Kinetics of the thermal dehydration of magnesium oxalate dihydrate in a flowing atmosphere of dry nitrogen
Kinetics of the thermal dehydration of magnesium oxalate dihydrate in a flowing atmosphere of dry nitrogen
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二水草酸镁在流动干燥氮气气氛中热脱水的动力学
DOI：
10.1021/j100310a024
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
Yoshio N. Ito
中科院分区：
文献类型：
--
作者：
Y. Masuda;K. Iwata;Ryōkou Ito;Yoshio N. Ito
本文利用在微型计算机上获得的大量准确的热重数据，详细研究了在干氮气中，镁碳化物的等温脱水动力学。这种脱水是以二维相界反应R2进行的。一般而言，相界反应中的成核速度非常快，只有遵循发生在反应物-产物界面上的化学过程才能确定反应速率。但目前的脱水受成核过程的影响，其脱水分数曲线呈S型特征，特别是在低于160℃的温度下。我们通过对脱水分数曲线的详细分析，成功地分别估算了成核速率常数KN和R2过程的速率常数K2。在较低温度下，KN值与K2值相当，而在较高温度下，KN值比K2值大得多，整个脱水过程具有自然R2反应的特征。由KN和K2的温度依赖性确定了两个过程的活化能和指前因子的值。成核过程分别为430kJ·mol~(-1)和3.73×1049·S~(-1)，二维相界过程分别为111kJ·mol~(-1)和3.40×10~9·S~(-1)。
The kinetics of isothermal dehydration of MgC204-2H20 in a dry nitrogen flow have been studied in detail by use of many accurate thermogravimetric data acquired on a microcomputer. This dehydration proceeded as a two-dimensional phase boundary reaction, R2. In general, the nucleation in the phase boundary reaction occurs so rapidly that the reactionrate is only determined by following the chemical process occurring at the reactant-product interface. However, the present dehydration was affected by the nucleation process, and itsdehydration fraction curve showed a sigmoidal character especially at lower temperatures than ca. 160 C. We succeeded in separately evaluating the rate constants kN for the nucleationand k2 for the R2 process by detailed analysis of the dehydration fraction curve. The value of kN became comparable to that of k2 at lower temperatures, whereas at higher temperature the former became much larger than the latter and the overall dehydration had a characteristic of natural R2 reaction. The values of activation energies and preexponential factors for both processes were determined from the temperature dependency of kN and k2. Those were 430 kJ mol'1 and 3.73 X 1049 s'1 for the nucleation process, and 111 kJ mol'1 and 3.40 X 109 s'1 for two-dimensional phase boundary process, respectively.