Corrosion Phenomena - Research Paper Example

Corrosion Phenomena Corrosion phenomena have been in existence for as long as the earth has existed. Commonly referred to as rust, the phenomenon is known to destroy the luster of objects and consequently shorten their lifespan. This paper borrows from various secondary sources to articulate the various forms of corrosion phenomena, determine the consequences and analyze the technological and chemical advances made in containing the problem, appreciating that controlling it could be almost impractical. Introduction Since the ancient days, corrosion has been noted to destroy the quality of lives and the technical progress of human beings. Historical evidence indicates that corrosion existed from prehistoric times but the causes were not curiously articulated. Important contribution could be attributed to Faraday (1791 to 1867) who related chemical action to electric current (Ahmad, 2006). This makes it possible to calculate the rate of corrosion using the first and second laws of Faraday. It was this electrochemical observation of corrosion that led to determination of scientific approach in controlling corrosion by Whitney in 1903. In the early eighteenth century, iron was observed to rapidly corrode in dilute nitric acid but in concentrated nitric acid, it remained intact. It was Evans who in 1923 through his classical electrochemical theory introduced the modern understanding of the phenomenon of corrosion with corrosion laboratories being established to allow for multidisciplinary contribution to the existent knowledge. Corrosion has been defined by Sivasankar as “the deterioration and ultimate destruction of a metal due to its reaction with the surrounding gaseous or liquid environment” (2008, p.467). Roussak and Gesser (2013) specifically define it as an electrochemical or chemical reaction involving a metal and the environment which deteriorates the metal and its properties. Thus, the definition notes that the process causes metals to exhibit natural tendencies of reverting back to native combined states as minerals such as carbonates, sulfides and oxides. Akhtar, Arif and Quraishi (2009) cite platinum and gold as the only ones that naturally exist as metals and would therefore not be susceptible to corrosion in normal atmospheric conditions, as such referred to as noble metals. Even though the term could be applied when referring to concrete, plastic and wood, it has found general application when referring to metal and particularly iron as steel. Metals would be susceptible to corrosion under different environmental conditions. For example, gold which exhibits resistance under atmospheric conditions would be corroded under ambient temperature and exposure to mercury. Iron on the other hand would gradually rust under atmospheric conditions but remains unaffected by mercury. Sivasankar (2008) documents the joint action of oxygen and moisture as constituting the normal atmospheric conditions. The scholar observes that steel in ice would not rust as water should be in liquid form for corrosion to occur. Common pollutants like dust particles, soot and ammonium sulfate particles and acidic gases like sulfur dioxide propagate the corrosiveness of the environment. Cicek and Al-Numan (2006) cite other typical environments considered to be corrosive and include soils, alkalies, acids, hydrogen sulfide, fuel gases, ammonia, fresh, salt, distilled and marine water and oxides of nitrogen. Types of Corrosion Phenomena Generally, all types of corrosion interrelate but take varied forms: it could be uniform or localized or could combine with other attacks forming more undesirable effects. This has been described by Roussak and Gesser (2013) as corrosion phenomena, which refers to corrosion-causing modifications on whatever part of a corrosion system. Uniform corrosion would be exhibited through even distribution of corrosion that causes the surface to be coated with the products of corrosion or clean. Ebadi, Basirun, Khaledi and Ali (2012) attribute this even distribution to cathodic and anodic sites on the surface of the metal. This form of attack makes fouling of metal a bigger problem as opposed to failure. But even though this form of corrosion phenomenon destroys structural materials to the greatest extent, it does not call for great concern because of the measurability of rate of attack by simple tests hence the predictability of plants and their components (Cicek & Al-Numan, 2006). The second form of corrosive phenomena considered as most destructive has been cited by Sivasankar (2008) as pitting. Pitting would result in localized attacks that would cause