Nitrogen‐containing steels have become an attractive material in industrial fields due to their excellent mechanical properties. Nevertheless, the current manufacturing methods to produce nitrogen steels are linked to technologies with high working pressures. Alloying elements such as Cr, Mn, and Mo enhance the solubility of nitrogen in the melt, which allows the production at atmospheric pressure. Herein, carbon–nitrogen martensitic steels are produced at low pressure (7 × 105 Pa). The composition is designed through the CALPHAD method using two carbon contents (0.7 and 1.3 wt%). The alloy is produced in an induction furnace under N2 atmosphere to mitigate desorption. Thermomechanical and heat treatments are performed. The alloys are analyzed using optical emission spectroscopy, X‐ray diffraction, optical microscopy, and scanning electron microscopy (SEM) with energy‐dispersive spectroscopy (EDS). The mechanical evaluation is conducted using hardness analysis. The steel presents a nitrogen content of 0.15 wt%, in agreement with the thermodynamic calculations. SEM and EDS results show the presence of Cr and Nb precipitates in a martensitic structure. The highest hardness values are obtained in specimens heat treated by tempering at 400 °C for 2 h and air cooling, achieving 57.4 and 59.7 Hardness Rockwell C for samples with 0.7 and 1.3 wt% C, respectively.
Molecular sieves of MCM-41 impregnated with MgO, MoO3, and Mo2C synthesized using a wet impregnation method. The compounds developed herein, were characterized by means of XRD, SEM-EDS and FT-IR techniques. The production capacity of acetaldehyde from ethanol was analyzed by catalytic processes employing as-synthesized MCM-41. The obtained results show that the changes in crystallinity of MCM-41 were due to the impregnation of oxides, which generate damage to the structure of MCM-41. However, the characteristics of the compounds are favorable, allowing them to be used as heterogeneous catalyst material due to the similarity of the characteristics between MCM-41 with and without of Mg and Mo oxides. The catalysis tests show the influence between the type of catalyst used and the temperature applied to the production process of acetaldehyde from ethanol, obtaining the best results in the samples impregnated with Mo2C at 250 °C, with a production percentage of acetaldehyde of 80.7% and 77.9% for the catalysts impregnated with 0.5% and 2.0% Mg and 3.0% Mo carbide, respectively.
Context: The high consumption of parts made from expanded polystyrene (EPS) generates environmental problems when disposed. Due to its low density and the low possibility of being utilized in other applications after its disposal, it is necessary to generate an alternative for the recovery and application of this type of waste. This work aims to generate an alternative in the application of EPS waste, particularly as a coarse aggregate in the manufacturing of lightweight concrete. Method: This study used discarded EPS containers as raw material. The material was cleaned, crushed and subsequently reduced in volume by applying acetone, generating pieces of polystyrene (R-PS) to be applied as a coarse aggregate for the manufacturing of lightweight concrete in different proportions. In addition, the pieces were subjected to a chemical attack process in order to observe their behavior. Results: The results show the degree of volume reduction of the EPS pieces by using different acetone ratios, establishing the best degree of reduction (in volume) of this material. Likewise, chemical attack tests show the behavior of R-PS against different agents in R-PS samples. Meanwhile, the failure tests on different concrete samples determine the best R-PS ratio as coarse aggregate for the manufacturing of lightweight concrete. Conclusions: The data obtained in this study show that the application of acetone on EPSW samples reduces its volume by up to 55 %. Concrete failure tests show that an optimum P-RS addition value, to be used as an aggregate in the manufacturing of lightweight concrete, is 7 %. This improves its resistance to chemical agents and weight reduction without significantly reducing the mechanical properties of concrete.
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