Key Engineering Materials Vol. 806

Abstract: Corrosion activity of the aircraft Al-Mg-Sc aluminium alloy has been studied using scanning electrochemical method. Microstructure analysis and phase composition have been determined in the present work. The reason of localized corrosion of the aluminium alloy has been established. This study promotes to understand the mechanism of the corrosion destruction of the material and to design technologies of its corrosion protection.

Abstract: Sn-containing oxide coatings were prepared via plasma electrolytic oxidation (PEO) of Ti plate in the electrolytes with [Sn^II-EDTA]^2- complex anions or SnO₂ particles in the anode and anodic-cathodic modes. The coatings formed in electrolyte with SnO₂ particles stabilized by SAS contain SnO₂ and Sn⁰. In the electrolyte with [Sn-EDTA]^2- complex anions, the SnO₂-containing coatings were formed in the anodic mode while Sn⁰-containing ones were obtained in the anodic-cathodic mode. SnO₂-containing structures formed in the electrolytes with [Sn-EDTA]^2- anions are shown to be active in catalytic oxidation of CO into CO₂ at temperatures above 350 °C. They can be the basis for the preparation of both carriers of catalytically active compounds and catalysts for redox reactions. Potentiometric tests showed that the Sn-containing PEO layers on titanium exhibit the most characteristic pH function for the metal oxide electrodes in the direct potentiometry and acid-base titration.

Abstract: This paper presents results of the application of Ti/ta-C films to micro drilling operation for machining. Tetrahedral amorphous carbon (ta-C) films were successfully deposited on WC-Co substrates by a filtered cathodic vacuum arc (FCVA) system. The mechanical and flexion properties of Ti/ta-C films were systematically investigated. The experimental results show that the Ti/ta-C coated micro drills have the excellent microhardness, adhesion and flexion properties and represent the optimal coatings for micro drilling applications. The role of the Ti –sublayer on a sintered powder tungsten carbide substrate is not only limited by the adhesion improvement, but it is mainly used to neutralise the grain boundary microcracks on a surface. The results of drilling tests carried out on PCB boards showed that the durability and drilling efficiency of tools coated by Ti/ta-C films are significantly higher than that of uncoated ones.

Abstract: Nowadays the most perspective, high-tech and productive process is friction stir spot welding. The most important part of this technology is to determine the temperature of the material in the stir zone. This parameter is easily counted by the amount of the heat input, put in the welding zone. We made experimental researches about the relation of the heat power, therotation speed and the diameter of the working tool. For that purpose an experimental scheme was chosen, which models a welding material (aluminum alloy AMg5) as an experimental tube 20 mm in diameter. The tool (shear steel P6M5) is modeled as a working plate. Measurements of the frictional moments depending on the rotation speed of the experimental working tube during the constant temperature are made on the prepared stand. By the experimental data the specific heat input and the heat power were counted on every concentric ring, 2 mm in width, in the end of the working tool, 20 mm in diameter. Also, the sum of the heat power for the whole tool during various rotation speed terms was counted too. On the stand throughout the experiment were determined all the thermal conductivity heat losses along the rod, which the experimental tube was pinned on, all the working plate heat losses through the gasket towards the working desk and the convection from the surface of the rotating experimental tube to the environment. According the data, any of these losses is from 3 to 10 percent. This is shown in the heat input counting.

Abstract: Temperature-programmed reduction (TPR) is a widely used method for characterization of oxide-based catalysts, sorbents, and functional materials, but its results lack quantitative assessment. Here, we present a novel approach to kinetic analysis of the TPR that can be applied to a large variety of systems involving multiple limiting stages. Implementation of cubic splines to approximate rate constant vs. conversion dependencies obtained from several TPR curves recorded at different heating rates yields in a set of kinetic parameters (activation energy and preexponential factors) for all reduction stages. Relationship between preexponential factor of the first reduction stage and the specific surface area of the sample has been shown. Reduction of hematite has been studied to prove the performance of the developed kinetic analysis technique.

