Study On Process Of Fabricating TiO₂ Thin Films By Mechanical Coating Technique And Photocatalytic Activity

In the numerous photocatalytic materials,TiO₂ thin film has been widely studied due to its non-toxic,high efficiency,low energy consumption,and so on.At present,numerous techniques have been used in the formation of TiO₂ thin films,such as sol-gel,PVD,CVD,and so on.However,very few people use mechanical coating technique.It has good application prospect because it has characteristics of simple process,light pollution and easy to produce on industrial scale.In this paper,the process of preparation of TiO₂ thin film by mechanical coating technique.First,preliminary research of preparation of aluminum film on ZrO₂ balls,and the effects of milling time,milling speed and ball-to-powder mass ratio on the thickness were investigated.Then TiO₂ thin film with 6 mm diameter alumina balls and 1 mm diameter ZrO₂ balls were fabricated,and film of structure,morphology and photocatalytic activity were investigated.Metal films on ceramic balls were fabricated successfully by mechanical coating technique.It had been found that milling speed and milling time have a significant impact on film forming by L₉（3⁴）orthogonal test.The optimized process parameters are:milling speed of 250rpm,milling time of 10h,and ball-to-powder mass ratio of 7:1.The aluminum film thickness has reached to 50μm.The aluminum powder deposited on the substrate by the cold welding,and mechanical bonding properties were good between film and substrate.Experiment for fabricating Ti film with 6mm diameter alumina balls showed that the film thickness increased first and then decreased with increasing of milling speed and time,and reached a maximum thickness of 20μm in 250rpm and 15h.Forming of the film is a dynamic process which can be divided into three stages,the formation and growth of metal deposition nuclei,the formation and thickening of the film,and the peeling of the film.During sintering,the increasing of heat treatment temperature resulted in higher degree of oxidation film,less surface porosity and more rounded particles,and lead to a film thickness of 30⁴0μm.With increasing of heat treatment temperature,milling time and amount of catalytic balls,photocatalytic degradation rate of film increased first and then decreased.The process of experiment for milling 15h,sintering 500℃and increasing 1 g/ml dosage of catalytic ball,the degradation rate reached 74.9%and had a good reusability.Experiment for fabricating Ti film with 1mm diameter ZrO₂ balls showed that the film thickness increased with increasing of milling speed and time.Ti film having a thickness of20μm become a variety of titanium oxide composite film include TiO₂,Ti₂O and TiO after heat treatment of 500℃.The photocatalytic degradation rate of film after heat treatment of500℃increased first and then stabilized with increasing of film thickness.Catalytic effect of20μm and 25μm thick film respectively prepared by ball milling 30h and 40h was 72.3%and69.1%.The film had a good reusability.The optimized experiment parameters of preparation process and photocatalysis are:（1）The substrate of alumina balls,milling time of 15h,milling speed of 250rpm,ball-to-powder mass ratio of 2:3,heat treatment temperature of 500℃,catalytic balls of 1g/ml,the degradation rate for 10mg/l methyl orange solution is 74.9%under 30 h uv radiation.（2）The substrate of ZrO₂ balls,milling time of 30h,milling speed of 300rpm,ball-to-powder mass ratio of 1:1,heat treatment temperature 500℃,catalyst balls of 1g/ml,the degradation rate reached 88.4%.