Review on Research and Progress of Corrosion Inhibitors

Transcription

1 Applied Mechanics and Materials Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Review on Research and Progress of Corrosion Inhibitors Xiaodong Zhao 1,2, a, Jie Yang 1, b and Xiqiu Fan 1, c 1 School of Electromechanical Engineering, Zhejiang Ocean University, Zhoushan, ,China 2 Institute of Oceanology, Chinese Academy of Sciences, Qingdao,266071,China a b c Pdanielxdzhao@yahoo.com.cn, P Pkittyangj@yahoo.com.cn, P Pxiqiufan@163.com Keywords: Corrosion inhibitor, Inhibition mechanism, Evaluation. Abstract. In this paper, research and progress of corrosion inhibitors are reviewed from the aspects of history, classification, inhibition mechanism, evaluation methods and development trend. It is of great theoretical significance and high social and economic value for development of new efficient and low toxicity corrosion inhibitor and deep research on the inhibition mechanism. Introduction Corrosion inhibitors refer to the chemical substances or compounds existing in the media with appropriate concentration and state, preventing or slowing down the corrosion of material (ASTM). It is one of the effective means to prevent metals from corrosion with proper use and addition of inhibitors. With a small amount of such substances corrosion rate of the metal in the medium significantly decreases, even to be zero, while the material maintains the original physical and mechanical properties. In 1860, the world's first patented corrosion inhibitor published in UK, "inhibitor for pickled plate", declared the era of research and application of corrosion inhibitor. Overview of Research on Inhibitor As early as in the mid-19th century, inhibitor had been used during acid pickling for rust and contamination removal technology. In 1870s pickling inhibitors for nonferrous metals (Cu, Zn, etc.) appeared. Among the various, large numbers of substances with corrosion inhibition effect, some products have been widely used for metal pickling, acid transportation and storage and protection from air and industrial medium, etc. Corrosion inhibitors in acid medium in early studies used to be raw materials and processed products of animals and plants, such as syrup, vegetable oil, bone glue, gelatin, etc. In the early 20th century, significant progress had been made in inhibitor research and corrosion materials changed from natural substances to minerals, such as coal tar, silicate, nitrate, chromate, etc. That is, organic material containing nitrogen, sulfur and oxygen had begun to be separated from the minerals and served as inhibitors. In the middle 1930s, synthetic organic corrosion inhibitor achieved success, which was regarded as a breakthrough in corrosion inhibitor technology, and a large number of organic substances were increasingly used for corrosion inhibitors in acid media. At the same time, inorganic corrosion inhibitors with high performance were used in the neutral medium, seawater, industrial water and other fields. With the application of corrosion inhibitor in industry, research on inhibition mechanism was increasingly developed, such as physical adsorption, chemical adsorption and integrated adsorption theory proposed in the 1950s. In the 1960s, scientists devoted to theoretical research in terms of molecule design of inhibitors, which promoted the development of the inhibitor theory, followed by a large number of high-performance corrosion inhibitor applied in industry. With the industrial pollution of the environment, inorganic corrosion inhibitors without pollution to ecological environment were on the focus in the 1970s. And with the use of high polymer corrosion inhibitors, scientists had begun to study organic inhibitors without pollution. In recent years, the concept of green chemistry being proposed, corrosion inhibitor has been developed in the performance and economics oriented and environment-friendly direction. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-06/03/16,16:50:05)

