Structural Transition Of Silicon Dioxide, Carbon And Silicon Under High Pressure And High Temperature

Silica is a kind of mineral that exists widely in nature. It has many kinds of polymorphs and each polymorph can transit another under different temperatures and different pressures, therefore, we can infer how the rocks near the Earth's surface form by the study of the silica near the Earth's surface. Coesite is a polymorph of silica existed in high pressure. Coesite is result of ultrahigh-pressure metamorphism. The discovery of coesite bearing rocks indicates that the rocks near the Earth's surface have been subducted by strong tectonic movement to the depth of more than 90km by plate movements and experienced ultrahigh-pressure metamorphism there.For 50 years,the study of coesite in the earth′s surface has been regarded as a"window"for knowing the earth.In labs, much work on the synthesis of coesite by a high static pressure and high temperature.,including the effect of the initial state of materials on the synthesis of coesite has been carried out.As a kind of typical extreme condition, high-pressure method has been developed fast recent years on the aspects of big chamber and high pressure. The properties of high-pressure method are shortening the distance between the atoms effectively, changing the states of electrons and affecting phrases changing courses. In the condition of high pressure and high temperature, the materials are given high energy. So the high pressure method is effective to synthesize new materials. High pressure and high temperature method can mimic the state in the Earth. That can enlighten and help us on comprehending many geologic phenomena.In this paper, we were selected the mixture of graphite,α-quartz and silicon(mixed mass ratio silicon : graphite :α-quartz = 18:1:6), the mixture of α-quartz, graphite and silicon (mixed mass ratio silicon : graphite :α-quartz = 3:3:1)as original materials. The original materials were treated with high-energy mechanical ball milling and high temperature and high pressure method combining the mixture of two structural phase transitions .The experimental results show that, the mixture of graphite,α-quartz and silicon (mixed mass ratio ofα-quartz: graphite: silicon = 6:1:18), after 10h ball milling, under 3.8GPa, 1273K temperature and pressure conditions, We found theα-quartz crystal; the sample after 15h and 20h ball milling , under 3.8GPa, 1273K temperature and pressure conditions, We found theα-quartz , silicon crystals, and coesite crystals. 15h than 20h milling samples of the formation of coesite stronger peak intensity, peak shape too. Samples after 40h ball milling in 3.8GPa, 1273K temperature and pressure conditions, We found Fe3Si.. There are Coesite synthesis of milling time threshold, that is, 15h≤tmil <40h.The mixture of graphite,α-quartz, and silicon (mixed mass ratio ofα-quartz: graphite: silicon = 1:3:3),the samples after 20h of ball milling in 3.8GPa, 1273K temperature and pressure conditions,we foundα-quartz crystal, graphite crystal and silicon crystal; milling 30h and 40h the sample in 3.8GPa, 1273K temperature and pressure conditions , coesite are generated. And milling of the samples obtained 40h is the single-phase coesite; milling 60h samples in 3.8GPa, 1273K under the conditions of temperature and pressure to form silicon carbide. There are also synthetic coesite threshold of the milling time, that is, 20h