iandol on thu 27 feb 03
Dear Friends,
The question was "Why does coarse grained Silicon carbide not react when =
used as an artificial reducing agent in a glaze, whereas ultra fine SiC =
does and gives lots of bubbles?"
This is due to the exposure of the surface to the materials which cause =
the reactions. The smaller the particle size the greater the specific =
surface area which becomes exposed. A 1 mm cube has a surface area of =
six square millimetres. Mill that single 1 mm cube until the cubes =
measure 1/1000 of millimetre and you have particles each with an area of =
6/1000 sq mm. But you have one billion particles. So the area becomes =
10^9 * 6/1000 sq mm which breaks down to six million square millimetres =
or sixty thousand square centimetres. I think that is six square metres, =
a lot of area which can react.
By comparison, a lump of coal weighing a kilogram takes some time ignite =
and burn continuously. But reduce it to micron sized powder, distribute =
it as an aerosol, make one spark and there will be one BIG BANG.
The same principle applies to glaze making and to firing clay. The =
smaller the particles the faster the firing. So well grogged clays need =
more time to mature and glazes which are compounded from minus #200 =
materials mature quickly, a thought which should raise some interesting =
questions and might provide solutions to worrying problems.
best regards,
Ivor Lewis
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