Rare-earth zirconate is one of the most promising candidate materials for the next generation thermal barrier coatings . However, at high temperatures the thermal conductivity of the rare-earth zirconate increases because of radiation. NiCr 2 O 4 , which can absorb the infrared photons intensely, was introduced to reduce the radiative thermal conductivity of Sm 2 Zr 2 O 7 . NiCr 2 O 4 and Sm 2 Zr 2 O 7 powders were prepared by coprecipitation method. The bulks of Sm 2 Zr 2 O 7 – x vol% NiCr 2 O 4 ( x =0, 5, 10, 15 and 20) composites were prepared by non-pressure sintering. The phase, microstructure and composition of the samples were characterized. The absorptivity and the thermal conductivity of the composites were also tested. The absorptivity of the composites was enhanced as increasing the content of NiCr 2 O 4 . The total thermal conductivities of the composites were higher than that of pure Sm 2 Zr 2 O 7 , but the recovery of the thermal conductivity of rare-earth zirconate was relived or disappeared in the testing temperature range.
The development of exceptionally active and stable electrocatalysts for the urea oxidation reaction (UOR) is a current research topic of interest. In this work, NiO/NiCr2O4 nanocomposites with different CrNi ratios (denoted as NiO/NiCr2O4-m, m = 1, 2, 3) were synthesized by a facile one-pot hydrothermal mothed without any template followed by a thermal treatment in N2 at 600 °C. The NiO/NiCr2O4-2 catalyst exhibited a large electrochemical surface area, which provided numerous accessible active sites and electronic transmission channels for the UOR. At a low catalyst loading of 50 μg cm–2, NiO/NiCr2O4-2 electrode delivered a current density of 994 mA cm−2 mg−1 (49.7 mA cm−2) in an electrolyte of 1.0 M KOH with 0.33 M urea at the potential of +0.5 V vs Ag/AgCl. The catalyst showed excellent redox characteristics and better stability compared to catalysts with other ratios of NiO/NiCr2O4, pure NiO and NiCr2O4 prepared similarly. Benefiting from the synergistic effect of NiO and NiCr2O4, multicomponent catalysts, particularly NiO/NiCr2O4-2, have demonstrated excellent electrocatalytic activities and are considered as promising candidates for direct urea fuel cells.
B. Meng,Q. S. Fu,X. H. Chen,G. S. Gong,C. Chakrabarti,Y. Q. Wang,S. L. Yuan
A series of polycrystalline NiCr2−xAlxO4 (0.1 ≤ x ≤ 0.25) spinel ceramics have been synthesized using a sol–gel method. DC magnetization measurements are carried out at different temperatures and magnetic fields. A novel magnetization reversal has been observed in the field cooling process for the x = 0.2 sample, which can be ascribed to the competition between two magnetic sublattices due to their different temperature dependences. The magnetic interaction evolution, related to the complex magnetic properties, is revealed by exchange constants that have been estimated according to ferrimagnetic Curie–Weiss fitting and mean field theory. The fitting result confirmed the evolution of antiferromagnetic and ferromagnetic components with Al substitution, which is supported by the observations from the isothermal magnetization measurements. The positive and negative values of the magnetic moment can be utilized for storage applications based on the results of magnetic switching effect measurements.
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