Vince Pitelka on sat 22 feb 03
brick in salt and/or soda firings
Craig wrote:
"I had posted earlier about the salt firings. Does anyone have any
experience with soda firings? How corrosive is the atomoshere in a soda
firing? From what I understand the sodium in a salt firing attacks the
silica in the bricks, will quickly destroy untreated soft brick, and that it
is necessary to have high alumina hard brick for the construction of a
decent salt kiln. I have been told that ITC will protect soft brick in a
salt kiln. Does anyone have any experience with this? Is the same thing true
of a soda firing?
Craig -
For reasons that I do not really understand, soda firing seems to have far
less solvent action on the refractory surfaces. As I said yesterday, ITC
will NOT protect softbrick from salt firing. The surfaces will degrade very
quickly. We build sprung-arch cross-draft softbrick soda kilns with a thin
coat of ITC-100 on the inside, and I would estimate we get about 100 firings
before we have to rebuild. We often turn the same bricks around and build
another kiln. Considering the number of wares that come out of those 100+
firings, this is a cheap kiln.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Office - wpitelka@tntech.edu
615/597-6801 x111, FAX 615/597-6803
http://iweb.tntech.edu/wpitelka/
Craig Edwards on sat 22 feb 03
brick in sal
Hello Craig;
I've just put a wash of alumina hydrate over the soft brick. It worked
great. The vapors did not attack them at all. I used rock salt. I had
problems if the salt came in contact with the brick ie. lay on the floor of
the kiln.. while it was vaporizing, but no problems with the bricks with the
vapor.
HOpe this helps.
Craig Edwards
New London
>From: Craig Dunn Clark
>Reply-To: Clayart
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Do soft brick stand up to "soda firings"? Does ITC protect soft
> brick in salt and/or soda firings
>Date: Fri, 21 Feb 2003 18:56:00 -0600
>
> I had posted earlier about the salt firings. Does anyone have any
>experience with "soda firings." How corrosive is the atomoshere in a soda
>firing? From what I understand the sodium in a salt firing attacks the
>silica in the bricks, will quickly destroy untreated soft brick, and that
>it is necessary to have high alumina hard brick for the construction of a
>decent salt kiln. I have been told that ITC will protect soft brick in a
>salt kiln. Does anyone have any experience with this? Is the same thing
>true of a "soda" firing?
>Thankyou
>Craig Dunn Clark
>619 East 11 1/2 st
>Houston, Texas 77008
>(713)861-2083
>mudman@hal-pc.org
>
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Gavin Stairs on sun 23 feb 03
brick in salt and/or soda firings
Hi Dave and Vince,
In discussing fluxes, we tend to discount the anions (oxide, carbonate,
chloride, fluoride, etc.) since so often they turn into oxides, which are
sort of part of the woodwork. But chloride and fluoride, to name but two,
do not just turn into oxides, and there is no need to invoke hydrogen to
turn chloride into an acid. It is already a strong flux by itself, and
that's why salt is stronger than soda. Soda is sodium carbonate, which
becomes sodium hydroxide, and that eventually becomes sodium oxide, so
there's little extra fluxing there. Just the soda. Salt becomes soda plus
chloride, which is stronger flux.
Gavin
At 02:44 PM 23/02/2003 -0700, Dave Finkelnburg wrote:
>Dear Vince,
> I am only guessing, but salt firings release chlorine atoms, which could
>then combine in the kiln with water from incoming air or water from hydrogen
>burning in the kiln. The combination is, of course, hydrochloric acid.
>That may be the difference. Certainly, there is no chlorine to speak of in
>a soda firing, but there is the same amount of soda in both cases.
Craig Edwards on sun 23 feb 03
brick in sal
Hello Lee: It's good to see you are doing well. Congratulations on your
graduation.
I brushed the alumina on the bricks. Spraying would probably work well also.
I just didn't have a sprayer.
I think that adding some kaolin to the alumina is a good idea, but to much
will cause the wash to create a substructure all its own. You might get some
spalling.
Your fellow student from Germany is probably a great resource. The salt
kilns in Hohr- Grenzhausen, Germany are the gold standard in my book. They
build their kilns like they build their cars. The newer kilns that are made
from soft brick are in pristine condition. Great maintenance!
This is where I picked up the alumina idea.
Reading Vince's post he has not had the same experience. I agree with you
Vince that clay shelves have no place in a salt kiln. My experience has been
that a wash on a kiln shelf does not penetrate and interact the same way as
on a soft-brick. All this is antidotal experience. My soft brick composition
is not the same as you have in Japan.
Best of luck:
Craig Edwards
New London
PS; Lee if you see a tall skinny young man at your show, it might be my
youngest son Dan. He is doing Japanese studies at Carleton, in Northfield
and will be there in June.
>Hi Craig,
>
> I just laid the hardbrick floor of my small wood kiln. Can
>you
>tell me how you applied the alumina to your soft bricks? They have some
>cheap "low duty" softbricks here that a friend has used in the same design.
>Says you can firer them 30 times, grind the surface down and fire another
>20
>times. I was thinking of ordering ITC, but it would take too long.
