Corrosion vs Degradation:
In our day to day life, practically every day we see gadgets, instruments etc that are rusted or corroded, especially when they are in the vicinity of a sea or when there is much humidity. Corrosion is a natural process of gradual deterioration of material, usually metals, by chemical or electrochemical reaction with their environment.
The chemistry of corrosion is complex: Consider a spot or a small area in a metal piece that is exposed to the weather. If it is an iron piece, oxidation takes place and that spot behaves as an anode. And the electrons released at this anodic spot move through the metal and go to another spot on the metal, that behaves as a cathode, and reduce oxygen at that spot in the presence of H+, which is probably available from carbonic acid (H2CO3) formed due to dissolution of carbon dioxide from air into water in moist condition of atmosphere. Hydrogen ion in water may also be available due to dissolution of other acidic oxides from the atmosphere.
The after effect of corrosion is oxide(s) or salt(s) of the original metal with the appearance of orange colouration. Corrosion can also occur in materials, which are not actual metal, for example, ceramics or polymers. In these materials, the term ‘degradation’ is used as corrosion degrades the useful properties of materials and structures affecting strength, appearance, permeability etc.[1]
Damages caused by corrosion include significant deterioration of natural and historical habitats and monuments as well as increase in the risk of catastrophic equipment failures.
Multifaceted Corrosion:
Corrosion seems to be an encompassing phenomenon which needs close attention and study to minimize its effects.
Chemical Corrosion: Corrosion is a major problem especially in the construction industry where various metals are used for structural purposes. There are different types of corrosions (at least 9 types): Moisture present in the atmosphere, rainwater etc acts as electrolyte triggering corrosion of the exposed metal surface. In metal tubes carrying moving fluids in it, the surface of metal gets deteriorated gradually by the abrasion of fast-moving fluids and cavities are also formed as a result. This is known as erosion corrosion caused by the relative movement between metal surfaces and corrosive fluids. Aluminum, zinc, lead etc are commonly affected when a uniform layer of rust is formed on the surface of metals and it is extended over the whole surface of the metal. This becomes worse when the metals are not protected by surface coating. In steel, aluminum, nickel alloys etc formation of rust in pits and holes on the surface starts as localized corrosion when protective oxide layer of the surface gets damaged or due to structural defects in metals. This is dangerous as it would cause failure of structure with a relatively low overall loss of material. Stress also could be a cause of corrosion when combined with corrosive environment and mechanical stress on the surface of the material. Initially, small cracks develop leading eventually to failure of the whole structure. This is observed in stainless steel when they are stressed in chloride environment, in brass materials when they are exposed to the presence of ammonia etc. In cases of defective welding, heat treatment of stainless steel, copper etc, inter-granular corrosion occurs along the grain boundaries.[2]
Biological Corrosion: In addition to chemical corrosion, there are other types or forms of corrosion: The presence and influence of microorganisms present in water, wastewater, or interior piping walls of both metal and non-metal material in the form of biofilm adhering to the inner surfaces of piping systems cause biological corrosion. Biological corrosion occurs mainly because of the formation of hydrogen sulfide gases produced by the metabolic activity of naturally occurring microorganisms in fluids. Once the sulfide gas makes its way to the surface, it reacts with air and moisture to form sulfuric acid which is highly aggressive to both metal and non-metal materials, leading to stress cracking on the inner walls of piping systems.[3]
Ecological Corrosion: Today, as an after effect of growing industrialization we have acid rain affecting the environment. Acid rain is the precipitation that contains high levels of nitric and sulfuric acids. Normal rain is slightly acidic, with a pH of 5.6, while acid rain generally has a pH between 4.2 and 4.4.[4] The damage caused by acid rain is on the increase. For example, when iron is exposed to an industrial atmosphere over a prolonged period of time, the result is formation of iron oxide or rust on the surface. In areas of heavy industrial pollution, presence of sulphur oxides, nitrogen oxides, hydrogen sulphide, ammonia, carbonyl sulphide and other pollutants amplify the acidity of the rainfall aggravating the situation. As rust is very porous to oxygen and water in the atmosphere, the corrosion process continues until the metal is entirely consumed.[5]
