大腔体压机腔体压强28 GPa的标定方法

Pressure Calibration Method of 28 GPa for Large-Volume Press

在大腔体压机中,一般利用压标物质相变时的电阻变化进行腔体压强标定,但目前仍缺少在22.5~34.5 GPa区间的相变压标物质。地球深部矿物50%MgSiO_(3)-_(50)%Al_(2)O_(3)(En_(50)Cor_(50))在高温高压下转变为钙钛矿结构,且在27 GPa以上钙钛矿结构MgSiO_(3)中溶解的Al_(2)O_(3)含量随压力升高而增加。为此,选取En_(50)Cor_(50)作为大腔体压机中28 GPa的压标物质进行高压腔体压强的间接标定。首先,利用常用压标物质的相变进行腔体压强标定,得到低压区系统油压-腔体压强的校正曲线(6.0~22.5 GPa);随后,根据低压区校正曲线及前人对En_(50)Cor_(50)的研究结果,估算28 GPa腔体压强对应的系统油压;将En_(50)Cor_(50)在预估油压、2000 K温度条件下保温3~7 h;最后,利用X射线衍射、拉曼光谱、电子探针等手段对En_(50)Cor_(50)进行测试分析。结果表明:在该条件下成功合成了布里奇曼石,且Al2O_(3)的溶解度大于13.7%,对照前人的研究结果,确定样品腔体压强约为29 GPa。该方法成功标定了大腔体压机在28 GPa附近的腔体压强,填补了大腔体压机在该压强范围的标定空白。

In the large-volume press(LVP),the pressure calibration for the sample chamber is generally carried out by using phase transitions of specific materials with resistance changes.But there are no suitable materials for pressure calibration in the range of 22.5-34.5 GPa.As we know,the mineral 50 mol%MgSiO_(3)-_(50) mol%Al_(2)O_(3)(En_(50)Cor_(50))systems in deep earth undergo structural transition to perovskite phase under high pressure and high temperature(HPHT)conditions.Moreover,the content of Al_(2)O_(3) dissolved in perovskite MgSiO_(3) increases gradually with raised pressure above 27 GPa.Therefore,En_(50)Cor_(50) was selected as the pressure calibration material for further calibrating 28 GPa in the LVP in this study,and this is an indirect pressure calibration method.First,the low-pressure calibration curve(6.0-22.5 GPa)of system oil pressure versus chamber pressure was obtained by using the phase transitions of different pressure calibration materials.Then,based on the low-pressure calibration curve and previous research results En_(50)Cor_(50),the estimated system oil pressure corresponding to the 28 GPa of chamber pressure is 65 MPa.At the estimated oil pressure,the En_(50)Cor_(50) samples were heated to 2000 K and maintained for 3-7 h.The results of X-ray diffraction,Raman,and electron probe measurements indicate that bridgmanite has been successfully synthesized,and the dissolved Al2O_(3) molar fraction is greater than 13.7%.According to the previous research results,the corresponding sample chamber pressure is about 29 GPa.This method successfully calibrated the sample chamber pressure around 28 GPa in the LVP,which fill in the blanks for calibrating this pressure range.