AlN Nanoparticles Research Articles

The study of neutron capture processes in AlN nanoparticles

The neutron capture processes in the AlN nanoparticles were investigated by computer modeling. Neutrons absorption were separately investigated for aluminum (Al) and nitrogen (N) atoms in the AlN nanoparticles. The modeling was performed separately for each stable Al and N isotopes, because the effective absorption cross-section of different types of isotopes of Al and N atoms is different. Moreover, effective cross-section spectra of neutron capture for aluminum and nitrogen atoms were comparatively investigated.

High purity and good dispersity AlN nanoparticles synthesized by an arc discharge with assistance of direct nitridation

The environmental–friendly synthesis of nanostructural aluminium nitride with high purity and good dispersity properites is regarded as a technical issue. In this paper, an arc discharge with assistance of direct nitridation has been put forward to synthesize aluminium nitride nanoparticles that simultaneously possess the high purity of more than 97%, the average particle size of 99.1 nm, and the specific surface area of 60.8 m2 g−1. Compared with the aluminium nitride prepared by direct nitridation of aluminium nanoparticles, the unique framework of the satellite structural and small-sized aluminium nanoparticles attached on larger-sized aluminium nitride nanoparticles is prepared by arc discharge, which can prevent effectively agglomeration and coalescence of aluminium nitride nanoparticles in the next nitridation process. In addition, the direct nitridation process requires a low temperature of 600 °C for 2 h, because the nonstructural aluminum particles are evenly distributed on the surface of aluminum nitride and process the low average diameter of 40 nm. The work provides an efficient technique to open up the possibility of technological advancement for preparing metal nitride nanoparticles with high purity and good dispersity.

Distilled Water-Based AlN + ZnO Binary Hybrid Nanofluid Utilization in a Heat Pipe and Investigation of Its Effects on Performance

The preparation and utilization of hybrid nanofluids in thermal systems have become popular nowadays owing to their improved thermophysical properties. Although a nanofluid suspension increases the performance of the thermal system, hybrid nanofluids improve the heat transfer performance more by removing the disadvantages of each component. The aqueous hybrid nanofluids consisting of AlN and ZnO nanoparticles were prepared under various mixing rates and tested in a wickless, thermosiphon-type heat pipe under various circumstances. The effects of both unary and hybrid utilization of nanoparticles in the nanofluid preparation process were taken into consideration. The hybrid nanofluids were prepared in the mixing ratios of 25:75, 50:50, and 75:25 for AlN and ZnO nanoparticles, respectively. The experiments were run by applying 3 different heating powers to the evaporator section, and three different cooling tap water mass flow rates to the condenser section. Temperature distributions on all heat pipe sections were monitored, efficiency and thermal resistance values for each unary and hybrid nanofluids were specified. The results showed that hybrid utilization of nanoparticles enhanced heat pipe characteristics more compared to its unary counterparts. The maximum decrement of 40.79 % was obtained in thermal resistance of the heat pipe under 150 W, 6 g·s−1 conditions.

Fabrication and Characterization of the Modified EV31-Based Metal Matrix Nanocomposites

Metal matrix nanocomposites (MMNCs) with high specific strength have been of interest for numerous researchers. In the current study, Mg matrix nanocomposites reinforced with AlN nanoparticles were produced using the mechanical stirring-assisted casting method. Microstructure, hardness, physical, thermal and electrical properties of the produced composites were characterized in this work. According to the microstructural evaluations, the ceramic nanoparticles were uniformly dispersed within the matrix by applying a mechanical stirring. At higher AlN contents, however, some agglomerates were observed as a consequence of a particle-pushing mechanism during the solidification. Microhardness results showed a slight improvement in the mechanical strength of the nanocomposites following the addition of AlN nanoparticles. Interestingly, nanocomposite samples were featured with higher electrical and thermal conductivities, which can be attributed to the structural effect of nanoparticles within the matrix. Moreover, thermal expansion analysis of the nanocomposites indicated that the presence of nanoparticles lowered the Coefficient of Thermal Expansion (CTE) in the case of nanocomposites. All in all, this combination of properties, including high mechanical strength, thermal and electrical conductivity, together with low CTE, make these new nanocomposites very promising materials for electro packaging applications.

