Mixture Of Nitrides Research Articles

Formation of nanosized particles encapsulated in boron nitride during low-temperature annealing of mechanochemically treated Fe?BN mixtures

Electron microscopic investigations and X-ray studies of mechanically activated mixtures of iron and boron nitride provide evidence of the transformation of hexagonal boron nitride into the amorphous state, which is shows up as a halo with maximum at d =3.35 Å in the electron diffraction patterns. According to the obtained electron microscopic data, the particles of iron and boron nitride after mechanical activation form aggregates with a size of 300–1000 nm. The iron particles exhibit a rather broad size distribution (from 3–7 nm to 100 nm), while the minimal size of the boron nitride particles is several tens of nanometers. Annealing of iron samples with boron nitride after preliminary mechanical activation, at a temperature of 860 °C, caused the formation of nanosized encapsulated particles of iron boride Fe 2 B. The surface of the Fe 2 B nanoparticles were coated with a shell composed of hexagonal boron nitride, 5–15 nm thick. The size of the encapsulated particles varies within a rather broad range from 30 to 50 nm to several hundred nanometers.

Formation of nanosized particles encapsulated in boron nitride during low-temperature annealing of mechanochemically treated Fe–BN mixtures

Electron microscopic investigations and X-ray studies of mechanically activated mixtures of iron and boron nitride provide evidence of the transformation of hexagonal boron nitride into the amorphous state, which is shows up as a halo with maximum at d=3.35 Å in the electron diffraction patterns. According to the obtained electron microscopic data, the particles of iron and boron nitride after mechanical activation form aggregates with a size of 300–1000 nm. The iron particles exhibit a rather broad size distribution (from 3–7 nm to 100 nm), while the minimal size of the boron nitride particles is several tens of nanometers. Annealing of iron samples with boron nitride after preliminary mechanical activation, at a temperature of 860 °C, caused the formation of nanosized encapsulated particles of iron boride Fe 2B. The surface of the Fe 2B nanoparticles were coated with a shell composed of hexagonal boron nitride, 5–15 nm thick. The size of the encapsulated particles varies within a rather broad range from 30 to 50 nm to several hundred nanometers.

Formation mechanism of electrically conductive nanoparticles by induction thermal plasmas

The purpose of this paper is to prepare electrically conductive nanoparticles such as borides, mixture of nitrides and borides by induction thermal plasmas. Another purpose is to correlate the prepared particle composition with thermodynamic parameters. For BNM (M=Ti, Cr, V) system that has low Gibbs free energy of nitridation and boridation, boride and nitride nanoparticles were prepared. While BNM (M=Co, Fe, Mo) system that has high Gibbs free energy of nitridation, boride nanoparticles were mainly prepared. For BNM (M=Ta, Nb) system that has much higher nucleation temperature of metal than that of boron, nanoparticles of nitride with small fraction of boride were prepared, because these systems have different nucleation mechanism. The composition of prepared nanoparticles depends on the Gibbs free energy as well as the nucleation temperature.

419 レーザクラッド固体潤滑膜の寿命に及ぼす形成雰囲気の影響

Thin solid lubricant layers were formed by a continuous CO_2 gas laser irradiation. Lubricant powders, mixture of graphite (C) and molybdenum disulfide (MoS_2), graphite and boron nitride (BN), were spread on a stainless steel (SUS316) substrate with a commercial brazing flux and subjected to scanned laser beam irradiation in an argon or air atmosphere. Clad layers were formed under different laser powers and specimen feed rates. It was found from the friction test that some clad layers with low friction and long life could be formed under optimum laser powers. The best lubricant layer with the longest life was obtained from graphite and boron nitride mixture processed in the air atmosphere.

Yield Stress Measurement of Silicon Nitride Suspensions

AbstractYield stress values of silicon nitride suspensions were measured via a novel slotted plate device and a constant stress rheometer and the results were compared. Test platform velocity, associated with the slotted plate method, was found to have a substantial effect on dynamic yield stress but not on static yield stress. The effects of suspension concentration and temperature on yield stress values were investigated. Yield stress measurements on mixtures of silicon nitride and alumina particles, as well as creep tests were performed.

