The high-temperature defluidization behavior of iron powder was investigated in different fluidizing gases (Ar, N-2, CO, H-2), especially in terms of the physical and chemical properties and change of the gas and solid phase at high temperatures. The agglomeration tendency, represented by the temperature required to reach defluidization, decreased with increasing gas velocity. The fluidization quality was improved by increasing gas density and viscosity, and thus the agglomeration tendency decreased. In particular, due to chemical adsorption of CO, an inert coating formed on the surface and thus reduced significantly the defluidization temperature. The thermo-mechanical analysis indicated that the iron powder performed the viscosity and adhesion activity due to surface softening and that the particle adhesion increased with increasing temperature. Based on the surface viscosity, the change of adhesive force calculated was in accordance with the observed trend of the minimum fluidization velocities, which suggested the increase of inter-particle force with temperature. (C) 2012 Elsevier B.V. All rights reserved.