Re: jumping ring demo

[brian whatcott <inet@INTELLISYS.NET>]

At 16:30 3/6/01 -0800, Larry Woolf wrote:

> Stating "a soft alloy with silver or copper" indicates an alloy of at least
> two elements, where one of the elements is silver or copper.

Yes

> It does not
> mean pure silver or pure copper.

Yes indeed!

If an element contains a small amount of
> impurities, it is generally not considered an alloy - it just has some
> impurities

I see your position. Not sure where you would draw the line between
an alloy and a metal with 'some impurities'.
Duralumin (of Graf Zeppelin, "oh the humanity of it" ) now known
as 2024 alloy is considered to be an alloy with about 4% copper.
Carbon steel contains as its principal alloying agent
0.1 to 0.9% carbon. Steel is inherently an alloy, I'd think.

I think you are saying that a material that has more than
...what shall I say, 0.1% alloying material 'qualifies',
 else it's just impure?

Another definition of an alloy is a solid solution of one material
 in another. Some materials mutually dissolve in any ratio.
Even in 'impurity' amounts!

> Silver tarnish due to the formation of silver sulfide, not silver oxide.

Yes.

> Your table indicates that pure gold is more resistive than commercial gold.
> These names have little meaning in terms of impurity content.  Resistivity
> is most affected by impurities that substitute at lattice sites, and is less
> affected by interstitial impurities.

Not my table, just a commercial list from an NDT web site.
By all means show me better numbers; the two rubber books I have
don't expatiate on the topic.

>  Resistivity is also sensitive to
> synthesis parameters such as heat treatment temperatures
> (grain size, defect density) and phase purity.
>
> Larry

Yes indeed!

> 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

At any rate, I now repeat my point (you might even say I am
standing on it) that an innocent physicist might well find
an aluminum tube for his 'jumping ring' demo consists of
the ubiquitous 6061, a quite tough alloy of resistivity 37 to 44
nano ohm.m rather than a soft alloy like 1100 which is still
quite accessible. A roof flashing roll at the hardware is
likely to be soft and comparively conductive.
 You could possibly solder a strip of that into a ring.
Ordinary solder is quite suitable, though there are others
needing less technique.

Is this really so controversial?

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