A very dense tungsten powder was coated by silicon from silane using the fluidized-bed chemical vapor deposition process. A reactor of reduced diameter was developed in order to decrease the weight of powders treated. Results show that the fluidization of this powder is possible in this reactor, but with non-optimal gas solid contact induced by the high powder density. Important disturbances of the fluidized-bed temperatures appeared in the presence of silane, due to a partial bed defluidization related to the cohesive nature of the deposit. These disturbances are clearly exacerbated by the exceptional density of the particles. This is probably why a powder agglomeration has been unavoidable when the bed temperature was too low and/or the silane inlet concentration too high. However, a set of operating parameters could be found, allowing a uniform and continuous coating of the whole powder surface.