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This article discusses methods for producing a material with gradient multilevel porosity by sintering layer-by-layer distributed α-Fe2O3 nanopowders and submicron powders. Nanopowders with an average particle size of 12 nm are obtained by coprecipitation and submicron powders in the form of hollow spheres are obtained by spray pyrolysis. The powders are consolidated by sintering in a muffle furnace, by hot pressing, and by spark plasma sintering (SPS) at various temperatures, loads, and holding times. It has been demonstrated that sintering in a muffle furnace and hot pressing do not allow one to obtain a compact sample of sufficient strength due to various activity of nano- and submicron powders. SPS produced powdered materials at holding temperatures of 700, 750, 800, and 900°C in 3 min. It has been established that a series of powders produced by SPS at 750°C is characterized by sufficient strength and an open porosity of 20% upon a total porosity of 37%. An increase in temperature in the frames of SPS leads to an increase in particle size in the bulk of nanopowders to the micron range and the partial destruction of hollow submicron spheres. While studying the phase composition of the produced samples, it has been revealed that it is identical to that of the initial powders. However, in the series of samples produced by hot pressing and SPS, the growth of crystals is observed in the bulk of nanopowders in the [001] direction of the highest electric and heat conductance along the punch axes. This is related with the temperature gradient between the bulk of nanopowders and punches and the lowest surface energy of plane (110), including the [001] direction. [ABSTRACT FROM AUTHOR]

The transport properties of p-type oxyselenides with the chemical composition Bi1 –xLaxCuSeO (x = 0.02, 0.04, 0.06) are investigated. An analysis of the temperature dependences of the material resistivity and charge-carrier concentration and mobility show that the substitution of La3+ for Bi3+ ions increases the carrier concentration, presumably, due to the generation of holes as a result of the formation of bismuth vacancies with an increase in the degree of substitution. [ABSTRACT FROM AUTHOR]

The paper is devoted to the modification of enamels for road marking on the basis of binding Akrokam-23 with multi-walled carbon nanotubes with an unmodified and oxidized surface. There are two methods to introduce nanotubes into the enamel traffic. One is to introduce nanotubes directly to the binder solution with intensive ultra-sonic dispersion. Another one is to obtain pre­liminarily dry powdered modifier (nanotubes concentrate in petroleum resin) which is soluble in road enamel. The aim of the investigation was to determine how method of introduction of nanotubes into enamel affects its wear resistance. Using method of thermogravimetric analysis the proper­ties of MWCNTs concentrates in the petroleum resin have been studied. The tests of obtained enamels on the wear resistance showed that the direct introduction of MWCNTs in enamel for road marking gives much greater strengthening effect than the introduction of petroleum resin concentrate. However the direct introduction is characterized by numerous technological diffi­culties. Surface modified carbon nanotubes which were introduced through the concentrate LES do not affect the value of wear resistance but the initial nanotubes increase this value by 20%. In the present study it is shown that the dependence between abrasive wear and concentration of MWCNTs possess significant minimum. When the concentration of multi-walled carbon nano­tubes equals to 0.001% the maximal increase of wear resistance (by 40%) can be achieved.

The article presents the possibility of increasing the water resistance of gypsum binders (GBs) obtained based on synthetic gypsum by introducing additives derived from industrial wastes. Regularities were obtained for the influence of the type and amount of additives on the water/gypsum ratio (W/G), strength indicators and water resistance of high-strength GB. The introduction of a single-component additive to improve water resistance does not have a significant effect. Complex additives based on Portland cement, granulated blast-furnace slag, electric steel-smelting slag, expanded clay dust and granite screenings of various fractions have been developed that make the maximum contribution to improving the water resistance of a high-strength GB based on synthetic calcium sulphate dihydrate, which made it possible to increase the water-resistance coefficient from 0.39 to 0.82., Competing Interests: Declaration of conflicting interestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Simultaneously hard and tough nitride ceramics open new venues for a variety of advanced applications. To produce such materials, attention is focused on the development of high-entropy ceramics, containing four or more metallic components distributed homogeneously in the metallic sublattice. While the fabrication of bulk high-entropy carbides and borides is well established, high-entropy nitrides have only been produced as thin films. Herein, we report on a newel three-step process to fabricate bulk high-entropy nitrides. The high-entropy nitride phase was obtained by exothermic combustion of mechanically-activated nanostructured metallic precursors in nitrogen and consolidated by spark plasma sintering. The fabricated bulk high-entropy nitride (Hf 0.2 Nb 0.2 Ta 0.2 Ti 0.2 Zr 0.2 )N demonstrates outstanding hardness (up to 33 GPa) and fracture toughness (up to 5.2 MPa∙m 1/2 ), significantly surpassing expected values from mixture rules, as well as all other reported binary and high-entropy ceramics and can be used for super-hard coatings, structural materials, optics, and others. The obtained results illustrate the scalable method to produce bulk high-entropy nitrides with the new benchmark properties.