New Coating & Metallizing Process of Refractory Metals & Compound in Molten Salt Bath

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Coating and metallizing of refractory metal or its compound by using a disproportionation reaction in molten salt has been studied. Titanium coating in NaCl-KCl equi-molar melt with Ti chloride or fluoride at 1000-1200K was mainly examined in this study. The results are summarized as follows ;1) The effects of some factors on the disproportionation reaction were clarified theoretically and experimentally. Titanium can be deposited by temperature change owing to the shift in the equilibrium. Titanium alloy coating should also be expected in the case that the substrate can form Ti alloy. Addition of fluoride in the bath may improve the rate of Ti deposition.2) Titanium metal deposited on alumina substrate by the simple immersion for hours, while Ti compound was seen on quartz glass substrate. These deposits seemed particle-like, and a dense coating layer wasn't obtained. The temperature gradient in the bath seemed effective in the improvement in the deposition rate.3) Dense and coherent Ti alloy layers up to 100μm were formed on Fe, Ni and carbon steel. The layer consisted of some layers with different composition, and almost the same Ti alloy layer was obtained in the bath with TiCl_8 and K_2TiF_6. The change in the formation rate indicated that the diffusion of the elements in the formed layer controlled the formation rate of the layer. Corrosion resistance of steel against saline was remarkably improved by our Ti alloy coating. A dense and coherent Ti metal layer of a few μm was obtained on stainless steel, and Cr seemed to influenced the peculiar behavior of stainless steel. Deposition in LiCl-KCl eutectic melt at lower temperature was also tried in this study, but enough Ti deposit wasn't obtained.4) MoO_2 was deposited on metal substrates in the melt with K_2MoO_4, while no deposit was obtained on ceramic.