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High entropy silicide (Mo 0.2 Cr 0.2 Ta 0.2 Nb 0.2 W 0.2)Si 2 (named as MeSi 2) coating was successfully prepared on Ta substrate by slurry sintering method. Firstly, precursor powders were initially obtained through mechanical alloying of silicide powders. Then powder slurry was coated on Ta substrate, and then the samples were sintered. For comparison, TaSi 2 coating prepared by halide-activated pack cementation method was synthesized. Subsequently, the static oxidation resistance of both MeSi 2 coating and TaSi 2 coating was examined at 1200 °C, results revealing that the MeSi 2 coating demonstrates an effective protection time of more than 60 h. The protective effect and duration of the MeSi 2 coating on Ta substrate are significantly greater than that of TaSi 2 , indicating an improvement oxidation resistance due to the high entropy effect of the silicide coating. After oxidation, the coating evolved an outer SiO 2 layer, followed by MeSi 2 , Me 5 Si 3 , TaSi 2 , and Ta 5 Si 3 layers. As the oxidation progressed, MeSi 2 gradually transformed into Me 5 Si 3 , leading to a loss of the coating's antioxidant capacity. [ABSTRACT FROM AUTHOR]

Nickel films of 40 nm thickness were obtained by means of magnetron sputtering on a single-crystalline silicon substrate. The films were subjected to rapid thermal treatment (RTT) for 7 s until the temperature increased from 200 to 550 °C. By means of the X-ray diffraction method, the structural-phase composition of nickel films before and after RTT was explored. The atomic force microscopy method due to direct contact with the surface under study, made it possible to accurately define the microstructure, roughness, specific surface energy and grain size of the nickel films before and after RTT, as well as to establish the relationship of these parameters with the phase composition and electrical properties of the films. Surface specific resistance was measured using the four-probe method. Based on XRD results, formation of Ni2Si and NiSi phases in the film was ascertained after RTT at 300 °C. At RTT 350–550 °C, only the NiSi phase was formed in the film. The microstructure and grain size significantly depend on the phase composition of the films. A correlation has been established between specific surface energy and resistivity with the average grain size after RTT at 350–550 °C, which is associated with the formation and constant restructuring of the crystal structure of the NiSi phase. [ABSTRACT FROM AUTHOR]

Ceramic-metal corrugated structures have attracted extensive attention because of their strong penetration resistance. In this study, the effects of geometric features and boundary constraints on corrugated structures consisting of a TC4 frame and five SiC ceramic prisms were explored by performing a series of ballistic tests. Deformation results were obtained using a three-dimensional scanner, and the dynamic response was observed using a high-speed imaging system. Numerical models of these tests were established and validated using experimental results. The results suggest that increasing the support and confining strength of ceramics delay their failure and increase their degree of breakage, thereby increasing the internal energy conversion ratio of the projectile and the energy absorption ratio of ceramics by 14% and 10%, respectively. Notably, a reasonable reduction in the strength of the frame partition expands the plastic deformation range of the frame and increases its energy absorption ratio by 10%. The conclusions of this study provide a reference for designing corrugated composite structures. [ABSTRACT FROM AUTHOR]

The surface reconstruction of electrochemically activated catalysts is an effective way to improve performance. However, there is currently a dearth of study on the surface reconstruction of silicide catalysts for hydrogen evolution reactions (HER). Here, a new HER electrocatalyst, LaRuSi3, is synthesized and electrochemically triggered it to produce Ru clusters on its surface. Experimental data and theoretical simulations reveal that Ru clusters optimize the charge distribution of LaRuSi3, which promotes the adsorption of water by Ru sites and improves the adsorption of hydrogen by Si sites. The conductivity and electrochemical active sites of the catalysts are also enhanced. The catalyst has an overpotential of 45 mV to attain a current density of 10 mA cm−2 in alkaline media, which exceeds the majority of other Ru‐based compounds. This work contributes to the exploration of more efficient novel silicides HER electrocatalysts and broadens the application of surface reconstruction techniques. [ABSTRACT FROM AUTHOR]

Multi-component high entropy oxides (HEOs) have attracted enormous attention due to their unique structures and potential applications. The conventional selection strategy to obtain HEOs is to search for equimolar cationic systems to maximize configurational entropy and avoid phase separation. We previously explored non-equimolar cationic rocksalt structure Mg–Co–Ni–Cu–Zn–O HEOs using cluster-plus-glue-atom model. In this paper, the mixing entropy, enthalpy and Gibbs free energy of constructed superclusters were numerically calculated and compared with the correlated crystal structure based on recent studies. It indicated the Gibbs free energy rather than mixing entropy agrees well with the phase stability of HEOs. Mg 28 Co 17 Ni 19 Cu 16 Zn 16 O 96 shows the optimal phase stability which is related to the lowest Gibbs free energy, reflecting a regular octahedral environment preferred by the cation composition in the system. Enthalpy and entropy are among important design criteria in determining the phase stability of HEOs but the function of enthalpy is obviously higher than that of entropy. This study provides a comprehensive way to access HEOs which is undoubtedly very important for the development of other non-equimolar cationic high entropy materials such as carbides, silicides, borides or nitrides. [ABSTRACT FROM AUTHOR]

The silicides (MeSi 2 , Me = Ta, Zr, W, Mo) with strong Si supply capability are promising for improving the loose and porous HfO 2 skeletons from ablation resistant coatings for carbon-based materials. Herein, MeSi 2 modified HfB 2 -SiC coatings prepared by spark plasma sintering were evaluated under oxyacetylene ablation condition (2.4 MW/m2) to analyze the protection mechanism. Experimental and theoretical analyses show that, MoSi 2 can be considered as the optimal Si additive and HfB 2 -SiC-MoSi 2 coating exhibits the lowest linear variation rate of −0.19 μm/s. The by-product retention of WO x and ZrO 2 derived from WSi 2 and ZrSi 2 will cause rapid thickening of Hf-Si-O layer, while the by-product (Hf 6 Ta 2 O 17) from TaSi 2 leads to severe consumption of HfO 2 skeleton (0.29 μm/s). The disparate mechanisms of MeSi 2 addition are jointly decided by the fluctuation of Hf-O bond length (0.219–0.229 nm) in Me modified HfO 2 solid solutions, as well as the differently dynamic consumption of MeO x by-products. [ABSTRACT FROM AUTHOR]

