Chapter 14 - Chemistry at extreme conditions: Approaching the Earth's major interface

Abstract

The chapter reviews the methodological aspects of investigation of chemical reactions in diamond anvil cell techniques (DACs). Core-mantle boundary (CMB) is one of the most inaccessible and enigmatic regions on the Earth. Clearly distinct chemical nature of the mantle (dominated by silicates and oxides) and the outer core (liquid iron-nickel alloy) suggests a possibility of multiple and complex chemical reactions at CMB. Recent investigations have revealed a very complex texture and/or heterogeneity of the Earth's CMB, and the importance of properties of iron for modeling composition and dynamics of the core and its interaction with the lower mantle. Because of the limitations of the diamond anvil cell (DAC) technique (small sample size, pressure and temperature gradients, potential contamination by carbon, risk of loss of materials on recovery, etc.), the study of chemical reactions at extreme conditions of CMB becomes difficult. Combination of different modern analytical techniques allows the elucidation of major trends in the behavior of the geophysically and geochemically important metal-oxide (for example, Fe-SiO2, Fe-Al2O3, and MgO-FeO) systems at pressures and temperatures of the Earth's deep interior. Diamonds are transparent to visible light, and historically, the simplest way to study processes in DACs is direct observation using an optical microscope. Raman and infrared (IR) spectroscopy are easily coupled with DACs and are sensitive to changes in local atomic arrangements. Internally (laser- or electrically) heated DACs are currently the only technique which allows the generation of static pressures and temperatures relevant to the conditions of the Earth's lower mantle and the CMB.