Computer modeling for the study of (n, p) and (n, α) modifications in AlN nanoparticles

The present study is devoted to an investigation of the (n, p) and the (n, α) modifications created by neutrons in AlN nanoparticles at different energies using computer modeling. The possible modifications under the influence of neutrons have been separately studied for the Al and the N atoms that forming AlN nanoparticles. Because the effective cross sections of the probable modifications are different in the various types of aluminum and nitrogen atoms, the modeling was performed separately for each stable isotope. The effective cross section spectra for the (n, p) and (n, α) modifications for the Al and the N atoms were mutually studied.

Experimental investigation on viscosity of AlN and SiC nanofluids

The quest for effective and efficient heat exchange systems has been a subject of recent research. Nanofluids are high performance ultra-modern heat transfer fluids with superior properties compared to those of regular heat transfer fluids. Therefore, studies on the viscosity of nanofluids are essential owing to its effect on the pumping requirements of thermal systems. This article investigates the influence of concentration and temperature on the dynamic viscosity of AlN and SiC nanofluids. Nanofluids with a volume concentration of 0.5–5% were prepared by dispersing AlN nanoparticles in ethylene glycol (EG), SiC in ethylene glycol, and SiC in distilled water (DW) using the two-step method. The experimental investigation on the viscosity of these nanofluids was performed at the temperature range of 28–60 °C using an Ostwald viscometer. It was observed that the measured nanofluids exhibited an increase in the viscosity with an increase in the volume concentration of nanoparticles. Specifically, for SiC/DW nanofluids at 0.5 and 5% volume concentration, the viscosity ratio was 1.023 and 1.435 times that of the base fluid. Moreover, the viscosity of nanofluids is reduced by increasing the temperature relative to that of their base fluids. The experimental values were compared with existing theoretical model, and their predictions are below the experimental results; therefore, correlation was derived on the basis of the experimental data. The margin of deviation of these models in predicting the viscosity of the studied nanofluids varied between −15 and 23% for AlN/EG; −7 and 21% for SiC/EG, and −11 and 4% for SiC/DW nanofluid.

Effect of Cold and Warm Rolling on the Particle Distribution and Tensile Properties of Heterogeneous Structured AlN/Al Nanocomposites.

Recently, heterogeneous structured metals have attracted extensive interest due to their exciting mechanical properties. In this work, an AlN/Al nanocomposite with heterogeneous distribution of AlN nanoparticles was successfully prepared by a liquid-solid reaction method combined with subsequent extrusion deformation, which behaves an excellent synergy of tensile strength and ductility. In order to further reveal the particle distribution evolution and the tensile property response during further deformation, a series of rolling treatments with different thickness reductions under room temperature and 300 °C was carried out. The results show that the yield strength and tensile strength of the composites increase significantly from 238 MPa, 312 MPa to 312 MPa, 360 MPa after 85% rolling reduction at 300 °C. While the elongation decreased from 15.5% to 9.8%. It is also noticed that the elongation and tensile strength of the nanocomposites increases simultaneously with increasing deformation. It is considered that the aluminum matrix strengthening effect accounts for the strength enhancement. The AlN spatial distribution in the matrix becomes more homogeneous gradually during the rolling, which is supposed to reduce the stress concentration between the particle and matrix and then promote the ductility increase.

Gas-Phase Chemical Reaction Mechanism in the Growth of AlN during High-Temperature MOCVD: A Thermodynamic Study.

We presented a comprehensive thermodynamic study of the gas-phase chemical reaction mechanism of the AlN growth by high-temperature metal-organic chemical vapor deposition, investigating the addition reactions, pyrolysis reactions, and polymerization of amide DMANH2 and subsequent CH4 elimination reaction. Based on the quantum chemistry calculations of the density functional theory, the main gas-phase species in different temperature ranges were predicted thermodynamically by comparing the enthalpy difference and free energy change before and after the reactions. When T > 1000 °C, it was found that MMAl, (MMAlNH)2, and (MMAlNH)3 are the three most probable end gas products, which will be the main precursors of surface reactions. Also, in high temperatures, the final product of the parasitic reactions is mainly (DMA1NH2)2 and (DMAlNH2)3, which are easy to decompose into small molecules and likely to be the sources of AlN nanoparticles.

