Sintering polycrystalline olivine and polycrystalline clinopyroxene containing trace amount of graphite from natural crystals

Abstract

Graphite-bearing polycrystalline olivine and polycrystalline clinopyroxene with submicron to micron grain size were successfully sintered from a single crystal of naturally occurring olivine ). The milled powders of both these crystals were sintered under argon gas flow at temperatures ranging from 1130 to 1350 °C for 2 h. As the sintering temperature increased, the average grain size of olivine increased from 0.2 to 1.4 µm and that of clinopyroxene increased from 0.1 to 2.4 µm. The porosity of sintered samples remained at an almost-constant volume of 2-5% for olivine and 3-4% for clinopyroxene. The samples sintered from powders milled with ethanol exhibited trace amount of graphite, identified via Raman spectroscopy analysis. As the sintering temperature increased, the intensity of the graphite Raman peak decreased, compared with both olivine and clinopyroxene peaks. The carbon content of the sintered samples was estimated to be a few hundred ppm. The in-plane size (L a ) of graphite in the sintered olivine was estimated to be <15 nm. Our experiments demonstrate new possibilities for preparing graphite-bearing silicatemantle mineral rocks, and this method might be useful in understanding the influence of the physical properties of graphite on grain-size-sensitive rheology or the seismic velocity of the Earth's mantle.

Third‐Order Padé Thermoelastic Constants of Solid Rocks

“…Therefore, the orthorhombic system of crystals can be transformed into an isotropic symmetry based on the averaging scheme and assuming the isotropic space distribution of each component for the application to validate our theoretical predictions. Experimental studies on polycrystalline olivines show that temperature has little influence on the porosity (Liebermann, 1972), even below 5% at 1300°C (Tsubokawa & Ishikawa, 2017). Figures 1a–1d and 2a–2d contrast the conventional and Padé‐approximant‐based thermoelastic constants with temperatures for the experimental data of polycrystalline RAM and OLA samples in Tables 1 and 2, respectively.…”

Crustal dynamics: unified understanding of geodynamic processes at different time and length scales

“…They found that an elastic matrix model is preferable to a Newtonian viscous model for analyzing the stresses involved in microboudinage of columnar tourmaline grains within the quartz matrix of the metamorphic tectonite. Tsubokawa and Ishikawa (2017) reported on the preparation of submicron polycrystalline olivine and clinopyroxene by sintering. Incorporation of trace amounts of graphite allows experimental investigations into the influence of graphite on mantle rheology and seismic velocity.…”

Experimental synthesis of Fe-bearing olivine at near-solidus temperatures and its decomposition during longtime heating

“…Numerous previous studies have synthesized Mg-Fe olivine. (Brindley and Hayami, 1965;Hanson et al, 1991;Mitchel et al, 1998;Ito et al, 2003;Ando et al, 2007;Ni et al, 2007;Tsubokawa and Ishikawa, 2017;Wang et al, 2017). Generally, solid-state reactions have been used for a long time now to synthesize forsterite (Mg2SiO4) crystals using MgO and SiO2 powder (Brindley and Hayami, 1965).…”