Growth of Quasi-Aligned AlN Nanofibers by Nitriding Combustion Synthesis
Growth of Quasi-Aligned AlN Nanofibers by Nitriding Combustion Synthesis
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DOI：
10.1111/j.1551-2916.2007.01747.x
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发表时间：
2007-08
影响因子：
3.9
通讯作者：
M. Radwan;Y. Miyamoto
中科院分区：
文献类型：
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作者：
M. Radwan;Y. Miyamoto
根据独特的微反应器模型，通过氮化燃烧合成形成准定向AlN纳米纤维。由铝和氮化铝稀释粉末（40/60 mol%）以及氧化钇和氯化铵作为添加剂（各 5 wt%）的混合物组成的炉料在 0.25 MPa 的低氮气压力下燃烧。合成的 AlN 产品的 FE-SEM 图像显示形成了球状晶粒（与原始 Al 反应物相同的形状和尺寸），该晶粒由薄的表面氮化物层或内部生长的准排列 AlN 纳米纤维的壳覆盖组成。剖面图呈海葵状。这种新颖形态的形成被认为是通过两阶段过程发生的。第一个发生在铝颗粒外部燃烧的初级阶段。点燃后，产生的热量导致氯化铵升华并分解成各种气态物质。这有效地中断了燃烧并减缓了反应温度的升高。此外，氧化钇与 Al 颗粒表面的原生氧化层相互作用，形成稳定的 Al-N-Y-O 外壳。第二阶段开始于各种气体物质，例如 HCl(g)、NH3(g) 和 N2(g) 通过地壳渗透到熔融的 Al 核心。 “壳核”系统起到“微反应器”的作用，氮化和生长过程都在内部发生。熔融的 Al 核自发卤化为 AlCl3 蒸气，氮化通过 AlCl3 和 NH3/N2 蒸气的气-气反应进行。然后，通过 VLS 和 VS 机制，AlN 纳米纤维在微反应器内准排列的气相中生长。
Quasi-aligned AlN nanofibers were formed by the nitriding combustion synthesis according to a unique micro-reactor model. A charge composed of aluminum and aluminum nitride diluent powders (40/60 mol%) with a mixture of yttria and ammonium chloride as additives (5 wt% each) was combusted at low nitrogen gas pressures of 0.25 MPa. The FE-SEM images of as-synthesized AlN product showed the formation of ball-like grains (same shape and size as the original Al reactant) that consisted of a thin surface nitride layer or crust cover quasi-aligned AlN nanofibers grown in the interior. The cross-sectional view is sea anemone like. Formation of this novel morphology is believed to occur through a two-stage process. The first one occurs at the preliminary stage of the combustion outside Al particles. After the ignition, the heat generated causes the sublimation and dissociation of ammonium chloride into various gaseous species. This effectively interrupts the combustion and slows down the increase of reaction temperature. In addition, yttria interacts with the native oxide layer present on the surface of Al particles and forms a stable Al–N–Y–O crust. The second stage begins by the infiltration of various gaseous species such as HCl(g), NH3(g), and N2(g) through the crust into the molten Al cores. The “crust–core” systems function as “micro-reactors” where both the nitridation and growth processes occur inside. The molten Al cores are spontaneously halogenated to AlCl3 vapors and the nitridation proceeds by the gas–gas reaction of AlCl3 and NH3/N2 vapors. The AlN nanofibers are then grown from the vapor phase quasi-aligned inside the micro-reactors by VLS and VS mechanisms.