Volume 36, Issue 3

The objective of this review is to create a body of knowledge on the theoretical and practical aspects of corrosion inhibition to prevent and/or to eliminate corrosion in natural environments such as water, air, and acids and in industrial facilities such as oil, natural gas, concrete, paints and coatings, electronics, and military equipment. Corrosion inhibitors (CIs) and volatile corrosion inhibitors (VCIs) are applied in diverse forms such as powders, pellets, aqueous, or solvent solutions and in impregnated papers; closed in pouches and sachets; and added to coatings. Natural CIs are extracted by water or organic solvents from suitable plants. They represent the advanced trends of corrosion management based on green chemistry.

There has been a strong interest worldwide in developing suitable technologies that can derive chemicals and materials from renewable biomass in a number of applications, including corrosion inhibitors. In spite of the efficacy of conventional inhibitors in corrosion control, current corrosion inhibitors exhibit toxicity and/or are non-biodegradable. Therefore, industry efforts are leading to the development of non-toxic and environmentally friendly “green” corrosion inhibitors from renewable resources. Extensive studies of different bio-based inhibitors show that a vast number of phytochemicals can be used as efficient corrosion inhibitors. This paper provides a comprehensive review of the corrosion inhibition properties of plant-derived chemicals classified under the parameters provided by botanical chemistry.

Phosphoric acid has been used in many industrial applications and can be in contact with a lot chemical and petrochemical equipment. Most of this equipment is made of steel alloys that may be damaged because of contact with acid. Corrosion inhibitors can be used for to protect steel alloys against several forms and various environments of corrosion. In this paper, the efficiency and applications of organic and inorganic inhibitors in different environments of phosphoric acid are investigated. More than 40 papers were collected and reviewed. Surveys of the stated works in phosphoric acid environments are documented. It was concluded that organic inhibitors performed as good corrosion inhibitors and are used widely. The use of inorganic inhibitors was limited. Most of studied inhibitors follow Langmuir’s adsorption isotherm, and the mechanism of the inhibition can be ascribed to the mixed effect on cathodic and anodic reactions. The synergistic effect was also addressed in the present work.

The selective dissolution of ferrite phase from the pearlite was studied in fuel-grade ethanol (FGE) to understand how it affects the stress corrosion cracking (SCC) mechanism of carbon steel in FGE. It was shown that microgalvanic coupling occurs between ferrite and cementite phases of the pearlite, leading to localized corrosion, which affects the SCC mechanism. The intergranular SCC mechanism stops at the pearlite, and the selective dissolution promotes the transgranular SCC mechanism. Cathodic polarization curves were measured for pure iron and cementite exposed to various FGE conditions. According to the results, cementite phase is, in most cases, a more favorable cathode in FGE.

Corrosion inhibitors with Cr +6 and Cr +3 are applied on the surface of metals to increase their chemical resistance when they are exposed to severe degradation conditions. For galvanized low-carbon steel strip, these compounds are applied to reduce corrosion mainly during transport operations of this metal. The performance of corrosion inhibitors deposited on the surface of galvanized steel strip was evaluated through combined physical and electrochemical modeling. The physical model takes into account direct exposure of specimens to different conditions including simulated marine, industrial and rain environments for periods up to 8 weeks. The efficacy of the experimental method was also evaluated using polarization resistance and gravimetric means. A good correlation between the evolution of the degradation phenomenon obtained directly from the physical model and the electrochemical and gravimetric data was found. The results showed that this method is an effective tool that allows the comparison of the performance of different corrosion inhibitors that could be used to prevent surface degradation of galvanized steel strip.

The aim of this paper was to evaluate the performance of two different modified zeolitic minerals as anticorrosion pigments in order to reduce or eliminate zinc phosphate in paints. In the first stage, the selected minerals were characterized and modified with cerium ions to obtain the anticorrosion pigments. Their inhibitive properties were evaluated by means of electrochemical techniques (corrosion potential measurements and polarization curves) employing a steel electrode immersed in the pigments suspensions. In the second stage, solvent-borne paints, with 30% by volume of the anticorrosion pigment, with respect of the total pigment content, were formulated. The performance of the resulting paints was assessed by accelerated (salt spray and humidity chambers) and electrochemical tests (corrosion potential measurements and electrochemical impedance spectroscopy) and compared with that of a control paint with 30% by volume of zinc phosphate. Results obtained in this research suggested that zeolites can be used as carriers for passivating ions in the manufacture of anticorrosion paints with at least reduced zinc phosphate content.