>If I
>can coat them with alumina (just the walls, not the arch), they might last
>until
>I need to build a bigger kiln.
>
> A fellow student from "old East Germany" (near Dresden) is
>here
>studying with a Master Kiln builder. He is documenting the building of a
>Noborigama next door to Hamada's compound. He says he has used a mixture
>of
>kaolin and alumina on softbrick in his noborigama back in Germany.
>
> Hey, I finish my apprenticeship this week! My graduation show is
>in
>June.
>
>Thanks!
>--
>
>Lee Love
>
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Dave Finkelnburg on sun 23 feb 03
brick in salt and/or soda firings
Dear Vince,
I am only guessing, but salt firings release chlorine atoms, which could
then combine in the kiln with water from incoming air or water from hydrogen
burning in the kiln. The combination is, of course, hydrochloric acid.
That may be the difference. Certainly, there is no chlorine to speak of in
a soda firing, but there is the same amount of soda in both cases.
Good firing,
Dave Finkelnburg
----- Original Message -----
From: "Vince Pitelka"
> For reasons that I do not really understand, soda firing seems to have far
> less solvent action on the refractory surfaces. As I said yesterday, ITC
> will NOT protect softbrick from salt firing. The surfaces will degrade
very
> quickly. We build sprung-arch cross-draft softbrick soda kilns with a
thin
> coat of ITC-100 on the inside, and I would estimate we get about 100
firings
> before we have to rebuild. We often turn the same bricks around and build
> another kiln. Considering the number of wares that come out of those 100+
> firings, this is a cheap kiln.
John Britt on mon 24 feb 03
brick in salt and/or soda firings
Snail,
In a salt kiln there are a lot of chlorides formed, like iron chloride,
copper chloride, etc. This causes the iron in the bricks to migrate.
This is evidenced brown color of a salt kiln vs the light (blue) color of
the soda only kiln.
John Britt
iandol on tue 25 feb 03
Dear Dave Finkelnburg,=20
It was recognised early last century that hydrochloric acid was only a =
secondary product in the Salt Aka NaCl glazing process. Check Barringer.
Thermodynamic calculations show that it would be most unlikely for NaCl =
to dissociate at a temperature below about 2700=B0 Celsius or 4892=B0 =
Fahrenheit to release free Chlorine.
The Chemistry between Sodium Chloride and the substances in a clay body =
or a refractory depends on the formation of a solution in which sodium =
chloride will dissolve. Free chlorine is the last substance to be =
released from this solution after all other reactions which are greedy =
for energy have combined with it to generate Silicon Tetra Chloride, =
Ferric Chloride, Aluminium Chloride and a few other delicious gaseous =
compounds. Research to this end was done in the UK circa 1958 (Alkali =
Inspectorate).
You can easily prove Soda, Sodium Carbonate, reacts directly with Silica =
by melting a sample of the mixture in a steel dish at about 1000=B0 =
Celsius 1832=B0 F.
Commentators on these processes have not understood that the atmosphere =
in a salt or soda kiln is pervaded with mostly Molten Particulate which =
impinge on a semi liquid surface if the clay is at its maturing =
temperature. The two fluids are miscible so one will diffuse into the =
other. Then you get the chemistry.
Yes, there is potential for the emission of Chlorine from a salt firing =
but it would need a degree of salt contamination in the soda for this to =
happen in a Soda firing.
Best regards,
Ivor Lewis.
iandol on tue 25 feb 03
Dear Friends
I do wish someone in one of the chemistry departments of some university =
somewhere on this Planet would grasp the nettle of Ceramic Arts =
Chemistry and give it a good retting.
And it is about time clay artists were willing to get their heads around =
materials science and the associated maths so they could employ the =
principles gifted to them by Prof. Willard Gibb when they propose =
hypothesis about the happenings in their kilns. So many processes are =
explained using imagination and conjecture as true fact and people are =
not even willing to get their eyes into any of the standard reference =
books.
Want to talk about which place to study ceramic arts!! Well if you get =
an interview ask your tormentors if they have read W. D. Kingery, H. K. =
Bowen and D. R. Uhlmann. If they have not, any technology they teach may =
be treated with suspicion.
I think it is pointless discussing any technical topic when you do not =
know the composition of the materials under discussion, do not know the =
Chemistry of the major components which are reacting, when you do not =
bring references to the table in support of argument, when you do not =
make standardised observations. But as an Art Form it is a great way of =
inventing Fairy Tales and Folk Legends.
Best regards to all, including the Lurkers.
Ivor Lewis. Who managed to get a copy of Stoker's Principles of =
Chemistry (1999)recently.
iandol on thu 27 feb 03
Dear John Britt <>
You say<chloride, copper chloride, etc. This causes the iron in the bricks to =
migrate.>>
I would be interested in knowing the source of your information relating =
to this phenomenon and can confirm the effect with respect to Iron. =
Migration of Iron from fire bricks happened at a Macgregor Summer School =
just over ten years ago. We were using white stoneware and porcelain and =
anticipating vibrant results from coloured slips.
The first firing was ruined by migration of Iron from the Pyrites =
contained in the fireclay bricks.
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