Ivor and Olive Lewis on tue 12 dec 06
Dear Luba,
Yes, I was speaking of Insulating Refractory bricks. My choice, based on =
seven years contact with the Heavy Clay Industries which gave me access =
to all of the Sewer Pipe Manufacturers in the North of England and =
Scotland, is for a high alumina dense brick. The fired mineral content =
is important, probably more important than the Oxide analysis. They =
should be high in Mullite.=20
My own preference is for a high alumina brick that contains little or no =
free silica. Other people will disagree with my choice but that's not my =
problem. I did use a protective coating that was about 80% aluminium =
hydrate and 20% Kaolin.
I would be wary of using high silica bricks. If there is free silica it =
will react with Sodium Carbonate.That glass coating people are talking =
about is molten at firing temperatures (Sodium Disilicate may be =
expected to melt below 900 deg C) and can do two things. One, it can =
dribble down onto the pots creating "Snotters". Secondly, when molten it =
can follow intergranular cracks into the interior of the refractory. I =
saw this in industrial salt (NaCl) glaze kilns. Takes a long time but it =
happens.
Tests I did in Salt firings between 1983 and 1988 showed clearly that =
Alumina and Silica, as single substances, did not appear to react with =
Sodium Chloride vapour. Kaolin was almost resistant to attack, Ball Clay =
formed good reticulated glazes and Potash felspar gave an excellent =
transparent glaze that crazed.
That Ten Percent CaO could be explained it you can give me the =
remainder of the analysis "Oxide" or "Seger" analyses
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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