Papers by Keyword: Rare Earth Oxide

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Authors: E.R. Andrievskaya, V.P. Red'ko, V.P. Smirnov, L.M. Lopato
Authors: Tomonori Nakamura, Harunobu Sano, Takehiro Konoike, Kunisaburo Tomono
Authors: Xiu Song, Lei Wang, Mitsuo Niinomi, Masaaki Nakai, Yang Liu, Miao Yong Zhu
Abstract: The microstructures and fatigue properties of the TNTZ added with Y or Y2O3 have been investigated. The results indicate that TNTZ added with Y or Y2O3 are all found to be composed of β phase and the small amount of Y2O3. The grain size of TNTZ added with Y or Y2O3 is smaller than that of TNTZ. The Young’s modulus of TNTZ added with Y or Y2O3 are maintained at a low level, and Young’s modulus of TNTZ added with Y is smaller than that of TNTZ added with Y2O3. The mechanical properties are both improved by adding Y or Y2O3, while the tensile strength of TNTZ added with Y2O3 is slightly higher than that added with Y. The high cycle fatigue limit of the alloys added with Y or Y2O3 are similar, while the low cycle fatigue strength of TNTZ added with Y is higher than that added with Y2O3. The improvement in fatigue properties ascribes to the microstructure refinement and the pining effect of Y2O3 particles. On the other hand, Y elements form Y2O3 with the Oxygen elements in the matrix, thus lead to the weakening of the Oxygen solution effect.
Authors: Sheldon M. Wiederhorn, Ralph F. Krause, František Lofaj, U. Täffner
Abstract: New data are presented on the tensile creep behavior of silicon nitride sintered with Lu2O3. The data are compared with two earlier sets of data collected on the same material. The older sets gave results that are difficult to explain theoretically: a high value for the stress exponent, n=5.33, and no cavitation. The new set of data also gave no cavitation, but gave a stress exponent, n=1.81, that can be rationalized theoretically in terms of solution-precipitation creep of the silicon nitride grains. An analysis of variance showed that one of the earlier sets of data was statistically consistent with the newer set, whereas the other set of data was not. Combining the two sets of data that agreed statistically yields a consistent picture of creep with a low value of the stress exponent and no cavitation. The stress exponent for the combined set of data is n=1.87±0.48 (95 % confidence limits). The tensile creep mechanism of the silicon nitride containing Lu2O3, solution-precipitation, differs from those of other silicon nitrides, for which tensile creep has been attributed to cavitation. Enhancement of the creep resistance of the silicon nitride sintered with Lu2O3 may be a consequence of the fact that Lu2O3 produces a more deformation resistant amorphous phase at the two grain junctions, than do Y2O3 or Yb2O3. In parallel, reducing the amount of secondary phase below a critical limit, or increasing the viscosity of the two grain boundaries relative to three-grain junctions reduces the ability of the material to cavitate during creep, and forces the creep mechanism to change from cavitation to solution-precipitation.
Authors: Claudinei dos Santos, Kurt Strecker, Francisco Piorino Neto, Cosme Roberto Moreira Silva, Flávia A. Almeida, Rui F. Silva
Abstract: The objective of this work was to evaluate the creep behaviour of Si3N4 based ceramics obtained by uniaxial hot-pressing. As sintering additive, an yttrium-rare earth oxide solid solution, designed RE2O3, that shows similar characteristics to pure Y2O3, was used. Samples were sintered using high-purity α-Si3N4 powder, with additive mixtures based on RE2O3/Al2O3 or RE2O3/AlN, at 5 and 20 vol.%, respectively. The sintered samples were characterized by X-ray diffractometry, scanning electron microscopy and density. Specimens of 3x3x6 mm3 were submitted to creep tests, under compressive stresses between 100 and 350 MPa at temperatures ranging from 1250 to 13750C in air. Samples with RE2O3/Al2O3 showed β-Si3N4 as crystalline phase, with grains of high aspect ratio, and a relative density around 99% of the theoretical density. The Si3N4/RE2O3/AlN samples presented α-Si3N4 solid solution, designed α-SiAlON, with a more equiaxed microstructure and slightly lower relative density (96-98%). The results of creep tests indicated that these ceramics containing α-SiAlON are the more creep resistant, with steady-state creep rates around 10-4 h-1, with stress exponents (n) in the range 0.67-2.53, indicating grain boundary sliding as the main creep mechanism.
