In article ,
Tim Williams wrote:
"DoN. Nichols" wrote in message
...
5.Epoxy mixed with metal powder
Similar feelings about these -- except that they might handle
two or three -- depending on how well cooled the mold is.
If they are indeed used, I would suspect the binder burns out (*cough*) on
the surface, leaving a somewhat temp-resistant layer of filler.
6.Graphite molds is there a way for me to make mold using it. I Would
like able to pour it.
*Pour* it? Graphite is a crystalline form of carbon. According
to my old copy of the _Handbook of Chemistry and Physics_, carbon's
melting point is 1350 C
Whoa! You missed a rather large factor there, DoN. ;-)
You're right. One of the problems of having to put on glasses
to read the small type in the _Handbook_, and having to take them off to
see the screen at about 24" distance from my eyes.
Re-reading I find 3550 C and 3500 C (6422 F and 6332 F
respectively).
Next closest thing I see on my periodic table is either terbium, dysprosium
or silicon. The latter makes the most sense since it's right below carbon.
As for carbon itself, it melts/sublimes (nearly the same at 1atm pressure)
somewhere around 4000°C, or about 7150°F. Just a *little* bit hard to
cast...
I mentioned the problem of it subliming below the melting point.
And, it looks as though you used one of the extended ASCII characters
for degrees, which displays as '\260' on my screen -- one reason for
avoiding using *any* extended ASCII character -- not everybody sees them
the same.
And we still have a disagreement of melting points (though not
as extreme as before). Mine is from the _Handbook of Chemistry and
Physics, 43rd edition_, (1961-1962). "(Description of) The Elements",
starting page 405, with Carbon on page 410-411. The first few lines
read:
"Carbon (L. icarbo/i, charcoal), C; at. Wt. 12.001; at. no.
6; m.p. 3550 deg C, sublimes above 3500 deg C; b.p. 4200 deg C;
sp. gr. amorphous 1.88, graphite 2.25, diamond 3.51; valence 3,
3, o4 4."
I don't think that the characteristics of Carbon, or our
knowledge of them, have changed that much since 1961. :-)
Forgive me for the use of HTML tags in there, but I was not sure
of any way to show italics to everyone -- some newsreaders may actually
*display* that as italics -- the rest will cue the reader that they
should be italics.
So -- what is the source for *your* figures, now that I have
corrected mine?
(neglecting whether it would form the right crystal form on cooling,
instead of diamond or some amorphous form)
Would be neat if molten carbon crystallized into diamonds, but unfortunately
that takes a lot of pressure, AFAIK.
Yep -- sometimes achieved by surrounding the carbon with steel
which shrinks in the chilling, generating the forces necessary -- but
only for very small diamonds.
Although I think they've been getting
around the extreme pressure or temperature things with CVD (chemical vapor
deposition), I should read up on the current tech (if it isn't a total trade
secret).
That would be interesting. I wonder what happens with vapor
deposition -- assuming that the "boats" can get hot enough to evaporate
carbon. If you started depositing it on a seed diamond, and on
something with a matching crystal lattice, the crystal might grow
nicely.
Just to put it into perspective, that melting point, which was
given in degrees C (1350) translates to 2462 F -- well above what I can
reach (1850 F) in my metal hardening oven.
Within reach of a good foundry furnace, though. My graphite-based crucibles
aren't falling apart in the heat, so I think you grabbed the wrong number
;-)
I did -- or at least typed the wrong one.
And since carbon dust from the machining can be rather abrasive,
depending on how pure the graphite is
Actually, I'm not sure if purity is the cause. IIRC, "graphite" is made
artificially by heaping ground charcoal or coke, lampblack, other junk and
pitch together into an electric furnace. The pitch decomposes to either
amorphous or graphitic carbon, binding together the mass; the other material
is recrystallized by the intense temperature, forming a polycrystalline
block. I've heard the structure described as nodules, globs, flakes and
other junk. It's still graphite, but it's kinda random I guess, and that's
why it's abrasive.
O.K.
I imagine natural graphite (probably damned expensive) would be wonderful
stock to machine.
I suspect so.
I don't know what metals are a proper choice for glass molds,
but it would have to be something which could run at a temperature near
that of the molten glass, so you don't get a sudden cooling and
fracture your workpiece.
Eh- pressed glass is made in warm (dark red heat, probably 1200°F) cast iron
molds. Worked glass is formed with steel and moistened wood tools!
(Lichtenfrost effect, anyone?)
You mean floating the glass above the wood on a film of steam?
Enjoy,
DoN.
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