Pyrophyllite
A Soft Hydrous Aluminum Silicate
Chemistry
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Volatiles
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Links to Other Materials
- Sericite - Related
- Andalusite - Related
- Cache
Miscellaneous
- Family: AlumSilicate
- Region: North America
- Mined At: Unspecified
- Raw Mineral: Yes
- Generic: Yes
Notes
Pyrophyllite is an aluminum silicate mineral with a similar chemical structure to talc (a magnesium silicate). It is non-plastic yet clay-like and often used in ceramic bodies to decrease thermal expansion and moisture expansion during service. It is a very soft white mineral (also resembling talc in physical appearance and feel).
Three types are found in nature:
-Micaceous foliated pyrophyllite (flaky with some fluxes).
-Crystalline (higher expansion and longer needle-like grains).
-Homogeneous variety known as massive pyrophyllite. It is used in refractories because it lacks fluxes and has a rounded grain with high lubricity that lends itself to pressing bodies. This type typically has a permanent expansion of about 2% to 2000F.
Because it expands when heated pyrophyllite counters the shrinkage of the plastic components in a mix (assuming that particles remain whole and undissolved to exert their influence on the surrounding matrix). Pyrophyllite-refractory clay combinations potentially have excellent volume stability and resistance to deformation at high temperatures.
In clay bodies, substitution of part or all of the silica will decrease thermal expansion (see also kyanite, mullite) while maintaining the level of maturity (although some adjustment in the feldspar will likely be needed). Pyrophyllite normally increases firing range and therefore decreases firing shrinkage. Thus if a body is too vitreous pyrophyllite can be substituted for feldspar to reduce expansion and maturity at the same time. It has the additional effect of increasing the strength of fired bodies if particles remain intact.
In electrical porcelain, large amounts (up to 95%) may be used in bodies for optimal electrical properties and high frequency characteristics (where zero porosity is not critical).
Pyrophyllite is also used as an ingredient in wall tile bodies since it has the effect of reducing moisture expansion.
Because of its stable nature and physical properties, pyrophyllite is employed in mold release and parting agents in foundry and structural clay products.
Phyrophyllite can be variable in nature, so factory blending and select mining are normal. Many other minerals can be found associated with it (e.g. kyanite, andalusite, topaz, quartz, sericite, chlorotoid, pyrite, chlorite, feldspar, hematite, magnetite).
Pyrophyllite is ideal for certain types of refractories because it is refractory and no calcining is needed. Its physical nature also helps to reduce wear and tear on molds and machinery that handle wet and dry product.
Some grades of Phyrophyllite can be variable in nature, so factory blending and select mining are normal. Many other minerals can be found associated with it (e.g. kyanite, andalusite, topaz, quartz, sericite, chlorotoid, pyrite, chlorite, feldspar, hematite, magnetite).
Some grades of pyrophyllite have a higher iron content that others and can darken the color of porcelain bodies. Also, porcelains that are highly vitreous can take pyrophyllite particles into solution, when this happens the effect of their low expansion properties is lost on the body.
Properties
Surface Modifier -
Pyrophyllite is often included in bodies to reduce thermal expansion. This material is also effective as a powder addition in low fire bodies.
URLs
- Wikipedia definition - http://en.wikipedia.org/wiki/Pyrophyllite
Suppliers
- Generic
Authors
- Tony Hansen (Owner)
XML
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<material name="Pyrophyllite" descrip="A Soft Hydrous Aluminum Silicate" generic="1" rawmineral="1" searchkey="Pyrophillite" loi="4.00">
<families>
<family name="AlumSilicate"/>
</families>
<regions>
<region name="North America"/>
</regions>
<oxides>
<oxide symbol="Al2O3" name="Aluminum Oxide, Alumina" status="" percent="28.300" tolerance=""/>
<oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="67.700" tolerance=""/>
</oxides>
<volatiles>
<volatile symbol="" name="" percent="4.000" tolerance=""/>
</volatiles>
<references>
<reference name="seealso" reason=""/>
<reference name="seealso" reason=""/>
</references>
<suppliers>
<supplier name="Generic" country="" url="" label=""/>
</suppliers>
<notes>
<note>Pyrophyllite is an aluminum silicate mineral with a similar chemical structure to talc (a magnesium silicate). It is non-plastic yet clay-like and often used in ceramic bodies to decrease thermal expansion and moisture expansion during service. It is a very soft white mineral (also resembling talc in physical appearance and feel).
Three types are found in nature:
-Micaceous foliated pyrophyllite (flaky with some fluxes).
-Crystalline (higher expansion and longer needle-like grains).
-Homogeneous variety known as massive pyrophyllite. It is used in refractories because it lacks fluxes and has a rounded grain with high lubricity that lends itself to pressing bodies. This type typically has a permanent expansion of about 2% to 2000F.
Because it expands when heated pyrophyllite counters the shrinkage of the plastic components in a mix (assuming that particles remain whole and undissolved to exert their influence on the surrounding matrix). Pyrophyllite-refractory clay combinations potentially have excellent volume stability and resistance to deformation at high temperatures.
In clay bodies, substitution of part or all of the silica will decrease thermal expansion (see also kyanite, mullite) while maintaining the level of maturity (although some adjustment in the feldspar will likely be needed). Pyrophyllite normally increases firing range and therefore decreases firing shrinkage. Thus if a body is too vitreous pyrophyllite can be substituted for feldspar to reduce expansion and maturity at the same time. It has the additional effect of increasing the strength of fired bodies if particles remain intact.
In electrical porcelain, large amounts (up to 95%) may be used in bodies for optimal electrical properties and high frequency characteristics (where zero porosity is not critical).
Pyrophyllite is also used as an ingredient in wall tile bodies since it has the effect of reducing moisture expansion.
Because of its stable nature and physical properties, pyrophyllite is employed in mold release and parting agents in foundry and structural clay products.
Phyrophyllite can be variable in nature, so factory blending and select mining are normal. Many other minerals can be found associated with it (e.g. kyanite, andalusite, topaz, quartz, sericite, chlorotoid, pyrite, chlorite, feldspar, hematite, magnetite).
Pyrophyllite is ideal for certain types of refractories because it is refractory and no calcining is needed. Its physical nature also helps to reduce wear and tear on molds and machinery that handle wet and dry product.
Some grades of Phyrophyllite can be variable in nature, so factory blending and select mining are normal. Many other minerals can be found associated with it (e.g. kyanite, andalusite, topaz, quartz, sericite, chlorotoid, pyrite, chlorite, feldspar, hematite, magnetite).
Some grades of pyrophyllite have a higher iron content that others and can darken the color of porcelain bodies. Also, porcelains that are highly vitreous can take pyrophyllite particles into solution, when this happens the effect of their low expansion properties is lost on the body.</note>
</notes>
</material>
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