Higher manganese silicides (denoted as MnSiγ ) are a prominent class of intermetallic compound for thermoelectric applications that crystallizes into a Nowotny Chimney Ladder (NCL) phase and constitutes a higher concentration of silicon with odd stoichiometry, typically represented by an irrational number. In this work, the genesis of Si odd stoichiometry and secondary phase relations in silicon-rich and silicon-deficient MnSix is presented to clarify the significance of labile (i.e., easily alterable) Si-subsystem in inheriting the modulated lattice structure with characteristic anharmonicity. The transport properties show an interrelation to the presence of a secondary phase, which is driven by the odd stoichiometry, where the thermoelectric figure of merit (zT) is found to be optimal for MnSi1.74. The structural characterization of rapidly solidified melt-spun ribbons and spark plasma sintered bulk specimens reveal a characteristic presence of MnSi and Si as secondary phases in Si-deficient (x ≈ 1.5) and Si-excess (x ≈ 2) compositions of nominal MnSix, respectively, that coexists with the major MnSiγ based NCL phase. This study provides the fundamental basis of phase evolution and the relevance of odd stoichiometry in silicon-rich manganese silicides which exhibit fascinating phonon dynamics in optimal MnSi1.74 stoichiometry. [ABSTRACT FROM AUTHOR]

To study the formation of silicides, dislocation-free ingots of single-crystalline silicon with a diameter of 65÷110 mm, grown by the Czochralski method, were used. When studying such silicon samples using electron microscopy, small-angle scattering of CO2 laser radiation, three types of defects were identified: swirl defects, impurity micro inclusions and impurity clouds. It has been shown that silicide inclusions with sizes of 8-20 μm are formed in the near-surface layer of doped silicon, and they decrease linearly deeper into the crystal. The electrical parameters of semiconductor chromium silicide were determined: resistivity 1800 μOhm·cm, thermopower coefficient 180 μV/k, Hall constant 1.2·10-2 cm3/Kl, hole concentration 6·1019 cm-3, charge carrier mobility 18.6 cm2/V·s, band gap (0.29±0.02) еV. [ABSTRACT FROM AUTHOR]

The temperature dependences of the thermoelectromotive force of chromium mono and disilicides in the temperature range 200℃÷+600℃ have been studied. For chromium disilicide, the dependence of the thermopower coefficient (α) on temperature (T) has three sections. Chromium monosilicide is characterized by a smooth increase in thermopower with increasing temperatures up to 200℃, and then its constancy. It was revealed that silicides rich in chromium atoms have lower thermopower values than silicides rich in silicon. The maximum thermo-EMF values of 110 μV/K and 190 μV/K were observed for chromium mono- and disilicides, respectively. It was revealed that for chromium silicides the dependence of the dimensionless parameter Q = Z∙T on temperature is linear. The possibility of predicting the technology of synthesis of semiconductor material with optimal thermoelectric properties using the dependence of thermopower on conductivity and the parameter Q on temperature is shown. [ABSTRACT FROM AUTHOR]

The oxidation products (MoO3 and V2O5) have low melting points and tend to sublimate at high temperatures despite that MoSi2 and VSi2 may possess good self-lubricating properties. To copewith this challenge, a high-entropy transition metal disilicide was designed in this work in which transition metal elements that could form high melting point oxides were deliberately added. The highentropy (Ti0.2V0.2Nb0.2Mo0.2W0.2)Si2 (HE-MSi2) with hexagonal structure was successfully prepared by SPS using Ti, V, Nb, Mo, W, and Si powders as the initial materials in thiswork. TheHE-MSi2 presents a high hardness (11.8±0.4GPa) and elastic modulus (387.2 ± 46.8 GPa). In particular, its hardness is higher than that of the corresponding disilicides. Noteworthy, HE-MSi2 demonstrated superior wear resistance when compared to Mo-Si-based ceramics (such as MoSi2, Mo5 Si3, and Mo5 SiB2), high-entropy carbides (such as (MoTaWVTi)C, (HfMoNbTaTi)C, and (TiVNbMoW)4.375, and traditional single-phase ceramics (including Sialon, Si3N4, Al2O3, SiC, and ZrO2). Meanwhile, at a high temperature of 600°C, the friction coefficient and wear rate were reduced to 0.64 ± 0.05 and (1.88±0.15)x106 mm³/N•m, respectively. The preferential oxidation of different elements of the HE-MSi2 was validated through systematical characterization of composition evolution, which was dominantly impacted by high temperature and friction induction. [ABSTRACT FROM AUTHOR]

This study introduces Sn-substituted higher manganese silicides (MnSi1.75, HMS) synthesized via an arc-melting process followed by spark plasma sintering (SPS). The influences of Sn concentrations on the thermoelectric performance of Mn(Si1−xSnx)1.75 (x = 0, 0.001, 0.005, 0.01, 0.015) are systematically investigated. Our findings reveal that metallic Sn precipitates within the Mn(Si1−xSnx)1.75 matrix at x ≥ 0.005, with a determined solubility limit of approximately x = 0.001. In addition, substituting Si with Sn effectively reduces the lattice thermal conductivity of HMS by introducing point defect scattering. In contrast to the undoped HMS, the lattice thermal conductivity decreases to a minimum value of 2.0 W/mK at 750 K for the Mn(Si0.999Sn0.001)1.75 sample, marking a substantial 47.4% reduction. Consequently, a figure of merit (ZT) value of ~0.31 is attained at 750 K. This considerable enhancement in ZT is primarily attributed to the suppressed lattice thermal conductivity resulting from Sn substitution. [ABSTRACT FROM AUTHOR]

The effects of Fe 2 O 3 addition on the electrical resistivity, thermal conductivity, and microstructure formation of SiC processed under Ar, N 2 , and N 2 + 5% H 2 sintering atmospheres were investigated. The use of N 2 + 5% H 2 resulted in the lowest electrical resistivity, improved thermal conductivity and enhanced flexural strength of SiC as compared to Ar and N 2. The use of 10 wt% Fe 2 O 3 resulted in an electrical resistivity of 3.8 × 10−1 Ω cm, a thermal conductivity of 20 W/m.K, and a flexural strength of 40 MPa with 33% porosity of samples sintered at 1250 °C under N 2 + 5% H 2. The in-situ formation of a network-like structure of iron silicide (Fe 3 Si) at contact points of SiC yielded a conductive path and reduced the electrical resistivity, while the formation of Si 3 N 4 improved the mechanical property. Although, all sintering atmospheres resulted in the formation of electrically conductive Fe 3 Si, but the use of N 2 + 5% H 2 produced samples with highest Si 3 N 4 content, lowest amount of oxide phase (SiO 2 and Si 2 N 2 O), and additionally densified the microstructure. [ABSTRACT FROM AUTHOR]

