Oligonary Nitrides and Oxonitrides of Si,P, Al,and B in Combination with Rare Earth or Transition Metals as well as Molecular Precursor Compounds with Nitrido Bridges M‐N‐Si (M = Ti,Zr, Hf,W, Sn)

A novel synthetic approach is presented leading to hitherto unknown nitridosilicates, oxonitridosilicates, oxonitridoaluminosilicates, carbidonitridosilicates, as well as nitridoborates and oxonitridoborates of rare earth elements, alkali, and alkaline earth metals. Typically, the respective metals were reacted with silicon diimide, aluminum nitride, or poly(boron amide imide), respectively, under pure nitrogen atmosphere utilizing a radiofrequency furnace. Usually, the compounds are obtained within short reaction periods as coarsely crystalline products. Zink nitridophosphates of the sodalite structure type were obtained by the reaction of phosphorus nitride imide with zinc or zinc chalcogenides, respectively. Several molecular metal silylamides and imides containing nitridobridges between the metals and silicon were obtained by the reaction of differently chlorinated disilazanes with metal chlorides. During these investigations hitherto unknown bis(trimethylsilyl)ammonium salts have been discovered. Furthermore, we report about the synthesis of N‐silyl metal hydrazides.     

Catalytic synthesis of bamboo-like multiwall BN nanotubes via SHS-annealing process

Bamboo-like multiwall boron nitride (BN) nanotubes were synthesized via annealing porous precursor prepared by self-propagation high temperature synthesis (SHS) method. The as-synthesized BN nanotubes were characterized by the field emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy. These nanotubes have uniform diameters of about 60 nm and an average length of about 10 μm. Four growth models, including tip, base, based tip and base-tip growth models, are proposed based on the catalytic vapor-liquid-solid (VLS) growth mechanism for explaining the formation of the as-synthesized bamboo-like BN nanotubes. Chemical reactions and annealing mechanism are also discussed.     

Synthesis of crystalline boron nanowires by laser ablation

Crystalline boron nanowires with tetragonal structure have been synthesized based on laser ablation of a B/NiCo target; the nanowires are sometimes single crystals and have a droplet at one end of the nanowire; the droplet contains B, Ni and Co elements, which indicates that the vapor-liquid-solid (VLS) mechanism may play a key role in the growth of the boron nanowires.     

Kinetic model of liquid B2O3 gasification in a hydrocarbon combustion environment: I. Heterogeneous surface reactions

As part of an ongoing program to model hydrocarbon assisted boron combustion, a kinetic model has been developed to describe gasification of the ubiquitous boron oxide coating that inhibits particulate boron ignition. This model includes homogeneous gas phase oxidation reactions, multi-component gas phase diffusion, heterogeneous surface reactions, and oxide vaporization. The kinetic processes are treated using a generalized kinetics code, with embeded sensitivity analysis, for the combustion of a one-dimensional (particle radius), spherical particle. This article presents the heterogeneous surface reactions used to describe oxide gasification and presents selected model results for a spherical boron oxide droplet which illustrate the dependence of the oxide gasification rates on the ambient temperature and particle diameter.     

Synthesis of BN coatings on carbon fiber by dip coating

BN coatings were deposited on carbon fibers by dip coating method. The deposited coatings were characterized by scanning electron microscopy, Fourier‐transformed infrared spectroscopy, X‐ray photoelectron spectroscopy and X‐ray diffraction. The influence of temperature on composition and structure of the coatings was investigated. Composition and structure examinations revealed that the crystallinity of the coatings increased with the increasing temperature, and the coating is a mixture of little oxides, turbostratic boron nitride and hexagonal boron nitride. Furthermore, experiments were also conducted in order to describe the growth mechanism, thus forming the basis of future growth of BN coating on fibers by dip coating. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and evolution of novel hollow ZnO urchins by a simple thermal evaporation process

Delicate hollow ZnO urchins have been fabricated by thermal evaporation of metallic zinc powders in a tube furnace without the use of additive, high temperature, or low pressure. The phase transformation, morphologies, and photoluminescence evolution of the ZnO products were carefully studied and investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and photoluminescence (PL) spectra. These studies indicated that the growth of hollow ZnO urchins involves the vaporization of Zn powder, solidification of liquid droplets, surface oxidation, sublimation, and self-catalytic growth of one-dimensional nanowires.     

