The Best Metal Which Is Most Corrosion-Resistant - Lab Report Example

Mechanical Engineering W5446, Selection of Common Engineering Materials Document type: Essay Area: Mechanical Engineering Date: 18th March, 2015 Introduction The main aim of this experiment was to determine the best metal which is most corrosion-resistant, to be used in buildings dogs’ enclosure Definition of terms Rust is the reddish matter that’s forms on the surface of the metal when they come into contact with air or moisture while, corrosion is a gradual destruction of metal due to the chemical reaction. The list of metal that was investigated were; copper, iron, steel, stainless steel, aluminum, and zinc. Electrochemistry is one branch of physical chemistry that’s concentrates on the chemical reaction that takes place in an electrode, electrolyte, and ionic conductor’s interfaces, whereby electric charges moves between electrolyte and electrodes. Its effects are documented in the galvanic series as shown below. Anodic end (More prone to corrosion) Magnesium Zinc Aluminium Carbon & Low Alloy (Structural) Steels Cast Iron Lead Tin Copper, Brass, Bronze Nickel (Passive) Titanium Stainless Steels 430/304/316 (In the passive state) Cathodic end (Less prone to corrosion) (Fontana & Greene, 1978) Oxidation is the reaction in which a metal element combines with oxygen. For example in the reaction of oxygen and magnesium whereby the magnesium is oxidized Reduction has its origin in Latin word which means lead back, this means that the reduction is opposite of oxidation. For example when carbon and magnesium oxide reacts at 2000C to form carbon monoxide and magnesium metal Experimental observation The following was observed on the changes in wire lengths; the changes in the wires are not the same all over the whole length, changes are more notable at the end points or the tips of the wires. This is probably because the end points or tips are the points where the ions leave and enter the wires. So there is either corrosion or deposition of materials, depending on the position of the concerned metal in the galvanic series When the three (3) sets of wire are compared, while using the galvanic series, metals that are Topmost on list are corroded more than metal below the list during galvanic corrosion. For the set of wires kept in tap water, the rate of corrosion decrease from zinc to stainless steel in this order; Zinc, Aluminum, Cast Iron, Copper, Stainless Steels.This mean, zinc is corroded most while stainless steels are corroded list For the set of wires kept in salt water, the effects of corrosion is more as compared to in tap water, their order is as follows; Zinc, Aluminum, Cast Iron, Copper, Stainless Steels .This means that zinc is most affected while stainless steels are less affected For the set of wires kept in air, the effects on metal are due oxidation and this oxidation affects metals that have ferrous in it or metals that are magnetic. Therefore, the order of oxidation is as follows; Cast Iron, Stainless Steels, Aluminum, Copper, Zinc. This because Copper and Zinc does not have ferrous as parts of its components. The cast-iron is most affected while copper and zinc are least affected by rust. The following is the grade rating that describes the changes in the observation Scale 5 4 3 2 1 Material zinc aluminum Cast iron copper Stainless steel Changes in Salt water Scale 1 2 3 4 5 Material zinc aluminum Cast iron copper Stainless steel Changes in Tap water Scale 5 4 3 2 1 Material Cast iron Stainless steel aluminum copper Zinc Changes in Fresh air KEY: 5 ------- cause severe effect 3--------Moderate effect 2--------Least effect The following are graphs drawn using above ratings and shows what happened to different metal under the three conditions Conclusion The combination of metals and environmental condition, which shows the greatest amount of oxidation are; Zinc in both salt and tap water and Cast iron in fresh air The combination of metals and environmental condition, which shows the least amount of oxidation are, Stainless steel in salt and Tap water, Zinc and copper in fresh air Variations The following was observed on the changes of the weights of wires in different conditions; the weights will change the metals that were submerged in both salt water and tap water while the change in the metals that were place in the air is very minimal. Probably there would be a big change in weights in wires submerged in salt water as compared to wires submerged in tap water. This is because both corrosion and oxidation or reduction is higher in metals place in salty water. The weights change is due to deposition or corrosion on the metal surface while, in the air there is very minimum change because there are no electrons due water which can cause both oxidation and corrosion. Temperature and salt concentration accelerates the rate of oxidation; this is because the temperature has two effects on the rate of reaction, first is the speed of reaction while the other one is due to the activation energy. This indicates that if there is limited energy to push the reaction then nothing will happen; also oxidation will double with every 10°C increase in temperature. Addition of more salt will increase the speed of oxidation, this is because there will be more ions in water so it contacts electricity better hence the rate of oxidation will go up. When there is very little supply of oxygen in water, then the rate of oxidation goes down. This means that the wire will rust slowly. The water that is not boiled means there is allot of oxygen hence oxidation is very high. This means that the wire in jar with water that was not boiled will rust fast as compared to wire in jar with boiled water. The change of PH of water affects the number of ions in the water, and these ions are responsible for conductivity. This means that when vinegar is added will make the water corrode the metals faster while addition of baking soda will make the water corrosive but not as corrosive as when it is acidic. This is because acidic water has Avery high rate of oxidation because of positive hydrogen ions (H+) What happened to Titanic shipwrecks is what is called electrochemical corrosion or single metal corrosion which happens because the materials or iron cannonballs is made of alloy, this means that one metal in an alloy become a node while another one became cathode while the sea water becomes electrolyte and the alloy are in contact with one another creating path for the flow of electron and causes corrosion. This process is not very serious and does not cause a major concern in the shipping industry. When this iron cannonballs is brought to the surface from the shipwreck location, the reaction or corrosion will stop because there are no materials that can act as electrolyte to enable the movements of ions. A good experiment to do in order to learn more about this phenomenon is too deep or submerge one wire which is an alloy in individual jar contain salt water and tap water. The changes in the wires should be noted for a period of one month while in the water. It is then exposed to fresh air and monitored for a period of one month. It will be noted that there is a corrosion taking place in wires submerged in water, but it is more pronounced in salt water, it will also be noted that the there will be no more corrosion taking place when the wires are taken out of water and exposed to fresh air . Paint is one way of preventing oxidation and corrosion, and this is because paints prevent oxidation to take place and also prevent electrons from moving from one point to another. Therefore, oxidation and corrosion happens on unpainted wires while it doesn’t occur in painted ones Reference Fontana, M.G, & Greene, N. D (1978).Corrosion Engineering (2nd ed., p. 32). New York: McGraw-Hill. Read More