Room-temperature synthesis of metal borides (original) (raw)
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Room-Temperature Synthesis of Nickel Borides via Decomposition of NaBH 4 Promoted by Nickel Bromide
We report the formation of nickel borides, at room temperature and pressure, from the decomposition of NaBH 4 promoted by the addition of nickel bromide at different concentrations in a dispersing organic medium, tetra-hydrofuran and pentane. The nickel borides, formed as amorphous powders, were analyzed, and the structure information served as input for modeling a periodic lattice structure with the same composition. Experimentally, the nickel boride phases were predominantly composed of a boron-rich phase with composition NiB 3. Combining FT-IR, X-ray diffraction analyses, and theoretical structure determination, we suggest for it a monoclinic structure, with symmetry group P2 1 /c, lattice parameters a =3.038 A ˚ , b = 8.220 A ˚ , c = 5.212 A ˚ , R = β = 90.00° and γ = 87.57°. The enthalpies of formation of the nickel boride phases, as well as the lattice stability, were calculated using density functional theory and density functional perturbation theory methods.
A General Solution Route toward Metal Boride Nanocrystals
Angewandte Chemie International Edition, 2011
Metal-boron alloys contain a boron covalent framework providing typical high chemical, mechanical, and thermal stability, which allows important applications, for example, for diborides (NbB 2) and hexaborides (CaB 6) as refractory materials. [1] New properties also arise from alloying; a prime example is the superconductivity of magnesium diboride, which exhibits the highest critical temperature (39 K) among classical superconductors. [2] Hexaborides are also relevant because of their field emission properties [3] and their potential for thermoelectricity (CeB 6). [4] Moreover, transition-metal borides are drawing attention as efficient (de)hydrogenation catalysts that can accelerate, for instance, emission of hydrogen from ammonia-borane or borohydrides within energyharnessing devices based on hydrogen technology. [5] Applications in hyperthermia, information storage, thermoelectricity, and catalysis would benefit from scaling down to the nanometer range, which could bring, as for all nanomaterials, modified, enhanced, and even novel properties that arise from the finite particle size. To date, only a few nanostructured borides have been reported. This paucity arises mainly because M-B systems are typically synthesized at high temperatures above 1100 8C. [6] Nanoscale materials have been obtained at lower temperatures (25-100 8C), but at the expense of crystallinity and stability, and such approaches yield pyrophoric compounds without applicability. [7] The scarce reported procedures for nanostructured crystalline systems rely on physical [5, 8] or chemical methods, [9] and none of them is demonstrated to be generally applicable to the wide and rich family of borides. Moreover, the majority of
In Situ Solid−Gas Reactivity of Nanoscaled Metal Borides from Molten Salt Synthesis
Metal borides have mostly been studied as bulk materials. The nanoscale provides new opportunities to investigate the properties of these materials, e.g., nanoscale hardening and surface reactivity. Metal borides are often considered stable solids because of their covalent character, but little is known on their behavior under a reactive atmosphere, especially reductive gases. We use molten salt synthesis at 750°C to provide cobalt monoboride (CoB) nanocrystals embedded in an amorphous layer of cobalt(II) and partially oxidized boron as a model platform to study morphological, chemical, and structural evolutions of the boride and the superficial layer exposed to argon, dihydrogen (H 2 ), and a mixture of H 2 and carbon dioxide (CO 2 ) through a multiscale in situ approach: environmental transmission electron microscopy, synchrotron-based nearambient-pressure X-ray photoelectron spectroscopy, and near-edge X-ray absorption spectroscopy. Although the material is stable under argon, H 2 triggers at 400°C decomposition of CoB, leading to cobalt(0) nanoparticles. We then show that H 2 activates CoB for the catalysis of CO 2 methanation. A similar decomposition process is also observed on NiB nanocrystals under oxidizing conditions at 300°C. Our work highlights the instability under reactive atmospheres of nanocrystalline cobalt and nickel borides obtained from molten salt synthesis. Therefore, we question the general stability of metal borides with distinct compositions under such conditions. These results shed light on the actual species in metal boride catalysis and provide the framework for future applications of metal borides in their stability domains.