Fabrication and Characterization of Aluminum Nitride Nanoparticles by RF Magnetron Sputtering and Inert Gas Condensation Technique

Aluminum nitride nanoparticles (AlN-NPs) were fabricated by a RF magnetron sputtering and inert gas condensation technique. By keeping the source parameters and sputtering time of 4 h fixed, it was possible to produce AlN-NPs with a size in the range of 2–3 nm. Atomic force microscopy (AFM), Raman spectroscopy, X-ray diffraction (XRD), and UV-visible absorption were used to characterize the obtained AlN-NPs. AFM topography images showed quazi-sphere nanoparticles with a size ranging from 2 to 3 nm. The XRD measurements confirmed the hexagonal wurtzite structure of AlN nanoparticles. Furthermore, the optical band gap was determined by the UV-visible absorption spectroscopy. The Raman spectroscopy results showed vibration transverse-optical modes A1(TO), E1(TO), as well as longitudinal-optical modes E1(LO), A1(LO).

AlN nanoparticles prepared through a gelation-polymerization process

A gelation-polymerization process is developed to fabricate AlN nanoparticles using boehmite sol, phenol, and formaldehyde as the starting materials. This process is characterized by simultaneously gelation and polymerization reactions to form two interactive three-dimensional networks in the same reactor. The gelation forms boehmite gel from the sol, while polymerization yields phenol-formaldehyde resin (PF). The interactive networks enable the formation of AlN nanoparticles entirely at 1300 °C from alumina and carbon. Meanwhile, the PF network prevents the crystalline of boehmite, increases the temperature for the dehydration reaction from boehmite to γ-alumina, and keeps the γ-alumina phase stable at temperature up to 1200 °C. The AlN nanoparticles are sintered to AlN ceramics without any sintering additives, and the thermal conductivity is 105 W m−1 k−1 for the ceramic with 92% relative density.

Individual/synergistic effects of Al and AlN on the microstructural evolution and creep resistance of Elektron21 alloy

The creep properties of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn (El21) alloys with additions of 0.25 wt% Al, 0.75 wt% AlN and 1 wt% AlN/Al nanoparticles (NPs) were studied over a stress range from 80 to 140 MPa at 240 °C, respectively. The individual/synergistic roles of Al and AlN in the El21 alloy were investigated systematically to reveal their creep strengthening mechanisms. Creep results show that individually all three additions of 0.25 wt% Al, 0.75 wt% AlN and 1 wt% AlN/Al could increase the creep resistance of El21 alloy apparently. However, the addition of mixed 1 wt% AlN/Al NPs shows the best strengthening effect on creep properties in El21 alloy. Microstructural characterizations reveal that the additions of Al and AlN increased the area fraction of intermetallic particles obviously. Blocky Al2Zr, Al2Zr3 particles and Al2(Nd, Gd) (Al2RE) particulates were observed in both El21 + 0.25% Al and El21 + 0.75%AlN. Nevertheless, when Al and AlN were simultaneously added into El21 alloy the formation of these blocky phases Al2Zr/Al2Zr3 was suppressed, and a larger amount of Al2RE phase was observed. This is attributed to the preferential reaction between AlN and Zr, which restricted the formation of Al–Zr phase and subsequently promoted the reaction of Al-RE phase. The dominant mechanism during creep at 240 °C was calculated to be viscous glide of dislocation. The simultaneous additions of Al and AlN NPs could lead to a more homogeneous distribution of intermetallic particles and increase the amount of Al2RE phase. Such kind of microstructures is beneficial for hindering the dislocation movement, transfer the load from matrix and alleviate the local stress concentration. Consequently, El21 + 1% AlN/Al exhibits the best creep properties among four alloys.

Investigation on the Thermal Conductivity of Mineral Oil-Based Alumina/Aluminum Nitride Nanofluids.

Al2O3/AlN–mineral oil nanofluids were prepared by dispersing commercially available Al2O3 and AlN nanoparticles into mineral oil. SEM measurements showed that the average diameter of the Al2O3 and AlN nanoparticles was about 55 and 50 nm, respectively. The experiments showed that the thermal conductivity systematically improved as the Al2O3 and AlN nanoparticles were introduced into the mineral oil. The thermal conductivity of the mineral oil-based nanofluids increased by 18% with a 1% volume fraction of Al2O3 and increased by 7% with a 0.5% volume fraction of AlN. The experimental data were compared with the values that were predicted by four typical thermal conductivity models, and a large disparity was disclosed between the models and the experimental data. After considering the thermal dynamic factors in the Al2O3/AlN–mineral oil nanofluids, a universal model is proposed that agrees well with the variation of thermal conductivity of the nanofluids.

