Bill Aycock on wed 12 nov 97
I hate to disagree with one of the best qualified experts we have, but- (to
me) words and definitions are very important. I worked for many years with
combustion processes, including advise and consultation to fuel chemists.
there is a vast difference between "Oxidation" as a process, and
"Oxidizing" as a condition. "Oxidation" means something is happening-
namely, an Oxidizing element is entering into combination with other
elements. "Oxidizing" describes a condition where there is enough
Oxidizing material present to participate, IF (important IF), there is
anything present that is ready to participate. The result of having an
Oxidizing atmosphere in contact with things that are perfectly happy at
their present state of combination is a "neutral" process.
Simple re-statement--- If the material in an Oxidizing atmosphere is
already oxidized to the normal state, the result will be a neutral exchange.
simpler re-re-statement-- In an electric kiln, the atmosphere is Oxidizing,
but the process is neutral.
At 07:50 AM 11/11/97 EST, Mark Ward wrote: (in part- I snipped some)
>----------------------------Original message----------------------------
>When I made my post about oxidation/reduction, I knew we were going to cover
>the same ground we have before.
>
>>>>>
>
>A neutral atmosphere is pretty much next to impossible to obtain in a gas
>fired kiln. Neutral means nothing is changing in the atmosphere of the kiln.
>
Right- in both an Electric and a fuel burning kiln. The key definition is
important- **nothing is changing. **
>
>You can not oxidize in an electric kiln. Oxidation firing in an electric kiln
>is a misconception. What everyone wrongly refers to as oxidation is really a
>neutral atmosphere. Nothing's really going on except the atmosphere just gets
>hotter along with the ware.
>
Wrong- the atmosphere IS Oxidizing, because there is a surplus of Oxygen
present. The result is a neutral firing, but only because all the
materials are already at their preferred state of Oxidation. If there are
materials present that are not at the preferred state- you had better
believe they WILL oxidize, even in an electric kiln, with or without a
power vent. Try sticking a small piece of paper into your peep hole.
>An electric kiln will give you a neutral firing.
>
RIGHT but only because the materials are happy with their current condition.
>A gas kiln will give you a reduction firing, a stoichiometric firing, or an
>oxidation firing. A stoichiometric ratio is achieved when there is perfect
>combustion....no excess oxygen (oxidation) or a deficit of oxygen
>(reduction). Some people mistakenly refer to a stoichiometric atmosphere as
>a neutral atmosphere.
>
Right- because you can control the level of Oxygen present, from the amount
in normal air, to a deficit, by furnishing a surplus of oxygen consuming
material- namely, the fuel. NOTE- the maximum amount of Oxygen present in
the atmosphere in a fuel burning kiln is THE SAME AS IN AN ELECTRIC KILN!
Bill- who COULD NOT resist participating in this , but happy he is out of
physical range, here on Persimmon Hill.
Bill Aycock --- Persimmon Hill --- Woodville, Alabama, US 35776
--- (in the N.E. corner of the State) ---
W4BSG -- Grid EM64vr --
baycock@hiwaay.net
Evan Dresel on fri 14 nov 97
I've been getting ready to dive into this one so it seems to be a good time.
I agree with Bill. Actually I see it more as a question of degree.
Oxidation-reduction is a continuum. You can be really oxidizing -- as Bill
described the condition where there is the potential to oxidize something or
really reducing where there is the potential to reduce something. There is
also lots of room in between. It's all kind of relative and there is no
point which can be described as neutral.
Maybe the best way to describe it is with an example like carbon. We all
know carbon in the form of graphite or charcoal, pure carbon, can burn --
that is be oxidized. When that happens you get carbon dioxide which is the
more oxidized form of carbon. But if you don't have enough oxygen around
you end up with carbon monoxide. Carbon monoxide is more oxidized than
charcoal but more reduced than carbon dioxide. Now in a gas kiln when you
shut off some of the air supply you produce carbon monoxide which has a
useful property of being able to diffuse into a pot and react with iron in
the clay or glaze. If there is any iron in it's oxidized form present then
it can be reduced by the carbon monoxide. In this reaction the carbon in
the carbon monoxide becomes more oxidized. You can't oxidize something
without reducing something else. You can oxidize something without oxygen
-- you just need any element in a more oxidized state than the thing you are
oxidizing. (oxygen gas just happens to be quite oxidized and plentiful and
has lent it's name to the whole process. Yep, that's confusing, but you
probably don't want to hear about electron transfer.)
Most elements can be found in several oxidation states. You can rank the
states for the element from most reduced to most oxidized. With all those
different elements in all their different states you get a lot of possible
chemical reactions at all different oxidation/reduction potentials.
-- Evan in W. Richland WA where there are lots of geese flying overhead.
At 06:25 PM 11-12-97 EST, you wrote:
>----------------------------Original message----------------------------
>I hate to disagree with one of the best qualified experts we have, but- (to
>me) words and definitions are very important. I worked for many years with
>combustion processes, including advise and consultation to fuel chemists.
>there is a vast difference between "Oxidation" as a process, and
>"Oxidizing" as a condition. "Oxidation" means something is happening-
>namely, an Oxidizing element is entering into combination with other
>elements. "Oxidizing" describes a condition where there is enough
>Oxidizing material present to participate, IF (important IF), there is
>anything present that is ready to participate. The result of having an
>Oxidizing atmosphere in contact with things that are perfectly happy at
>their present state of combination is a "neutral" process.
>
>Simple re-statement--- If the material in an Oxidizing atmosphere is
>already oxidized to the normal state, the result will be a neutral exchange.
>
>simpler re-re-statement-- In an electric kiln, the atmosphere is Oxidizing,
>but the process is neutral.
>
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