jonathan edward byler on fri 8 dec 06
Ivor Lewis,
I was browsing through looking for info on bricks, etc. for building
a sodium vapour kiln and stumbled across a thread where you were
asking about bricks and temp ratings, etc. and that this had not
been properly answered.
The IFB (insulating fire brick) made by thermal ceramics here in the
US come in many types for many applications. Despite what one member
noted, the 'K' actually is a type of brick offered by thermal
ceramics. The types are TC, K, JM, and Insalcor. The "K" or "K
factor" refers to the thermal conductivity factor of the brick (part
of the mathematical formula-- w/m times k) this is a standard rating
system, ASTM C 201.
The k type bricks have the best thermal conductivity ratings of the
aforementioned brick types offered by thermal ceramics. The JM types
have high alumina content 67-69.9 percent. The TC and JM types have
a higher cold crush strength amongst other things.
My understanding is that the K type bricks, which have a higher CaO
content than others are inherently more resistant to alkaline
atomspheres than the other brick types. Also having the higher K
factor than the other bricks means that they should insulate better
for a given wall thickness... From what I understand, the K type
bricks are the ideal ones to use for ceramics applications.
The number following the K, TC, or JM as the case may be, is for the
expected hot face temp that the bricks can withstand. ie. 23 =
2300F, 25 = 2500F, 26 - 2600F, etc.
Other manufacturers use a similar number system, but I don't know
anything about the letter prefixes that they use.
This info is readily available from Thermal Ceramics. They were kind
enough to fax me the data sheets for the bricks I was interested in.
The data sheets include physical properties, chemical analysis, and
thermal conductivity information.
hope that helps some,
jon byler
Ivor and Olive Lewis on sun 10 dec 06
Dear Jon Byler ,
I commend you for your diligent research. I am sure others will make use =
of your information.=20
I have no experience of firing with Sodium Carbonate though I have built =
kilns for firing with Sodium Chloride. For several reasons my preference =
was to use dense high alumina stock and place an adequate sheathing of =
insulation around the core of the kiln. One thought that dominated my =
thinking ( in the early 80's) was that a porous brick would adsorb salt =
vapour. This would condense then solidify. Then, when the kiln was =
reheated and the salt melted it would act as a solvent and destroy the =
brick form inside. This was based on the knowledge that Sodium Carbonate =
fusion is used to render mineral samples water soluble for analysis, the =
molten substance having strong solvent properties
Do the manufacturers of bricks using a proportion of Calcium in their =
compositions explain why this enhances their resistance to Alkali vapour =
? Do they distinguish between the effects of different fuming materials?
L.A.Lay (Corrosion Resistance of Ceramics. NPL, 1983) gives a maximum =
service temperature for "Impervious Mullite" in contact with fused =
Sodium Carbonate of 900 Deg C but say Alumina is resistant to this =
corrosive at that temperature
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Vince Pitelka on sun 10 dec 06
Ivor Lewis wrote
"I have no experience of firing with Sodium Carbonate though I have built
kilns for firing with Sodium Chloride. For several reasons my preference was
to use dense high alumina stock and place an adequate sheathing of
insulation around the core of the kiln. One thought that dominated my
thinking ( in the early 80's) was that a porous brick would adsorb salt
vapour. This would condense then solidify. Then, when the kiln was reheated
and the salt melted it would act as a solvent and destroy the brick form
inside. This was based on the knowledge that Sodium Carbonate fusion is used
to render mineral samples water soluble for analysis, the molten substance
having strong solvent properties."
Ivor is right on in his statements above. High alumina in a brick is fine
for wood firing or reduction firing, but not for salt or soda. As he
states, the brick remains porous, and the sodium vapors enter the brick,
causing internal breakdown and spalling of the hotface. It is a horrible
thing to witness after one puts a great deal of time and money into kiln
construction. We all know that an alumina-china clay wash resists salt
deposition on furniture and shelves, but that is no indication of what will
happen in a brick. In a salt or soda kiln, you need an impermeable barrier,
and a higher-silica brick promotes surface glaze that effectively seals the
brick from further vapor penetration. We always think of higher refractory
as more durable and resistant, but in salt and soda kilns it requires a
different mindset.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Hank Murrow on sun 10 dec 06
On Dec 10, 2006, at 4:45 PM, Vince Pitelka wrote:
>
> Ivor is right on in his statements above. High alumina in a brick is
> fine
> for wood firing or reduction firing, but not for salt or soda. As he
> states, the brick remains porous, and the sodium vapors enter the
> brick,
> causing internal breakdown and spalling of the hotface. It is a
> horrible
> thing to witness after one puts a great deal of time and money into
> kiln
> construction. We all know that an alumina-china clay wash resists salt
> deposition on furniture and shelves, but that is no indication of what
> will
> happen in a brick. In a salt or soda kiln, you need an impermeable
> barrier,
> and a higher-silica brick promotes surface glaze that effectively
> seals the
> brick from further vapor penetration. We always think of higher
> refractory
> as more durable and resistant, but in salt and soda kilns it requires a
> different mindset.
I think it is in the archives somewhere, but I would ratify Ivor's &
Vince's remarks here. At the U or Oregon, we built a salt kiln which
used high silica bricks which we found in an A.P.Green yard north of
Spokane...... maybe Mica, WA. Anyway, the kiln developed a lovely
bottle green glaze on the inside, and took forever to be ready for
demolition. Actually, it took the removal of the kiln due to the
construction of a new kiln building to finish it. Never found those
bricks again. High silica for salt.......... worked a treat.
www.murrow.biz/hank
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