Stable Boride Research Articles

High-Throughput Screening for Boride Superconductors.

A high-throughput screening using density functional calculations is performed to search for stable boride superconductors from the existing materials database. The workflow employs the fast frozen-phonon method as the descriptor to evaluate the superconducting properties quickly. Twenty-three stable candidates were identified during the screening. The superconductivity was obtained earlier experimentally or computationally for almost all found binary compounds. Previous studies on ternary borides are very limited. Our extensive search among ternary systems confirmed superconductivity in known systems and found several new compounds. Among these discovered superconducting ternary borides, TaMo2B2 shows the highest superconducting temperature of ∼12 K. Most predicted compounds were synthesized previously; therefore, our predictions can be examined experimentally. Our work also demonstrates that the boride systems can have diverse structural motifs that lead to superconductivity.

Amorphous cobalt-iron boride nanoparticles grown on B, N-doped carbon frame for efficient electrocatalytic oxygen evolution

Commencing from low-cost transition metal-based electrocatalysts, improving the catalytic activity and resource utilization is one of the ways to reduce the overall cost of hydrogen production from water cracking and improve energy conversion efficiency. Herein, the bimetallic cobalt-iron boride nanoparticles grown on the B, N-doped carbon frame (noted as CoFeB@BNC) was successfully synthesized by one-step pyrolysis boronizing using CoFe-zeolite imidazole frame (CoFe-ZIF) as the precursor and H3BO3 as the boron source. The excellent OER activity of CoFeB@BNC composite is attributed to the synergy of metal boride sites and additional B, N-doped carbon sites. Its overpotential is 297 mV at 10 mA cm−2 and 332 mV at 50 mA cm−2. Meanwhile, Tafel slope is only 43 mV dec−1, showing faster OER kinetics. The introduction of appropriate amount of Fe creates high conductivity of CoFeB@BNC composite and significantly accelerates OER kinetics. The CoFe-ZIF precursor has a large number of structure defects, which provide abundant mesoporous and active sites for the CoFeB@BNC composite. The B, N-doped carbon frame improves the conductivity and stability of the material. This work provides a feasible strategy for the design and preparation of Fe-doped ZIF-67 precursor and its derived highly active and stable boride catalyst.

Thermodynamic and kinetic analysis of CrB2 and VB2 formation in molten Al–Cr–V–B alloy

Transition metal impurities such as chromium (Cr) and vanadium (V) in solution deteriorate electrical conductivity of smelter grade aluminium (Al). These impurities can be removed from solution via boron treatment in which borides form upon their in-situ reaction with boron (B)-bearing substances. However, Cr removal from smelter grade Al solution is not well understood. A disagreement related to chromium boride (CrB2) formation in molten Al in the presence of other transition metals (V, Ti, Zr, Fe) by adding Al–B master alloy has been reported in literatures. This study presents an effort to understand the mechanism of Cr removal from Al–0.50%Cr–0.50%V (mass fraction) alloy by adding Al–B (AlB12) master alloy at 1023 K in the Al alloy solution. Results indicate that Cr removal from molten Al–0.50%Cr–0.50%V alloy by forming stable borides cannot be achieved at 1023 K; whereas excess of B in the solution preferentially forms aluminium boride (AlB2) over CrB2 during boron treatment of molten Al. The underlying kinetics of V removal from molten Al–0.50%Cr–0.50%V alloy revealed that early reaction stage is controlled by [B]/[V] mass transfer through liquid phase and mass transfer coefficient (km) was measured to be 9.6×10−4 m/s. The later reaction stage was controlled by [B]/[V] diffusion through boride (VB2) ring. This study, therefore, advocates to investigate alternative ways to remove Cr from molten Al.

