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Vol 25, No 4 (2016)
- Year: 2016
- Articles: 7
- URL: https://journals.rcsi.science/1061-3862/issue/view/12278
Article
SHS-produced Co2+Ti4+-doped barium and strontium hexaferrites: Static and dynamic magnetic properties
Abstract
Static and dynamic magnetic properties of SHS-produced BaFe12–2x(CoхTiх)O19 (х = 1.0, 1.1, 1.2) and SrFe12–2y(CoyTiy)O19 (0 ≤ y ≤ 1.0) hexaferrites were characterized by magnetization and FMR measurements. Dynamic properties of SrFe12–2y(CoyTiy)O19 hexaferrites were rationalized in terms of not only magnetic anisotropy but also the anisotropy of magnetomechanical ratio. SHS-produced ferrites can be recommended for designing radar-absorbent coatings and other SHF devices operating in the range 20–50 GHz.
203-209
Gas emission during combustion of mechanically activated Ni–Al mixtures
Abstract
The features of gas emission taking place during combustion of green compacts prepared from mechanically activated Ni–Al blends were studied experimentally. The volume of released impurity gases and their evolution rate were determined for different conditions of mechanical activation. The presence of a maximum in the amount of evolved gases as a function of mechanoactivation (MA) time (τ) was associated with the processes of gas capturing during MA and their subsequent pressing-out with increasing τ.
210-214
Composite W–Cu powders by joint reduction of oxides in combustion mode
Abstract
Composite powders W–Cu were prepared via joint reduction of WO3 and CuO oxides with Mg‒C combined reducer in a combustion mode by using the method of coupled reactions. Combustion phenomenology and the processes of phase and microstructure formation were investigated by thermocouple and copper- wedge techniques combined with XRD, SEM, and EDS analyses. Thermal conditions of combustion and phase composition and microstructure of products were found to depend on a Mg/C ratio in green mixtures. It was established that the magnesiothermic reaction was preceded by the stage of low-caloric carbothermal reduction. Slow propagation of combustion wave was found to favor the complete reduction of oxides and formation of target W–Cu composite nanopowder.
215-223
Polycrystalline silicon nitride fibers by combustion synthesis
Abstract
SHS nitriding of Si in the presence of added (NН4)2(COO)2 ∙ H2O and FeCl3 ∙ 6Н2О under pressure of nitrogen gas was explored by XRD and SEM. The additives were used with an intention to transpose the nitriding reaction into the gas phase and thus to allow the deposition of Si3N4 from the gas phase. Thus prepared Si3N4 had a shape of polycrystalline fibers formed by 1D crystals of varied morphology and by the assemblies of nanosized crystals. Phase composition, fiber length, and shape of nanocrystals were found to depend on nitrogen pressure. Synthesized fibers can find their application in heat insulation of aircrafts, fabrication of coatings, deep purification filters, etc.
224-228
Spark plasma sintering of β-SiAlON–BN composites from combustion-synthesized powders
Abstract
Investigated was the spark plasma sintering (SPS) of β-SiAlON/0–30 wt % BN ceramic composites. The raw materials (β-Si5AlON7 and BN powders) were prepared by infiltration-mediated combustion synthesis (CS). Experimentally established were the following process parameters for SPS of composites with high relative density (>95%) and flexural strength of 250–300 MPa: (a) heating rate 50 deg/min, (b) maximum temperature 1650–1750°C, (c) and holding time 5 min.
229-233
Reactive nanofoils for joining refractory and dissimilar materials
Abstract
Heterogeneous nanostructured foils produced by magnetron deposition or mechanical processing represent a new class of reactive materials. They are composed of layers or clusters of different phases (typically with a size of 10–100 nm) that can react with each other with strong heat release. The reaction, being initiated locally, spontaneously propagates across the entire foil in the form of high-temperature wave. Some examples of promising practical applications of these foils in advanced technologies, such as joining dissimilar materials, were presented.
234-237
Multilayer coatings on Ti substrate by SHS method
Abstract
Explored was the deposition of multilayer TiCx–TixSiy-based coatings onto Ti substrate by SHS method. Sandwich-type green multilayer structures were assembled from Ti foils and Ti + 0.5C, Ti + Si, 5Ti + 3Si, and Ti + 0.65C pellets and ignited under 1 atm of Ar and a load (400 g). Burned sandwiches were characterized by SEM, EDS, and XRD. In all cases, we observed good metal–ceramic joining. Prerequisites for such a joining are (i) the presence of the liquid phase in combustion products, (ii) good metal–ceramic wettability, and (iii) closeness of reaction temperature to the melting point of substrate.
238-242