WardBurner@aol.com on tue 11 nov 97
When I made my post about oxidation/reduction, I knew we were going to cover
the same ground we have before. I'm already starting to get questions....."I
was taught that...". I'll repost my original, followed by a sample question
I received, then my reply;
Joyce asked;
<<<and neutral when firing in a reduction kiln, I would be most
appreciative. >>>>>
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.
This is far from what is happening. Combustion is a violent process at the
molecular level and releases quite a bit of energy (heat) and by products
(water vapor, carbon dioxide, carbon monmoxide, nitrous oxide, ect.) An
oxidation atmosphere, on the other hand, is one where there is an excess of
oxygen (one of the main components of combustion). Here's the shock for most
people;
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.
An electric kiln will give you a neutral firing.
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.
For new folks on the list, we've been through this before....so there's no
reason to start an argument over this. If that much loved (and maybe famous)
teacher of your's called an electric firing "oxidation", they were wrong and
didn't know it.>>>>
So the first question I get from someone goes like this;
<<<
referred to the fact that oxygen was present during and electric firing.
That reduction was called that because you reduce the oxygen supply to the
gas. I understand what you are saying, but isn't there oxygen present in
the electric kiln?>>>>
My answer to them;
<<<apart by the combustion process. Because of this, virtually all of it remains
in a nonreactive state. Electric firings are neutral not oxidation. As I
mentioned in my post, many people have been taught something that is
wrong.>>>>
Now Vince pointed out that these terms have been in use for years and nobody
is going to change. Granted, and I don't intend to try to change anyone. But
when someone asks a question that involves confusion about terms, I tell them
the "right" answer not the accepted answer.
As far as Vince's question about air entering the electric kiln and thus
creating an oxidation atmosphere......My answer is the same as when Vince
asked this last year. This air and the oxygen in it are almost entirely
nonreactive. Electric kilns produce a neutral firing, not an oxidation
firing.
Marc Ward
Ward Burner Systems
PO Box 333
Dandridge, TN 37725
USA
423.397.2914 voice
423.397.1253 fax
wardburner@aol.com
Ric Swenson on wed 12 nov 97
Another angle to understand in electric/gas firings are the concepts of
RADIANT HEAT and CONVECTION.
I will not pretend to be an expert in this arena, but simply put, in an
electric kiln the heat starts from the electric elements (by way of
electrical 'resistance' and OHMS' LAW, et al......wire coils / glo-bars /
whatever) and RADIATES inward, toward the wares and each piece, as it
heats up, radiates inward to the next piece, etc. A somewhat slow process
and one that has a neutral atmosphere that does not rely on 'air' for
"combustion"...(doesn't an electrical element heat in a vacuum?)
CONVECTION heat relys on the movement of heated air/gases (flame)
travelling from source of ignition ( of the fuel source/propane/nat.
gas/wood/whatever) and following the flame path to the exit flue because a
"draft" exists that pulls the heated gases / air that direction...through
the wares and shelves, heating them, as it heads for the exit. The damper
controls the flow to some extent.
Other thoughts?
HTH
Ric
>----------------------------Original message----------------------------
>When I made my post about oxidation/reduction, I knew we were going to cover
>the same ground we have before. I'm already starting to get questions....."I
>was taught that...". I'll repost my original, followed by a sample question
>I received, then my reply;
>
>Joyce asked;
>
><<<>and neutral when firing in a reduction kiln, I would be most
>appreciative. >>>>>
>
>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.
>This is far from what is happening. Combustion is a violent process at the
>molecular level and releases quite a bit of energy (heat) and by products
>(water vapor, carbon dioxide, carbon monmoxide, nitrous oxide, ect.) An
>oxidation atmosphere, on the other hand, is one where there is an excess of
>oxygen (one of the main components of combustion). Here's the shock for most
>people;
>
>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.
>
>An electric kiln will give you a neutral firing.
>
>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.
>
>For new folks on the list, we've been through this before....so there's no
>reason to start an argument over this. If that much loved (and maybe famous)
>teacher of your's called an electric firing "oxidation", they were wrong and
>didn't know it.>>>>
>
>So the first question I get from someone goes like this;
>
><<<>
>referred to the fact that oxygen was present during and electric firing.
