Preparation And Properties Of Al₂O₃-Cr₂O₃ Solid Solutions As Buoyancy Markers And Their Application In Geochemistry

The properties of the melt under high pressure are one of the leading problems in the study of deep earth matter,which is very challenging.Silicate is one of the important components of the earth's interior,and its melt has highly physical and chemical activity.Therefore,understanding the properties of the silicate melt under high pressure conditions is of great significance to establish the differentiation and kinetic model of the earth's internal material.However,few reliable data have currently obtained on density,which reflects one of the important properties of silicate melts.Although"sink-float"method has been widely used to measure the density of silicate melt under high pressure,however,the"sink-float"method usually uses natural mineral as the density reference ball,which has a high limitation.Therefore,the preparation of a stable density reference ball with high resolution is an urgent task in the study of density measurement of melt under high pressure using the"sink-float"method.We prepared Al₂O₃-Cr₂O₃ solid solution buoyancy markers with different stoichiometric ratios at atmospheric pressure,and the conventional and synchrotron radiation X-ray diffraction under normal pressure and high-pressure conditions.The main research results are as follows:1.Al₂O₃-Cr₂O₃ solid solution was successfully grown by optical floating zone melting method.Buoyancy markers with different densities were obtained by changing the content of Cr₂O₃ in Al₂O₃-Cr₂O₃ solid solution at atmospheric pressure.The Gibbs mixing free energy of this solid solvent increases with increasing Cr₂O₃ content,and the thermal activity,longitudinal wave sound velocity and shear sound velocity,volume elastic modulus decrease with increasing Cr₂O₃ content.2.Three samples of Al₂O₃ and Cr₂O₃ metering molar ratios of 7:3,9:1 and 9.5:0.5were selected as the X-ray diffraction research objects under the condition of synchrotron radiation,and the samples were characterized by high-pressure synchrotron radiation X-ray diffraction technology,and the volume elastic modulus of Al₂O₃-Cr₂O₃ solid solvent with different measurement ratios is obtained,which provides an experimental basis for calculating the density of the buoyancy markers under different pressures.3.Using natural minerals as a buoyancy markers,the density of Huinan peridotite melt was measured under high pressure.According to the conclusion of the peridotite melt density experiment,the possible mantle location of Huinan peridotite was preliminarily inferred.