Effect of a Support on the Properties of Zinc Oxide Based Sorbents

We present the comparative analysis of three Zn-based sorbents for the process of sulphur removal from hot coal gas. The sorbents were prepared by a slurry impregnation of TiO2, SiO2 and Al2O3, resulting in complex, multiphase materials, with the dominant phases of Zn2TiO4, Zn2SiO4 and ZnAl2O4, respectively. We have analyzed the effect of supports on the phase composition, texture, reducibility and H2S sorption. We have found that the phase composition significantly influences the susceptibility of the investigated materials to reduction by hydrogen. Zn2TiO4 have been found to be the easiest to reduce which correlates with its ability to adsorb the largest amount of hydrogen sulphide—up to 4.2 gS/100 g—compared to the other sorbents, which absorb up to 2.2 gS/100 g. In the case of Zn2SiO4 and ZnAl2O4, this effect also correlates with reducibility—these sorbents have been found to be highly resistant to reduction by hydrogen and to absorb much less hydrogen sulphide. In addition, the capacity of ZnAl2O4 for H2S adsorption decreases in the subsequent work cycles—from 2.2 gS/100 g in the first cycle to 0.8 gS/100 g in the third one. Computational analysis on the DFT level has shown that these materials show different thermodynamic stability of sulphur sites within the unit cells of the sorbents. For Zn2TiO4 and Zn2SiO4, the adsorption is favorable in both the first and second layers of the former and only the top layer of the latter, while for zinc aluminate it is not favorable, which is consistent with the experimental findings.

Cavitation erosion damage of self-fluxing NiCrSiB hardfacings deposited by oxy-acetylene powder welding

This paper comparatively investigates the cavitation erosion damage of two self-fluxing NiCrSiB hardfacings deposited via the oxy-acetylene powder welding method. Examinations were conducted according to the procedure given by ASTM G32 standard. In order to research cavitation erosion (CE), the vibratory apparatus was employed. The cavitation damaged surfaces were inspected using a scanning electron microscope, optical microscope and surface profilometer. The hardness of the A-NiCrSiB hardfacing equals 908HV while that of C-NiCrSiB amounts to 399HV. The research showed that the CE resistance of C-NiCrSiB is higher than that of A-NiCrSiB. The results demonstrate that in the case of multiphase materials, like the NiCrSiB hardfacings, hardness cannot be the key factor for cavitation erosion damage estimation whereas it is strongly subjected to material microstructure. In order to qualitatively recognise the cavitation erosion damage of the NiCrSiB self-fluxing hardfacings at a given exposure time, the following factors should be respected: physical and mechanical properties, material microstructure and also material loss and eroded surface morphology, both stated at specific testing time. The general idea for the cavitation erosion damage estimation of the NiCrSiB oxy-acetylene welds was presented.

SYNTHESIS OF CERIUM YTTRIUM COSTABILIZED ZIRCONIUM DI-OXIDE BY SOLGEL PROCESS

The Sol–gel route was used to synthesize Ceria– Yttria co-stabilized Zirconia (CYSZ) nanoparticles. The addition of stabilizing oxides to pure Zirconia, such as CaO, MgO, CeO2, and Y2O3, allows for the formation of multiphase materials, which are referred to as CoStabilized Zirconia. Cerium Oxide CeO2 and Yttrium Oxide Y2O3 are co-stabilized with Zirconium Oxide in this study. The creation of nanostructured coatings has been shown to boost the efficiency of TBCs by lowering thermal conductivity, increasing bonding power, and increasing thermal cycling lifetime, according to researchers. The crystallinity and stabilization of cubic crystalline phases were studied by energy dispersive X-ray spectroscopy (EDAX) at different calcination temperatures in the range of 500°C to 1200°C, and surface morphology and compositional analysis were studied by scanning electron microscopy using the sol-gel process (SEM). The research yielded interesting results, but it was discovered that when Zirconium Dioxide was synthesized using the sol-gel process, the tetragonal phase was not present; thus, other methods to obtain the tetragonal phase would be needed in the future for the application of Thermal Barrier Coating.

A multiscale homogenization procedure to predict the elasto-viscoplastic behavior of polymer-based nanocomposites

It has been demonstrated that adding a few percent of nanoscale reinforcements, leads to remarkable improvement in mechanical properties of the polymers such as stiffness, damping, and energy absorption. These lightweight materials are attractive substitutes for the heavy metallic structural parts in the automotive, military, aerospace and many other industries. However, due to complexity of these multiphase materials, accurate modeling of their behavior in real loading cases is still ambiguous. The impact simulation is a vital step in design procedure of a vehicle, where a strain rate-dependent model of its components is required. In this paper, an elasto-viscoplastic modeling procedure of the polymer-based nanocomposites, assuming the elastic behavior of the nano-phase is presented; whereas the polymeric matrix deformation is dependent to the loading rate and is characterized by the method of Genetic algorithm optimization-based fitting to the experimental observations. By introducing a modified Halpin-Tsai method, the nanocomposite is then modeled as a homogenized material where the modification algorithm is the main challenge. A combination of approaches including parametric analysis, central composite design of experiments and response surface method is proposed to modify the tangent modulus of the polymeric matrix to be passed as the input to the Halpin-Tsai equations. Finally, the procedure is implemented to a set of epoxy-GNP nanocomposites under unidirectional compressive loads with different rates and the stress-strain curves are predicted with a decent precision.

Quantum Size Effects Arising from Nanocomposites Physical Doping with Nanostructures Having High Electron Affinit

This article considers main problems in application of nanostructured materials in high technologies. Theoretical development and experimental verification of methods for creating and studying the properties of physically doped materials with spatially inhomogeneous structure on micro and nanometer scale are proposed. Results of studying 11 quantum size effects exposed to nanocomposites physical doping with nanostructures with high electron affinity are presented. Theoretical and available experimental data were compared in regard to creation of nanostructured materials, including those with increased strength and wear resistance, inhomogeneous at the nanoscale and physically doped with nanostructures, i.e., quantum traps for free electrons. Solving these problems makes it possible to create new nanostructured materials, investigate their varying physical properties, design, manufacture and operate devices and instruments with new technical and functional capabilities, including those used in the nuclear industry. Nanocrystalline structures, as well as composite multiphase materials and coatings properties could be controlled by changing concentrations of the free carbon nanostructures there. It was found out that carbon nanostructures in the composite material significantly improve impact strength, microhardness, luminescence characteristics, temperature resistance and conductivity up to 10 orders of magnitude, and expand the range of such components’ possible applications in comparison with pure materials, for example, copper, aluminum, transition metal carbides, luminophores, semiconductors (thermoelectric) and silicone (siloxane, polysiloxane, organosilicon) compounds