First Principles Study On The Bonding And Absorption Properties Of Titanium Conversion Coating On Aluminium Substrate

Marine engineering aluminum alloys must be implemented with anticorrosive surface-treatment to resist the corrosion from sea water. Titanium conversion coating on aluminum alloys is the most promising treatment because of its high efficiency, good performance and low environmental pollution. One important constitution of titanium conversion coating on aluminum is Ti O2. On evaluating the anti-corrosion property of conversion coating, the bonding with substrate and the absorption to particular particals are two important items. The present thesis studied the bulk and surface properties of Al and Ti O2, binding properties of Al(111)/Ti O2(110) interface, and absorption properties of Cl and O on Ti O2(110) surface.For the study of bulk and surface properties of Al and Ti O2, the results show that the most stable surface of Al is(111) and the surface energy is 0.763 J/m2. The(110) orientation of Ti O2 surface is the most stable surface for most strongest bonding of Ti atom with O atom and the surface energy is 0.572 J/m2. Atoms at surface are more active for abundant dangling bonds.For the study of Al(111)/Ti O2(110) interface, after relaxation, oxygen atoms bond with aluminum atoms at interfacial zone through the twisting and distortion of [Ti O6] structures of Ti O2 layer, which allows oxygen atoms to approach the aluminum atoms at the interface. The Al-O bonds at the interface show mainly ionic characteristics. The more complicated Al-O structures are, the more Al-O bonds are, together with the stronger interface is. The maximum ideal work of separation is 21.8 J/m2, resulting a firmest interface bonding of Ti O2(110) with Al(111) due to strong Al-O bonding. Therefore, there are excellent bonding characteristics of Ti O2 with aluminum alloy as a potential substrate for titanium conversion coating.For the study of absorption properties of Cl and O atoms on Ti O2(110) surface, the results show that the most stable adsorbed position of Cl atom on Ti O2(110) surface is Ti top postion and the absorption energy is-1.055 e V. The most stable adsorbed position of O atom on Ti O2(110) surface is Ti bridge position and the absorption energy is-3.783 e V. The absorption energy will decrease for the existance of vacanciesat surface. The absorption energy of O atom on surface with vacancy is lower than that of Cl atom. Therefore, regardless of the existence of vacancies at Ti O2(110) surface, when Cl atom coexists with O atom at Ti O2(110) surface, O atoms are always adsorbed first. In order to increase the anti-corrosion property of titanium conversion coating, vacancy defect should be avoided at surface.