Novel environment friendly corrosion inhibitor pigments based on naturally occurring clay minerals (original) (raw)
Related papers
Innovative Infrastructure Solutions
This is the first study to look into the use of modified feldspars as anticorrosive pigments in the coatings industry. Herein, novel anticorrosive composite pigments were prepared by the chemical deposition of thin films of different oxides (e.g., zinc oxide and vanadium oxide with doloresite phase) on the surface of feldspar, which comprises 80% of the whole structure. A new vanadium oxide (e.g., doloresite) was chosen due to its IV oxidation state and excellent anticorrosive characteristics. ZnO is also well-known for its high resistance to corrosion. Firstly, the synthesis of the composite pigments was done, and then, they were characterized via XRD, SEM/EDX, XRF, and TGA. The composite pigments were incorporated into solvent-based epoxy coatings to evaluate their anticorrosive performance on reinforced concrete steel. Their corrosion resistances were determined using linear polarization resistivity and electrochemical impedance spectroscopy techniques. The physico-mechanical pro...
Lanthanum-exchanged zeolite and clay as anticorrosive pigments for galvanized steel
2014
A wide variety of inhibitive pigments is now being offered as possible alternatives to chromate and lead compounds for painted metals protection. Unfortunately, the most wide spread of these substitute pigments, zinc phosphate, has, at present, raised some environmental concern because phosphate causes the eutrophication of water courses and zinc itself is toxic. The aim of this research was to study the anticorrosive performance of a mixture consisting of zinc phosphate, modified zeolite and clay (bentonite) in order to diminish phosphate content in paints. The zeolite and the clay were exchanged with La(III) ions, as inorganic green inhibitor. In the first step, the anticorrosion protection by La(III) ions in solution was assessed by electrochemical tests. In the second step, an epoxy-polyamide paint formulated with the pigment mixture applied on galvanized panels was studied by salt spray test and electrochemical noise measurements (ENM). The results showed that it was possible to replace part of the zinc phosphate content in the paint with the exchanged zeolite and the clay.
Montmorillonite as corrosion protective pigment
Corrosion Science, 2018
MMTs are not inert; rather, they may act as smart pigments with complementary properties being activated as the coating is damped with corrosive medium. Beyond barrier properties, montmorillonites (MMTs) may improve coatings performance by active corrosion inhibition. Also, regulation of pH suggests smart anticorrosive action of hydrophylic MMTs for acid media. Organophilization treatments of MMTs may have collateral effects on coatings performance. Benefits may depend on testing conditions, MMT type and content.
Corrosion inhibition of galvanized steel with inorganic pigments
Materials Science
Lacquer coatings on a metal are, as a rule, multiple and consist of a base coating, several layers of the basic coating, and a decorative layer [1]. The base coating is a promoter of adhesion for such coatings and contains mainly inorganic inhibiting pigments which electrochemically protect the metal base after the formation of through defects in the coating and penetration of the corrosion medium into the metal. Chromate pigments are widespread anticorrosive modifiers for lacquer base coatings [ 1]. They efficiently protect steels against corrosion in neutral and weakly acid media. However, their application is limited by ecological requirements. At the same time, one intensively searches for substitutes of less harmful pigments for chromates. Before proceeding to the investigation of polymeric coatings containing anticorrosive pigments (possible substitutes for strontium chromate), it is necessary to estimate the protective function of extracts of these pigments without polymeric binder. Having analyzed the information on pigments produced by industry, we took strontium chromate, zinc phosphate modified with zinc molybdate, and aluminum triphosphate.
Recent Development in Clay Based Functional Coating for Corrosion Protection
Key Engineering Materials
There is a large variety of techniques available to protect metals from various types of corrosion. Till date chromate containing metal coatings is one of the most commonly used methods. Layered clays are basically of two types depending on the type of ion exchange capacity. In the recent years different researchers demonstrated the use of such cation/ anionic clays as potential nanocontainers for the inhibitors. These nanocontainers can be used in the coating to induce self-repairing capacity when the coating surface is damaged. Due to the disturbance in the pH and availability of chloride ions clay based nanocontainers can release the inhibitor to protect the surface. In the recent year use of anionic clay like hydrotalcites or layered double hydroxides are much studied in comparison to cationic clay like montmorillonite. This review critically analysed the potential of these clay in the future development of self-healing coating.
Evaluation of mechanically treated cerium (IV) oxides as corrosion inhibitors for galvanized steel
Electrochimica Acta, 2011
The use of cerium salts as corrosion inhibitors for hot dip galvanized steel has been object of a numerous studies in the last few years. The role of cerium ions as corrosion inhibitors was proved: cerium is able to block the cathodic sites of the metal, forming insoluble hydroxides and oxides on the zinc surface. This fact leads to a dramatic decrease of the cathodic current densities and, therefore, to a reduction the overall corrosion processes. On the other hand, the potential of cerium oxides as corrosion inhibitors was also proposed. However, the real effectiveness of this kind of anticorrosive pigments has not been clarified yet.
