Corrosion-inhibiting efficiency of the protective coatings with pigment particles and conducting polymers

摘要

The widespread corrosion protection of metal construction materials based on low carbon steel is the application of organic coatings created from anticorrosion paints. This method secures the chemical, barrier or electrochemical reaction of an anticorrosion pigment with a metal alone or with the corrosive environment penetrating the protective organic coating. Conducting polymers as polyaniline PANI have recently been described as a new class of pigments for the corrosion protection. For an efficient corrosion protection, PANI has to be uniformly distributed in a close vicinity of protected metal. For anodic passivation, the electrical contact with metal is necessary. Polyaniline, however, has a bad adhesion and, moreover, during the redox processes changes its density, and thus also its volume; the delamination of PANI-containing layers may be a serious consequent problem. The delamination problems may be prevented, if the PANI is introduced into the whole volume of the coating. In the present study, PANI has been introduced into the protective coatings in a formof inorganic pigments surface-modified with a PANI overlayer. The coating of particles takes place in situ during the polymerization of aniline. The deposition of PANI on suitable carrier particles can solve the problems caused by the changes in PANI density and/or volume during the conversion of individual forms. When carrier particles are used, it can be anticipated that they will sediment in the deposited paints to produce a barrier layer during drying. At the same time, the deposited PANI is brought in contact with the metal, thus fulfilling its role of a primer. The amount of PANI can be therefore considerably reduced because PANI-coated objects manifest themselves in many respects as PANI particles. Pigments alone and after coating with PANI phosphate have been investigated with respect to corrosion protection and compared with the properties of commercial corrosion protection pigment and the effect of pigment particle surface treatment with conductive polymer on the corrosion inhibiting properties of organic paints was investigated. Inorganic pigments based on ferrites with combinations of the divalent cations Mg and Zn and sulfides Mo a W have been used for this purpose. The anticorrosion properties of the composite pigments were tested on model paints with a modified alkyd resin and epoxy resins as the binders. The effect of the pigments on the mechanical properties of the paint films was also examined. The anticorrosion efficiency and mechanical properties of the paints with the pigments modified with PANI were found superior to those of the initial pigments. The highest anticorrosion efficiency was observed with the ferrite-based pigments. The anticorrosion efficiency was found to increase with increasing Zn contents of the pigments.