Zirconia is a hard, crystalline material with a high melting point and chemical stability. It is abrasion and corrosion-resistant and has excellent ion-conductive properties, making it a versatile material for applications in aerospace, electronics, automotive, chemical industry, fuel cells and medical devices.
A wide range of zirconia powders are produced at Imerys state-of-the-art processing facilities in the USA, Germany and China serving an industrial client base worldwide. These fine-grade zirconia powders are used for a variety of applications, including oxygen sensors, SOFC components, automotive parts, cutting tools, ceramic filters, assay crucibles and tools and dies.
The optimum mixing ratio of carbon-containing materials to zirconia powder is a matter of importance and depends on the specific application. Ideally, the mole ratio of C in the carbon-containing material to Si02 in the zircon powder falls between 0.4 and 2.0.
Stabilized or partially stabilized zirconia can be obtained by a synthesis process in which a stabilizing metal oxide is added to a mixture of zircon powder and carbon-containing material. These metal oxides include, for example, MgO, CaO, Y 203 or CeO2.
Zr02 purity is a measure of the total amount of Zr02 present in the zirconia powder as well as any stabilizing oxide component. In order to obtain a zirconia powder with the desired Zr02 purity, the concentration of the stabilizing oxide should be at least 0.5 mole% and the total amount of Zr02 must not be less than 20 mole%.
In addition, a suitable temperature must be employed in the desiliconizing heat treatment. This is important since the metastable tetragonal phase in pure zirconia can transform into the monoclinic phase with a progressive change in volume when heated to a low temperature (200-300degC). This transformation can be triggered by water, which penetrates the cracks and eventually degrades the strength of the sintered body.