The dynamic corrosion behaviors of Ti-6Al-4V alloy in acid artificial saliva containing fluoride ion were traced using electrochemical techniques,optical microscope,scanning electron microscopy,energy dispersive spectrometer and roughness tester.The experimental results indicate that a negative shift of corrosion potential as well as a continuous decrease in impedance for the alloy exists with increasing immersion time,and the degradation rate of the alloy presents the trend of first increase then decrease following the dissolution of passivation film and the formation of corrosion products.The accumulated fluoride ion on the alloy surface accelerates the fracture of passivation film,and the occurrence and development of corrosion of alloy are mainly located at the sites where the formation and shedding of white particles are composed of fluoride compounds,resulting in the decrease of corrosion resisting property of the alloy.A possible model is proposed to elaborate the dynamic corrosion behavior of the alloy.
YANG LixiaWU YuntaoCHEN ShuoXIAO YuanqiangCHEN SenHAO ShuoWANG Junxia
Effect of solution concentration on the structures and corrosion inhibition behavior of γ-APS films fabricated on surface of low carbon steel was systematically studied by EIS, RA-IR, and AFM. The experimental results indicated that the impedance ofy-APS silane treated substratcs and the cross-linking degree of γ-APS films gradually increased with the increasing solution concentration. There was some noticeable transformation in molecular orientation and protective performance of y-APS films when solution concentration was above 10vo1%. High cross-linking degree and changes in molecular orientation generated γ-APS films with excellent protective performance and ordered arrangement.
The aim of this work was to study the degradation behavior of Ti-6Al-4V alloys for dental applications in acidic artificial saliva with fluoride ion using electrochemical techniques, optical microscopy, scanning electron microscopy（SEM）, and energy dispersive spectrometry（EDS）. The experimental results showed that fluoride ion had significant influence on the degradation of Ti-6Al-4V alloys, and there was an obvious critical concentration of fluoride ion（about 0.1wt%）. With increasing fluoride ion concentration, the corrosion potential（Ecorr） of alloys moved toward negative and the impedance of alloys decreased, meanwhile, noticeable transformation from minimum corrosion to severe pitting corrosion was observed on alloys surface following the dissolution of TiO2 passive films, leading to the decrease of the corrosion resistance of alloys. The electrochemical dissolution of TiO2 passive films involved a nucleophilic attack of fluoride atom to the titanium atom of TiO2. In addition, Ca^（2＋）and Na~＋ in acidic saliva may involve the surface reactions and make the reactions more complex.
The influence of acetic acid on dynamic behavior of hydrolazation and film forming of an expoxy-silane compound （y-GPS） was investigated by conductivity meter, IR and AFM. The experimental results show that there is an optimal pH value（pH=4-5） for hydrolysis of silane solution, and with the prolongation of hydrolytic time, the promotion of acetic acid on the hydrolyzation of silane solution become more obvious. During the adsorption and film forming process, acetic acid could promote the formation of Si-O-Fe bond, which activates hydroxyl group of silanol unit and facilitates this hydroxyl group to react with adjacent silanol unit forming linear condensation polymers.
