Preparation And Performance Optimization Of NiO-Cr₂O₃-SiC High Emissivity Coating

With the rapid development of modern science and technology, novel functionalradiation materials have been broadly applied in space and aeronautics, industry andarchitecture materials, and many other areas in production and life. Infrared radiationcoatings with high emissivity have especially played an important role in space andmilitary fields. For instance, the space shuttle will produce a large amount of heat inatmosphere because of frictions, and excessive heat will disable or even paralyze theflight system. Therefore when the surface temperature of spacecraft is higher than thelimit, insulation coating with high emissive materials is required in order to maintainstable and durable work of spacecraft.This study chose SiC, Al2O3, MoSi2, and Co2O3as the main components, andPOSS60as the binding agent, NiO and Cr2O3sol as the additive agents to modify theoverall properties. High emissivity coatings with exceptional film forming ability andstrong binding force with the substrate were prepared by transition layer. NiO, Cr2O3,and NiO/Cr2O3sol were introduced to the coating by composite sol-gel method. In themeantime the best preparation technologies, relevant structures and properties of thecoatings were also studied.First of all, POSS60compounded with NiO/Cr2O3sol was selected as the basiccomponent of transition layer due to its excellent film-forming and thermal resistantability after thermal shock resistance test, micro-morphology test, infrared spectrum test.Four different high emissivity component systems, including Si-Al-Mo-Co series,Si-Al-Mo-Co-Ni series, Si-Al-Mo-Co-Cr series and Si-Al-Mo-Co-Ni-Cr series wereprepared by ball mill and composite sol-gel method. Emissivity coatings were sinteredat high temperatures after homogeneous spray, after that were characterized by SEM,TEM, emissivity and thermal shock resistance tests. The results indicated that surfacemorphology and performance of coatings were influenced by dosage, spray, dryingtemperature, and sintering. The increase of temperature and time will magnify the sizeand density of the samples.High emissivity materials sintered at different temperatures were characterized byXRD, SEM, TEM and FT-IR tests, respectively. The relationship between structure, morphology and properties were studied, as well as the mechanism and improvementmethods of the radiation materials. With higher sintering temperature, crystal formshave become more complete and the emissivity of coatings decreased slightly becauseits integrity was effected. After radiation performance and thermal shock resistance tests,the emissivity of2-4series materials modified by metal oxide sol has increased from5μm to25μm at different levels, and their thermal shock resistance has also enhanced atthe same time, which indicated the composite sol-gel method and doping of multiplehigh emissivity components had helped to improve the comprehensive performance ofcoatings.As one kind of the novel, efficient radiation materials, high emissivity materialradiates heat energy to outer environment effectively, which fulfills the goals of heatradiation, energy conservation, heat preservation, etc. Undoubtedly, high emissivitymaterials are of great value in military, industrial, and manufacture aspects.