A recently published theory of de-fluidisation of gas fluidised beds has been extended to the case of sintering produced by surface and volume diffusion. The theory was tested against a recently published investigation of the sintering and de-fluidisation behaviour of iron particles at temperatures above 700 K. The theory successfully predicted the dependence on temperature of the gas velocity required to prevent de-fluidisation as a function of the activation energy for surface diffusion. The assumptions made in the theory and the effects of scale are discussed.