Synthesis Of Aluminum Nitride Research Articles

Density functional theory study of the reaction mechanism of aluminum nitride synthesis by sol–gel method

In recent years, aluminum nitride has undergone significant advancements and has found extensive application in optoelectronic and microelectronic devices due to its remarkable physicochemical properties. The quality of aluminum nitride powder plays a critical role in determining device performance, thus making the synthesis of high-quality powder a prominent area of research. The sol–gel method is a widely used approach for producing superior powders. In this study, we investigated the ammonolysis-polymerization mechanism of tris(dimethylamino)aluminum monomer and dimer using Gaussian16 software at the B3LYP-D3BJ/6-311G(d,p) level. Our objective was to provide theoretical guidance for the experimental synthesis of aluminum nitride powders using the sol–gel method. Our findings demonstrate that the ammonolysis reaction of tris(dimethylamino)aluminum dimer proceeds through six spontaneous steps. The two calculated polymerization steps also exhibit spontaneous behavior. All reactions demonstrate rapid occurrence, suggesting the theoretical feasibility of the ammonolysis-polymerization reaction of tris(dimethylamino)-aluminum dimer for synthesizing aluminum nitride.

Self-propagating high-temperature synthesis and sintering of AlN‒Y<sub>2</sub>O<sub>3</sub>‒Al<sub>2</sub>O<sub>3</sub> compositions

The results of studies on the synthesis of aluminum nitride and AlN‒Al2O3‒Y2O3 compositions with a low oxygen impurity content by the SHS method are presented. The dependence of the lattice parameter c of aluminum nitride on the oxygen impurity content is shown. The conditions for the synthesis of AlN‒Y2O3 compositions with a low oxygen content in the structure of aluminum nitride are determined. The dependence of the composition of oxide phases in compositions on the content of yttrium oxide in the reaction mixture is shown. The optimal content of yttrium oxide in the compositions has been determined. The results of sintering AlN‒Al2O3‒Y2O3 composite powders with different oxygen content in the aluminum nitride structure are shown.

Synthesis of Aluminum Nitride Using Sodium Aluminate as Aluminum Source

At present, the carbothermal reduction and nitridation process is an important method for the large-scale preparation of aluminum nitride powder in industry, but the tremendous energy consumption caused by long-term high temperatures seriously restricts its practical application. To solve this problem, the (NaAlO2+C) mixture with a mole ratio of NaAlO2:C = 1:3 was prepared based on sodium aluminate and carbon black which has been ball milled with anhydrous ethanol as a grinding liquid. The crystal structure evolution and nitridation reaction behavior of sodium aluminate at 800–1600 °C under a nitrogen atmosphere in the presence of carbon were systematically studied employing XRD, SEM, and ICP-MS. The results showed that: high energy θ-Al2O3, η-Al2O3 can be excited by heating sodium aluminate to 1400 °C under a nitrogen atmosphere in the presence of carbon. The transformation process between sodium aluminate and aluminum nitride is carried out via the direct nitridation of θ-Al2O3, η-Al2O3. Benefiting from the direct nitridation of η-Al2O3 and θ-Al2O3, high-purity aluminum nitride powder with a particle size of 0.50 ± 0.18 μm was synthesized at 1400 °C. This work provides a new path for reduced energy consumption in the aluminum nitride industry.

Low temperature synthesis of aluminum nitride from anhydrous aluminum chloride-organic amine complex

Low temperature synthesis of aluminum nitride from anhydrous aluminum chloride-organic amine complex

Thermodynamic and kinetic analyses of vacuum synthesis of AlN by the alumina carbothermal reduction nitridation method