A Hydride Route to Alkali Metal Borides: A Case Study of Lithium Nickel Borides
Chemistry - A European Journal, 2019
Ternary lithium nickel borides LiNi3B1.8 and Li2.8Ni16B8 have been synthesized by using reactive LiH as a precursor. This synthetic route allows for the better mixing of the precursor powders, thus facilitating fast preparation of the alkali metal containing ternary borides. This method is suitable for "fast screening" of multicomponent systems comprised of elements with drastically different reactivities. Crystal structures of the compounds LiNi3B1.8 and Li2.8Ni16B8 were reinvestigated by combination of X-ray single crystal/synchrotron powder diffraction data, solid state 7Li and 11B NMR, and scanning transmission electron microscopy which allow determination of fine structural details including split position of Ni sites and ordering of B vacancies. Field dependent and temperature dependent magnetization measurements are consistent with spin glass behavior for both samples.
Catalysis Today, 2008
Nickel borides doped with elements of first transition series (Cr, Mn, Fe, Co, Cu, and Zn) MNiB, 4% (w/w) respect to Ni, and prepared with the same method as NiB, were used in the glucose and the nitrobenzene hydrogenation reactions. The amorphous catalysts were prepared by chemical reduction of nickel and metallic (Cr, Mn, Fe, Co, Cu, and Zn) salts with borane-tetrahydrofurane (BH 3 -THF) complex in aprotic solvent (THF anhydrous). Different techniques were used to characterize these materials. The MNiB amorphous structure was verified by XRD. The results show that bimetallic borides follow a pattern related to the nature of the dopants metal. The oxidation stability, magnetic susceptibility and catalytic effect are correlated with parameters of each dopants metal. SEM studies show the same spongy-morphology in all cases. The logarithm of the ratio between bimetallic boride and nickel borides specific rates, for nitrobenzene hydrogenation, follow a linear relation with respect to the same relation for glucose hydrogenation. These results demonstrate that the dopants effect on the free activation energy is the same for both reaction systems. This effect could be related with electronic modifications introduced by the dopants metal on nickel boride. #
Chemistry of Materials, 1992
The deposition of both metal-rich and boron-rich thin-film phases of nickel boride from boron-containing precursor compounds by a cluster deposition process is reported. The thin films were characterized by EDXA, AES, SEM, XRD, FT-IR, TEM, and electron diffraction experiments. The films were shown by AES to be compositionally uniform in the bulk sample. Film thicknesses up to 3 l m were readily prepared by controlling the flow rate of the borane into the cell, the substrate temperature, and the duration of the deposition. The stoichiometric composition of the films was controlled by regulating the deposition temperature, the borane flow rate into the reador, and the base vacuum conditions during the film formation. A relationship was found to exist between the temperature during deposition and the film composition with a maximum nickel content reached at approximately 530 "C. The effect of annealing both the nickel-rich and the boron-rich films was studied by SEM, XRD, and electron diffraction experiments. SEM data for the annealed boron-rich f i showed the formation of perfect hexagonal crystals in a channelled columnar matrix. Electron diffraction data showed that this crystalline phase is hexagonal Ni7B3 isolated in a Ni3B matrix. The as-deposited nickel-rich f i were found by XRD studies to be primarily pure nickel, containing relatively small amounts of the Ni3B phase relative to the pure nickel phase. This has been attributed to the precipitation of boron-rich phases as very small crystallites at the grain boundaries of the pure nickel material. XRD spectra for the boron-rich films showed that the films consisted of Ni3B with no pure nickel observed. Annealing of these films did not result in the formation of pure nickel phases in the XRD spectra.
Modern Research in Catalysis, 2016
Nickel borides doped with transition metal (Cr, Mn, Fe, Co, Cu, and Zn) MNiB, 4% w/w respect to Ni were prepared by chemical reduction of nickel and metallic salts in methanol solution with borane-tetrahydrofurane (BH 3 -THF) complex obtained in aprotic solvent (THF anhydrous). Different techniques were used to characterize these materials. The MNiB amorphous structure was verified by XRD. Thermal treatment in N 2 shows Ni˚, Ni 2 Band NiO phases. Spongy-morphology was evident by SEM studies in all cases. XPS and TEM show that doped and non-doped nickel boride was present as Ni˚ in metallic state as principal phase and nickel alloying with boron was observed in minor quantities. The oxidation stability, magnetic susceptibility and catalytic effect are correlated with parameters of each dopant metal.