The metastable zone width (MSZW) and the induction times for the cooling crystallization of ammonium aluminum sulfate dodecahydrate from unseedecl aqueous solution were measured using focused beam reflectance measurement (FBRM). Dependence of MSZW on cooling rate and saturation temperature and dependence of the induction time on supersaturation and temperature were systematically investigated. Classical 3D nucleation based approach of Sangwal was employed to correlate MSZW with cooling rate. Linear plots of (T*/Delta T-max)(2) versus In R gave values of the parameters F-1, F, and Z. According to the classical theory, the primary nucleation mechanism was identified and the interfacial energy was calculated. (C) 2014 Elsevier B.V. All rights reserved.