>
>That reduction was called that because you reduce the oxygen supply to the
>
>gas. I understand what you are saying, but isn't there oxygen present in
>
>the electric kiln?>>>>
>
>My answer to them;
>
><<<>apart by the combustion process. Because of this, virtually all of it remains
>in a nonreactive state. Electric firings are neutral not oxidation. As I
>mentioned in my post, many people have been taught something that is
>wrong.>>>>
>
>Now Vince pointed out that these terms have been in use for years and nobody
>is going to change. Granted, and I don't intend to try to change anyone. But
>when someone asks a question that involves confusion about terms, I tell them
>the "right" answer not the accepted answer.
>As far as Vince's question about air entering the electric kiln and thus
>creating an oxidation atmosphere......My answer is the same as when Vince
>asked this last year. This air and the oxygen in it are almost entirely
>nonreactive. Electric kilns produce a neutral firing, not an oxidation
>firing.
>
>Marc Ward
>Ward Burner Systems
>PO Box 333
>Dandridge, TN 37725
>USA
>423.397.2914 voice
>423.397.1253 fax
>wardburner@aol.com
#####################################
From: Ric Swenson, ( home ) : P.O. Box 494,
North Bennington, VT 05257 - 0494 U.S.A
home telephone ( 802 ) 447 - 4744
( work ) : Bennington College, Route 67 - A
Bennington, Vermont 05201 - 6001
( 802 ) 440 - 4621 ( fax 440 - 4582 )
email: rswenson@bennington.edu
#####################################
" If you want to teach a bear to dance,
..... you should be prepared to dance.....
..... until the bear gets tired. "
Vince Pitelka on thu 13 nov 97
>As far as Vince's question about air entering the electric kiln and thus
>creating an oxidation atmosphere......My answer is the same as when Vince
>asked this last year. This air and the oxygen in it are almost entirely
>nonreactive. Electric kilns produce a neutral firing, not an oxidation
>firing.
>
>Marc Ward
>Ward Burner Systems
Marc -
I apparently missed that answer last year. Could you please explain why the
oxygen is nonreactive. Is it because there are two oxygen molecules bonded
together with a strong bond? If that is the answer, what is the minimum
temperature required to dissociate the oxygen and make it reactive?
Thanks -
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Cameron Harman on fri 14 nov 97
HTH conveys the thoughts of many, including some kiln
designers from well known firs. The science is that most
heat is transferred by radiation in either a fuel fired kiln
or an electric fired kiln.
The difference is in how that radiation is generated .. OK
that's confusing, In an electric kiln the radiation is from
the radiating source, then from piece to piece as the heat
works its way inward.
In a fuel fired kiln about 40% of the radiation is from the
walls and directly from the burner, about 40% is from the
radiating flue gasses that come into the kiln as products of
combustion. It is, therefore, EXTREMELY important to direct
the flue gases to where you want them to go. this is the
essence of kiln design and is too complicated to go into
here.
Let us just say that above about 400 degrees F only about
10% of the heat is transferred by convection in any kiln.
The only exceptions are specialty furnaces such as aluminum
heat treating furnaces in which very large high temperature
fans are used to get enough velocity to the hot gases to
actually increase the percentage of heat transfer by that
method.
This is not written to put HTH down, not at all. It is
merely to point out that conventional wisdom, as good as it
is, sometimes misleads our minds into going in the wrong
direction. It is most important to keep thinking even if on
rare occasions one is on the wrong track .. better than not
going at all.
Another thing, it is absolutely right that there is a
connection to the oxidation thread. If you have a fuel fired
kiln with bad control over the draft and improper placement
of the lanes for the products of combustion to get to the
flue (which is typical of most kilns), then a windy day will
greatly affect the heat transfer and you can get a shift
from reduction to oxidation as well as a shift in the hotter
spots in the kiln (also leading to interesting results).
Adjusting the flues does not solve the problem, it may only
move it around. You cannot change the inherent design of a
kiln by moving a damper.
Sorry, I got carried away, it is , to me, an interesting
discussion.
