Amy Yanalunas on wed 19 feb 97
Hi Again!
I'm interested in possible methods Clayarters have used to turn the
oxidation environment of an electric kiln into a reduction environment.
Has anyone tried addition of CO2 while firing or a CO2/Argon mixture
piped in through one of the peeps during firing? I think this could be
a very cheap way to reduce the oxidation environment in an electric kiln
thereby reducing the wear on the firebrick due to oxidation. And I can
use all the glazes I love!
I am a hobby potter looking forward to the arrival of my electric kiln,
but am in love with the glaze affects achieved with a reduction
environment (Unfortunately I don't have the time, nor the finances to
build/purchase a gas kiln). Tryin' to get double duty outa my purchase
so to speak ;) And heck if it works for welding environments why not
try it with pots too?
Can't wait to hear some responses!
Amy
Don Jung on thu 20 feb 97
Amy, I too tossed the idea about and I still don't rule it out
completely, but after some research, it may be more difficult than you
describe. By piping in CO2, you don't actually achieve a reduction
atmosphere...but simply a neutral atmosphere which is what an electric
kiln usually has anyways. To create a reduction atmosphere, there has
to be some reaction taking place that will create an imbalance in the
amount of oxygen available to complete the reaction.
So with your idea, something still has to burn while you pipe in the
CO2. Since the CO2 may not give up the Oxygen that readily, it will
likely speed up the reduction process and reduce the amount of
combustible material required. With just CO2, there's probably not
enough ingredients in the glaze or atmosphere that will react and draw
the Oxygen from the glaze ingredients to create the reduction effects
you want. Testing of course will be the real proof. I believe it's
possible with the right choice of combustibles and a combination of
saggars and control of the gas entering the kiln. When I get more time,
I'll probably look into it more.
You may also want to clarify if an electric kiln (not oxidizing)
atmosphere deteriorates firebrick faster. The kiln elements will also
probably take a beating with a reduction atmosphere.
Keep coming with those ideas...and test safely.
Don Jung
Kensington Pottery Club
Vancouver BC
Amy Yanalunas wrote:
>
> I'm interested in possible methods Clayarters have used to turn the
> oxidation environment of an electric kiln into a reduction environment.
> Has anyone tried addition of CO2 while firing or a CO2/Argon mixture
> piped in through one of the peeps during firing? I think this could be
> a very cheap way to reduce the oxidation environment in an electric kiln
> thereby reducing the wear on the firebrick due to oxidation. And I can
> use all the glazes I love!
....snip
Bill Aycock on fri 21 feb 97
At 07:01 AM 2/20/97 EST, you wrote:
>----------------------------Original message----------------------------
>..but simply a neutral atmosphere which is what an electric
>kiln usually has anyways.
>You may also want to clarify if an electric kiln (not oxidizing)
>atmosphere deteriorates firebrick faster.
>Kensington Pottery Club
>Vancouver BC
>
Sorry- an electric kiln does not have a neutral atmosphere, it is oxidizing.
If you dont believe me, try dropping a piece of paper through the peep hole
when the temp is about 900 F- You will see a good example of oxidation
(burning, that is)
I have seen enough references to this situation that I wonder which school
started the error. This is what is called a fossil- it persists despite all
attempts to correct it.
Bill, on Persimmon hill.
Bill Aycock --- Persimmon Hill --- Woodville, Alabama, USA
--- (in the N.E. corner of the State)
also-- W4BSG -- Grid EM64vr
Dave and Pat Eitel on sat 22 feb 97
>----------------------------Original message----------------------------
>At 07:01 AM 2/20/97 EST, you wrote:
>>----------------------------Original message----------------------------
>>..but simply a neutral atmosphere which is what an electric
>>kiln usually has anyways.
>>You may also want to clarify if an electric kiln (not oxidizing)
>>atmosphere deteriorates firebrick faster.
>
>>Kensington Pottery Club
>>Vancouver BC
>>
>Sorry- an electric kiln does not have a neutral atmosphere, it is oxidizing.
