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Phase equilibrium relations in the V2O3-La2O3 system were investigated by X-ray powder diffraction and metallographic techniques. Binary mixtures, prepared from high-purity V2O3 and La2O3 powders, were equilibrated at 1600° C and then arc-melted under a partial pressure of argon. The specimens were heat-treated at various predetermined temperatures for prolonged periods and the phases present were identified by reflected-light microscopy and X-ray powder diffraction. The system consists of only one binary compound LaVO3. A eutectic between V2O3 and LaVO3 was established at 1750° C and 19 mol % La2O3 and also between LaVO3 and La2O3 at 1765° C and 75 moi % La2O3. No appreciable solid solubility was detected in the system. 相似文献
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Phase relationships in the system Si3N4-SiO2-La2O3 总被引:1,自引:0,他引:1
Phase relationships in the system Si3N4-SiO2-La2O3 have been investigated after cooling from 1700° C. Two phases, 2Si3N4·La2O3 (monoclinic) and La5 (SiO4)3N (hexagonal), were identified; the other two phases in the system, LaSiO2N (monoclinic) and La4Si2O7N2 (monoclinic), were found to dissociate to La5 (SiO4)3N and a glass after cooling from temperatures above 1650° C. The unit cells of 2Si3N4·La2O3, LaSiO2N and La4Si2O7N2 have been determined and compared with those of preceding works. The results are discussed in relation to the intergranular phases observed when Si3N4 is sintered with La2O3 additions. 相似文献
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R. R. Wills S. Holmquist J. M. Wimmer J. A. Cunningham 《Journal of Materials Science》1976,11(7):1305-1309
Examination of compositions in the system Si3N4-Y2O3-SiO2 using sintered samples revealed the existence of two regions of melting and three silicon yttrium oxynitride phases. The regions of melting occur at 1600° C at high SiO2 concentrations (13 mol% Si3N4 + 19 mol% Y2O3 + 68 mol% SiO2) and at 1650° C at high Y2O3 concentrations (25 mol % Si3N4 + 75 mol % Y2O3). Two ternary phases 4Y2O3 ·SiO2 ·Si3N4 and 10Y2O3 ·9SiO2 ·Si3N4 and one binary phase Si3N4 ·Y2O3 were observed. The 4Y2O3 ·SiO2 ·Si3N4 phase has a monoclinic structure (a= 11.038 Å, b=10.076 Å, c=7.552 Å, =108° 40) and appears to be isostructural with silicates of the wohlerite cuspidine series. The 10Y2O3 ·9SiO2 ·Si3N4 phase has a hexagonal unit cell (a=7.598 Å c=4.908 Å). Features of the Si3N4-Y2O3-SiO2 systems are discussed in terms of the role of Y2O3 in the hot-pressing of Si3N4, and it is suggested that Y2O3 promotes a liquid-phase sintering process which incorporates dissolution and precipitation of Si3N4 at the solid-liquid interface.Visiting Research Associate at Aerospace Research Laboratories, Wright-Patterson Air Force Base, Ohio 45433, under Contract No. F33615-73-C-4155 when this work was carried out. 相似文献
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The system HfO2-Yb2O3 was investigated in the 0 to 100 mol % Yb2O3 range using X-ray diffraction analysis, linear thermal expansion measurements and melting point studies. At high temperatures, the system is dominated by wide regions of solid solutions based on HfO2 and Yb2O3 separated by a two-phase field which appears to extend to the solidus. The extent of the cubic hafnia and ytterbia C-type solid solution fields was established using the precision lattice parameter method. At low temperature (< 1800° C) two ordered phases were found in the system, one at 40 mol % ytterbia with ideal formula Yb4Hf3O12, and another at 70 mol % ytterbia with formula Yb6HfO11. Four eutectoid reactions and a peritectic reaction cubic ytterbia solid solution cubic hafnia solid solution + liquid at 67 mol % and 2380° C have been established in the system. By incorporating the known tetragonal-cubic hafnia and C-type-hexagonal ytterbia transition temperatures, and the melting points data in the system, a tentative phase diagram is given for the system HfO2-Yb2O3. 相似文献
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K. Komeya Y. Haruna T. Meguro T. Kameda M. Asayama 《Journal of Materials Science》1992,27(21):5727-5734
The oxidation behaviour of silicon nitride composed of Si3N4, Y2O3, Al2O3, AlN and TiO2 was investigated in dry and wet air at 1100–1400 °C. The oxidation rates were confirmed to obey the parabolic law. An activation energy of 255 kJ mol–1 was calculated from the Arrhenius plots of the results of oxidation in an air flow. In still air the oxidation rate was larger than that in an air flow, but the oxidation rate in flowing air was not affected by the air flow rate. -cristobalite and Y2O3·2SiO2 were formed in oxidized surface layers. These crystal phases increased with increasing oxidation temperature. In particular, a higher content of -cristobalite was obtained in still air oxidation. The existence of water vapour in flowing air greatly promoted the oxidation.Concurrent with Kanagawa Academy of Science and Technology. 相似文献
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A wet-chemical approach has been applied to derive fine powders with various ceria and yttria compositions in the CeO2-Y2O3 ZrO2 ceramic system by the co-precipitation method. The characteristics of the as-derived powders have been evaluated through differential thermal analysis, thermogravimetric analysis, BET surface-area analysis, and inductively coupled plasma technique. The hardness and fracture toughness of the as-sintered specimens were evaluated by the indentation method. A highly toughened ceramic withK
