Ivor and Olive Lewis on fri 15 dec 06
Dear Vince Pitelka,
To comment on the "Kruzite" bricks you used I would need both an Oxide =
(Seger) analysis and a Mineral analysis. If you can provide this =
information and tell me which substance you were using to achieve a =
vapour glazed surface I will attempt to explain your observations.
Accepting the experience of High Alumina Brick with Sodium Carbonate as =
you describe it, then people need to consider what has been observed and =
what a detailed examination of the affected refractories revealed, then =
balance that against a mineralogical and Oxide analyses of the original =
refractory and its mode of manufacture.
The question becomes "Which component of the refractory fabric was =
attacked by corrosive vapour (Sodium Carbonate in this instance)."
Corrosion is inevitable. It proceeds by three avenues. The first is as =
you describe, penetration along grain boundaries. The second is along =
crystal lattice weaknesses in individual mineral grains. The third, and =
most obvious would be by preferential chemical attack of the most =
vulnerable component.
Refractories should be designed so that they eliminate those compounds =
which are most vulnerable to chemical attack. This is done by increasing =
the Alumina content, as recommended by Prof Kingery and his Co-authors.
Best regards
Ivor Lewis.
Redhill,
South Australia.
.
Vince Pitelka on sat 16 dec 06
Ivor -
As I said in my post, it was a salt kiln built with Kruzite high-alumina
hardbrick that gave us so much trouble. As I understand it, high alumina
bricks intended for periodic kilns (frequent heating and cooling) tend to=
be
quite porous in order to retain high-enough thermal shock resistance to
avoid fracturing, and thus the porosity is open to sodium entry. We were
charging the kiln with moistened rock salt. All I can tell you is that t=
he
brick swelled up internally, and spalled off on the hotface surface. Whe=
n
we had this experience, I emailed other salt firers - Jack Troy, Wil
Shynkaruk, John Neely, and others, and they all confirmed the same
experience with high-alumina brick in salt firing. We had several differ=
ent
grades of Kruzites, and I believe that they were 70% and 80% alumina.
Hope that clarifies things. Do you know if it is possible to have a
high-alumina brick dense enough to prevent the sodium entry, but
thermal-shock-resistant enough to stand up to the relatively quick heatin=
g
and cooling in a studio kiln?
- 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/
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