My first reference is from my dad. He's not a treeguy, but he owns a boat on the Gulf of Mexico. On the back of the boat, beneath the waterline, is a big hunk of metal called a 'zinc' named so because it's simply a big block of zinc. It is attached by a conductor line that's in direct contact with the metal parts of the engine. Corrosion protection is offered to the metal parts of the engine through the preferential consumption of the zinc. It's an electrochemical law of electricity first described by
Alex Volta back in the late 1700's. At the same time another dude,
Galvani was doing similar investigations and came up with electrical laws that stand today because
these physical laws do not change. They involve far more discussion as to how they works, but Zinc, in contact with ferrous metals, will be sacrificed preferentially, keeping the ferrous metal from itself becoming corroded (oxidized).
On a side note, chrome and iron work opposite to this. Chrome is protective as long as the surface of the chrome plating is unbroken. Once the iron beneath is exposed, it will preferentially corrode, as shown by the bumper on my Toyota.
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The next reference is from a metallurgist who listened as I asked corrosion questions specifically about our cable systems. He shared with me electromotive force, valence electrons and other stuff I'll spare you the details, but specifically I asked him about the zinc coating on the cable, life expectancy, and very specifically, the area inside the tree and whether this area was going to be more prone to corrosion. He said electrochemistry doesn't work that way. Anode protection, as he called it, offers
galvanic protection of the entire cable, not a specific part of the same cable. He asked me if I've ever seen a zinc galvanized cable that is rusting in one area and still coated in zinc in another. I told him I've seen plenty of rusty cables. He asked if I've seen any rusty cables that still had zinc on them. I had to answer honestly "No." He said that's because all the zinc needs to be consumed before the iron will oxidize. "How about ungalvanized cable attached to galvanized thimbles and galvanized lags?" Same thing, the zinc on the thimbles and lags will be sacrificed, or 'spent' before corrosion begins on the cable itself, as long as there is direct contact of the two dissimilar metals. Interesting.
What about the Zinc coating 'flaking off' when the strands of the cable are opened up and one central strand bent? He was looking at a picture I had of a traditional cabeling splice. "Like this?" I said, well, kinda, but then showed him a picture of a wedge and ferrule termination. He said
hot-dip galvanization of iron forms a
metallurgical bond to the parent metal where the two metals form a 'contact alloy'. It is not a 'plating' or simple surface coat and is not applied electrically through an anodization process like chrome. The steel is simply dipped in molten zinc and the natural bonding occurs.
What about nicks that may occur on the surface of the cable, exposing a portion of the iron hidden beneath? What about the cut ends of the cable? Again, the laws of electrochemistry apply. He also said zinc oxide and zinc carbonate (elemental zinc reacting with oxygen and carbon dioxide in the air) is a powerful surface protectant of the zinc itself and will surface-coat adjacent exposed iron, as long as there is direct contact. He said if bending and 'delamination' were a real concern, we should be more concerned with opening up the cable and winding 7 individual strands around and around the mother cable as compared to putting a mild bend in one single strand. "However", he says, "Electrochemically speaking, its all the same."
....pruning, storm damage?? )
