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Unread 09-08-2012, 10:41 AM
SuenosAzules SuenosAzules is offline
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Join Date: May 2010
Location: Palm Beach Gardens, Florida
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Default Galvanic Corrosion - One of the Biggest Enemies in the Water

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Galvanic Corrosion - One of the Biggest Enemies in the Water


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Hello, I wanted to write today to talk about galvanic corrosion. For those of you not familiar with galvanic corrosion it is an electrochemical reaction when one metal corrodes from another when both are immersed in an electrolyte that is conductive (such as sea water). Dissimilar metals and metal alloys have different electrode potentials when two or more of these metals exist in the same electrolyte. When this happens a galvanic couple is created and depending upon the nobility of the metal (which I will talk about further on in this article) one metal will become the anode and another metal will become the cathode (both are electrodes). To explain the difference between an anode and a cathode in simplest terms, an anode is the metal that current flows in to, a cathode is the metal that current flows out from. Do not confuse an anode and cathode with positive or negative charges or voltage. An anode and cathode can both be positively charged. It is the direction of current flow between the two metals that matters. Once the galvanic couple is formed between the two metals, the anode metal will dissolve into the electrolyte (the sea water). During this process the charged ions and atoms are interchanged with electrons at the electrodes and pass through the sea water. This process is known as electrolysis. In a simple way to explain this, electricity passing through the water between two electrodes is electrolysis. The resulting reaction is galvanic corrosion. The rate at which this occurs is dependant on water temperature, the salinity in the water, nearby dissimilar metals in the water, and free flowing current that may exist in the water. This galvanic couple process is how a common household battery works. The result is the electric current produced from the reaction. Given the size of a body of water (such as in a salt water river at a marina) this electrochemical reaction can be measured in millivolts (mV).
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Capt. John Banister, Marine Surveyor
Palm Beach Gardens, Florida
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