Corrosion-resistant coatings for high-temperature high-sulfur-activity applications. Final report

摘要

The research described in this report is intended to assistant in developing the technology for the production of molybdenum and molybdenum carbide coatings. These coatings have the potential to serve as an alternative to present methods of protecting metal parts at positive potential, of high-temperature sulfur or sulfide batteries. Two methods have been employed. In Task 1, Study of Molybdenum Carbide Electrodeposition from Oxide Based Molten Salts, dense, well-adherent molybdenum carbide coatings have been deposited on mild steel substrates by electrochemical deposition from a Na(sub 2)WO(sub 4)-K(sub 2)WO(sub 4) molten bath containing alkali molybdates and carbonates. Coatings with thicknesses up to 30 (mu)m have been prepared at cathodic current densities between 30 and 50 mA.cm(sup (minus)2) under air as ambient atmosphere. Addition of Na(sub 2)B(sub 4)O(sub 7) to the basic non-lithium bath composition causes significant quality and morphology improvements. It is shown that the initial stages of the molybdenum carbide electrodeposition can be described by a model involving instantaneous nucleation and 3-D diffusion-controlled growth. In Task 2, Preparation of Mo and Mo(sub 2)C by Plasma-Enhanced Chemical Vapor Deposition, using factorial experimental design, a series of experiments has been carried out to investigate the PECVD process with Mo(CO)(sub 6) as a precursor. Information about the effects of the chamber pressure, saturator temperature, gas composition and gas flow rate was obtained by experiments. Elemental analysis of the thin film was carried out by Auger electron spectroscopy. Further investigations are being carried out on the basis of thermodynamics, heterogeneous kinetics, and mass transport, in conjunction with measurements of evaporation rate and analysis of the solid and gaseous phases.