AbstractUltrafine single‐phase aluminium nitride (AlN) particles were successfully synthesized by the vacuum carbothermal reduction nitridation (VCRN) method at shorter times and lower temperatures. The mechanism of the process was investigated. By analyzing the X‐ray diffraction (XRD) patterns and thermodynamic calculations, the main reaction path was determined to be Al2O3→Al2CO→Al4C3→Al5C3N→AlN. By investigating the kinetics mechanism, the process was a gas–solid reaction model, which was controlled by the crystalline chemical reaction from 0.5 to 1.5 h, combination control from 1.5 to 2 h, and gas diffusion control from 2 to 2.5 h. Moreover, the apparent activation energy (Ea) was calculated from the nitridation ratio, the value obtained, 237.71 kJ mol–1, is 31% of the energy reported for the conventional synthesis method. These results show that ultrafine AlN could be effectively synthesized at 1823–1873 K and 300 Pa N2 pressure for 2.5 h.

Carbothermal Reduction Synthesis of Aluminum Nitride from Al(OH)3/C/PVB Slurries Prepared by Three-Roll Mixing.

Polyvinyl butyral (PVB) was used in the Al(OH)3/carbon black/ethanol slurries by the three-roll mixing to prepare AlN powder using the carbothermal reduction–nitridation (CRN) process in the experiments. The effects of PVB addition on the synthesis of AlN powder were studied by viscosity, tap density, XRD, SEM and TG measurements. The results showed that the PVB layer covering on the surface of Al(OH)3 particles reduced the viscosity of Al(OH)3/carbon/ethanol slurry and increased the dispersion homogeneity of Al(OH)3/carbon raw powder. The tap densities of the Al(OH)3/carbon mixtures after three-roll milling could be increased with the increase in PVB addition. In the CRN process, most of the PVB covering Al(OH)3 particles evaporated and supplied the passage for nitrogen removal to the particles. Based on the experimental data, the role of PVB on the mixing and CRN process was discussed.

Rapid Synthesis of Aluminum Nitride Nanopowders from Gaseous Aluminum Chloride

The synthesis of aluminum nitride (AlN) powders is traditionally completed through a thermal nitridation process, in which the reacting aluminum powders are combined with nitrogen at high temperatures with a long reaction time (usually several hours). Moreover, the occurrence of agglomeration within the melting Al particles results in a poor dispersibility of AlN powders, with a low efficiency of nitridation. In this study, an atmosphere-pressure microwave plasma preceded the rapid gas-gas synthesis process. In the reactor, the gaseous aluminum chloride (AlCl3) reactant was fed at different positions (R1, R2, R3) to react with nitrogen at various reaction temperatures (690~1150°C) to rapidly produce AlN nano powders (in several seconds). The process was operated at a total flow rate of 13 slm with NH3 gas content of 0 or 0.77% and an applied power of 1200/1400 W. Results showed that the high purity and dispersibility of AlN powders were found at a AlCl3 feeding position closer to the resonant cavity of the reactor (R3, 1150°C). The AlN particle size was in the range of 25-50 nm. The experiments indicated that the gas-gas reaction for rapidly synthesizing AlN nanopowders can be successfully carried out via an AlCl3-N2 plasma-chemical approach.

High-performance mesoporous (AlN/Al2O3) for enhanced NH3 yield during chemical looping ammonia generation technology

Chemical looping ammonia generation (CLAG), including the N-sorption/desorption steps of the N-carrier, is increasingly important due to the high demand for formation of carbon-free fuel. The N-sorption step, the synthesis of aluminum nitride (AlN) by the carbothermal reduction, has been widely studied for improving the purity and stability of aluminum nitride. However, there are few studies on how to enhance the porosity and thus N-desorption reactivity of AlN, one of the key issues for the CLAG. Therefore, in this paper, a supported Al-based nitrogen carrier (AlN/Al2O3) with mesoporous structure, in which 5% of Y2O3 was added as a catalyst, was developed with excess aluminum oxide (γ-Al2O3) and the corresponding N-desorption of the generated N-carrier was studied with a stationary bed reactor, X-ray diffraction (XRD), Brunner-Emmet-Teller (BET) measurements, Raman spectra and scanning electron microscope (SEM). The results showed that using the excess aluminum oxide in N-sorption step significantly led to the significant improvement in N-carrier's porosity and thus N-desorption reactivity, which did not vary with change in carbon types. Also, the N-sorption performance of γ-Al2O3 with carbon black was better than that with graphite due to their different carbon crystal structures. In addition, the effect of other parameters including the mole ratio of Al2O3:C, reaction temperature on the N-sorption performance of the N-carrier were studied. It was found that the specific surface area of the mesoporous structured Al-based AlN, synthesized with mole ratio of Al2O3: C being 3:3 at 1200 °C, reached to>70 m2/g, which was the best one for good NH3 synthesis performance.

