Condensation experments using a forsterite evaporation source in H_2 at low pressures

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    • TSUCHIYAMA Akira
    • Department of Earth and Space Science, Graduate School of Science, Osaka University


Condensation experiments have been carried out with a new condensation furnace in H<SUB>2</SUB> at low pressures (1.4, 1.4×10<SUP>−1</SUP>, and 1.4×10<SUP>−2</SUP> Pa) using an evaporation source of forsterite powder heated at about 1500°C. Large amounts of condensates (up to a few hundreds of mg) were recovered as a function of temperature (from about 1350°C to room temperature) at 1.4 Pa, where the evaporated molecules from forsterite sufficiently collided with H<SUB>2</SUB> molecules. Forsterite, forsterite + silicon, forsterite + silicon + enstatite and amorphous material condensed with decreasing temperature under a reducing condition in a Ta crucible, while forsterite, forsterite + clinoenstatite and amorphous materials condensed near a neutral redox condition in a Mo crucible. These condensation sequences are essentially the same as fractional condensation sequences expected from the phase diagrams in the system Mg–Si–O–H constructed by thermodynamic calculations. Kinetic effects are also superimposed on the fractional condensation. For example, dendritic crystals of forsterite and clinoenstatite, and amorphous materials condensed due to nucleation delay of the silicates. Each whisker of the den-drites was formed by the vapor-liquid-solid growth mechanism with metastable nucleation of melt droplets. The elongation of clinoenstatite whiskers (c-axis) is different from that in interplanetary dust particles (a-axis). Euhedral forsterite crystals (a few μm in size and elongated to the c-axis), which condensed at high temperatures (>1000°C), have similar size and morphologies of olivine in matrix of chondrites. Condensation of clinoenstatite at high temperature (about 900°C) may indicate easy pyroxene condensation in the primordial solar nebula.


  • Mineralogical Journal

    Mineralogical Journal 20(2), 59-80, 1998-04-01

    Japan Association of Mineralogical Sciences

References:  40

Cited by:  1


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