Hollow Corundum Microspheres in Ceramic Filters


Hollow corundum microspheres (hereinafter, HCM) are used to create micro- and ultrafiltration in ceramic filters.
The combination of spherical shape of the inner cavity and extended surface of corundum microspheres enables us to achieve
unique filtering characteristics. The combination of various proportions of grains of ceramic materials (Al2O3, TiO2, SiC) and
hollow corundum microspheres enables us to obtain porous structure with prescribed properties. E.g. a combination of large
grains of aluminium oxide and small HCM, or small grains of aluminium oxide and large HCM.
Using a bifractional mixture of microspheres with large and small diameter in
ceramic filters, one can obtain unique properties of the end product.
Adding of 3 to 5% of HCM when producing cylindrical filtering elements reduces the pressing force required to extrude ceramic
mixture to the mould 1.5 to 2 times.

Volumetric deformation and coefficient of thermal expansion of HCM

When ceramic filters with HCM are annealed, their volumetric deformation reduces twice or thrice. This happens due to the low
coefficient of thermal expansion of corundum microspheres when they are heated or cooled. The reduced volumetric deformation
of the ceramic filter after annealing to the size provided in the drawing ensures a reduced amount of raw ceramic mixture used and
higher quality of the end product.

Mechanical strength and sphericity of HCM

The spherical shape and relatively high strength of corundum microspheres (40-120 MPa) ensures wonderful mobility of raw ceramic mixture in the process of jar-moulding.
When moulding in a hydraulic press, the pressing force reduces 1.5 to 2 times due to the reduction of internal friction of ceramic mixture components when redistributing and binding
in the mould. The reduction of energy intensity of this operation enables us to save a pretty large amount of electricity at the manufacturing stage of ceramic filters.