Topic Report Draft

Introduction- This extended experimental investigation is aimed at investigating the scientific principle of corrosion rate, both in regards to magnesium and zinc. In order to examine the concept thoroughly, the variables of salt and aeration will be altered and the different effects noted. Magnesium is a highly versatile, reactive metal which reacts easily with water to create hydrogen bubbles in solution. When in contact with air, an impenetrable oxide is formed which protects the rest of the metal from corrosion. Zinc, however, is less reactive than magnesium due to its lower standard electrode potential, though acts as a strong reducing agent. Corrosion rate is known to increase when salt concentration is increased, as the water holds a greater capacity to carry a charge due to its increased amount of electrons in solution. Aeration is also thought to increase corrosion rate (in comparison to metals in stagnant solutions), as oxygen is the main component in corrosion. If there are increased oxygen levels, then there will be increased corrosion. Discussion- Corrosion is generally known as any degradation of materials through chemical methods, which is commonly with some reference to metals. There are two very broad areas of corrosion, the first being known as Direct Chemical Attack and the second Galvanic Corrosion. Galvanic corrosion occurs when two metals with dissimilar properties are placed in each other’s presence with a connection of an electrolyte. In this situation, the Galvanic series can be referred to in order to determine which metal becomes cathodic and anodic if a reaction should take place. In the following experiment, however, the Direct Chemical Attack (or generalised) area of corrosion will be investigated. The Direct Chemical Attack method refers to when metals are exposed to their environment, commonly in terms of moisture and air. In this situation, the metals are not reacting in cells; rather any part of the metal exposed to that environment should react accordingly. In order for corrosion to occur, an oxidation-reduction reaction must occur, generally with respect to anodes and cathodes. An oxidation-reduction reaction can only occur when there is two equal half reactions, one oxidising and one reducing. This is to ensure that any electrons being transferred have somewhere to go. - how does corrosion occur (reactions) As previously mentioned, the presence of sodium chloride at a corrosion site is theorised to increase the corrosion rate. Therefore, it could be assumed that an increase in in the sodium chloride concentration would correspond with an increase in the rate of corrosion of a particular substance. - Salt concentration effect Oxygen, being a major ingredient in order for corrosion to occur, can consequently affect the rate of corrosion. In the following experiment, both the magnesium and zinc are being exposed to solution instead of air. However, as oxygen is present in water (in a comparatively small proportion compared to air) in varying amounts, the corrosion of a substance in that water will differ depending on the level of dissolved oxygen. The dissolved oxygen content present in water is generally approximately 0.001%, while the oxygen content of air is approximately 21%. However, moisture is obviously a major factor in the increased corrosion rate in wet or humid environments. -aeration effect (dissolved oxygen) Magnesium and Zinc, although both metals, have differences in properties which causes corrosion, and consequently corrosion rate, to differ. - difference between magnesium and zinc - density, SA