Yttrium oxide

Yttrium oxide also is used to produce yttrium-iron-garnets, which are very effective microwave filters.  [c.74]

Pure hafnium dioxide transforms into the tetragonal stmcture at about 1700°C. The difference between the heating transformation temperature and the cooling transformation temperature is 40—80°C, considerably less than for zirconia. The hafnium dioxide undergoes a shrinkage of about 3% upon transforming into the tetragonal phase. The tetragonal form converts to a cubic polymorph having the fluorite stmcture above 2600°C. The fluorite stmcture can be rendered stable at lower temperatures by addition of erbium oxide, yttrium oxide, calcium oxide, or magnesium oxide. Compared to zirconium oxide, the higher transformation temperature of hafnium oxide, pure or stabilized, has aroused considerable interest (64) and should lead to several specialized appHcations. Reference 64 is a thorough review of hafnium oxide and hafnium oxide-toughened ceramics.  [c.445]

In the yttrium oxide europium phosphor, a uv photon is absorbed at the Eu " activator center and emission comes directly from this same center after relaxation. This fact contributes to the high quantum efficiency, in excess of 90%, of this phosphor. The excitation band is due to a ligand (O ) to metal (Eu " ) charge-transfer transition and has a maximum at roughly 230 nm. As a result, the absorption of 254 nm uv radiation is not high with plaques reflecting 25—35% of this radiation, depending on the europium concentration. Because the green and blue phosphor components of the blend are generally good absorbers of 254-nm radiation and because a lot of red emission, the amount depending on the desired color of the lamp, is required in triphosphor blends to achieve white light, the yttrium oxide phosphor is the most expensive component of the blend.  [c.290]

Pressureless sintering of a- and P-SiC powders can also be achieved by the addition of aluminum and/or aluminum compounds together with carbon or rare-earth elements (95—105). Boron-free, aluminum-containing sintering aids inhibit grain growth (95,104). Aluminum oxide together with yttrium oxide as additives yield a fine and unique microstmcture (104). A Hquid-phase sintering mechanism has been reported in this aluminum oxide and rare-earth oxide-doped SiC system (104,106). Fine microstmcture, good chipping resistance, and over 800 MPa (116,000 psi) room temperature strength have been reported (97,104). Creep resistance and other high temperature related properties are not as good as the boron- and carbon-doped SiC, in general.  [c.466]

Fluorescent spectra of yttrium oxide in pulsed glow discharge were investigated under different conditions. A few series of lines have been identified as YO lines 613.21, 614.84, 616.51, 617,91 nm 647.06 648.65, 650.25 nm 584.19, 585.88, 587.35 nm. All these lines belong to transitions between oscillation levels (v ) of main ground state and oscillation levels (v O of first excited state IT. The lines show different dependence on laser delay time. The explanation is as following while glow discharge is mnning, part of YO molecules are in excited oscillation states, so that in fluorescence spectmm are present lines, corresponding to transitions with all oscillating quantum numbers v, v" = 0, 1, 2, 3. .. After glow discharge quenching the population of excited levels with v = 1,2, 3. .. decrease, the higher is excited level the faster is decreasing. The intensities of corresponding fluorescence lines fall down. From the other hand the population of main ground state with v = 0 increases due to relaxation of molecules from excited levels. The intensity of corresponding fluorescence line grows.  [c.412]

Reference has been made already to the existence of a set of inner transition elements, following lanthanum, in which the quantum level being filled is neither the outer quantum level nor the penultimate level, but the next inner. These elements, together with yttrium (a transition metal), were called the rare earths , since they occurred in uncommon mixtures of what were believed to be earths or oxides. With the recognition of their special structure, the elements from lanthanum to lutetium were re-named the lanthanons or lanthanides. They resemble one another very closely, so much so that their separation presented a major problem, since all their compounds are very much alike. They exhibit oxidation state -i-3 and show in this state predominantly ionic characteristics—the ions.  [c.441]

III) nitrate 4-water (III) oxide (III) sulfate 8-water Yttrium chloride fluoride  [c.270]

Yttrium barium copper oxide [107539-20-8]  [c.1081]

Yttrium iron oxide [12063-56-8]  [c.1081]

