Experimental study on kinetics of the olivine-spinel phase transition.

在本研究中，我们利用镁GeO_4类似物提出了橄榄石-尖晶石转变的初步动力学数据，已经在0.07 GPa下进行了作为H_2O含量的函数的等温实验，以考察H_2O含量对Mg_2GeO_4橄榄石-尖晶石转变的影响。在本研究中，还尝试使用新引进的高压型反应器在较高压力(0.15 Gpa)下进行附加动力学实验，但大多数运行都因机器故障(主要是压力泄漏)而失败。在一系列实验中，包封了少量的氢氧化镁，通过改变其量来控制H_2O(X)的含量，并随时间进行水热加热。通过将每组温度和X‘s下的实验数据与Avrami方程进行拟合，得出了橄榄石-尖晶石相变首次可检测到的特定时间(Ts)。得到了每组温度下的T_s和0.07 Gpa下的X_s。然而，由于在每组温度和0.15 GPaX的情况下只成功地进行了几次运行，具体时间无法确定。因此，不能系统地讨论压力(0.07~0.15 Gpa)对Mg_2GeO_4橄榄石*尖晶石转变动力学的影响。然而，考虑到即使是少量的H_2O也能极大地激活Mg_2GeO_4橄榄石*尖晶石相变的形核速率，可以肯定地说，压力的影响似乎比水的量对转变的影响要小得多。

In the present study, we aimed to propose the preliminary kinetics data for the olivine*spinel transition by using the Mg_2GeO_4 analogue, Isothermal experiments had already been carried out as a function of H_2O content at 0.07GPa to examine the effect of the amount of H_2O on the Mg_2GeO_4 olivine-spinel transition. In the present study, the additional kinetic experiments were also tried to carry out at the higher pressure(0.15GPa)by using a newly-introduced high-pressure type reactor, but the most of these runs met with failure simply because of the machine trouble (mainly a pressure leak). In a series of these experiments, small amounts of Mg(OH)_2 was enclosed to control the content of H_2O (X) by varying its amount, and was heated hydrothermally as a function of time. By fitting the experimental data at each set of temperatures and X's to the Avrami equation, a specific time (ts) was derived at which the olivine-spinel phase transition is first detectable. The ts had been obtained at each set of temperatures and X's at 0.07GPa. However, since only a few runs were successfully performed in each set of temperatures and X's at 0.15GPa, the specific times could not be determined. Consequently, the effect of the pressure (between at 0.07GPa and 0.15GPa) on the kinetics of the Mg_2GeO_4 olivine*spinel transition could not be systematically discussed. However, it may safely be said that the effect of the pressure seems to be considerably smaller than the effect of the amount of H_2O on the transition by considering the fact that even a small amount of H_2O drastically activates the nucleation rate in the Mg_2GeO_4 olivine*spinel transition.