ABSTRACT
In recent years, the use of cermets has shown significant growth in the industry due to their interesting features that combine properties of metals and ceramics, and there are different possible types of cermets, depending on their composition. This review focuses on cemented tungsten carbides (WC), and tungsten carbonitrides (WCN), and it is intended to analyze the relationship between chemical composition and processing techniques of these materials, which results in their particular microstructural and mechanical properties. Moreover, the use of cermets as a printing material in additive manufacturing or 3D printing processes has recently emerged as one of the scenarios with the greatest projection, considering that they manufacture parts with greater versatility, lower manufacturing costs, lower raw material expenditure and with advanced designs. Therefore, this review compiled and analyzed scientific papers devoted to the synthesis, properties and uses of cermets of TiC and WC in additive manufacturing processes reported thus far.
ABSTRACT
In this study, titanium dioxide powder obtained by the sol-gel method and TiO2 nanotubes, were prepared. In order to increase the TiO2 photoactivity, the powders and nanotubes obtained were modified by dye sensitization treatment during the oxide synthesis. The sensitizers applied were Quinizarin (Q) and Zinc protoporphyrin (P). The materials synthesized were extensively characterized and it was found that the dye sensitization treatment leads to modify the optical and surface properties of Titania. It was also found that the effectiveness of the dye-sensitized catalysts in the phenol and methyl orange (MO) photodegradation strongly depends on the dye sensitizer employed. Thus, the highest degradation rate for MO was obtained over the conventional Q-TiO2 photocatalyst. In the case of the nanotubes series, the most effective photocatalyst in the MO degradation was based on TiO2-nanotubes sensitized with the dye protoporfirin (ZnP). Selected catalysts were also tested in the phenol and MO photodegradation under visible light and it was observed that these samples are also active under this radiation.
ABSTRACT
In the last ten years, there has been an acceleration in the pace at which new catalysts for the water-gas shift reaction are designed and synthesized. Pt-based catalysts remain the best solution when only activity is considered. However, cost, operation temperature, and deactivation phenomena are important variables when these catalysts are scaled in industry. Here, a new catalyst, Au/TiO2-Y2O3, is presented as an alternative to the less selective Pt/oxide systems. Experimental and theoretical techniques are combined to design, synthesize, characterize and analyze the performance of this system. The mixed oxide demonstrates a synergistic effect, improving the activity of the catalyst not only at large-to-medium temperatures but also at low temperatures. This effect is related to the homogeneous dispersion of the vacancies that act both as nucleation centers for smaller and more active gold nanoparticles and as dissociation sites for water molecules. The calculated reaction path points to carboxyl formation as the rate-limiting step with an activation energy of 6.9 kcal mol-1, which is in quantitative agreement with experimental measurements and, to the best of our knowledge, it is the lowest activation energy reported for the water-gas shift reaction. This discovery demonstrates the importance of combining experimental and theoretical techniques to model and understand catalytic processes and opens the door to new improvements to reduce the operating temperature and the deactivation of the catalyst.
