ABSTRACT
High emissivity coatings for high temperature were widely used in many cases such as energy-saving of the industrial furnace, improving the thermal efficiency of infrared heaters, thermal control of the spacecraft and so on because they have the effect of enhancing the radiation and the cooling. Due to the low value of the infrared emissivity and poor thermal shock resistance at high temperature environment become a constraint on engineering application. So how to prepare coatings with high infrared emissivity in the 3~5μm wave band with a good thermal shock resistance has become the key technology of praparation of high emissivity coatings. In this thesis, the relationship between the thermal resistance and ahesive structure as well as the relationship between the infrared emissivity and the filler structure were systematically studied. Meanwhile, the mechanism of thermal shock resistance of the coating was studied, too. The inherent relationship and physical nature between the preparation of filler and the infrared emissivity of the coatings were systematically studied by experimental research. By adjusting process parameters, high emissivity coatings with high infrared emissivity near to 0.92 at 600℃ were prepared. The role and mechanism of a variety of coating additives in improving the thermal shock resistance of high infrared emissivity coatings for high temperature, were obtained. Then the thermal shock resitance of coatings was improved.
The main findings and conclusions were as follows:
1. By studied the desigh principle of high temperature coating, the qualifications of high temperature adhesives were obtained. The results indicated that a strong bond and spatial network structure were contributed to thermal resistance. Meanwhile, the inherent relationship and physical nature between the infrared emissivity and the coating microstructure were obtained through studying the desigh principle of high emissivity coating. The results indicated that high infrared emissivity fillers must have the spinel structure of which the emissvity in the 3~5μm band had a increase due to the presence of chemical doping and the intensified of the electronic transitions.
2. Acording to the desigh principle, effect of adhesive structure and modified adhesive properties on thermal resistance of adhesive were examined. Meanwhile, the filler composition, heat treatment temperature and heat treatment time were examined. It found that copper oxide play an important role in preparation of spinel structure.
3. By studied the preparation and optimization techniques of high emissivity coating, the coatings with high infrared emissivity in the 3~5μm band near to 0.9 at 600℃. And there was a positive temperature coefficient effect between the infrared emissivity and the temperature.
4. The dynamic thermal environment performance such as thermal shock resistance of the coatings was studied. The thermal shock resistance was improed through the adhesive modified, filler modified and substrate pre-modified, respectly.
Key words: thermal resistance, infrared emissivity,fillers, coatings, thermal shock resistance
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