Generally we think of people-centered environment, known as anthropocentrism. It is the thinking that environmental protection is important only in so far as it affects human beings. But we need to be aware of other life forms, such as animals, plants, landscapes, etc, which create the atmosphere or milieu for our well-being. So we need to keep in mind environmental ethics which would include biocentrism and ecocentrism.[6]
Awareness and Steps to be taken:
There is need to become aware of so many types as well as factors that cause corrosion. Awareness is the first step to prevent corrosion. Then, our concerted efforts should not only find out the sources but also looks into means to minimize and if possible, to eradicate corrosion process. Metallurgy is an area of study and research. Often it is possible to chemically remove the effects of corrosion. For example, phosphoric acid in the form of naval jelly is often applied to ferrous tools or surfaces to remove rust. Corrosion removal should not be confused with electropolishing, which removes some layers of the underlying metal to make a smooth surface. For example, phosphoric acid may also be used to electropolish copper but it does this by removing copper, not the products of copper corrosion.[7]
Suitable and effective corrosion inhibitors could be used. Apart from anodic and cathodic inhibitors, mixed inhibitors such as silicates and phosphates could be used as softeners in domestic water to prevent formation of rust water. Similarly, volatile corrosion inhibitors such as morpholine or hydrazine could be used in boilers to prevent corrosion in condenser tubes.[8]
Awareness and education about corrosion could include, the use of non-corrosive metals, such as stainless steel or aluminium; ensuring that the metal surface stays clean and dry, if necessary using drying agents; using coating or barrier product such as grease, oil, paint or carbon fibre coating; making a layer of backfill, for example, with limestone, with underground piping, etc.[9]
Need for Ethics in Research:
Shifting from material to environmental corrosion, we could also think of social corrosion caused by increasing inequality and ethnic diversity corroding social cohesion and harmony. Social exclusiveness, religious fundamentalism, racial supremacy, etc would corrode unity and harmony in any nation. As one of the focus area of LIFE is ethics, this area of social corrosion could be addressed. On the one hand we could work on scientific ways and means to address corrosion causes and effects, and on the other hand, we could work out the ethical principles that need to be taken into account in manufacturing quality products that might minimize or eliminate the onset of corrosion process. Corrosion profession, especially among the researchers, certified professionals dealing with chemical products, and manufacturing industries, is the commitment to protect people and environment from the ill effects of corrosion.
When we think of any change in reality, we could think of three stages or phases: First people need to change, then based on input and available information and analysis their perception changes, and finally this leads to perspective-change, bringing in new reality.
I am sure that the presence and sharing of experts in this area would be enlightening us all, during the conference, not only to be aware of the phenomenon but also to take all necessary steps to address the ill effects of corrosion. I congratulate the LIFE research team, especially the organizing Secretary Dr John Mary and the Director Dr Selvanayagam for this timely innovative effort. All the best.
Francis P Xavier SJ
03Mar2023
[1]https://en.wikipedia.org/wiki/Corrosion#:~:text=Corrosion%20is%20a%20natural%20process,to%20controlling%20and%20preventing%20corrosion.
[2] https://theconstructor.org/structural-engg/steel/different-types-corrosion/35536/
[3] https://www.trenchlesspedia.com/definition/2706/biological-corrosion
[4] https://www.nationalgeographic.com/environment/article/acid-rain
[5] https://www.penflex.com/environmental-corrosion-of-stainless-steel/#:~:text=Environmental%20corrosion%20is%20a%20naturally,chemical%20nature%20of%20the%20material.
[6] https://www-pub.iaea.org/MTCD/publications/PDF/te_1270_prn.pdf
[7]https://en.wikipedia.org/wiki/Corrosion#:~:text=Corrosion%20is%20a%20natural%20process,to%20controlling%20and%20preventing%20corrosion.
[8] https://www.cor-pro.com/corrosion-protection-services/types-of-corrosion-inhibitors/
[9] https://www.twi-global.com/technical-knowledge/faqs/what-is-corrosion