Strained gallium nitride nanowires

Gallium nitride nanowires were synthesized on silicon substrates by chemical vapor deposition using the reaction of gallium and gallium nitride mixture with ammonia. Iron nanoparticles were used as catalysts. The diameter of nanowires is uniform as 25 nm and the lengths are 20–40 μm. The nanowires have single crystalline wurtzite structure with a few stacking faults. A careful examination into x-ray diffraction and Raman scattering data revealed that the separations of the neighboring lattice planes along the growth direction are shorter than those of bulk gallium nitride. The nanowires would experience biaxial compressive stresses in the inward radial direction and the induced tensile uniaxial stresses in the growth direction. The shifts of the band gap due to the stresses have been estimated using the experimental data, showing that the reduction of the band gap due to the tensile stresses can occur more significantly than the increase due to the compressive stresses. The temperature-dependent photoluminescence (PL) of the nanowires exhibit a strong broad band in the energy range of 2.9–3.6 eV. The PL could originate from the recombination of bound excitons. The strong room-temperature PL would be in line with the existence of strains inside the nanowires. The peak appears at the lower energy than that of the epilayer, which is consistent with the decrease of the band gap predicted from the x-ray diffraction and Raman data. The various strengths of stress may result in the widely distributed PL energy position.

Effect of high-energy implantation on TAFe titanium alloy

Implantation of non-metallic ions in transition metals such as titanium typically forms high-melting phases at low temperatures. In this work, we study the effect of N + implantation into a specific titanium alloy (Ti–5 wt.% Al–2.5 wt.% Fe) recently used for orthopedic prostheses. High-dose (10 18 at cm −2) nitrogen implantation at 1 MeV was performed. Specimens were held at a constant temperature ( T imp=−30 °C) and the current density was fixed at 1.5 μA cm −2 to avoid heating and fast diffusion processes during treatment. Nano-indentation results show small effects on mechanical properties, especially on hardness (with Δ H/ H=35%) and elastic modulus (with Δ E/ E less than 10%). Grazing incidence X-ray diffraction results indicate the formation of titanium nitrides TiN 0.3. Samples have been annealed for 1 and 3 h at different temperatures in an argon atmosphere to enhance the nitriding process. At low temperature (350 °C) no evolution of hardness profiles are observed. However, at high temperature (500 °C), a significant increase of the hardness in the near surface region ( H=12 GPa) and at a specific indentation depth ( H=8.5 GPa) are detected. These variations are respectively correlated with the formation of a thin oxide film (TiO 2) and a layer composed of a mixture of titanium nitrides (TiN+Ti 2N) around the ion range. This study shows that the implanted sample can be divided into different layers corresponding to different nitride species as a function of nitrogen concentration distribution.

Reaction of Hydride Phases of Zirconium Intermetallic Compounds with Molecular Nitrogen

Reaction of hydride phases of zirconium intermetallic compounds with molecular nitrogen wasstudied at 293, 973 K, nitrogen pressure of 10 MPa. At 293 K, hydride-nitride phases crystallizing inthe structural types of the initial hydride phases are formed in all cases, whereas at 973 K finely dispersedheterophase mixtures of zirconium, molybdenum, and vanadium nitrides with 3d transition metals or mixtures of zirconium nitride with vanadium, molybdenum, chromium, and manganese nitrides are formed.

Structural and Optical Properties of Strained Gallium Nitride Nanowires

AbstractBulk-quantity single crystalline wurtzite gallium nitride nanowires with a mean diameter of 25 nm were synthesized on silicon substrate using a catalyst-assisted reaction of gallium and gallium nitride mixture with ammonia. They exhibit a strong and broad photoluminescence in the energy range of 2.9-3.6 eV with no yellow band. X-ray diffraction and Raman scattering data suggest that the nanowires would experience biaxial compressive stresses in the inward radial direction and the induced tensile uniaxial stresses in the wire axis. The blue photoluminescence would originate from the recombination of the bound excitons under the compressive and tensile stresses.

粉末製造及び処理技術 Ｂ‐Ｃ‐Ｎ系ナノチューブの合成

B-C-N nanotubes prepared by a plasma evaporation method were characterized by a transmission-electron microscopy (TEM) and an electron-energy-loss spectroscopy (EELS). The nanotubes obtained were divided into three types of carbon-, boron nitride-, and combined nanotubes of boron nitride with carbon. However, BCXN nanotubes of homogeneous phase could not be obtained. This indicated that a stable phase in the experimental condition was in the mixtures of carbon and boron nitride rather than in a homogeneous phase of BCXN compounds. Also the effect of temperatures on the formation of nanotubes was studied. Resultantly it was shown that nanotubes were formed at higher temperatures than 3000 K and, on the other hand, nanocapsules were formed at lower temperatures than 3000 K. Based on the microstructural data obtained, the formation mechanisms of both nanotubes and nanocapsules were described.

