This thesis is the result of an investigation undertaken to study some of the important factors affecting the deposition of metallic diffusion coatings on other metals immersed in a fused salt bath….
There are many methods which have been devised to obtain diffusion coatings on various metals. One which is quite well known and used commercially is the process of “chromizing” which produces a diffusion layer if chromium on another metal. One method of “chromizing” consists of immersing the specimen to be coated in a mixed chloride fused bath containing chromium metal flakes. Another method consists of packing a low carbon steel in intimate contact with powdered chromium in the presence of hydrogen gas and heating to temperatures between 1200⁰ and 1400⁰ C. Still another method, which was developed in Germany, consists of passing gaseous chromium chloride over steel to be chromized at temperatures between 900⁰ and 1000⁰ C. Typical high temperature applications of chromized steel includes heating and cooking appliances, heat treatment equipment, fixtures and jigs, etc.
A somewhat similar process has been developed at Missouri School of Mines for producing diffusion coatings of titanium on metals. This process consists of using either a plate of metallic titanium fixed adjacent to the metal to be coated and immersing the assemblage in an alkali salt mixture which has been fused, or packing the metal article in titanium powder and the salt mixture and then fusing the salt. The mechanism of deposition is not exactly known; however, it is presently thought that the deposition occurs from a “pyrosol” or metal fog.
Since “chromizing” has been proved to be generally quite applicable to commercial processes and the formation of diffusion coatings of titanium appears to be also commercially applicable, especially where corrosion resistant coatings are desired, it was thought that an investigation of diffusion coatings of other metals, such as manganese, uranium, and zirconium would prove to be quite profitable. Zirconium diffusion coatings are of special interest since it is a highly corrosion resistant metal which seemingly is impossible to deposit by electrolytic methods from aqueous solutions.
A process similar to the ones used for titanium was used to deposit manganese, uranium, and zirconium diffusion coatings. Chromium was also included to serve as a comparison with the other diffusion coatings, since these coatings have undergone extensive investigation and many data are in the literature. A metal plate was used as the source of the coating metal, thus minimizing the oxidation problem associated with the use of metal powders --Introduction, pages 1-3
