热分析法研究冬凌草甲素的热稳定性和分解动力学

Thermal Stability and Decomposition Kinetics of Oridonin by Thermal Analysis Method

研究加热条件下冬凌草甲素的热稳定性、分解动力学和贮存期。利用热重-微商热重（TG-DTG）和差热-微商差热（DTA-DDTA）分析技术，测得冬凌草甲素在氮气气氛中不同升温速率（β）下的热分解曲线，结合使用Kissinger法、Ozawa法、Coats-Redfern法和Achar法进行动力学分析，根据热分解的表观活化能（Ea）和指前因子（A）计算推断冬凌草甲素的贮存期。结果显示：随着升温速率的提高，冬凌草甲素的热分解温度逐渐升高，冬凌草甲素失重分两阶段：1）206．4-493．0℃，失重率为84．8％；2）493．0-669．6℃，失重率为15．2％。DTA和DDTA曲线249℃出现一个主要吸热峰，675℃出现一个主要放热峰。冬凌草甲素的第一阶段热分解机制是三维扩散控制，对应的函数名称是Zhuralev-Lesokin-Tempelman方程。测得平均Ea为145．95kJ／mol，A为4．87Х10^10min^-1；根据第一步热分解的Ea和A推断，在室温25℃下，冬凌草甲素的理论贮存期为4-5年。

Thermal decomposing curves of oridonin at different heating speeds were obtained in the nitrogen atmosphere by TG-DTG and DTA-DDTA techniques to study the thermal stability, decomposition kinetics, and shelflife of oridonin under the heat condition. Four thermal analysis kinetic methods （Kissinger, Ozawa, Coats-Redfern and Achar） were used to speculate the probable mechanism of thermal decomposing reaction and the kinetic parameters including activation energy Ea and pre- exponential factor A. The shelflife of oridonin at room temperature （25℃） was calculated by the kinetic parameters of the first stage. With the increase of the heating rate, thermal decomposing tempreture of oridonin rose. The TG curve showed the decomposition of oridonin could be divided into two steps. The first weight loss rate was 84.8% from 206.4 ℃ to 493.0 ℃ and the second weight loss rate was 15.2% from 493.0 ℃ to 669.6 ℃. The DTA and DDTA curves showed an endothermic peak at about 249℃ and an exothermic peak at about 675℃. The most probable kinetic mechanisms of the first stage thermal decomposition were three-dimensional diffusion and the corresponding mechanisms followed Zhuralev-Lesokin-Tempelman Equation. The average apparent activation energy （Ea ） was 145. 95 kJ/mol and the pre-exponential factor （A） was 4.87Х10^10min^-1. The theoretical shelflife of oridonin at room temperature was about 4 -5 years.