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The restrictions imposed by the processes of diffusion, evaporation, and coating substrate reactions on the choice of potential protective coating materials for tungsten were studied analytically and experimentally. The diffusive restriction is the most limiting and eliminates many refractory oxides with otherwise satisfactory attributes. The diffusive properties of rare earth sesquioxides and complex refractory oxides were explored by means of oxidation experiments and a layer growth experiment respectively. Mass spectrometric studies of the vaporization of refractory complex oxides were carried out to determine the applicability of the Wagner-Hauffe method of predicting vaporization rates. Provided certain thermodynamic approximations are valid and the vapor species over the complex oxide are the same as those over the pure component oxides, the predictions yield order of magnitude accuracy. A survey and exploration of reactions of possible coating materials with tungsten was performed emphasizing promising materials from the diffusion studies. (Author).
Oxidation at elevated temperatures of Zr-Th, Zr-Y, Hf-Y, Hf-W, Hf-W-Re, Al-Cr-Sn, and Al-LaSn alloys, as well as ZrN, HfN and ZrN-ThN combinations was studied in order to clarify specific aspects of the problem of protecting W against oxidation at high temperatures. Experimental results showed that there was much less tendency for ZrO2, ThO2 and HfO2 scales to crack during growth at high than at low temperatures. Multiphased scales were more resistanct to spalling than single-phased scales, and protective oxides were grown many alloys. However, even in sound and coherent scales composed of these oxides, O diffused so rapidly that it is doubtful that they could form the basis of a protective system at 2000 C. (Author).
Oxidation at elevated temperatures of Zr-Th, Zr-Y, Hf-Y, Hf-W, Hf-W-Re, Al-Cr-Sn, and Al-LaSn alloys, as well as ZrN, HfN and ZrN-ThN combinations was studied in order to clarify specific aspects of the problem of protecting W against oxidation at high temperatures. Experimental results showed that there was much less tendency for ZrO2, ThO2 and HfO2 scales to crack during growth at high than at low temperatures. Multiphased scales were more resistanct to spalling than single-phased scales, and protective oxides were grown many alloys. However, even in sound and coherent scales composed of these oxides, O diffused so rapidly that it is doubtful that they could form the basis of a protective system at 2000 C. (Author).