GB847800A - Method for forming metal sulfide coatings - Google Patents

Abstract

Organic tetrathiomolybdates and tetrathiotungstates of formula R2MS4 where R is an organic ammonium radical, the free base of which is volatile below 300 DEG C. at atmospheric pressure, and M is molybdenum or tungsten, may be prepared by introducing hydrogen sulphide into a solution of molybdic or tungstic acid in the presence of an excess of the base or by double decomposition of water-soluble thiomolybdates or thiotungstates with water soluble salts, e.g. hydro-chlorides, of the bases. The products are soluble in water or depending on the size of the organic radicals, in lower alcohols, glycols, amines, amino-alcohols, ethers or polyoxyethylene compounds; the presence of a small amount of the base corresponding to the tetrathiomolybdate or tungstate increases solubility and improves stability of the solution. Specified amines are mono-, di- and tri-methylamine, the various ethylamines, morpholine, piperazine, diethylene triamine and octylamine.ALSO:Molybdenum or tungsten disulphide coatings are formed on a bearing surface by applying to the surface and thermally decomposing thereon a compound R2MS4 where R is NH4 or an organic ammonium radical, the free base of which is volatile below 300 DEG C. and M is molybdenum or tungsten. The compound is preferably applied, e.g. by spraying, dipping or brushing, as a solution in water, lower alcohols, glycols, amines, amino alcohols, ethers or polyoxyethylene compounds, to which if desired there may be added a small amount of a free base corresponding to or similar to that of the compound, or of a volatile wetting agent. For best penetration the surface is treated with a warm saturated solution, after or whilst subjecting to a vacuum to evacuate crevices, or whilst subjecting to ultrasonic vibration. The surface may if desired be etched or sand blasted before applying the solution. The thermal decomposition may be carried out in a single step to evaporate the solvent, decompose to form a trisulphide (this may take place at 250-300 DEG C. at 1 atmosphere) and decompose the trisulphide to a disulphide (this may take place at 450-480 DEG C. at 1 atmosphere or as low as 340 DEG C. at 1 mm. Hg.). These changes may alternatively be carried out separately in two or three stages. Specified organic basis are monomethylamine, dimethylamine, trimethylamine, ethanolamines, morpholine, piperazine, diethylenetriamine and octylamine. Examples refer to (1) impregnating a sintered iron bearing with a hot saturated solution of ammonium tetrathiomolybdate in ethyl alcohol containing monomethylamine after subjecting the sintered bearing to a vacuum, repeating the procedure, drying and heating the bearing in a nitrogen atmosphere at 450 DEG C. to form a molybdenium disulphide coating; (2) coating a furnace chain heated to 350 DEG C. by passing it through a bath containing a solution of (NH4)2WS4 in water containing triethanolamine and a polyglycol; a lubricating WS2 layer is formed; (3) treating the sliding surfaces of a stoneware sulphuric acid pump with an ammoniacal aqueous monomethylammonium tetrathiomolybdate solution and then heating at 480 DEG C. in a stream of a nitrogen to form a self-lubricating p acid-resistant MoS2 film.