The effect of particle size, density, charge and air velocity on transfer efficiency, evenness and separation of mixtures during powder coating was investigated using modeling and experimentation. Electrostatic and nonelectrostatic coating was tested using 28, 234 and 342 mu m NaCl and 195 mu m starch powders. Transfer efficiency increased as particle size, density or charge increased or as air velocity decreased. Evenness increased as particle size or density decreased, as velocity increased, or as charge increased to a peak. Electrostatic coating produced higher transfer efficiency and evenness than nonelectrostatic coating. Improvement in transfer efficiency and evenness due to electrostatics increased as NaCl size, density, charge or air velocity decreased. Powder mixtures did not separate by size during coating but did separate by density and charge. Starch was affected more by the collisions and charging than NaCl, which caused the separation. (c) 2007 Elsevier Ltd. All rights reserved.