An investigation of the reduction mechanisms and magnesiothermic reactions in ZrC-Ni nanocomposite synthesis (original) (raw)
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Ceramics International, 2015
Nanostructured ZrC powder was synthesized by the mechanochemical process in a high-energy ball mill by a magnesiothermic reaction. The effects of various amounts of Mg (stoichiometric and over-stoichiometric) on synthesis efficiency of the ZrC powders were investigated. The synthesized powders were studied by X-ray diffraction (XRD), differential thermal analysis (DTA), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Zirconium carbide (ZrC) was produced after 30 h milling. Thermodynamic calculation showed the reaction to be a mechanically induced self-sustaining one (MSR). DTA analysis indicated that the temperature of exothermic reaction decreases significantly after 12 h milling.
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A new route to prepare zirconium carbide preceramic powders has been developed using alkoxides polymerized with polyalcohols. Preceramics were pyrolized under vacuum to form metal carbides/metal oxide materials. Best carbide yields were obtained using very low heating rates (0.5°C/min) and reaction time at final temperature higher than 30 min. An explanation of the possible parameters that govern zirconium carbide formation is presented.
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This thesis presents the results of an investigation into the synthesis of ultrafine zirconia powders by mechanochemical processing. The purpose of this investigation was to identify different reaction mechanisms and to establish the effects of process variables on the properties of the final zirconia powders, specifically the average particle size and phase content. All of the reaction systems that were investigated in this study involved reaction of anhydrous chloride precursors with an exchange reagent. However, despite this fundamental similarity, the systems were found to exhibit significantly different reaction kinetics. Depending on the exchange reagent used and the presence of inert diluent, chemical reaction of the precursors either occurred gradually during milling, by mechanically activated combustion, or only during post-milling heat-treatment. Reaction of the ZrCU + 2MgO system occurred gradually during milling and resulted in the formation of ultrafine Zr02 particles embedded within a matrix of M g C l 2. This allowed ultrafine Zr02 powders to be synthesised by either milling the precursors until complete reaction was achieved or by milling for a short duration and then driving the reaction to completion by low temperature heat treatment. The average particle size of the Zr0 2 product formed by reaction of ZrCU + 2MgO was found to decrease with milling time d o w n to a lower limit. In contrast, the addition of M g C l 2 diluent to the reactant mixture was found not to have any significant effect on the average particle size. The effect of milling duration and dilution is consistent with previous studies that suggest the average particle size is determined by the effective reaction volume. Reactant mixtures that used Li20 as the oxide exchange did not undergo chemical reaction during milling. Milling merely resulted in amorphisation of the ZrCl 4 and overall microstructural refinement. Chemical reaction, with the consequent formation of Z r 0 2 and LiCl, only occurred during post-milling heat-treatment. The mechanism of
The Use of ZrO2 Waste for the Electrolytic Production of Composite Ni–P–ZrO2 Powder
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Ni–P–ZrO2 composite powder was obtained from a galvanic nickel bath with ZrO2 powder. Production was conducted under galvanostatic conditions. The Ni–P–ZrO2 composite powder was characterized by the presence of ZrO2 particles covered with electrolytical nanocrystalline Ni–P coating. The chemical composition (XRF method), phase structure (XRD method) and morphology (SEM) of Ni–P–ZrO2 and the distribution of elements in the powder were all investigated. Based on the analyses, it was found that the obtained powder contained about 50 weight % Zr and 40 weight % Ni. Phase structure analysis showed that the basic crystalline component of the tested powder is a mixed oxide of zirconium and yttrium Zr0.92Y0.08O1.96. In addition, the sample contains very large amounts of amorphous compounds (Ni–P). The mechanism to produce the composite powder particles is explained on the basis of Ni2+ ions adsorption process on the metal oxide particles. Current flow through the cell forces the movement of...
