The sintering behavior of eight recovery boiler dusts was evaluated by pressing them into pellets, heating them at temperatures from 300 to 700 degreesC, and recording the change in diameter of the pellets with time. The eight dusts sintered at widely different rates that did not correlate well with dust composition. Analysis of the rate of sintering showed that dusts containing chloride began to sinter via evaporation-condensation of NaCl, but the mechanism eventually changed to solid-state diffusion. Dusts with less chloride changed sooner to solid-state diffusion sintering. The apparent rate constants for sintering by evaporation-condensation of NaCl correlated well with the first melting point of the dusts. This correlation provides a method for estimating the relative sintering tendency of dusts, and for evaluating process operational changes to reduce the sintering rate of deposits. (C) 2004 Published by Elsevier Ltd.