E45 Corrosion Lab Report Questions

E45 Corrosion Lab Report Questions - E45 Lab Questions(May...

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E45 Lab Questions (May 8, 2008) Norbert Wang Corrosion Lab Questions Question 1: The larger the voltage of the interface, the less likely the metal will corrode. The order of the galvanic series can be predicted by ordering the voltage interfaces of the metals tested in the lab. The more anodic metal will have a lower voltage whereas the more cathodic metal will have a higher voltage. The expected order of the galvanic series from most anodic to most cathodic is as follows: Zn, Al, Fe, MS, Ni, Br, Cu, and Ti. Table 1 shows the interface voltages of each metal ordered from most cathodic (top) to most anodic (bottom). The order based on the experimental results does not follow the same trend as expected. One of the major changes is the placement of Ti in the order. Ti should be the least reactive but it is shown to react quite a lot experimentally. The reason for this is because Ti forms a pacifying layer when introduced into saline solution. Gases from the atmosphere can create oxides on the surfaces of the metals, making their voltages differ slightly. Moreover, the experimental results are only partially accurate compared with expected results. Question 2: As long as the voltage between the cathode and anode in the solution is non-zero, there will be a redox reaction. Therefore since each metal had a non-zero interface voltage, they must all corrode to some extent. Question 3: Reaction rate is dependent on galvanic voltage and the rate of diffusion of the ions. If the distance between the electrodes is short, less diffusion is needed to transport ions across. Therefore the reaction rate should be faster. The greater the voltage the greater the reaction rate and thus the greater the rate of corrosion. Surface area of the electrode also has an impact on rate of reaction. The greater the surface area the larger the flux of ions moving through that electrode and thus a larger galvanic voltage.
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Question 4: The voltage is affected by impurities in the solution. For example, if there are impurities in
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This note was uploaded on 01/21/2010 for the course ENGIN 45 taught by Professor Devine during the Fall '07 term at Berkeley.

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E45 Corrosion Lab Report Questions - E45 Lab Questions(May...

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