| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 103 === Recently, the use of energy is increasing and the main source of energy is still burning fossil-based raw materials. However, the burning of fossil will produce exhausts such asSO2, SO3, NO2, H2O, and HCl. When the exhausts contact with the metal on the cooling side, acidic substances are formed by condensation, including HCl, HNO3, and H2SO4, and corrosion occurs. Heat exchanger is a common equipment in the petrochemical industry. How to prevent the corrosion of heat exchanger is very important. The acid-proof glass-based coating will be a good candidate to protect heat exchanger steel tubes from corrosion.
This study focuses on two parts. One is to analyze the glass-based coating on a commercial heat exchanger steel tube so as to gain better understanding on the mechanism of bonding between the glass coating and steel substrate. The other part is to improve the heat transfer properties of the glass coating by increasing the degree of crystallinity and adding SiC powders in the glass-based coating. The results show that the commercial coating is mainly composed of silicon oxide and alkali oxide, while the presence of cobalt and nickel oxide is critical to bond the glaze to the steel substrate. Reaction occurs at the interface to generate uneven surface, which provides sufficient mechanical locking force. The degree of crystallinity has little effect on the heat conductivity because crystalline grains are dispersed in an amorphous matrix. In contrast, the addition of silicon carbide particles in the glass matrix improves heat transfer properties when a nickel layer pretreatment is employed to reduce the interfacial resistance. The presence of 10 wt% silicon carbide powders in a commercial glass coating results in approximately 40% increase in the heat conductivity.
Finally, this thesis develops a testing procedure to evaluate the performance of a glass coating on heat exchanger steel tubes for the petrochemical industry, including optical microscopy, SEM, TEM, XRD, EPMA, DSC, and TGA to characterize the microstructure and defect of the glass coating.
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