The growth of ZrO2 particles in spray flames is studied at production rates of 100 and 300 g/h by thermophoretic sampling (TS) and image analysis of transmission electron microscope (TEM) micrographs. At each TS location, the corresponding temperature of the particle-laden spray flame is measured along the centerline by Fourier transform infrared (FTIR) spectroscopy. The product powder is analyzed by nitrogen adsorption and TEM. The measured evolution of primary particle size distribution is presented and quantitatively explained, accounting for aerosol coagulation and sintering. The evolution of the average agglomerate size and number of primary particles per agglomerate is calculated and compared to TEM micrographs. (C) 2004 American Institute of Chemical Engineers.