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氧化铝（Al2O3）粉体因具有优异的机械性能、良好的耐高温性和化学稳定性等，在工业上得到了广泛的应用。形貌规则、分散性好的球形Al2O3粉体因具有大的堆积密度、好的流动性等促使制备的产品表现更优异的性能。本文从热等离子体制备的球形Al2O3粉体的特性出发，围绕其在两个领域的应用展开研究。第一，利用 Al2O3粉体制备陶瓷时由于Al-O键能较高，需要较高的烧结活化能，进而需要较高的烧结温度。常用的无压烧结因简单易行、利于工业化等优势，在实际生产中被广泛应用，但却难以制备高致密度、高机械性能的陶瓷。第二，将Al2O3粉体作为填料制备高导热的聚合物基复合材料。由于填料的添加，在复合材料中形成大量的填料/基体界面，界面的出现严重降低热量传输的效率，即在界面处产生界面热阻，影响复合材料整体的热传输性能。针对以上两个Al2O3粉体在实际应用中出现的问题，本论文对热等离子体制备的球形Al2O3粉体的特性进行考察，开展了在高性能Al2O3陶瓷与高导热聚合物基复合材料两个应用领域的研究。主要研究内容如下：（1）首先，对热等离子体制备的球形Al2O3粉体的特性进行了研究，包括颗粒的形貌、粒径、分散性、晶型结构、元素组成及其制备的浆料的特性等。研究发现，Al2O3粉体不仅具有窄的粒径分布，且颗粒分散性较好。同时，颗粒表面光滑、内部结构致密，结晶性较好。通过改变原料铝粉的加料速率，可实现对Al2O3粉体粒径的调控。将Al2O3粉体分散到水中制备的浆料具有较好的分散稳定性，颗粒长时间悬浮在浆料中不沉降，进一步研究发现Al2O3颗粒在中性的水溶液中表现出较高的zeta电位。随着固含量的增加，Al2O3浆料的粘度提高，表现出剪切稀化特征。（2）将热等离子体制备的球形Al2O3用于制备高性能的Al2O3陶瓷。原料粉体经过湿磨处理后，与未处理的粉体相比，表现出更高的烧结活性。湿磨颗粒在1600℃下烧结2 h，陶瓷的致密度可达到98.7%，且具有较高的弹性模量（400.2 GPa）与硬度（22.9 GPa）。分析粉体湿磨前后的烧结活化能发现，在烧结初期，湿磨后的粉体的烧结活化能（498.8 kJ/mol）远低于未处理粉体的烧结活化能（685.9 kJ/mol）。对颗粒的进一步表征发现，湿磨后的颗粒内部产生较多的应变，表面出现了非晶相，内部出现了更多的位错，这大大提高的粉体的烧结活性，从而降低了烧结温度。（3）利用热等离子体制备的球形粉体的分散好、粒径细等优势，结合粉体的烧结传质特性，制备了枝状Al2O3（b-Al2O3），将其填充到酚醛树脂（PR）中制备了具有更高的热传输性能的导热复合材料。对复合材料热导率提升的机理进行研究，发现b-Al2O3颗粒通过其枝状结构的互相搭接在基体中形成了连续的网络状结构，降低了热量传输时的界面热阻，进而提高了PR材料的热导率（1.481 W m-1 K-1）。同时，基于b-Al2O3在PR基体中形成的连续网络结构及二者间较好的界面结合力，PR复合材料的热膨胀性能大大提升。（4）基于第三部分的研究，利用喷雾干燥与高温烧结工艺制备了三维连续网络结构的Al2O3球（N-Al2O3），对其结构表征发现，与b-Al2O3相比，N-Al2O3不仅具有更多维度连续的结构，而且内部具有均匀贯通的孔隙。将其填充到PR基体中发现，PR基体渗入到N-Al2O3的孔隙，因而制备的N-Al2O3/PR复合材料具有无机-有机两相贯穿结构。由于N-Al2O3球更加连续的网络结构，更大程度的降低了热量传递时的界面热阻，将PR材料的热导率大幅度提升至4.01 W m-1 K-1，是纯PR材料热导率的18倍多。同时，复合材料的力学性能、热稳定性能与介电性能均得到改善。;Alumina (Al2O3) powder has been widely used in industry because of its excellent mechanical properties, high temperature resistance and chemical stability. The spherical Al2O3 powder with regular morphology and good dispersion has better performance because of its large packing density and good fluidity. Based on the characteristics of spherical Al2O3 powders prepared by thermal plasma, this paper focuses on its application in two fields. First, because of the high bond energy of Al-O, it needs higher sintering activation energy and higher sintering temperature to prepare Al2O3 ceramic. The commonly used pressureless sintering is widely used in practical production due to its advantages of simplicity and industrialization, but it is difficult to prepare ceramics with high density and high mechanical properties. Secondly, Al2O3 powder is used as filler to prepare polymer composite with high thermal conductivity. Due to the addition of fillers, a large number of filler/matrix interfaces are formed in the composite. The appearance of the interface seriously reduces the efficiency of heat transfer, that is, the interface thermal resistance is generated at the interface, which affects the overall heat transfer performance of the composite. In view of the two problems in the practical application of Al2O3 powders, we investigate the characteristics of spherical Al2O3 powders prepared by thermal plasma, and carry out research in the two application fields of high-performance Al2O3 ceramics and high thermal conductive polymer composites. The main research contents are as follows:(1) Firstly, we study the characteristics of the spherical Al2O3 powders prepared by thermal plasma, including the morphology, particle size, dispersion, crystal structure, element composition and the properties of the