>
>If you dont believe me, try dropping a piece of paper through the peep hole
>when the temp is about 900 F- You will see a good example of oxidation
>(burning, that is)
>
>I have seen enough references to this situation that I wonder which school
>started the error. This is what is called a fossil- it persists despite all
>attempts to correct it.
>
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 Eitel
Cedar Creek Pottery
Cedarburg, WI
pots@cedarcreekpottery.com
http://www.cedarcreekpottery.com
Don Jung on sun 23 feb 97
Haste makes waste...didn't clarify and think it through enough before
pressing the button. I don't consider myself an expert...so if I'm off
base, I appreciate everyone's clarification/corrections :). I think
it's just the use of the word oxidation that may suggest that something
more is happening. I believe Oxidation and Electric kiln firings have
been too loosely equated and I hope I don't confuse the issue.
Practically speaking Bill, I think you're correct...but as will most
things...I also think...it depends. My use of the description neutral
is to suggest that the atmosphere in an electric kiln is not a
significant contributor to the glaze firing. It doesn't react with and
change much (stays neutral) whereas the gas fired reduction kiln has a
very reactive atmosphere and affects the glaze ingredients. So where
was I going...ah yes, if you substituted the oxygen atmosphere with some
other gas (non combustable), that it wouldn't significantly change the
glaze firing.
Oxygen is in an electric kiln and since most are not tight enough to
keep out any new air, there will likely be more oxygen introduced as the
air moves, or if a peep is opened. Kilns with vents will definitely get
air and oxygen introduced. So if something that wants to burn and
oxidize, it can in an electric, but glaze on a pot doesn't oxidize...it
just matures oui/non?
I believe someone mentioned that an electric may actually achieve a
reducing atmosphere during a bisque firing...under the right
conditions. This is due to the burning out of organic stuff, but it's
usually short lived as new air is introduced (hot air rising, expanding
and sneaking out...new air drawn in). Heck we could discuss more if
you want...off list or on?
As for Dave's question about paper introduced when the oxyprobe says
neutral...If the temp is high enough, I believe the paper will change
state and create the condition of reduction. It's looking around
excitedly for oxygen or something similar to complete a reaction. If
oxygen is taken from the glaze or somewhere, it'll 'burn' or 'flame on'
when it finds oxygen.
Hardly complete, but gotta stop and digest it before I confuse everyone
and myself.
Thanks...always looking to expand my knowledge and give what I can.
Don Jung
In sunny Vancouver BC!
Dave and Pat Eitel wrote:
>
> ----------------------------Original message----------------------------
> >----------------------------Original message----------------------------
> >At 07:01 AM 2/20/97 EST, you wrote:
> >>----------------------------Original message----------------------------
> >>..but simply a neutral atmosphere which is what an electric
> >>kiln usually has anyways.
> >>You may also want to clarify if an electric kiln (not oxidizing)
> >>atmosphere deteriorates firebrick faster.
> >
> >>Kensington Pottery Club
> >>Vancouver BC
> >>
> >Sorry- an electric kiln does not have a neutral atmosphere, it is oxidizing.
> >
> >If you dont believe me, try dropping a piece of paper through the peep hole
> >when the temp is about 900 F- You will see a good example of oxidation
> >(burning, that is)
> >
> >I have seen enough references to this situation that I wonder which school
> >started the error. This is what is called a fossil- it persists despite all
> >attempts to correct it.
> >
> 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 Eitel
> Cedar Creek Pottery
> Cedarburg, WI
> pots@cedarcreekpottery.com
> http://www.cedarcreekpottery.com
Ric Swenson on sun 23 feb 97
>----------------------------Original message----------------------------
>>----------------------------Original message----------------------------
>>At 07:01 AM 2/20/97 EST, you wrote:
>>>----------------------------Original message----------------------------
>>>..but simply a neutral atmosphere which is what an electric
>>>kiln usually has anyways.
