We address the problem of the stability in a fluidized bed. The criteria for predicting transition are interpreted in a new light. Starting with the Hamaker theory, we also propose a novel constitutive relation for the interparticle forces of attraction of van der Waals type and show that it can augment the global stability in the fluidization processes. Numerical simulations of the equations of motion are presented to describe the effects of the van der Waals forces in the formation of clusters and in the deposition of fines on the walls.