prepared slurry. It is found that Al2O3 powder not only has narrow particle size distribution, but also has good particle dispersion. In addition, the surface of the particles is smooth, the internal structure is compact and the crystallinity is good. The size of Al2O3 powder can be controlled by changing the feeding rate of Aluminum powder. The slurry prepared by dispersing Al2O3 powder into water possesses good dispersing stability, and the particles are suspended in the slurry for a long time without settling. Further studies show that Al2O3 particles show high zeta potential in neutral aqueous solution. With the increase of solid content, the viscosity of Al2O3 slurry increases and the slurry is shear thinning.(2) The spherical Al2O3 prepared by thermal plasma is used to prepare Al2O3 ceramics with high performance. Compared with the untreated powder, the ball milled powder shows higher sintering activity. The relative density of the ceramic can reach 98.7% after sintering at 1600℃ for 2 h, and the ceramic owns high elastic modulus (400.2 GPa) and hardness (22.9 GPa). The results show that the sintering activation energy of ball milled powder (498.8 kJ/mol) is much lower than that of untreated powder (685.9 kJ/mol) at the initial stage of sintering. Further characterization of the particles shows that there are more strains in the ball milled particles, amorphous phase on the surface and more dislocations in the particles, which greatly improve the sintering activity of the powder and reduced the sintering temperature.(3) Based on the advantages of the spherical Al2O3 prepared by plasma, such as good dispersion and fine particle size, together with the sintering mass transfer of powder, the branched Al2O3 (b-Al2O3) is prepared and filled into the phenolic resin (PR) to prepare polymer composite with higher heat transfer performance. The heat transfer mechanism of composite is studied, it is found that the b-Al2O3 particles form continuous network structure in matrix through the overlapping of the branch structure, which reduces the thermal resistance of the interface during the heat transfer, and then improves the thermal conductivity of the PR (1.481Wm-1K-1). In addition, due to the continuous network structure formed by b-Al2O3 in PR matrix and the better interface bonding force between filler and matrix, the thermal expansion performance of PR composite is greatly improved.(4) Based on the third part of the study, network Al2O3 spheres (N-Al2O3) with three dimensions continuous structure are prepared by spray drying and high temperature sintering process. The structural characterizations show that N-Al2O3 has more continuous structure compared with b-Al2O3, and possesses uniform and connected pores. After fully embedded into PR, PR matrix infiltrates into the pores of N-Al2O3, thus the prepared N-Al2O3/PR composite has interpenetrating structure of N-Al2O3 and PR. Due to the more continuous structure of N-Al2O3, the interfacial thermal resistance of PR composites is reduced to a greater extent, and the thermal conductivity of PR material is greatly increased to 4.01 W m-1 K-1, which is more than 18 times of that of pure PR. Furthermore, the mechanical properties, thermal stability and dielectric properties of the PR composite are also improved.
|欧阳玉阁. 球形氧化铝粉体在陶瓷和导热复合材料上的应用研究[D]. 中国科学院大学,2020.|
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