Formation of Forsterite Grains and Direct Observation of The Sublimation of Crystal Formation Grain

Abstract

Forsterite crystal fine grains have been produced by flushing SiO powders into the flame during MgO grain formation in mixture gas of Ar (80 %) and 02 (20 %) at 13 kPa. Experimental studies on the sublimation of forsterite grains upon heating at 10-6 Pa have been carried out using a high-resolution transmission electron microscope. The spherical crystalline grains became polyhedral at 973 K, which corresponded to the temperature at which the stall state appeared. Coalescence and sublimation occurred at 1093 K. The sublimation rates of forsterite grains with a size of 40 to 100 nm with the structure of Mg2SiO4 were estimated. The sublimation of grains near the crystallization temperature indicates the reason that no crystal silicates appear in the interstellar medium.