Resonance method under fluid pressure to determine pressure derivatives of elastic constants and its application to the earth's interior

1. 气体压力和弹性常数压力导数下的实验以钢球为测试材料，在0.1GPa的氦气压力下进行了腔谐振测量，得到了几种环面模态（TM）和球面模态（SM）的压力依赖性。根据TM数据确定流速压力梯度为dG/dP=1.80 （] SY.+-）。[] [au:]体积模量的压力导数由SM数据确定为dKs/dP=4.27 （] SY.+-）。[) 0.27，假设样品-气体耦合可以忽略不计。结果表明，该方法的计算结果是合理的，验证了空腔共振法的有效性。在水中的测量和对高压的展望表明，在1atm充水的空腔测量中，不仅可以检测到TM，还可以检测到一些SM。由于水在1atm处的阻抗与氦气在1GPa左右的阻抗相对应，这一事实为更高的压力提供了一个有希望的前景。基于傅里叶变换（FT）方法（Suzuki et al., 1993），利用数字化示波器建立了一种新的数据采集系统。结果表明，该系统几乎可以检测到所有模式的光谱峰。烧结试样的应用采用高温高压烧结法制备了球形试样，测定了其弹性常数。结果表明，通过制备不同孔隙度的样品并外推至零孔隙度，可以得到有效的多晶样品弹性常数。

1. Experiments under gas pressure and pressure derivatives of elastic constantsMeasurements of cavity resonance were carried out up to 0.1GPa under helium gas pressure, using a steel sphere as test material, and pressure dependence of several toroidal (TM) and spheroidal modes (SM) were obtained. Pressure gradient of regidity was determined from TM data as dG/dP=1.80 (〕SY.+-.〔) 0.03. Pressure derivative of bulk modulus was determined from SM data as dKs/dP=4.27 (〕SY.+-.〔) 0.27, assuming the specimen-gas coupling is negligible. The determined values are very reasonable for steel, and this approves the validity of the present method of cavity resonance.2. Measurements in water and perspective to higher pressureIt has revealed that not only TM but some SM can be detected in the measurements with the cavity filled with water at 1atm. Since the impedance of water at 1atm corresponds to that helium gas at about 1GPa, this fact gives a promising perspective to higher pressure.3. A New data acquisition systemA new data anquistion system based on Fourier transform (FT) method (Suzuki et al., 1993) was established with a digitizing oscilloscope. It was demonstrated that spectral peaks of almost all modes can be detected with the new system.4. Application to sintered samplesSpherical samples were prepared from polycrystalline pyrope synthesized and sintered at high temperature and high pressure, and elastic constants were determined. It was shown that we can obtain valid values of elastic constants from polycrystalline samples by preparing samples with various porosities and by extrapolating to zero porosity.