Aluminum Nitride Nanopowders Research Articles

Adhesive strength of nano-size particles filled thermoplastic polyimides. Part-II: Aluminum nitride (AlN) nano-powder–polyimide composite films

Adhesive properties of thermoplastic polyimides (PI) filled with aluminum nitride (AlN) nano-powder are investigated. Two PIs, one amorphous (oxydiphthalic anhydride (ODPA)/3,4′-oxydianiline (3,4′-ODA)/phthalic anhydride (PA)) and the other a semi-crystalline (3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/3,4′-ODA/PA) are synthesized via two-step method involving formation of poly(amide acid) (PAA) followed by thermal or chemical imidization to obtain PI in film or powder forms, respectively. AlN in low wt% (up to 1.5%) is added at PAA stage and mixed by mechanical agitation and sonication. Viscoelastic behavior and mechanical properties of PI films are determined using DMTA and tensile testing. Adhesive properties are determined by measuring lap shear strength (LSS) of single lap joints prepared with films and powder oligomides. Scanning electron microscopy (SEM) of fractured surfaces is carried out to determine failure modes. The result shows that with increasing AlN wt%, increase in elastic modulus and tensile strength of AlN–PI composite films is observed, whereas strain at break decreases. The viscoelastic behavior of the AlN–PI composite films also changes from liquid-like to solid-like with increasing AlN wt%. LSS measurements show that with increase in AlN wt% the LSS increased initially but after a critical value was observed to decrease. SEM analysis concluded that this decrease in LSS was attributed to poor melt behavior of PIs containing higher wt% of AlN. Measurement of LSS in elevated temperature environment showed that retention of LSS in joints prepared with AlN–PI composite films was better as compared to joints prepared with neat PIs.

Size Effect of AlN on the Performance of Printed Circuit Board (PCB) Material-brominated Epoxy Resin

Many properties of brominated epoxy resin, a type of material widely used in printed circuit boards (PCBs), such as the coefficient of thermal expansion (CTE) (pre and post Tg), dielectric constant (Dk), dissipation factor (Df), tensile strength, and Young’s modulus, have been evaluated according to size and content in terms of the weight of the aluminum nitride (AlN) filler. It has been found that the performance of epoxy resin improves significantly when AlN is used as the filler. Excellent properties were obtained when 2.3 μm AlN was added till 50 wt%; i.e., CTE (pre Tg) = 27 ppm/°C, Tg= 128 °C, Df = 0.016, Dk = 7.5, and Young’s modulus = 7.5 GPa. The SEM results show that the dispersion of AlN nanopowder filler is largely homogeneous.

Synthesis of AlN Nanopowder from γ‐Al2O3by Reduction–Nitridation in a Mixture of NH3–C3H8

Aluminum nitride (AlN) powders were synthesized by gas reduction–nitridation of γ‐Al2O3using NH3and C3H8as the reactant gases. AlN was identified in the products synthesized at 1100°–1400°C for 120 min in the NH3–C3H8gas flow confirming that AlN can be formed by the gas reduction–nitridation of γ‐Al2O3. The products synthesized at 1100°C for 120 min contained unreacted γ‐Al2O3. The27A1 MAS NMR spectra show that Al–N bonding in the product increases with increasing reaction temperature, the tetrahedral AlO4resonance decreasing prior to the disappearance of the octahedral AlO6resonance. This suggests that the tetrahedral AlO4sites of the γ‐Al2O3are preferentially nitrided than the AlO6sites. AlN nanoparticles were directly formed from γ‐Al2O3at low temperature because of this preferred nitridation of AlO4sites in the reactant. AlN nanoparticles are formed by gas reduction–nitridation of γ‐Al2O3not only because the reaction temperature is sufficiently low to restrict grain growth, but also because γ‐Al2O3contains both AlO4and AlO6sites, by contrast with α‐Al2O3which contains only AlO6.

Synthesis and characterization of nanocrystalline aluminum nitride from a low temperature combustion precursor

In recent years, a lot of interest has been shown in aluminum nitride nanopowder. This is because that AlN has high thermal conductivity, high thermal stability, high electrical resistivity, low dielectric constant, and a thermal expansion coefficient matched with silicon [1]. AlN is a promising material for hybrid substrates in circuits, heat sinks, and high power/high frequency electronic devices [2], and is also important for infrared and ultraviolet optoelectronic parts and surface acoustic wave devices [3, 4]. In addition, AlN can be used for melting crucibles, cutting tools, and fillers for polymer. Although AlN powders have been synthesized by many methods [5], the commercially available AlN powders have been mainly produced by carbothermal reduction process. However, a high calcining temperature (more than 1600 ◦C) and long mixing times of the alumina and carbon source is still required to obtain high-quality AlN powder [6]. The present work is concerned with the synthesis of AlN nanocrystalline powder from a new carbothermal reduction process with a low temperature combustion precursor. The method was adopted due to the possibility of obtaining a uniform mixture of nano-sized alumina and carbon from a low temperature combustion reaction of a solution of aluminum nitrate, urea, and cane sugar. Stoichiometric amounts of aluminum nitrate (Al(NO3)3·9H2O) and urea were first dissolved in double distilled water and then mixed with aqueous cane sugar solution in a beaker. The amount of urea as fuel, which can react completely with aluminum nitride, was calculated using the method of Jain and Adiga [7], while the amount of cane sugar was calculated according to the molecular ratio of aluminum and carbon (nAl/nc = 1.8–2.5). The resultant solution was heated at 200–300 ◦C in a muffle furnace to produce loose and brown-black precursor powders containing amorphous alumina and carbon. The precursor powder was placed in graphite crucible, and calcined in a graphite furnace at 1500 ◦C for 2 h with a flowing nitrogen atmosphere. After the carbon was removed at 700 ◦C for 2 h in air, the resultant nanocrystalline powder was uniaxially pressed at ∼100 MPa into cylindrical compacts 10 mm in diameter and 8 mm in height, which were then pressurelessly sintered in N2 at 1800 (5 ◦C/min) for 2 h, in a graphite furnace.

