Structure Modification Of TiO₂Film And Its Novel Application For Promoting The Anti-contamination Performance Of High Voltage Outdoor Insulators

The insulators for outdoor high-voltage insulation usually suffer from thepollution flashover, imperiling the reliability of the high voltage power system. Thoughvarious measures have been carried out, the pollution flashover is still unable to beprevented fundamentally because of the irresistible accumulation of contaminations onthe surface of insulators. Photocatalysis is a “green” technology for the environmentalremediation issues with solar energy. Titanium dioxide （TiO₂）, is considered to be oneof the ideal photochemical materials due to its merits, has become the most extensivelystudied photocatalyst in the researches, especially in the application researches ofphotocatalysis. We seek to use the self-cleaning and electrical properties of TiO₂function film for promoting the anti-contamination performance of highvoltageinsulators. In addition, modification research is also carried out to further upgrade thephotocatalytic performance of TiO₂film by modulating the characters of TiO₂structure.It is of great significance to ascertain the structure-activity relationship of the TiO₂filmand broaden its application fields, in both theoretical and practical aspects.In this thesis, the TiO₂coated porcelain insulators were prepared successfully, andthe function mechanism of the TiO₂film in promoting the anti-contaminationperformance was investigated systematically. According to the weakness of TiO₂filmin the practical application, a new method of controlling the location of defect sites wasused to improve the photocatalytic performance of TiO₂film. Furthermore, the actionmechanism of these defect sites in photocatalysis was also studied in detail. Theseworks are as follows:（1） The TiO₂sol was coated on the porcelain insulators byspraying method to prepare the photoinduced self-cleaning insulators. Thephysicochemical properties, self-cleaning and electric performances of the as-preparedporcelain insulators have been tested comparetively.（2） Using ANSYS forfinite-element method （FEM） analysis, the electric field distribution of insulator wassimulated by static electric FEM. Based on the study above, the influence mechanismof TiO₂semiconductor film on the electric performance of porcelain insulators was proposed.（3） A distinct modification method by introducing defects into the TiO₂multilayer was presented to improve the photocatalytic performance of TiO₂film. Thechemical states of these defects were characterized in detail. Furthermore, theinfluences of defect sites on the photocatalytic performances were studied, and aninteractive activation model was also proposed to clear the role of defects in theelectron transfer process.The research work obtained some new results and insights as follow:（1） Anuniform and compact TiO₂film can be prepared on the porcelain insulators byspin-spraying method. Compared with the uncoated insulators, the TiO₂coatedinsulators exhibits a stronger self-cleaning ability in the heavy pollution environmentdue to the excellent photocatalytic performance of TiO₂films.（2） In our study, theelectric performances of TiO₂coated insulators do not decline for the existence of TiO₂film, which is of semi-conductivity and hydrophilicity. Instead, even higherperformances are observed in the tests of wetting flashover and artificial contaminationflashover. The growths in the flashover voltages of insulators are determined to be6%¹2%.（3） Based on the electric field simulation results, the TiO₂film can amelioratethe distribution of electric field along the insulator, subsequently suppress theoccurrence and development of the partial discharge, and promote the flashover voltageof the insulators finally.（4） Defective TiO₂films are successfully prepared by acombination of cold plasma treatment and sol-gel dip-coating technology. Moreover,the defects can exist between two TiO₂layers to form the TiO₂film with “interfacedefects”.（5） These defects, no matter whether they are located at the surface or at theinterface, can improve the photoactivity of the TiO₂film. The defects are considered toact as functional electron traps to reduce the recombination of electrons and holes,resulting in the promoted photocatalytic properties of TiO₂films. However, the locationof defects played an important role in the adsorption and photodegradation behaviors ofthe RhB dye molecules.（6） Moreover, the interface defects are proved to be morestable than the surface defects, indicating that this modification method is value inpractical application.The innovations of this thesis are as follows:（1） The TiO₂photocatalytic film isfirstly applied for preventing the high voltage porcelain insulators from pollutionflashover. The study not only provides a new way to deal with the pollution flashoveraccident of insulators, but also broadens the application fields of photocatalysistechnology.（2） The “interface defects” are propounded and successfully prepared forthe first time. Interface defects, which are more stable than the surface defects, can also affect the photoinduced electron-hole recombination process, and promote thephotoactivity and photoinduced hydrophilicity of TiO₂film. Furthermore, the influenceof defects’ location on the photocatalytic reaction behaviors has been discussed in detail.The effect mechanisms of defects on the photocatalysis are also proposed. This studywould be of great benefit to offer a general theoretical guide and a realization way forimproving TiO₂photocatalytic performances.