valve of a type commercially available and used to control fluid systems however it should be understood that essentially the same function desired of the valve assembly 34 could be achieved with two solenoid valves acting out of phase as well as other types of valve arrangements a suitable configuration for the coating can 20 is schematically represented in fig3 as with conventional vapor phase deposition processes known in the art the coating process of this invention is carried out in an inert or reducing atmosphere provided by the carrier gas within the can 20 the can 20 is represented in fig3 as containing components represented as turbine blades 14 to be coated by reactive vapors generated from donor mixtures 16 within the can 20 the donor mixtures 16 are preferably in a granular or pellet form though other forms may also be used and may contain any of the previously noted donor and activator materials though the use of other materials is also possible if a diffusion aluminide coating is desired particularly suitable donor materials include aluminum alloy particles and suitable activators include ammonium aluminum or alkali metal halides if aluminum halide e g alf 3 is used as the donor material a separate activator may not be required chromium is a suitable donor material for producing a chromide coating with suitable activators including ammonium or alkali.