阳极氧化涂层的等离子体晶化致密化及其绝缘导热性能研究

Due to the existence of amorphous phase and perforated nanopores, the thermal conductivity and insulating properties of oxide coatings prepared by anodic oxidation are much lower than that of crystal and compact alumina, which increases the difficulty in preparing the thermal conductive insulating coatings. This project proposes constructing the electrochemical system which can firstly cause the combination reaction of hydroxyl and then trigger the discharge of hydroxyl. The anodized coating with a thickness of 100 microns can be developed by the combination reaction of hydroxyl. Then, the colloidal anodized coating will be driven to crystallize and densify by virtue of the ionization heat and shock wave generated by oxygen ionization. The effect law of electrochemical system parameters on the growth kinetics of anodized coating, the diameter and distribution of perforated nanopores will be studied. The intensity of oxygen plasma is regulated by current peak and waveform timing state. The covariation relationship between the intensity of oxygen plasma on anodic surface and the degree of crystallization and densification of anodized coating with different microstructure and thickness will be revealed under condition of the self-discharge of hydroxyl. Thermal conductivity and breakdown strength represent the physical properties of crystallization and densification, respectively. The change law of two physical properties with the crystallinity of amorphous oxide coating and the compactness of transport channel of hydroxyl in anodized coating will be characterized. Preparation condition of the highly compact crystalline alumina ceramic coating with a thickness of 100 microns will be summarized. The project aims at offering theoretical support for preparation of the thermal conductive insulating coatings which can be applied in high integration power devices.

针对阳极氧化法制备的氧化物涂层因存在无定形相和贯通型纳米孔，而使其绝缘导热性能远低于高致密Al2O3涂层应有水平这一高导热绝缘涂层制备难题，本项目申请拟构建先使OH-化合反应、以生长出百微米厚度的阳极氧化涂层，再引发OH-析氧离化、借助氧气离化产生的离化热和冲击波驱使先期生成的胶体态氧化物发生晶化、致密化转变的电化学体系。研究电化学系统参量对阳极氧化涂层生长动力学、贯通型纳米孔直径与分布状态的影响规律；揭示OH-自放电析氧条件下，受电流峰值和波形时序状态调控的阳极表面氧等离子体强度，与不同显微组织结构及厚度的胶体态阳极氧化涂层晶化、致密化程度之间的协变关系；表征出导热系数和击穿强度两个分别代表晶化和致密化的物理性能指标，随无定型氧化物涂层晶化程度和层内OH-传输通道消减程度的变化规律；归纳出百微米厚度高致密度Al2O3陶瓷层制备的实验条件，为高集成度功率器件绝缘导热涂层的制备提供理论参考。

阳极氧化法于铝基板表面制备的氧化物涂层因存在无定形相和贯通型纳米孔，而使其绝缘导热性能远低于高致密Al2O3涂层应有水平。本项目将等离子体物理知识与阳极氧化技术原理有机融合，提出“先阳极氧化增厚再等离子晶化致密化重构”的创新思路，借助液固界面氧气离化产生的离化热和冲击波使胶体态阳极氧化涂层发生晶化、致密化。研究结果表明，在液相环境、介质阻挡放电情况下，铝阳极氧化涂层孔径超过20nm是可经等离子体放电处理晶化转变的必要因素，且保障铝阳极氧化涂层表面电阻的均匀性是实现等离子体在阳极氧化涂层表面自组织均匀放电的关键。. 氧等离子体放电处理会促使铝阳极氧化涂层发生致密化重构，孔隙率降低为原有的1/3，且孔隙率的降低程度随起始阳极氧化涂层厚度的降低而增加。同时，等离子放电处理后，铝阳极氧化涂层外层的相组成从无定形态转变成α-Al2O3，中间层由γ-Al2O3与非晶相组成，而膜基界面涂层仍为非晶态。这是因为热量传递的衰减特性造成涂层晶化程度的渐变式分布。多孔阳极氧化涂层经氧等离子体放电处理后可实现大厚度（60 μm以上）、厚度可调、高致密度的Al2O3涂层的制备。涂层的整体热导率达到22.975±0.204 W/m·K，热扩散系数最高为60.876±0.541 mm2/S。热导率随着涂层厚度的增加而增加，热扩散系数随着厚度的增加而减少，研究成果为高集成度功率器件绝缘导热涂层的制备提供了理论参考。. 与常规微弧氧化技术相比，采用该创新方法制备相同厚度的Al2O3陶瓷层可节约46%的电量消耗。大厚度、高密度的Al2O3陶瓷层也可以有效提高铝合金的摩擦磨损、耐腐蚀性能。随着铝合金强度的不断提升，铝对钢顺序替代产生的减重效果，已引起舰载机、登陆艇等国防装备，高铁、汽车结构件及电子产品壳体等民用行业的高度关注。针对铝合金应用于如上行业而必须解决的遭弹射冲击不剥落、遇乱石飞溅不破损、异金属连接不腐蚀等防护涂层制备难题，本项目的实验结果也可以为其提供理论指导。