Pyrophyllite heat treated at 1250°C - 1300°C

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Pyrophyllite (Aluminium silicate) is a machinable mineral which, after heat treatment, assumes many of the properties of fired ceramics. It is ideal for prototypes, experimental and pilot scale productions where high accuracy is required on small parts. When this material is heat treated it hardens and its properties change; we therefore supply Pyrophyllite in three grades:

  • The natural material. Extremely easy to fabricate, but of rather low strength.
  • Heat treated to 800 - 1000 °C. This grade is characterized by its low thermal conductivity and coefficient of thermal expansion, resulting in very good thermal shock resistance. This version of the heat-treated material can be machined to final size with tungsten carbide tools.
  • Heat treated to 1250 - 1300 °C. This grade is characterized by its excellent electrical properties, high strength and hardness. This version of the heat-treated material can only be machined with diamond tooling.

This material data has been provided by Matmatch.

All metrics apply to room temperature unless otherwise stated. SI units used unless otherwise stated.
Equivalent standards are similar to one or more standards provided by the supplier. Some equivalent standards may be stricter whereas others may be outside the bounds of the original standard.

Ashby charts





23.0 °C

2.4 - 2.55 g/cm³

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0.01 %

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Compressive strength

23.0 °C

151.6 MPa

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Flexural strength

23.0 °C

82.7 MPa

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Hardness, Mohs

23.0 °C

7 [-]

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Tensile strength

23.0 °C

34.4 MPa

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Coefficient of thermal expansion

600.0 °C

6E-6 - 8E-6 1/K

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Max service temperature

1100 °C

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Thermal conductivity

23.0 °C

1.9 W/(m·K)

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Vicat softening temperature

1600 °C

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Dielectric constant

23.0 °C

5.2 [-]

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Dielectric strength

23.0 °C

24 kV/mm

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5mm thick test piece

Loss factor

23.0 °C

0.05 [-]

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Power factor

23.0 °C

1000 - 1300 [-]

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Technological properties

Chemical composition

Silica - 56.8%, Alumina - 33.37%, Ferric oxide - 0.79%, Titanium Dioxide - 2.42%, Calcium Oxide - 0.29%, Magnesium Oxide - 0.24%


Pink to dark brown


Typical characteristics of the Pyrophyllite material include: Machinable, thermally insulating, good thermal shock properties, good mechanical stability once fired. The key features of Pyrophyllite Heat Treated at 1250 °C - 1300 °C are: Good electrical properties in humid conditions, high abrasion resistance, will give <3µm surface finish, high dielectric strength, fair dielectric constant, high mechanical stability, only diamond grinding can be used to adjust sizes. Over 1000 °C a gradual shrinkage takes place and the machined component loses some of the volume expansion that has occurred. As the material densifies the sizes will return to within ± 1% of the machined sizes. Any size alteration will have to be carried out by wet grinding. Diamond with coolant is best but Green grit wheels suffice on prototypes. Always allow Furnace to cool naturally to 200 °C before removing parts. Never wet the unfired material for machining. Safe maximum operating temperature 1100 °C.