Zinc ultrafine powder is widely used as key raw material for anti-corrosion paint in recent years. Inert gas condensation (IGC) is one of the primary means for preparing zinc ultrafine powder with a clean interface. As condensation is the most important process that determines the powder's size, this paper presents new models for radiative and convective cooling in condensation process by studying the microphysical mechanisms. In order to study the microphysical mechanisms of zinc nucleation process in the inert gas condensation, this paper established mathematical expressions to deduce the bonding probability of collisions between condensation nuclei particles and vapor molecules during the nucleation process. The two models have been used to predict the diameter of zinc condensation nucleus. Compared with experiments that have been done, the prediction errors are only less than 7%. This may provide a theoretical method for prediction of ultrafine powder diameter in IGC. (C) 2014 Elsevier B.V. All rights reserved.