Cameron Harman
--
**********************************************************
Cameron G. Harman, Jr. 215-245-4040 fax 215-638-1812
e-mail kilns@kilnman.com
Ceramic Services, Inc 1060 Park Ave. Bensalem, PA 19020
see our web site at http://www.kilnman.com/potters.html
THE place for total kiln and drier support
**********************************************************
David Woodin on sat 15 nov 97
Along with this thread of though, that is why the ITC 100 and 296 product
reduces the amount of energy used whether electric or gas to heat pottery or
whatever in a kiln.
WardBurner@aol.com on sat 15 nov 97
Vince,
you asked;
<<<I apparently missed that answer last year. Could you please explain why the
oxygen is nonreactive. Is it because there are two oxygen molecules bonded
together with a strong bond? If that is the answer, what is the minimum
temperature required to dissociate the oxygen and make it reactive?
Thanks ->>>>
That's it. Strong bonds (see previous post). I don't know the exact temp
where molecular dissociation occurs, but when dissociation occurs you have
that odd state of matter known as plasma. Plasma's HOT!!! stuff, but the odd
thing is that plasma is (quoting Webster's) " a high temperature, ionized gas
that is electrically neutral". Alot of plasma research is in the field of
Nuclear fusion. The inside of the sun is plasma. I thought it was you that
asked last year, oh well, the blur that is my memory....
Marc Ward
Ward Burner Systems
PO Box 333
Dandridge, TN 37725
USA
423.397.2914 voice
423.397.1253 fax
wardburner@aol.com
Teri Seeley on mon 17 nov 97
> What we really need here are some definitive, clear, explanation. No one
> has provided that yet. That surprises me, considering some of the ace
> chemists and engineers on this list.
I'm not an ace chemist, but here goes:
Whether oxidation takes place in an electric kiln is largely a function
of the composition of the glazes themselves. The major constituents of
most ceramic glazes are oxides and hence are already by definition
"oxidized". However, some oxides exist in naturally reduced states and
are thus candidates for further oxidation. Two that come to mind
are Cu2O and FeO. At high temperatures and in the presence of oxygen
they would be candidates for further oxidation to the more stable forms
of CuO and Fe2O3 respectively. Given that this transition is
reversible,
i.e. occurs in both directions in high fire *reduction* kilns, depending
on changes in atmosphere, I would suspect that the temperature in a
high fire *oxidation* kiln (say 2350 F) and the presence of
replenishable oxygen would be sufficient to oxidize Cu2O and FeO to
their more stable forms.
Note that there are other heat related chemical reactions that take
place
in both oxidation and reduction kilns which are unrelated to
atmosphere.
For example, the decomposition of carbonates and sulfates into oxides
with the corresponding release of CO2 and SO2.
Bill
--
Theresa and William Seeley 410 486-3171 (voice)
Villa Nova Pottery 410 484-6273 (fax)
4015 Buckingham Rd. Baltimore, MD 21207
"186,000 miles/second is not just a good idea - it's the law!"
David Hendley on mon 17 nov 97
If you all can STAND one more comment,
No matter what evidence is presented in this discussion,
firing in an electric kiln will be called an "oxidation firing".
There are too many years of history to change it.
If I cut my finger I ask for a "Band-aid", not an
"adhesive bandage".
If I sneeze I ask for a "Kleenex", not a "facial tissue".
And if you want a glaze recipe I will give you a
"xerox copy", even though the copy machine I use is a Canon.
Also, things change over time.
If I'd been to a party in the 1940's and everyone enjoyed themselves
I might report that "Everyone was gay".
I certainly wouldn't say that today, unless I had something
quite different in mind, even though it might still be correct.
There are two reasons to use language:
1) to be understood and communicate an idea, and
2) to NOT be understood, but to sound knowledgeable or condencending.
Professionals, such as doctors and lawyers often speak for reason #2.
If your goal in speaking is to be understood, you will just
have to accept that some of the things you say may not be
technically correct, but hey, we're dealing with
unpredictable, not always rational human beings.
David Hendley
Maydelle, Texas
See David Hendley's Pottery Page at
http://www.sosis.com/hendley/david/
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