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.  [c.440]

High Temperature Corrosion. The rate of oxidation of magnesium adoys increases with time and temperature. Additions of berydium, cerium [7440-45-17, lanthanum [7439-91-0] or yttrium as adoying elements reduce the oxidation rate at elevated temperatures. Sulfur dioxide, ammonium fluoroborate [13826-83-0] as wed as sulfur hexafluoride inhibit oxidation at elevated temperatures.  [c.334]

Nickel—aluminum has been used for parts repair. Complex alloys of chromium, aluminum, yttrium, and another metal can be appHed for oxidation and corrosion resistance. Before spraying, the part must be cleaned of oil and dirt. Standard aqueous or solvent cleaners are sufficient. Molded surfaces must be coated with a special paint to promote metal adhesion or blasted with fine aluminum oxide grit of 250—177 lm. Use of iron grit may lead to staining of the surface. Grit blasting is difficult to automate, and manual blasting may give quaUty control problems because there is Httle change in appearance after the operation. Arc spray coating must foUow the grit blasting as soon as possible or blasting must be repeated.  [c.135]

Another common and important use of plasma is spray coating of materials with plasma-melted substances (167,168). Plasma torches heated by d-c arcs can be hand-held for spray coating (22). Plasma spraying is employed to apply oxidation-resistant coatings to metals for example, ceramic coatings of aircraft engine components and a proprietary cobalt—chrornium—alurninum—yttrium coating for gas-turbine blades (169,170) (see Refractory coatings). High temperature, self-lubricating coatings have also been appHed to materials using plasma techniques (171).  [c.116]

Yttrium-Barium-Copper Oxide  [c.482]

Calcium metal is an excellent reducing agent for production of the less common metals because of the large free energy of formation of its oxides and hahdes. The following metals have been prepared by the reduction of their oxides or fluorides with calcium hafnium (22), plutonium (23), scandium (24), thorium (25), tungsten (26), uranium (27,28), vanadium (29), yttrium (30), zirconium (22,31), and most of the rare-earth metals (32).  [c.402]

Electrical and Electronic Applications. Silver neodecanoate [62804-19-7] has been used in the preparation of a capacitor-end termination composition (110), lead and stannous neodecanoate have been used in circuit-board fabrication (111), and stannous neodecanoate has been used to form patterned semiconductive tin oxide films (112). The silver salt has also been used in the preparation of ceramic superconductors (113). Neodecanoate salts of barium, copper, yttrium, and europium have been used to prepare superconducting films and patterned thin-fHm superconductors. To prepare these materials, the metal salts are deposited on a substrate, then decomposed by heat to give the thin film (114—116) or by a focused beam (electron, ion, or laser) to give the patterned thin film (117,118). The resulting films exhibit superconductivity above Hquid nitrogen temperatures.  [c.106]

This also illustrates the use of different wavelengths of light to obtain much more infomration on the nature of the film. Here A and T are plotted versus the wavelength of light ( ) and the line drawn tln-ough these data represents a fit calculated for the various fihns of yttrium oxide deposited on silica as shown at tire bottom of the figure [40],  [c.1888]

Yttrium oxide is one of the most important compounds of yttrium and accounts for the largest use. It is widely used in making YVOr europium, and Y2O3 europium phosphors to give the red color in color television tubes. Many hundreds of thousands of pounds are now used in this application.  [c.74]

Cera.mics, Chemical and stmctural properties of the rare earths are used in the technical ceramics (qv) industry. Tetragonal or cubic forms of zHconia are stabilized by the addition of small quantities of rare-earth oxides, particularly yttrium oxide (1 to 10 mol %). Advantage can be taken of the ionic conductivity induced by the substitution of tetravalent zirconium by trivalent cerium and its variation with oxygen partial pressure to make zHconia-based sensors (qv). The good thermomechanical properties of yttria-stabiHzed zHconia make it useflil for the preparation of cutting tools (see Tool materials). Also, when the cubic form of zHconia is fliUy stabilized, ie, Y2O2 content about 7 mol %, optical properties are so close to those of diamond that zHconia is often used in imitation jewelry (26) (see Gemstones, gemstone materials).  [c.547]