Aluminum Nitridation in a Solar-Heated Vibrating Fluidized Bed Reactor

A vibrating fluidized bed reactor was constructed and interfaced with the High-Flux Solar Furnace at the National Renewable Energy Laboratory in Golden, CO. Various precursor mixtures of aluminum and aluminum nitride were heated for approximately 10 to 15 minutes using focused sunlight with an intensity as high as 2000 kW/m2. Particles ranging in size from 2 μm to 10 μm were produced with the heating and fluidization process. X-ray diffraction and chemical composition analyses of the product indicate virtually complete conversion of aluminum to aluminum nitride for some precursor mixtures. High conversion was also achieved using multi-pass processing.

In Situ Thermocouples in Macro-Components Fabricated Using SALD and SALDVI Techniques. I. Thermochemical Modeling

To fabricate macro-structural SiC components containing an In Situ SiC/C thermocouple using an integrated SALD and SALDVI technique, thermodynamic analyses on the involved reactant gases have been performed with the CET89 code based on the minimization of the system free energy. The gaseous precursors considered include tetramethylsilane (TMS) and methyltrichlorosilane (MTS) for the deposition of silicon carbide, and methane, ethylene and acetylene for the deposition of carbon. Reactions between disilane and acetylene and between TMS and ammonia have also been thermodynamically calculated for the deposition of silicon carbide and silicon nitride (for use as an insulation layer between the thermocouple and the matrix), respectively. Based on these analyses, four characteristic temperature zones have been defined for the decomposition of silicon carbide from TMS. A silicon nitride deposition map has been built for the TMS and ammonia system. The deposition temperature range of silicon nitride is found to increase with the total pressure of TMS plus ammonia and the addition of hydrogen, and be affected by the ratio of TMS to ammonia. The addition of hydrogen also introduces a stable silicon carbide and silicon nitride mixture zone that otherwise does not exist. The co-deposition of graphite with silicon carbide and silicon nitride is found in the TMS-containing systems at certain conditions. However, the threshold temperature at which graphite co-deposition occurs can be increased by the addition of hydrogen, thereby eliminating or reducing the graphite co-deposition. Based on these thermodynamic analyses, the gaseous precursors for the deposition of silicon carbide, silicon nitride and carbon have been selected for further experimental evaluation, the result of which is reported in part II of this series.

The formation of aluminium nitrideboron carbidealuminium composites by wetting assisted infiltration

The possibility of producing aluminium matrixed aluminium nitrideboron carbide composites by pressureless wetting assisted infiltration has been shown. Cold isostatically pressed cup-shaped preforms of boron carbide (1–10 wt%) aluminium nitride mixtures were sintered at 1400–1600 °C in nitrogen atmosphere and then infiltrated with aluminium under 6.5 kPa argon at 1250 °C. Pore diameter in the preforms increased with increase in sintering temperature. Infiltrated samples which were sectioned and polished showed no infiltration front. Higher B 4C contents (4–10%) and sintering temperature (1600 °C) resulted in full infiltration. In the sintered preforms AlN was the only phase observed. However, in the infiltrated materials both AlN and Al were observed.

Nitridation in the Processing and Preparation of Metals and Ceramics

The formation and separation of metal nitrides from a variety of materials including ferroalloys, oxides, natural materials and minerals is an important component in current materials processing practice. Ferroalloys like ferroniobium and ferrovanadium undergo nitridation by ammonia yielding a mixture of iron nitrides and the refractory metal nitride. Acid leaching effectively separates the iron nitride from the mixture. Niobium nitride thus obtained is used to produce niobium metal by pyrovacuum treatment. Vanadium nitride converts to metal when pyrovacuum treatment is followed by electrorefining. Nitride suitable for decomposition to metal can be obtained from niobium pentoxide by reacting ammonia or by reacting a mixture of carbon and nitrogen. Rice husk is a ready-made intimate mixture of silica and carbon. It can be converted to silicon nitride or to a mixture of silicon carbide and silicon nitride by carbonitrothermic reduction. β sialon can be directly prepared from kaolinite by carbonitrothermic reduction. Ilmenite is another mineral amenable to nitridation processing. It yields after reaction with nitrogen in presence of carbon, a separable titanium nitride-iron mixture. All these attractive features of nitridation have been discussed in this paper. The possibility of incorporating nitridation into the process flowsheets has been highlighted.

