Synthesis Of AlN Research Articles

Synthesis of AlN: Eu2+ green phosphors by a simple direct nitridation method.

Eu-doped aluminum nitride phosphors were successfully prepared using simple direct nitridation of a metallic aluminum and Eu2 O3 powder mixture in flowing ammonia. AlN formed at reaction temperatures >900°C, and Eu3+ transformed into the secondary oxide phase EuAl2 O4 in the nitridation condition. Phase pure AlN was obtained by post-heat treatment of the nitridated product at 1600°C for 3h in a nitrogen atmosphere, with an Eu2+ doping concentration<0.5%. The phosphors exhibited broad green emission centered at 521nm under 363nm excitation. The luminescence of the phosphor was significantly influenced by the post-heat treatment temperature, which affected the dissolution of Eu2+ , phase purity, crystallinity, and particle size of the AlN host.

In Situ Synthesis and Formation Mechanism of AlN in Mg-Al Alloys

In-situ synthesis of AlN-Mg composite materials by the gas bubbling method was investigated using nitrogen as the gaseous precursor in the temperature range of 700 °C to 800°C. The proofs of a direct reaction of N 2 and Al to form AlN in Mg-Al alloy melt were found. Microstructure analysis confirms the formation and the uniform distribution of AlN phases in the alloy. An optimum process to form in situ AlN phase in Mg-Al based alloys has been obtained.

Carbothermal synthesis of micro-scale spherical AlN granules with CaF2 additive

In this work, we purposefully reported a simple yet efficient carbothermal synthesis strategy to prepare micro-scale spherical AlN granules just by using CaF2 as promoting additive. The effects of synthesis parameters, such as CaF2 content, N2 gas pressure, reaction temperature, upon the nitridation rate, surface morphology and particle size were comprehensively investigated. It was established that elevated N2 gas pressure, high reaction temperature and abundant Ca-aluminates liquid synergistically promoted the formation of micro-scale spherical AlN granules. Additionally, the reduction and nitridation of intermediate Ca-aluminates played a significant role in improving the nitridation rate, increasing the particle size and forming the smooth spherical appearance. More significantly, the underlying reaction mechanism in the carbothermal synthesis of spherical AlN with CaF2 additive was also tentatively proposed.

Fabrication of AlN particles and whiskers via salt-assisted combustion synthesis

High-quality AlN ceramic particles and whiskers were synthesized via salt-assisted combustion with the addition of AlN and NaCl, KCl, or MgCl2 to the raw Al powders. The experiments were carried out at nitrogen pressures between 0.2 and 1.0MPa. The results show that 20–30mass% salt is required to achieve complete nitridation of Al. The sensible and latent heats of these salts afford effective heat absorption during the reaction, which greatly reduces the amount of diluent AlN required compared with the conventional combustion synthesis of AlN. In addition, AlN particles are obtained when NaCl or KCl is added, whereas irregular whiskers are obtained with MgCl2.

Morphology-controlled Synthesis of Hexagonal AlN Whiskers by Direct Nitridation of Aluminum and Alumina Mixture

AbstractHexagonal 1D AlN whiskers were synthesized by direct nitridation of aluminum and alumina. The effect of the atmosphere was investigated based on thermodynamic calculation. A green body compacting alumina with different particle size in between 44–420 μm in graphite crucible was found to be favorable for the large-scale synthesis of AlN at 1650 °C for 3 h in flowing nitrogen atmosphere. XRD result indicated that hexagonal AlN phase with high purity has been successfully synthesized. SEM and TEM analysis indicated that the whiskers possessed uniform morphology with 100–200 nm in diameter and length up to microns. The formation mechanism was further proposed based on the experimental results.

Synthesis of three-dimensional AlN–Si3N4 branched heterostructures and their photoluminescence properties

Three-dimensional AlN–Si3N4 branched heterostructures are synthesized via extended vapor–liquid–solid and vapor–solid growth of one-dimensional Si3N4 nanostructures and AlN nanocones successively.

The Research of AlN-Mo Nano Composite Ceram

In this paper six sides top technology of high temperature and high pressure, in AlN nanopowder mixed with Mo powder, synthesis of AlN - Mo. Nanocomposite ceramics Using X-ray diffraction (XRD), scanning electron microscope (SEM) and vickers hardness instrument of AlN - Mo in the nanocomposite ceramics phase structure, morphology, size and hardness of the characterization, compared with AlN nanoceramic, discusses the AlN - Mo of nanocomposite ceramics new features.

