Extent Of Nitridation Research Articles

Impacts of Temperature and Time on Direct Nitridation of Aluminium Powders for Preparation of AlN Reinforcement

Aluminium nitride (AlN) is an important technical ceramic with outstanding strength and thermal conductivity that has important applications for advanced heat sink materials and as a reinforcement for metal-based composites. In this study, we report a novel, straightforward and low-cost method to prepare AlN powder using a vacuum tube furnace for the direct nitridation of loose aluminium powder at low temperatures (down to 500 ∘C) under flowing high-purity nitrogen. Small amounts of magnesium powder (1 wt.%), combined with aluminium, promote nitridation. Here, we characterise the effects of time (up to 12 h) and temperature (490 to 560 ∘C) on nitridation with the aim to establish an effective regimen for the controlled synthesis of an aluminium nitride reinforcement powder for the production of metal matrix composites. The extent of nitridation and the morphology of the reaction products were assessed using scanning electron microscopy and X-ray diffraction analyses. AlN was detected for all nitriding temperatures ≥ 500 ∘C, with the highest yields of 80% to 85% obtained at 530 ∘C for times ≥ 1 h. At this temperature, nitridation proceeded rapidly, and there was extensive agglomeration of the reaction products making it difficult to reprocess into powder. At lower temperatures around 510 ∘C, a relatively high proportion of AlN was attained (>73% after 6 h) while retaining excellent friability so that it could be manually reprocessed to powder. The synthesised reinforcement consisted of micro- or nano-crystalline AlN comingled with metallic aluminium. The ratio of AlN and metallic aluminium can be readily controlled by varying the nitriding temperature. This provides a flexible and accessible method for the production of AlN-reinforcement powders suited to the production of metal matrix composites.

Effects of magnesium, tin and nitrogen on the sintering response of aluminum powder

In this work the effects of magnesium and tin on the sintering response of air atomized aluminum powder were considered. The nature of the raw powders and their concentrations were key experimental variable. Compacts of pure aluminum powder sintered poorly and reacted with the purified nitrogen atmosphere. This was manifested as a subtle mass gain. Tin dampened this effect for all concentrations considered (0.1–2 w/o). The reduction was maximized with a tin addition of 1.5 w/o. Magnesium additions improved the sintering response of the aluminum powder and increased the propensity for reaction with gaseous nitrogen. Aluminum nitride was confirmed as the principal reaction product. The extent of nitridation was influenced by the amount of magnesium present and the raw powder form utilized (elemental, master alloy). The most desirable sintering response was observed in an Al–1.5Sn–1.5Mg alloy made exclusively from elemental powders. This system sintered to near full theoretical density (99.5%) yet no observable amount of nitridation had transpired. The system exhibited excellent tensile ductility ( ɛ f ∼15%) for a press-and-sinter aluminum P/M alloy.

Multiscale Modeling and Analysis of the Nitridation Effect of SiC/SiO<sub>2</sub> Interface

We explain the role of nitrogen in simultaneously increasing the inversion channel mobility and reducing the threshold voltage of SiC MOSFET. A variety of computational techniques have been used to compute the atomic scale configuration of a nitridated SiC/SiO2 interface, and the corresponding change in Fermi level, inversion channel mobility, and threshold voltage. X-ray photoelectron spectroscopy (XPS) has been used to investigate the SiC/SiO2 interface to determine the nitrogen concentrations and chemical bonding. We elucidate the physics behind improved channel mobility due to NO anneal and demonstrate that the trade-off between threshold voltage and inversion channel mobility can be correlated to the extent of nitridation.

Tuning aerosol‐assisted vapor phase processing towards low oxygen GaN powders

AbstractHerein, are reported studies of various experimental conditions aimed at optimizing the Aerosol‐Assisted Vapor Phase Synthesis (AAVS) of GaN powders. In general, the process utilizes affordable oxygen‐bearing gallium precursors in aqueous/methanol solutions to initially prepare nano‐sized GaNx Oy powders of spheroidal morphology. Subsequent pyrolysis of the GaNx Oy intermediate in a NH3 atmosphere converts the powders to sub‐micron, crystalline GaN powders that usually contain some residual oxygen. The application of appropriate solvents, e.g. , methanol, in the aerosol powder generation stage and the use of pyrolysis temperatures in the range 900–1000 °C may improve both the extent of nitridation and, to certain degree, the control over average particle sizes. The characteristics of the AAVS‐produced materials are compared with those for bulk GaN powders obtained by direct nitridation of commercial gallium oxide. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of spherical AlN particles by gas-reduction-nitridation method

Spherical AlN particles were synthesized by reduction-nitridation of spherical Al2O3 particles using NH3 and propane (C3H8) as reactant gases. Phase analysis of the reaction products was performed by XRD and the extent of nitridation was evaluated by weight loss measurement. Experimental results indicated that C3H8 addition was effective in accelerating the rate of nitride formation. SEM analysis revealed that the product powder maintained the particle morphology of the initial Al2O3 powder. Up to 94% of the starting material was converted to AlN at 1500°C within 0.5 h via a single-step synthesis process.

