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FLINT 200M / SIL-CO-SIL 75
Ground Silica
SIL-CO-SIL® Ground Silica products
are produced from high purity silica, precision ground from 125 to
45 micron topsize. Our ground silicas are inherently inert,
bright white, with low moisture and are at least 99.5%
Si02.
FLINT - (SiO2) (m.p. 3119o F/1715o C) is the dark porous variety of
chert that contains organic matter (chert is a hard, extremely dense,
dull to semi-glossy sedimentary rock which is microcrystalline to
cryptocrystalline quartz). True flint is very fine (cryptocrystalline)
hydrated silica (1% molecular bound water) and is less dense than Quartz
Sand due to a fine porous structure. The name flint is a carry over
from England and France in which the true flints were prepared by
calcination and grinding. Many geologists and archeologists suggest
that the term flint be discarded or used only to identify artifacts of
prehistoric humans (see also Silica).
SILICA - SiO2 (m.p. 3119oF/1715oC) is second only to clay in
significance as a ceramic material, and it is the most abundant mineral
in the earth’s crust. The principal siliceous materials are:
Crystalline Quartz, Quartzite, Sandstone, Silica Sand, “Organic” and
Amorphous Silica: including Flint and Diatomaceous Earth. Silica is
frequently referred to as “Potter’s Flint” and is often just ground
sandstone. It is used interchangeably with Quartz. Silica or Quartz is
used in clay bodies to modify shrinkage, porosity, and strength (these
modifications are affected by particle size and crystallinity). Quartz
has a phase transition at 1063o F/573o C, i.e. the Quartz inversion.
Upon firing, this inversion occurs rapidly and results in volume
expansion, which can lead to firing cracks in clay bodies high in Free
Quartz. In glazes, Silica is the most common glass former. It serves
to control the fusibility and viscosity, which are dependent on the
amount of Silica in the glaze. Typical mesh size of 200 (>74
microns), 325 (> 45 microns), and 400 (>30 microns) are offer
varing applications in clay bodies and glazes. The coarser 200 mesh
helps to control shrinkage while the finer 325 and 400 mesh are useful
in glazes for their reactivity and ease of going into solution.

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