IC>25 MPa m1/2 was achieved with the composition 5.5 mol% CeO2-2 mol% YO1.5-ZrO2. The relationship between the mechanical properties and the compositions of stabilizers, CeO2 and Y2O3 is discussed with respect to the degree of tetragonal to monoclinic transformation as well as the grain size of the as-sintered ceramics. 相似文献
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The (metastable) tetragonal phase in 3–4 mol% Y2O3-ZrO2 alloys undergoes a transition to the monoclinic form in the 200–300 °C temperature range. Microcracking due to the volume change at this transition has been detected in these compositions by sharp acoustic emission during heating. The phase change was confirmed by X-ray diffraction, dilatometry and scanning electron microscopy. The monoclinic tetragonal transition in ZrO2-1 mol% Y2O3 alloy at 850–750 °C and the same phase change in 2, 3, 4 and 6 mol% Y2O3 compositions at the eutectoid temperature of about 560 °C was also clearly signalled by the acoustic emission counts during heating and cooling. There was no significant acoustic emission activity on heating and cooling the 9 and 12 mol% Y2O3 compositions, which are cubic. The acoustic emission data thus confirm the phase relations in the 1–12 mol% Y2O3 region, established by conventional methods such as differential thermal analysis, dilatometry and X-ray diffraction. 相似文献
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1.IntroductionRareearthoxidesareofgreatimportanceinsci-enceandtechnology.Mallyoftheseglassesexhibitanumberofextremepropertyvalues.Theyhavehighparamagneticsusceptibilities,hightransformationtemperatures,adustableexpansioncoefficieots,verylowheliumpermeabilityanddirectcurrelltcon-ductivity,highchemicaldurabilityandidealhightem-peraturepropertieswhichmakethembecomeexcel-lentcandidatematerialsinmanyfieldssuchasop-tics,laserapplicationsinsevereserviceconditionsandFaradayrotators.Extensiveexperimen… 相似文献
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ZrO2-Y2O3 alloys with yttria contents between 2.0 and 6.3 mol% were prepared by arcmelting. The microstructure of the alloys after isothermal ageing was examined by electron microscopy. It was found that a modulated structure was formed in alloys aged at appropriate temperatures. The modulated structure resembles the structure of spinodally decomposed metallic alloys and ceramics. The range in which the modulated structure is developed is inside the cubic-tetragonal two-phase region of the ZrO2-Y2O3 system. The modulated structure is associated with metastable phase decomposition. 相似文献
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Long Periodic Structure in ZrO2-Y2O3 Ceramics 总被引:1,自引:0,他引:1
Jiancun RAO Yu ZHOU Douxing LIDepartment of Materials Science Harbin Institute of Technology Harbin ChinaSolid Atomic Imaging Division Shenyang National Laboratory for Materials Science Institute of Metal Research ChineseAcademy of Sciences Wenhua Road Shenyang China 《材料科学技术学报》2004,20(2):226-227
A new type of long periodic structure has been found in Zr02-Y2O3 ceramics in annealed states. High resolution electron microscopy (HREM), selected area electron diffraction, and computer simulation have been used to reveal the presence of the long periodic structure. The unit-cell of the long periodic structure consists of a cubic ZrO2 unit cell and L10- like phase one. 相似文献
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H. Watanabe K. Hirota O. Yamaguchi S. Inamura H. Miyamoto N. Shiokawa K. Tsuji 《Journal of Materials Science》1994,29(14):3719-3723
In compositions having ZrO2/Y2O3=(74.25–71.25)/(0.75–3.75) (mol% ratio) with 25 mol% Al2O3, metastable t-ZrO2 solid solutions crystallize at 780° to 860°C from amorphous materials prepared by the simultaneous hydrolysis of zirconium, yttrium and aluminium acetylacetonates. Hot isostatic pressing has been performed for 1 h at 1130 and 1230°C under 196 MPa using their powders. Two kinds of material are fabricated: (i) perfect ZrO2 solid-solution ceramics and (ii) composites of ZrO2 solid solution and -Al2O3. Their mechanical properties are examined, in connection with microstructures and t/m ZrO2 ratios. Composites with a homogeneous dispersed -Al2O3 derived from solid-solution ceramics result in a remarkable increase of strength. 相似文献
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N. L. Savchenko P. V. Korolev S. Yu. Tarasov S. N. Kul’kov 《Technical Physics Letters》2000,26(6):461-463
Quantitative parameters of the surface structures and the wear resistance of a ZrO2-Y2O3 ceramic tested by friction on a steal disk have been determined. It is shown that the friction contact gives rise to quasiperiodic
cracks on the friction surface of the ceramic and leads to the formation of a transfer layer. It is established that the wear
intensity correlates with the intercrack spacing along the sliding direction and the amount of the steel counterbody elements
on the ceramic surface. 相似文献
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根据硬盘基板用材料的要求,制备了MgO-A12Oa-SiO2-TiO2-Y2Oa高弹性模量玻璃(120GPa).玻璃的弹性模量随组成的变化服从Makishima-Mackenzie理论,MgO、A12O3、TiO2、Y2O3等具有较高单位体积离解能的氧化物有利于提高玻璃的弹性模量.但玻璃弹性模量的理论计算值低于测试值.这是因为Makishima-Mackenzie理论没有考虑玻璃内阳离子的具体配位状态,对MgO、Y2O3堆积密度因子的推导存在误差.因此利用Makishima-Mackenzie理论发展高弹性模量玻璃时应对MgO、Y2O3等氧化物的计算进行修正. 相似文献