Also known by the name “china clay”. A pure form of hydrated aluminum silicate clay.

The formula for kaolin is usually given as Al2Si2O5(OH)4. It has many uses that include:

  • The making of porcelain and chinaware.
  • As a refractory for bricks and furnace linings.
  • As a pigment and filler in paints.
  • As a filler in plastics.
  • As an abrasive powder.
  • Ground kaolin is used as a filler in rubber

Kaolin presents a real problem in the seal business because some of the solid particles are less than one micron in size, and will penetrate between lapped seal faces. Most of the particles run between 1.2 and 2.0 microns with a pH of 4.0 to 6.5.

You seal kaolin just like any other slurry, but in addition, you need dual seals with a pressurized barrier fluid between the faces to prevent solids from migrating between the faces.

The tandem version of dual seals is shown in the following illustration

 Water makes a good barrier fluid if the seal is not subject to freezing temperatures