Reseach On The Preparation And Electrochemical Properties On Stainless Steel Of Polypyrrole, Polyaniline

The conductive polypyrrole （PPy） and polyaniline （PAni） have the advantages ofenvironmental stability, easy synthesis, high conductivity, redox reversibility and soon, and there are important application and researching values in sensors,optoelectronic devices, metal anti-corrosion, life sciences and battery, etc. In this work,PPy and PPy-PAni copolymers were prepared on stainless steel （SS）. Corrosionprotection of the conductive polymers for stainless steel was studied by linear sweepvoltammetry curve, potentiodynamic polarization curve, corrosion potential-time curveand electrochemical impedance spectrum, redox behavior was studied by cyclicvoltammetry curve. Morphology was observed with scanning electron microscopy.Conductivity was measured by four-probe.1. The preparation and corrosion prevention of Na₂MoO₄doped PPy, PAni copolymerand bilayer polymer coatingsPPy-PAni-MoO₄^2-and PPy-PAni copolymer were prepared on stainless steel bycyclic voltammetry in pyrrole+aniline+oxalic acid solution with0.01mol L^-1Na₂MoO₄or not. Corrosion protection for stainless steel of PPy-PAni and PPy-PAni-MoO₄^2-copolymer were studied. The results showed that the MoO₄^2-had a catalytic effect onelectrodeposition and could accelerate pyrrole oxidation, and also it could inhibit theanodic dissolution of stainless steel. The protection of PPy-PAni-MoO₄^2-for stainlesssteel increased with time during2h immersion in0.1mol L^-1HCl, while PPy-PAni losttotally after2h immersion. The charge transfer resistance （R2-ct） of SS/PPy-PAni-MoO₄was higher than SS/PPy-PAni, corrosion protection of PPy-PAni-MoO₄^2-for stainlesssteel exhibits better and longer.PPy-PAni-MoO₄^2-copolymer in pyrrole+aniline+oxalic acid solution containing0.001mol L^-1or0.03mol L^-1Na₂MoO₄were prepared by cyclic voltammetry. The effectof Na₂MoO₄concentration on corrosion protction of copolymers for stainless steel wasstudied. When the concentration of Na₂MoO₄was0.001mol L^-1, the electrodepositionrate of copolymer was the bigest, but when increased to0.03mol L^-1, the ratesignificantly reduced, when increased to0.05mol L^-1, the copolymer could hardly bedeposited. Potentiodynamic polarization and corrosion potential-time test showed thatthe protection of copolymer on stainless steel was the best prepared in0.001molL^-1Na₂MoO₄and the worst one was prepared in0.03mol L^-1Na₂MoO₄. The bilayers composed of PPy-MoO₄^2-and PPy-PAni-MoO₄^2-(PPy-MoO₄^2-/PPy-PAni-MoO₄^2-and PPy-PAni-MoO₄^2-/PPy-MoO₄^2-) were prepared in the solutioncontaining0.01mol L^-1Na₂MoO₄by cyclic voltammetry. Corrosion protection of PPy-PAni-MoO₄^2-copolymer and these bilayers for stainless steel were studied. Potentio-dynamic polarization in1mol L^-1H2SO₄and0.1mol L^-1NaCl showed that the corro-sion protection of PPy-PAni-MoO₄^2-copolymer was the best, and PPy-Na₂MoO₄/PPy-PAni-Na₂MoO₄showed the worst.2. Redox behavior and corrosion protection of PPy prepared in alkaline solutionPPy(MoO₄^2-) were prepared on stainless steel at10°C or40°C in the pH10solutioncontaining0.001mol L^-1Na₂MoO₄by cyclic voltammetry (denoted by10°CSS/PPy(MoO₄^2-) or40°CSS/PPy(MoO₄^2-)), and aslo PPy(WO₄^2-)(40°CSS/PPy(WO₄^2-) or40°CSS/PPy(WO₄^2-)) were prepared at10°C or40°C in the pH10solution containing0.001mol L^-1Na₂WO₄. The redox behavior and corrosion protection for stainless steelof these PPy（MoO2--4） and PPy（WO24） were studied. The results showed that theelectrodeposition behavior of PPy(MoO₄^2-) and PPy(WO₄^2-) were substantially similar,but the electrodeposition rate in the solution containing WO₄^2-was greater, and wasgreater at10°C than at40°C. The redox reversibility of PPy(MoO₄^2-) prepared at10°Cwas better than40°C, and also the doping degree was higher. MoO₄^2-was not involvedin the redox of PPy, and retained in the PPy framework which only the cation infiltrateinto the PPy coating to balance charge. The effect of temperature on electrodepositionof PPy was great, while on redox activity was small. WO₄^2-was not involved in theredox of PPy, which was similar to MoO₄^2-. The corrosion protection of PPy dopedwith MoO₄^2-for stainless steel was better than WO₄^2-, and PPy prepared at10°Cshowed better than at40°C.3. The conductivity of PPy and its factorPPy doped with sodium dodecyl benzene sulfonate （SDBS） and p-toluenesulfonicacid （HTSO） was prepared on stainless steel by potentiotatic. The effect of SDBS orHTSO concentration on morphology and conductivity of PPy were studied. PPy couldhardly be electrodeposited in an aqueous solution just containing SDBS, but depositedafter adding HTSO. Increasing HTSO, the PPy conductivity increase, and PPy surfaceshows spherical particles in groups or massive aggregation. Increasing SDBS, the PPyconductivity decrease, while surface shows small spherical particles with uniformarrangement.The study on the effects of potential and temperature on PPy conductivity showedthat the conductivity of PPy prepared at0.6V was the biggest, and rapidly decreased when potential increased to0.9V. The PPy conductivity decreased as temperatureincreased when prepared at5°C,30°C and50°C, while almost unchanged afterexposing to the air when prepared at5°C. Reducing temperature and potential couldgenerate short polymer chains easily and form ordered structure to increase delocalizeddegree of carrier, thus the PPy conductivity increased.The study on PPy conductivity after soaking in pH2.5, pH10and pH12solutionrespectly showed that the higher pH, the lower conductivity. The PPy conductivitydecreased with exposing time in the air, but the conductivity decreased the fastest afterexposing to the air with pH12solution immersion.