The growing demand for composite materials capable of enduring prolonged loads in high-temperature and aggressive environments presents pressing challenges for materials scientists. Ceramic materials composed of silicon carbide largely possess high mechanical strength at a relatively low density, even at elevated temperatures. However, they are inherently brittle in nature, leading to concerns about their ability to fracture. The primary objective of this study was to develop a novel technique for fabricating layered composite materials by incorporating SiC-based ceramics, refractory metals, and their silicides as integral constituents. These layered composites were produced through the liquid-phase siliconization method applied to metal–carbon blanks. Analysis of the microstructure of the resultant materials revealed that when a metal element interacts with molten silicon, it leads to the formation of a layer of metal silicide on the metal's surface. Furthermore, three-point bending tests exhibited an enhancement in the bending strength of the layered composite in comparison to the base silicon carbide ceramics. Additionally, the samples demonstrated a quasi-plastic nature during the process of destruction. [ABSTRACT FROM AUTHOR]

The silicides ScT2Si2 (T = Ru, Rh, Os) were synthesized by arc-melting of the elements and subsequent annealing in sealed silica ampoules. They crystallize with the rarely observed HfFe2Si2 type structure, space group Pbcm. The structures of ScRu2Si2 (a = 761.64(4), b = 730.70(6), c = 521.07(6) pm, wR = 0.0314, 633 F2 values, 31 variables) and ScOs2Si2 (a = 771.10(8), b = 736.68(7), c = 521.88(5) pm, wR = 0.0479, 623 F2 values, 31 variables) were refined from single crystal X-ray diffractometer data. The refinements showed small degrees of Ru/Si respectively Os/Si mixing on one 4c site, leading to the refined compositions ScRu1.96(1)Si2.04(1) and ScOs1.91(1)Si2.09(1). The monomeric building units in both structures are two slightly distorted, crystallographically independent RuSi5 respectively OsSi5 square pyramids, which are condensed via common edges. The resulting densely packed [Ru2Si2] and [Os2Si2] networks leave voids for the scandium atoms with coordination number 18: Sc@Si8Ru8Sc2 and Sc@Si8Os8Sc2. Temperature dependent magnetic susceptibility measurements of ScRu2Si2 and ScOs2Si2 indicate Pauli paramagnetism. Solid-state 29Si and 45Sc static and MAS NMR spectroscopy reveal significant Knight shifts and a strong influence of the T/Si mixing on the experimental NMR line shapes. A larger overall 29Si magnetic shift for ScRu2Si2 compared to ScOs2Si2, although with a negative sign for one of the 29Si resonances, suggests stronger paramagnetic effects for ScRu2Si2, in agreement with the magnetic susceptibility measurements. [ABSTRACT FROM AUTHOR]

This work is devoted to the production of a ceramic target (ZrSi2–ZrB2–MoSi2)/Cr by hot pressing of products of self-propagating high-temperature synthesis and deposition of coatings in the Zr–Si–Mo–B system by DC magnetron sputtering and high-power pulsed magnetron sputtering. The composition and structure of the initial powder mixtures, SHS products, a two-layer functionally graded target, and coatings deposited during its sputtering have been studied. It is shown that the developed target (ZrSi2–ZrB2–MoSi2)/Cr can be successfully used to obtain coatings with a dense homogeneous defect-free structure, including at high-energy sputtering regimes, peak current of 50 A, and peak power of 50 kW. [ABSTRACT FROM AUTHOR]

The orientation relationships between the β-phase and the S2 silicides (Ti, Zr)6Si3 (a = 0.7055 nm, c = 0.3673 nm) in titanium pseudo-β-alloy VT47 are studied. The distribution of the crystallographic directions on an inverse pole figure in the β-phase coordinates is presented. A large sample of silicides is studied, and absence of single orientation relationships between the β-phase and the S2 silicides in the alloy after rolling and annealing is inferred. Variants of nucleation of S2 silicides are considered on the basis of the theory of nucleation and of data on the Ti – Zr – Si system. Amechanism of the loss of β/S2 orientation relationships in the process of thermomechanical treatment of the alloy is suggested. The Ti/Zr proportion at a constant content of Si is shown to grow with the sizes of the silicides. The silicide particles affect the initial aging state of alloy VT47. They serve free surfaces for nucleation and growth of β-phase during aging and make its distribution more uniform. [ABSTRACT FROM AUTHOR]

Liquid-assisted processes that occur in iridium–silicon carbide diffusion couples have been studied in the temperature range 1500–1800°C at different heat treatment times. We have examined the microstructure and determined the elemental and phase compositions of the diffusion zone forming above eutectic temperatures and/or the melting points of individual reaction products: iridium silicides. The microstructure of the diffusion zone forming under liquid formation conditions has been shown to differ from that forming under the conditions of solid-state reaction between iridium and silicon carbide. At temperatures above 1700°C, the silicon content of the Ir–Si melt exceeds 50 mol %, which leads to crystallization of the Ir3Si4 and Ir3Si5 phases during cooling. The carbon resulting from reaction between iridium and SiC undergoes graphitization with increasing heat treatment temperature and time. [ABSTRACT FROM AUTHOR]

The photovoltaic performances of n-i-p or inverted p-i-n BaSi2 homojunction solar cells are limited by the parasitic high light absorption of n-BaSi2 or p-BaSi2 window layer. In this work, diverse electron transport materials (ETMs) and hole transport materials (HTMs) are employed instead of BaSi2 as window layers to promote the performances of BaSi2 solar cells, and the effects of different ETMs and HTMs were simulated and comprehensively studied. For n-ETM/i-BaSi2/p-BaSi2 solar cells, the solar cell with ZnO exhibits the highest efficiency of 28.21%. As increasing the thicknesses of ETM layer from 5 nm to 100 nm, the efficiency for n-BaSi2/i-BaSi2/p-BaSi2 solar cell decreases seriously from 24.52% to 15.99%, while the solar cells with wide band gap ETMs including SnO2, TiO2 and ZnO show neglectable change in performances. The performances n-ETM/i-BaSi2/p-BaSi2 solar cells are affected by donor like defects more than acceptor like defects in i-BaSi2. For p-HTM/i-BaSi2/n-BaSi2 solar cells, employing Cu2O, CuI, CuSCN or NiO as HTM layer produces evident valence band discrepancies at HTM/i-BaSi2 interfaces. Heavy doping in HTM layer is necessary desired to overcome the energy band barriers. As increasing the thicknesses of HTM layer from 5 nm to 100 nm, the efficiency for p-BaSi2/i-BaSi2/n-BaSi2 solar cell also decreases from 24.52% to 15.99%, while the solar cells with wide band gap HTMs including CuI, CuSCN and NiO show neglectable change, and the efficiency for p-Cu2O/i-BaSi2/n-BaSi2 solar cells decreases slightly from 25.86% to 24.88%. The performances of p-HTM/i-BaSi2/n-BaSi2 solar cells are affected by acceptor like defects more than donor like defects in i-BaSi2. [ABSTRACT FROM AUTHOR]

