Bill Aycock on sun 23 feb 97
At 08:41 AM 2/22/97 EST, you wrote:
>Bill--I remember hearing that oxidation didn't occur unless a fuel was
>being burned, so I always assumed electric kilns fired with neutral
>atmospheres. Has anyone else been under this impression? If I put paper
>into my kiln when the oxyprobe indicates a neutral atmosphere, will the
>paper not ignite?
>
>Later...Dave
>
Dave- correct- oxidation itself needs a fuel, but we are talking about the
state of the atmosphere in the kiln, and its potential for action, not the
action itself. If The paper ignites and burns, it means the potential for
oxydation was present, and you added the fuel, in the form of paper, and
caused actual oxydation to take place.
If the gas in the kiln has unreacted oxygen in it, and no unreacted fuel, it
is called "oxydizing". Common air is in that state; we live in an oxydizing
atmosphere, not a neutral one. If the gas in the kiln has a surplus of fuel,
it is called "reducing". In both these cases, with no other gas of the
opposite character to react with, the gases work on the solid material
present, when the temperature is high enough. In the case of the paper, that
Temperature is 451 Deg F (remember the book?)
A reducing atmosphere will strip oxygen from the compounds in the kiln, with
those that are weakly bound changing first. an Oxydizing atmosphere will
donate oxygen to the materials. Both these actions change the character of
the material acted on. The change we usually want is a change in color,
which we get by such changes as are possible with copper and iron, as examples.
Tom Buck has pointed out that an Oxyprobe can read neutral inside a vase
(for example) in an electric kiln. I have to believe him, because his
experience in this regard is much more than mine. However, what a guage
reads and what it means are dependant on calibration. I do not know how such
a probe is calibrated, but I will bet that it is set to read "Neutral" in
the open air, and that is not neutral. Air has about 20% by weight of
unreacted Oxygen in it, which is what we take advantage of when we fire up
one of those wonderful Ward Burners to "cook" our pots.
Bill, wishing the surplus O2 on Persimmon Hill would burn away his aches and
pains.
Bill Aycock --- Persimmon Hill --- Woodville, Alabama, USA
--- (in the N.E. corner of the State)
also-- W4BSG -- Grid EM64vr
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