盐卤硼酸盐化学 Ⅻ.MgO·3B_2O_3·7H_2O的热行为和脱水动力学

CHEMISTRY OF BORATE IN SALT LAKE BRINE ⅩⅠⅠ. THERMO-BEHAVIOUR OF MgO ·3B_2O_3 ·7H_2O AND KINETICS OF DEHYDRATION

通过对合成MgO·3B__2O_3·7H_2O的热分析研究确定热脱水反应的阶段、温度和产物,给出脱水过程的热化学反应方程式.利用甲醇、水与三氧化二硼之间的酯化反应进行相分离,确定该化合物高温结晶化产物的物相组成为晶态六硼酸镁(2MgO·3B_2O_3)和无定形B_2O_3.对该化合物的TG和DTG数据进行处理结果,给出了相应的非等温热脱水反应动力学方程.

In this paper, the thermo-behaviour of MgO ·3B2O3 ·7H2O and kinetics of dehydration during heating have been studied by DTA, TG, DTG, X-ray powder diffraction and IR-spectra. It is found that there appears only two phase transition process during dehydration as following The results of X-ray powder diffraction and IR-spectra show that the product of the first step dehydration at 122℃, MgO ·3B2O3 ·5H2O,is different from that of the natural mineral. At 762℃ , the amorphous product of dehydration ,MgO ·3B2O3, will be decomposed to form an amorphous B2O3 and crystal 2MgO ·3B2O3 of which the composition is confirmed by chemical analysis after esterification with methyl-alcohol. The Freeman-Carroll method was used to calculate the parameter in kinetic equations of dehydration using the data of TG and DTG. It is obtained that the kinetic equations of step of dehydration are as following: the kinetic equation of the first step of dehydration is the kinetic equation of the second step of dehydration is