Extreme Expansion and Reversible Hydrogen Solubility in h.c.p. Titanium Stabilized by Colossal Interstitial Alloying

Titanium and its alloys are very reactive and have a high affinity to interstitial elements. Titanium is one of the metals that forms very stable borides, carbides, nitrides, oxides, and even hydrides. The solubility of nitrogen and oxygen in the hexagonal crystal structure of (metallic) titanium is very high; on the other end limited quantities of boron, carbon, and hydrogen can be dissolved. In the present contribution, we report on a significant increase in the solid solution limit of hydrogen in hexagonal close-packed (h.c.p.) titanium, where the h.c.p. crystal lattice is stabilized by deliberate interstitial alloying with high quantities of nitrogen or oxygen atoms. The presence of nitrogen/oxygen prevents the hydrogen-induced transformation of the h.c.p. titanium lattice to a face-centered cubic (f.c.c.) titanium lattice that occurs if no oxygen or nitrogen is present. The hydrogen content that can be accommodated at room temperature in h.c.p. titanium is as high as an unprecedented 50 at. pct from about 0 at. pct and causes an anisotropic expansion of the hexagonal lattice. This finding showcases that there could be an unexploited potential for combining large quantities of interstitials in titanium-based lattices.

A survey investigation on the stability, electronic and elastic properties of hexagonal ternary transition-metal borides by first-principles calculations

The crystal structure, stability, elastic constants and electronic structures of a class of ternary transition-metal borides with the general formula of h-M2AB2 (where M is a 3d, 4d and 5d transition metal; A is Al, Ga, In; and h represents a hexagonal structure) were investigated using the first-principles calculations within the framework of density functional theory (DFT). The stability of the h-M2AB2 was assessed with the cohesive energy, formation energy and phonon dispersion curves. In general, h-M2AB2 crystallizes in a hexagonal structure, and consists of six-member boron rings (B6) and interleaved M and A layers. The h-M2AB2 containing an IVB-M and VB-M is more energetically favorable with respect to the orthorhombic MAB phase. The lattice constants and bond lengths of the ternary borides are highly dependent on their chemical composition. All the stable borides exhibit metallic transport behaviors. The solid B-B bonding is responsible to the good stability and high bulk modulus of h-M2AB2. The high ductility of late-transition-metal borides is attributed to the delocalized M d and A p electrons. The correlations between the elastic property and the electronic structure of h-M2AB2 were also discussed.

Comparison of Thermodynamic Predictions and Experimental Observations on B Additions in Powder-Processed Ni-Based Superalloys Containing Elevated Concentrations of Nb

Boron additions to Ni-based superalloys are considered to be beneficial to the creep properties of the alloy, as boron has often been reported to increase grain boundary cohesion, increase ductility, and promote the formation of stable boride phases. Despite the importance, it is not well understood whether these improvements are associated with the presence of elemental boron or stable borides along the grain boundaries. In this investigation, two experimental powder-processed Ni-based superalloys containing elevated levels of Nb were found to exhibit increased solubility for B in the γ matrix when compared to similar commercial Ni-based superalloys. This resulted in an overall lower B concentration at grain boundaries that suppressed boride formation. As the predictive capability of CALPHAD database models for Ni-based superalloys have improved over the years, some discrepancies may still persist around compositionally heterogeneous features such as grain boundaries. Improved quantification of the characteristic partitioning of B as a function of the bulk alloy composition is required for understanding and predicting the stability of borides.

Effect of process parameters on the formation of boron-titanium and titanium-boron multi-layered diffusion coatings on interstitial-free steel

Boronizing (boron diffusion) is one of the treatments applied to improve the surface properties of steels. In this study, an interstitial-free (IF) steel was boronized and titanium diffused in order to gain knowledge about the diffusion mechanism. Boronizing was carried out electrothermochemically at 900°C by applying a current density of 0.10 or 0.40 A/cm2 for 45 or 120 minutes in a salt bath containing 100% Na2B4O7 while titanium diffusion was performed thermally at 1000°C for 2 hours. Single-layered diffusion coatings were formed by either boronizing or titanium diffusion whereas multi-layered diffusion coatings were generated by both boronizing and titanium diffusion. One part of the study was concerned with first boronizing and then titanium diffusion while a reverse sequence of the process, i.e. first titanium diffusion and then boronizing, was applied in the other part. The generated single-layered and multi-layered diffusion coatings were characterised by using an optical microscope, a scanning electron microscope equipped with an energy dispersive spectrometer, and an X-ray diffractometer. Occurrence of six chemical reactions during titanium diffusion was assumed and the standard formation enthalpies of these reactions were calculated by using a database. On investigating the microstructure, it was understood that both a boride layer and a titanium based diffusion layer were formed by first boronizing and then titanium diffusion. However, it was observed that the previously formed titanium based diffusion layer inhibited the diffusion of boron atoms in case of first titanium diffusion and then boronizing. On the other hand, if the duration of boronizing and the current density applied during this treatment that was carried out after titanium diffusion were increased, formation of boride phases, as well as of a titanium based diffusion layer, was achieved. The semi-quantitative atomic per cent chemical analyses carried out by the energy dispersive spectrometer and X-ray diffraction analyses pointed out the formation of metastable boride phase of Fe3B, as well as stable boride phases of Fe2B and FeB on the surface of the IF steel that was only boronized. It was concluded that the standard formation enthalpies of the six supposed chemical reactions were negative, indicating that these reactions could occur at a normal atmospheric pressure. In addition, most of the products of these reactions were detected in the X-ray diffraction analyses.

