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首页> 外文学位 >Coating particles with alumina nanolayers utilizing atomic layer deposition in a fluidized bed reactor.
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Coating particles with alumina nanolayers utilizing atomic layer deposition in a fluidized bed reactor.

机译：在流化床反应器中利用原子层沉积用氧化铝纳米层涂覆颗粒。

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There is a current need to provide simple methods to place conformal, pinhole-free, nanoscale-thickness films on fine particles. Such processing can be done using atomic layer deposition (ALD) in a fluidized bed reactor, as will be shown in this thesis. This work is the first application of ALD to coat bulk quantities of fine powders. A fundamental understanding of the fluidization of fine cohesive particles at reduced pressure along with the ALD processing of these particles is the major focus of this thesis. The applications for such nanocoated particles are broad and can be found in many different areas of materials science including microelectronics, defense, biomedical, consumer products, advanced materials, and others.; The minimum fluidization velocity (umf) of fine cohesive particles at reduced pressure can be calculated using a balance of forces method. Two additional forces are added to a general force balance on a particle with an upward gas flow under vacuum conditions. The final equation is a quadratic in umf, and can be used to accurately describe umf for a variety of particle sizes, shapes, and densities. Additionally, as fine particles are coated with an alumina film, the cohesive forces between the particles will change. For the particles of interest in this thesis, the change in the cohesive force is small.; Experiments for alumina deposition on 1.5 · 10−4 m (150 μm) diameter nickel particles, several different sized boron nitride (BN) particles (from 5 · 10−6 to 1.5 · 10−4 m (5 to 150 μm) average diameter), and fine (∼5 · 10−6m (5 μm)) iron particles were conducted using trimethylaluminum (TMA) and water as dosing reagents at 450 K. Successful deposition of alumina films, with thickness controllable at the angstrom level, was observed based upon TEM imaging, ICP-AES, XPS, particle size distributions, surface area analysis, and WDS imaging. Nickel particles are coated quite easily. For BN platelet particles, a small exposure (3.25 · 102 Pa·s (2.5 · 106 L)) of the reagent gases will coat the edge planes only. A larger dose of 1.3 · 104 Pa·s (1 · 108 L) will coat the entire particle. After 10 ALD cycles, the exposure can be lowered back to 1.3 · 102 Pa·s (1 · 10 6 L) as the film is then growing on alumina and not BN. Improved interfacial adhesion between epoxy and the filler material is noted for alumina-coated BN particles. Nanocoated iron particles show improved oxidation resistance relative to uncoated particles, as long as the film is greater than 2.5 · 10−9 m (25 Å) thick.
机译：当前需要提供简单的方法来将保形的，无针孔的，纳米级厚度的膜放置在细颗粒上。如本文中将显示的，这种处理可以在流化床反应器中使用原子层沉积（ALD）来完成。这项工作是ALD涂覆大量细粉的首次应用。对细小的内聚颗粒在减压下的流态化以及这些颗粒的ALD处理的基本理解是本论文的主要重点。这种纳米涂层颗粒的应用很广泛，可以在许多不同的材料科学领域中找到，包括微电子，国防，生物医学，消费品，先进材料等。细小的内聚颗粒在减压下的最小流化速度（u mf ）可以使用力平衡法计算。在真空条件下，通过向上的气流，将两个附加力添加到粒子上的总体力平衡中。最终方程是u mf 的二次方程，可用于精确描述各种粒径，形状和密度的u mf 。另外，当细颗粒被氧化铝膜覆盖时，颗粒之间的内聚力将改变。对于本文关注的颗粒，内聚力的变化很小。在直径1.5·10 −4 m（150μm）的镍粒子，几种不同尺寸的氮化硼（BN）粒子（从5·10 −6 到平均粒径为1.5·10 -4 m（5至150μm），并使用（约5·10 -6 m（5μm））的铁颗粒进行了研磨。三甲基铝（TMA）和水作为定量试剂，在450 K下。基于TEM成像，ICP-AES，XPS，粒度分布，表面积分析和WDS，观察到成功沉积了氧化铝膜，厚度可控制在埃级成像。镍颗粒很容易涂覆。对于BN血小板颗粒，少量的反应气（3.25·10 2 Pa·s（2.5·10 6 L））将仅覆盖边缘平面。较大的1.3·10 4 Pa·s（1·10 8 L）剂量将覆盖整个粒子。经过10次ALD循环后，由于薄膜随后在氧化铝上而不是在氧化铝上生长，因此可以将曝光降低至1.3·10 2 Pa·s（1·10 6 L）。国阵对于氧化铝涂层的BN颗粒，环氧树脂和填料之间的界面粘合性得到了改善。纳米涂层的铁颗粒相对于未涂层的颗粒表现出改善的抗氧化性，只要薄膜的厚度大于2.5·10 -9 m（25Å）即可。

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