Aluminum has several characteristics that make it a bad choice for any current
First is the fact that when placed in soil under even the smallest current it
wants to return to the state it was as a ore. Hence you get a nice white
powder/scale like the bauxite it was refined from.
Second you always have a problem with migration out from under any setscrew
connection.(That's why its not a common housewireing practice after the fiasco
in the early 70's and all the fires traces to connections that loosen up after
a year) Thermal cycling with the large coefficient of expansion and its natural
softness of wiring grade Al explains all. When used in electrical services they
either use a special crimped lug of if setscrew it must be re-tightened on a
yearly biases. The lack of yearly checks on Al wire is the most common service
Third is that Al will form aluminum oxide in minutes on freshly bared Al.
This is the black stuff you get on your hands putting your antennas together.
It is a very poor conductor and is more of a problem with plumbers delight type
of construction as compared with antennae that use insulated from the boom
Aluminum is a wonderful metal, they just haven't yet figured out how to make
it hard and corrosion resistant and still high conductivity. The smelter that
produced the purest Al for wire was shut down due to a buyout by competitor
wire manufacturer from overseas. Go figure?
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