Progress in Organic Coatings, 2020
Pigments are considered as the major content of paints that can help in preventing corrosion. In this work, epoxy based pait system was applied on reinforced concrete steel to evaluate its anticorrosive performance. This system is based on new core-shell pigments which are composed of a core of different calcium carbonate sources (natural calcite, marble waste and eggshell) covered with thin shell of zinc ferrite to compare their anticorrosive effect. The corrosion resistance of the coatings was evaluated in 3.5 % NaCl for 28 days via two electrochemical methods; open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). The measurements revealed that coated concrete steel with paints containing zinc ferrite/marble was the best in its corrosion protection performance showing that although the cores are all based on calcium carbonate, the source can affect the performance.
Efficiency of certain chromate-free pigments for the corrosion protection of galvanized steel
Materials Science
By using electrochemical methods of a.c. and d,c. and electron microscopy, we investigated the corrosion behavior of galvanized steel in a slightly acid medium that simulates atmospheric precipitation and contains extracts of chromate and chromate-free pigments. We established that the joint use of phosphate and calcium-containing pigments can ensure efficient corrosion protection on a par with chromate pigments due to the formation of a phosphate film with high barrier properties on a metal. A galvanized steel sheet painted under laboratory conditions is widely used for the production of roofs and the facing of walls [l]. The varnish-paint coating applied to it consists of a primer and a top layer. To improve the protective properties, anticorrosive pigments (very often, toxic chromates) are added to the primer. For this reason, there is an intensive search for alternatives to chromate corrosion inhibitors of metals. Phosphate pigments are rather promising substitutes for chromates. They belong to nonoxidized inhibitors of the anodic type, and the efficiency of their protection depends on the amount of oxygen in a corrosive medium [2]. However, in the presence of ions of metal, phosphates can work;as cathodic inhibitors by depositing a protective film with barrier properties on the surface of the metal. According to the data presented in [3], bivalent ions of calcium and zinc increase the anticorrosive efficiency of polyphosphates. This is explairied by the formation of a barrier layer on cathodic sections that retards the free ingress of oxygen to the surface of iron. By using the method of potentiokinetic polarization of iron in a diluted aerated orthophosphate solution, one established in [4] that the addition of a small amount of calcium salts leads to inhibition of the cathodic reaction due to the appearance of a film of slightly soluble calcium phosphates on the surface of the metal, which restricts the ingress of oxygen to the surface of the metal. One can form a film with protective properties on the surface of metal in corrosive solutions containing phosphate inhibitors and calcium salts. However, the behavior of inhibitors dissolved in corrosive media considerably differs from the behavior of anticorrosive pigments dispersed in an organic coating. As a rule, they are slightly soluble and their action is screened by a polymeric binder. The aim of the present work is to study the efficiency of the inhibition of corrosion of a hot-galvanized steel by chromate-free pigments that are dissolved in a medium followed by the formation of ions of calcium and phosphate. Materials and Testing Procedure We used electrochemical impedance spectroscopy. Tests were carried out in a three-electrode electrochemical cell with a working area of 4.5 cm 2. We use a calomel electrode as the reference one and a platinum electrode as the operating one. We carried out measurements with an ASM potentiostat and a Solartron frequency response analyzer 1250 at the corrosion potential by applying a.c. with an amplitude of 10mV and a frequency from 10,000 to 0.005 Hz to the specimen. We processed impedance spectra by the Boukamp method [5]. Simultaneously, we recorded potentiodynamic polarization curves with an AutoTafel device. We performed all electrochemical measurements in a corrosion solution with inhibiting pigments that simulates acid rain precipitation in European countries [6]. We used phosphate (A), calcium-containing (B), and control chromate (C) pigments. To make saturated solutions-extracts, we added 2 g of each pigment to 1 liter of an acid rain solution and used a magnetic mixer. After a day, they were twice filtered to remove the undissolved fraction. In a
Progress in organic coatings, 1995
The inhibition efficiencies of zinc chromate, barium metaborate, calcium silicate, amino carboxylate, calcium barium phosphosilicate, aluminum triphosphate and a modified zinc phosphate on the corrosion of steel and zinc were determined by polarization experiments on pigment extracts. Zinc phosphate and zinc chromate were the best and were studied further to determine the effect of pH and chloride concentration on their inhibition of steel. Zinc chromate is adversely affected by high concentration of chloride ions, which effect seems to be less pronounced on zinc. A low pH, although increasing the solubility of zinc phosphate, does not increase its efficiency. The pigments were also incorporated into an epoxy-poly(amide) binder, applied to cold-rolled steel and galvanized steel, exposed at a marine exposure station and the degradation monitored by electrochemical impedance spectroscopy. There was a general correlation between the results of pigment extract studies and atmospheric exposure except in the case of phosphate pigments on cold rolled steel.