Influence of the gadolinia content in the processing and properties of the alumina-gadolinia composite

The alumina-gadolinia (Al2O3-Gd2O3) composite is of great interest to the nuclear technology. The association of the alumina neutronic inertia and mechanical and chemical stability, with the gadolinium high cross section for thermal neutrons absorption makes this material a potential candidate for employment in the nuclear industry. In the experimental activities, commercial powders of alumina and gadolinia were used, with equivalent particle diameters of 0.65 and 2.1 μm, respectively. Mixtures of powders with eight different concentrations, ranging from 0.0 up to 6.6 % mol of Gd2O3, were prepared and five types of samples were produced. The powders mixtures were obtained using the spray dry method, starting from suspensions homogenised in ball mill. The conformation process was performed, using two methods: hydraulic uniaxial pressing and isostatic pressing; whereas the sintering process was carried out in a furnace with molybdenum disilicide heating elements. The chemical characterization revealed exclusively the presence of the alumina (Al2O3) and gadolinium aluminate (GdAlO3) phases. The physical characterization showed that the density decreased with the reduction of the gadolinium aluminate content. A tendency of decrease of the medium equivalent diameter of the grains with the increase of the gadolinium aluminate content was observed, even so the deviations standard associates did not allow the confirmation of this tendency. The hardness of the pure alumina is superior to the hardness of the composites, that they were shown equivalent. The flexural strength and the elastic properties increases proportionally with the gadolinium aluminate content, if considered the effect of the porosity. The linear thermal expansion was not influenced, even so the thermal diffusivity of the components decreased significantly with the presence of the GdAlO3. The gadolinium aluminate generated a significant increase in the values of activation energy during the sintering process. (author)