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BME83 corrosion lab4

BME83 corrosion lab4 - Laboratory 4 Corrosion BME 83L...

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Laboratory 4 Corrosion BME 83L Section 02L Instructor: Prof. Monty Reichert T.A.: Nicole Bell Laboratory Performed on March 20, 2007 Nigel Chou Shijie
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Abstract In this laboratory the aim is to explore the properties and processes related to galvanic corrosion through a series of corrosion tests on Aluminum, Titanium, Copper and Zinc, and in so doing to gain an appreciation of the considerations taken in selecting metallic materials for in-vivo applications such as implants. A galvanic series is first constructed from galvanic voltages measured between metals in a voltaic cell set-up, using Zinc and Titanium as reference electrodes. In order of decreasing nobility, the series obtained is: Copper, Titanium, Aluminum and Zinc. Next, the effect of anode to cathode ratio is explored using Zinc and Copper foils of different dimensions in the same set-up as above. The results showed that increasing the anode to cathode ratio resulted in a decrease in the current. Thirdly, the effect of depletion zone was tested by halting the stirring of the salt solution and observing the subsequent drop in current. The time taken for the current to drop to a stable value was measured to be approximately 120s. Finally the time taken for a passivation layer to form after abrasion by sanding was tested for Titanium and Aluminum samples, and the rate of formation appeared to be slightly higher for Aluminum. In conclusion, various aspects of galvanic corrosion were tested and yielded results that could be explained by a theroetical understanding of corrosion processes. 1
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Introduction In this laboratory the purpose is to understand one of the important types of corrosion that occur in metallic biomaterials – Galvanic corrosion, and how this phenomenon affects the choice of metals to be used in in-vivo biomedical applications. Various properties of galvanic corrosion will be examined through a series of four tests on Aluminum, Titanium, Copper and Zinc. The four tests analyze the relative nobility of the metals (galvanic series), the effect of cathode to anode ratio, the effect of depletion zones around the electrodes and the time taken for a passivating layer (a thin, adherent layer of oxide that acts as a barrier to corrosion) to be formed. In doing so, we hope to gain an appreciation of how various forms of corrosion-rate analysis factor into the design of metallic implants. Galvanic corrosion occurs when two dissimilar metals or alloys are electrically coupled while exposed to an electrolyte (e.g. body fluid). The less noble and more reactive metal in the particular environment will experience corrosion while the more noble and less reactive metal will be protected from corrosion [1]. The metal that corrodes is said to be anodic to the metal that is protected. The tendency of metals to react with one another can be described with a galvanic series, which is a table in which the metals ranked in order of their tendency to react with each other, that is, in order of anodicity.
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