Low-Temperature Synthesis of Aluminum Nitride by Addition of Ammonium Chloride.

Aluminum nitride (AlN) is highly insulating and has a high thermal conductivity. AlN also has the advantages of being nontoxic and chemically stable. Therefore, it is a suitable sealing material for electric devices. Previous studies have shown that the addition of NH4Cl has a large influence on the formation of AlN and can effectively be used in its low-temperature synthesis without the use of special equipment. However, it has not been clarified whether NH4Cl simply promotes the reaction between Al and nitrogen or directly contributes to the nitridation reaction. In this study, which was part of a series of studies on the development of low-temperature synthesis methods for AlN, the nitridation behaviors of Al in Al–N2, Al–NH4Cl–N2, and Al–NH4Cl–He systems were determined, and the effects of the heating temperature and amount of NH4Cl on the nitridation behavior were examined in detail. When NH4Cl was added, AlN began to form at 600 °C, a formation temperature that was approximately 200 °C lower than that when only Al powder was heated under a nitrogen stream. The fact that the formation of AlN was also observed when the NH4Cl-added Al powder was heated under a helium gas stream confirmed that nitrogen derived from NH4Cl contributed to the formation of the AlN. Furthermore, based on the experimental results, the reaction mechanism was clarified, and the kinetic parameters for the nitridation of Al were determined.

Two-Stage Plasma-Thermal Nitridation Processes for the Production of Aluminum Nitride Powders from Aluminum Powders.

The synthesis of aluminum nitride (AlN) powders is traditionally done via the thermal nitridation process, in which the reaction temperature reaches as high as 960 °C, with more than several hours of reaction time. Moreover, the occurrence of agglomeration in melting Al particles results in poor AlN quality and a low efficiency of nitridation. In this study, an atmosphere-pressure microwave-plasma preceded the pre-synthesis process. This process operates at 550 °C for 2–10 min with the addition of NH4Cl (Al: NH4Cl = 1:1) for generating a hard AlN shell to avoid the flow and aggregation of the melting Al metals. Then, the mass production of AlN powders by the thermal nitridation process can be carried out by rapidly elevating the reaction temperature (heating rate of 15 °C/min) until 1050 °C is reached. X-Ray Diffractometer (XRD) crystal analysis shows that without the peak, Al metals can be observed by synthesizing AlN via plasma nitridation (at 550 °C for 2 min, Al: NH4Cl = 1:1), followed by thermal nitridation (at 950 °C for 1 h). Moreover, SEM images show that well-dispersed AlN powders without agglomeration were produced. Additionally, the particle size of the produced AlN powder (usually < 1 μm) tends to be reduced from 2–5 μm (Al powders), resulting in a more efficient synthesizing process (lower reaction temperature, shorter reaction time) for mass production.

