Estimation of the Effect of Redox Treatment on Microstructure and Tendency to Brittle Fracture of Anode Materials of YSZ–NiO(Ni) System

The effect of reduction treatment in a high-temperature (600 °C) hydrogen-containing environment on the microstructure and tendency to brittle fracture of YSZ–NiO(Ni) materials for solid oxide fuel cell anodes has been studied. To assess the crack growth resistance of the ceramics, the Vickers indentation technique was adapted, which allowed estimating the microhardness and fracture toughness of the material in the complex.The requirements for high porosity of the anodes to ensure functional properties show that the strength may be an insufficient characteristic of the bearing capacity of the anode. More structurally sensitive characteristics are needed to assess its crack growth resistance.The average levels of microhardness of YSZ–NiO ceramics in the as-sintered state and YSZ–NiO(Ni) cermets (2.0 GPa and 0.8 GPa, respectively) and their fracture toughness (3.75 MPa·m1/2 and 2.9 MPa·m1/2, respectively) were experimentally determined.It was found that the microstructure of YSZ–NiO(Ni) cermet after redox treatment is formed by a YSZ ceramic skeleton with refined Ni-phase grains combined in a network, which provides increased electrical conductivity. Along with higher porosity of the cermet, its fracture toughness is not lower than that of the one-time reduced cermet due to the implementation of the bridging toughening mechanism of fracture.The proposed treatment method allowed forming the microstructure of the anode material, resistant to crack propagation under mechanical load. The propensity of the anode material to brittle fracture on the basis of evaluation of its crack growth resistance and analysis of the microstructure and fracture micromechanism was substantiated. This result is interesting from a theoretical point of view. From a practical point of view, the developed technique allows determining the conditions of redox treatment in the technology of manufacturing fuel cell anode

The effect of electrolyte composition on the plasma electrolyte oxidation and phase composition of oxide ceramic coatings formed on 2024 aluminium alloy

Purpose: Purpose of this work is to analyse the process of synthesis of oxide ceramic coatings in plasma electrolytes on 2024 aluminium alloy and to form an electrolyte which allows to reduce energy consumption for the coating formation. Design/methodology/approach: The oxide ceramic coatings were synthesized on 2024 aluminium alloy. The coatings were formed by the alternate application of anode and cathode pulses to the sample. X-ray diffraction analysis of coatings was performed on a DRON-3.0 X-ray diffractometer using CuKa radiation. The thickness of the coatings was determined using a CHY TG-05 thickness gauge. The porosity of the coatings was investigated by analysing the micrographs of the plasma electrolyte oxidation (PEO) coatings obtained on a scanning electron microscope at x500 magnification using the image processing technique. Findings: The electrolyte with 5 g/l H2O2 additive have been elaborated as an optimal composition for synthesis of a coating with an increased content of corundum (a-Al2O3) as compared to a coating synthesized in the same mode in the 3KOH+2Na2SiO3 electrolyte without H2O2. This synthesis mode allows obtaining a coating with a high corundum content at low energy consumption. Research limitations/implications: For further optimization of the synthesis modes, it is necessary to analyse the influence of the phase composition and porosity of the obtained oxide ceramic coatings on their microhardness, wear resistance, and corrosion resistance. Practical implications: Based on the developed modes of synthesis of the coatings, it will be possible to obtain wear and corrosion resistant oxide ceramic coatings with predetermined functional properties and to reduce energy consumption for their formation. Originality/value: Methods for accelerating the formation of coatings have been proposed and tested, in particular, by adding various amounts of hydrogen peroxide to the electrolyte. The content of oxides in the obtained coatings, in particular, their ratios at various concentrations of hydrogen peroxide in the electrolyte, were determined by X-ray phase analysis. The modes of synthesis of the coatings were developed which allow obtaining a continuous coating without cracks with simultaneous decreasing porosity from 4.32% to 3.55-3.53%

Methane as a resource: can the methanotrophs add value?

Methane is an abundant gas used in energy recovery systems, heating, and transport. Methanotrophs are bacteria capable of using methane as their sole carbon source. Although intensively researched, the myriad of potential biotechnological applications of methanotrophic bacteria has not been comprehensively discussed in a single review. Methanotrophs can generate single-cell protein, biopolymers, components for nanotechnology applications (surface layers), soluble metabolites (methanol, formaldehyde, organic acids, and ectoine), lipids (biodiesel and health supplements), growth media, and vitamin B12 using methane as their carbon source. They may be genetically engineered to produce new compounds such as carotenoids or farnesene. Some enzymes (dehydrogenases, oxidase, and catalase) are valuable products with high conversion efficiencies and can generate methanol or sequester CO2 as formic acid ex vivo. Live cultures can be used for bioremediation, chemical transformation (propene to propylene oxide), wastewater denitrification, as components of biosensors, or possibly for directly generating electricity. This review demonstrates the potential for methanotrophs and their consortia to generate value while using methane as a carbon source. While there are notable challenges using a low solubility gas as a carbon source, the massive methane resource, and the potential cost savings while sequestering a greenhouse gas, keeps interest piqued in these unique bacteria