Analysis of trace metals in thin silicon nitride films by total-reflection X-ray fluorescence

The validity of a matrix withdrawal method for the analysis of trace metals in silicon nitride films on silicon wafers by total-reflection X-ray fluorescence has been evaluated with samples contaminated with diluted standard solutions of eight metals (Ca, V, Cr, Fe, Ni, Cu, Ta, W). The nitride matrix was removed by a decomposition step with HF vapor at ambient conditions followed by the vaporization of the product at a temperature higher than 240°C. The recovery of added metals was determined first directly after vaporization and secondly after preconcentration by the droplet collection (DC) method. The recovery of metals after vaporization at a temperature of 300±50°C was generally close to 100%, except for Cu whose recovery was approximately 40%. The efficiency of the DC step was approximately 50% for most metals but only 10–20% for Cu and Cr. Thus for most metals the total recovery was close to 50%, which is acceptable for analytical purpose. The recovery of Cu and Cr was studied in more detail considering the influence of the thickness of the nitride film, the vaporization temperature, and the composition of the DC solution. The total recovery of Cu increased from approximately 10 to 40% by lowering the temperature of the vaporization step and using a more concentrated DC solution. The recovery of Cr by DC was markedly influenced by the thickness of the nitride film with no great benefit of using a more concentrated DC solution.     

Cobalt boron nitride: A novel heterogeneous catalyst for the synthesis of medicinally important α-amino quinoline phosphonates

A novel cobalt supported on boron nitride (CoBNT) heterogeneous catalyst for the synthesis of α-amino quinoline phosphonates (AQPs) is reported in the present work. The CoBNT was synthesised by simply mixing boron nitride in a solution of cobalt acetate, under an inert atmosphere for 7 d followed by filtration; the yield was 94%. It exhibited excellent catalytic properties for the synthesis of 16 novel AQPs in a one pot mixture containing 2-methoxy 3-formyl quinoline, aniline derivatives and diethyl phosphite. Reactions were rapid, products were easily worked-up and were obtained in more than 90% yield. The CoBNT also exhibited higher catalytic activity than conventional catalysts and was re-used five times without significant decrease in catalytic activity.     

Relationships in synthesis of chromium nitride by combustion of ferrochrome in nitrogen

Nitridation of commercial ferrochrome in the self-propagating high-temperature synthesis mode was studied. The influence of the key parameters of the process (nitrogen pressure, sample diameter, particle size distribution of the initial powder) on synthesis and phase composition of the combustion products was elucidated. The microstructural features of nitrided ferrochrome and chromium nitride were examined by electron microscopy. Acid enrichment of the synthesis products in a hydrochloric acid solution was studied in relation to the composition of nitrided ferrochrome. Chromium nitride with the residual iron content of 0.3 wt% was obtained, and its thermal stability and corrosion resistance were examined.     

Synergic nitrogen source route to inorganic fullerene-like boron nitride with vessel, hollow sphere, onion, and peanut nanostructures

In this paper we describe the large-scale synthesis of inorganic fullerene-like (IF-like) hexagonal boron nitride with vessel, hollow sphere, peanut, and onion structures by reacting BBr(3) with the synergic nitrogen sources NaNH(2) and NH(4)Cl at 400-450 degrees C for 6-12 h. The composition of products could be confirmed to be pure boron nitride with hexagonal structures by the XRD patterns and FT-IR, XPS, and EDXA spectra. The representative HRTEM images clearly reveal the layerlike features of the products. Here, the peanut-like structure of the IF-like BN is reported for the first time, and added to the list as one kind of new morphology of BN nanomaterials. The similarity in the structure between h-BN and graphite is responsible for the formation of IF-like BN with nanostructures of vessels, hollow spheres, peanuts, and onions.     