The second interesting class of ceramic tool material under development is based on Si N, either nearly pure Si N (except for some minor additions of sintering aids) or having various additions of aluminum oxide, yttrium oxide, and TiC (123—134). It is a spin-off of the high temperature—stmctural ceramics technology developed in the 1970s for automotive gas turbines and other high temperature appHcations. Ford Motor Co. developed a ceramic tool of Si N having additions of ca 12% yttria (Grade S 8). Norton Co. developed a Si N ceramic based on MgO but has never commercialized it for cutting tool appHcations. Instead, it concentrated on advanced stmctural appHcations, including hybrid ceramic bearings. Similarly, General Electric and Westinghouse also developed Si N -based ceramics for high temperature—stmctural appHcations but did not extend them to cutting tools.  [c.213]

For elimination of intramolecular energy losses, we have synthesized ligands with high hydrophobisity - perfluoro-P-diketones R -CO-CH -CO-R, (R = CgF j or CgF R = phenyl or a-thienyl), that without second ligand eliminate completely water molecules from the inner coordination sphere. These ligands we have used in analysis at determination of Sm, Eu, Nd, Yb microamounts in high-purity lanthanide and yttrium oxides.  [c.82]

Solid oxide fuel cells consist of solid electrolytes held between metallic or oxide elecU odes. The most successful fuel cell utilizing an oxide electrolyte to date employs Zr02 containing a few mole per cent of yttrium oxide, which operates in tire temperature range 1100-1300 K. Other electrolytes based  [c.244]

In 1794 the Finnish chemist J. Gadolin, while examining a mineral that had recently been discovered in a quarry at Ytterby, near Stockholm, isolated what he thought was a new oxide (or earth ) which A. G. Ekeberg in 1797 named yttria. In fact it was a mixture of a number of metal oxides from which yttrium oxide was separated by C. G. Mosander in 1843. This is actually part of the fascinating story of the rare earths to which we shall return in Chapter 30. The first sample of yttrium metal, albeit very impure, was obtained by F. Wohler in 1828 by the reduction of the trichloride by potassium.  [c.944]

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.  [c.528]

Europium oxide is now widely used as a phospor activator and europium-activated yttrium vanadate is in commercial use as the red phosphor in color TV tubes. Europium-doped plastic has been used as a laser material. With the development of ion-exchange techniques and special processes, the cost of the metal has been greatly reduced in recent years.  [c.178]

Nitrogen was identified as a primary embrittling impurity in chromium in the early 1950s. However, even pure chromium single crystals are known to be brittie at ambient temperatures, thereby presenting a significant problem in developing ductile chromium alloys. Nevertheless, several promising approaches to improve ductiHty and/or strength have been reported. Several ductile Cr—MgO alloys made by a powder process have been developed in the United States, the MgO improving oxidation resistance as weU. AHoy development in the United States also has combined both soHd-solution strengthening by tungsten or molybdenum with precipitate strengthening by carbides, and small amounts of yttrium or yttrium and lanthanum for solute scavenging and slightly improved oxidation resistance (58). Other chromium alloys having improved strength but only marginally increased ductiHty have been developed in AustraHa and the former Soviet Union. In all cases there is a trade-off between high temperature strength and low temperature ductiHty.  [c.127]

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.  [c.290]

Nickel—Chromium. Nickel and chromium form a soHd solution up to 30 wt % chromium. Chromium is added to nickel to enhance strength, corrosion resistance, oxidation, hot corrosion resistance, and electrical resistivity. In combination, these properties result in the nichrome-type alloys used as electrical furnace heating elements. The same alloys also provide the base for alloys and castings which can withstand hot corrosion in sulfur and oxidative environments, including those containing vanadium pentoxides which are by-products of petroleum combustion in fossil-fuel electric power plants and in aircraft jet engines. AHoy additions to nickel—chrome usually are ca 4 wt % aluminum and ca <1 wt% yttrium. Without these additions, the nichrome-type alloys provide hot oxidation or hot corrosion resistance through the formation of surface nickel—chromium oxides. Aluminum provides for surface AI2O2  [c.6]

