**1. Introduction**

174 Corrosion Resistance

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DOI**:** 10.1021/ie9015039

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The word corrosion is as old as the earth, but it has been known by different names.

Corrosion is known commonly as rust, an undesirable phenomena which destroys the luster and beauty of objects and shortens their life. A Roman philosopher, Pliny (AD 23-79) wrote about the destruction of iron in his essay 'Ferrum Corrumpitar'. Corrosion since ancient times has affected not only the quality of daily lives of people, but also their technical progress. There is a historical record of observation of corrosion by several writers, philosophers and scientists, but there was little curiosity regarding the causes and mechanism of corrosion until Robert Boyle wrote his 'Mechanical Origin of Corrosiveness.'

Philosophers, writers and scientists observed corrosion and mentioned it in their writings:


The most important contributions were later made by Faraday (1791-1867) who established a quantitative relationship between chemical action and electric current. Faraday's first and second laws are the basis for calculation of corrosion rates of metals. Ideas on corrosion control started to be generated at the beginning of nineteenth century. Whitney (1903) provided a scientific basis for corrosion control based on electrochemical observation. As

Comparative Study of Porphyrin Systems Used as Corrosion Inhibitors 177

inorganic matrixes because such a hostguest approach can improve the efficiency of photoinduced charge separation by preventing back electron transfer. Moreover, organicinorganic composite materials sometimes offer unique properties that are not available in

In this paper we intend to test the corrosion resistance of two other types of organic inhibitors and to study in which conditions they behave similarly to an anticorrosive paint. The corrosion resistance was studied by cyclic voltammetry, in 20% Na2SO4 electrolyte solution, Tafel tests and in the salt spray chamber, using diverse exposure conditions.

Fig. 1. Structure of 5,10,15,20 tetrakis(1-methyl-4pyridyl)21H,23H-porphine,tetra-p-fosylate

Fig. 2. Structure of 4,4',4',4'''(porphine-5,10,15,20-tetrayl)-tetrakis (benzeric sulfonic acid).

The initial data consisted of 2 types of porphyrins dissolved KOH, H2SO4 and benzonitrile,

a. 0.2 g of Na4TFP Ac porphyrin (C44H26N4Na4O12S4 × H2O) dissolved in 40 ml 10% KOH,

The two types of organic inhibitors used in this study for comparison are:


any of the individual parts.[ Bose et al,2002].

salt.

**2. Experimental** 

as presented bellow, as the first set:

mentioned as system A.

early as in eighteenth century it was observed that iron corrodes rapidly in dilute nitric acid but remains intact in concentrated nitric acid. Schonbein in 1836 showed that iron could be made passive. It was left to U.R. Evans to provide a modern understanding of the causes and control of corrosion based on his classical electrochemical theory in 1923. Corrosion laboratories established in M.I.T., USA and University of Cambridge, UK, contributed significantly to the growth and development of corrosion science and technology as a multi disciplinary subject. In recent years, corrosion science and engineering has become an integral part of engineering education globally. [Ahmad, 2006]

The strong damaging effects of corrosion require establishing and taking some control measures. In accordance with the ways in which corrosion manifest, the supporting material and the specific local conditions, corrosion control can take different forms. Surely that here should also be added the use of materials maximum resistant to corrosive environment in order to limit the corrosion effects.

The practice of corrosion prevention by adding substances which can significantly retard corrosion when added in small amounts is called inhibition. Inhibition is used internally with carbon steel pipes and vessels as an economic control alternative to stainless steels and alloys, and to coatings on non-metallic components. One unique advantage is that adding inhibitor can be implemented without disruption of a process. The addition of an inhibitor (any reagent capable of converting an active corrosion process into a passive process) results in significant suppression of corrosion.

Corrosion inhibitors are substances when added in small amounts in a corrosive environment reduces significantly the corrosion rate for metallic material in contact with the environment.

A typical good corrosion inhibitor will give 95% inhibition at concentration of 80ppm, and 90% at 40ppm. Some of the mechanism of its effect are formation of a passivation layer (a thin film on the surface of the material that stops access of the corrosive substance to the metal), inhibiting either the oxidation or reduction part of the redox corrosion system (anodic and cathodic inhibitors), or scavenging the dissolved oxygen.

Some corrosion inhibitors are hexamine, phenylenediamine, dimethythanolamine, sodium nitrite, cinnamaldehyde, condensation products of aldehydes and amines, chromates, nitrites, phosphates, hydrazine, ascorbic acid, and others.

