Yttria powder

Hruschka, M.K.M. et al.. Processing of P-silicon nitride from water-hased a-silicon nitride, alumina and yttria powder suspensions, J. Am. Ceram. Soc., 82, 2039, 1999. 

Rhodes used oxalic acid co-precipitation method to produce lanthanum doped yttria powder and sintered by controlled transient solid second-phase sintering method. Materials with near theoretical total transmittances and specular transmittance within 6% of theoretical were obtained. 

M. Akinc and A. Celikkaya, Preparation of yttria powders by emulsion precipitation, in Adv. 

A. Celikkaya and M. Akinc, Synthesis and characterization of yttria powders by emulsion pre-... 

Figure 1.25 Morphology of yttria powder prepared by the precipitation of yttrium nitrate (a) without the addition of and (b) with the addition of SO4" [299].

Ultra-flne-grained highly reactive yttria powders, suitable especially for the preparation of transparent ceramics, are prepared by various methods including combustion synthesis [293], precipitation [294, 295], hydrothermal synthesis [296], electrospray pyrolysis [297], and sol-gel [298]. In order to improve the dispersion and sinterability of yttria powders, seed crystals are often added [296]. A significant refinement of yttria powders prepared by precipitation from solution may be achieved by the addition of sulfate ions to the reaction mixture [299] (Figure 1.25). 

Prep iU ation of the first PY6 material for the baseline properties demonstration was initiated. Tlie silicon nitride and yttria powders were batched in SWECO mills to make up approximately 20 kg total batches. These were then milled and discharged. Three... 

Selection of the silicon nitride and yttria powders for use in the program constitutes the accomplishment of Milestone 114301. The test specimen geometry and test procedure are considered satisfactory for the accomplishment of the program. This completes milestone 114319. Overall execution of the remainder of the program is on schedule. 

Table 5. Summary of Yttria Powder Characterization Data ...

The coatings all contain the stabilized cubic phase. No second phases, tetragonal zirconia or yttria oxide, were detected. With sol-gel processed YSZ, residual porosity was removed after firing at 900°C for 5 h (Okubo, 1996). This densification temperature is lower than in the solid-state preparation where zirconia powders are reacted with yttria powder. 

Nanocrystalline yttria (Y2O3) powders with most suitable characteristics for the fabrication of yttria crucibles were synthesized by the sol-gel method [85]. The combustion synthesis method was used starting with high-purity (99.9%) yttrium nitrate hexahydrate and citric acid. Different fuel to oxidant (citric acid/nitrate) ratios (0.25, 0.5, 0.75, 1.0, and 1.1) were tested. These mixtures were heated at 373 K until a viscous gel was formed, and its decomposition into powder formation was realized by thermal treatment at 473 K for 3 h. In all mixtures, yttria powders were obtained by thermal treatment at 1073 K. Scanning electron microscopy (SEM) showed that these powders were porous, whereas high-resolution transmission electron microscopy (HRTEM) revealed that they consist of randomly oriented cuboidal nanocrystallites with an average crystallite size of about 17-30 nm. In order to obtain dense ceramics, the powders were compacted as pellets at 120 MPa and were sintered at 1673 K. Pellets with a sintered density as high as 98-99% of the theoretical density could be obtained from powders prepared with fuel to oxidant ratios (/ ) of 0.75 and 1.0. 

A new type of Hquid-phase sintered SiC using yttria [1314-36-9] 2 3 oxide additive and submicrometer SiC powder for enhanced... 

Powders of zirconia and yttria were alloyed in a Fritsch planetary microball mill Pulverisette 7, as reported previously [13,14]. The resulting specimens were examined by XRD, TEM, SAED and HRTEM with EDS. 

One of the first studies of how these secondary phases form was performed by van Roosmalen and Cordfunke. These authors used SEM/EDS and XRD to study postannealed diffusion couples of LSM and YSZ as well as pressed and fired powder mixtures of LSM and YSZ. These experiments showed that reaction products in sufficient quantity to detect by XRD (1—3%) form at temperatures as low as 1170 °C. The two principle reaction products observed were La2Zr207 (LZ) and SrZrOs (SZ), with the relative amount of LZ and SZ depending on the La/Sr ratio in the LSM. Calcia- and baria-doped LaMnOs were found to be similarly reactive with YSZ, and reactivity of LSM with YSZ having 3% or 8% yttria was found to be similar. In the case of the diffusion couples, the layer of reaction products formed at the interface was found (using SEM) to be on the order of 1 /xm after 600 h at 1280 °C and 10—15 fim after 600 h at 1480 °C. By employing Pt diffusion markers... 

Polycrystalline yttria-stabilized zirconia (YSZ-8) disks were prepared using 8 mol % Y203-doped zirconia powder (TOSOH zirconia, TZ-8Y, TOSOH Corp.). The powder was pressed uniaxially into disks which were cold isostatically pressed at 40,000 psi and then sintered at 1450°C for 4 h. Pt paste (Engelhard 6926) was painted on both faces of the YSZ-8 disks. Pt wires (0.0025 cm diam) were connected to the YSZ by using Pt meshes (150 X 150 mesh, 0.005 cm wire diam, Unique Wire Weaving Co., Inc.). 

For refractory applications, when the mixed oxide route is followed, temperatures as high as 1900 °C are necessary to sinter to high density. The high interest in SOFCs has stimulated efforts to develop novel fabrication routes to zirconia ceramics and yttria-stabilized sub-micron sized powders have been prepared which sinter to 95% theoretical density at a temperature as low as 1150 °C [4],... 

A new type of liquid-phase sintered SiC using yttria [1314-36-9J, Y20, as the oxide additive and submicrometer SiC powder for enhanced densification, produces a material which can be densified without the application of pressure (13). This material, sintered from cold isostatically pressed billets, appears to be comparable to silicon nitride in strength and fracture toughness. 

Ceramic powders of exceptional purity with very fine particle sizes (ca. 10 nm) have been prepared by precipitation of hydrolyzed oxides from high purity alkoxides . Yttria-stabilized zirconia is prepared by mixing high purity zirconium and yttrium isopropoxides in n-hexane, with water added dropwise to precipitate the oxides quantitatively. The homogeneity of the oxides results in stabilized cubic Zr02 at very low temperatures. Cyclic organoaluminum amides are used to prepare nonoxides such as sulfides and AIN- . 

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