Conductive Film Materials Based on Thermally Stable Fluorine-Containing Polyamide and Nickel Boride

The development of resistor materials science and, namely, the feasibility of developing a composite film material based on the thermally stable polyamide and nickel boride as current-conducting filler, is considered. A process for producing films is developed: the films are obtained by coating the glass substrate with polymer solution with a pre-dispersed filler, followed by forming at 80°C with subsequent drying at 150°C until constant weight. The microstructure and topography of the film surface is studied by SEM and AFM. The formation of two-layer composite with the formation of conducting cluster (when the content of the conducting phase is >30 wt.%) from the substrate side is shown. Volt-amps diagrams are studied and analyzed by the differential method. The R(T) dependence is obtained and the temperature resistance coefficient is determined; the latter is positive and its value is 1.67 · 10–3 °C–1.

Effect of boron addition on the oxidation resistance of silicide protective coatings: A focus on boron location in as-coated and oxidised coated niobium alloys

Multilayered silicide coatings are developed to protect Nb alloys from high temperature oxidation. Their efficiency is improved using a second halide-activated pack-cementation step consisting in a boronizing treatment. This work focuses on the location and quantification of boron in the multi-layered silicide coating in order to study the role of boron. The observations are performed on the cross sections of coated samples, in both as-coated and oxidised (Air–1200°C–100h) states. Characterisation of boron is performed in a FEG-SEM using a coupled WDX-EDX system. It was observed that EDX cannot be used to locate B in a matrix containing Nb, but WDX has sufficient spectral resolution to do it. The synthesis of calibration specimens (TiB2, NbB2 and (Nb0.5 Ti0.5)B2) was required for boron quantitative analysis. The analytical conditions are reported and justified. The compositions determined for borides formed in the coating were relevant with the phase diagrams and the thermodynamic data available for this system. If present in the oxidation products, boron should be in very low amounts because it was not observed during the investigation. Nevertheless, it can be suggested that for high temperature application, the formation of highly stable borides in the coating subsurface is helpful because, in case of crack formation, borides promptly form a boro-silicate glass with a low melting temperature, which is responsible for the self-healing of the oxide scale.

Removal of Vanadium from Molten Aluminum-Part I. Analysis of VB2 Formation

Aluminum has been used as an alternative to copper for electrical conductor applications. However, the presence of certain impurities in aluminum, such as V, Ti, Zr, Cr, and Fe, has detrimental effect on its electrical conductivity. These impurities can be removed by the addition of an Al-B master alloy containing AlB2 or AlB12 phase, known as boron treatment. The detailed mechanism of borides formation, however, is not well understood. In the current study, a systematic investigation of vanadium diborides (VB2) formation in the Al-V-B alloys was carried out. The study comprised thermodynamic assessment and experimental investigation on the Al-V-B system under typical industrial processing conditions. It was predicted from thermodynamic analysis that VB2 are stable borides of V and do not dissolve readily in the temperatures ranging from 948 K to 1173 K (675 °C to 900 °C). The experimental investigation showed that the mechanism of VB2 formation and V removal in an Al-V-B system is complex as it involves a number of steps such as chemical reaction, mass transfers in bulk liquid and inside the VB2 ring, and diffusions of B and V through the VB2 layer. Comparative analysis of thermodynamic and experimental results showed that the aluminum alloys were far from equilibrium and that the overall process was limited by the kinetics of B diffusion through the VB2 ring.

