Question From Reader:
After doing numerous tests, we have found the aluminum to completely fail corrosion testing (in part due to dissimilar metals of stainless, brass, and aluminum). Since our system relies in part on continuity, our performance may suffer if the aluminum corrodes. Can you give me some options with stainless steel and a copper alloy? I am open to large variations in conductance but would like to see something with tensile strength comparable to our current material. I want to reduce conductance and improve corrosion resistance so stainless seems like the natural choice.
Answer From Dexmet's Ken Mull:
First the science. When lightning strikes, the electrical energy vaporizes the aluminum taking out the initial energy punch, it then flows along the conductive surface looking for ground. The primary material characteristic then becomes the heat of vaporization. The heat of fusion and the electrical resistivity are not as important since the heat of fusion for all metals is insignificant by comparison and the electrical resistivity does not come into play until after the strike has occurred. A comparison between aluminum and copper yields a 2:1 difference by weight in favor of the aluminum since aluminum has a much higher heat of vaporization by weight than does the copper. So if you wish to switch to copper at the same weight as your current configuration the result would be a reduction in energy potential of ~50%.
You also mention switching to stainless steel for better corrosion potential. I cannot find the heat of vaporization for stainless steel but can for iron. Iron has a similar value of the heat of vaporization as does copper which would make it similar to the copper in terms of protection, however I am not sure how much of an effect the added chrome and nickel will have on the heat of vaporization since at the moment my search for the heat of vaporization for stainless steel has turned up blank.
Finally, after the strike, the electrical energy needs to flow towards ground and the electrical energy moving through stainless steel with it's higher resistance (3x over aluminum) may heat up the surrounding material, potentially melting the surfacing layers.
I realize this may not completely answer your question and to verify any change you will need to re-test.
One last comment, changing to either copper or stainless steel will impact on the price since both materials are more expensive than aluminum.