Preparation, Characterization And Photo-Catalytic Property Of Microarc Oxidation TiO₂ Films

TiO2 films were prepared by means of a self-made multi-functional MAO power supply in our laboratory and the growth characteristics, phase component and surface morphology of the TiO2 films were studied by optical microscope, SEM and XRD. The nanocrystal TiO2 films with fine photo-catalytic properties were prepared through the optimization of technical parameters.This dissertation consists of three parts:In the first part, we studied the effects of the parameters of electrolytic solution on critical voltage of electrical breakdown, the growth rate, phase component as well as surface morphology. The experiment results show that critical voltage of MAO electrical breakdown, which has nothing to do with the concentration, depends on the category of electrolyte solution. The average growth rate of the film prepared at constant current density is invariable against treatment time in different electrolyte solution and the rate is the highest in solution of Na2CO3 and it is the lowest in solution of Na3PO4. The average growth rate of the film prepared at constant voltage decreases gradually as the treatment time extends. The TiO2 films prepared in different electrolyte solution all contain Anatase and Rutile TiO2 but the contents vary in different samples. Rutile is found mainly in the TiO2 film prepared in Na2CO3 solution while Anatase is mainly in the film prepared in Na3PO4 solution. The concentration of electrolyte has great impact on the content of Rutile and Anatase at constant voltage. As the concentration of electrolyte goes denser, the relative content of Rutile increases and decreases successively; on the contrary, the relative content of Anatase decreases and increases successively. The surface structure of TiO2 film is of close relationship with the category of electrolyte solution. The TiO2 films prepared in Na2CO3 solution have coarse surfaces and uneven holes both in size and distribution; the films prepared in Na3PO4 solution have smooth surfaces which are porous and the holes distribute evenly while on the surface of the films prepared in Na2SiO3 solution, uneven grainy structures appear.In the second part, the effects of electric parameters on the growth rule, phase component and the surface morphology of the MAO films were studied under different experimental conditions. The results show that in MAO process, the visible current variety can be divided into 4 phrases under constant voltage as the treatment time extends; the dynamic resistance and the resistance rate of the TiO2 film vary in phases in the process of film-forming. In MAO process, voltage varies in phases under constant current density as the treatment time extends. With porous surface morphology, the TiO2 film is mainly composed of Anatase and Rutile; with the increasing current density, the growth rate increases from rapidness to tardiness and the surface roughness increases. The dimension and the density of the micropole increases and decreases respectively; Anatase decreases gradually while Rutile increases. There is a distinct interface between the TiO2 film and the substrate; in addition, many micropores exist in TiO2 film. TiO2 films prepared at variable voltage are porous and consist mainly of Anatase and Rutile. With the increased voltage, the growth rate of TiO2 film increases first and then decreases and the surface roughness increases. The dimension of micropores increases while the density decreases gradually. Anatase in the film decreases while Rutile increases gradually until finally it occupies the leading place in the film. The TiO2 films prepared at variable impulse frequency are porous and the growth rate, the surface roughness as well as the dimension of micropore decrease respectively with the increased frequency while the density of micropores increases gradually. The film is mainly composed of Anatase, Rutile and a few of TiO2-x, among them the relative content of Anatase and Rutile has nothing to do with the treatment frequency while the content of TiO2-x decreases with the increased frequency. The surfaces of the TiO2 films prepared at different duty cycle are porous. As the duty cycle increases, the growth rate increases swiftly first and then slows down while the surface roughness increases gradually. The dimension of the micropores increases first and then decreases while the density decreases first and then increases. The film consists mainly of Anatase, which decreases gradually, and Rutile which increases gradually with the increased duty cycle.In the third part, through the adjustment of the technical parameters, the TiO2 films with grainy structure and nanocrystal structure on the surface respectively were prepared; the growth rate, phase structure, surface morphology and photo-catalytic properties were studied. The results show that in the electrolyte solution composed mainly of Na2SiO3, TiO2 films with grainy surface form on the surface of Titanium Alloys. The thickness of TiO2 films increases with increased treatment time while the growth rate of the film decreases slowly. The TiO2 film mainly consists of Rutile, the relative content of which decreases gradually with increased treatment time, and Anatase, the relative content of which increases gradually as the treatment time extends. Meanwhile, on the surface of the porous TiO2 film, large number of TiO2 grains whose dimension ranging from 300nm to1μm appear. As the treatment time extends, the width of discharging channel and the dimension of TiO2 grain increase gradually while the densities decrease. In the electrolyte solution mainly composed of Na2CO3, TiO2 films with 40-80nm dimension nanocrystal on the surface were prepared on Titanium Alloys through the adding of Na2SiO3 and the adjustment of technical parameters. TiO2 film is mainly composed of a large number of Rutiles and a few of Anatases; the dimension of nanocrystal on the surface decreases first and then increases with the increased treatment time and the specific surface area increases to the maximum when the treatment time is 20 min. Through the deseperating experiment of the films with grainy and nanocrystal TiO2 on their surfaces respectively on Rhodamine B, the divergence of microstructure on the surface has great effect on the performance of photocatalysis. The smaller the grain is, the better the effect of catalysis is. In the carbonate solution with silicate,when the sample is prepared for 20 minutes, the dimension of nanocrystal is about 40 nm, the desperating effect on Rhodamine B is the best and its photodegradation rate is over 82%.