Some nut trees accumulate mineral elements. Hickory nut is notable as an accumulator of aluminum compounds (30) the ash of its leaves contains up to 37.5% of AI2O2, compared with only 0.032% of aluminum oxide in the ash of the Fnglish walnut s autumn leaves. As an accumulator of rare-earth elements, hickory greatly exceeds all other plants their leaves show up to 2296 ppm of rare earths (scandium, yttrium, lanthanum, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium). The amounts of rare-earth elements found in parts of the hickory nut are kernels, at 5 ppm shells, at 7 ppm and shucks, at 17 ppm. The kernel of the Bra2d nut contains large amounts of barium in an insoluble form when the nut is eaten, barium dissolves in the hydrochloric acid of the stomach.  [c.272]

Platinum and iridium cmcibles are used for the growth of high purity crystals of specialty materials such as the rare earths. Examples include gadolinium gallium garnet and yttrium aluminum garnet for use in electronic memory chips and lasers (qv). The high melting point and oxidation resistance of the PGMs minimi2e contamination of the melt. Platinum laboratory apparatus is routinely used in chemical analysis.  [c.173]

Emulsions have been employed to produce spherical powders of mixed cation oxides, such as yttrium aluminum garnets (YAG), and many other systems (15). Sol—gel powder processes have also been appHed to fissile elements (16). Spray-formed sols of UO2 and UO2—PUO2 were formed as rigid gel spheres during passage through a column of heated Hquid. Abrasive grains based on sol—gel-derived mixed alumina are important commercial products (1). Powders for superconductors, eg, the YBaCuO system, and magnetic ceramics were also developed using the sol—gel technology (see Magnetic materials).  [c.249]

Yttrium—barium—copper oxide, YBa2Cu202 is a newly developed high T material which has been found to be fully superconductive at temperatures above 90 K, a temperature that can be maintained during practical operation. The foremost challenge is to be able to fabricate these materials into a flexible form to prepare wines, fibers, and bulk shapes. Ultrapure powders of yttrium—barium—copper oxide that are sinterable into single-phase superconducting  [c.482]

One of the many possible ways of classifying ceramics is according to use. One group is the bulk or commodity ceramics that have had relatively httie processing beyond the constituent raw materials. These are primarily low value-added materials such as brick, tile, pottery, and abrasive grain (see Abrasives). At the other extreme are the engineering or fine ceramics that are characterized as low volume, high value-added, highly processed materials having carefully controlled properties (see Advanced ceramics). Some of the main types of engineering ceramics include (/) electronic ceramics, which include dielectrics, ferroelectrics (qv), ferromagnetic ceramics, piezoelectrics, and superconductors (see also Ceramics AS electrical materials) (2) stmctural ceramics, which are strong, fracture-resistant materials such as siUcon nitride [12033-89-5] Si N, siUcon carbide [409-21 -2] SiC, and toughened zirconium dioxide [1314-23-4] ZtO, (3) wear-resistant ceramics, such as the carbides, nitrides, and borides (see Boron compounds Toolmaterials) (4) optical ceramics such as Cr doped AI2O2 (mby [12174-49-17) siUcon dioxide [7631-86-9J, Si02, fiber lead lanthanum zirconium titanate (PLZT) and yttrium aluminum garnet (YAG) and (5) bioceramics, which are low or controlled reactivity materials for in-body use such as aluminum oxide [1344-28-17, AI2O2, and hydroxyapatite [1306-06-5] (see Prosthetic and BioPffiDiCALdevices).  [c.301]

Garnets have played an important role in the development of highly sophisticated microwave devices since the development of yttrium—iron garnet, yttrium iron oxide [12063-56-8]. The iron is strongly constrained to be trivalent in order to maintain electrical neutraUty in the crystal, which is essential for low microwave losses. Garnets have lower values of saturation magneti2ation than spinels, but provide superior performance in microwave devices because they have a narrower resonance line width.  [c.359]

See pages that mention the term Yttrium oxide : [c.1081]    [c.1081]    [c.1081]    [c.1081]    [c.287]    [c.56]    [c.302]    [c.521]    [c.847]    [c.431]    [c.116]    [c.125]    [c.542]    [c.375]    [c.6]    [c.302]    [c.302]   
Chemistry of the elements (1998) -- [ c.949 ]