Hydrogen adsorption on carbon-doped boron nitride nanotube

The adsorption of atomic and molecular hydrogen on carbon-doped boron nitride nanotubes is investigated within the ab initio density functional theory. The binding energy of adsorbed hydrogen on carbon-doped boron nitride nanotube is substantially increased when compared with hydrogen on nondoped nanotube. These results are in agreement with experimental results for boron nitride nanotubes (BNNT) where dangling bonds are present. The atomic hydrogen makes a chemical covalent bond with carbon substitution, while a physisorption occurs for the molecular hydrogen. For the H(2) molecule adsorbed on the top of a carbon atom in a boron site (BNNT + C(B)-H(2)), a donor defect level is present, while for the H(2) molecule adsorbed on the top of a carbon atom in a nitrogen site (BNNT + C(N)-H(2)), an acceptor defect level is present. The binding energies of H(2) molecules absorbed on carbon-doped boron nitride nanotubes are in the optimal range to work as a hydrogen storage medium.     

Scalable exfoliation for few-layered hexagonal boron nitride nanosheets (BNNSs) by microwave-assisted expansion and liquid nitrogen intercalation

The low cost and facile scalable exfoliation route for two-dimensional hexagonal boron nitride (h-BN) was still indispensable for potential applications. In this work, we presented a convenient and scalable exfoliation for few-layer BNNSs. Taking advantage of the advantages of swift heating of microwave and ultra low temperature vaporization of liquid nitrogen, bulk h-BN was high-efficiently exfoliated into few-layer BNNSs. The as-exfoliated BNNSs had a 2−6 nm thickness and approximately 7.91% yield, exhibiting scalable, facile and environment-friendly features. Furthermore, the as-exfoliated BNNSs were applied as additive in oil for reducing friction of oil. The COF of the BNNSs-based grease reduced by 20.10% compared to grease, and the antiwear performance decreased by 55.8% and 45.1% relative to grease and h-BN-based grease.     

Over 1.0 mm-long boron nitride nanotubes

Over 1.0 mm boron nitride nanotubes (BNNTs) were successfully synthesized by an optimized ball milling and annealing method. The annealing temperature of 1100 °C is crucial for the growth of the long BNNTs because at this temperature there is a fast nitrogen dissolution rate in Fe and the B/N ratio in Fe is 1. Such long BNNTs enable a reliable single tube configuration for electrical property characterization and consequently the average resistivity of the long BNNTs is determined to be 7.1 ± 0.9 × 10⁴ Ω cm. Therefore, these BNNTs are promising insulators for three dimensional microelectromechanical system.     

Phase transformation of boron nitride under hypothermal conditions

Phase transformation among different boron nitride (BN) phases in hydrothermal solution was investigated. It was found that hexagonal boron nitride (hBN) firstly formed in the solution at relatively low temperature (i.e., 220 °C). After that, a spot of hBN began to transform into wurtzite boron nitride (wBN) and cubic boron nitride (cBN) at 230 °C. More and more hBN converted into wBN and cBN with the increase in temperature, and this transformation process completed at 300 °C. In this paper, we have explained the mechanism of the above phase transformation by using a reported “puckering mechanism”.     

The structure and reactivity of iron nitride complexes

The structure and reactivity of discrete iron nitride complexes is described. Six-coordinate, four-fold symmetric nitrides are thermally unstable, and have been characterized at cryogenic temperatures by an arsenal of spectroscopic methods. By contrast, four-coordinate, three-fold symmetric iron nitrides can be prepared at room temperature. A range of diamagnetic iron(IV) nitrides have been reported and in some cases, isolated. Among these are the isolable, yet reactive, tris(carbene)borate iron(IV) nitrides. These complexes can effect two-electron nitrogen atom transfer to a range of substrates, in some cases with complete atom transfer occuring through Fe-N bond cleavage. These nitrides are also active in single electron pathways, including the synthesis of ammonia by a mechanism involving hydrogen atom transfer to the nitride ligand. One-electron oxidation of a tris(carbene)borate iron(IV) nitride leads to an isolable iron(V) complex that is unusually reactive for a metal nitride.     

