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Technetium-99m is the clinically most used radionuclide worldwide. Although many techniques can be applied to separate 99 Mo and 99m Tc, the most commonly used method is the column chromatography with alumina as stationary phase. However, the alumina nowadays used has limited adsorption capacity of molybdate ions which implies the need to develop or improve materials to produce high specific activity generators. In this paper, alumina was obtained by a solid state method and heat treatments at different conditions. The powders had a microstructure with porous particles of γ, δ, θ and α-Al 2 O 3 phases as well as specific surface area between 36 and 312 m 2 g -1.Most interesting results were reached by powders calcined at 900 o C for 5 hours which had high chemical stability and a molybdenum adsorption capacity of 92.45 mg Mo per g alumina.

Silicon nitride is a ceramic material widely used in various structural applications at high temperatures owing to its excellent combination of mechanical and thermal properties. To increase the application of Si 3 N 4 , many researches have been developed to improve its fracture toughness and processing conditions. In this study, the sintering and microstructure of Si 3 N 4-TiN composites, containing Al 2 O 3 and Y 2 O 3 as sintering aids, were studied. Samples were obtained by the conventional method of mixing powders and sintered at 1750 ºC/1 h and 1815 ºC/1 h under nitrogen atmosphere. Density values of the samples were determined by the Archimedes method, reaching values between 96.9% and 98.0% of theoretical density, with a porosity of less than 0.5%. The sintered samples were analyzed by X-ray powder diffraction and scanning electron microscopy. The results showed the materials reached high fracture toughness, low hardness and a microstructure with TiN grains dispersed in a β-Si 3 N 4 matrix containing an amorphous intergranular phase.

Silicon nitride ceramics with SiO 2 , CaO, and MgO as sintering aids were investigated in view of biomedical applications. In the current study, samples with four different compositions were pressureless sintered at 1750 C for 1 h under a nitrogen atmosphere. The samples were evaluated concerning densification, microstructure, mechanical properties, and in vitro bioactivity. Microstructures with elongated β-Si 3 N 4 grains dispersed in an intergranular phase and with densities from 78.77 to 97.14% of the theoretical density were obtained. Higher contents of SiO 2 resulted in the best densification and mechanical properties. Besides, replacements of CaO by MgO in the initial compositions affected Young's modulus and in vitro bioactivity.Considering the samples with relative density higher than 94.14%, those with lower values of Young's modulus had lower SiO 2 /MgO ratios. After immersion in SBF (Simulated Body Fluid), the samples with high porosity and/or partial replacements of CaO by MgO had their surfaces coated with a layer rich in calcium and phosphorus, morphologically similar to hydroxyapatite. Hence, producing silicon nitride ceramics with the potential to be used as orthopedic implants must consider ideal amounts of additives. In this article, the best combination of mechanical properties and mineralization capability was reached by the composition with low content of MgO, and high content of SiO 2 and CaO.