[SMP36-11] Density measurements of Fe up to 25 GPa based on X-ray absorption
Keywords:Diamond anvil cell, X-ray absorption method, Earth core
Terrestrial planets, such as Earth, Venus, Mars, and Mercury, have metallic liquid and/or solid cores. The cores consist of mainly Fe and Ni with small amounts of light elements. Chemical compositions of solid state cores have been estimated by density measurements of crystalline core materials in a number of previous studies. On the other hand, there are a few previous studies on density measurements of liquid samples because of technical difficulties. Although Morard et al. (2008, 2013) obtained densities of liquid Fe with light elements by structure analyses from XRD patterns, accuracy of the densities was under debate because they used XRD patterns with narrow reciprocal lattice spaces. In this study, we have measured densities of crystalline Fe and amorphous materials using an X-ray absorption method in order to avoid problems of small diffraction angles due to a diamond anvil cell (DAC).
High pressures measurements were performed using DAC with gaskets having 3 sample chambers. Fe or amorphous samples were loaded in a sample chamber for density measurements. Powders of KCl, KBr, or RbBr as references for thickness were also loaded in another sample chambers. After XRD patterns were taken from all samples and references, absorption profiles were also measured. Experimental pressures were determined using pressure averages between KCl, KBr, or RbBr. Densities based on the X-ray absorption method were obtained using the Lambert Beer law with mass absorption coefficients from NIST data base. Densities of crystalline Fe were obtained up to 25 GPa and densities obtained based on X-ray absorption method were consistent with those by XRD.
High pressures measurements were performed using DAC with gaskets having 3 sample chambers. Fe or amorphous samples were loaded in a sample chamber for density measurements. Powders of KCl, KBr, or RbBr as references for thickness were also loaded in another sample chambers. After XRD patterns were taken from all samples and references, absorption profiles were also measured. Experimental pressures were determined using pressure averages between KCl, KBr, or RbBr. Densities based on the X-ray absorption method were obtained using the Lambert Beer law with mass absorption coefficients from NIST data base. Densities of crystalline Fe were obtained up to 25 GPa and densities obtained based on X-ray absorption method were consistent with those by XRD.