Plainsman Clays | PYRO
Pyrophyllite
Pyrophyllite is an aluminium silicate mineral, mined and ground as a rock. In a body it lowers thermal expansion and reduces shrinkage.
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Pyrophyllite is used in whiteware and tile bodies, and in stoneware bodies that need better resistance to thermal shock. It loses its chemically bound water between about 500°C and 900°C, and from about 1100°C and on it forms mullite, the needle shaped crystal that gives a fired body much of its strength, leaving an amorphous silica in the spaces between. Part of the reason it reduces shrinkage is that it expands a little on the way up, as it gives up that water, before contracting again higher in the firing, so it works against the shrinking of the clay around it. It is refractory in its own right, which widens the range a body will fire over.
- An aluminium silicate, mined and ground as a rock
- Lowers thermal expansion and reduces fired shrinkage
- Forms mullite from about 1100°C, which gives a fired body much of its strength
- Refractory in its own right, so it widens a body's firing range
