Composites consisting of Fe66Cr10Nb5B19 alloy particles and a copper matrix were obtained by spark plasma sintering (SPS) at 700 and 800 degrees C. As copper does not form compounds with any of the alloy components, it can be considered as an inert matrix. The initial state of the Fe66Cr10Nb5B19 alloy was glassy. During SPS of Cu-40 vol % Fe66Cr10Nb5B19, densification was complete at 630 degrees C. As the sample was not fully dense upon reaching the glass transition temperature of the alloy (521 degrees C), the metallic glass particles changed their morphology and surface topography to fill the pore space, which was enabled by the viscous flow of the supercooled liquid. Fracture of the sintered composites occurred along the Cu/Fe66Cr10Nb5B19 interface and through the contacts between the Fe66Cr10Nb5B19 particles.

In this study, in situ WC-Cu-based composites containing graphite were fabricated from a mixture of W, C (graphite) and Cu powders by high-energy mechanical milling and subsequent reactive spark plasma sintering (SPS). The synthesis of the carbides occurred during the SPS stage. In order to investigate the effect of graphite concentration on the structure and properties of the composites, the W-C(graphite)-Cu mixtures with three different molar ratios of elements (1:1:3, 1:1.3:3 and 1:1.7:3) were prepared. The graphite not converted into carbides remained unreacted in the sintered compacts. The combination of mechanical milling and SPS resulted in the formation of unconventional microstructures. The Cu-rich regions of re-solidified material are located between the composite areas, in which the WC and W2C particles are distributed uniformly. As the concentration of graphite was increased, the hardness and electrical conductivity of the composites decreased. The concentration of graphite in the composites influenced the morphology of the worn surfaces formed under dry sliding conditions. The WC-W2C-Cu-graphite composite (processing conditions: W-C(graphite)-3Cu mixture, 15 min of milling, SPS at 980 degrees C) shows an attractive combination of properties: a hardness of 250 HV, an electrical conductivity of 25% of the International Annealed Copper Standard, a residual porosity of less than 5%, a coefficient of friction of 0.58 in a pair with a WC-6Co ball, and a specific wear rate of 0.6 x 10-5 mm3 N-1 m-1.

An Al-Cu-Fe alloy coating was deposited on the surface of diamond microcrystals via mechanical treatment of the powder mixtures in a planetary mill. The diamond crystals were 100 mu m in size and had shapes close to truncated octahedron and cuboctahedron. The Al62.5Cu25Fe12.5 alloy was chosen as a model material to demonstrate the possibility of the coating formation from a brittle alloy on a hard substrate. The treatment was performed in steel vials with no balls added. During the treatment, fine particles of the alloy deposited selectively on the {1 1 1} facets of the diamond crystals. The material transfer from the alloy particles to the diamond facets was explained by considering the interaction of the particles with the wall of the vial.

In the present work, the possibility of forming graphite intercalation compounds by treatment of partially graphitized diamond crystals by sulfuric acid in the presence of an oxidizer was demonstrated. The elemental mapping of the acid-treated crystals showed that sulfur and oxygen were localized in the graphite phase, which formed around the vertices and edges of the crystals. Mass-spectrometry was used to study the stages of thermal decomposition of the synthesized intercalation compound. When the intercalation compound decomposed, the graphitic layers were oxidized by sulfuric acid and SO2 evolved with the maximum on the evolution curve at 250 ℃. The adsorbed water and functional groups present on the graphite surface were eliminated at lower temperatures. The proposed synthesis method can be used for obtaining intercalated graphite-modified diamond, which is promising for applications in electronic devices.

The action of an electric pulse of high current density on a powder compact can induce multiple physical phenomena, including inter-particle sintering and melting of the material. The present work was aimed at studying the morphological and structural features of metallic glass-crystalline metal compacts consolidated by applying a single electric pulse. A 40 vol% Fe66Cr10Nb5B19 metallic glass-Cu mixture was consolidated under pressure by a pulse of electric current generated by a capacitor bank. The input energy was varied to determine the formation conditions of a robust composite compact. The possibility of consolidating a mixture of a Fe-based metallic glass and copper by a single pulse of electric current while avoiding crystallization of the glassy component was demonstrated.

The modification of diamond crystals by metallic particles or films is an important step in the development of diamond-based composites and heterostructures. While the interaction of diamond with single metals is addressed in many studies, the formation of interfaces between diamond and binary alloys is much less investigated. In the present work, the deposition method of Ag-Ge alloy particles on the diamond surface was developed. The Ag-Ge particles were selectively deposited on the {100} facets of synthetic diamond micro- crystals. The essential step of the process is annealing of diamond/Ag-Ge (particles, films) in an oxygen- containing atmosphere at a temperature of 651 degrees C. The Ag-Ge particles showed morphological features different from those of the unalloyed silver particles deposited on the diamond surface under the same conditions. The Ag-Ge particles demonstrated a core-rim morphology, a germanium rim encircling a silver core. The morphology of the Ag-Ge alloy particles was independent of the formation route. The possible reason for the formation of particles of this morphology is discussed. This work contributes to an understanding of the features of the interaction of diamond with binary alloys.

