| 摘要 |
<p>A ferrous article is coated with another metal by halide diffusion in the presence of a substance such as ammonium nitrate which generates nitrous oxide upon heating to the diffusion temperature. Coating may be effected in the following ways: (1) by packing the article in a composition comprising sand, the coating metal or a halide thereof, ammonium nitrate, and one or more ammonium halides and then heating; (2) by coating the article with a solution containing ammonium nitrate together with one or more ammonium halides, surrounding the article with a sand/coating metal mixture, and then heating; (3) by coating the article with a suspension, solution or dispersion containing a coating metal halide and ammonium nitrate with or without ammonium halides, and then heating; or (4) by covering the article with a carrier impregnated with a suspension, &c., as in (3), and then heating. Specified coating metals are chromium, vanadium, manganese, niobium, tantalum, tungsten and aluminium. If desired, the coated article may be coated with aluminium by applying aluminium chloride and heating. Diffusion is effected in a box which is sealed with a composition which forms a liquid glass at diffusion temperature and is saturated with respect to the coating metal.</p> |
