On Oct 26, 11:07 am, "Adam Corolla"
wrote:
wrote in message

ups.com...





On Oct 25, 8:43 pm, "Harold and Susan Vordos" wrote:
wrote in message

oups.com...

On Oct 19, 11:53 pm, "Harold and Susan Vordos" wrote:
"Todd Rich" wrote in message

...

Adam Corolla wrote:
snip-----

If it wasn't my only one, I've got a sintered 5# block from work.
An
unneeded engineering sample. I'll ask and see if they have any
others,
but I don't think they'll have one for a couple of weeks/months. It
is
weird how dense it is.

If you thinktungsten'sweird to handle, try gold, or even platinum.
Both
are heavier, platinum by a considerable amount. It's about 10%
heavier
than
gold, which is about 12% heavier thantungsten. Both are very strange
to
hold, and easily slip from your grip.

Harold

Harold,

If I'm not mistaken, gold has a density of 19.32 grams/cc andtungsten
has a density of 19.3, making them almost identical. You are correct
about the platinum, though, as it has a density of 21.45.

Thanks. Earlier, someone pointed out that I was mistaken, thattungsten
and gold are almost identical in specific gravity. I quickly verified
that they were correct, although there's considerable debate on the true
specific gravity oftungsten. There seems to be a consensus on the
reason. Tungstenis not melted when processed, but is worked via powder
metallurgical procedures. It, apparently, doesn't always end up at the
same level of density, or concentration. Can you add anything to that
concept?

Harold- Hide quoted text -

- Show quoted text -

Yes, I can elaborate a bit. Tungstenhas the highest melting point of
any metal, making it difficult to consolidate by smelting, melting,
and casting. Typically,tungstenis liberated from the ore by
chemical extraction as opposed to smelting. Crushed ore is sent
through a series of chemical reactions until one is left, finally with
tungstenoxide powder. This powder is then roasted in a hydrogen
furnace to yeild water and very puretungstenpowder. This powder
then must be consolidated. In the powder metallurgy process, the
powder is blended with a small amount of binder and pressed under high
pressure to form a fragile bar. This bar is placed in a molybdenum
tray and put into a hydrogen furnace to presinter. The solidifies the
bar a bit and drives out the binder. This bar is then placed in a
"sintering bottle" which is a quartz tube with two spring-loaded,
water-cooled contacts. A large electric current is then passed
through the bar, which heats it to very high temperatures. The bar
then sinters, or consolidates, shrinking as this happens, thus the
need for the spring loaded holders. The sintered bar is not fully
dense. Depending on the particle size and the sintering temperature
it is about 88% to 96% dense. However, this bar is usually densified
further by millwork, typically rolling or drawing, so that the final
product will come quite close to theoretical density. This is by far
the most common way of consolidatingtungsten, but there are others
such as arc casting, electron beam melting, and plasma spraying. Some
of these methods will produce a result that is very near or at
theoretical density.

Inkydog

That's fascinating. You might want to consider adding that info to
Wikipedia.

Wouldtungstenbe melted if there was a way to make an effective crucible
that wouldn't melt or react with thetungsten?- Hide quoted text -

- Show quoted text -

Tungsten does melt. You have correctly discerned that the issue
becomes containing it. Molds of carbon which may be water-cooled and/
or plasma sprayed with a tungsten coating are used in the arc casting
process. There are other methods as well which utilize water cooled
tubes where powder forms thin layer which is continually melted by an
arc or an electron beam. Powder is continually added and the
solidified cylinder which is created moves downward out of the tube as
each new layer is melted. Thus only a small amount of material is
melted at any one time. You will generally not ever see large
quantities of molten tungsten in a big crucible, such as those found
in a steel refinery.