Yttrium coating

In 1996, a report appeared in Nature of experiments in which a 500 nm thick film of yttrium (coated with a 5-20 nm layer of paUadium to prevent aerial oxidation) was subjected to 10 Pa pressure of H2 gas at room temperature. ... 

The heavy mineral sand concentrates are scmbbed to remove any surface coatings, dried, and separated into magnetic and nonmagnetic fractions (see Separation, magnetic). Each of these fractions is further spHt into conducting and nonconducting fractions in an electrostatic separator to yield individual concentrates of ilmenite, leucoxene, monazite, mtile, xenotime, and zircon. Commercially pure zircon sand typically contains 64% zirconium oxide, 34% siUcon oxide, 1.2% hafnium oxide, and 0.8% other oxides including aluminum, iron, titanium, yttrium, lanthanides, uranium, thorium, phosphoms, scandium, and calcium. 

In order to make an efficient Y202 Eu ", it is necessary to start with weU-purifted yttrium and europium oxides or a weU-purifted coprecipitated oxide. Very small amounts of impurity ions, particularly other rare-earth ions, decrease the efficiency of this phosphor. Ce " is one of the most troublesome ions because it competes for the uv absorption and should be present at no more than about one part per million. Once purified, if not already coprecipitated, the oxides are dissolved in hydrochloric or nitric acid and then precipitated with oxaflc acid. This precipitate is then calcined, and fired at around 800°C to decompose the oxalate and form the oxide. EinaHy the oxide is fired usually in air at temperatures of 1500—1550°C in order to produce a good crystal stmcture and an efficient phosphor. This phosphor does not need to be further processed but may be milled for particle size control and/or screened to remove agglomerates which later show up as dark specks in the coating. 

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. 

Calorised Coatings The nickel- and cobalt-base superalloys of gas turbine blades, which operate at high temperatures, have been protected by coatings produced by cementation. Without such protection, the presence of sulphur and vanadium from the fuel and chloride from flying over the sea promotes conditions that remove the protective oxides from these superalloys. Pack cementation with powdered aluminium produces nickel or cobalt aluminides on the surfaces of the blade aerofoils. The need for overlay coatings containing yttrium have been necessary in recent times to deal with more aggressive hot corrosion conditions. 

The sacrificial core approach entails depositing a coating on the surface of particles by either the controlled surface precipitation of inorganic molecular precursors from solution or by direct surface reactions [2,3,5,6,8,9,33-35,38], followed by removal of the core by thermal or chemical means. Using this approach, micron-size hollow capsules of yttrium compounds [2], silica spheres [38], and monodisperse hollow silica nanoparticles [3,35] have been generated. 

Garnets are important gems, abrasives, microwave systems components, magnetic bubble memories, and laser hosts. For the latter, yttrium aluminum garnet is the most important. It also plays an important role in aircraft turbines where it forms a protective coating on the turbine blades. 

PPG Industries has developed a substitute for lead in a coating process used widely in the auto industry. The replacement is yttrium that, though much less studied than lead, is considered orders of magnitude lower in hazard. In addition it was discovered that as yttrium is used in the process it is converted to yttrium oxide that is appears to be non-toxic by ingestion, in stark contrast to lead. As PPG customers implement yttrium overthe next several years, it is projected that the use of approximately one million pounds (some 454 tonnes) of lead will be avoided. 

Plaza, R.C.,Gonzalez-Caballero, F. Delgado, A.V. (2001) Electrical surface charge and potential of hematite/yttrium oxide core-shell coated colloidal particles. Coll. Polymer Sci. 279 1206-1211... 

Yttrium reacts with water vapor at high temperatures, usually above 750°C, forming a protective oxide coating. 

Typically, filtration is used to separate bound from free using 96-well plates in a total volume of 200 iL, but SPA technology using yttrium silicate wheatgerm agglutinin-coated beads in 384-well plates and a total volume of 60 pL has also been used [43]. 

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)... 

One important aspect of such coating processes is the generality of the procedure. It would appear that specific surface characteristics of the preformed particles are not necessarily essential for the successful deposition of the new layer. For example, yttrium basic carbonate coatings were produced on zirconium basic sulfate... 

Using the same procedure, spherical nanosize particles of hematite were coated with yttrium basic carbonate and showed that various surface thermodynamic properties of these systems were essentially those of yttria (37). 

In most cases the coating alone may be changed on subsequent treatments (e.g., by calcination at elevated temperatures), such as by converting basic carbonates into oxides. However, in some instances the shell and the core may interact to yield a different compound. For example, silica particles coated with Y(0H)C03 on heating to IOOO°C reacted to yield yttrium silicate, Y2Si207, which was restricted to the shell, as long as the amount of silica in the core was in molar excess (32). 

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