Αντιδιαβρωτικές ιδιότητες οργανικών επικαλύψεων με πιγμέντα φιλικά προς το περιβάλλον

Abstract

The aim of this thesis is the study of the resistance of different organic coatings containing volatile corrosion inhibitors environmentally friendly and their anti corrosive performance when applied to steel surfaces in sea environment. In the context of this paper, studied 7 coatings systems of 2 categories: a.) organic solvent (SB) and especially 4 coating systems (SB1,SB2,SB3,SB4) with different density in anticorrosion pigment and 1 system of organic coating with volatile corrosion inhibitor (VCI) and b.) water soluble (WB) especially 2 systems of organic coatings (WB1,WB2) containing resin with anticorrosive properties. Coatings in the first category contained two types of anti-corrosive pigments, oxyaminophosphate salt of magnesium and zinc phosphate pigment.As well as these systems contain volatile corrosion inhibitors. Zinc phosphate (Zn3 (PO4) 2 * 2 - 4H2O) was the first and most important alternative "green" phosphate pigment was used in place of chromate pigments. Magnesium pigments are ecological anticorrosive pigments as they do not contain any evidence to be responsible for toxicity. Even though these pigments are manufactured at high temperatures they show high thermal stability. The anticorrosive coatings contain corrosion inhibitors in ionic form under the name of "volatile inhibitors", creating a protective layer of ions at the steel surface that stops the electrolytic action between anode and cathode regions. The volatile corrosion inhibitors are defined as compounds or mixtures of compounds (usually organic amine base-soluble in water) with high vapor pressure (107-10-2 mmHg) that can prevent general corrosion of metallic materials. In the field of organic coatings the use of corrosion inhibitors makes it possible to prepare organic coatings friendlier to the environment with the possibility of better corrosion protection and the ability to heal itself. The requirement for the protection of the environment impose on paint industries, to produce paints with lower content in volatile organic compounds (VOCs). Thus one way to reduce these, is the steady reduction in the use of organic solvents and the creation of new coatings in which we use water as solvent which as a dispersion medium allows to avoid pollution problems by solvent evaporation. The second category of waterborne coatings,which are studied, contains acrylic resin with anticorrosive properties. The anticorrosive properties of these products are based on the fact that almost no water or vapor will migrate through the polymer membrane, since no water or oxygen can penetrate into the metal substrate, so therefore there is no corrosion. Because of this unique feature, the aqueous dispersion requires no filling or anticorrosive pigment for optimum performance. This means that it is possible to deliver very high gloss in pigmented coatings with superior anticorrosive properties. The degree of corrosion protection of the coatings was estimated by determining the density of the corrosion current icorr, linear polarization resistance Rp and the corrosion rate CR as a function of exposure time of the coated specimens in a sea enironment NaCl 3,5% w/w. In addition to this we examine the change in the corrosion potential of the coated samples according to the exposure time in the corrosive environment. The durability of organic coatings was studied by assessing their physicochemical properties. For this study used the following methods:  Estimation of coating system adhesion by the cross cut test  Estimation of coating system adhesion by the pull-off test  Estimation of coating system flexibility by the Conical mandrel bending test Summarizing the main outcomes from this thesis it is concluded that: The coatings contain volatile inhibitors (VpCI) have very good anti-corrosion properties in the coating but lose their mechanical properties and adhesion. Moreover both anticorrosive,adhesion and mechanical properties are very good in organic coatings (SB).On the contrary,huge disadvantage is the environmental pollution due to the organic solvent.In the end,in coatings with water-soluble resins (WB) we observe changes in the anticorrosive properties by changing the composition of the coating. Generally, WB coatings do not exhibit good electrochemical properties.Adhesion is increased when the emulsion of the resin increases. The mechanical properties vary and can be placed between the mechanical properties of the two previous categories of organic coatings.