Effect Of PH Value And Chloride Ion On Corrosion Behaviour Of Pure Titanium And Cobalt-Chromium Alloy

Objective:The electrochemical corrosion tests of pure titanium and cobalt-chromium alloy were carried out in artificial saliva solutions with different pH values and NaC1concentrations. The corroded surface morpHologies of pure titanium and cobalt-chromium alloy were observed by scanning electron microscope (SEM). The corrosion properties of cobalt-chromium alloy in these artificial saliva solutions with different pH values and NaCl concentrations were compared with those of pure titanium, thus the reference is provided by this investigation for reasonably choosing metallic repair material used for clinical medicine.Method:Six sets of experimental solutions with pH value of6.8and NaC1concentrations of0.9%,2%,3%and pH value of4.0and NaC1concentrations of0.9%,2%,3%were prepared. Pure titanium (24specimens) and cobalt-chromium alloy (24specimens), underwent the same surface pretreatment, were randomly grouped into the six experimental solution groups. Their electrochemical corrosion tests were carried out in these solutions. One specimen was chosen randomly from each group after electrochemical test in order to observe its corroded surface morpHology using SEM.Result:1. The change trend of the self-corrosion potentials (Ecorr) for pure titanium and cobalt-chromium alloy in six kinds of artificial saliva solutions is not obvious. However, the self-corrosion current densities (Icorr) of pure titanium are much lower than those of cobalt-chromium.2. The self-corrosion current densities (Icorr) of cobalt-chromium alloy in acid artificial saliva solutions are much larger than those in neutral ones, and these current densities increase as the increasing concentration of NaCl. The breakdown potential (Eb) ofé'´é“¬alloy decreases as the increasing concentration of NaC1in acid artificial saliva solution. The potential range for the breakdown of oxide film (Ev) is shortened as the increasing concentration of NaCl in acid artificial saliva solution.3. The self-corrosion current densities (Icorr) of cobalt-chromium alloy in neutral artificial saliva solutions increase as the increasing concentration of NaC1(There is no statistical significance in0.9%and2.0%NaCl solution, whereas other groups have statistical significance). The breakdown potential (Eb) of cobalt-chromium alloy decreases as the increasing concentration of NaC1in neutral artificial saliva solution. The potential range for the breakdown of oxide film (Ev) is shortened as the increasing concentration of NaC1in neutral artificial saliva solution.4. The self-corrosion current densities (Icorr) of pure titanium in acid artificial saliva solutions are much larger than those in neutral ones, and these current densities increase as the increasing concentration of NaCl. However, the breakdown behaviour for oxide film is only observed in2.0%and3.0%NaC1solution. The breakdown potential (Eb) of pure titanium decreases as the increasing concentration of NaCl in acid artificial saliva solution. The potential range for the breakdown of oxide film (Ev) is shortened as the increasing concentration of NaCl in acid artificial saliva solution.5. There is no obvious statistical difference for the self-corrosion current densities (Icorr) of pure titanium in neutral artificial saliva solutions with different concentrations of NaCl. The breakdown potential is not observed according to the polarization curves.Conclusion:1. Chloride ion plays a deleterious role on the corrosion resistance (pitting corrosion) of cobalt-chromium alloy under the conditions of neutral and acid solutions.The corrosion resistance of cobalt-chromium decreases as the increasing concentration of chloride ion, which is more obvious in acid solution.The increasing concentration of chloride ion plays a more important role on accelerating the pitting corrosion of cobalt-chromium alloy compared with the decrease of pH value. However, the decrease of pH value favours the corrosion process of cobalt-chromium alloy in comparison with the increasing chloride ion. 2. The impact of chloride ion on the corrosion property of pure titanium is not significant under the condition of neutral solution. However, the corrosion resistance of pure titanium decreases as the increasing concentration of chloride ion under the condition of acid solution. Moreover, pure titanium is susceptible to pitting corrosion as the increasing concentration of chloride ion when the concentration of NaCl reaches2.0%.3. The corrosion resistance of pure titanium was better than that of cobalt-chromium alloy in the neutral and acid oral environment with chloride ion...