Yttrium resistance

Fig. 7 Creep-resistance of the eutectic fiber consisting of interpenetrating phases of alpha-alumina and yttrium-aluminum-garnet (YAG) up to very high temperatures compared with other types of oxide fibers... 

The compound consisting of yttrium, copper, and barium oxide, commonly called compound 1-2-3, was formed in 1987 by research scientists at the universities of Alabama and Houston. It had limited superconducting capabilities. It has been known for some time that conductors of electricity such as copper resist, to some extent, the flow of electrons at normal temperatures, but at temperatures near absolute zero (zero Kelvin = -273°C), this resistance to the flow of electrons in some materials is reduced or eliminated. The 1-2-3 compound proved to be superconducting at just 93°K, which is still much too cold to be used for everyday transmission of electricity at normal temperatures. Research continues to explore compounds that may achieve the goal of high-temperature superconductivity. 

There are two allotropic (crystal forms) of terbium, both of which are dependent on its temperature. The alpha ((a) form exists at room temperatures and up to temperamres of 1,298°C, and the beta ( 3) form exists beyond these temperamres. Although terbium is a silvery metal that resembles aluminum and feels hke lead, it is much heavier than either of these two elements. It is placed in the yttrium subgroup (lanthanide series) of the rare-earths. It is also resistant to corrosion. 

Yttrium alloys have many applications. The metal doped with rare earths such as europium is used as phosphor for color television receivers. When added to iron, chromium, vanadium, niobium, and other metals it enhances resistance of these metals and their alloys to high temperature oxidation and recrystallization. It is a deoxidizer for vanadium and other nonferrous metals. Yttrium-aluminum garnets are used in lasers and in jewelery gemstones. Yttrium-iron garnets are used as transmitters and as transducers of acoustic energy. 

Baddeleyite has a monocHnic structure with space group Plljc. The Zr + ion has seven-fold coordination, while the idealized ZrOz polyhedron is close to tetrahedral orientation, where one angle in the structure is different significantly from the tetrahedral value. Natural baddeleyite is a raw material for zirconium. In industry ZrOz, named usually zirconia, is important in areas such as surface chemistry, where its activity as a red ox material and its acid-based functions are important. As a ceramic material, zirconia can resist very high temperatures and its stabihzed form, yttrium-stabihzed zirconiiun, shows remarkable mechanical properties. 

The exceptional properties of the alloy are due in no small way to the yttrium component which together with the aluminium forms a stable and firmly bound oxide layer that exhibits excellent resistance to exhaust gas emissions at high temperatures over prolonged periods.( ) At the same time, it provides an ideal surface to receive another coating of metal or metal oxide which, in the context of catalyst applications, is most essential. At the present time most catalytic convertors utilise ceramic substrates which are prone to damage by both mechanical and thermal shock. 

Yttrium is also used in other areas of metallurgy notably as a component of certain nickel-base and cobalt-base superalloys of the NiCrAlY and CoCrAlY type.(3) These alloys possess excellent corrosion and oxidation resistance, properties that have attracted the attention of the aero-engine industry where they are used as protective coatings on turbine blades. The alloys, when applied by vapour deposition, form an oxide coating that exhibits remarkable adhesion, a property attributed largely to the yttrium component acting to prevent the formation of voids at the oxide/substrate interface.(4)... 

Without it the alloys show significantly less resistance to cyclic oxidation which would suggest that, as with yttrium in Fecralloy, the lanthanum is acting to provide a firmly bound oxide barrier. 

Film Critical Current Densities Critical current densities of thin films have been reported by several hundreds of papers a few representative but by no means inclusive are noted here in addition to those mentioned above. Desirable attributes of thin films for technology are high transition temperature to zero resistance, high critical current, low substrate temperature during deposition, no high temperature post anneal, and atomically smooth surface without pinholes. A thermal coevaporation of yttrium, barium, and copper in an oxygen atmosphere have been deposited by Berberich (34) on substrates at 650°C with Tc s of 91 K on MgO and 89 K on SrTiOs without post anneal. Although critical currents of 106 A/cm2 were obtained at 4 K, values of 104 A/cm2 were found at 77 K. However,... 

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