GLAZED ALUMINA
High alumina ceramics are impermeable materials which do not normally require any additional surface treatment to make them suitable for High Vacuum and Ultra High Vacuum applications. The highest electrical performance is obtained when using carefully cleaned and dried unglazed alumina. Surface resistivity under these circumstances is normally 10¹³ Ohm-cm at ambient temperature.

Glazed alumina components can be supplied, when requested, which will withstand the metallizing and brazing processes without degradation of the glaze. Surface resistivity will, however, be that of the glaze material typically 10¹² Ohm-cm at ambient temperature.

The glazed exterior finish acts as a dirt/contamination repellent and reduces the risk of a 'contamination path' forming across the insulator; it can also be cleaned more easily than unglazed alumina.

METAL MEMBERS
To ensure maximum integrity and reliability for Ultra High Vacuum applications only certain metals are employed in the construction of all our products.

42% Nickel Iron	The normal material employed, having the closest expansion match to alumina therefore providing optimum ceramic-to-metal joint strength.
Nickel	For compliance and resistance to corrosion.
Copper-Nickel Alloy	Normally only employed where the product has to be non-magnetic. Typical examples being Monel™ and Ferry™.
OFHC Copper	Oxygen free high conductivity copper provides a material with high thermal and electrical conductivity suitable for conductors and heat sinks.
Stainless Steel	A non-structural material used for flanges, end terminations and occasionally conductors.