Synthesis of nearly spherical AlN particles by an in-situ nitriding combustion route

Abstract

Spherical AlN powders with micrometer size have attracted great attention owing to their good fluidity and dispersity. However, the industrial preparation methods usually require high temperature and long soaking time, which lead to the high cost and limit the wide application of the products. Herein, nearly spherical AlN particles with the average size of 2.5 μm were successfully synthesized via an in-situ combustion synthesis method. The effect of N 2 pressure, NH 4 Cl content and Al particle size on the combustion reaction procedure, phase composition and microstructure of the products was systematically investigated. The results showed that the decreased N 2 pressure, increased NH 4 Cl content and Al particle size led to the decreasing of combustion temperature and speed, which further affected the morphology of the products. As a result, low N 2 pressure (0.2 MPa), a small amount of NH 4 Cl (0.5 wt%) and fine Al particles (~2.5 μm) contributed to a moderate combustion temperature and facilitated the formation of nearly spherical AlN particles. In addition, based on the gas-releasing assisted quenching experiments and thermo-kinetic analysis, a two-step growth mechanism for the nearly spherical AlN particles was rationally proposed. The present method shows the advantages of low cost and high efficiency for preparing nearly spherical AlN particles, which can be used as raw materials for electronic substrates and fillers for packaging materials.

Continuous SiC skeleton reinforced highly oriented graphite flake composites with high strength and specific thermal conductivity

“…The advanced TMMs should have the characteristics of low density, high strength, and high thermal conductivity (TC) perpendicular to the inferior mechanical properties and high CTE in outplane direction of the highly oriented graphite blocks lead to the failure under harsh service environments [11]. In order to overcome the obstacles, some studies attempted to promote the mechanical properties of the graphite-based composites by using metal and ceramic powers (such as Cu, AlN, and SiC) as reinforcements [12][13][14]. However, the huge differences between metal/ceramic powders and GF particles in size, shape, and dimension lead to the inhomogeneous distribution of metal/ceramic reinforcements in GF matrix [15], which makes the flexural strength improvement rather limited.…”

Effect of carbon nanotube hybrid on the microstructure and properties of AlN skeleton-reinforced highly oriented graphite flake composites

“…The z-axial TC of the composites varied slightly with an increase in the Al2O3@CNT concentration, which can be attributed to fact that the TC in this direction was dominated by the AlN skeleton. Owing to the higher TC of AlN (~120 W/m/K) [36,37] than that of the GFs in the z-axial direction (15 W/m/K) [9] and the formation of the AlN skeleton in the composites, the phonons transferred mainly along the AlN skeleton in the z-axial direction. The TC in the x-y plane exhibited an abrupt decrease from 442 W/m/K for AlN/GF to 253 W/m/K for 0.5CNTs-AlN/GF and then slightly increased to 275 W/m/K for 2CNTs-AlN/GF.…”

Synthesis of submicron AlN powder using dynamic/thermochemical method

“…13 AlN powders can be obtained in various methods such as direct nitridation (DN) (gas-liquid), 14,15 carbothermal reduction and nitridation (CRN) (solid-solid), 3,5,[16][17][18][19][20] chemical vapor deposition (gas-gas), 21 synthesis from organometallic precursor (liquid-liquid), 22 from Al 2 S 3 reaction with ammonia (NH 3 ) (solid-gas) 23 and NH 3 mixed with propane (C 3 H 8 ) use to synthesize AlN from alumina (Al 2 O 3 ) 3 as well as different aluminum oxide precursors. 24 There are also some innovative approaches to produce AlN powders such as microwave plasma processing, 25 combustion synthesis, 26,27 DN-assisted arc discharge, 28 and dynamic/CRN (DCRN), 29 among which CRN and DN are the most convenient for industrial-scale production 15 with CRN being the widely used methods to synthesize AlN powders as well as whiskers. 30 The reason behind CRN method being more attractive than its DN counterpart lays within the high-quality AlN powders it provides as higher resistance against moisture and higher sinterability of powders.…”