A ZrC-ZrSi2-Al2O3 powder system was designed and used for preparing ZrC composite coating. Tailored microstructures such as densely packed ZrC-ZrSi2 whiskers and nanosized alumina grains were observed in the coating lamellae. The zirconia derived from the oxidation of zirconium carbide and zirconium silicide during the plasma spraying process contributed to the formation of the near-eutectic alumina-zirconia area. The formation mechanism of the composite coating was discussed based on the characterization of the coating lamellae and the as-prepared coating demonstrated promising mechanical properties due to the coordination of whiskers and eutectic microstructure. [ABSTRACT FROM AUTHOR]

Characterization of thermoelectric transport properties for temperature sensing, cooling, and energy harvesting applications is necessary for a reliable device performance in progressively minimized computer chips. In this contribution, we present a fully automated thermovoltage and sheet resistance measurement setup, which is calibrated and tested for the production of silicon- and silicon-germanium-doped as well as silicide complementary metal–oxide–semiconductor-compatible thin films. A LabVIEW-programmed software application automatically controls the measurement and recording of thermovoltages at individually defined temperature set points. The setup maps average temperature and temperature differences simultaneously in the regime from 40 to 70 °C. The Seebeck coefficient calculated by means of the inversion method was used to eliminate the offset voltage influence. Finally, we present and discuss the Seebeck coefficient as well as the sheet resistance for application-specific different temperature set points of several doped poly-Si, poly-SiGe, and silicides. [ABSTRACT FROM AUTHOR]

Benefiting from its light weight, unique microstructure and high thermal stability, SiCN ceramics have attracted extensive attention in the field of electromagnetic wave (EMW) absorption. However, due to its poor impedance matching performance and single loss mechanism, the EMW absorption performance of SiCN ceramics requires further improvement. Herein, we introduced Ni and graphene into polysilazane to fabricate Ni x Si y /Graphene/SiCN composite ceramics by polymer derived ceramics (PDCs) route. The introduction of Ni not only facilitated the formation of various phases, including Si 3 N 4 , Ni 2 Si, Ni 31 Si 12 , graphite carbon and Si 2 N 2 O, but also catalyzed the in-situ generation of one-dimensional carbon nanotubes (1D CNTs). When the addition content of Ni was 6 wt% and the addition content of graphene was 2 wt%, the Ni x Si y /Graphene/SiCN composite ceramics exhibited the optimal EMW absorption performance. The minimum reflection loss (RL min) of Ni x Si y /Graphene/SiCN composite ceramics reached -52.13 dB at 7.6 GHz with the thickness of 2.7 mm, and widest effective absorption bandwidth (EAB) reached 3.56 GHz (14.44-18 GHz) at 1.26 mm. The dielectric loss was enhanced by carbon materials (turbostratic carbon, 1D CNTs and 2D graphene) and various phases, while the magnetic loss was improved by Ni and nickel silicide. The synergism of multiple loss mechanisms and good impedance matching lead to excellent EMW absorption properties of Ni x Si y /Graphene/SiCN ceramics. [ABSTRACT FROM AUTHOR]

Metal silicides and silicates belong to the silicon‐based non‐oxide and oxide ceramics family with exceptional properties. Silicides face fatal oxidation at low temperatures and intrinsic brittleness, whereas silicates face instability in phase at high temperatures which restricts its usage in vast engineering applications. Hence, the ceramic community introduced the concept of high entropy in metal silicides and silicates. Since 2019, high entropy silicides and silicates, a multicomponent system, have created new avenues for materials discovery and design. High entropy silicides displayed elevated properties than the traditional silicides aiming its applications in microelectronic, high‐temperature oxidation resistance coatings, and structural materials. Similarly, high entropy silicates displayed improved properties than the traditional silicates making them the most promising materials for environmental and thermal barrier coating applications for hot section components in gas turbines. The review focuses on specific case studies to emphasize the latest research and developments in high entropy silicides and silicates. Synthesis approaches employed in developing high entropy silicides and silicates and their structural and microstructural outcomes are addressed. The possible application is predicted based on the overview of the properties explored to date. The review concludes with future possibilities offered by the high entropy silicides and silicates. [ABSTRACT FROM AUTHOR]

The regularities of the formation of thin Mn/Si (111) nanofilms during solid-phase deposition of Mn on Si under conditions of ultrahigh vacuum (P = 1 0 − 7 Pa) and thin Mn4Si7/Si (111) nanofilms during annealing of the Mn/Si system have been studied. It has been established that silicon atoms diffuse into the Mn film up to a thickness of Θ = 1 0 –12 monolayers, and Mn in Si up to Θ = 8 –10 monolayers, therefore, a transition layer of nonstoichiometric MnxSiy silicide is formed at the Mn–Si interface. After heating at T = 1 0 5 0 K, the higher manganese silicide (HMS) Mn4Si7 is formed. In particular, it was found that the bandgap of Mn4Si7is E g ≈ 0. 7 2 eV, and the electron affinity is χ ≈ 3 eV and in the work, the optimal thermal diffusion conditions for the formation of stoichiometric Mn4Si7 silicide are determined. It is shown that at T ≤ 1 0 0 0 K, a partial formation of a chemical bond between manganese and silicon atoms occurs. At 1100 K, a thin Mn4Si7 film with a good stoichiometric composition is formed. [ABSTRACT FROM AUTHOR]

Thin films of superconducting V 3 Si were prepared by means of RF sputtering from a compound V 3 Si target at room temperature onto sapphire and oxide-coated silicon wafers, followed by rapid thermal processing under secondary vacuum. The superconducting properties of the films thus produced are found to improve with annealing temperature, which is ascribed to a reduction in defects in the polycrystalline layer. Critical temperatures (T c ) up to 15.3 K were demonstrated after thermal processing, compared to less than 1 K after deposition. The T c was always found to be lower on the silicon wafers, by on average 1.9 ± 0.3 K for the annealed samples. This difference, as well as a broadening of the superconducting transitions, is nearly independent of the annealing conditions. In situ XRD measurements reveal that the silicide layer becomes strained upon heating due to a mismatch between the thermal expansion of the substrate and that of V 3 Si. Taking into account the volume reduction due to crystallization, this mismatch is initially larger on sapphire, though stress relaxation allows the silicide layer to be in a relatively unstrained state after cooling. On oxidized silicon, however, no clear evidence of relaxation upon cooling is observed, and V 3 Si ends up with an out-of-plane strain of 0.3% at room temperature. This strain increases as the sample is cooled down to cryogenic temperatures, though the deformation of the polycrystalline layer is expected to be highly inhomogeneous. Taking into account also the reported occurrence of a Martensitic transition just above the critical temperature, this extrapolated strain distribution is found to closely match an existing model of the strain dependence of A-15 superconducting compounds. [ABSTRACT FROM AUTHOR]

