In situ and ex situ X-ray diffraction, and transmission electron microscopy were used to investigate the calcination of four samples of zirconia manufactured using two different zirconia reactant solution concentrations (0.81 M and 1.62 M) with precipitation carried out at pH 3 and 12. The calcinations were investigated over the temperature range from room temperature to 1000 degrees C. It was found that varying the precipitation conditions resulted in differing calcination routes; it is believed that variations in particle size and initial degree of hydration are responsible for these differences. It was also found that the initial phase produced after calcination was tetragonal zirconia, which underwent a process of crystallite growth to a size of similar to 30 nm before transformation from tetragonal to monoclinic. (C) 2009 Elsevier B.V. All rights reserved.