Additional information on Fused Yttria Stabilised Zirconium Oxides
STABILISED ZIRCONIUM OXIDES: Monoclinic zirconium oxide can be restricted in its applications due to the phase transformations it undergoes during heating. These phase transformations lead to changes in volume resulting in structural cracking and failure. These phase alterations can be controlled by the addition of dopants known as stabilisers. Once stabilised, zirconia can be used in applications running at temperatures in excess of 2200 degrees centigrade. Zircomet Limited offers a range of stabilised fused and co-precipitated zirconia powders.
STABILISED ZIRCONIUM OXIDE, FUSED: Fused zirconium oxide can be stabilised during the fusion process by the addition of stabilisers such as yttria, magnesia and calcia. After fusion the material is crushed and milled to different particle sizes. Zircomet Limited supplies a range of YSZ, MgSZ and CaSZ powders with particle size distributions produced for specific applications or to customer specification.
STABILISED ZIRCONIUM OXIDE, CHEMICALLY CO-PRECIPITATED: The chemical co-precipitation of intermediate zirconium and dopant compounds produces a very homegenous product with the doping element well dispersed within the structure. The precipitate is then calcined under controlled conditions to produce very specific particle size, morphology and surface area. All of these physical characteristics are very important in the powder's performance. Zircomet Limited offers a range of yttria and magnesia stabilised co-precipitated zirconia powders for structural/engineering ceramics and refractories. Stabilised zirconia powders can be supplied as raw powders or in granular form for spray coating or pressing.
Pure zirconium oxide (unstabilised) is monoclinic at room temperature but its structure changes to a tetragonal form at around 1000 degrees C. With this phase change there is a large volume change that results in structural cracks leading to a very low thermal shock resistence. Partial stabilisation of zirconia occurs with the addition of a dopant material such as 3-4mol% yttria, 2-3mol% magnesia or 8mol% calcia. This leads to a mixture of structural phases at different temperatures. A mixture of cubic, monoclinic and some tetragonal phase up to 1000 degrees C. and tetragonal at higher than 1000 degrees. Due to the tetragonal phase at higher temperatures partially stabilised zirconia is also known as tetragonal zirconia polycrystal (TZP). It is generally believed that microcracks and induced stress amongst the different phases are reasons for the toughening in partially stabilised zirconia. Partially stabilised zirconia tends to be used when high temperatures are needed. The low thermal conductivity ensures a low heat loss and the high melting point (2,700 degrees C.) means stabilised zirconia regreactories can be used in temperatures in excess of 2200 degrees C. Partially stabilised zirconia is also finding increased application in specialist structural/engineering ceramics. Fully stabilised zirconia is generally achieved with dopant levels of 8mol% yttria, 16mol% magnesia or 16mol% calcia. A fully stabilised zirconia has a structure which is a cubic solid solution which has no phase transformation from room temperature up to 2500 degrees C. Fully stabilised zirconia is a very good ion conducting ceramic and is used in applications such as oxygen sensors and solid oxide fuel cells.
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