Mechanochemical reactions in Co80B20 and Co60B40 mixtures during ball milling and postannealing

The solid-phase interaction of cobalt with boron during high-energy ball milling of Co80B20 and Co60B40 mixtures was studied. It was found that Co3B boride forms during the mechanical alloying of components in the presence of both modifications of Co with a reduction in the size of blocks of up to 7–15 nm. The transformation of the metastable Co3B phase into stable Co2B and CoB borides is observed in the temperature range of 590–700°C.

In situ generated catalysts for NaBH 4 hydrolysis studied by liquid-phase calorimetry: Influence of the nature of the metal

Several metal chloride salts have been evaluated as precursors of in situ generated catalysts for borohydride hydrolysis. The apparatus used for this study is a reaction calorimeter coupled with a hydrogen volumetric flow-meter. Successive additions of low and high concentration solutions of NaBH 4 were performed within this system in order to determine the stability of the catalysts and the poisoning effect of residual metaborate. Both the kinetics of hydrogen production and the concomitant calorimetric signal were studied from this perspective. This work highlights the occurrence of two different types of behaviours among the in situ generated catalysts, and demonstrates that those metals which can be readily oxidized and form stable boride species are the best catalysts for the catalytic borohydride hydrolysis reaction, at a lower cost compared to precious metals. The performances of these catalysts are not affected by the concentration of the NaBH 4 solution, and the rate of hydrogen generation remains constant during the reaction.

Physicochemical laws of the interaction of nickel aluminides with alloying elements: II. Interaction of nickel aluminides with alloying elements and/or interstitial phases

The Ni-Al-X (X is an interstitial element or phase) phase diagrams are analyzed to reveal systems that can be used as the basis for designing promising alloys and natural composites based on nickel aluminides reinforced by interstitial phases (natural composites I). The most thermally stable materials are shown to be heterophase alloys and composite materials (CMs) located in the eutectic-type (including degenerate eutectic) pseudobinary sections of ternary or multicomponent phase diagrams. They exhibit insignificant (or zero) dissolution of interstitial phases at operating temperatures and the absence of an intense interaction between CM components (natural composites II). Natural composites I based on the NiAl-or Ni3Al-interstitial phase alloys produced upon cooling from a melt can be reinforced by the refractory thermally stable rigid interstitial phases, namely, borides and carbides, that are present in pseudobinary sections in equilibrium with these nickel aluminides, since the elements forming these phases dissolve completely in matrix melts and the mutual solubility of these phases in the solid state is low. Such borides are TiB2 and HfB2 in equilibrium with β-NiAl, and such carbides are, e.g., TiC and HfC in equilibrium with β-NiAl and La2C3, NbC, and TaC in equilibrium with γ′-Ni3Al. Natural composites II should be produced using solid-phase methods (NiAl with AlN, Y2O3, Al2O3) or a combination of methods, where a refractory interstitial phase of the Al2O3 or Y2O3 type is solid and the intermetallic NiAl or Ni3Al matrix is liquid. NiAl-TiB2 (HfB2), NiAl-Al2O3 (Y2O3), and Ni3Al-La2C3 (NbC, TaC) composites are considered as examples.

Wetting and interface interactions in the B 4C/Al–Me (Me [dbnd]Cu, Sn) systems

The wettability of B 4C in contact with non-carbide and non-boride forming liquid metals (such as Cu or Sn) has been the subject of several studies. These metals do not wet boron carbide unless a reactive element is added to the melt. The present study is concerned with the addition of Al which completes the series of reactive elements added to the non-wetting metals. While Si represents the elements that form stable carbides and Ti represents the elements that form stable borides, Al belongs to the group of elements that form ternary borocarbides. The wetting experiments in the B 4C/(Me–Al, Me Cu, Sn) systems have shown that a ternary product, namely Al 8B 4C 7 was formed at the interface and that wetting is governed by the thermodynamic properties of the binary liquid system.

