Steve Slatin on thu 8 jun 06
Fred --
I'm willing to explain it, but whether it's
correct or comprehensible is another matter ...
Reduction is the opposite of oxidation. In
reduction, the oxidation number (the + or -
number that shows when you have an ion as opposed
to a molecule) is reduced, in oxidation, it is
increased. The reason for the use of the word
'oxidation' is that oxygen is the great oxidizer
... and maniupulating the oxygen concentration in
something oxidizes, or reduces, the compound.
Metals that are fully reduced either nucleate
crystal grains to form pure metal crystals, or
migrate to be incorporated into existing lattice
sites, causing growth of metal crystals.
There are different ways to reduce the oxidation
number. John Britt showed us that you can get
iron hot enough so it'll reduce to a pure metal
from heat alone. Neat trick, he makes great oil
spot glazes with it.
A second way is with carbon monoxide -- CO -- in
the kiln, which will 'pull' oxygen from oxidized
metals at the surface of the glaze, leaving a
reduced -- pure metal -- behind. Since there's
lots of CO in an incomplete burn of carbon
materials, wood, coal, gas, and oil kilns can
generate lots of CO for reduction.
Also, you can have a reaction take place within
the melting glaze. Silicon carbide -- SiC -- in
a melting glaze allows the Si becomes one ion
(which then bonds into the uber-molecule of
glaze) and the C another, within the melted
solution. If the C runs into CO2 they make two
CO (carbon monoxide) ions.
I understand that it works best with very, very
finely ground SiC (which makes sense, it doesn't
melt until 2700 C, so it's not going to migrate
much by itself within the melt).
-- Steve S
--- Fred Parker wrote:
> Can anyone explain (or direct me to a resource
> that can explain) "local
> reduction" in an electric kiln? I have read
> here and there that silicon
> carbide can induce "local reduction" thereby
> enabling such as copper reds
> in an electric kiln, presumably without
> damaging elements. I found much
> discussion in the archives, but it seems to be
> between folks who already
> understand it -- and I don't. If anyone has
> had any success trying it,
> and is willing to share info, I'd much
> appreciate it.
Steve Slatin --
The angel lay in a little thicket. It had no need of love; there was nothing anywhere in the world could startle it ...
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
Fred Parker on thu 8 jun 06
Can anyone explain (or direct me to a resource that can explain) "local
reduction" in an electric kiln? I have read here and there that silicon
carbide can induce "local reduction" thereby enabling such as copper reds
in an electric kiln, presumably without damaging elements. I found much
discussion in the archives, but it seems to be between folks who already
understand it -- and I don't. If anyone has had any success trying it,
and is willing to share info, I'd much appreciate it.
Thanks,
Fred Parker
| |
|