small holes to appear on a metal. This would be promoted by conditions of stagnant type and low velocity in which concentrated corrosive bubbles would form. It predominantly gets affected by chloride ions though Ahmad (2006) indicates that hypochlorites and bromides occasionally would propagate this action. Roussak and Gesser (2013) further contribute to this body of knowledge noting that alloys high in chromium reduce pitting corrosion as opposed to nickel which offers minimal resistance to this corrosion phenomenon. The difficulty in detection of this corrosion phenomenon has been attributed to the coverage of the pits by corrosion products by Cicek and Al-Numan (2011) and could take even years before they become visible. The acceleration of pitting increases once a pit forms on a metal. Galvanic corrosion occurs with the coming into contact of dissimilar metals and their immersion in a conductive medium leading to generation of an electric potential. This results in the increase in the rate of corrosion for the more active, known as anodic metal and decrease in the corrosion of the more noble, referred to as cathodic metal (Ebadi et al., 2012). The resultant corrosion could be localized or uniformly distributed. In this form of corrosion, an electrochemical series that has its basis on the standard thermodynamic data with regard to metals would be used to rank metals to show which one gets anodic and which gets cathodic in a galvanic couple. Galvanic effects would further be determined by the resistivity of environment and distance from cathodic and also area ratio effect. Erosion-corrosion would commonly occur in softer metals after the stripping away of the protective film where they would be attacked through abrasive affects of corrosive fluid on the metal surface (Poornima, Nayak & Shetty, 2012). As such, it would be characterized by waves, holes and grooves but with a directional pattern resulting from the removal of corrosion product, or solid metal in extreme cases, through mechanical processes or flow velocity. This form of corrosion has been said to be rapid and more commonly unexpected unless for tested alloys with appropriate conditions. Finally, microbial corrosion referring to the deterioration of metals through conventional corrosion processes, stimulated or modified by activity of living organisms could influence corrosion in varied environments including natural waters, sea waters, soil and in natural petroleum products. According to Roussak and Gesser (2013), microorganisms affect corrosion by influencing corrosion reactions directly, producing deposits and slimes that yield crevice corrosion and creating conditions that propagate corrosion through metabolic products. These could either be aerobic, requiring the presence of oxygen or anaerobic, possible in oxygen free environment. El-Lateef, Abbasov, Aliyeva and Ismayilov (2012) give the reaction occurring in anaerobic corrosion as: Fe2+ + CO2-3 FeCO3 Impact of Corrosion Phenomena It has been noted that corrosion reduces the luster of metals. For example, pure iron II hydroxide which occurs as white would be changed to a greenish hydrated iron III oxide due to partial oxidation in the air. 2Fe(OH)2 + H2O + ½O2 2Fe(OH)3 This equation represents other various forms through which corrosion could occur and thus impact on the quality of substances. One of these includes hydrogen permeation where hydrogen atoms diffuse into metals through vacancy mechanism or interstitial mechanism (Sethi, Chaturvedi, Upadhyay & Mathur, 2007). Interstitially, the atoms permeate through the interstitial sites without displacing the matrix atoms. The atoms could also jump into unoccupied sites, referred to as vacancies through vacancy mechanism. These bubbles trapped in such a metal could interfere with its transmitter performance. Sethi et al. (2007) acknowledge that corrosion phenomena could lead to consequences that could not be desirable among which include plant shutdowns which could negatively impact on consumers and industries. It could also lead to loss of products through leaking containers, fuel tanks, oil and water transportation lines and storage tanks which could cause severe hazards and accidents. Ahmad (2006) observes that more than 25% of water gets lost through such leakages. Similarly, corrosion products could cause contamination of dyes, pharmaceuticals and chemicals which could have dire consequences on consumers. The corrosion products that insulate pipelines and heat exchanger tubing cause loss of efficiency in piping capacity and heat transfer (El-Lateef et al., 2012). The magnitude in which corrosion occurs would be dependent on metal’s