Yttrium oxide particles

Figure 6-7. Scanning electron micrographs for yttrium oxide particles obtained by calcination of yttrium oxalate particles for 6h at 823 K. (a) and 1073 K (b). (Reprodueed with permission from ref. 60. Copyright 1998 American Chemical Society)...

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... 

The size of the nanodroplets can be controlled in the range of 5 - 80 nm by changing the concentration ratio of water/surfactant in the microemulsion system. By this method, yttrium oxide [67], cerium oxide [68-70], neodymium oxide [71], and erbium oxide [72, 73] nanoparticles have been synthesized. The average particle size of the particles adopts values in the range fi om 2 to 70 nm, which depends on the synthesis conditions. 

The papers [79,80] give consideration to the radiation tolerance of ferrite steel hardened with yttrium oxide (YjOj) particles of 20 nm. Two types of radiation treatment were used, in particular irradiation with helium ions that results in the formation of barely point defects and bombardment with high-energy (150 keV) iron ions. In the latter case, defects were mainly formed in displacement cascades, whose size ranges within 2-3 nm. It has been established that the changes in the distribution of dispersed phase and its component composition were not observed whatever methods were used to create defects. 

Using the same technique, it is also possible to precipitate composite particulates. The latter can be homogeneous of exact stoichiometry, as exemplified by pure or doped barium titanates [9]. To achieve these conditions rapid mixing is required, such as by using the controlled double jet precipitation process. In contrast, slow precipitation results, as a rule, in internal inhomogeneity, that is, the composition changes from the center to the periphery, although the particles may still be perfectly spherical, as observed with mixed alumina/silica [10] or copper/ lanthanum and copper/yttrium oxides [11]. 

Aiken B, Matijevic E (1988) Preparation and properties of uniform coated inorganic colloidal particles, 4. Yttrium basic carbonate and yttrium-oxide on hematite. J Colloid Interface Sci 126 645-649... 

Akinc and Celikkaya [169], on the other hand, synthesized yttrium oxide where the stock solution of yttrium (0.25 M) was prepared in a similar way this solution was dispersed in toluene as the continuous phase, containing a dissolved mixture of Span 60 (Sorbitan monostearate) and Tween 80 (the most satisfactory volume ratio was 2 1) as emulsifier. Triethanolamine was used as the precipitating agent, while methanol was used for breaking the emulsion. A standard emulsion formulation had 150 ml of the water phase dispersed in 430 ml of the oil phase, with 10 g of Span 60 and 8 ml of Tween 80. The spherical particles of Y2O3 obtained by calcination at 700 C had a size range of 0.2-2 pm, peaking at around 0.6 pm. In another work, Celikkaya and Akinc [192] destabilized the system after precipitation by addition into acetone. 

Refractory Fibers Recently, zirconia-based insulating material with a low density and a low thermal conductivity has been developed in the form of fibers, paper, felt, board and shaped articles. The material is a cubic zirconia soHd solution stabilized with yttria, and has a maximum usable temperature of >2100 C. The innovative fabrication technique involves the use of an organic precursor fiber as a structural template, impregnated with an aqueous solution of zirconium chloride and yttrium chloride. The metallic salts are deposited within the organic fiber, which can subsequently be burned off by a controlled oxidation. The hollow remainder is then fired at a sufficiently high temperature (800-1300 °C) so as to induce crystallization, after which the oxide particles are sintered to develop a ceramic bond. Other techniques to produce refractory fibers involve phase inver-... 

In stainless steels for high-temperature applicahons, RE metals, chiefly yttrium, are used to improve the oxidation resistance. Yttrium is also used in ODS aUoys (Oxide Dispersion Strengthened). Yttrium oxide parhcles with grain size 50-1500 A are distributed in a matrix of some high-aUoy material. The finely dispersed Y Oj particles obstruct the dislocahon movement in the alloy and thus improve the creep properties at high temperature. The ODS ahoy is manufactured by extrusion or by HIP (Heat Isostatic Pressing). 

However, the paper [97] reported contrary results of dissolution in the oxide particles during neutron and electron irradiations. Allen et al. [104] also pointed out that the displacement energy for Y and O in yttrium oxide is 57 eV [105,106], while that for... 

Certain et al. reported the results of Ni-ion irradiation tests on 14 YWT at —75,100, 300, 450, and 600°C [107]. The analysis shows that the Y-Ti-0 oxide clusters were dissolved into a solid solution at only —75°C irradiation up to 100 dpa, somewhat similar to the dissolution of the initial yttrium and titanium oxide particles dissolution... 

Meso-Macroporous Yttrium Oxides The self-formation phenomenon was also used for the preparation of hierarchically porous yttriiun oxides by a controlled polymerization of yttrium butoxide in aqueous media [12,141,144], The synthesized yttrium oxides are 0.5-2 pm in size and are covered by a smooth surface. The fissure particles with funnel-hke and parallel macrochannels below the smooth surfeice were observed by higher resolution SEM observations (Figure 32.13b). The yield of the synthesis as well as the amount of macropores per particle continuously decreases with increasing initial synthesis pH values. The macropore diameters are 1-5, 2-8, and 5-10 pm for syntheses carried out in acidic, neutral, and basic media, respectively. The macropore walls are formed by a regation of mes-ostructured nanoparticles giving a supplementary interparticle porosity centered at 30 nm. A third level of porosity is demonstrated by the inhomogeneous pores centered at 3-7 nm for syntheses in acidic and neutral media and 5-15 nm in an alkaline medium. As for all the previously described compositions, the meso-macroporous yttria structures are amorphous at the atomic scale. 

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. 

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