LED辐射散热用导热/绝缘/高发射率微弧氧化涂层结构性能调控与机制

The objective of the research is to propose a novel fabricating method of ceramic coatings with Al2O3-SiC-AlN on aluminum substrate for heat dissipation of high-power leds by simple one-step microarc oxidation technique, and further understand the interrelationship between microstructure and thermal conductivity,insulating as well as emissivity. Such special structural coatings are expected to be an effective way to resolve the key issues on increasing the light lumen and lifetime, by enhancing the conductivity and radiative heat dissipation. This research will focus on: tailoring the contollable growth of Al2O3 based ceramic coatings by adding high emissivity nano SiC and AlN additives into the electrolyte, and revealing the effects of surface activating SiC and AlN as well as microarc oxidation processing parameters on microarc discharging behaviours, coating growth and microstructure; and investigating the effects of coating composition and structure(including phase composition, micropores defects and distribution state of nano particles additives in the coating) on spectral emissivity, thermal conductivity and insulation properties, revealing the enhancing mechanisms of emissivity and conductivity by morphology controling and SiC-AlN doping; taking the self-constructive LED junction temperature test equipment to examine the p-n junction temperature decreasing by heat dissipation effect of thermal radiation coating, and further understand the interrelationship between temperature decreasing and spectral emissivity distribution. Finally, the process parameters and coating structure were optimized to obtain the high performance radiative heat dissipation coating. The proposed project has a broader societal impact on scientific disciplines and engineering applications. Not only will it enriches the thermal controling theories of radiative heat dissipation, but will also explore and find the novel way to fabricate radiative heat dissipation coating of aluminum substrate for high-power leds.

针对LED高效散热以降低芯片p-n结温、提高光通量及延长寿命的关键问题，提出在LED封装铝基板两侧一步微弧氧化原位构建含SiC与AlN协同提高导热与热发射性能的纳米Al2O3-SiC-AlN全新结构陶瓷涂层，实现导热/绝缘/高发射率辐射散热三重功能。通过微弧氧化电解液中高发射率高导热SiC和AlN纳米粒子的表面活性剂改性及匹配掺杂，研究纳米SiC与AlN粒子分散特性及氧化工艺参数对放电过程、涂层生长与微观结构的作用机制；揭示涂层相组成、孔隙率及掺杂陶瓷粒子在涂层中的分布状态等对发射率、热导率及绝缘特性的影响规律，阐明微观结构调控与SiC-AlN协同强化热发射及热导率的物理机制；以LED结温测温装置考察铝封装双侧涂层结构（特别是发射率分布特性）对辐射降温性能影响，优选出高辐射散热涂层与工艺。本课题对于探索LED封装用金属基板绝缘散热涂层新方法、丰富散热涂层理论具有重要学术与应用价值。

铝合金散热器的表面发射率低、使辐射散热能力差，而且在苛刻的海洋服役环境下抗腐蚀性能差，这制约了铝合金基板在高可靠、长寿命大功率电子器件上的拓展应用。本项目提出纳米粒子辅助同步烧结微弧氧化技术、微弧氧化/旋涂(或电沉积)复合技术，分别构建出纳米SiC和hBN粒子改性的辐射散热抗腐蚀微弧氧化复合涂层以及辐射散热–疏水–抗腐蚀多层复合涂层。研究微弧氧化、纳米粒子改性及多层复合涂层的组织结构与表面发射率、辐射散热、疏水、抗腐蚀等性能的关系，揭示粒子改性微弧氧化纳米复合涂层及微弧氧化多层复合涂层的形成机理与作用机制。.研究表明，发现在膜基界面处的持续微弧放电，会诱导涂层在膜基界面处的“局部累积放电生长”；通过调控“累积放电生长”区域尺寸，可优化微弧氧化涂层的界面结构与性能，为微弧氧化涂层设计提供新思路。为提高铝合金微弧氧化涂层的发射率系数进而增强辐射散热能力，构建了纳米粒子辅助同步烧结微弧氧化纳米复合涂层，分别制备出SiC、hBN及SiC/hBN协同改性纳米复合涂层，并提出纳米粒子由低温玻璃相辅助烧结快速粘结成膜形成机理。为提高铝合金的高发射率辐射散热与抗腐蚀综合性能，构建出氧化铝/石墨烯(Al2O3/rGO)辐射散热–疏水–抗腐蚀双层复合涂层。此外，构建出氧化铝/十六酸铈(Al2O3/CH)辐射散热–超疏水–抗腐蚀双层复合涂层。.铝合金的发射率仅为0.1~0.2，微弧氧化涂层仅能提高8~20μm波段内的发射率值至0.8；纳米hBN粒子改性涂层在3~20μm宽波段内的平均发射率达0.8；SiC和SiC/hBN改性复合涂层，3~20μm宽波段内的平均发射率值高达0.88~0.9。在5W恒功率热源测试条件下，微弧氧化及SiC、hBN及SiC/hBN纳米复合涂层的散热效率分别为13%、21%、17.2%和22.3%；同样条件下，Al2O3/rGO和Al2O3/CH多层复合涂层的散热效率为15%和14.1%，表明涂层发射率的提高显著改善散热性能。微弧氧化及纳米改性复合涂层改善极化电阻1个数量级以上。而疏水Al2O3/rGO复合涂层表面接触角为114.42°，相比于金属基体，极化电阻提高1个数量级。此外，超疏水Al2O3/CH复合涂层，表面接触角高达165.5°，极化电阻可提高2~3个数量级。