Experimental hydrothermal characteristics of minichannel heat sink using various types of hybrid nanofluids

The hydrothermal characteristics of minichannel heat sink are analyzed experimentally by using deionized (DI) water based different nanoparticles mixture dispersed hybrid nanofluids. Al2O3, MgO, SiC, AlN, MWCNT and Cu nanoparticles are considered for this study. Different nanoparticles combinations (oxide-oxide, oxide-carbide, oxide-nitride, oxide-carbon nanotube and oxide-metal) in 50/50 vol ratio with base fluid (DI water) have been taken as coolants for volume concentration of 0.01%. Effects of volume flow rate (0.1–0.5LPM), fluid inlet temperature (20–40 °C) and Reynolds number (50–500) are studied for heat flux of 50 W/cm2. Convective heat transfer coefficient and pressure drop are increased by about 42.24% and 22% for Al2O3 + MWCNT hybrid nanofluid. The maximum reduction of 21.36% in thermal resistance is obtained for Al2O3 + MWCNT hybrid nanofluid in comparison to DI water. Heat transfer effectiveness and figure of merit are above one for all the hybrid nanofluids which conclude that hybrid nanofluid is better option for electronics cooling over DI water. Al2O3 + MWCNT hybrid nanofluid is better in terms of heat transfer effectiveness; whereas, Al2O3 + AlN hybrid nanofluid (oxide-nitrite mixture) has maximum heat transfer coefficient to pressure drop ratio and coefficient of performance.

The Effects of Aluminum-Nitride Nano-Fillers on the Mechanical, Electrical, and Thermal Properties of High Temperature Vulcanized Silicon Rubber for High-Voltage Outdoor Insulator Applications.

AlN nanoparticles were added into commercial high-temperature-vulcanized silicon rubber composites, which were designed for high-voltage outdoor insulator applications. The composites were systematically studied with respect to their mechanical, electrical, and thermal properties. The thermal conductivity was found to increase greatly (>100%) even at low fractions of the AlN fillers. The electrical breakdown strength of the composites was not considerably affected by the AlN filler, while the dielectric constants and dielectric loss were found to be increased with AlN filler ratios. At higher doping levels above 5 wt% (~2.5 vol%), electrical tracking performance was improved. The AlN filler increased the tensile strength as well as the hardness of the composites, and decreased their flexibility. The hydrophobic properties of the composites were also studied through the measurements of temperature-dependent contact angle. It was shown that at a doping level of 1 wt%, a maximum contact angle was observed around 108°. Theoretical models were used to explain and understand the measurement results. Our results show that the AlN nanofillers are helpful in improving the overall performances of silicon rubber composite insulators.

Influence of AlN Nanoparticle Addition on Microstructure and Mechanical Properties of Extruded Pure Magnesium and an Aluminum-Free Mg-Zn-Y Alloy

A pure Mg and a ZW0303 alloy metal matrix nanocomposite reinforced with AlN nanoparticles were prepared assisted by mechanical stirring and sonication for deagglomeration of particles. The produced nanocomposites were investigated to determine the influence of the AlN nanoparticles during indirect extrusion on the microstructure and texture development, as well as the resulting hardness and mechanical properties. For pure Mg, grain refinement and hardness increase due to the addition of AlN were revealed in the as-cast and the extruded condition. For ZW0303, the same was found for the as-cast condition. However, contamination of the alloy with Al significantly changes the recrystallization behavior during extrusion. This is directly related to the removal of solute Y due to the formation of intermetallic particles. Particle and grain size effects were distinguished for this alloy.

Influences of AlN/Al Nanoparticles on the Creep Properties of Elektron21 Prepared by High Shear Dispersion Technology

Elektron21 (E21) and its composites with additions of 0.25 wt.%, 0.5 wt.%, and 1 wt.% AlN/Al nanoparticles (NPs) were fabricated by a high shear dispersion technology. Their creep properties were investigated over a stress range between 80 MPa and 140 MPa at 240°C. The grain size exhibits an obvious increase with the addition of AlN/Al NPs compared with the monolithic E21 alloy. Increasing the content of AlN/Al NPs leads to a pronounced improvement of creep resistance. Microstructural analysis shows that, with the addition of 1% AlN/Al NPs in E21, the distribution of the intermetallics Mg3RE becomes much more homogeneous and their size is reduced. Such Mg3RE particles can prevent the dislocation slip more efficiently during creep. Besides these Mg3RE particles, the additional formation of Al2RE and Al2Zr3 phases, which results from the reactions of AlN/Al NPs and the alloying elements Zr and REs, could act as thermal stable particles to improve the creep resistance. Finally, the remained AlN NPs without reactions are beneficial for the improvement of the creep resistance to some extent due to Orowan strengthening.

