Electrode Position Mechanism, Adhesion and Corrosion Performance Of
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Ž . Synthetic Metals 114 2000 225–234 www.elsevier.comrlocatersynmet Electrodeposition mechanism, adhesion and corrosion performance ofž / polypyrrole and polyN-methyl pyrrole coatings on steel sub strates Wencheng Su, Jude O. Iroh ) Department of Materials Science and Engineering Uni Õersity of Cincinnati, Cincinnati, OH 45211-0012, USA Received 11 November 1999; accepted 11 November 1999 Abstract Ž . Polypyrrole and poly N-met hylpyr role coat ings have been success fully electr odepos ited on stee l substrates from aqueous oxalate soluti ons. In acidi c soluti ons, the elec trode positi on proce ss was charact eriz ed by three distinct stages . In this work the elec trode posit ion Ž . Ž . proce ss was first inves tigate d by scan ning elect ron micro scopy SEM , X-ra y diffract ion XRD and FTIR techn iques . The adhesion and corrosion performance of the electrodeposited coatings were then evaluated by single lap shear tests and tafel tests, respectively. Our resul ts revea l that deposit ion of FeC O P 2H O crystal laye r first establis hed the passiva tion of steel at the end of the first two stage s, but 2 4 2 the formed FeC O P 2H O pass ive layer is subse quently decomposed followe d by elec tropol ymerization of pyrro le. Our resul ts also 2 4 2 show that electrochemical process parameters had significant effects on the adhesion and corrosion performance of the electroposited Ž . pol ypyrrole and pol y N-met hylpyr role coat ings. Polypyrrole coating s exhibited better adhes ion and corro sion performa nce than Ž . poly N-met hylpyr role coati ngs. q 2000 Published by Else vier Science S.A. Ž . Keywords: Polypyrrole; Poly N-methylpyrrole ; Electrodeposition mechanism; Adhesion; Corrosion 1. Introduction Steel is the most interesting commodity metal from a technological point of view; however, it must be protected against corrosion under normal environmental conditions. App lic ati on of pol yme r coa tings on ste el substrates is w x per hap s the most widely used met hod in industries 1 ; however, current coating techniques often involve the use of toxic chemicals such as chromates and volatile organic w x solvents 2 . Due to environme ntal conce rns, indust ries are now looking for new effective and nontoxic coating tech- niques tha t can mee t cur rent and fut ure env iron men tal restrictions. Ž Aqueo us elect roche mical polymeriza tion elect ropoly - . meriza tion may be an alternative which can eliminate the us e of toxi c chemical s. Adva nt ages of aque ous el ec- Ž . tropol ymeriz ation includ e: i The aqu eous so lutions used are environmentally favourable. The use of aqueous solu- tions also greatly lowers the costs for materials and waste Ž . dispo sal. ii This te chniq ue comb ines th e format ion of the ) Corre spon ding auth or. Tel.: q 1-513-556-30 96; fax: q 1-513-556- 2569. Ž . E-mail address: jiroh @ucen g.uc. edu J.O. Iroh . polymer and deposition of the coating in one process. The proce ss is energy-effective and can be easi ly automated. Ž . iii . Mild reaction conditions such as room temperature, low current or potential are used. The production cost is Ž . rel ati vel y low. iv The pro per tie s of the coatin gs can be con trolle d by var ying the rea cti on par ameters such as curre nt densi ty, monomer type, monomer conce ntrati on, electrolyte type, electrolyte concentration, pH of the reac- tion medium and the reaction time. Recen tly the elect ropoly meriza tion of pyrrole on iron electrodes has been investigated with the aim of producing w x unifo rm and st rongly adhere nt coat ings 3–14 . It was found that only a few reaction systems could lead to the w x format ion of polypy rrole coa tings on iron sub strat es 5– 14 . In our previous work, we have systematically investigated the eff ect of ele ctr och emi cal process par ameters on the Ž . formation of polypyrrole and poly N-methy lpyrro le coat- ing s on ste el sub str ate s from aqu eous oxa lat e soluti on w x 8–11 . We also successfully characterized the composition w x and structu re of the electro depos ited coati ngs 12–14 . In this paper, we furthe r inves tigate d the elect rodep ositio n mec han ism, adhesion and cor rosion per for mance of the Ž . polyp yrrole and poly N-me thylpyrrole coa tings on ste el substrates. 0379-6779 r00r$ - see front matter q2000 Published by Elsevier Science S.A. Ž . PII: S0379-6779 99 00306-9
