A.Yu. Potanin

Silicon carbide ceramics SHS-produced from mechanoactivated Si–C–B mixtures

We investigated the influence of mechanical activation (MA) and initial temperature T0 on combustion temperature Tc and burning velocity Uc for 90% (Si + C)–10% (4B + C) mixtures as well as on product morphology. Mechanical activation was found to strongly change the size and morphology of Si and graphite particles (by a factor of 6–8), lead to accumulation of micro strains, and increase the reactivity of green mixture. An increase in T0 was found to proportionally increase the values of Tc and Uc but produce little or no influence on the phase composition of product. The SiC powder consisting of 50–100 nm crystallites was obtained by diminution of combustion product and then used to prepare, by hot pressing, a ceramic PVD target for magnetron sputtering.

Synthesis of high-temperature Mo5SiB2-based ceramics in the combustion mode

This study is devoted to the synthesis and investigation of the Mo5SiB2-based ceramic material (T2 phase). The influence of the initial temperature on basic combustion parameters is shown. It is found that preheating the reaction mixture enables the initiation of the combustion in the self-oscillatory mode and the initial temperature dependences of the combustion temperature and rate have a linear character. The effective activation energy of the SHS process is calculated. Some variants of chemical reactions between Mo, Si, and B are proposed to explain the combustion mechanism in the investigated ternary system. Compacted samples are obtained using the forced SHS compaction. The phase composition, structure, and properties of synthesized ceramic materials, in which Mo5SiB2 grains are the main component with an average size of 10–20 μm, are studied. The lines of Mo3Si and Mo intermediate phases, the total fraction of which does not exceed 4%, are identified as well. The produced T2 phase-based material has a high specific density and hardness.

Kinetics and High-Temperature Oxidation Mechanism of Ceramic Materials in the ZrB2–SiC–MoSi2 System

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.

Synthesis of Ceramic Materials Based on Titanium Carbide with a Cobalt Binder for the Pulsed Electrospark Deposition of Bioactive Coatings with an Antibacterial Effect

The goal of this study was to produce biocompatible ceramic materials in the Ti–C–Co–Ca3(PO4)2–Ag–Mg system by combustion mode synthesis. The influence of cobalt on combustion parameters of the mixture, structure, and properties of the products was investigated. Compact ceramics consist of a combined grain frame of nonstoichiometric titanium carbide (TiC0.5–TiC0.6) with the titanium phosphate (Ti3POx) phase homogeneously distributed along grain boundaries and local isolations of calcium oxide (CaO). The introduction of cobalt promotes the formation of a complex phosphide CoTiP and TiCo intermetallic compound. Alloying with silver and magnesium leads to the formation of a silver-based solid solution.

Metal-Doped MgB2 by Thermal Explosion: A TRXRD Study

The work aimed at preparation of the MgB2 doped with alloying metals (Al, Cu, Ag, Zn) by SHS in a mode of thermal explosion. The measured combustion temperatures fell within the range 940–1030°С. Detailed XRD analysis has shown that, among other selected metals, it is solely Al that can enter the MgB2 lattice. According to time-resolved XRD results, the formation of final product (Mg, Al)B2 in the Mg–Al–B system involved no intermediate phases. But in the Mg–Cu–B system, the volume reaction additionally yielded MgB4, Cu2Mg, and CuMg2 due to the presence of the liquid phase. In final products, the agglomerates of MgB2 grains had a size of 500–1000 nm, while the size of Cu2Mg and CuMg2 inclusions was within 0.5–2 μm.

Dynamics of phase formation during the synthesis of magnesium diboride from elements in thermal explosion mode

The influence of the heating rate of the Mg + 2B mixture on the dynamics of the phase formation during the thermal explosion in the helium medium is investigated by the time-resolved X-ray diffraction method. It is shown that the MgB2 phase appears without the formation of intermediate compounds. The presence of impurity oxygen is a substantial factor affecting the formation kinetics of MgB2. The oxide film on the surface of magnesium particles has no time to form with the heating rate of the charge mixture of 150–200°C/min. A result of this circumstance is the reaction diffusion mechanism of the Mg + 2B = MgB2 reaction immediately after the melting of magnesium. Synthesis products mainly consist of MgB2 and MgO traces at a level of 5%. The thermal explosion temperature is 1100°C. A comparatively thick oxide film which retards melt spreading and shifts the onset of the formation reaction of MgB2 by 8–9 s grows on the magnesium surface at a heating rate of 30–50°C/min. Synthesis products contain MgB2 and up to 15% MgO. The thermal explosion temperature is 1020°C in this case.