Tungsten Facts (was: Re: Coil Meeting...)

["Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Finn, Gary, Chip and all Tungsten´ers,

----- Original Message -----
From: Tesla List <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, June 29, 1999 1:38 AM
Subject: Re: Coil Meeting...

> Original Poster: Finn Hammer <f-hammer-at-post5.tele.dk>
> Tesla List skrev:
> > Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> snip
> > I wonder if the tungsten has a higher resistance that causes
> > extra heating?
> I asked the chief metallurgist at "Danit", a danish sinter metal
> factory, about this recently, He said the conductivity of Tungsten
> carbides is in the range of 1/10 to that of copper.
>
Snip

Okay, now let me make some sawdust out of all the hairs and
splinters already produced ....;o)).

You (Finn) wrote something similar a while ago. I think you are
confusing Tungsten (Wolfram) and Tungsten Carbide. Tungsten
carbide is used to make lathe and mill tools (for example). This
is NOT what is (usually) used in rotary spark gaps as electrode
material. Instead, we use the pure metal Tungsten.

Here is a little more info on this interesting metal:

Tungsten literally means heavy stone. Tungsten is derived from
tungsten oxide (wolframite) heated with charcoal (it is a simple
reduction process). The word Wolfram comes from the fact that
tungsten (before "tungsten" was known to mankind) "consumes"
tin. Scientists, at the time, were trying to extract tin from
cassiterite (tinstone). Both this and wolframite are very often
found together in nature. They noted that the tin was consumed
by the tungsten "like a wolf". Hence the german name "Wolfram".

In the early days of incandescent lamp manufacturing, a carbon
filament (core) was coated with tungsten hexachloride. This
carbon wire was later heated to incandescence in an atmosphere
of pure hydrogen. The carbon filament completely dissolves and
leaves a "pure" tungsten carbide filament. This was then further
heated in a stream of of hydrogen (I believe at sub
incandescence), which reduced the filament to pure tungsten.
This results in a tubular shaped form. The reason this was done, is
because tungsten is not very ductile. This means you can´t just wind
a filament from a piece of tungsten wire, because it will break.

Tungsten is a very stable element. Tungsten is non-soluable in
most regents. Just about the the only thing that will really attack
tungsten is a mixture of hydrofluoric and nitric acid, although
interesting results can be had by putting tungsten filings into
fluorine or in iodine pentafluoride (DON´T do it, unless you
know how to handle these dangerous chemicals!).

Chemical facts:
---------------------
Density: 19.5 gr/cc
Melting point: 3410°C
Boiling point: 5530°C
(This is why it is incrediably difficult to get the
tungsten out of the raw ore.)

Resistance -at-:
20°C: 5.5µohms per cm
1700°C: 55µohms per cm
(so I wouldn´t worry about electrode resistance,
even in sintered form ;o})

Tensile strength -at-
20°C: 100,000-550,000 psi
1000°C: 75,000 psi

Hardness a la Brinell: 2570
(which is why Terry ruined his files ;o])

Electronegativity 2.36eV
(This is why tungsten is not "interested" in
combining readily with other materials.)

Total emissivity at 2000°C: 0.28
(Iron BOILS at a "few" (2750°C) degrees more.
So, this is a very low (good for us) factor.)

>From the above, we can see why Tungsten is such a great
material for our RSG electrodes.

Coiler greets from germany,
Reinhard