The effect of [formula omitted] ratio on the condensation of planetary material

Abstract

The condensation temperatures of refractory silicates and oxides in a gas of cosmic composition are strongly dependent on the C O ratio. As the ratio increases from 0.4 to 0.9 (solar ~ cosmic ~ 0.6), condensation temperatures of compounds such as A1 2O 3, Ca 2Al 2SiO 7, MgAl 2O 4, Mg 2SiO 4 and MgSiO 3 decrease by 50–100°. As C O increases from 0.9 to 1.0, these temperatures drop an additional 300–400°. Other chemical differences result when C O $ ̆ 0.9 include: a new suite of high temperature minerals appears (graphite, CaS, Fe 3C, SiC and TiN); the reaction CO + 3H 2 → CH 4 + H 2O proceeds to the right at higher temperatures; and iron, whose condensation temperature is unaffected, condenses at higher temperatures than any silicate or oxide.