THE ZONMET THERMODYNAMIC AND KINETIC MODEL OF METAL CONDENSATION

Abstract

The ZONMET model of metal condensation is a FORTRAN computer code that calculates condensation with partial isolation–type equilibrium partitioning of the 19 most abundant elements among 203 gaseous and 488 condensed phases and growth in the nebula of a zoned metal grain by condensation from the nebular gas accompanied by diffusional redistribution of Ni, Co, and Cr. Of five input parameters of the ZONMET model (chemical composition of the system expressed as the dust/gas [D/G] ratio, nebular pressure [Ptot], isolation degree [ξ], cooling rate (CR), and seed size), only two—the D/G ratio and the CR of the nebular source region of a zoned Fe,Ni grain—are important in determining the grain radius and Ni, Co, and Cr zoning profiles. We found no evidence for the supercooling during condensation of Fe,Ni metal that is predicted by the homogeneous nucleation theory. The model allows estimates to be made of physicochemical parameters in the CH chondrite nebular source regions.