The heat-resistant Ti–Al–Zr–Si alloys (base Ti–(6–7)Al–(2–3) Zr–(1–1.5)Si and additionally alloyed Ti–(6–7)Al–(3–5)Zr–(1–1.5)Si–(2–4)Sn), obtained by electron beam smelting were studied. Deformation was carried out in the β- or upper part of the (α+β)-area by means of forging and rolling into a strip. The base alloy was subjected to rolling in the upper part of the α+β-area, and the fine-grained uniform structure with a grain size of 10–20 μm was obtained. Internal stresses and defective substructure of the deformed alloy intensify the decomposition of the solid solution and promote the formation of evenly distributed dispersed silicides, which allows obtaining high strength and heat resistance characteristics. Tensile tests at 20; 650 and 700°C of the Ti–(6–7)Al–(2–3)Zr–(1–1.5)Si alloy samples after deformation and annealing also showed a rather high level of the tensile strength and yield strength. After 20 h exposure at the operating temperature of 700°C, the structure becomes more equilibrium, due to which the strength of the deformed alloy decreases, and the relative elongation increases. Additional alloying of the base alloy with zirconium and tin slightly increases plasticity and decreases heat-resistant properties. [ABSTRACT FROM AUTHOR]

The ternary silicide ErNi4.04Si0.96 was synthesized by arc-melting of stoichiometric quantities of the elements, and its crystal structure has been determined using single-crystal X-ray diffraction data. The compound crystallizes in the CaCu5 structure type: hexagonal space group P6/mmm, Pearson code hP6, Z = 1; a = 4.874(3), c = 3.959(2) Å, V = 81.5(1) Å3; R1 = 0.0239, wR2 = 0.0503, for 67 independent reflections with I > 2σ(I) and eight variables. The erbium and nickel atoms occupy the crystallographic positions 1a and 2c, respectively. The position 3g is occupied by a mixture of Ni and Si atoms. The structure of this silicide represents a packing of bipyramidal units built from nickel and Ni/Si atoms. [ABSTRACT FROM AUTHOR]

The article presents the research results on the interaction of tricalcium phosphate with the products of carbothermic reduction of silicon oxide (SiOg, SiC, iron silicides). The research was carried out by computer thermodynamic modeling using the HSC-6.0 software package. It was established that SiOg, Si, and SiC are highly reactive towards tricalcium phosphate at relatively low temperatures. It was found that, according to the formation degree of gaseous phosphorus from Ca3(PO4)2, silicon-containing reducing agents form a decreasing series: (SiOg, Si)>SiC>FeSi2>FeSi. [ABSTRACT FROM AUTHOR]

Noble-metal free topological FeSi electrocatalyst is controllably designed using a solvent-free microwave method for efficient electrocatalytic hydrogenation of nitrobenzene. Benefiting the high surface coverage of active H* intermediates, FeSi achieves nitrobenzene conversion of 99.7% and aniline yield of 93.8% in neutral medium, which are superior to previous candidates and FeSi synthesized via the traditional arc-melting method under same conditions. [Display omitted] Electrocatalytic hydrogenation of nitrobenzene (Ph-NO 2) reaction (EHNR) has been considered as a potential alternative to the traditional thermocatalytic process in the production of high-value aniline (Ph-NH 2). However, due to the absence of robust catalyst and low surface H* coverage, the EHNR faces the challenges of undesired performance and indetermined mechanism. Herein, we construct a type of noble-metal free topological FeSi (M-FeSi) materials through a solvent-free microwave strategy for efficient EHNR in neutral medium. Impressively, benefiting from abundant active H* intermediates on the surface of M-FeSi catalyst, the topological M-FeSi catalyst exhibits 99.7% conversion of Ph-NO 2 and 93.8% yield of Ph-NH 2 after 200 C in neutral medium, which are superior to previous candidates and FeSi catalyst synthesized via the traditional arc-melting method under same conditions. Besides, theoretical calculations validate that high surface H* coverage over M-FeSi catalyst is conducive to switching the rate-determining step from Ph-NO 2 * → Ph-NO* to Ph-NO* → Ph-NHOH*, and thus decreasing the total energy barrier of electrocatalytic Ph-NH 2 production. [ABSTRACT FROM AUTHOR]

More than 1000 crystalline silicide materials have been screened for thermoelectric properties using first-principles atomistic calculations coupled with the semi-classical Boltzmann transport equation. Compounds that contain radioactive, toxic, rare, and expensive elements as well as oxides, hydrides, carbides, nitrides, and halides have been neglected in the study. The already well-known silicides with good thermoelectric properties, such as SiGe, Mg2Si, and MnSix, are successfully predicted to be promising compounds along with a number of other binary and ternary silicide compositions. Some of these materials have only been scarcely studied in the literature, with no thermoelectric properties being reported in experimental papers. These novel materials can be very interesting for thermoelectric applications provided that they can be heavily doped to give a sufficiently high charge carrier concentration and that they can be alloyed with isoelectronic elements to achieve adequately low phonon thermal conductivity. The study concludes with a list of the most promising silicide compounds that are recommended for further experimental and theoretical investigations. [ABSTRACT FROM AUTHOR]

Si-based materials are considered as promising candidates for thermoelectric materials, owing to several advantages such as non-toxicity, abundance, and high stability. One of the strategies to develop high-efficiency Si-based thermoelectric materials with enhanced figure of merit zT is increasing the μH/κlat ratio, where μH and κlat are the Hall mobility and lattice thermal conductivity, respectively. In the present study, we synthesize a bulk Si–Ti nanocomposite composed of Si and Ti silicide by a combined method of melt-spinning and spark plasma sintering and examine the thermoelectric properties. The obtained results are compared with the data for Si–V and Si–Ni nanocomposites reported previously by the authors' group. In the comparison, we focus on (1) size and distribution of the precipitates, (2) the interface between Si and the precipitates, and (3) volume fraction of the precipitates; and investigate the effects of these three factors on keeping high μH and reduction of κlat. Based on the comparison, it is revealed that the uniform distribution of the precipitates and the coherent interface between Si and metal silicide lead to large μH/κlat ratio and thus enhanced zT in the nanocomposites composed of Si and metal silicides. [ABSTRACT FROM AUTHOR]

