝酸铵(AN)的晶型转变与结晶特征进行研究,获得了相应转变过程的特征规律并根据Kissinger方程计算了相变动力学参数。结果表明,随着升温速率从100K/s增加到5 000K/s,AN各相变的峰形在逐渐增宽,Ⅴ→Ⅳ型晶转起始温度显著向低温漂移,Ⅳ→Ⅲ型、Ⅲ→Ⅱ型、Ⅱ→Ⅰ型晶转起始温度略向高温漂移。从-10~-3 500K/s的降温速率试验中,AN可逆的各级相变均存在显著"过冷"现象,AN的结晶峰温、Ⅰ→Ⅱ型、Ⅱ→Ⅲ型、Ⅲ→Ⅳ型晶转峰温均向低温方向偏移,AN在-10~-500K/s和-1 000~-3 500K/s两种降温速率范围下其结晶、Ⅰ→Ⅱ型晶转、Ⅱ→Ⅲ型晶转活化能值Ea分别为761.11、570.98、700.71kJ/mol和102.48、82.16、166.76kJ/mol,指前因子ln(A/s-1)分别为-213.27、-183.76、-267.25和-29.26、-26.71、-64.38。

Investigation on Phase Transformation Characteristics and Regulars of Ammonium Nitrate(AN) Using Flash DSC

The crystal transformation and crystallization characteristics of ammonium nitrate(AN)were studied using Flash DSC method. The characteristic regulars corresponding to the transformation process were obtained, and the phase transformation kinetic parameters were calculated based on Kissinger′s equation. The results show that with the increase of heating rate from 100K/s to 5000K/s, the shape of each phase transformation peak of AN gradually widens. The starting temperature of the crystal transformation of Ⅴ→Ⅳ is significantly shifted to low temperature, and the starting temperature of the crystal transformation of Ⅳ→Ⅲ、Ⅲ→Ⅱ、Ⅱ→Ⅰis slightly shifted to high temperature. In cooling rate test from -10K/s to -3500K/s, there were obviously super-cooled phenomenon in the reversible phase transitions of AN, the peak temperature of the crystallization of AN, Ⅰ→Ⅱ,Ⅱ→Ⅲ,Ⅲ→Ⅳ are shifted to low temperature. The activation energies Ea of the crystallization and crystal transformation of Ⅰ→Ⅱ、Ⅱ→Ⅲ under two kinds of cooling rate range -10~-500K/s and -1000~-3500K/s are 761.11, 570.98, 700.71kJ/mol and 102.48, 82.16, 166.76kJ/mol, respectively. The pre-exponential factors ln (A/s-1) are -213.27、-183.76、-267.25 and-29.26、-26.71、-64.38,respectively.