Re: jumping ring demo

[brian whatcott <inet@INTELLISYS.NET>]

I made some cautionary comments about the dangers of scientific nit-picking
(on which I believe I have some expertise) and wrote this....
> > A soft alloy with silver or copper can be more conductive
> > than pure aluminum.
At 13:51 3/6/01 -0500, John S. Denker stood on several things, then wrote:

> Can you give an example of a AgCu alloy that (at room temperature) is
> softer than the pure state of the dominant constituent?
>
> Can you give an example of a AgCu alloy that is a better conductor than the
> dominant constituent?


Can anybody see a difference between the following two positions?

 "A soft alloy with silver or copper can be more conductive
than pure aluminum." (me)
...is not the same as
"Can you give an example of a AgCu alloy that (at room temperature) is
> softer [and or a better conductor]  than the pure state of the
dominant constituent?"   (you)

Anyway, backing away from debating games, here you go with some
conductivity numbers
(but see below for Terms & Cons):

Gilding metal        31 nano ohm.meter
Aluminum Alloy 1100  29
Aluminum alloy 7072  29
Aluminum 99.99%      27
Gold, pure           25
Gold commercial      23
Copper deoxidized    20
Copper, electrolytic 17
Silver, pure         16 nano ohm.meter


Though I don't specially believe it, there *is* an example
of John's 'touchstone' case in the list above. Can you see it?

There is another comparison that I find much more interesting.
The conductivity of aluminum alloy 7072 is comparable to Aluminum
alloy 1100.
 The former has quite a dollup of zinc - the latter is
relatively pure. Wonder what's going on here?

An anecdote that comes to mind: The US Navy used to run
a strip/plate shop for waveguides which were specified
(and perhaps still are) as copper body, silver plated.
 After a certain amount of sea service which is a searching
materials test no doubt, the siver plate was degraded.
More than one engineering sailor will tell you however, that
in a choice of oxidized copper, and oxidized silver,
 silver still wins.

Another anecdote: Once upon a time, IBM was king of office machines,
of which the tabulator was the mightiest (not to mention most expensive)

On one sad day at an office where the IBM tabulator was to be retired
in favor of a computer, some of the absolutely beautiful relays were
pulled. The replacable contacts were made of flexible silver alloy wires,
or silver plate wires. Or they had been.
 The whole silver confection was deepest black, in the ambient atmosphere
of the office which overlooked the phosphorus processing plant.
 (But then, a walk down the road could produce a succession of pops
and crackles too, reminding one of the active ingredient of the red-top
match. What's a 'match', I hear...)



brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!