>>>You may also want to clarify if an electric kiln (not oxidizing)
>>>atmosphere deteriorates firebrick faster.
>>
>>>Kensington Pottery Club
>>>Vancouver BC
>>>
>>Sorry- an electric kiln does not have a neutral atmosphere, it is oxidizing.
>>
>>If you dont believe me, try dropping a piece of paper through the peep hole
>>when the temp is about 900 F- You will see a good example of oxidation
>>(burning, that is)
>>
>>I have seen enough references to this situation that I wonder which school
>>started the error. This is what is called a fossil- it persists despite all
>>attempts to correct it.
>>
>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 Eitel
>Cedar Creek Pottery
>Cedarburg, WI
>pots@cedarcreekpottery.com
>http://www.cedarcreekpottery.com
_______reply_________
Electric kilns heat by means of radiating the heat from coils to the
potttery....Neutral atmosphere...beacuse nothing is "burning"
Oxidation and reduction have to do with convection heating...ie gases
travelling through the kiln from the burner to the flue and in transit
heating the pottery.
Watch the Movie "Farenheit 451" THAT is the temperature at which paper
burns (a good flick about the obvious stupidity of book burning") It
matters very little HOW the paper gets to 451 degrees....it burns.
It is different with firing pots....the atmosphere of the kiln can
radically change the effects of the coloring oxides in glazes. Reduction
started ...they say in lore.......when the Chinese potter produced copper
red colors....at first by accident...and when the Emporor insisted that he
reproduce the colors...and the potter could not....he was thrown in the
kiln and what do you know ??? the smokey atmosphere again produced
copper red colors! Pigs thrown in to the firing chamber assured later
potter of a good reducing atmosphere...lacking in oxygen...."reduced" in
oxygen rather than rich in oxygen....or oxydizing. People used to throw
asphaltum into electric kilns trying to get "reducing" effects. I do not
recommend this for your kiln...or for your lungs...
Ric Swenson, Bennington, Vt
Gavin Stairs on mon 24 feb 97
....
>>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?
....
Hi All,
An electric kiln, with an unmodified air astmosphere, is oxidizing because
of the presence of oxygen in the air. There is no fuel burnt, which keeps
the oxygen level high. An electric kiln can be more oxidizing than any fuel
kiln, unless you inject oxygen by itself.
If you thrust a piece of paper into a reducing atmosphere which has been
completely exhauster of oxygen, it will no burst into flame. It will char,
letting loose even more carbonaceous gases. In pottery, we normally mean
that a reduction atmosphere is rich in carbon and carbon compounds that
would normally react with oxygen to form CO2. The excess carbon reacts with
oxides (and other stuff) to produce carbides and free metals, which give
copper and other metallic glazes, as well as certain lustres.
Gasses like CO2, N2 and Ar are shield gases, which do not react (much) with
ceramic oxides, and are therefore neutral. A fuel kiln which has just
enough air to burn all its fuel is said to be neutral, since there is
neither free oxygen nor free carbon or CO. The kiln atmosphere then
consists of N2, CO2 and H2O, with traces of other gases, like Ar. Note that
hot H2O is very corrosive, so to call a neutral atmosphere unreactive is not
strictly true. But it does not exhibit the strong oxidation or reduction
effects of the other cases.
We depend on the oxidation reactions of some phase of the firing to oxidize
the glaze and body chemicals to oxides from the raw recipies that we make
up. It is only after this is done that we begin to reduce, in order to
exploit the other effects noted above. While any kiln is cooling, if we are
not careful to keep supplying carbon, the atmosphere may turn oxidizing, and
remove all the carbon in the ware.
Of course, such a short note could not possibly explore all the possible
complexities. Kiln reactions rarely go to completion, or to equilibrium.
So not all of the original stuff may be oxidized, and not all of the carbon
may be removed, etc. Thus there is an enormous range of variations
possible. And I haven't even mentioned diffusion.