sensitivity to the specific environment. These consequences have been noted to pose adverse effects on the national economy, though to varied degrees from a country to another. Citing a survey conducted jointly by the National Association of Corrosion Engineers and the Federal Highway Agencies, Ahmad (2006) notes that corrosion phenomena directly costs the US about USD 276 billion of its gross domestic product. This cost could not be attributed to annual periods due to the long time taken to conduct cost structure which makes it difficult to update the information every year. But it is estimated to cost 3.1% of the annual GDP. In the UK, this percentage ranges between 4 and 5 while in Japan, the cost stands at 5,258 trillion Yen per year. Of this cost, 35% could be saved through adoption of appropriate control measures. The majority of spenders in corrosion according to Sivasankar (2008) include petrochemical, construction, petroleum, transportation and pulp and paper industries. Advances in Containing Corrosion It remains almost impractical to eliminate corrosion, hence Sivasankar (2008) advocates for control as opposed to prevention. Scientists have devised substances which when introduced to the environment in minimal concentration retards corrosion. These substances collectively have been defined by the National Association of Corrosion Engineers as corrosion inhibitors (Cicek & Al-Numan, 2011). The American Society for Testing and Materials specifically identifies a corrosion inhibitor as a unitary or combination of chemical substances which when presented to the environment in appropriate concentrations would reduce or inhibit corrosion. Therefore, the inhibiting substance should be present to maintain a surface film with good circulation and lack of stagnant areas being necessary for the maintenance of inhibitor concentration. This means that corrosion inhibition is reversible. Corrosion inhibitors function by inducing the formation of a thick corrosion product, changing the environmental characteristics so as to reduce aggressiveness and adsorbing a thin film on the corroding material surface. There are those that would remove oxygen so as to minimize cathodic reaction. The effectiveness of corrosion inhibitors would be determined by temperature, pH and water chemistry with cost and toxicity of a majority of these chemicals being a limiting factor. A majority of these corrosion inhibitors would be determined based on their reaction on the surface of the metal. Also referred to as passivating inhibitors, anodic inhibitors act by slowing down corrosion by repassivation or stabilization of the damaged passive film through formation of insoluble compounds or prevention of adsorption of aggressive anions by competitive adsorption. These inhibitors have found wide application in treating cooling water systems, steel-concrete composites and cooling system metals (Cicek & Al-Numan, 2011). Whereas direct passivating inhibitors oxidize themselves, indirect passivating inhibitors do not oxidize and therefore call for the presence of oxygen. Nitrates (NO-2) and chromates (CrO2-4) have been cited as the best oxidizers in directly passivating steel in deaerated solutions but have been used minimally due to their toxicity (Ebadi et al., 2012). While oxygen exists in abundance in open systems, addition of oxidizing salts such as analogues of chromates and molybdates would be needed in closed systems for indirect passivation to function. For example, at the metal/solution interface, ferrous ions would react with molybdate ions forming a complex that would be oxidized further to form an insulative ferric-molybdate that would cover metal surface with an adherent protective film. Fe → Fe++ + 2e- On the other hand, cathodic inhibitors would slow down corrosion through reduction of cathodic reaction rate in the corrosion system. They could form precipitates on cathodic locations so as to limit access to the cathodic reaction species, referred to as precipitation inhibitors by Cicek and Al-Numan (2011). Zinc and magnesium salts and bicarbonates are examples of this type of inhibitors. ½O2 + H2O + 2e → 2OH- But the danger of pitting looms with the sole use of anodic inhibitors. As such, cathodic inhibitors would be incorporated into the formulated performance obtained by combining inhibitors as opposed to summing up individual performances. Referred to as mixed inhibitors, this demonstrates the synergy that exists between chromate and zinc ions. The methods discussed demonstrate how the environment has been conditioned to reduce corrosion. But El-Lateef et al. (2012) bring into perspective ways of conditioning the