Study of self-propagating high-temperature synthesis of aluminium nitride using a laser monitor

This study focused on the synthesis of aluminium nitride (AlN) by combusting aluminium nanopowder in air. To investigate the combustion of aluminium nanopowder, a copper bromide laser monitor was used. The optical system equipped with brightness amplification allowed the elimination of the background lighting effect and enabled the high time-resolved recording of the process. In particular, the laser monitor enabled us to detect changes in the morphology and optical properties of the surface of the aluminium nanopowder sample as well as to observe the propagation of the combustion waves in spite of the intense background lighting during combustion. The main time parameters of the combustion of aluminium nanopowder in air were determined. To improve and facilitate the processing of laser monitored high-speed video recordings, we proposed to analyse the time dependence of the intensity of the output signal of the laser monitor. The dependence was used to successfully detect the occurrences of all combustion waves and describe their dynamics. The time dependence also favourably represented the evolution of the reflection coefficient of the combustion products of aluminium nanopowder. This is the first time that this property of aluminium nanopowder has been investigated. The reflection coefficient evolution coupled with video recordings of the sample surface development during the combustion of nanopowder could be used to control the combustion process.

Synthesis of aluminum nitride nanostructures via chemical vapor deposition method with nickel as catalyst

The authors successfully synthesized aluminum nitride (AlN) nanowires by chemical vapor deposition (CVD) using aluminum (Al) powderand ammonia (NH3) as starting materials with nickel (Ni) as catalyst. The morphologies, the composition and structure information ofsamples were characterized by scanning electron microscopies (SEM), transmission electron microscopies (TEM), X-ray diffraction (XRD)and X-ray photoelectron spectroscopy (XPS). Nanostructures with manifold morphologies were obtained by tuning the growth temperatureand the growth time. The AlN nanowires are proved to have the wurtzite structure as demonstrated by XRD. The growth mechanism of AlNnanowires assisted with Ni catalyst is proposed to explain the nucleation and growth of nanowires.

Oxygen Nitrogen Mixture Effect on Aluminum Nitride Synthesis by Reactive Ion Plasma Deposition

In the work we investigate synthesis of aluminum nitride films using reactive ion plasma deposition in oxygen/nitrogen gas mixture for application as optical elements for power semiconductor lasers. The experimental refractive index of synthesized AlNO films is dependent on oxygen composition and is decreasing in diapason from 1.76 to 2.035 at elevation of the oxygen fraction.It is shown that the AlN films synthesized by pure nitrogen plasma are polycrystalline and textured. The oxygen presence in discharging gas results to growth of amorphous phase of the AlNO film.

Design and optical study of a microwave plasma torch in nitrogen used for the evaporation of aluminium wires

A microwave torch in nitrogen has been designed for the evaporation of aluminium (Al) wires potentially to be used for the synthesis of aluminium nitride (AlN). The torch, created on the tip of a metallic nozzle, is compatible with vacuum conditions and can be operated in continuous mode up to atmospheric pressure. Al wires to be evaporated are fed through the axis of the nozzle. Time‐resolved photography is applied to analyse the time evolution and stability of the interaction of the Al wire with the discharge. Optical emission spectroscopy is used (a) for the determination of the gas temperature of the active discharge, which is found to be in the range 1500–3500 K depending on the experimental conditions, and (b) for the estimation of the densities of Al and N atoms in the afterglow region, which are in the range 1011–1012 and of 1013–1014 cm−3, respectively. It is found that the part of the Al wire that is directly exposed to the nitrogen torch absorbs a considerable amount of the microwave energy, supporting its evaporation. In addition, the dissociation of molecular nitrogen has to be considered as an important process of power dissipation. Further technical development of the torch is necessary for the envisaged synthesis of AlN.

Comparative research of plasma-assisted milling and traditional milling in synthesizing AlN

In this paper, traditional milling and discharge plasma-assisted milling are employed to synthesize aluminum nitride (AlN) powder at nanometer scale by milling the mixture of aluminum and lithium hydroxide monohydrate. AlN powders can be generated in traditional milling and plasma-assisted milling in an hour milling time. Differential thermal analysis curves show that the reaction temperature of the powders treated by plasma-assisted milling is lower than that of traditional milling. These results indicate that plasma-assisted milling has higher efficiency in the synthesis of AlN, getting smaller crystallite size and activating powder. Moreover, an optical emission spectrum is employed to demonstrate the active species in plasma. The different formation process of AlN in the two-milling process, and the promotion effects of plasma in the milling process are discussed.

