Three embodiments of apparatus for gas coating particles suspended in a fluidized bed within a coating chamber are illustrated, each having a base plate with a center opening, an extension nozzle assembly arranged in the opening and mounted on a movable two-piece internally cooled gas probe for supplying reactant gas to the nozzle and an annular unloading passage surrounding the probe and in communication with a side unloading chute. In the three embodiments, different means are provided for raising and lowering the nozzle assembly to permit unloading of coated particles and provide access to the nozzle assembly.