Scandinavian Journal of Caring Sciences

Porous ceramic materials were sintered from fine SiC filler powder produced via SHS with binders SiO2 and MgO at temperatures of 800–1300°C. The effect of sintering temperature on the properties of the resulting ceramics such as pore size, open porosity, bending strength, and pure water permeability was investigated. SiC-based membrane rejected completely solid SiC particles with D50 = 0.5 μm while maintaining stable permeability and physical and mechanical characteristics after repeated filtration/regeneration cycles.

MgAlON ceramics were prepared by combined use of self-propagating high-temperature synthesis of Al + Al2O3 + MgO + Mg(ClO4)2 mixtures doped with sintering agent LiF, CaCO3 or La2O3 + Y2O3 + MgO and pressureless sintering. The effect of additives on the combustion process and phase formation of synthesized products, as well as their subsequent sintering was studied. Introduction of 10 wt % CaCO3 was shown to lower the combustion temperature followed by stopping the combustion front. It was revealed that the density of sintered ceramic materials reaches 90% of the theoretical value. The sintered sample prepared by doping with 0.6 wt % CaCO3 was found to possess the highest density (3.3 g/cm3) and light transmittance (16%).

Cast Mo–Nb–Ta–(Cr,V,Zr,Hf) refractory high-entropy alloys were first prepared via gravity-assisted SHS metallurgy. It was shown that the ingots crystallize from the liquid state, in which a homogeneous distribution of constituting elements is provided. The phase composition of synthesized RHEA ingots was revealed to be doped component dependent. Combined reduction of metals of V (Nb, Ta, V) and VI (Cr, Mo) groups formed single-phase alloys with a bcc crystal structure. MoNbTaCr alloys doped with Zr or Hf having hexagonal crystal structure were found to consist of fcc and hcp phases in addition to bcc solid solution.

V2AlC powder was prepared through self-propagating high-temperature synthesis of VO2/Mg/Al/C mixture in molten NaCl followed by leaching in dilute hydrochloric acid. The synthesized product included V2AlC, vanadium aluminides and carbides, as well as MgO and MgAl2O4. The phase composition was found to be magnesium and carbon content dependent. Optimum component ratios and acid leaching conditions were determined for the successful synthesis of V2AlC MAX phase.

In the category of oxides, spinel oxides can be identified by their chemical formula. Spinel oxides have the structure AB2O4 and are distinguished by their amazing magnetic, electric, and multiferroic properties. Additionally, they exhibit a wide variety of functional responses. A description of the experimental, structural, and electrical properties of Co1–xLaxCr2O4 (where x = 0 and 0.05) was presented in this study for the very first time. During the course of the experimental characterization, data on AC conductivity and dielectric parameters, as well as XRD and SEM micrographs, were collected. It was demonstrated beyond a reasonable doubt that a spinel cubic structure is produced by the XRD characteristics of each sample. The scanning electron micrographs (SEM) showed that every single one of the samples is very porous. An overall increasing trend of the dielectric constant was seen in the La3+ doped CoCr2O4 sample as the concentration of La3+ increased. This is a result of the probable hopping of Cr2+ to Cr3+, as well as an increase in the average crystallite size with La doping. Koop’s phenomenological theory was utilized in order to provide an explanation for the AC conductivity, and the hopping process was utilized in order to characterize the electrical properties of each sample. All of the samples exhibited outstanding alternating current conductivity and a low dielectric loss tangent at higher frequency ranges throughout the whole spectrum.

Cu2Se thermoelectric compound containing up to 5 wt % SiC was prepared via self-propagating high-temperature synthesis. Doping SiC was shown to improve the thermoelectric properties and get 20% increase in the electrical conductivity and 60% increase in the Seebeck coefficient. The thermoelectric power factor of Cu2Se–5 wt % SiC was found to be 14.4 μW cm–1 K–2 at 900 K, which is 3 times higher than that of Cu2Se.

