Elastic wave velocities and densities of iron and candidate iron alloys are important properties for understanding the seismological observations of Earth’s core. Several methods have been applied to measure the elastic wave velocities of iron and iron alloys at room temperature. Recently, measurements have been extended to simultaneous high-pressure and high-temperature conditions. Birch’s law, which is the linearity between density and compressional wave velocity (VP), is applicable to the experimental results of density and VP at high pressure and room temperature. The effect of temperature on Birch’s law is discussed, and it is not negligible at temperatures greater than 1,000–2,000 K. The VP and density of hcp Fe are extrapolated to pressure and temperature conditions of the inner core. VP of hcp Fe at 330–360 GPa is higher than the inner core seismic velocity, thus suggesting that iron should be alloyed with other elements so as to reduce not only its density, but also its velocity at inner core conditions. The VP of Fe–Si, Fe–H, and Fe–C alloys is slower than that of Fe at the pressure of the inner core. If the temperature effect on Birch’s law is taken into account, Si and H can be candidates for the major light elements in the inner core, while C, O, and S may not be included or exist as minor constituents.

The combination of double-sided laser heating in the diamond anvil cell and detailed chemical analysis of the recovered samples is a promising approach to explore the chemistry of the Earth’s deep interior from the lower mantle to the core. Routine recovery of laser-heated samples coupled with chemical and textural characterization at the submicron scale is the key to expand knowledge of chemical interactions and melting at extreme conditions, particularly in complex systems. Recent technical developments have allowed us to investigate element partitioning and melting relations at pressures approaching the Earth’s inner-core boundary. In this chapter, we review the techniques used for recovering tiny laser-heated samples and analyzing their chemical compositions and quenched textures, while highlighting key experiments that address silicate–metal element partitioning during mantle–core differentiation, silicate melting relations with applications to early magma ocean crystallization and deep mantle melting, and melting relations in iron-alloy systems relevant to the core. The results have drastically expanded our understanding of element redistribution at deep chemical boundaries and the chemical evolution of the deep mantle and the inner core. Finally, we emphasize the need for standardized protocols to obtain consistent, reproducible results and streamlined procedures to promote good practice and increase productivity. A broad collaboration with a systematic approach would further advance the field of high-pressure geochemistry.

Elastic wave velocities and densities of iron and candidate iron alloys are important properties for understanding the seismological observations of Earth’s core. Several methods have been applied to measure the elastic wave velocities of iron and iron alloys at room temperature. Recently, measurements have been extended to simultaneous high-pressure and high-temperature conditions. Birch’s law, which is the linearity between density and compressional wave velocity (VP), is applicable to the experimental results of density and VP at high pressure and room temperature. The effect of temperature on Birch’s law is discussed, and it is not negligible at temperatures greater than 1,000–2,000 K. The VP and density of hcp Fe are extrapolated to pressure and temperature conditions of the inner core. VP of hcp Fe at 330–360 GPa is higher than the inner core seismic velocity, thus suggesting that iron should be alloyed with other elements so as to reduce not only its density, but also its velocity at inner core conditions. The VP of Fe–Si, Fe–H, and Fe–C alloys is slower than that of Fe at the pressure of the inner core. If the temperature effect on Birch’s law is taken into account, Si and H can be candidates for the major light elements in the inner core, while C, O, and S may not be included or exist as minor constituents.

The combination of double-sided laser heating in the diamond anvil cell and detailed chemical analysis of the recovered samples is a promising approach to explore the chemistry of the Earth’s deep interior from the lower mantle to the core. Routine recovery of laser-heated samples coupled with chemical and textural characterization at the submicron scale is the key to expand knowledge of chemical interactions and melting at extreme conditions, particularly in complex systems. Recent technical developments have allowed us to investigate element partitioning and melting relations at pressures approaching the Earth’s inner-core boundary. In this chapter, we review the techniques used for recovering tiny laser-heated samples and analyzing their chemical compositions and quenched textures, while highlighting key experiments that address silicate–metal element partitioning during mantle–core differentiation, silicate melting relations with applications to early magma ocean crystallization and deep mantle melting, and melting relations in iron-alloy systems relevant to the core. The results have drastically expanded our understanding of element redistribution at deep chemical boundaries and the chemical evolution of the deep mantle and the inner core. Finally, we emphasize the need for standardized protocols to obtain consistent, reproducible results and streamlined procedures to promote good practice and increase productivity. A broad collaboration with a systematic approach would further advance the field of high-pressure geochemistry.