In order to clarify the formation condition of zinc rusts such as layered zinc hydroxynitrate (Zn-5(OH)(8)(NO3)(2).2H(2)O: ZHN), ZnO particles were aged with aqueous Zn(NO3)(2).6H(2)O solution at 6-140 degrees C for 48 h. Further, adsorption of H2O and CO2 on ZHN was examined for simulating study of atmospheric corrosion of galvanized steel. The ZHN was formed at 6 C and the ZnO completely disappeared, meaning the hydrolysis of ZnO particles in aqueous Zn(NO3)(2)center dot 6H(2)O solution to recrystallize as ZHN. Increasing the aging temperature improved the crystallinity of layered structure of ZHN, showing a maximum at 85 C. The formed ZHN was hexagonal plate-like particles. The particle size was dependent of the crystallinity of layered structure of ZHN. The specific surface area of ZHN was decreased on elevating the aging temperature, showing a minimum at 85 degrees C. The adsorption of H2O and CO2 was enhanced on increasing the crystallinity of layered structure of ZHN, meaning that these molecules are adsorbed not only on particle surface but also in interlayer of ZHN. These facts infer that the preferred orientation of plate-like ZHN particles leads to the formation of compact rust layer on galvanized steel and to the enhancement of corrosion resistance. (C) 2009 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.