(163u) Studying Different Factors on Corrosion of Coated Titanium Anodes in a Nacl Solution

Titanium anodes contain base metal made from titanium that has been coated with thin layers of different oxides such as RuO2, IrO2, TiO2. These anodes mainly used in related technology with Electro-chemical process especially in chlorine-electrolysis systems. Long life time, low over-voltage, for free chlorine and high purity of produced chlorine gas are some reasons for using these anodes. One of the important aims for who work in electrolytic industries is to near work potential to the thermodynamics potential, which are related to some other factors. And generally, there is no exact mechanism and life time working for these anodes and we have tried to reveal some their aspects.

EXPERIMENTAL

In this research, since coated anodes samples charged under fixed amperage. Thus Galvanostatistic Graphs used for studying and observing corrosion and coating dissolution as well as studying their stability. For this reason, activated tests were elected (using diluted solution of NaCl instead of industrial and concentration solutions ) so that corrosion phenomena shall be observed in very low period of the samples life.The adopted(and earned) graph reveals this fact that corrosion and dissolution of coatings shall be done in three stages: Start of dissolution shall be commenced in a short period after doing test. Gradual progress of coating dissolution, that its duration is longer than before and after stages. In this state the potential shall increase with lower slop. Final stage or instant progress of coating that takes little time allocated that part of the graph that in a very short period of time we face with high increase of potential.

RESULTS and DISCUSSION

It should be noted that by passing short period of time after dissolution, potential of base metal will be exceed for pitting potential. Therefore titanium base metal shall face with sever local corrosion and the coated samples will be total corroded. In this regard, Electro-active elements such as Ru and Ir shall leave from coat in gradual dissolution manner. What remains on the surface of titanium metal is titanium oxide accompany with little contents of RuO2 and IrO2. In other words, with gradually dissolution of coatings the existing chain of electrical conductivity in the said coating will find high separation and conducts the same as non-coated titanium, that make resistance oxide layer on the surface. Also the effect of some different factors are mentioned hereunder: By increasing concentration of Cl Ions, the life of coated titanium anodes as well as corrosion period will be increased. By increasing imposed current density, the life of samples as well as corrosion period will be decreased. High concentration and acid solutions have no significant changes in comparison with neutral solutions. But in alkaline solution, in addition to observing picks in Cathode branches, there is slop change in Anode branch, Finally by increasing pH the life of anodes decreased and dissolution reactions will be occurred in lower potentials.