Aluminum Nitride Powder Research Articles

Fabrication of dense aluminum nitride ceramics via digital light processing-based stereolithography

In this research, we report a novel approach to fabricate complex-shaped aluminum nitride (AlN) ceramics via digital light processing (DLP)-based stereolithography. The rheological behaviors, curing kinetics, and mechanical properties were investigated. Compared to unmodified AlN powders, AlN powders modified by stearic acid and oleic acid showed better wettability with resin. The excess cure widths, cure depths, and depth sensitivities of the AlN suspensions with modified powders were decreased. However, their critical energy was increased because of the increased absorbance of the modified AlN powders. Finally, complex-shaped AlN ceramic parts were fabricated by DLP with sintered-body relative densities exceeding 99% of the theoretical density. The flexural strength and hardness of the sintered sample were 398 ± 10.4 MPa and 10.47 ± 0.08 GPa, respectively, indicating prospective applicability in the industry.

Preparation and performance of alumina ceramic coating doped with aluminum nitride by micro arc oxidation

The present work is focused on the preparation and performance of micro arc oxidation (MAO) ceramic coating doped with aluminium nitride (AlN) on 6061 Al alloy. The results reveal that AlN-doped ceramic coatings could be prepared by plasma discharge with AlN powder or urea added into the electrolyte. Although AlN-doped MAO ceramic coatings present more distinct porous features than those without AlN, they achieved excellent thermal conductivity and insulation performance due to the physical properties of AlN. Compared with the uncoated Al substrate, MAO coatings with or without AlN doping all exhibited an improved wear resistance. AlN-doped MAO coating could considerably inhibit the formation of a transfer layer. This alumina ceramic coating doped with AlN is anticipated to be applied in the field of light-emitting diode (LED) aluminum substrate.

Study on Preparation and Properties of Polyurethane-Based AlN Potting Compounds

Polyurethane (PU) is a widely used polymer material. Adhesives prepared with polyurethane as the base material can bond a variety of materials and have excellent performance. In the electronic packaging industry, the potting compounds prepared by using polyurethane as the base material and aluminum nitride powder as the thermally conductive filler has excellent thermal conductivity, which adapt to the increasingly miniaturization and high integration requirements of integrated circuits, and can dissipate the heat generated by components in time, which can keep the device in the best state during using and keep its efficiency and stability. With the continuous development of the microelectronics industry, the advantages of potting compounds with excellent thermal conductivity in the market will become more and more obvious.

Fabrication of AA6016/(Al2O3 + AlN) hybrid surface composite using friction stir processing

Friction Stir Processing (FSP) could be a new solid-state processing technique assisted by the Friction Stir Welding Principle (FSW), now commonly used in the manufacture of the metal surface composite due to its superior features. Composites are constructed materials consisting of two or more component materials with significantly different physical or chemical properties and remaining separate and distinct in the finished structure at a macroscopic level. The reinforcements impart their unique mechanical and physical properties for reinforcing the properties of the matrix. Since no fusion occurs during FSP, problems arise with liquid-solid interactions between the two reinforcing hard particles and removing liquid aluminium. This makes the FSP a potential fabrication tool for Al-MMC’s. In various proportions, alumina and aluminum nitride powders were mixed and packed inside the groove made inside the aluminum plate. Designed and manufactured high carbon high chromium tool with a cylindrical pin with the threaded profile. The parameters considered for the FSP were rotational speed, axial load, and speed of power travel. The plates were then cleaned, and the specimens were also prepared in compliance with metallurgical specifications from FSPed plates. The metallurgical properties of treated AMMC’s were measured by using optical microscopy. The specimen’s micro hardness is measured using Vicker’s Hardness machine. Thus the effect of varying the hardness composition of the reinforcement material was studied.

