Chemical vapor deposition from metal (Cr, Mo, W) carbonyls in a conical spouted bed vacuum reactor with a downflow reactant feeding

Abstract

A vacuum set-up with a conical spouted bed reactor for LPCVD of coatings onto powders, where a volatile solid substance is used as a CVD precursor (reactant), is developed. Structurally, the reactor is a cone with a vertical axis, fluidizing gas is supplied through the bottom branch, and reactant vapor is supplied from the evaporator through a thermostated nozzle into the top of the spouted particle bed (substrate powder). Examples given include the deposition of chromium, molybdenum, and tungsten coatings from carbonyls Cr(CO)6, Mo(CO)6, and W(CO)6 onto diamond powders with grain sizes from 150 to 500 μm, when coatings up to 1 μm thick were obtained at the reactor efficiency (the degree of the reactant conversion to the coating) within 42–77 %. In addition to the set-up design and process parameters, the saturated vapor pressure of carbonyls, chemical reactions during the deposition from carbonyls, and fluidized bed hydrodynamics are discussed.