Abstract
With the increasingly stringent specifications for materials of technological importance, interest has grown in the properties of the "Refractory Hard Metals". The work described in this thesis is concerned with the stability of titanium diboride and zirconium diboride. The resistance to oxidation of compacted samples has been studied over the temperature range 650-1050 C and pressure of oxygen ranging from atmospheric to 200 mm Hg. Total pressures of oxygen were used throughout. Powder samples of titanium diboride were also examined. Both gravimetric and volumetric techniques have been used to follow the oxidations, and the suitability of each is discussed bearing in mind the voldtility of boric oxide. The temperature and pressure dependence of the parabolic reaction rate constants have been obtained for the compacted boride samples. For the powder samples, however, quantitative results have little validity owing to the undetermined variation of surface area during oxidation. Values for the energy of activation of the reactions have been calculated and the results compared with others reported in this field. From the data obtained, and by comparisons with simpler known systems, an attempt has been made to elucidate possible oxidation mechanisms. Lack of data on diffusion coefficients or activation energies of diffusion has hindered the precise interpretation of the results.