The kinetics of the chlorination of neodymium oxide has been investigated by thermogravimetry between 312 degrees C and 475 degrees C, and for partial pressures of chlorine ranging from 10 kPa to 50 kPa. The starting temperature for the reaction of neodymium oxide with chlorine was determined to be about 250 degrees C, leading to neodymium oxychloride as product. The results showed that, for temperatures below 425 degrees C, the system is under chemical control and the formation of the oxychloride progresses through a nucleation and growth mechanism. The influence of chlorine mass transport through the bulk gas phase and through the boundary layer on the overall reaction rate was analyzed. In the absence of these two mass-transfer steps, a reaction order of 0.39 with respect to chlorine partial pressure, and an activation energy of 161 +/- 4 kJ mol(-1) were determined. A complete rate equation has been successfully developed. (C) 2012 Elsevier B.V. All rights reserved.