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本文采用热重法(TG)和差热分析法(DTA)测定了大黄酸和大黄素的DTA,TG-DTG曲线。两者的DTA曲线中皆有两个较为明显的吸热峰,第一个在熔化过程中出现,第二个发生在热分解过程中并伴随有明显的失重现象。TG曲线均有一个失重平台,失重率在90%以上。用TG-DTG法对两者在非等温条件下进行热分解动力学研究,把从TG-DTG曲线中取得的数据和31个不同的方程采用Achar微分法和Madhusudanan-Krishnan-Ni-nan(MKN)积分法对其进行非等温分解动力学研究,得到动力学参数活化能(E和指前因子A)和分解动力学机理及方程。得出结论:大黄酸和大黄素的动力学方程为dα/dt=Aexp(-E/RT)3/2(1-α)4/3[1/(1-α)1/3-1]-1和dα/dt=Aexp(-E/RT)3/2(1-α)2/3[1/(1-α)1/3]-1,其分解等合3D抗理。二者的活化能E(kJ/mol)分别为117.6和86.79,lnA/s-1分别是36.72和27.44。
In this paper, the DTA and TG-DTG curves of rhein and emodin were determined by thermogravimetry (TG) and differential thermal analysis (DTA). Both of the DTA curves have two distinct endothermic peaks, the first occurring during the melting process and the second occurring during the thermal decomposition process with a significant weight loss. The TG curve has a weightlessness platform with a weight loss rate of over 90%. The TG-DTG method was used to study the thermal decomposition kinetics of the two under non-isothermal conditions. The data obtained from the TG-DTG curve and 31 different equations were analyzed using Achar differential method and Madhusudanan-Krishnan-Ni-nan (MKN). Integral method was used to study the kinetics of non-isothermal decomposition, and the activation energy (E and pre-exponential factor A) of kinetic parameters and the decomposition kinetics and equations were obtained. It is concluded that the kinetic equation of rhein and emodin is dα/dt=Aexp(-E/RT)3/2(1-α)4/3[1/(1-α)1/3-1] -1 and dα/dt = Aexp(-E/RT)3/2(1-α)2/3[1/(1-α)1/3]-1, whose decomposition is equivalent to 3D resistance. The activation energies E (kJ/mol) of the two were 117.6 and 86.79, respectively, and the lnA/s-1 were 36.72 and 27.44, respectively.