Molybdenum (Mo)/4H-silicon carbide (SiC) Schottky barrier diodes have been fabricated with a phosphorus pentoxide (P 2 O 5) surface passivation treatment performed on the SiC surface prior to metallization. Compared to the untreated diodes, the P 2 O 5 -treated diodes were found to have a lower Schottky barrier height by 0.11 eV and a lower leakage current by two to three orders of magnitude. Physical characterization of the P 2 O 5 -treated Mo/SiC interfaces revealed that there are two primary causes for the improvement in electrical performance. First, transmission electron microscopy imaging showed that nanopits filled with silicon dioxide had formed at the surface after the P 2 O 5 treatment that terminates potential leakage paths. Second, secondary ion mass spectroscopy revealed a high concentration of phosphorus atoms near the interface. While only a fraction of these are active, a small increase in doping at the interface is responsible for the reduction in barrier height. Comparisons were made between the P 2 O 5 pretreatment and oxygen (O 2) and nitrous oxide (N 2 O) pretreatments that do not form the same nanopits and do not reduce leakage current. X-ray photoelectron spectroscopy shows that SiC beneath the deposited P 2 O 5 oxide retains a Si-rich interface unlike the N 2 O and O 2 treatments that consume SiC and trap carbon at the interface. Finally, after annealing, the Mo/SiC interface forms almost no silicide, leaving the enhancement to the subsurface in place, explaining why the P 2 O 5 treatment has had no effect on nickel- or titanium-SiC contacts. [ABSTRACT FROM AUTHOR]

The growth development of nanometer thick Mo and Si layers was studied using in situ laser deflection and Low Energy Ion Scattering (LEIS). The growth stress obtained from changes in wafer curvature during growth is correlated to changes in the surface stochiometry monitored by LEIS. For Si on Mo, the compressive-tensile-compressive stress development could be explained by the formation of interfacial silicide compounds and the transition between these and the bulk growth of Si. For Mo on Si, a strong initial tensile stress due to silicide formation saturates upon reduced availability of free Si at the growing Mo surface, followed by a near instantaneous tensile increase in stress related to the amorphous-to-crystalline phase transition, which coincides with the end of the compound formation, as determined with LEIS. [ABSTRACT FROM AUTHOR]

The silicides RE3Pd20Si6 (RE = Sc, Y and Lu) were synthesized from the elements by arc-melting. The structures of Y3Pd20Si6 and Lu3Pd20Si6 were refined from single crystal X-ray diffractometer data: Mg3Ni20B6 type, F m 3 ‾ m , a = 1216.04(8) pm, wR = 0.0328, 219 F2 values, 14 variables for Y3Pd20Si6 and a = 1211.69(10) pm, wR = 0.0374, 217 F2 values, 14 variables for Lu3Pd20Si6. The isotypy of Sc3Pd20Si6 was confirmed on the basis of a Guinier powder pattern (a = 1202.8(3) pm). The RE3Pd20Si6 structures contain two crystallographically independent RE sites with relatively large coordination numbers, i.e. RE1@Pd16 and RE2@Pd12Si6. These polyhedra are arranged in a CaF2 related pattern with RE2@Pd12Si6 forming the fcc substructure and the RE1@Pd16 polyhedra filling the tetrahedral voids. The silicon atoms have slightly distorted square antiprismatic palladium coordination (4 × 239 pm Si–Pd1 and 4 × 245 pm Si–Pd2). Temperature dependent magnetic susceptibility measurements of the Lu3Pd20Si6 sample indicate Pauli paramagnetism. [ABSTRACT FROM AUTHOR]

In recent years, breakthroughs in electronics technology have upgraded the physical properties of the metal oxide semiconductor field effect transistor (MOSFET) toward smaller sizes and improvements in both quality and performance. Hence, the growth field effect transistor (GFET) is being promoted as one of the worthy candidates due to its superior material characteristics. A 14 nm horizontal double-gate bilayer graphene field effect transistor (FET) utilizing high-k and a metal gate, which are composed of hafnium dioxide (HfO2) and tungsten silicide (WSix) respectively. Silvaco ATHENA and ATLAS technology computer-aided design (TCAD) tools are used to simulate the design and electrical properties, while Taguchi L9 orthogonal arrays (OA) are used to optimize the electrical properties. The threshold voltage (VTH) adjustment implant dose, VTH adjustment implant energy, source/drain (S/D) implant dose, and S/D implant energy have all been investigated as process parameters, while the VTH adjustment tilt angle and the S/D implant tilt angle have been investigated as noise factors. When compared to the initial findings before optimization, the IOFF has a value of 29.579 nA/µm, indicating a significant improvement. Findings from the optimization technique demonstrate excellent device performance with an IOFF of 28.564 nA/µm, which is closer to the international technology roadmap for semiconductors (ITRS) 2013 target. [ABSTRACT FROM AUTHOR]

This paper describes experimental studies and a mathematical model of mechanical activation and high-temperature synthesis during the Nb–2Si combustion. The model is constructed in the macroscopic approximation. Synthesis regimes are determined depending on the duration of joint mechanical activation of the reagents. The kinetic parameters of grinding of the initial powder mixture and the mechanochemical synthesis of the reaction product are obtained on the basis of experimental data by the inverse problem method. [ABSTRACT FROM AUTHOR]

To improve the wear resistance of high-strength and high-conductivity Cu–Cr–Zr alloys in high-speed and heavy load friction environments, coatings including Ni–Cu, Ni–Cu-10(W,Si), Ni–Cu–10(Mo,W,Si), and Ni–Cu–15(Mo,W,Si) (with an atomic ratio of Mo,W to Si of 1:2) were prepared using coaxial powder-feeding laser cladding technology. The microstructure and wear performance of coatings were chiefly investigated. The results revealed that (Mo,W)Si2 and MoNiSi phases are found in the Ni–Cu–10(Mo,W,Si) and Ni–Cu–15(Mo,W,Si) coating. WSi2 phases are found in the Ni–Cu–10(W,Si) coating. The degree of grain refinement in Ni–Cu–10(Mo,W,Si) was greater than that of the Ni–Cu–10(W,Si) coating after the effect of Mo. The excellent wear resistance and micro-hardness of the Ni–Cu–15(Mo,W,Si) coating were attributed to the increase in its dispersion phase, which were approximately 34.72 mg/km and 428 HV, 27.1% and 590% higher than the Cu–Cr–Zr substrate, respectively. The existence of silicide plays an important role in grain refinement due to the promotion of nucleation and the inhibition of grain growth. In addition, the wear mechanism transformed from adhesive wear in the Ni–Cu coating with no silicides to abrasive wear in the Ni–Cu–15(Mo,W,Si) coating with high levels of silicides. [ABSTRACT FROM AUTHOR]