On the carbonitrothermic reduction of vanadium pentoxide

Vanadium nitride was prepared by heating a mixture of vanadium pentoxide and graphite powder under a flowing nitrogen atmosphere. The resultant nitride was evaluated by powder X-ray diffraction and chemical analysis. The effects of various experimental parameters, such as oxide-to-carbon ratio, nitrogen flow rate, nitriding temperature and time, compacting pressure, etc., on the extent of nitridation as well as the purity of the vanadium nitride, were studied.

The Nitridation Kinetics of Pyrolyzed Rice Husk

Silicon nitride was formed by nitriding acid-leached and pyrolyzed rice husk in a nitrogen atmosphere. The nitridation kinetics of the pyrolyzed husk pellet over a temperature range of 1473−1723 K were studied by a thermal gravimetric analysis (TGA) technique. The effects of gas flow rate, pellet size, pellet-forming pressure, initial grain sizes, and temperature on the extent of nitridation were examined extensively. Experimental results showed that the nitridation rate of the pyrolyzed husk pellet was distinctly faster than the conventional C/SiO2 mixture process. The rate expressions of the nitridation of the pyrolyzed husk pellet were determined. The activation energy was found to be 115 ± 1 kJ/mol. The reaction was mainly controlled by the diffusion of the gaseous reactant through the product layer. A kinetic model of the nitridation process was developed, and it gave good agreement with the experimental results.

Rapid Thermal Annealing of Titanium in an Ammonia Ambient: Kinetics and Film Properties

AbstractThe reaction between titanium and ammonia to form titanium nitride in a rapid thermal annealer has been studied as a function of process temperature and substrate conditions. The films produced have been characterized by Rutherford Backscattering, Sputtered Neutral Mass Spectroscopy and four point probe electrical resistivity measurements. On oxide substrates, below 720°C only dissolution of nitrogen within the titanium is observed leading to an increase in the specific resistance of the film. Above 720°C, stoichiometric titanium nitride begins forming leading to a drop in the specific resistance of the film. Only in the vicinity of 800°C is all the titanium consumed to form TiN. However, temperatures beyond 700°C cause dissolution of oxygen within the titanium. On silicon substrates, the competing reactions of nitridation and silicidation at the two interfaces govern the extent of nitridation.

Pulsed Laser Processing of Targets Immersed in Liquid Media

ABSTRACTThis report describes a study of the formation of TiN thin films produced by laser irradiation of titanium targets immersed in liquid nitrogen. Three fluence thresholds have been determined, corresponding to: (i) surface melting in gaseous nitrogen (0.7 J/cm2) (ii) surface melting under liquid nitrogen with TiN formation (1.2 J/cm2) and (iii) gross melting accompanied by the generation of periodic surface structures ( >2.0 J/cm2). Data obtained from transmission electron microscopy, Auger spectroscopy, and XPS studies show that the rapid solid-statecooling rates ( l010deg/sec ) result in a supersaturated, twinned hcp structure with solute contents up to 40 at% nitrogen.Theoretical estimates suggest that the majority of the incident excimer laser radiation is absorbed by the target with subsequent thermal transfer to the liquid producing a highpressure shock wave originating at the liquid-solid interface. Pressures up to 4.3 GPa are predicted with the expanding vapor layer reaching a terminal velocity after 5 μs and a total lifetime of 28 μs. Such a lifetime is considerably longer than the thermal pulse in the substrate (from a I-dimensional heat flow analysis). The results are discussed with reference to such estimates. Because the thermal diffusivity far exceeds that of the solute, the extent of nitridation is determined predominantly by the first 200 ns of the thermal pulse experienced by the target.

Synthesis Induced by Laser Irradiation at Liquid/Solid Interfaces

AbstractSynthesis of transition metal nitrides induced by excimer laser irradiation of metal foils immersed in liquid nitrogen was studied. Nitrogen incorporation was found by sputtering Auger Electron Spectroscopy in all six investigated metals (Ti, Zr, Hf, V, Nb and Ta). X-ray diffraction was used to determine the compounds formed. The morphologies of the irradiated surfaces often indicated that the surfaces had gone through a molten state. Micronthick mononitrides were grown on Ti, Zr and Hf, whereas Ta and Nb formed Ta2N and Nb2N respectively. The nitrides on V were not satisfactorily identified. The extent of nitridation correlates with the thermodynamic driving force, i.e. the Gibbs free energy for nitride formation.

Kinetics of N 2+ and N + reactions with Mo AT ⩽ 100 eV impact energies

The kinetics of nitridation of polycrystalline Mo by N 2 + and N + have been investigated in the 7.5–100 eV impact energy range. Auger electron spectroscopy has been used to monitor the nitride growth as a function of ion fluence and energy for both N 2 + and N +. Bi-exponential nitride concentration versus dose curves are typical of this system. These data are interpreted within a proposed model which employs both surface and subsurface nitrogen binding sites and incorpo- rates sputtering and bombardment induced transport between the two layers. Fitting this model to the data yields apparent reaction cross sections σ and the extent of nitridation Δ N. Two measures of initial capture probability, (1) the experimental initial slope and (2) the product σΔ N, are used to characterize reactivity.

Nitridation of lithium

The first page of this article is displayed as the abstract.