Aqueous sol–gel processing of precursors and synthesis of aluminum oxynitride powder therefrom

For the first time, aluminum oxynitride (ALON) powders were synthesized using the precursors processed through aqueous sol–gel procedures. Appropriate quantities of aluminum nitride (AlN) powder and aqueous boehmite sol were mixed to obtain molecular stoichiometry of AlON. However, during the course of process, AlN powders reacted with the aqueous boehmite sol and disintegrated into its hydrated compounds. Such reactions altered the molecular stoichiometry between boehmite and AlN which was initially formulated for the eventual formation of AlON. Extensive investigations were carried out to analyse the behavior of AlN during the sol–gel processing. Hydrolysis of AlN in the aqueous sol–gel medium was circumvented by subjecting AlN to a surface modification process. The homogeneously dispersed boehmite sol and AlN mixture was further gelled, dried, and heat treated at temperatures between 1600 and 1850 °C for the formation of AlON powder. AlON phase formation was confirmed through XRD investigations, and its physical and microstructural properties were also evaluated through FESEM and TEM analyses. AlON powder with an average particle size of 490 nm was successfully synthesized in this study. This process is suitable for producing AlON powder in bulk quantities, and it can be used readily for further processes such as shaping and sintering to produce various optical products based on AlON.

Researches on silane coupling agent treated AlN ceramic powder and fabrication of AlN/PTFE composites for microwave substrate applications

A study on water-resistant treatment of aluminum nitride (AlN) ceramic powder and the fabrication of AlN/PTFE(Polytetrafluoroethylene) composites for microwave substrate applications were described. AlN ceramic powder were modified by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (F8261). The dosage of F8261 ranged from 0.8 to 1.6 wt%. FTIR and XPS were employed to characterize surface elements of aluminum nitride powder before and after modification. We soaked different AlN powder with deionized water, tested the pH of soaking liquid and observed changes of surface appearance via SEM. Among these modified AlN ceramic powder, 1.2 wt% F8261 modified AlN ceramic powder performed best. This powder not only had the maximum contact Angle (θ = 150.8o) and minimum surface energy (0.92 J/m2), but also had characteristic absorption peak of coupling agent (2922 cm−1, 2856 cm−1). Test results suggested that 1.2 wt% F8261 can make AlN powder obtain strong hydrophobicity, and greatly enhance the stability of AlN in wet environment. In another part, the optimal modified AlN powder and PTFE were combined, and the mass percentage of ceramics ranged from 15 to 45 wt%. Performance evaluation of above samples on the dielectric properties and thermal conductivity was accomplished by measuring their microstructure, moisture absorption and density. With 40 wt% filler, composites displayed satisfactory thermal conductivity (0.80 W/m K), reliable dielectric constant (er = 3.23), admissible dielectric loss (tan δ = 0.0059) and low water absorption (0.02%).

Mechanism and Research on Preparation of AlN Powder by Carbon Thermal Reduction Method

The alumina and activated carbon used as raw materials were prepared by chemical precipitation method. The uniformed aluminum nitride precursor was synthesized by mechanical mixing process. The effects of nitride temperature and time on the diameter of the particle were studied in detail. Ultrafined aluminum nitride powder was prepared by carbon-thermal reduction method. The results show that the precursor has better activity and nitride reaction proceeds rapidly. The complete conversion can be got at 1600°C for 2h. After calcination, it can be seen from the XRD graph that the powder with uniform size distribution has high AlN content.

Investigation of the effects of silica coating on the thermal conductivity and porosity of aluminum nitride after sintering

ABSTRACTThis paper describes a method of applying a silica coating on aluminum nitride and investigations concerning the thermal conductivity between the coating layer and the aluminum nitride as well as the effect of the silica coating layer on the density of samples containing aluminum nitride and glass after sintering. The coating was carried out using polycarbosilane that was transformed into silica by pyrolysis under an airflow. The measured thermal conductivities of all the samples were within an error of less than 10 W/m·K. The porosity of a sintered sample containing the silica-coated aluminum nitride powder and glass powder was decreased by about 10% compared to that of a sintered sample comprising pure aluminum nitride powder.