The corrosion inhibitors are added not only in aqueous solutions, but also in oils and fuels, the liquid cooling etc. can also be organic additives and coatings (varnishes, paints) on metallic surfaces.

The presence of a chemical compound in an environment, even in small concentrations, can lead to significant changes in speed and form of corrosion of a metallic material in contact with the environment. The acceleration or inhibition of corrosion processes are specific methods, dependent of metal-corrosive environment characteristics.

Corrosion inhibitors are selected on the basis of solubility or dispersibility in the fluids which are to be inhibited.[ Rahimi,2004]

Porphyrins are well-known for their biological, catalytic, and photochemical properties. Considerable effort has been devoted to confining porphyrin molecules in microporous

early as in eighteenth century it was observed that iron corrodes rapidly in dilute nitric acid but remains intact in concentrated nitric acid. Schonbein in 1836 showed that iron could be made passive. It was left to U.R. Evans to provide a modern understanding of the causes and control of corrosion based on his classical electrochemical theory in 1923. Corrosion laboratories established in M.I.T., USA and University of Cambridge, UK, contributed significantly to the growth and development of corrosion science and technology as a multi disciplinary subject. In recent years, corrosion science and engineering has become an

The strong damaging effects of corrosion require establishing and taking some control measures. In accordance with the ways in which corrosion manifest, the supporting material and the specific local conditions, corrosion control can take different forms. Surely that here should also be added the use of materials maximum resistant to corrosive environment in

The practice of corrosion prevention by adding substances which can significantly retard corrosion when added in small amounts is called inhibition. Inhibition is used internally with carbon steel pipes and vessels as an economic control alternative to stainless steels and alloys, and to coatings on non-metallic components. One unique advantage is that adding inhibitor can be implemented without disruption of a process. The addition of an inhibitor (any reagent capable of converting an active corrosion process into a passive process) results

Corrosion inhibitors are substances when added in small amounts in a corrosive environment reduces significantly the corrosion rate for metallic material in contact with the

A typical good corrosion inhibitor will give 95% inhibition at concentration of 80ppm, and 90% at 40ppm. Some of the mechanism of its effect are formation of a passivation layer (a thin film on the surface of the material that stops access of the corrosive substance to the metal), inhibiting either the oxidation or reduction part of the redox corrosion system

Some corrosion inhibitors are hexamine, phenylenediamine, dimethythanolamine, sodium nitrite, cinnamaldehyde, condensation products of aldehydes and amines, chromates,

The corrosion inhibitors are added not only in aqueous solutions, but also in oils and fuels, the liquid cooling etc. can also be organic additives and coatings (varnishes, paints) on

The presence of a chemical compound in an environment, even in small concentrations, can lead to significant changes in speed and form of corrosion of a metallic material in contact with the environment. The acceleration or inhibition of corrosion processes are specific

Corrosion inhibitors are selected on the basis of solubility or dispersibility in the fluids

Porphyrins are well-known for their biological, catalytic, and photochemical properties. Considerable effort has been devoted to confining porphyrin molecules in microporous

(anodic and cathodic inhibitors), or scavenging the dissolved oxygen.

methods, dependent of metal-corrosive environment characteristics.

nitrites, phosphates, hydrazine, ascorbic acid, and others.

integral part of engineering education globally. [Ahmad, 2006]

order to limit the corrosion effects.

in significant suppression of corrosion.

which are to be inhibited.[ Rahimi,2004]

environment.

metallic surfaces.

inorganic matrixes because such a hostguest approach can improve the efficiency of photoinduced charge separation by preventing back electron transfer. Moreover, organicinorganic composite materials sometimes offer unique properties that are not available in any of the individual parts.[ Bose et al,2002].

In this paper we intend to test the corrosion resistance of two other types of organic inhibitors and to study in which conditions they behave similarly to an anticorrosive paint. The corrosion resistance was studied by cyclic voltammetry, in 20% Na2SO4 electrolyte solution, Tafel tests and in the salt spray chamber, using diverse exposure conditions.

The two types of organic inhibitors used in this study for comparison are:


Fig. 1. Structure of 5,10,15,20 tetrakis(1-methyl-4pyridyl)21H,23H-porphine,tetra-p-fosylate salt.

Fig. 2. Structure of 4,4',4',4'''(porphine-5,10,15,20-tetrayl)-tetrakis (benzeric sulfonic acid).