Synthesis of nanocrystalline diamond films on smooth WC-Co cemented carbide substrates

Nanocrystalline Diamond Films (NDFs) are deposited on WC-Co cemented carbide substrates by the bias-enhanced hot filament Chemical Vapour Deposition (CVD). A new pretreatment method is performed to diffuse boron into WC-Co substrate without surface roughening of smooth substrates. The new CVD processes are used to enhance the secondary nucleation, reduce the grain size of nandiamond and promote the growth of NDFs by appropriately increasing acetone concentration, lowering the reactive gases pressure and adding Ar gas in the reactive gases. Research results show that the boronization pretreatment can result in the formation of the stable cobalt boride compounds on the substrate surface, thus effectively ensure the adhesion of smooth diamond films. NDFs consist of nanocrystalline diamond with grain sizes range from 20 to 60 nm. The surface roughness of NDFs is measured at Ra < 50 nm. The diamond-coated drawing dies with these NDFs show obvious effect in the practical application.

Influence of the degree of oxygen rarefaction in a medium on the interaction of boron carbide with titanium alloys

We describe the mechanism of processes at the metal-saturating medium interface in the course of thermodiffusion saturation of titanium in boron carbide at temperatures that do not exceed the point of polymorphic transformation of titanium alloys. We have established the influence of oxygen partial pressure over a layer of boron carbide on the character of interaction between the saturating medium and titanium. We show the possibility to form stable boride coatings on a titanium matrix.

Preparation of Dispersion-Strengthened Coppers with Niobium Carbide and Niobium Boride by Mechanical Alloying

The present study examines nanocomposites prepared by mechanical alloying of copper with other transition elements, which will produce a dispersion of stable boride and carbides reinforcement particles within a nanostructured copper matrix, at room temperature. Copper, niobium, boron and graphite powder mixtures were mechanically alloyed for several hours in a planetary ball-mill, in argon atmosphere and using a stainless steel container. The powder mixtures were produced with nominal composition of 10-30 vol.% NbC and 7-10 vol.% NbB2, using powders of pure elemental Cu, Nb, synthetic graphite and crystalline boron. The microstructural changes during milling of these powder mixtures were studied using X-ray diffraction, optical microscopy, scanning electron microscopy and microhardness measurements.

Thermally Stable Boride Ohmic Contacts on n-ZnO

The annealing temperature dependence of contact characteristics on bulk single-crystal n- ZnO using a TiB2/Pt/Au metallization scheme deposited by sputtering are reported. The contacts are rectifying for anneal temperatures < 700C but transition to Ohmic behavior at higher temperatures and exhibit a minimum specific contact resistivity of 5x10-4 Ω. cm after 800C anneals. Higher temperatures lead to severe contact metallurgy intermixing and a sharp increase in specific contact resistivity associated with an increase in sheet resistance of the ZnO under the contact. Pt, Ti, Zn and B outdiffuse through the Au layer at 800C while at higher temperatures the contact morphology is destroyed. These boride- based contacts show much higher thermal stability than previous metal schemes used as Ohmic contacts on ZnO and are promising for high temperature device applications.

Thermally Stable Boride Ohmic Contacts on n-ZnO

not Available.

A fast and low-cost room temperature process for TiB2 formation by mechanosynthesis

Nanometric particles of titanium diboride can be produced by solid state room temperature reduction of boron(III) oxide, titanium dioxide with magnesium metal. The reaction is driven by high-energy ball milling powder mixtures of easily available materials like B2O3, TiO2 and Mg and involves a thermite route that allows for very short reaction times (lower than 2 h) under the proper milling conditions. The two thermite reactions, one between TiO2 and Mg and the other between B2O3 and Mg are nearly-instantaneous, the one starting first providing sufficient heat for reaching the ignition temperature for the other reaction to take place, and are immediately followed by reaction between elemental Ti and B to provide titanium diboride. The evolution of the reaction was followed as a function of time by X-ray diffraction (XRD), showing a gradual decrease in crystallite size of the reactant TiO2, with formation of intermediate reaction products, and once a near-instantaneous reaction takes place it produces mostly MgO and TiB2 as final products. Intermediate reaction products like less stable borides are also produced, but prolonged milling time for 1 h more results in the most stable boride TiB2 and MgO as only products. MgO was removed by leaching in diluted HCl and pure titanium diboride was obtained with a typical molar yield of 81%. The TiB2 powders are formed of impact welded aggregates of small particles of homogeneous dimension of about 50–100 nm.