Zirconia Overview

The UCM Group is one of the world’s leading producers of electro-fused zirconia grains and powders.

Zirconia (ZrO2) is one of the most sophisticated raw materials presently used in refractories and ceramics, offering a unique combination of properties.

High refractoriness (melting point of pure oxide 2700ºC)
Chemically inert – resistant to corrosion / erosion by slags and fluxes
Low thermal conductivity
High electrical conductivity at elevated temperatures when alloyed with other oxides
High strength and toughness (when fabricated as an engineering ceramic)

The potential of pure zirconia as a refractory raw material is hindered by the fact that it is polymorphic, existing in monoclinic form at room temperature, becoming tetragonal at 1170ºC and finally cubic at 2300ºC.

The monoclinic to tetragonal change is accompanied by a reversible change in volume of around 5%, leading to cracking of the grains and subsequent failure in the fired refractory. UCM’s process of electro-fusing zirconia, allows undesirable volumetric change to be modified during fusion by the addition of measured quantities of cubic oxides such as calcia, magnesia, yttria, etc. These stabilising oxides form a solid solution with the zirconia and give rise to a structure that is a mixture of cubic and monoclinic zirconia. This material (termed “partially-stabilised zirconia” (PSZ)) exhibits the optimum balance of thermal expansion and thermal shock resistance properties making it ideally suited to demanding refractory applications.

When zirconia is stabilised with magnesia or yttria, transformation-toughened advanced ceramics with exceptional levels of strength and toughness can be produced.

When stabilised with 8^wt/o to 16^wt/o yttria the unique electrical properties of zirconia can be exploited in applications such as oxygen sensors and solid oxide fuel cells.

Partially stabilised zirconia is also used in the form of thermal-spray or plasma-spray powders in order to provide high performance thermal barrier coatings on metallic components. Typical applications are turbine blades and associated components for both aircraft and for land-based gas turbines. Other applications are found in the electronics industry.

UCM manufactures fused zirconia at Unitec Ceramics Ltd in the UK and at Universal America Inc. in Tennessee, USA. Thermal Plasma Spray powders are produced at Muscle Shoals Minerals Inc. in Alabama, USA.

Radioactivity

Zirconia is a non-toxic material but it does contain low-level concentrations of natural radioactivity. UCM produces zirconia with the lowest levels of radioactivity that current best practise allows and is the preferred supplier to refractory and ceramics manufacturers who are sensitive to this issue.