The central part of the La–Ni–Si system has been investigated at 800 °C by means of single crystal X-ray diffraction, microscopy and analytical microprobe techniques. The result led to the identification of four new metal-rich silicides: LaNi2Si (R3¯m, a = 4.0263(3) Å, c = 15.066(2) Å, Z = 3), La2Ni3Si2 (P21/c, a = 6.8789(7) Å, b = 6.2167(3) Å, c = 12.214(1) Å, β = 90.92(1), Z = 4), La3Ni3Si2 (Pnma, a = 7.501(2) Å, b = 14.316(4) Å, c = 6.149(2) Å, Z = 4), La6Ni7Si4 (Pbcm, a = 6.066(1) Å, b = 7.488(1) Å, c = 29.682(5) Å, Z = 4). LaNi2Si belongs to the SrCu2Ga structure type, which is not represented among silicides, while La2Ni3Si2 crystallizes in its own structure type. Both compounds feature layered polyanionic motifs consisting of Ni and Si, which are separated by La. Instead, La6Ni7Si4 and La3Ni3Si2 are characterized by polyanionic networks. The former compound belongs to the Pr6Ni7Si4 structure type, with only two other representatives (Ce and Nd); the latter has been observed only with Rh and Ir. The two structures reveal close structural relationships having multiple identical slabs. Tight-binding electronic structure calculations by linear muffin-tin-orbital methods were performed for LaNi2Si, La2Ni3Si2 and La3Ni3Si2 to gain insights into their structure–bonding relationships. Their band structures suggest a metallic character for all compounds. The overall crystal orbital Hamilton populations are dominated by polar Ni–Si bonds, though homoatomic Ni–Ni and La–Ni(Si) bond contributions are not negligible. The variety of bonding patterns may serve as a logical explanation for the number of discovered compounds in this system as well as for the diversity of the observed structures. [ABSTRACT FROM AUTHOR]

CoCrFeNi is a well-studied face centered cubic (fcc) high entropy alloy (HEA) that exhibits excellent ductility but only limited strength. The present study focusses on improving the strength-ductility balance of this HEA by addition of varying amounts of SiC using an arc melting route. Chromium present in the base HEA is found to result in decomposition of SiC during melting. Consequently, interaction of free carbon with chromium results in the in-situ formation of chromium carbide, while free silicon remains in solution in the base HEA and/or interacts with the constituent elements of the base HEA to form silicides. The changes in microstructural phases with increasing amount of SiC are found to follow the sequence: fcc → fcc + eutectic → fcc + chromium carbide platelets → fcc + chromium carbide platelets + silicides → fcc + chromium carbide platelets + silicides + graphite globules/flakes. In comparison to both conventional and high entropy alloys, the resulting composites were found to exhibit a very wide range of mechanical properties (yield strength from 277 MPa with more than 60% elongation to 2522 MPa with 6% elongation). Some of the developed high entropy composites showed an outstanding combination of mechanical properties (yield strength 1200 MPa with 37% elongation) and occupied previously unattainable regions in a yield strength versus elongation map. In addition to their significant elongation, the hardness and yield strength of the HEA composites are found to lie in the same range as those of bulk metallic glasses. It is therefore believed that development of high entropy composites can help in obtaining outstanding combinations of mechanical properties for advanced structural applications. [ABSTRACT FROM AUTHOR]

Nowotny Chimney-Ladder (NCL) compounds are attracting increased attention as good thermoelectric (TE) materials. Although the TE properties of Si-based NCL compounds such as higher manganese silicides are well investigated, those of Ge-based ones are scarcely studied. Here, we demonstrate that a series of the Ge-based NCL compounds in the Mo13Ge23-Ru2Ge3 pseudobinary system, i.e., Mo1-xRuxGe1.769, shows quite low lattice thermal conductivity as well as good electrical properties like a material called phonon-glass electron-crystal and thus it shows good TE properties. By tuning the valence electron concentration, the TE properties are optimized and the maximum zT, called materials dimensionless figure of merit, reaches 0.23 for x = 0.6 in Mo1-xRuxGe1.769, which is approximately 15 times higher than that of x = 0 in Mo1-xRuxGe1.769, i.e., Mo13Ge23. [ABSTRACT FROM AUTHOR]

Resonant two-photon ionization spectroscopy has been used to investigate the spectra of the diatomic late transition metal silicides, MSi, M = Fe, Ru, Os, Co, Rh, Ir, Ni, and Pt, in the vicinity of the bond dissociation energy. In these molecules, the density of vibronic states is so large that the spectra appear quasicontinuous in this energy range. When the excitation energy exceeds the ground separated atom limit, however, a new decay process becomes available—molecular dissociation. This occurs so rapidly that the molecule falls apart before it can absorb another photon and be ionized. The result is a sharp drop to the baseline in the ion signal, which we identify as occurring at the thermochemical 0 K bond dissociation energy, D0. On this basis, the measured predissociation thresholds provide D0 = 2.402(3), 4.132(3), 4.516(3), 2.862(3), 4.169(3), 4.952(3), 3.324(3), and 5.325(9) eV for FeSi, RuSi, OsSi, CoSi, RhSi, IrSi, NiSi, and PtSi, respectively. Using thermochemical cycles, the enthalpies of formation of the gaseous MSi molecules are derived as 627(8), 700(10), 799(10), 595(8), 599(8), 636(10), 553(12), and 497(8) kJ/mol for FeSi, RuSi, OsSi, CoSi, RhSi, IrSi, NiSi, and PtSi, respectively. Likewise, combining these results with other data provides the ionization energies of CoSi and NiSi as 7.49(7) and 7.62(7) eV, respectively. Chemical bonding trends among the diatomic transition metal silicides are discussed. [ABSTRACT FROM AUTHOR]

A trade-off between thermoelectric performance and cost-effectiveness makes commercial thermoelectric power generation possible in green energy applications. In this direction, FeSi 2 based thermoelectric material has excellent potential and possesses low-cost, earth abundance and non-toxic constituent elements; still, the thermoelectric performance of FeSi 2 materials is inferior to other mid-temperature thermoelectric materials. Also, the fabrication methods and synthesis routes are complex and time-consuming processes, restricting their competitiveness in mid-temperature applications. This work reports a simple processing strategy for β-FeSi 2 synthesis employing arc-melting and spark plasma sintering techniques. The improved thermoelectric performance and remarkable mechanical properties were realised using these techniques. A substantial improvement in the hardness value of ≃ 6.5 GPa and fracture toughness value of ≃ 3.18 MPa√m was achieved, mainly due to its microstructural features. The processing-structure-properties relationship was established to ensure FeSi 2 based thermoelectric materials' commercial viability. [ABSTRACT FROM AUTHOR]

