Molybdenizing

the application of a molybdenum coating to the surface of items made of steel, titanium, niobium, and other metals to increase their hardness, surface strength, and corrosion resistance in nitric acid. Molybdenizing with subsequent siliconizing is used to increase the heat resistance at high temperatures. Molybdenizing is carried out using a number of techniques. Molybdenum or ferromolybdenum powders are applied in a hydrogen stream at 900°-1000°C.

In gaseous media, molybdenizing may be carried out in a stream of hydrogen and hydrochloric acid in the presence of molybdenum or ferromolybdenum: a gaseous mixture forms at 300°-400°C, and the molybdenum is deposited on the article at 800°-1000°C. If a hydrogen stream is passed through molybdenum pentachloride, Mods, at 300°C, the mixture obtained decomposes at 800°-1000°C, with deposition of molybdenum onto the part. In molybdenizing in a mixture of vapors of molybdenum hexacarbonyl, Mo(CO)⁶, with hydrogen or argon, the Mo(CO)⁶ decomposes above 250°C. Therefore, in practice the process is carried out in the temperature range from 250°C (at which high-hardness molybdenum carbide forms on the surface of the part) to 850°C.

In liquid media, methods of molybdenizing include electrolysis in a bath with a melt of sodium molybdenum oxide, Na2MoO4, and reduction of molybdenum from the melt at 1150°C by passing hydrogen or previously dissociated ammonia through the bath.