Microwave-assisted combustion synthesis of AlN–SiC composites using a solid source of nitrogen

In this paper, the synthesis of Aluminum Nitride–Silicon Carbide composites through a combustion reaction among aluminum, silicon nitride (as the solid source of nitrogen) and carbon powders was investigated by X-ray diffraction and scanning electron microscopy. The combustion reaction was initiated through the ignition of the powder mixture by microwave heating in a domestic oven, thereby led to the synthesis of the desired ceramic. To achieve a higher-quality product, some parameters were altered during the synthesis. These included the mixing time, the amount of carbon in the reactant mixture and the weight of the reactant compacts. The product was not affected dramatically by the alteration in the first two parameters; however, the increase in the weight of the samples made it possible to achieve a more complete combustion and a higher degree of conversion to the products. It can be concluded that the procedure used in this work successfully leads to the synthesis of the product with no need to apply an electric field or utilize a nitrogen atmosphere.

ChemInform Abstract: Combustion Synthesis of Aluminum Nitride: A Review

AbstractReview: 61 refs.

Combustion Synthesis of Aluminum Nitride: A Review

Aluminum nitride has been acknowledged as an important industrial material because of its unique combination of high thermal conductivity and high electrical resistivity. Although there have been several excellent reviews on the synthesis of aluminum nitride, little has been mentioned on the combustion synthesis of AlN. In this work, the combustion synthesis methods for synthesis of AlN are reviewed and classified according to the phases involved in the reaction, the types of reactants (and additives) used and the design principles for the synthesis processes. Problems critical to combustion synthesis of AlN to obtain products with high product yields and low impurity contents are summarized and discussed.

Synthesis and photoluminescence of AlN:Mn hexagonal maze-like complex nanostructure

The AlN:Mn hexagonal maze-like complex nanostructure was prepared via a simple thermal chemical vapor deposition process without structure-directing templates or catalysts. The optical property of the product was investigated by room-temperature photoluminescence (PL) measurement. Two emission bands centered at 490nm and 600nm, respectively. In addition to a familiar red-orange band centered at 600nm originating from intra 3d-electrons transition of Mn2+ ion, another strong broad blue-green band around 490nm is related to VAl3−−3×ON+ defect complexes. The results indicate that the AlN:Mn maze-like complex nanostructure has a certain amount of Al vacancies, and the growth mechanism can be ascribed to nucleus arrangement and preferential growth.

The Effects of Fluxes on AlN:Eu2+Blue Phosphors Synthesized by a Carbothermal Reduction Method

Different fluxes had been used in the preparation of AlN:Eu2+blue phosphors by the carbothermal reduction method. The influence of these fluxes on the phase composition, crystallinity, particle size, and photoluminescence (PL) of the produced phosphors was investigated. X‐ray diffraction and microstructure characterizations showed that both CaF2and BaF2were excellent nitridation promoters for the synthesis of AlN:Eu2+phosphors, because pure and highly crystallized AlN was obtained with 3 wt% fluxes. The use of CaF2flux resulted in phosphors which featured a very weak blue shift emission due to lattice distortion and lattice imperfection caused by the incorporation of Ca into the AlN host, according to the results of IR spectra, decay curves, and the changes in lattice parameters. In comparison with phosphors produced without the use of fluxes, the use of BaF2flux resulted in phosphors with higher PL intensity by a factor of 2.4, which were produced at lower soaking temperature and shorter soaking time. Finally, a simple reaction mechanism for the nitridation process was also suggested.

Synthesis of AlN–TiN nanostructured composite powder by reactive ball milling and subsequent thermal treatment

In the present article, synthesis of AlN–TiN nanostructured composite by high-energy ball milling process (HEM) of Ti and AlN by 1:1 molar ratio and subsequent heat treatment was investigated. The microstructural evolution of samples was studied by scan electron microscopy (SEM) and energy dispersive X-ray analysis (EDS), composition map analysis by electron probe micro-analyzer (EPMA) and phase determination using X-ray diffraction (XRD) patterns. It was found that a Ti(Al,N) solid solution was formed at the early stages of milling and while Al causes the Ti lattice to contract, N has the opposite effect. The nonlinear variation of interplanar distance and c/ a ratio of Ti is considered due to the competition between these two processes during MA and finally led to complete dissolution of Al and only 1 at.% of N in Ti lattice. On further milling, mechanochemical reaction between Ti solid solution and AlN took place in the gradual mode which led to the formation of TiN with an average crystallite size of 10 nm. It is generally acknowledged that the reactions between Ti and AlN includes three stages: (i) reduction of AlN under the effect of Ti; (ii) diffusion of dissolved Al and N atoms into the Ti lattice and (iii) reaction between Al,Ti and N. XRD results revealed that annealing of the milled powders resulted in greater formation of “in situ” TiN particles from supersaturated solid solution and increases the crystallite size of TiN from 10 nm to 14.62 nm.

Synthesis of porous nano-sized AlN by chemical vapor synthesis

We report the synthesis of AlN powders by the chemical vapor synthesis of an AlCl3–NH3–N2–H2 system. The starting material was gasified AlCl3, generated using a preheating system. AlCl3 gas was transported to a tube furnace in NH3–N2–H2 atmosphere. We synthesized highly crystalline AlN at over 900 °C. The average size of the spherical AlN particles decreased from 250 to 40 nm with increasing reaction temperature in the tube furnace. Porous nano-sized particles synthesized at high reaction temperatures have low oxygen contents and high thermal stability.