Authors: Yoshihiro Hirata, Naoki Matsunaga, Soichiro Sameshima
Abstract: This paper reports the influence of sintering additives (RE2O3, Al2O3RE2O3, RE = Yb, Y and Gd, 13 vol%) and mixing effect of 30 nm SiC powder with 800 nm SiC powder on phases of grain boundaries, grain size of SiC, fracture toughness and strength of SiC hot-pressed at 1950°C under 39 MPa of applied pressure. Rare earth ions were uniformly adsorbed on negatively charged SiC particles with 150 nm Al2O3 particles in aqueous suspensions at pH 5. A rapid densification of SiC with one component RE2O3 occurred above 1700°C when a liquid of SiO2 (formed on SiC particles)RE2O3 system was formed. The Al2O3RE2O3 additives lowered a liquid formation temperature to 14001500°C and enhanced the densification rate of SiC. An increased solubility of 30 nm SiC in a liquid during dissolution-precipitation process provided an amorphous phase of SiCSiO2Al2O3RE2O3 system at grain boundaries and suppressed the grain growth of SiC. The fracture toughness of dense SiC was dominated by the grain boundary thickness controlled by grain size of SiC and amount of oxide additives. Mixing of 30 nm SiC with 800 nm SiC improved greatly the strength of SiC with two component oxides and the mean flexural strengths reached 740810 MPa.
Authors: Yan Yan Zhu, Run Xu, Ze Bo Fang, Yu Zhao, Hui Yu Li, Jing Chen, Hai Jing Cao
Abstract: Reflectance design and synthesis for Er2O3 single layer and Er2O3/TiO2 double layer are made. The optimum reflectance and thickness are determined. The developed simulator can be used for the optimization of antireflecting coatings for optoelectronic devices to improve the power output parameters.
Authors: Suo Mei Zhang, Zi Dong Wang
Abstract: Pure carbon, pure iron and single crystall silicon were firstly loaded into a pure graphite crucible to obtain a hypereutectic Fe-C melt by carburizing at high temperatures in this paper. The powder of oxide La2O3 and CeO2 were added respectively to the melt under the same process conditions and cast iron samples were obtained. The graphite morphology of the samples was observed under optical microscope and SEM. Matrix of the samples were etched by electrolysis way. At last non-ferrous residue on the surface of cast iron samples was gathered, calcined,observed under SEI and BEI and analysed with EDS to find the trace of oxide La2O3 or CeO2. The results showed that oxide La2O3 or CeO2 was really added into the melt but the morphology of graphite did not change. The only effect of the oxides was making the amount of graphiteto increase slightly. All the results of this paper indicat that the oxide La2O3 or CeO2 is possibly the base for graphite flake to precipitate but is not a sufficient condition for graphite to nodularize.
Authors: Jaroslav Sedláček, Dušan Galusek, Pavol Šajgalík
Abstract: The microstructure evolution and mechanical properties of alumina doped with rare earth oxide and rare earth-aluminosilicate glass has been investigated in order to understand better the impact of rare earth addition on hardness and fracture toughness. The aims of the present work are to examine the possibly beneficial effects of selected rare earth oxide added to alumina by two different routes in enhancing mechanical properties. The specific systems considered in this work were as follows: liquid phase sintered alumina containing RE2O3 (RE = La, Y) and RE2O3 – Al2O3 – SiO2 glassy phase up to 5 wt. %. The Vickers hardness and fracture toughness have been compared with the undoped alumina.
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