Enhancing the creep resistance of AlN/Al nanoparticles reinforced Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn alloy by a high shear dispersion technique

A high shearing dispersion technique (HSDT) was utilized for the first time to incorporate AlN/Al nanoparticles in Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn (Elektron21) alloy. Compressive creep tests of unreinforced and reinforced Elektron21 alloys were performed at 240 °C with an applied stress of between 70-140 MPa. The results show that HSDT is an effective way to incorporate the nanoparticles and therefore to improve the creep resistance of El21 alloy by about one order of magnitude with 0.5% AlN/Al nanoparticles (NPs) compared with unreinforced alloy. The calculation of true creep stress exponent indicates that the viscous glide of dislocation and dislocation climbing are the rate controlling mechanisms during creep deformation. The microstructural observations show that the grains changed from equiaxed to dendritic grains with the addition of NPs by HSDT. Grain refiner Zr in Elektron21 alloy was partly consumed by Al atoms from the nano-powder mixture to form stable compound leading to grain coarsening. After high shearing, AlN NPs are effectively dispersed without any discernible clusters. The eutectic phases of El21 + 0.5AlN/Al composite become less continuous, much thinner, and are more homogeneously distributed in the alloy, which helps to pin the grain boundary sliding and hinder the dislocation movement inside the grain. The existence of AlN NPs is helpful for modifying the morphologies of α-Mg dendrites during solidification and thus resulting in obtaining thinner and hyper-branched eutectic phases in the nanocomposite. As a result, the creep resistance of reinforced alloy is additionally improved.

Experimental investigations on the thermal properties of binary molten salt based AlN nanofluids for high temperature applications

Typical binary nitrate (NaNO3-KNO3 as 60:40 rat io by weight) based AlN nanofluid was prepared by a two-step solutionmethod. The specific heat capacities of nanofluids with AlN amount ranging from 0.5 to 4 wt. % were investigated. The results suggest a good compatibility between AlN and molten binary nit rates. Meanwhile, AlN nanoparticles are proved to be an effective additive in improving the thermal properties of binary nitrates. For binary nitrate-based materials, samples with AlN amount as 1 wt. % shows the best thermal enhancement of specific heat capacity.

Effects of Electron Beam Irradiation on Insulation Characteristics of Epoxy/AlN Nanocomposites

Superconducting magnet is one of the core components of international thermonuclear experimental reactor (ITER). Due to the harsh operating environment, for the sake of ensuring the stable operation of the superconducting magnet, the superconducting magnet insulation is required to have excellent electrical and irradiation resistance. However, pure epoxy resin is difficult to adapt to the harsh environment in the ITER, so it needs to be modified to improve its insulation performance. In this paper, the epoxy/AlN nanocomposites with 1 wt% filler content of AlN nanoparticles were prepared, and the dispersion of nanoparticles was observed. High-energy electron beam was used to treat nanocomposites with the dose of 300, 500, and 700 kGy. The relative permittivity and conductivity of the nanocomposites after irradiation were tested. In addition, the data of surface potential were measured after surface charging for analyzing the dynamic behavior of surface charge and calculating the trap distribution of the nanocomposites with various irradiation doses. The flashover voltage of the nanocomposites influenced by irradiation in LN2 was also analyzed. The results show that irradiation can cause the change of trap distribution and flashover voltage, and the change trend is not monotonous.

Surface Potential and Breakdown Characteristics of Epoxy/AlN Nanocomposites Under DC and Pulse Voltages

In dc high-temperature superconducting fault-current-limiter (HTSFCL) operation, epoxy resin used as the current lead insulation withstands dc voltage. In the case of lightning stroke or line fault, HTSFCL needs to withstand the additional pulse voltage, which is several times greater than that of the dc voltage, and the polarity may be different from that of the dc voltage. It intensifies the electric field distortion, induces partial discharge, and causes insulation failure. To improve the insulation properties of the current lead, the epoxy/aluminum nitride (AlN) nanocomposites with the filler content of AIN nanoparticles of 0, 1, 3, and 5 wt% were prepared. The trap distribution of the sample was acquired to clarify the effects of AlN content on the surface potential behaviors. The results show that the amplitude and the polarity of the pulse voltage can affect the surface charge accumulation of the sample under dc voltage. Moreover, the addition of AlN nanoparticles improves the breakdown voltage of the sample in LN 2 under dc and pulse voltages.