The outstanding physical properties make TM 5 Si 4 silicides become the potential silicon-based transition-metal ultrahigh-temperature materials. In present work, we adopt the first-principles scheme to explore the structural stability, mechanical properties and explain the hydrogenated mechanism of Ti 5 Si 4 , Zr 5 Si 4 and Hf 5 Si 4 using the electronic structures. And the investigation increases the theoretical support for the developments and applications of TM 5 Si 4 silicides. Three hydrogenated models have shown that the hydrogen displays the stability for hydrogenated TM 5 Si 4 compounds. Furthermore, the introduction of hydrogen occupation has weakened the elastic properties of TM 5 Si 4. The metallic property of TM 5 Si 4 and three hydrogenated models was confirmed by the electronic structures. The localized hybridization between hydrogen and TM 5 Si 4 confirm the hydrogenated structural stability. • Hydrogenation mechanism of TM 5 Si 4 silicides is studied by first-principles calculations. • We find that hydrogen is a thermodynamic stability in TM 5 Si 4 silicides. • The hydrogen weakens the elastic moduli and hardness of TM 5 Si 4 silicides. [ABSTRACT FROM AUTHOR]

Owing to the high melting points and high-temperature stability, transition-metal disilicides are potential components for aerospace, automotive, and industrial engineering applications. However, unwanted oxidation known as PEST oxidation severely limits their application owing to the formation of volatile transition metal oxides, especially in the temperature range of 500–1000 °C. To overcome this problem, a new class of high-entropy disilicides, (Mo 0.2 Nb 0.2 Ta 0.2 V 0.2 W 0.2)Si 2 , was selected by first-principles calculations and then successfully fabricated using a hot-pressing sintering technique. Furthermore, the phase evolution, thermal expansion behavior, thermal conductivity, and oxidation behavior were systematically investigated. Compared with MoSi 2 , (Mo 0.2 Nb 0.2 Ta 0.2 V 0.2 W 0.2)Si 2 possessed a lower thermal conductivity (10.9–14.7 W·m−1·K−1) at 25–1000 °C, higher thermal expansion coefficients (8.6 ± 1.3–6 K–1) at 50–1200 °C, and especially an excellent thermal stability at 500–1000 °C owing to slow diffusion and selective oxidation. This work provides a strong foundation for the synthesis and application of high-entropy disilicides. [ABSTRACT FROM AUTHOR]

Palladium-containing silicon oxycarbide (SiPdOC) ceramics were synthesized using polymethylsilsesquioxane modified with palladium acetate as a single-source precursor. Thus, pyrolysis in argon at 1100 °C led to nanocomposites consisting of Pd 2 Si nanocrystallites dispersed in an amorphous SiOC matrix. Exposure of SiPdOC to higher temperatures resulted in the precipitation of PdSi in addition to Pd 2 Si. The temperature-dependent evolution of the phase composition and microstructure in SiPdOC were analyzed using XRD and TEM respectively and rationalized by a ThermoCalc-based thermodynamic assessment showing the feasibility of the possible reactions. The formation of PdSi was perceived because of the shift in the Pd-Si atomic composition towards the higher Si side, caused by the diffusion of Si present in the matrix into the Pd-Si melt, formed upon the heat-treatment above the melting point (1390 °C) of Pd 2 Si. Further, Raman spectroscopic investigation indicated that Pd catalytically enhanced the graphitization of the free carbon in SiPdOC ceramics. • Pd modified Silres MK upon thermolysis and heat-treatment resulted in crystallization of silicides of Pd in SiOC matrix. • The formation of Pd 2 Si and PdSi was rationalized by thermodynamic analysis and microstructural characterization. • Catalytic graphitization of free carbon in Pd modified SiOC was analyzed using Raman spectroscopy and TEM. [ABSTRACT FROM AUTHOR]

We study the biomedical Ti–18Nb–4Zr–xSi cast alloys with a silicon content of 0.5–1.5 wt.%. Quenching in water was carried out within the temperature range 900–1200°С with durations of holding equal to 5 min and 1 h. It is discovered that the procedure of heating of these alloys to the temperatures of quenching leads to the decay of nonequilibrium phases, and the silicon content is redistributed between the phases in a solid solution and silicides. Since almost all silicon is bound with zirconium and titanium and form silicides, the hardness of the Ti–18Nb–4Zr–xSi alloys mainly depends on the amount of silicides and constitutes 26–28 HRC. Moreover, its maximum values are reached for the alloys with eutectoid compositions containing 0.8–1.2 wt.% Si characterized by the most intense release of finely divided silicides. The increase in the silicon content of the hypereutectoid alloys leads to an increase in the sizes of silicides, as well as to the formation of larger amounts of the β-phase in the as-cast Ti–18Nb–4Zr–xSi alloys, and as a result, their hardness noticeably decreases. For low quenching temperatures (within the range 900–1000°C), the complete eutectoid destruction accompanied by the formation of relatively large stable (Ti, Zr)3Si silicides leads to a decrease in hardness < 25 HRC. In the course of quenching of the as-cast Ti–18Nb–4Zr–xSi alloys at temperatures ≥ 1100°C, we observe the formation of more finely divided silicides, which increases the level of hardness of the eutectoid alloys up to 38–39 HRC. The observed changes in the parameters of the α″-phase demonstrate that, as a result of partial dissolution of silicides in the course of quenching at 1200°C, silicon passes into a solid solution and the amount of large silicides on the grain boundaries increases. Therefore, the level of hardness of the analyzed quenched alloys decreases. [ABSTRACT FROM AUTHOR]

Formation of MoSi2–spinel (MgAl2O4) composites with a wide composition range of MoSi2/MgAl2O4 = 1.0–5.0 was studied by thermitic combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS). Two combustion systems conducted contained not only Mo and Si powders, but also different thermite reagents of 7/12 MoO3 + Mg + 1/2 Al and MoO3 + 2 Al in the presence of Al2O3 and MgO, respectively. In agreement with the calculated adiabatic reaction temperatures, measured combustion temperature and flame-front velocity decreased with increasing MoSi2/MgAl2O4 ratio. The XRD analysis indicated that MoSi2 was formed in α and/or β phases and that β-MoSi2 dominated as the combustion temperature above 1550 °C but α-MoSi2 prevailed as the temperature below 1350 °C. Spinel MgAl2O4 was produced through the dissolution of thermite-produced Al2O3 and MgO into pre-added MgO and Al2O3, respectively. The fracture surface morphology of the products exhibited that granular MoSi2 particles were distributed over or embedded partially into the dense and connecting substrate formed by MgAl2O4. [ABSTRACT FROM AUTHOR]