Corrosion

Chemistry assignment Introduction: Throughout modern day society metals are constantly used, in fact mankind has been heavily dependent on metals for the last several hundred years. But the science behind metals has only been discovered in recent years and has now become known to people that we simply could not live without them. Metals make up around 80% of the elements (currently discovered). They are used in everyday items that society depends on, such as: cars, re-bars for building, window frames, kettles, fridges and many more things.

These are the most basic uses of metals, but the need for metals also enters a chemical level, they are massively important in chemistry. The aim of this report is to determine what the best prevention method of corrosion will be in the ships in two different conditions; cold, deep water and warm, shallow water. It will also analyses these prevention costs and Justify which prevention method would be the best (environmentally and financially) or if it is simply better to allow the ships to fully corrode and clean up the spill afterwards; so basically prevention or cure?

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This report can be quite limited in the sense that it is simply based on research, here is no physical evidence from the authors own experiments to support the claims. It is all simply based on the research of similar previous scenarios, and runs on the basis that these ships will corrode in the same ways the ships in this investigation will. Once this investigation is complete, this report will then be able to advice people as to which kind of approach should be taken to solving this problem of the sunken ships.

This could potentially lead to helping governments or companies as to how they should react to this environmental problem, ideally saving the environment from damage. Metals are catalyst and speed up chemically reactions, scientists use metals for this purpose frequently to experiment with things at an accelerated rate. Metals allow things to have color. There would be no batteries or electricity as currents are formed by the difference of reactivity between two metals.

The requirement for metals is not Just on the basis of things that people want to make their lives easier through; cars, technology, electricity and other things people indulge in. Metals are also needed in the physiological sense as well, because basically without metals living organisms would not exist. No iron means no Mongolia which means oxygen isn’t moving round your body. No calcium means no bones. No life would even be possible as we know it without metals, without magnesium there is no photosynthesis, no trapping of the sun’s energy and therefore no food chain and no life. Cooked after the same way that they look after us. Metals are constantly under a natural threat called corrosion. ‘Corrosion is the gradual destruction of material, usually metals, by chemical reaction with its environment. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen. (Stats, 2011) Corrosion has been a problem even since the early days of using metals, it is costly and time consuming to deal with. Given time corrosion can cause a horrendous amount of damage, if left unnoticed corrosion can eat through any amount of metal.

This assignment basically focuses on the chemistry of corrosion, the main type of corrosion under focus being the corrosion of iron, forming the substance commonly known as rust. The idea of this study is to develop a way in which ships that were sunk in WWW containing oil can be neutralized from ever possibly releasing oil into the ocean. The study will focus mainly on the differences between corrosion in warm shallow water and deep cold water. Discussion: Metal corrosion is the oxidation of metals. Oxidation is defined as ‘complete or partial loss of electrons or gain of oxygen’ (Clark, 2002), hence the term ‘oxidation’.

The opposite of this is reduction. Reduction is defined as ‘complete or partial gain of electrons or loss of oxygen’ (Clark, 2002). In these definitions, by ‘partial loss or gain’ it is talking about in the case of covalent bonding where the elements share electrons. But one element obviously has to be more electronegative so it pulls the electrons loser to it, hence it is partially reduced. Oxidation and reduction go hand in hand, one cannot happen without the other, reactions that involve oxidation and reduction are called redo reactions.

Redo reactions are written in half reactions to show electron flow, change in oxidation states and to use E values. An oxidation number is a positive or negative number assigned to an atom to indicate its degree of oxidation or reduction. In redo reactions these oxidation numbers change due to oxidation and reduction. The process of corrosion is quite a complex one. For this process to occur, there first has to be oxidation and reducing agents. The oxidation agent is usually 02 from the air or it is dissolved in water. The oxidation agent is usually 02 from the air or dissolved in H2O. The oxidant causes oxidation and is reduced.

The product of oxidation/corrosion can be a metal oxide or a metal oxide hydrate. In electrochemical reactions, the electrons are produced by a chemical reaction in one area, the anode. The electrons then travel through a metallic path and are consumed by a different chemical reaction in another area, the cathode. In an electrochemical ell, four things are required. They are; an anode, a cathode, an electrolyte and a metal. The anode is the metal surface where electrons and ions are produced through oxidation Ions flow through the electrolyte; the electrons remain in the metal and are free to move around.