Happy firing, Gavin
Bill Aycock on mon 24 feb 97
At 10:21 AM 2/23/97 EST, you *** (Ric Swenson) *** wrote:
>----------------------------Original message----------------------------
>
>_______reply_________
>
>Electric kilns heat by means of radiating the heat from coils to the
>potttery....Neutral atmosphere...beacuse nothing is "burning"
>
>Oxidation and reduction have to do with convection heating...ie gases
>travelling through the kiln from the burner to the flue and in transit
>heating the pottery.
>.lacking in oxygen...."reduced" in
>oxygen rather than rich in oxygen....or oxydizing.
>Ric Swenson, Bennington, Vt
>
>Ric- I'm sorry to tell you this -- but-- that is wrong. The source of the
heat, and whether there is "burning" or not, to supply the heat, is not what
determines the potential for reaction that we normally refer to as
"reducing", "Neutral" or "Oxidizing". Granted, it is easier to get into a
reducing state if you have a fuel to consume the oxygen as part of your
process, but just because the heat source is electric doesn't make it
neutral-- that is controlled by the atmosphere in the kiln, not the heat source.
Air in a kiln is oxidizing, unless you do something to consume the O2. An
electric kiln does not normally do that. The fact that there is no
combustion does not mean that it is neutral, it just means that everything
that can oxidize is already there. Please note the formula for most of the
ingredients-- eg, Na2O-K20-Al2O3-SiO2-CaO- all these are already oxidized,
and dont need any more. Now, if there is organic matter, or sulfur present,
or if you add a fuel to "get" the O2, you can achieve neutrality.
There is more folklore about this subject than there is about many of our
processes. The story about the pig is just one of them.
Bill- thinking about sacrificing a cat that is bugging me to be fed- here on
Persimmon Hill
Bill Aycock --- Persimmon Hill --- Woodville, Alabama, USA
--- (in the N.E. corner of the State)
also-- W4BSG -- Grid EM64vr
Vince Pitelka on mon 24 feb 97
>Has anyone tried addition of CO2 while firing or a CO2/Argon mixture
>piped in through one of the peeps during firing? I think this could be
>a very cheap way to reduce the oxidation environment in an electric kiln
>thereby reducing the wear on the firebrick due to oxidation. And I can
>use all the glazes I love!
Amy -
Neat idea, but I don't think it will work. I'll look forward to some other
opinions on the subject, but here's my feeling on this idea. CO2 will not
produce a reducing atmosphere, because CO2 is what is produced BY a reducing
atmosphere. To have a reducing atmosphere in a kiln, you need superheated
unoxidized carbon floating around in the kiln, desperately looking for
oxygen to combine with to form CO and/or CO2. What we refer to as a
reducing atmosphere reduces the clay by oxidizing (combusting) the carbon.
Regarding the firebrick, oxidation is not harmful to the refractory. It is
reduction that causes wear and tear on refractory, especially if it is being
fired to it's upper limit of performance in a reducing atmosphere.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
Richard Burkett on tue 25 feb 97
Vince says:
>To have a reducing atmosphere in a kiln, you need superheated
>unoxidized carbon floating around in the kiln, desperately looking for
>oxygen to combine with to form CO and/or CO2. What we refer to as a
>reducing atmosphere reduces the clay by oxidizing (combusting) the carbon.
Actually, gases like hydrogen and CO (carbon monoxide for those who fear
only intials) are MUCH more effective at producing reduction than atomic
carbon floating around the kiln. Hydrogen is particularly effective in that
it is both one of the most aggressive atoms in wanting to combine with
oxygen, AND the smallest atom, allowing it to go almost anywhere seeking
oxygen atoms with which to combine. Carbon atoms, by comparison are
relatively huge. While carbon does play a big part - it certainly helps
to keep stray oxygen atoms busy as it floats through the kiln - the
hydrogen is probably the thing most affecting your bricks and ware during
reduction.
Richard Burkett rburkett@rohan.sdsu.edu
San Diego State University
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