Inhibition of corrosion

The corrosion rate of metals may be reduced by the addition of inorganic or organic compounds, called inhibitors, to their environment. The inhibitor efficiency T is defined as the relative reduction of the corrosion current density  

The detailed mechanism is often not fully understood. A blocking of active sites is often postulated for anodic dissolution or cathodic reduction of redox systems. However, the conclusions were mostly drawn indirectly from electrokinetic data, and a detailed investigation with surface analytical methods is still missing. The chemical reaction steps and their inhibition at surface sites should be further investigated systematically by methods like XPS, AES, STM, SFM, etc. Most of the knowledge is still empiric. However, the results of electrochemical investigations are very valuable for a better corrosion protection of materials in industrial applications. Some few principles of inhibition are discussed in the following sections. 

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Because the heat distortion temperature of cured epoxy resins (qv) increases with the functionality of the curing agents, pyromellitic dianhydride is used to cross-link epoxy resins for elevated temperature service. The dianhydride may be added as a dispersion of micropulverized powder in liquid epoxy resin or as a glycol adduct (158). Such epoxies may be used as an insulating layer in printed circuit boards to improve heat resistance (159). Other uses include inhibition of corrosion (160,161), hot melt traffic paints (162), azo pigments (163), adhesives (164), and photoresist compounds (165). 

Complete inhibition of corrosion in waters containing high concentrations of chloride is difficult, if not impossible to achieve economically. Despite this, many such systems make use of inhibitors to give marked reductions in corrosion rates. 

All of these three properties of the oxide films on metals are influenced by the anion composition and pH of the solution. In addition the potential of the metal will depend on the presence of oxidising agents in the solution. Inhibition of corrosion by anions thus requires an appropriate combination of anions, pH and oxidising agent in the solution so that the oxide film on the metal is stable (the potential then lying between the Flade potential and the breakdown potential), and protective (the corrosion current through the oxide being low). 

Adsorption is, of course, of major importance in the inhibition of corrosion by organic compounds (adsorption inhibitors) that have the ability to adsorb strongly on the metal surface, thus impeding the dissolution reaction and reducing the corrosion rate. It follows that the coverage of a metal surface by adsorbed inhibitor can be evaluated from the relationship... 

G. Trabanelli, F. Zucchi, and G. Brunoro. Inhibition of corrosion resistant alloys in hot hydrochloric acid solutions. Werkstoffe Korrosion, 39(12) 589-594, December 1988. 

Determination Test, Weight loss test, Eschke test, Salt spray test and Sulphur dioxide test at 50°C. Mechanism of inhibition of corrosion and surface study of mild steel was also studied by Metallurgical Resesarch Microscopy and Scanning electron Microscopy. 

Abstract The flotation mechanism is discussed in the terms of corrosive electrochemistry in this chapter. In corrosion the disolution of minerals is called self-corrosion. And the reaction between reagents and minerals is treated as inhibition of corrosion. The stronger the ability of inhibiting the corrosion of minerals, the stronger the reagents react with minerals. The two major tools implied in the research of electrochemical corrosion are polarization curves and EIS (electrochemistry impedance spectrum). With these tools, pyrite, galena and sphalerite are discussed under different conditions respectively, including interactions between collector with them and the difference of oxidation of minerals in NaOH solution and in lime. And the results obtained from this research are in accordance with those from other conventional research. With this research some new information can be obtained while it is impossible for other methods. 

The ditetrazolium salts (309) have been patented for use in electrochromic electrodes which are used in display devices <89JAP01230026) and tetrazolium salts have also been developed for cell bioassays for neurotoxins active on voltage-sensitive sodium channels <93MI 417-03). Tests for inhibition of corrosion of zinc and brass carried out on 5-aminotetrazole showed it to be ineffective relative to other azoles <86MI 417-01). A number of tetrazoles including the 5-amino, 5-methyl, and 5-phenyl derivatives have been separately incorporated into surfactants used for corrosion inhibition with copper in water <9lMl4l7-07). Photopolymerizable resin compositions which are highly resistant... 

The above sections outlined two methods for the inhibition of corrosion. One (cathodic protection) is entirely electrochemical in nature and consists in moving the... 

In this lecture I will deal with the mechanisms involved in first, the dissolution or corrosion of iron and second, in the inhibition of corrosion by the formation of various types of oxide films. A few definitions will help to focus attention on the specific nature of my subject. 

The study of such transfer processes was one of the purposes of a fairly extensive investigation of the inhibition of corrosion of iron in hydrochloric acid by acetylenic corrosion inhibitors. The parameters of this investigation were the concentration of the acid, the concentration of the inhibitor, the flow rate and the oxygen concentration in the corrosive medium. While most of the experimental data were obtained by means of the so called resistance probe, polarization measurements were carried out in order to elucidate some of the more peculiar results. The experimental arrangement is more fully explained in (2H). 

The inhibition of corrosion in defects of organic coatings could be shown by means of scanning reference electrode techniques [139, 140]. Recently, Zou and... 

B.N. Popov, G. Zheng, R.E. White, Surface treatment for inhibition of corrosion and hydrogen penetration of type 718 aUoy, Corrosion 50 (1994) 613-619. 

In the case of IRB, the results of a piece of research concluded that the static or nonstatic regime of the environment could have a profound effect on acceleration or inhibition of corrosion. As may be inferred from this research, if the system is closed so that dilution of ferrous ions is not happening, corrosion may be slowed down otherwise, in an open system where dilution of ferrous ions is possible, corrosion acceleration can be expected. 

Al-Rawajfeh, A. E. Al-Shamaileh, E. M. Inhibition of corrosion in steel water pipes by ammonium pyrrolidine dithiocarbamate (APDTC). Desalination 206 (2007) 169. 

Ahmad, N, MacDiarmid, AG. 1996. Inhibition of Corrosion of Steels with the Exploitation of Conducting Polymers. Synth. Met., 78,103. 

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