International Journal of Self-Propagating High-Temperature Synthesis最新文献

Decagonal quasicrystals in Al–Co–Ni and Al–Co–Cu systems were first prepared by SHS method. XRD analysis showed that the synthesis of Al–Co–Cu system yields Al₇₀Co₁₅Ni₁₅ quasicrystalline phase; meanwhile, in the Al–Co–Ni system, the synthesized product contains Al₇₀Co₁₅Ni₁₅ quasicrystals as a basis with minor addition of cubic Al₅₈Co₇₆Ni₆₆ phase. Both synthesized materials have weak magnetic properties with maximum magnetization of 0.145–0.730 emu/g for the applied magnetic field of 10 kOe.

The combustion initiation of condensed mixture with unlimited mass by limited high-temperature spot was mathematically modelled. It was shown that in contrast to the sample critical diameter, at which the combustion dies out due to heat loss, the critical radius of the hot spot upon initiation of large-volume gas-free mixture is determined only by its physicochemical characteristics (Zel’dovich number).

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 (T_ad) 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.

Experimental dependences of the combustion velocity on the size of titanium particles for powder and granular mixtures of 5Ti + 3Si, Ti + C^am, (Ti + C^am) + 20% Cu, (Ti + C^am) + 20% Ni, Ti + C^cr (with amorphous carbon in the form of soot and with crystalline carbon in the form of graphite) were compared. The results of experiments were explained by the retarding effect of impurity gases in powder mixtures when the conditions of warming up the particles before the combustion front were met. For all the studied granular mixtures, where the influence of impurity gases on the combustion velocity was leveled, analytical dependences of the combustion velocity on the size of titanium particles were in good agreement with the conclusions of the convective–conductive combustion model.

Lithium aluminate samples were obtained in reactions of solution combustion synthesis (SCS) with various types of fuel (glycine, leucine, and urea) from aluminum and lithium nitrate solutions. The simultaneous thermal analysis (STA) of precursors obtained in conditions of fuel and oxidizer stoichiometry showed the presence of impurities due to incomplete decomposition of initial salts containing carbon fragments of fuel and nitrate groups. An exception was the precursor from the dual-fuel SCS reaction, φ (glycine : urea) = 1 : 3, in which pure γ-LiAlO₂ powder was formed. Replacement of lithium nitrate with lithium carbonate was found to reduce the process temperature and the relative amount of organic fuel. As a result, the content of carbon fragments in the precursor significantly decreased after synthesis.

TiC–NiTi cermet composites were fabricated by forced SHS compaction from (Ti + C + Ni) mixtures with varying content of Ni + Ti from 28 to 90 wt %. The phase composition and microstructure were characterized by X-ray diffraction method, scanning electron microscopy, and energy dispersive spectroscopy. The microstructure of composites was shown to contain spherical TiC particles surrounded by the matrix including TiNi₃, TiNi(B2), Ti₂Ni, and Ti₃Ni₄ phases. As Ni + Ti content was increased, there was a change in the stoichiometry of TiC (from TiC₁ to TiC_0.43) and its particle size (from 6.5 to 0.2 μm). It was found that the microhardness of TiC–NiTi composites dropped markedly from 23.5 to 6.4 GPa.