Abstract: We have studied temperature-induced phase transitions in PbZrO₃ thin films by X-ray diffraction. By tracing the temperature dependence of superstructure reflections we show that the onset of antiferroelectric ordering takes place highly continuously on cooling and another, presumably ferroelectric phase is present at high temperatures, between the antiferroelectric and cubic phases. To clarify the possible reason for this behavior, we have investigated the X-ray diffraction profile with momentum transfer along the normal to the film surface and carried out the relevant simulation using the formalism of scattering by inhomogeneously deformed sample. From the analysis it follows that the near-interface layer is effectively compressed along the normal to the film. We associate this observation with the presence of dislocations through which the film is relaxed. The results suggest that the reasons for the phase transition sequence modification in thin films can be associated with inhomogeneous distribution of stress and defects in the near-interface area.

Abstract: The hydrolytic lignin (HL) derivatives have been prepared via its physical activation (high-temperature annealing in vacuum) followed by chemical modification (fluorination). It was found that the graphitized product of thermal activation up to 1000 °C at a low temperature gain rate of < 2 °C/min under high vacuum shows an enhanced specific surface area (215 m²/g), that makes it potentially useful as sorbent, catalytic substrate, or electrode material. It was revealed from the experimental data the manufactured graphitized material consists of nanometric structural blocks, possibly nanographites and/or few-layer nanographenes. The edges of graphenes in agglomerates in activated hydrolytic lignin (AHL) have armchair and zigzag shapes. The nontrivial electronic structure of the zigzag edges, along with the electronic conductivity and the ability of AHL to absorb oxygen, can cause an increase in the energy intensity of lithium battery (LB) manufactured using AHL.The carbon-fluorine bond of semi-ionic type was detected in HL and AHL fluorinated in the temperature range of synthesize 60 – 300 oC. The fluorinated forms of both HL and its thermally activated product show increased values of operating voltage due to the participation of fluorine bound to carbon in the electrochemical process.

Abstract: The paper is devoted to studying the effect of the specific surface area (SSA) of SiO₂ nanopowders (3 wt.%) added to BaSO₄ powders of a micron size on grain size distribution and diffuse reflectance spectra (ρ_λ) within the UV, visible, and near IR regions. Additionally, the authors have examined the spectra alteration (Δρ_λ) after irradiating with electrons (E=30 KeV). It has been established that mere mixing of the powders at a low concentration of nanoparticles leads to the post-irradiation decrease in the reflective power and to the subsequent increase in the reflectance coefficient stability.

Abstract: There is serious concern that fat-soluble phthalates such as di (2-ethylhexyl) phthalate, or DEPH. Phthalates are not chemically bonded to the PVC and will with time escape by evaporation or by extraction when in contact with liquids. Raman spectroscopy excited with a 785 nm laser can be used to determine the content of plasticizers in commercial flexible polyvinyl chloride (PVC) construction plastics. This method is very convenient for rapid non-destructive remote determination of phthalates, such as for quality control of production lines, quality control or at customs.

Abstract: The ZrW_2-xMo_xO₈ (0≤x≤2) system has a unique property - a negative coefficient of thermal expansion (CTE), that is it shrinks when heated. Such materials solve the problem of undesirable thermal expansion of composites in many areas. In contradistinction to ZrW₂O₈ and ZrMo₂O₈, this system has anomalously low CTE values [1,2] and adverse phase transition is shifted to a lower temperature, unlikely area for operation [3,4]. At the same time, the fundamental question remains about the mechanism of formation of ZrW_2-xMo_xO₈(0≤x≤2). According to [5,6], pure cubic ZrW₂O₈ and ZrMo₂O₈ are obtained by thermal decomposition of the precursor ZrM₂O₇(OH)₂· 2H₂O, where (M = Mo, W). However, the structure of the precursor is extremely sensitive to various changes in the synthesis process. To date, there are a number of works devoted to the hydrothermal synthesis of precursors ZrW_2-xMo_xO₇(OH)₂·2H₂O (0≤x≤2) solid solutions, however, not all formulations were obtained during the hydrothermal reaction. The study of their thermal properties, as well as structural and phase transformations are not fully studied. Within the paper it was first time proposed to obtain full number of nanosized materials by the hydrothermal method and also to study the nature of the thermal expansion of each member of the solid solution. The obtained data will solve many technical problems associated with dimensional nonvariance in the electronic, oil and gas, optical industry, medicine and rocket engineering.