Corrosion Lab Report

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Introduction Corrosion is a process through which metals in manufactured states return to their natural oxidation states . In their manufactured state, metals are at reduced stability and these metals tend to spontaneously return to their natural state. This process is what we call corrosion and it is governed by redox reactions in which the metal is oxidised by its surroundings. For this process to occur it has to be favoured both thermodynamically (spontaneous) and electrochemically. It is thus an inevitable process. Environmental factors such as pH, salt concentration, and oxygen concentration, along with the velocity of the fluid and temperature contribute to the process of corrosion and the rate at which it occurs. Corrosion usually occurs…show more content…
This is indicative of a slow corrosion rate between the pH range of between 2 and 7. The slope is almost flat but has a greater value at the pH of 2. This means that although the corrosion rate of aluminium is almost constant through this range, it however is accelerated in acidic conditions. The negative corrosion rate at Ph 7 suggests that there is an accumulation of mass on the surface of this sample. For this to happen it would mean that in neutral/ basic solutions aluminium tends to act as the cathode, undergoing reduction and instead of losing electrons it is gaining them. This causes what is known as cathodic protection of the sample. From figures 1 and 2 in the appendix it can be seem that aluminium is the least affected by corrosion of all the specimens. The oxide layer is stable in the general pH range of…show more content…
Initial attack occurs at anodic areas on the surface, where ferrous ions go into solution. Electrons are released from the anode and move through the metallic structure to the adjacent cathodic sites on the surface, where they combine with oxygen and water to form hydroxyl ions. These react with the ferrous ions from the anode to produce ferrous hydroxide, which itself is further oxidised in air to produce hydrated ferric oxide (i.e. red rust.) However, after a period of time, polarisation effects such as the growth of corrosion products on the surface cause the corrosion process to be stifled. New, reactive anodic sites may be formed thereby allowing further corrosion. In this case, over long periods, the loss of metal is reasonably uniform over the surface, and this is usually described as 'general
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