Formation of a MnFeCoNiCu high-entropy alloy by detonation spraying of a powder blend followed by laser treatment is reported for the first time. As the blend components differ by the deposition efficiencies, the composition of the deposited material may differ from the composition of the feedstock powder. In the coating formed from an equimolar mixture, the concentrations of iron and nickel are significantly higher than in the feedstock mixture. The composition of the feedstock powder is adjusted via decreasing the concentrations of nickel and iron to render the composition of the deposited layer close to the desired composition. A mixture containing 26Mn+11Fe+22Co+13Ni+28Cu (at.%) forms a Mn20Fe18Co22Ni18Cu22 coating. The laser treatment of the deposited layer allows for producing solid solutions of face-centred cubic structure. In the resolidified material, the interdendritic space is enriched by copper.

This investigation focuses on the structural characteristics of AlFeCoNiCu high-entropy alloys (HEAs) fabricated using two approaches. The alloys were obtained by the spark plasma sintering (SPS) or hot pressing (HP) treatment of layers deposited by detonation spraying of a mixture of the elemental powders. The feedstock powder mixture used for the spraying was also directly consolidated by SPS under the same conditions (without any pre-alloying treatment). The goal of this work was to conduct a comparative analysis of the compositional and structural features of AlFeCoNiCu HEAs formed by different methods. The SPS treated deposited layer showed a more uniform structure and composition than the alloy obtained directly by SPS of the powder mixture. All alloys processed by SPS or HP were face-centered cubic solid solutions. The alloys obtained from the deposited precursors showed deviations from the nominal composition of the powder mixture. However, the compositional differences and nonuniformities did not affect the hardness of the alloys or the influences of these factors compensated each other.. This work shows that, for practical applications, thick samples of AlFeCoNiCu can be produced by SPS of the elemental powder mixtures, while for thin layers and coatings detonation spraying followed by SPS/HP can be applied.

In the present work, the morphological changes of flat-facet and curved-facet diamond microcrystals of natural origin during vacuum annealing at 1800 degrees C were studied. It was found that the morphological changes caused by graphitization of natural diamond microcrystals are very similar to those observed in the case of synthetic diamond microcrystals. The formation of graphite during annealing of the flat-facet natural diamond micro-crystals starts from the edges of the crystals. However, when the curved-facet crystals are annealed, graphite forms over the entire surface of the crystals at the same time. The results of the present work confirm the presence of orientation relationships between the parent diamond and the graphite forming upon annealing.

In this work, two different methods, thermal decomposition and chemical reduction with hydrogen peroxide, were used to prepare metallic Ag and hybrid Ag2O/Ag particles via pseudomorphic transformation of the Ag2O microcubes. The as-prepared particles were characterized by X-ray diffraction (XRD), scanning electronics microscopy (SEM), energy-dispersive spectroscopy (EDS), and thermogravimetry (TG). Experimental results showed that, in both cases, the resulting Ag particles retained the shape and size of the Ag2O ones, although their microstructure differed significantly. Thus, the silver particles that composed the cubic aggregates prepared via chemical reduction of Ag2O with hydrogen peroxide were significantly smaller than those produced via thermal treatment of Ag2O. Thermogravimetric analysis showed single-step decomposition with a total mass loss of 67

In the present work, structural and morphological changes occurring during thermal decomposition of two isomers, silver oleate and silver elaidate (C17H33COOAg), were studied. It was found that thermal decomposition of both isomers results in the formation of ordered self-assembled nanostructures, which form in situ during the process. For investigating the changes occurring upon heating of silver oleate and silver elaidate, transmission electron microscopy and time-resolved small-angle and wide-angle X-ray diffraction were employed. It was found that, upon heating, the salts first experience transitions into various liquid crystal states and then into an isotropic liquid. The onset temperature of thermal decomposition of silver oleate and silver elaidate was found to be 200 °C and 230 °C, respectively. The products of thermal decomposition, the self-assembled structures, were composed of ordered silver nanoparticles.

Morphological and structural changes of spark plasma sintered Cu-10 wt% Al materials in salt spray environment were studied. The tested materials possessed the same elemental composition but different phase compositions (Cu-Al composite, Cu(Al) solid solution and Cu-Cu(Al)-Cu9Al4 alloy). The oxide films formed on the surface of the corroded samples were confirmed to be enriched with Al. The subsurface regions of the Cu-Al composite and Cu(Al) solid solution did not reveal any microstructural changes after the salt spray test. When the Cu-Cu(Al)-Cu9Al4 alloy corroded, the aluminum contained in the alloy oxidized such that the oxide particles formed both on the surface of the sample and in the subsurface region. While the Cu-Al composite and Cu(Al) solid solution maintained integrity, the Cu-Cu(Al)-Cu9Al4 alloy experienced swelling and cracking during the salt spray test.