Development of Materials Based on the NiAlCrMoCo System Reinforced with ZrO2 Nanoparticles
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This paper describes thermodynamic modeling of the NiAl–CrMoCo system with the calculation of the equilibrium composition and thermodynamic parameters of the system. NiAl-Cr-Mo-Co alloy samples of equiatomic composition, including those with a small addition of zirconium oxide nanoparticles, were obtained by spark plasma sintering of mechanically alloyed powders. It was found that the material had a two-phase structure with wedge-shaped regions enriched in cobalt and molybdenum with a gradient distribution. In addition, in the regions enriched with (Cr, Mo) phase, a lamellar σ phase was found. Fractographic analysis showed a positive effect of the fine-grained wedge-shaped regions on the damping of crack propagation. The alloy with the addition of zirconium oxide nanoparticles had a bending strength and an elastic modulus of 611 MPa and 295 GPa at 25 °C, and 604 MPa and 260 GPa at 750 °C, respectively, when tested in vacuum.
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The reduction behavior of nickel oxide (NiO) and zirconia (Zr) doped NiO (Zr/NiO) was investigated using temperature programmed reduction (TPR) using carbon monoxide (CO) as a reductant and then characterized using X-ray diffraction (XRD), nitrogen absorption isotherm using BET technique and FESEM-EDX. The reduction characteristics of NiO to Ni were examined up to temperature 700 °C and continued with isothermal reduction by 40 vol. % CO in nitrogen. The studies show that the TPR profile of doped NiO slightly shifts to a higher temperature as compared to the undoped NiO which begins at 387 °C and maximum at 461 °C. The interaction between ZrO2 with Ni leads to this slightly increase by 21 to 56 °C of the reduction temperature. Analysis using XRD confirmed, the increasing percentage of Zr from 5 to 15% speed up the reducibility of NiO to Ni at temperature 550 °C. At this temperature, undoped NiO and 5% Zr/NiO still show some crystallinity present of NiO, but 15% Zr/NiO shows no NiO i...
Eastern-European Journal of Enterprise Technologies, 2021
Peculiarities of formation of microstructure in composites based on chemically synthesized zirconium nanopowders obtained by the method of decomposition from fluoride salts were considered. Hydrofluoric acid, concentrated nitric acid, aqueous ammonia solution, metallic zirconium, and polyvinyl alcohol were used. It was established that the reduction of porosity in nanopowders in the sintering process is the main problem in the formation of high-density materials. Analysis of various initial nanopowders, their morphology, and features of sintering by the method of hot pressing with direct transmission of electric current was made. Peculiarities of obtaining the composites based on them with the addition of Al2O3 nanopowders applying the electric sintering method were considered. It was shown that the increase in the content of alumina nano additives leads to an increase in strength and crack resistance of the samples due to simultaneous inhibition of abnormal grain growth and formati...
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In this work, the influence of catalyst preparation temperature on its structure was investigated. We have synthesized 12 different Ni/ZrO2 catalysts by varying the calcination temperature, time, and active metal content, and these catalysts will be further used in the carbon dioxide methanation reaction. Structure and properties of the catalysts were determined using XRD and SEM analysis. Therefore, Ni content of the catalysts were measured by ICP-OES.Regarding to the crystal size calculation using XRD data by Scherer equation, when calcination time was increased the average crystal size of nickel oxide was decreased from 42.38 nm to 38.93 nm whereas it decreased to 39.23 nm when the calcination temperature was increased. This shows that the distribution of active metals in the catalyst increases when the heat treatment parameters are increased. In addition, it can be assumed that the activity of the catalyst can be enhanced when the calcination temperature and time were increases.
Materials Science Forum, 2010
Nickel oxide-yttria stabilized zirconia (NiO-YSZ) for use as solid oxide fuel cell anode were synthesized by coprecipitation to obtain amorphous zirconia and crystallized β-nickel gels of the corresponding metal hydroxides. Hydrothermal treatment at 200°C and 220 psi from 2 up to 16 hours, under stirring, was performed to produce nanocrystalline powder. The as-synthesized powders were uniaxially pressed and sintered in air. Powders were characterized by X-ray diffraction, laser scattering, scanning and transmission electron microscopy (SEM/TEM), gas adsorption technique (BET) and TG-DTA thermal analysis. Ceramic samples were characterized by dilatometric analysis and density measurements by Archimedes method. The characteristics of hydrothermally synthesized powders and compacts were compared to those produced without temperature and pressure application. Crystalline powders were obtained after hydrothermal process, excluding the calcination step from this route. The specific surface area of powders decreases with increasing time of hydrothermal treatment while the agglomerate mean size is not affected by this parameter.