Synthesis and characterization of boron nitride sponges as a novel support for metal nanoparticles

This paper describes a simple synthetic route for the synthesis of hexagonal boron nitride (h-BN) powders with high specific surface area, in which BBr3, NH4Cl and Al powders are used as starting materials. The structure and composition of the powders were characterized by electron diffraction, Fourier transformation infrared spectroscopy and X-ray photoelectron spectroscopy in the selected area. X-ray diffraction shows wide peaks of crystalline h-BN with the particle size on the nanometer scale, and transmission electron microscopy reveals that the products have a novel spongy morphology. Silver nanoparticles loaded h-BN sponges were prepared via a one-step synthesis method. Different reaction conditions for the formation of h-BN sponges were also investigated.     

Determination of boron and nitrogen in boron nitride

Improved techniques are described for the determination of boron and nitrogen in pure boron nitride. Controlled fusion of boron nitride with sodium carbonate in a muffle furnace is followed by a potentiometric titration of the boric acid. A special quartz vessel is described for the determination of nitrogen. The boron nitride is fused with sodium hydroxide and the resulting ammonia is swept into a receiver and titrated with standard hydrochloric acid. Boron and nitrogen values with their standard deviation are given for a typical pure boron nitride.     

Ab initio prediction of 15N-NMR chemical shift in α-boron nitride based on an analysis of connectivities

Hydrogen-saturated cut-outs of hexagonal boron nitride have been used to model the solid state. Model compounds have been geometry optimized by means of density functional theory, whereas chemical shift calculations have been carried out at the coupled-perturbed Hartree–Fock level of theory employing gauge-including atomic orbital (GIAO) basis sets. The reliability of results has been tested against experimental values for chemical shifts in stable molecules with similar structural elements. With increasing cluster size, viz. a vanishing influence of the saturating hydrogens on the innermost nitrogen atoms, we find a convergence of ¹⁵N chemical shifts. A classification scheme for the chemical environment of a nitrogen atom has been set up according to its bonding graph including the second coordination sphere. For a given connectivity, chemical shifts vary within a few parts per million, thus enabling us to predict a ¹⁵N-NMR chemical shift of −285 ± 5 ppm for solid α-boron nitride. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 716–725, 1998     

Low-temperature solid state synthesis and in situ phase transformation to prepare nearly pure cBN

Cubic boron nitride (cBN) is synthesized by a low-temperature solid state synthesis and in situ phase transformation route with NH(4)BF(4), B, NaBH(4) and KBH(4) as the boron sources and NaN(3) as the nitrogen source. Furthermore, two new strategies are developed, i.e., applying pressure on the reactants during the reaction process and introducing the structural induction effect. These results reveal that the relative contents of cBN are greatly increased by applying these new strategies. Finally, almost pure cBN (～90%) crystals are obtained by reacting NH(4)BF(4) and NaN(3) at 250 °C and 450 MPa for 24 h, with NaF as the structural induction material. The heterogeneous nucleation mechanism can commendably illuminate the structure induction effect of NaF with face center cubic structure. In addition, the induction effect results in the cBN nanocrystals presenting obvious oriented growth of {111} planes.     

Energetic stability of boron nitride nanostructures doped with one carbon atom

We have investigated, using first‐principles calculations, the role of a substitutional carbon atom on the geometric stability of boron nitride monolayers, nanotubes, and nanocones. It is shown that the formation of energy depends on the number of atoms for the monolayers and on the diameter for the tubes. It is also found, for the carbon‐doped boron nitride nanotubes, that the value for the strain energy approaches the one obtained for nondoped tubes with increasing diameter. For the structural stability, we have verified that the doping, which introduces an excess of nitrogen or boron, makes each structure more favorable in its reverse atmosphere, i.e., excess of nitrogen is more stable in a boron‐rich growth environment, whereas excess of boron is preferred in a nitrogen‐rich condition. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010