Fabrication and characterization of aluminum nitride sponges using a mixture of two porous formation methods

ABSTRACTA method for the fabrication of interconnected ceramic sponges was used in the present work, designed by using a combination of two different, aqueous gel casting and sacrificial template, using aluminum nitride powder (99.97%) with a mean size of 2.4 micrometers. Two types of sponges were made by using two different monomers, acrylamide and methacrylamide, the resultants sponges have 60% of porosity after being sintered and pyrolyzed at temperature of 1673 K using an inert atmosphere of argon for 1 h. The hydrolysis evolution of this ceramic powder during the gelcasting process was studied by measuring the pH during the stirring time, the microstructure changes during the time of exposure were observed in a SEM. XRD were made to study the present phases after the gel was eliminated by thermal treatment at 873 K using an oxidizing atmosphere, observing a formation of up to 4 %wt. of cubic alumina phase which was made after the hydrolysis products. Infrared spectroscopy was used to study the changes in the ceramic powder.

The Influence of Aluminum Nitride Nanoparticles on the Structure, Phase Composition, and Properties of TiB/Ti-Based Materials Obtained by SHS Extrusion

Compact ceramic long-dimensional materials based on titanium monoboride modified with aluminum nitride dopants (3 and 5 wt %) were obtained via SHS extrusion. Titanium monoboride was produced using azide technology of self-propagating high-temperature synthesis (SHS-Az). Small dopants of nanoscaled aluminum nitride powder exert a strong influence on the phase composition, structure, and physicomechanical properties of samples prepared by SHS extrusion. Scanning electron microscopy data reveal the refinement of the main titanium monoboride phase grains in modified samples. The most pronounced refinement of titanium monoboride grains is observed as the AlN nanopowder content is increased to 5 wt %. The combustion characteristics (temperature and combustion rate) are measured in an installation simulating the real SHS extrusion conditions. It is established that AlN at its content of 3 wt % in the initial charge interacts with the titanium matrix during combustion with the formation of the Ti2AlN and Ti4AlN3 MAX phases. AlN at a concentration of 5 wt % undergoes decomposition during combustion with release of titanium nitrides and pure aluminum, as well as the TiB, TiB2 and Ti2AlN phases. Modified compact ceramic materials are shown to exhibit higher microhardness in comparison with samples without using nanomodified AlN dopants.

Preparation of aluminum nitride by combustion of a Mg-Al alloy

Abstract Aluminum nitride (AlN) was synthesized by combustion of spherical Mg–Al alloy particles in air. Alloy powder was freely poured on a sample table, which formed a cone with a diameter of 1-2 cm. A commercial electro-thermal furnace was used to ignite the cone to start the synthesis. During the combustion, the temperature was measured and the actual burning process was recorded by a video camera. The morphology and phase makeup of the raw powders and the synthesized AlN powders were analyzed by scanning electron microscopy and X-ray diffraction. The thermodynamic properties and ignition temperatures were studied using differential scanning calorimetry and thermogravimetric analysis. Moreover, the effects of the Mg–Al alloy particle size (212.8 μm, 124.1 μm, 61.1 μm, and 29.5 μm) on the morphology of AlN were investigated. The results show that the combustion of Mg greatly promoted the nitridation of Al and that Al in both large and small alloy particles could be completely converted into AlN. The combustion products of the alloy consisted of two different layers: an upper white layer containing MgO and a lower black layer containing AlN. More AlN whiskers formed when small particles were used. However, very small Mg–Al alloy particles hindered the formation of AlN whiskers.

