Phase transitions and surface stability of the WO3γ-Al2O3 system

The solid state transitions of the WO₃γ-Al₂O₃ system have been investigated in the temperature range 873–1323 K. The formation of α-Al₂O₃ and Al₂(WO₄)₃ phases and the thermal desorption of W(VI) attached to the γ-Al₂O₃ surface have been studied as function of the treatment time. The inhibition of the phase transition to α-Al₂O₃ and therefore the stabilization of the surface has been observed at 1323 K for samples with 7% WO₃ content. This stabilization is critically affected by the tungsten content. An explanation for the stabilization of the alumina surface is proposed.