Preparation Of Conducting Polymers And The Research For Their Protection On Stainless Steel

Since Deberry reported firstly that the deposited polyaniline(PANi) on stainless steel (SS) could offer good corrosion protection to it; conducting polymers have been the focus of research in the field of metal protection due to their easy synthesis, good environment stability and they usually can protect the metals well. To improve the protection of conducting polymers and their protection mechanism for metals still need to be deeply researched. In the paper, the conducting polymers were prepared in different conditons, the protection performances and mechanism of these conducting polymers were investigated by methods such as scanning electron microscopy(SEM), infrared spectroscopy(IR), potentiodynamic polarization curve and corrosion potential-time curve etc..PANi doped with phosphoric acid was electrochemically synthesized on SS and the undoped PANi was prepared by immersing the doped PANi in 1mol/L NH4OH for 4h. The doped and undoped PANi were characterized by SEM and IR. Their anti-corrosion performances to stainless steel in 1mol/L Na2SO4 solution were investigated; the SS protected by doped and undoped PANi in 1mol/L H2SO4 was also studied. Results indicated that SEM microphotographs showed the holes in both of the doped and undoped PANi. In 1mol/L Na2SO4 solution, both kinds of PANi shifted the corrosion potential of stainless steel towards positive direction remarkly; the undoped PANi protected stainless steel mainly by its barrier effect, the doped PANi could passivate stainless steel and its protection time was longer than the undoped PANi. In 1mol/L H2SO4 solution, the doped PANi could reduce the corrosion rate of SS remarkly and prevent it from corrosion for a long time. The undoped PANi could be dedoped into doped PANi by sulfuric acid. The dedoped PANi could protect SS for a longer time than PANi doed with phosphoric acid.Bilayer composites of PANi and polypyrrole (PPy) were electrochemically synthesized on SS, their anti-corrosion performances to stainless steel were investigated in lmol/L H2SO4 solution. Their morphologies were studied by SEM. The results showed that the bilayer composites were more compact than PPy and less compact than PANi. The protection time of PPy/PANi was longer than PANi/PPy. The protection of PANi to SS was poorest.Aniline and pyrrole were codeposited on stainless steel to synthesize the conducting copolymer composites of PPy and PANi by electrochemical method in p-toluenesulfonic(HTSO) acid. Their anti-corrosion performances to SS in lmol/L H2SO4 were studied. The results exhibited the corrosion rate of SS protected by copolymer composites was less than PPy and PANi. The protection time of colymer composites were between PPy and PANi, their protection time was longer than PPy.Aniline and pyrrole were codeposited on stainless steel to synthesize the conducting copolymer composites of PPy and PANi by electrochemical method using sodium dodecylbenzene sulfonate(SDBS) and HTSO as electrolyte. They were characterized by SEM and FTIR. Results showed the conducting copolymer composites of PPy and PANi were smoother and more compact than PANi and PPy; the copolymers were more efficient in protecting stainless steel and their protection time were longer than PANi, PPy meanwhile prolonged with the amount of dodecybensulfonate anion and PANi in copolymer composites increased.The conducting copolymer composites prpared in SDBS and HTSO could protect SS better than conducting copolymer composites prpared in HTSO. Large size dopant could prolong the protection time of the coating.