Preparation of spherical AlN powders by combined microemulsion method and carbothermal method

Abstract In this study, a two-step strategy for the preparation of micron-sized spherical aluminium nitride (AlN) powder by the combined micro-emulsion method in conjunction with the carbothermal reduction nitridation (CRN) route was designed. The spherical AlN powder with perfect dispersibility was prepared after a heat treatment at 1550 °C for 2 h in flowing N2. The effects of the aluminium fluoride (AlF3) content, reaction temperature and the introduction of yttrium oxide (Y2O3) on the nitridation ratio and on the morphology of granules, in particular, were investigated by XRD analysis and SEM. Additionally, the promotion mechanism of AlF3 and Y2O3 on the nitridation reaction was also discussed. Specifically, one of the underlying formation mechanisms of the spherical granules with the aid of AlF3 and Y2O3, and suggestions on the selection of additives for the CRN synthesis of spherical AlN powder were logically proposed.

Synthesis of AlN nanopowder coated with a thin layer of C, using a thermal plasma reactor

High-purity nanocrystalline aluminum nitride powders were synthesized by using a 12 kW non-transferred arc plasma. The synthesis was conducted in a versatile, new designed, one-chamber thermal plasma reactor (TPR). The novel experimental assembly incorporated better working conditions like: high temperature gradient between the crucible and reactor's wall, and high super-saturation of the system by nitrogen and carbon. Thermodynamic modelling of the synthesis was conducted in order to achieve the best conditions for AlN formation. In this study, aluminum discs of Al 1100 were used as precursor material and pure nitrogen was the only gas used as reagent and plasmogenic gas. Nanopowders collected from reactor's wall were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-Ray diffraction (XRD). Synthesized h-AlN nano-powders were found to be free of oxides and aluminum metal. A thin carbon-layer around the particles was detected. TEM results indicated that the carbon-layer was around 5 and 10 nm. This outcome could make a significant difference with other synthesis reported in the literature since the occurrence of the carbon-layer, could delay AlN oxidation, prevent hydration, and could avoid the agglomeration of the particles.

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.

Exposure of Tantalum Carbide, Silicon Nitride and Aluminum Nitride to Chlorine Trifluoride Gas

Widely used coating materials, such as tantalum carbide, silicon nitride and aluminum nitride, were exposed to chlorine trifluoride gas at various temperatures. The tantalum carbide powder was etched and vaporized by a quick and significant exothermic chemical reaction at temperatures higher than room temperature. The silicon nitride powder was etched that produced volatile products at temperatures higher than 250°C. An aluminum nitride plate and powder showed a slight increase in weight at temperatures higher than 500°C due to fluorination. The aluminum nitride plate thickness increased causing a surface smoothing effect without any cracking. The aluminum nitride is expected to work as the anticorrosive coating material to the chlorine fluoride gas at high temperatures, thus allowing fluorination.

Effect of mechanical activation of powders BN–(TiN, AlN) on the structure of composite material obtained by ultrahigh pressure sintering

The mechanical activation (MA) of the hexagonal boron nitride (hBN) and aluminum nitride (hAlN) powders as well as powder mixtures hBN-hAlN and hBN-hAlN-TiN are researched. MA of the mixtures leads to an increase in their specific surface area and decreases the particle size to 30-300 nm. In the course of MA amorphization of hAlN and formation of the cubic AlN are observed. As a result of the sintering under ultrahigh pressure the nanostructured ceramic materials on the basis of the mixtures after MA are formed, and the structure depends on the technological parameters of sintering.

Study of ZrN-AlN formation solid-phase reaction in a nitrogen atmosphere during microwave heating

This paper is devoted to the discussion of the experimental results on the solid-phase synthesis of the nitride material ZrN-AlN. A mixture of powders of metallic zirconium and aluminum nitride was heated by means of microwave radiation in a nitrogen atmosphere for 90 minutes. Phase composition by sample volume and electron microscopy of the surface were studied to confirm the solid-phase reaction of zirconium with aluminum nitride. Thermodynamic calculations showed that several possible processes happen at once and lead to the formation of the nitride material ZrN-AlN in a nitrogen atmosphere. Experimental results showed a relatively low content of zirconium nitride (32.8 mol.%) and a significant content of metallic zirconium residues (8.8 at.%) in the upper layers of the sample despite contact with the gas phase. While in the sample volume, the conversion of metallic zirconium to nitride was almost complete (the content is 74.9 mol.%). Experimental observations have shown that, due to microwave heating, the formation of characteristic coral-like growths on the surface of particles with the concentration of chemical impurities, due to the purity of the initial reagents, is evident.