Two-stage plasma nitridation approach for rapidly synthesizing aluminum nitride powders

Abstract

Kinetic Study of Synthesis of Aluminum Nitride Using Carbon Reduction and Subsequent Nitridation Method

Kinetic Study of Synthesis of Aluminum Nitride Using Carbon Reduction and Subsequent Nitridation Method

Low‐Temperature Synthesis of Aluminum Nitride from Transition Alumina by Microwave Processing

Aluminum nitride (AlN) was synthesized by carbothermal reduction and nitridation method from a mixture of various transition alumina powders and carbon black using 2.45 GHz microwave irradiation in N2 atmosphere. We achieved the synthesis of AlN at 1300–1400°C using 2.45 GHz microwave irradiation for 60 min. Our results suggest that θ‐Al2O3 is more easily nitrided than γ‐, δ‐, and α‐Al2O3. On the other hand, nitridation ratio of samples synthesized in a conventional furnace under nitrogen atmosphere were zero or very low. These results show that 2.45 GHz microwave irradiation enhanced the reduction and nitridation reaction of alumina.

Low temperature aluminum nitride thin films for sensory applications

A low-temperature sputter deposition process for the synthesis of aluminum nitride (AlN) thin films that is attractive for applications with a limited temperature budget is presented. Influence of the reactive gas concentration, plasma treatment of the nucleation surface and film thickness on the microstructural, piezoelectric and dielectric properties of AlN is investigated. An improved crystal quality with respect to the increased film thickness was observed; where full width at half maximum (FWHM) of the AlN films decreased from 2.88 ± 0.16° down to 1.25 ± 0.07° and the effective longitudinal piezoelectric coefficient (d33,f) increased from 2.30 ± 0.32 pm/V up to 5.57 ± 0.34 pm/V for film thicknesses in the range of 30 nm to 2 μm. Dielectric loss angle (tan δ) decreased from 0.626% ± 0.005% to 0.025% ± 0.011% for the same thickness range. The average relative permittivity (εr) was calculated as 10.4 ± 0.05. An almost constant transversal piezoelectric coefficient (|e31,f|) of 1.39 ± 0.01 C/m2 was measured for samples in the range of 0.5 μm to 2 μm. Transmission electron microscopy (TEM) investigations performed on thin (100 nm) and thick (1.6 μm) films revealed an (002) oriented AlN nucleation and growth starting directly from the AlN-Pt interface independent of the film thickness and exhibit comparable quality with the state-of-the-art AlN thin films sputtered at much higher substrate temperatures.

The Advanced Aluminum Nitride Synthesis Methods and Its Applications: Patent Review.

High purity nanosized aluminum nitride synthesis is a current issue for both industry and science. However, there is no up-to-date review considering the major issues and the technical solutions for different methods. This review aims to investigate the advanced methods of aluminum nitride synthesis and its development tendencies. Also the aluminum nitride application patents and prospects for development of the branch have been considered. The patent search on "aluminum nitride synthesis" has been carried out. The research activity has been analyzed. Special attention has been paid to the patenting geography and the leading researchers in aluminum nitride synthesis. Aluminum nitride synthesis methods have been divided into 6 main groups, the most studied approaches are carbothermal reduction (88 patents) and direct nitridation (107 patents). The current issues for each group have been analyzed; the main trends are purification of the final product and nanopowder synthesis. The leading researchers in aluminum nitride synthesis have represented 5 countries, namely: Japan, China, Russia, South Korea and USA. The main aluminum nitride application spheres are electronics (59,1 percent of applications) and new materials manufacturing (30,9 percent). The review deals with the state of the art data in nanosized aluminum nitride synthesis, the major issues and the technical solutions for different synthesis methods. It gives a full understanding of the development tendencies and of the current leaders in the sphere.