Properties of AlN Powder Synthesized by Self-Propagating High Temperature Synthesis Process

The synthesis of AlN via self-propagating high-temperature synthesis (SHS) was attempted, using various ratio of Al powder mixed with AlN powder as diluents. Al and AlN powder mixtures with various weight ratios were ignited a nitrogen atmosphere with various amounts of carbon as additives. High crystalline AlN by SHS were successfully synthesized. The microstructure development during the reaction and the influence of these additives were determined by SEM and XRD analysis. A mechanism for the formation of high purity AlN with a very low content of residual oxygen (&lt;0.8wt %) was proposed.

Combustion synthesis of hexagonal AlN–SiC solid solution under low nitrogen pressure

AlN–SiC solid solutions were synthesized by self-propagating combustion of powders consisting of Al, Si and carbon black (CB) under low nitrogen pressure (0.1–0.5 MPa), with the molar ratio of Al and Si, and nitrogen pressure as the main investigating parameter. The products were mainly AlN–SiC solid solution with a residual Si, and the morphology was of hexagonal crystal. Nearly pure AlN–SiC solid solution, also having the best solid-solution homogeneity in this study, was obtained by adding extra CB to the starting powders. The best Al/Si molar ratio was 1 or 1.5 and the combustion results indicated that better combustion produced a higher combustion temperature, greater product purity, and better solid solution homogeneity. Increasing nitrogen pressure (from 0.1 to 0.5 MPa) moderately increased the combustion temperature and the product homogeneity, but combustion velocity increased by around 65%. The full width at half maximum (FWHM) of AlN–SiC solid solution's (1 1 0) XRD peak, served as the homogeneity index for the AlN–SiC solid solution (D. Kata, K. Shirai, M. Ohyanagi, Z.A. Munir, J. Am. Ceram. Soc. 84 (2001) 726–732.), of all samples were summarized with the reported values in the literature, where our FWHM values were comparable to the reported data.

Synthesis of AlN–SiC solid solution through nitriding combustion of Al–C–Si 3N 4 in air

A simple way of fabricating AlN–SiC solid solutions (AlN–SiCss) through the combustion reaction of aluminum, carbon and Si 3N 4 powder mixtures in air is reported. X-ray diffraction analysis, scanning electron microscopy and energy dispersive spectroscopy are employed to analyze the phase composition and microstructure of the as-synthesized products. It is found that the phase composition of the product changes gradually with the increase in air infiltration distance, accompanied by variation in the partial pressure of N 2/O 2 at different locations of the powder compacts. Homogeneous single-phase AlN–SiCss powders with well-crystallized hexagonal morphologies and a fine particle size of 3 μm can be obtained within a suitable distance range of N 2 infiltration. Thermodynamic analysis of the Al–C–Si 3N 4–air combustion reaction system was conducted based on the N 2/O 2 diffusion kinetic model, and the calculated results are in good agreement with the experimental phenomenon.

Synthesis of AlN from Li 3N and Al: Application to vapor phase epitaxy

We performed synthesis of AlN using Al and Li 3N. In this method, there are two problems that must be solved for obtaining single-phase AlN. One of them is suppression of Li 3AlN 2 formation and the other is precipitation of LiAl from the residual source materials during the cooling process. In the present work, we analyzed phase stability of products and found that AlN was stable at high temperatures and low Li–N/Al molar ratios. However, the products still contained LiAl and Al. Therefore, we examined the effectiveness of vapor phase epitaxy for separating AlN from the extra phase (LiAl and Al formed from residual source materials). From the experimental results, feasibility of vapor phase epitaxy was confirmed. That is, we can deposit only an AlN layer on a sapphire substrate by optimizing the growth conditions, i.e., temperature range above 1150 °C and Li–N/Al molar ratio less than 1.

Synthesis of GaN, AlN, and GaAlN Powder via a Three-step Nitrate Conversion Process

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Combustion synthesis of AlN with melamine as an additive

Melamine (C3H6N6) was used as an additive for synthesizing aluminum nitride by combustion synthesis. It was found that at least 0.1 M of melamine addition to 1 M of aluminum and 0.8 MPa of nitrogen pressure were necessary to initiate a stable reaction. In addition to melamine, however, use of aluminum nitride as a diluent and application of forced nitrogen flow yielded better results. Analyzing the reaction temperatures, reaction rates, nitrogen contents, x-ray diffraction patterns, and scanning electron microscopy photographs, the optimum conditions for synthesizing AlN were established: (i) reactants were 90 wt% (1 M Al + 0.1 M melamine) + 10 wt% AlN diluent, (ii) chamber pressure was 0.9 MPa, and (iii) nitrogen flow rate was 15 l/min. Under these conditions, aluminum nitride with the stoichiometric nitrogen content of 34 wt% could be obtained.