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This work continues the earlier studies focusing on fabrication of heterophase micropowders and consolidated ceramics based on HfB2–HfC–SiC ultra-high-temperature boride/carbide compositions via self-propagating high-temperature synthesis (SHS) and hot pressing (HP). The effect of NH4Cl addition on the morphology and microstructure of the SHS powders was studied. Composite micropowders characterized by particle size of 0.2–10 μm and 40–50% content of the submicron-sized fraction were fabricated. The structure, mechanical and thermophysical properties, kinetics and mechanism of high-temperature oxidation of hot-pressed ceramic materials composed of 57–72 wt % HfB2, 14–20 wt % HfCx, 10–14 wt % SiC, and 8–15 wt % HfO2 were studied. They are found to have hardness up to 18.9 GPa, crack resistance up to 9.7 MPa m0.5, bending strength up to 400 MPa, temperature diffusivity up to 22.6 mm2/s, and thermal conductivity up to 59 W/(m K). The power law describes their oxidation kinetics. The protection mechanism against oxidation involves the formation of a multilayered heterogenous oxide film consisting of HfO2, HfSiO4, and borosilicate glass. [ABSTRACT FROM AUTHOR]

This work is devoted to the production of a ceramic target (ZrSi2–ZrB2–MoSi2)/Cr by hot pressing of products of self-propagating high-temperature synthesis and deposition of coatings in the Zr–Si–Mo–B system by DC magnetron sputtering and high-power pulsed magnetron sputtering. The composition and structure of the initial powder mixtures, SHS products, a two-layer functionally graded target, and coatings deposited during its sputtering have been studied. It is shown that the developed target (ZrSi2–ZrB2–MoSi2)/Cr can be successfully used to obtain coatings with a dense homogeneous defect-free structure, including at high-energy sputtering regimes, peak current of 50 A, and peak power of 50 kW. [ABSTRACT FROM AUTHOR]

In this study, we investigate the self-propagating high-temperature synthesis (SHS) and consolidation of heterophase MoSi2–MoB ceramics alloyed with ZrB2. A thermodynamic analysis of the combustion temperature (Tad) and the equilibrium composition of synthesis products was performed for the Zr–Mo–Si–B system. The effect of varying Zr and B concentrations on combustion kinetics was studied in detail. The resulting heterophase SHS powders showed high structural and chemical homogeneity, though were noticeably agglomerated. We identified optimal consolidation conditions and achieved compact ceramics with a phase composition identical to the original SHS powder. The ceramic structure consists of a matrix of MoSi2 grains with interspersed needle-like ZrB2 grains and polyhedral inclusions of MoB. This work establishes a basis for the preparation of MoSi2–MoB–ZrB2 ceramics with excellent hardness, fracture toughness, thermal conductivity, and high-temperature oxidation resistance. [ABSTRACT FROM AUTHOR]

The synthesis method of aluminium oxynitride (AlON) powders by nitriding of Al/Al2O3 mixture under highpressure nitrogen is proposed. The novelty of this method consists in adding KClO4 or Mg(ClO4)2 and extra Al into the starting mixture (Al+Al2O3) to cause the exothermal aluminium oxidation reaction, which therefore initiates the aluminium nitriding reaction. The microstructure and phase composition of the AlON powders obtained by self-propagating high-temperature synthesis are demonstrated by means of SEM and XRD analysis. Diffuse reflection spectra of AlON powders have been measured and the values of band-gap energy have been calculated. Optical transmission and reflection characteristics of the AlON ceramic samples sintered from AlON powders at 1930°C have been studied. The influence of the technological parameters of ceramics production on their transparency is revealed - the most transparent sample is obtained from the powders synthesized with the Mg(ClO4)2 additive and sintered for 6 h. [ABSTRACT FROM AUTHOR]

This study is devoted to the fabrication of the ZrB2-SiC-(MoSi2) compact ceramics according to hybrid technology (self-propagating high-temperature synthesis (SHS) + hot pressing), as well as to investigating its phase composition, structure, and high-temperature oxidation kinetics. Reaction mixtures are prepared according to the following scheme: mechanical activation (MA) of Si + C powders; wet admixing of Zr, B, and Si + C MA-mixture powders; and drying mixtures in a drying oven. The ZrB2-SiC SHS composite powder is formed in a reactor in a combustion mode by elemental synthesis. Compact samples with a homogeneous structure and low residual porosity not exceeding 1.3% are formed by hot pressing the SHS powder. Two compositions are selected for testing, notably, the first one calculated for the formation of ZrB2 + 25% SiC; the second composition is similar to the first one, but with the addition of 5% of the MoSi2 commercial powder. The microstructure of the samples is presented by dispersed dark gray rounded SiC grains distributed among light faceted ZrB2 grains. The sample with the MoSi2 additive has a more finely dispersed structure. The high-temperature oxidation of the samples at 1200°C results in the formation of SiO2‒ZrB2-(B2O3) complex oxide films on their surface with a thickness on the order of 20-30 μm, which serve as an efficient diffusion barrier and lower the oxidation rate. Their structure also contains ZrSiO4 complex oxide after prolonged holding (longer than 10 h). In addition, an insignificant weight loss of the samples is observed after 10 h testing, which is caused by the volatilization of gaseous oxidation products (B2O2, CO/CO2, MoO3). The sample with the MoSi2 additive shows better resistance to oxidation. [ABSTRACT FROM AUTHOR]