Combustion synthesis of fine aluminum nitride powders under micropositive N2 pressure with water additive

AbstractFine aluminum nitride (AlN) powders were prepared by a facile and efficient way of combustion synthesis under micropositive N2 pressure of 0.15 MPa and with 3 wt% water as additive. By this approach, the maximum combustion temperature was well regulated to a low value. The influence of water on the reaction rate, the phase composition, and crystal growth of the products was systematically investigated. The addition of water was crucial to the complete nitridation of Al. Furthermore, H2O vapor played a two‐sided role in the reaction. It could accelerate the reaction by promoting the diffusion of Al vapor and N2 and restrain the nitridation rate by absorbing heat.

Aluminum nitride surface functionalized by polymer derived silicon oxycarbonitride ceramic for anti-hydrolysis

Aluminum nitride (AlN) features an extremely interesting combination of very high thermal conductivity and excellent electrical insulation; therefore, it has been widely used in the high power electronic devices. The hydrolytic reaction of aluminum nitride powder decays the shelf-life and lowers the high power operating performance of the electronic devices. A protecting film of the polymer derived silicon oxycarbonitride ceramic is coated and fully wrapped on the surface of aluminum nitride powder against facilitating hydrolysis. Poly (organosilazane) precursor is incorporated with the commercial aluminum nitride powder pyrolyzed at 700 °C under argon environment for few hours to form a core-shell structure with a film thickness, 10–20 nm of silicon oxycarbonitride (SiCNO) ceramic shell and the aluminum nitride core. Measuring the pH value of SiCNO/AlN core-shell powder in deionized water at room temperature is to observe the hydrolytic behavior that its pH value is stable to maintain about 10 at ambient environment over ten days, whereas for the characterization of the reaction products, XRD, SEM and TEM analyses are employed. The hydrolytic behavior measured at 90 °C also shows that the SiCNO/AlN core-shell powder is still able to keep the protection from high temperature hydrolysis. XRD spectra proves that the characteristic crystalline peaks of SiCNO/AlN core-shell powder after hydrolysis over ten days are still the same as those of the commercial aluminum nitride powder before hydrolysis. These results directly indicate that the polymer derived silicon oxycarbonitride ceramic film fully protects the aluminum nitride powder from hydrolysis. When the content of silicon oxycarbonitride shell reduces to reach certain value, the hydrolytic protection gradually vanishes for long time.

Preparation core/shell-type microparticles consisting of cBN cores aluminum coating via composite method

The mechanically mixed aluminum and cubic boron nitride (cBN) powder are important raw materials for preparing super-hard metal cutting tools. So aluminum shell-coated cBN may have significant economic potential. A Brownian motion based electrostatic self-assembly route in liquid salt of high temperature was developed using silica nanolayer bridge joint for the aluminum coating of cBN microparticles. In this approach, piranha solution method was first used to activate the surface of cBN cores, the silica nanolayer via sol-gel method served as the substrate for an outer aluminum coating of cBN cores. Coating of aluminum on cBN cores was accomplished by a self-assembly process from a liquid state solution of molten salt and aluminum powders. To distinguish small amounts of non-reacted aluminum powders which acted as aluminum source with the core - shell structure product, bromoform (CHBr3) was used to separate both of them due to the density differences. Samples were characterized by SEM, XRD, EDX and DSC. The contribution of our work lies in the creation of a novel strategy to fabricate a light metal element coating on the inert material particles in view of the versatility of sol-gel process and the controllability of the molten salt process.