2 4064 Frontiers of Manufacturing and Design Science Inhibitors have been used for nearly one and a half century, and extensive research has been carried out about various inhibitors. However, inhibitor has its limitation, that is, certain corrosion inhibitor is effective only in a few media for some kinds of materials, but not very effective in other media, or even harmful. The inhibition effects of many organic inhibitors are mainly influenced by chemical structure, which vary greatly due to the different structure and different environment or media. Therefore, as new materials and corrosive environment continuously emerge, there is still an urgent requirement for new corrosion inhibitors. Classification and Inhibition Mechanism In view of the wide range, complex mechanism and extensive applications of corrosion inhibitors, at present there is no a unified classification yet. Based on the inhibition mechanism, the most common classifications are as the following. Classification according to the mechanism of electrochemical process. Electrochemical process of metal corrosion includes cathodic and anodic process. According to whether the inhibitor in the medium mainly inhibits the cathodic reaction or anodic reaction, or the both simultaneously, corrosion inhibitors can be divided into the following three categories: (a)cathodic type inhibitor. The addition of cathodic type inhibitor increases the polarization extent of cathode process, thus inhibiting the cathodic reaction. The rate of cathodic reaction decreases, resulting in the negative offset of corrosion potential of the conjugated system and the decrease of the corrosion current correspondingly. As cathodic type inhibitor, the positive ions generally move towards the cathode surface and generate a protective film or cover layer, increasing the polarization of cathodic process. This type of inhibitor causes the negative offset of corrosion potential, and insufficiency of addition results in lower efficiency of corrosion inhibition other than the acceleration of metal corrosion. Therefore, the cathodic corrosion inhibitor is also called "safe inhibitor", such as calcium carbonate, zinc sulfate, polyphosphate, arsenic ions and antimony ions. (b)anodic type inhibitor. Anodic type inhibitor can inhibit the anodic reaction, increase polarization, reduce the anodic reaction rate and induce the positive offset of corrosion potential. As these inhibitors, the negative ions generally move towards the anode surface and promote passivation, reducing the corrosion rate. When the addition content of this type of inhibitors is insufficient, the passivation layer generated can not fully cover the anode surface. Then the area of anode without protection is much smaller than that of cathode, resulting in a "large cathode-small anode" corrosion battery, which accelerates the corrosion of metals. Therefore, the anodic type inhibitor is also known as "hazardous inhibitor", such as nitrite, silicate, chromate, phosphate and so on. (c)mixed type inhibitor. Such inhibitors can inhibit the anode and cathode process simultaneously, while increase the cathodic and anodic polarization, and reduce the anode and cathode reaction rate, resulting in a large decrease of the corrosion current. As the cathode and anode polarization both increase, the corrosion potential changes little. Examples of this type of inhibitors are nitrogen-containing organic compounds(such as amines and amine nitrite), sulfur-containing organic compounds(such as thiol, thioether), and nitrogen, sulfur compounds(such as thiourea and their derivants). Classification according to the layer structure on metal surface. The inhibition effect of inhibitor on the electrode in electrolyte solution is due to that the inhibitor or the electrolyte with it act on the metal surface and change the surface. This change can be represented as adsorption of oxide film and precipitation film, or adsorption of ions, molecules on metal surface. From the physical chemistry point of view, the effect of inhibitors can be divided into three types: oxide film, precipitation film and adsorption film. (a)oxide film inhibitor. Such inhibitors can oxidize metal directly or indirectly, forming a passive oxide film on the metal surface, or fix the original unsound oxide film with the deoxidation product of corrosion inhibitor, resulting in the inhibition of metal ionization process, which reduce the corrosion of metals. These inhibitors generally have a passivation effect for metals, also known as passivants. Oxide-film type inhibitor has high inhibition efficiency and good performance, but insufficiency of addition may result in pitting corrosion as

3 Applied Mechanics and Materials Vols "large cathode-small anode" formed on the metal surface. This type of inhibitor is also known as "hazardous inhibitor", including dichromate, chromate, potassium permanganate, nitrate, nitrite and other inorganic corrosion inhibitors. (b)precipitation film inhibitor. Precipitation film inhibitor can react with the ions in medium (such as calcium, iron ions, etc) or metal ions in the corrosion product layer and generate precipitation film attached to the metal surface. Precipitation film covers the cathode surface and inhibits the cathode process of electrochemical corrosion, in this case are phosphates, polyphosphates, organic phosphates, silicate, etc. Sometimes the film can cover the entire metal surface, inhibiting both anode and cathode process of electrochemical corrosion of metal. For example, some complexing agents containing oxygen, sulfur and nitrogen atom groups are able to react with the metal ions, forming precipitation film of insoluble complexes, simultaneously inhibiting the electrochemical process. (c)adsorption film inhibitor. Adsorption film inhibitors are mostly organic corrosion inhibitors. Such inhibitors have good absorbability on the metal surface in the corrosive medium, which changes the nature of the metal surface and inhibits the metal corrosion. When adsorption film inhibitor is added to the medium and located on active sites by adsorption, on the one hand, the charge state and interface property of the metal surface are changed, the energy state on the surface remaining stable, the activation energy of corrosion reaction increasing, and the corrosion rate slowing down. On the other hand, nonpolar groups of the inhibitor molecule adsorbed can form a hydrophobic protective film on metal surface and suppress the corrosion related transfer of the charge or material, reducing the corrosion area as well as the corrosion rate. Most organic inhibitors contain polar groups centered by atoms of nitrogen, oxygen, sulfur and phosphorus, such as amines, aldehydes, alkynol, organic phosphorus compounds, sulfoacid, carboxylic acid and their salts, organic sulfur compounds, heterocyclic compounds, has a certain capacity of supplying electrons. Coordination bond is formed and chemical adsorption occurs, with corrosion inhibitor covering on the metal surface, blocking the contact between the metal surface and the acidic media, resulting in the effect of inhibition[1~8]. Evaluation of Corrosion Inhibitor Weight loss method. Weight loss test is the most classic and important means for performance evaluation of corrosion inhibitor, by which the corrosion rate is determined through measuring the quality change of the metal specimens immersed in corrosion medium after a certain time, reflecting the average corrosion during a period of time. Weight loss test adapted to general corrosion is the basic method of measuring corrosion while it is convenient, visual and easy-operational. In addition to used for evaluation and preparation by screening of inhibitors widely, in most cases it serves as a kind of standard method to verify the accuracy of other test methods. Electrochemical method. Corrosion and inhibition of it are electrochemical in essence, and inhibition results from the adsorption of material on the electrochemical interface. The inhibition process of inhibitor on the metal corrosion is also the inhibited process of electrochemical reaction; therefore, various electrochemical methods should be used to track the change of metal corrosion rate and the electrochemical behavior on the metal electrode surface. In addition, the modernization of electrochemical technique gives prominence to its quick, simple, information-rich features and electrochemical method has become the basic and important means for study of inhibitors on the behavior and mechanism of metal corrosion. The most often used electrochemical methods for corrosion inhibitor are electrochemical impedance spectroscopy(eis), potentiodynamic polarization and constant electric quality, etc. Scanning electron microscopy(sem). SEM has large depth of field, good stereoscopic sensation, wide-range magnification, continuously adjustability, high resolution, large sample room space and so on advantages with simple sample preparation, which is an effective tool for the study of surface analysis. The basic principle is the focusing and imaging using electron beam. That is, secondary electrons from the excitation of the sample surface atoms by the incident electron beam are received and modulated by electronic detectors, resulting in images. Secondary electrons have low energy,

