Yttrium oxide zirconia stabilization

Christel, P., Meunier, A., Heller, M., Torre, J.P., and Peille, C.N. (1989) Mechanical properties and short-term in-vivo evaluation of yttrium oxide-partially-stabilized zirconia. J. Biomed. Mater. Res., 23 (1), 45-61. 

Yttrium oxide partially stabilized zirconia (YPSZ) has been advocated as an alternative to alumina (Christel et al., 1989 Cales and Stefani, 1995). TTiis class of ceramic has a higher toughness than alumina since it can be transformation toughened and is used in bulk form or as a coating (Filiaggi et al., 1996a, 1996b). There are currently approximately 150,000 zirconia components in clinical use (Cales and Stefani, 1995). 

Conceptually elegant, the SOFC nonetheless contains inherently expensive materials, such as an electrolyte made from zirconium dioxide stabilized with yttrium oxide, a strontium-doped lanthanum man-gaiiite cathode, and a nickel-doped stabilized zirconia anode. Moreover, no low-cost fabrication methods have yet been devised. 

Oxygen sensors, in low volume use as part of a closed loop emission control system for automotive applications since 1977, have seen wide-spread use starting with the 1981 model year. At the present time, a partially stabilized zirconia electrolyte using yttrium oxide as the stabilizer appears to be the most common choice for this application. 

Yttrium compounds are frequently useful host materials for later Ln + ions, as mentioned in Section 5.4.4 Eu Y2O2S is the standard material for the red phosphor in virtually all colour and television cathode ray tubes, whilst Eu Y203 is used for energy-efficient fluorescent tubes. Yttrium oxide is used to stabilize zirconia (YSZ), yttrium iron garnets (YIG) are used in microwave devices, and of course YBa2Cu307 is the classic warm superconductor. Yttrium, like scandium, is naturally monoisotopic. Y has I = 1/2 though signals can be difficult to observe, valuable information can be obtained from NMR studies. 

The basic elements of a SOFC are (1) a cathode, typically a rare earth transition metal perovskite oxide, where oxygen from air is reduced to oxide ions, which then migrate through a solid electrolyte (2) into the anode, (3) where they combine electrochemically with to produce water if hydrogen is the fuel or water and carbon dioxide if methane is used. Carbon monoxide may also be used as a fuel. The solid electrolyte is typically a yttrium or calcium stabilized zirconia fast oxide ion conductor. However, in order to achieve acceptable anion mobility, the cell must be operated at about 1000 °C. This requirement is the main drawback to SOFCs. The standard anode is a Nickel-Zirconia cermet. 

Single oxide ceramics, e.g. aluminium oxide (AI2O3, alumina) and zirconium dioxide (Zr02, zirconia), are bioceramics of an inert nature. An inert ceramic does not form a bonding to bone similar to those bioceramics of bioactive nature. Alumina bioceramics are in the pure aluminium oxide form, whereas zirconia bioceramics are partially stabilized by additional oxides, e.g. yttrium oxide, calcium oxide or magnesium oxide. 

In many applications rare earths are used as additives. As mentioned in sect. 2, yttrium oxide is doped into zirconia to stabilize the appropriate structure for ionic conduction. 

Another application is in tire oxidation of vapour mixtures in a chemical vapour transport reaction, the attempt being to coat materials with a tlrin layer of solid electrolyte. For example, a gas phase mixture consisting of the iodides of zirconium and yttrium is oxidized to form a thin layer of ytnia-stabilized zirconia on the surface of an electrode such as one of the lanthanum-snontium doped transition metal perovskites Lai j.Srj.M03 7, which can transmit oxygen as ions and electrons from an isolated volume of oxygen gas. 

Liu J and Barnett SA. Thin yttrium-stabilized zirconia electrolyte solid oxide fuel cells by centrifugal casting. J Am Ceram Soc 2002 85 3096-3098. 

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