Nucleation and growth of dust grains

Classical nucleation theory must be modified for the condensation of small, solid dust grains. Ion nucleation is unimportant, and exchange reactions with gas molecules are required. For carbon-rich stellar atmospheres, hydrocarbons act as intermediaries for converting acetylene gas into carbon particles. For oxygen-rich atmospheres, magnesium silicate grains form by surface nucleation. Sputtering and coalescence of grains is discussed.