Synthesis, characterization and photoluminescence of aluminium nitride nanopowders through anAlCl3 aided CVD route

Single-phase AlN nanopowders, with average diameter of about 70 nm, were synthesized through anAlCl3 aided CVD route; the formation process is also discussed in this paper. XRD and HRTEMrevealed that the AlN nanopowders obtained are wurtzite structured with lattice constants ofa = 3.1114 Å andc = 4.9792 Å. The photoluminescence spectrum showed that there is a deep-level blue luminescenceband centred at 2.54 eV in AlN nanocrystals. This method is a simple and efficient way tosynthesize AlN nanopowders.

Synthesis of Aluminum Nitride Nanopowder by Gas‐Reduction–Nitridation Method

Aluminum nitride (AlN) nanopowder was successfully synthesized from transition alumina nanopowder using an NH3–C3H8 gas mixture as a reduction–nitridation agent. Phase‐pure, nanocrystalline AlN powder with a specific surface area of 36.4 m2/g and a mean particle size of 51 nm was prepared under typical reaction conditions. The resulting AlN nanopowders possessed excellent sinterability, allowing full densification in conventional processing, even without the addition of sintering aids.

Synthesis and sintering properties of aluminium nitride nanopowder prepared bythe gas-reduction–nitridation method

Aluminium nitride (AlN) nanopowder was successfully synthesizedfrom transition alumina nanopowder via a new single-stepnitridation process. A gas mixture of NH3–C3 H8was employed as a reduction–nitridation agent, which enables direct nitridation oftransition alumina at processing temperatures of 1200–1400 °C. AlNpowder prepared under typical reaction conditions was found to bephase-pure and nanocrystalline, with a specific surface area of36.4 m2 g−1 and a mean particle size around50 nm. The AlN nanopowders produced could be densified to a pore-freestate in conventional processing, without resort to the use ofsintering aids. SEM observation revealed markedly small grain sizesin the sintered specimens compared with the commonly processed AlN.

Synthesis and consolidation of aluminium nitride nano-powders

Synthesis and consolidation of aluminium nitride nano-powders

Synthesis of aluminum nitride nanowires

Aluminum nitride (AlN) nanowires were synthesized by co-heating a mixture of Al and AlN nanopowders produced by nitrogen plasma-molten Al reaction in N 2 atmosphere at 750–850°C for 1 h. The morphology and structure of AlN nanowires were investigated using transmission electron microscopy (TEM) and X-ray diffraction techniques (XRD). The obtained AlN nanowires are either surface-smooth stick or bamboo-like structured. TEM observations showed that the AlN nanowires have a diameter of approximately 10–50 nm and a length of 500 nm–500 μm.

Novel technique for synthesis and consolidation of aluminium nitride nanopowders

In this paper, the use of a microwave plasma method for the synthesis of aluminium nitride nanopowders is described. The powders were consolidated to near theoretical densities using the unique rapid consolidation technique, plasma pressure consolidation (P2C), developed by MMI. Rapid consolidation of nanopowders is an ideal requirement for better mechanical and thermal properties in the consolidated part, as it retains the fine microstructure preventing anomalous grain growth. Microwave plasma synthesis resulted in aluminium nitride nanopowders (85–200 nm), which were consolidated to near theoretical density using P2C in <5 min without sintering additives. The effect of yttria (3 wt-%) as a sintering additive on the thermal conductivity (TC) of aluminium nitride was also evaluated and compared with TC values obtained from additive free AlN consolidated samples.

Infrared Spectroscopic Investigation of Chemisorption on Chemically Synthesized Aluminum Nitride Nanopowders with 2-Pyrrolidinones

The chemical nature of a nanoparticle surface is of crucial importance in controlling the interparticle forces during powder processing. As a continuation of a FT-IR spectroscopy study on the surface chemical structure of the chemically synthesized aluminum nitride (AlN) nanopowders, the adsorption of two representative cyclic amides, i.e., N-methyl-2-pyrrolidinone (NMP) and 2-pyrrolidinone (NHP), have been investigated. Upon adsorption of these cyclic amides, strong hydrogen bonding between the amide carbonyl oxygen and the surface hydroxyl groups was evident. The unusual thermal stability for the hydrogen bonding observed with NMP was explained as being due to the enhancement by secondary interactions between the NMP amide carbonyl group and the surface Lewis acidic sites, such as Al3+. With the adsorption of NHP at room temperature, besides the formation of strong hydrogen bonding, a striking 100 cm-1 shift to higher wavenumbers was observed for both the carbonyl and amide C−N stretching bands. This has been interpreted as the formation of complex coordination between the amide nitrogen and the surface acidic sites. The amide N-coordinated complex plus the carbonyl O-coordinated hydrogen bonding promote a synergistic effect for strengthening the NHP adsorption on the AlN surface.