Mineral condensation in stellar outflows

This chapter summarizes aspects of the major and trace element equilibrium condensation chemistry of expected minerals forming in circumstellar environments of late-type stars (red giant, supernovae, novae). The overall elemental composition is the primary factor controlling the composition of mineral condensates, followed by the density (total pressure and temperature) within the ejecta outflows. For near-solar elemental compositions, mineral condensation sequences are like those computed for a solar composition gas. The carbon-to-oxygen (C/O) ratio governs the redox state of the condensate mineralogy. At C/O from solar to about unity, oxides remain initial condensates with subtle changes for the initial condensing phase and lower condensation temperatures as C/O≈1 is approached. At C/O above unity graphite, carbides, and sulfides are prominent due to the lack of oxygen. Silicates form over a wide range in C/O. Changes in total pressure as well as metallicity also affect the condensate types and their condensation sequences. As presolar grains originated from several generations of different stars the consideration of metallicity is quite important. Starting condensation temperatures for major element minerals and phases, as a function of total pressure and metallicity, are provided for solar-like elemental compositions, which apply to condensation in circumstellar envelopes of red giant and supergiant as well as asymptotic giant branch stars with C/O ratios below unity. The metallicity-dependent chemistry of graphite and carbide condensation at C/O ratios near unity and above is described.