In the present work, the surface of synthetic diamond microcrystals was modified by treating them in vials of a planetary mill without milling balls with a silver powder added. The initial diamond crystals were 100 mu m in size and had a cuboctahedral shape. During mechanical treatment, the crystals retained their shape, while the silver particles deposited on the {111} facets of diamond. The walls of the vials were worn due to the abrasive action of the diamond crystals, which resulted in the deposition of Fe-based particles on the same diamond facets. Annealing of the surface-modified diamond crystals at 650 degrees C in air caused redistribution of silver over the surface of the crystals. In the annealed diamond crystals, the silver particles were found only on the {100} facets, while the {111} facets were still coated with the Fe-based particles. In the present work, the surface of synthetic diamond microcrystals was modified by treating them in vials of a planetary mill without milling balls with a silver powder added.

The microstructure and mechanical properties of partially reacted and non-reacted Al–Fe66Cr10Nb5B19 metallic glass composites obtained by spark plasma sintering were comparatively analyzed. For the first time, the compositional features of core-shell particles formed upon the partial reaction of the Fe66Cr10Nb5B19 metallic glass with aluminum were examined using transmission electron microscopy combined with elemental mapping. The key finding is that iron of the alloy selectively dissolved in aluminum. The inner layer of the shell formed via diffusion of aluminum into the metallic glass. The introduction of the glassy reinforcement did not lead to such a dramatic ductility reduction as the formation of a complex “metallic glass core-thick intermetallic shell” reinforcement. In the non-reacted composite, the glassy reinforcement did not reveal its full potential in terms of the strengthening effect.

In the present work, the evidence of the melt formation at the contacts between composite TiC-Cu particles formed by high-energy ball milling was found in the microstructure of compacts obtained by spark plasma sintering at real temperatures of the sample of 725–925 °C. The voltage drop associated with a contact that could have been heated up to the melting point of copper was calculated to be much higher than the voltage across the whole sample during SPS. As the formation of melt could not be attributed to simple overheating of small cross-sectional area contacts (bridges), another explanation of the observed effect was sought. A mechanism based on the micro-arc formation was proposed to explain the observed melt formation in the sintered composites.

The present work reports the formation of Fe-Au metastable alloys by galvanic replacement, pressureless spark plasma sintering (SPS) and acid treatment. The reaction of partial galvanic replacement between micrometer-sized iron particles and HAuCl4 solution allowed synthesising core-shell Fe@Au particles. When the Fe@Au particles were treated in HCl solution, iron was selectively dissolved and hollow Au particles were formed. Pressureless SPS of the Fe@Au core-shell particles led to the formation of a metastable intermetallic phase, FeAu3, and a supersaturated solid solution, Au(Fe). The latter was resistant to HCl solution; at the same time, the FeAu3 phase decomposed during HCl treatment to form a porous gold structure. This work shows that a combination of galvanic replacement, SPS and acid treatment can be used for the preparation of metastable Fe-Au alloys with different phase compositions and particle morphologies.

An understanding of the structural changes induced by the ovalization treatment of diamonds is necessary to produce crystals with controlled sizes and morphologies. In this investigation, the treatment of natural diamonds in a rotary vortex apparatus was used to modify the surface morphology of the particles and obtain the ovalized crystals. The size of the starting diamond crystals was in the 250–350 μm range. In the product of treatment in the rotary vortex apparatus, particles with sizes above 300 μm were ovalized, while those with sizes below 300 μm demonstrated irregular shape. The formation of particles of irregular shape during the treatment was caused by the fracture of the starting diamond crystals along the defect regions. The ovalized crystals were formed by “blunting” the edges and vertices of the starting crystals under the action of friction forces. The ovalized diamond consisted of a crystalline core and a defect shell. The crystals were subjected to oxidative etching to reveal the structural changes of the surface layers caused by the ovalization treatment. During oxidative etching, the ovalized crystals developed a system of etch pits over the entire surface. In contrast, the oxidative etching of the starting (untreated) diamonds showed the facet selectivity.

Melt-blown polymer fiber materials are frequently used in the face mask manufacturing. In the present work, a melt-blown polypropylene tape was modified by silver nanoparticles using chemical metallization. The silver coatings on the fiber surface consisted of crystallites 4-14 nm in size. For the first time, these materials were comprehensively tested for antibacterial, antifungal and antiviral activity. The silver-modified materials showed antibacterial and antifungal activities, especially at high concentrations of silver, and were found to be efficient against the SARS-CoV-2 virus. The silver-modified fiber tape can be used in the face mask manufacturing and as an antimicrobial and antiviral component in filters of liquid and gaseous media.

In the present work, the morphological changes of synthetic diamond microcrystals of cuboctahedral shape upon oxidative etching in oxygen or synthetic air at elevated temperatures were studied. It was found that, at the early stages, selective etching of the {111} facets occurs, resulting in the formation of triangular etch pits. Crystals etched at 600-700 degrees C up to high transformation degrees are of skeletal type: in these crystals, the {111} facets are severely etched. At temperatures above 700 degrees C, the {100} facets start demonstrating etch pits. These pits are of square shape and have a stepped morphology. Oxidative etching at 900 degrees C leads to the formation of diamond crystals of antiskeletal type at high transformation degrees (30-50 %). It is suggested that the observed change in the morphology of the diamond crystals with temperature of the oxidative etching is related to the change in the ratio of the etching rates of the {111} and {100} facets.