Laura Conley on fri 31 jul 98
1) Hamer says that CdS produces yellows - does this mean that the S doesn't
vaporize? If S does vaporize and the Cd doesn't, does Cd form an oxide? If
the S oxidizes does the Cd vaporize too (thus solving the 2nd part of this)?
2) What actually happens to gold chloride, silver chloride, etc.? Do they
choose between a) reducing to the metal (no oxygen, the chloride vaporizes) and
b) becoming an oxide in the glass (and if so, what is the formula)?
Or is there another option?
3) What about bismuth? I know it can be Bi2O3, but what about when it is
reduced to mother of pearl? Is it just Bi?
Thanks,
Laura Conley
Tom Buck on tue 4 aug 98
Laura Conley:
Here's some more stuff....what ya doin'? are you about to sit for BS
finals? I give some comment below each question you sent.....
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
On Fri, 31 Jul 1998, Laura Conley wrote:
> ----------------------------Original message----------------------------
> 1) Hamer says that CdS produces yellows - does this mean that the S doesn't
> vaporize?
Yes, that is exactly it. The Cd and S are tightly bound into a molecular
species with high bond energy so the molecule doesn't decompose until
very high temps are reached, way beyond usual.
BUT! CdS goes from solid to vapour (sublimes) at under 1000 C (actual temp
depends on some other factors). The fumes are highly toxic.
> 2) What actually happens to gold chloride, silver chloride, etc.? Do
> they choose between a) reducing to the metal (no oxygen, the chloride
> vaporizes) and b) becoming an oxide in the glass (and if so, what is the
> formula)? Or is there another option?
Both precious metals are prone to stay as such, altho' silver will react
with oxygen and sulfur (tarnish).
The gold chloride decomposes below 300 C and becomes gold metal which is
non-reactive and stable to very high temps. In an oxidation kiln, the free
Cl- ions probably react with water molecules from the body and exit the
kiln as such (a range of choices are available including HCl). Gold will
not go to an oxide form since it decomposes too at under 300 C.
Silver chloride is more like NaCl, highly stable it will
melt at 455 C and remain stable as a liquid till 1700 C when it goes to
vapour. But if it is in a reducing atmosphere the compound will
change to Silver metal (it won't go to oxide since the oxide is not stable
at these low temps). Silver metal melts at 981 C, boils at 2212 C, so
Silver is metallic at raku temps. Again, the chloride will react with kiln
gases and form various compounds.
3) What about > bismuth? I know it can be Bi2O3, but what about when it
is reduced to > mother of pearl? Is it just Bi?
The stable form of Bismuth is either the metal or one of the oxides, and
one, Bi2O3, is the form that is most likely. The metal becomes liquid at
271 C, and stays in the liquid form til 1500 C. So, in a raku firing the
metal will be generated from Bismuth nitrate basic, the common commerical
form of bismuth compounds. In oxidation, however, Bi2O3 will form.
Bi2O3 has three different crystalline structures, and they switch
one to the other at temps from 700 to 860 C. The white/light yellow
crystal may dominate at temps below 700 C if cooling occurs rapidly so
that the grey/black crystal doesn't form.
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