The cathode is where the electrons flow to through the metal. The electrons are used in chemical reactions that occur where the cathode touches the electrolyte. Each electron that is lost at the anode is then used at the catholic. Electrolytes are solutions that are capable of conducting electricity through he movement of charged ions. The actions flow from the anion and to the cathode, the anions flow from the cathode to the anode. One very form of corrosion is the process of rust. The following reactions and equations explain the process of rust.

As mentioned prior, for corrosion to occur, four things are required: an anode, a cathode, a metal and an electrolyte. Think of a block of iron, it is impure and has carbon. If moisture then forms on the iron block, the iron now has the potential now has the potential to create rust since the E value is positive so the reaction is spontaneous. As the following half reactions show: Stage 1 Oxidation – Fee 02 + OH + e- Cell = E red + E oxide Stage 2 + 02 Half Reactions Oxidation – Reduction – Fee+ Fee+ + e- OH- = (+0. V+ + . V) = +0. 84 fee . H2O + OH 202- E = +. V Reduction – E = -. V E = +1. V Cell = Erred + E oxide = (+1. 23 +-. V) = + . V This electrochemical series is galvanic as it generates its own electricity and this reaction is spontaneous. When there is a scenario with the example previously used oxygen dissolves into water, iron oxides and electrons go to the cathode. The electrons go to form OH- wrought the metal and the Fee+ ions left over flow through the electrolyte and react with the OH ions to form Fee(OH)2. This forms a circuit as in a galvanic cell. After this there is the more simple reaction, shown in the second set of half reactions above.

The rate and process of corrosion is dependent on many parameters including temperature, dissolved oxygen content, salinity, water chemistry, pH, pollution/ roughness. Most electrochemical reactions proceed at faster rates with increasing temperature, approximating to a doubling of rate for each 1 CO rise in temperature his is usually because it can dissolve it or even crack it, allowing more surface area to be corroded. The oxygen levels increase due to photosynthesis by marine plants and by the action of the waves while the oxygen levels decrease due to the demand for oxygen created from the decomposition of organic matter.

The dissolved oxygen content often varies as a function of the season and depth at any given location. In general, when either the temperature or salinity increases, the dissolved oxygen content in seawater decreases. Metal corrosion rates are usually higher in shallow eater, where temperatures are higher than in deep cold water. Water chemistry is important because a higher pH means there are fewer free hydrogen ions, and that a change of one pH unit reflects a tenfold change in the concentrations of the hydrogen ion. Low pH acid waters accelerate corrosion by providing a plentiful supply of hydrogen ions.

The effects of corrosion in deep water is different to that of the effects of shallow water. Corrosion in deep water is slowed because of the low temperatures. Also because of the growth of anaerobic bacteria which only seem to appear on ships that eave sunk below 1 km. Shipwrecks at depth are extensively corroded; this corrosion is the result of anaerobic bacterial as well as electrochemical reactions. Ethanol and oxygen CHICHI + [0] ethnic acid, where the ethanol gets oxides COACH In seawater, the higher the temperature, the more conductive it is, and since the deeper it gets the colder it gets it is obviously less conductive.

Because of this low conductivity the amount of catholic protection current that will be formed will be much less than normal. This causes a chemical problem; there is not enough current available, so more anodes are needed. In a sense the sea is basically a natural sacrificial and corrosive chemical environment. Sunken shipwrecks in shallow waters which are exposed to warm tropical water temperatures will usually deteriorate at a greater rate than cold deep water wrecks.

This is because of the several unavoidable environmental factors such as: shallow oxygenated waters in lagoon or near shore environments, microbial attack, the impact of storms, unstable bottom sediments and storms and other natural events that could damage or rip off bacteria build. These natural effects can tangentially reduce a sunken shipwreck back to its original basis chemical elements. In deep cold water, an oil spill can create an oil plume. When this happens not all of the oil goes to the surface. Some of it is slowed or captured by the cold water molecules.

Oil plumes within the deep waters pose a danger to life within that area, which can be the habitat of plank-tonic microorganisms and deep water fish. Upon impact with around by currents. But almost immediately the more toxic and volatile components of oil separate and go into the atmosphere and water soluble components speared onto the surrounding water. Lighter insoluble components form thin films that spread and move more extensively than the thicker oil. Waves cause the oil to break up into smaller particles and eventually mix and bond with water particles.