4 4066 Frontiers of Manufacturing and Design Science move in the form of curves and are detectable. Therefore SEM is able to accurately reflect the uneven surface topography, which is very suitable for the observation of surface morphology of specimen after corrosion. Development Trend of Corrosion Inhibitor Corrosion inhibitor is very important in the metal corrosion protection work and plays an increasingly important role in the development of national economy. In view of the corrosion protection of thermal equipment and other industrial field, application of inhibitor is an effective, economic means. Progress has been made on the inhibitor development in terms of the theory, testing techniques and methods, which have greatly promoted the exploitation and application of new products of inhibitors. Further work should be focused on these aspects: research on the inhibition mechanism and relationship between molecular structure and inhibition effect, design and synthesis of new efficient and low toxicity corrosion inhibitor; manufacture of easily biodegradable corrosion inhibitor using natural raw materials thereby expanding the application field of corrosion inhibitor; manufacture of low cost, environmentally friendly pickling corrosion inhibitor from industrial by-products of chemical, pharmaceutical industry; research on pickling inhibitor additives. In short, technology development and application of corrosion inhibitor should be oriented to highly efficient, multi-functional (such as corrosion inhibition, scale inhibition, rot resistance, sterilization, etc.), non-toxic, pollution-free direction to achieve more great progress in cooperation with industry departments and international cooperation and exchanges in research. Development trend of inhibitor science requires not only exploitation of new corrosion inhibitor compounds with high efficiency and low toxicity, but also thorough understanding and explanation of mechanism and relationship between molecular structure and inhibition effect with various modern testing means and theoretical chemical analysis to guide the development of application and practice. Therefore, it is undoubtedly of great theoretical significance and high social and economic value for development of new efficient and low toxicity corrosion inhibitor and deep research on the inhibition mechanism. Acknowledgement This material is based upon work funded by Program of Department of Education of Zhejiang Province(Y )and Program of Science and Technology Department of Zhejiang Province(No.2008C14096, No.2009C11148 ). References [1] M. Vishnudevan, M. Natesan: Bulletin of Electrochemistry Vol.16(2000), p [2] S. Sathiyanarayanan, C. Marikkannu: Applied Surface Science Vol.241(2005), p [3] M.A. Pech-Canul, M.Echeverria: Corrosion Engineering Science and Technology Vol.38(2003), p [4] E. S. Ferreira, C. Giacomelli: Materials Chemistry and Physics Vol.83(2004), p [5] F. C. Giacomelli: Materials Chemistry and Physics Vol. 83(2004), p [6] M. A.Quraishi: Materials Chemistry and Physics Vol.77(2003), p [7] M. Lebrini, M. Lagrenée: Corrosion Science Vol.47(2005), p [8] F. Bentiss, M. Lebrini: Materials Chemistry and Physics Vol.87(2004), p

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