Low-Earth-orbit exposure of carbon-based materials aboard Shuttle flight STS-46

Six different types of carbon and carbon-boron nitride composites were exposed to low Earth orbit (LEO) aboard Space Shuttle flight STS-46. The samples received a nominal atomic-oxygen fluence of 2.2 x 10 atoms/cm in 42 h of exposure. Pyrolytic graphite and highly oriented pyrolytic graphite showed significant degradation, and the measured erosion yield was within a factor of 2 of published values. The erosion yield of pyrolytic boron nitride was found to be 2.6 X10 cnrVatom in plasma asher exposure, over 42 times lower than that of pyrolytic graphite. This low erosion yield makes graphite-boron nitride mixtures quite resistant to LEO exposure. Evidence suggests that the graphitic component was preferentially etched, leaving the surface boron nitride rich. Atomic-oxygen resistance increases with boron nitride composition. Carbon-fiber-carbon composites eroded in LEO, and the carbon pitch binder was found to etch more easily than the graphite fibers, which have much higher atomic-oxygen resistance.

Interfacial Fracture Between Boron Nitride And Silicon Nitride And Its Applications To The Failure Behavior Of Fibrous Monolithic Ceramics

AbstractMechanical tests show that fibrous monolithic ceramics can exhibit graceful failure in bending due to marked crack deflection at silicon nitride/boron nitride interfaces. Model sandwich specimens were manufactured from polycrystalline silicon nitride with interphases consisting of mixtures of silicon nitride and boron nitride. The interfacial fracture resistances of the specimens were measured, and the results were correlated to the failure behavior of fibrous monolithic ceramics. It was found that the three modes of failure observed in fibrous monoliths can be correlated with the interfacial fracture resistance. In addition, anisotropy in the properties of the interphases were found to have a profound influence on crack deflection.

Thermogravimetric Determination of Carbon, Nitrogen, and Oxygen in Aluminum Nitride

A thermogravimetric method for the measurement of carbon, nitrogen, and oxygen in aluminum nitride is described. Since carbon oxidation occurs at lower temperatures than the oxidation of the aluminum compounds, thermogravimetric analyses in the respective temperature regimes can yield measurement of the oxygen, nitrogen, and carbon content. Thermogravimetric analyses were performed on mixtures of aluminum nitride and carbon with various concentrations in order to evaluate the accuracy of this method. The results were compared with those obtained by the hot gas extraction method. Errors produced by overlapping of the temperature ranges of the reactions were evaluated and experimental conditions were optimized to minimize error. This method can produce reliable results at elemental concentrations higher than a few percent. The absolute errors of the C/AI, N/Al, and O/Al atomic ratios were less then 0.02. The detection limit was evaluated to 0.2 wt% of each element. The applicability of the method to the study of the kinetics of the nitridation reaction was demonstrated.

Nitride glasses obtained by high-pressure synthesis

THE incorporation of nitrogen in oxide glasses can lead to improved physical properties such as hardness and refractive index1–4; one might accordingly expect to see a further improve-ment in glasses containing nitrogen as the only anion. But while there are now many examples of non-oxide glasses in the halide and chalcogenide families5–8, the formation of pure nitride glasses has not hitherto been demonstrated. Here we report the formation of glasses in the system Li3N-Ca3N2-P3N5, by the rapid quenching of fused mixtures of the nitrides at high pressures. The use of high-pressure conditions prevents thermal decomposition of the nitride mixtures to gaseous nitrogen. The new nitride glasses are stable in air, have remarkably high refractive indices (1.97–2.0), hardness exceeding that of silica glass, and high glass transition tempera-tures (7g > 700 °C).

Crystallization and Properties of a Si‐Y‐Al‐O‐N Glass‐Ceramic

Glasses have been prepared in the Si ‐Y‐Al O‐N system by melting mixtures of silica, alumina, yttria, and silicon nitride. One particular glass containing 17 equiv% N has been investigated to Observe the crystallization at temperatures in the range 1050o‐1300oC. The major crystalline phase observed is Y2Si2O7, existing as the α form below 1200oC and the β form above this temperature. Properties of the glass‐ceramic, including thermal expansion coefficient, hardness, electrical resistivity, and creep have been assessed.

ChemInform Abstract: Preparation of Mixtures of Silicon Oxynitride and Silicon Nitride by the Reaction of Calcium Silicide with Ammonium Chloride.

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