This gives the water that tan- yellow color often seen in floating oil slicks. There are several ways of combating corrosion, they are: cleaning, preventing condensation, purifying the atmosphere, use of corrosion inhibitors, protective coatings and sacrificial coatings. There are several commercial ways to solve the problem of corrosion. The main way is by applying polymeric materials in comparatively thick, robust coatings. These coatings give protection against corrosion and mechanical damage. It basically means that it covers the metal so that it is not in contact with water.

Another method similar to using polymeric materials is to chemically coat the materials, this is called paginating metals. Anointing treatments for aluminum may incorporate phosphate or chromate ion, and so-called “chemical anointing” may be used to enhance the resistance of aluminum to atmospheric attack. There are also several types of emperors answers to these problems of corrosion they are wrappings which may be greased or waxed, temporary protective materials can be applied to metal surfaces to exclude moisture and dust. These wrappings can also take the form of pastes or a slushy like substance.

Catholic protection (CAP) is an electrochemical method used for preventing corrosion phenomena on a metallic surface. It can only be applied to metals exposed to conductive environments, and objects immersed in sea water can be particularly efficiently protected due to the very good properties of electrical conductivity of the medium. The basic principle of the method is based on the possibility of reducing the open circuit potential of an actively corroding metal by circulating a continuous current between an electrode, made of a less noble metallic material (sacrificial anode), and the object to be protected.

In the ships that we are investigating for this assignment, it is highly unlikely that they are made of a completely pure metal or alloy. Metals corrode differently and at different rates. This can be seen by looking at the table of reactivity, it has been proven that if two metals are in contact with each other and are in a position where hey will corrode; the more reactive metal will become what is known as a ‘sacrificial anode’ and it will corrode completely before the other metal will even be effected. In the text it is said that there are copper nails, steel plates.

These steel plates will have a number of impurities on them if different metals that may interfere with the corrosion of the ships, but the copped nails will have little to no impact on the rate of corrosion as they are so low on the reactivity series. Recommendations: problems of corrosion in sunken ships. These include catholic protection, cleaning, retention from dust, drying the atmosphere and preventing condensation, purifying the atmosphere, use of corrosion inhibitors and protective coatings. It is also quite possible to leave the ships where they are and allow corrosion to complete and deal with it after.

A lot of these methods are inadequate for this scenarios in this assignment for obvious reasons. Oil cannot be released into the environment as it will cause extensive damage and could easily go out of hand. Other methods such as cleaning cannot be used as it requires the ship to be submerged. Hot tapping could tie easily be used for ships located in warm shallow water as they can be accessed fairly easily compared to the ships in the deeper water. While this method is easily the most expensive it is one of the most effective.

The same cannot be done for ships in deep water. Since the ships are so deep it would be idiotic to attempt to send people down to use heat lances to hot tap a ship and then send oil up to km up to the surface. But there is another alternative. The use of sacrificial anodes would be the most effective and easiest method to use. This method is much cheaper than hot aping and is installed much quicker than hot tapping can be done. But the only problem is that it is only a temporary solution and the anode sent down would have to be replaced regularly.

Conclusion: The aim of this report was to investigate the possible damages and impacts of sunken WWW ships containing large amounts of fuel, lying dormant at the bottom of the ocean. And also to investigate the best way to undergo prevention of corrosion in these ships in both deep and shallow water scenarios.. It was found after much research that the method of prevention of the ships in deep, cold water was a sacrificial anode that would corrode in the place of the steel ships. It was also the same for ships that were in warm shallow water.

Sacrificial anodes were found to be the best source of corrosion prevention in all underwater conditions. Hot tapping is also a possibility, this method is quite expensive but may become necessary if some ships are located in shallow waters that are constantly in heavy storms which could damage the hull of the ship, releasing oil. The reasoning behind these choices were that the other methods, including , cleaning, protection from dust, drying the atmosphere and preventing condensation, riffing the atmosphere, use of corrosion inhibitors and protective coatings) all require one main factor; the ship cannot be in water.

This is obviously a very big dilemma. It would be quite impossible to raise ships from deep depths of the ocean and as for the ships in shallow water, it was cost unbelievable amounts of money. On top of that, after spending all that money to get it out, you would Just put it back in after wards after these other methods were put into place. It would make more sense so Just keep the ship out of water than put it back.

Jesse
from Nandarnold

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