metal in an effort to preventing corrosion. This could be achieved through either coating or alloying the metal. Coating involves interposing resistant coating between the metal and the environment with the coating being made up of another metal such as zinc, a protective coating which has been derived from the metal itself such as aluminum oxide or organic coatings like plastics, paints, resins, oils and greases. The action could be more complex than simple, barricading the metal from the environment, as the coating could contain corrosion inhibitors such as the zinc coating used on steel or iron which confers cathodic protection. Alloying produces an alloy that would be more corrosion resistant, such as the ordinary steel being alloyed with nickel and chromium to produce stainless steel which produces a film of chromium sesquioxide, Cr2O3. Ahmad (2006) acknowledges that corrosion being an electrochemical process could be measured through the determination of the changes occurring in the metal potential over time with the application of electrical currents. El-Lateef et al. (2012) uses this phenomenon to develop an electrochemical corrosion control where corrosion reactions would be curbed through passing of cathodic and anodic current into the metal. For instance, electrons could be passed into the metal up to a metal/electrolyte interface so that the anodic reaction stifles and the rate of cathodic reaction increases, referred to as cathodic protection. This would only be applicable in the presence of an appropriate conducting medium like water or earth through which there would be current flow to the metal that needs to be protected. Commonly, steel would be protected by lowering the potential of the metal surface by 300mV or 400mV in natural waters or soil. Anodic protection could also occur in particular chemical environments through the passage of current that would take electrons out of the target metal and thus raise its potential. This would be initially noted to stimulate anodic corrosion but a protective layer of oxidized passive film would form on the surface in favorable circumstances. Conclusion and Recommendation Corrosion phenomena destroy the quality of substances, particularly metallic substances which compromises the effectiveness of their functioning. Among the common corrosion phenomena include pitting, uniform corrosion, galvanic corrosion, erosion-corrosion and microbial corrosion. This comes with massive economic implication which varies from one country to another. It has been noted that prevention of corrosion would be an impractical venture. As such, it would be needful to undertake appropriate measures to control the menace due to the massive negative impact it has on plants and machineries and human life in general and the cost that comes with it. Measures that would effectively control corrosion check on the environment or the metal surface so as to minimize the interaction of the metal and the environment so propagating corrosion. Regular surveys should be made on plants and machineries to check on corrosion levels. References Ahmad, Z. (2006). Principles of corrosion engineering and corrosion control. Burlington, MA: Butterworth-Heinemann. Akhtar, S., Arif, M. & Quraishi, M. A. (2009). Use of chemical corrosion inhibitors for protection of metallic fiber reinforcement in ferrocement composites. The Arabian Journal for Science and Engineering, 34(2), 105 – 113. Cicek, V. & Al-Numan, B. (2011). Corrosion chemistry. Salem, MA: Scrivener Publishing. Ebadi, M., Basirun, W. J., Khaledi, H. & Ali, H. M. (2012). Corrosion inhibition properties of pyrazolylindolenine compounds on copper surface in acidic media. Chemistry Central Journal, 6(163). Retrieved 9 March 2013 from http://journal.chemistrycentral.com El-Lateef, H. M. A, Abbasov, V. M., Aliyeva, L. I. & Ismayilov, T. A. (2012). Corrosion protection of steel pipelines against CO2 corrosion – A review. Chemistry Journal, 2(2), 52 – 63. Poornima, T., Nayak, J. & Shetty, A. N. (2012). Corrosion inhibition of the annealed 18 Ni 250 grade maraging steel in 0.67M phosphoric acid by 3,4-dimethoxybenzaldehydethiosemicarbazone. Chemical Sciences Journal. Retrieved 9 March 2013 from http://astonjournals.com Roussak, O. V. & Gesser, H. D. (2013). Applied chemistry: A textbook for engineers and technologists. New York, NY: Springer Science+Business Media. Sethi, T., Chaturvedi, A., Upadhyay, R. K. & Mathur, S. P. (2007). Corrosion inhibitory effects of some Schiff’s bases on mild steel in acid media. Journal of Chilean Chemistry, 52(3), 1206 – 1213. Sivasankar, B. (2008). Engineering chemistry. New Delhi: McGraw-Hill Education. Read More