This investigation aimed to synthesize Ti–5Al–5V–5Mo–3Cr–1Zr (Ti–55531) alloy by energy-efficient “hydride cycle” (HC) method. From X-ray powder diffraction it was found that the synthesized alloy consists of two phases: HCP α and BCC β. Scanning electron microscopy (SEM) unveiled discernible surface characteristics on the Ti–55531 alloy, delineating two predominant phases with distinct variations in light and dark shades. These observed phases corresponded to microstructural compositions attributed to the α and β phases. The interaction of obtained Ti–55531 alloy with hydrogen in self-propagating high-temperature synthesis (SHS) mode was studied. It was demonstrated that the compacted alloy without preliminary crushing or mechanical treatment could absorb 3.4 wt % of hydrogen during the SHS process. Additionally, it was determined that the synthesized hydride of multicomponent alloy consists of two phases: TiH2 phase with FCC structure and β-phase with BCC structure. The thermal stability of synthesized hydride was analyzed using differential thermal analysis (DTA) method, revealing a hydrogen desorption process characterized by two endo-peaks at 334 and 574°C.

Cast Mo–Cr, W–Cr, and Cr–Al master alloys were prepared via centrifugal SHS metallurgy. The effect of variation in component fractions in green mixtures (100 – α)(Cr2O3 + Al) + α(MoO3 + Al) and (100 – α)(Cr2O3 + Al) + α(WO3 + Al) on the synthesis of Mo–Cr and W–Cr alloys, respectively, was thermodynamically analyzed. Thermodynamic calculation of Cr–Al master alloy production was presented and provided the necessity of using a complex oxidizing agent, chromium(III) oxide and chromium(VI) oxide in a certain ratio. Experiments for Mo–Cr, W–Cr, and Cr–Al systems proved the necessity of applying overloading at an acceleration of no less than 50 g to prolong the lifetime of the melt. Introduction of functional additives CaF2 (fluorspar) and sodium hexafluoroaluminate Na3[AlF6] (cryolite) to the green mixture lowered the melting temperature of the slag phase (reduced its viscosity) and facilitated the phase separation. EDS and mass spectroscopy analyses showed that the chemical compositions of synthesized master alloys are close to their calculated and target values. XRD results revealed the existence of solid solutions based on target elements.

The work investigated the modes of synthesis of titanium carbide with a nichrome binder from granular charges containing up to 30 wt % nichrome or a mixture of nickel and chromium powders taken in the same ratio as in the alloy. Using the conditions for the transition of combustion from conductive to convective mode, the impurity gas content in the studied mixtures was quantitatively assessed. It was shown that for mixtures of 0.6-mm granules, a safe conductive synthesis mode is realized. For charge of 1.7-mm granules, if a mixture of Ni and Cr powders was added to the initial sample, the convective combustion mode took place when Ti + C content was more than 90 wt %. When adding nichrome powder, the convective mode was caused by more than 80 wt % of Ti + C. Replacing the nichrome powder in the initial granular charge with mixture of Ni and Cr powders did not change the phase composition of the combustion products.

Selective laser melting (SLM) was first used to deposit products made of SHS-produced intermetallic alloy Ti20Al3Si9 powder on the Ti substrate. It was shown that formed Ti20Al3Si9 alloy/Ti substrate composites have a strong bond. The influence of SLM parameters for processing SHS-produced powder on microstructure and phase composition of clad samples was studies.

Titanium carbide (TiC) powder was synthesized by the magnesiothermic combustion of the TiO2-rich alteration product leucoxene and activated carbon (AC) in argon. Leucoxene and C were combined at a molar ratio of 1.0 : 1.5, and the effect of magnesium (Mg) fuel in the reaction system was studied at ratios of 1.0, 1.5, 2.0, 2.5, and 3.0. XRD analysis showed that the as-leached powder from a reactant mixture with a Mg molar ratio of 3.0 has fewer unwanted phases, and that leucoxene, C, Mg mixed at 1.0 : 1.5 : 3.0 produce TiC powder of a higher purity than the other reacted mixtures. The higher purity of the product was due to the more exothermic character of the combustion reaction, which had a higher enthalpy of reaction (ΔH) and adiabatic temperature (Tad). SEM observation of the as-leached powder revealed agglomerated fine particles of sub-micrometer size. The TiC powder was successfully coated with nickel by an electroless plating process. SEM/EDX demonstrated that the Ni-coated TiC powder consists of Ni particles smaller than 500 nm, which are well distributed on TiC particles.