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1.
M. Kobayashi T. Meguro K. Komeya T. Yokoyama J. Funahashi T. Kameda 《Journal of Materials Science》2000,35(16):4129-4136
The effect of TiO2 content on the oxidation of sintered bodies from the conventional Si3N4-Y2O3-Al2O3-AlN system was investigated. Sintered specimens composed of Si3N4, Y2O3, Al2O3, and AlN, with a ratio of 100 : 5 : 3 : 3 wt% and containing TiO2 in the range of 0 to 5 wt% to Si3N4, were fabricated at 1775 °C for 4 h at 0.5 MPa of N2. Oxidation at 1200 to 1400 °C for a maximum of 100 h was performed in atmospheres of dry and wet air flows. The relation between weight gain and oxidation time was confirmed to obey the parabolic law. The activation energies decreased with TiO2 content. In the phases present in the specimens oxidized at 1300 °C for 100 h in dry air, Y3Al5O12 and TiN, which had existed before oxidation, disappeared. Alpha-cristobalite and Y2O3·2TiO2 (Y2T) appeared in their place and increased with increasing TiO2 content. In those oxidized at 1400 °C, -cristobalite was dominant and very small amounts of Y2O3·2SiO2 and Y2T were contained. There was a tendency for more -cristobalite to form in oxidation in wet air than in dry air. Therefore, moisture was confirmed to affect the crystallization of SiO2 formed during oxidation. Judging from the lower activation energy, the crystallization, and the pores formation, we concluded that the addition of TiO2 decreases oxidation resistance. 相似文献
2.
Experimental results of the reaction occurring between aqueous solutions of AgNO3 and Na2S2O3 were presented in this work. It has been demonstrated that these reagents form two phases to which the summary formulas: -Ag8S4O4 and -Ag6S3O4 were ascribed. The -Ag8S4O4 phase crystallizes in a tetragonal system and has the following parameters of the unit cell: a = b = 0.72052 nm, c = 0.51140 nm, V = 0.26550 nm3, Z = 1, dx = 6.60 g/cm3. At 223°C -Ag8S4O4 undergoes an irreversible, endothermic polymorphic transition. The heat of this transition amounts 8.03 × 10–3 J/mol. A high-temperature polymorphic form -Ag8S4O4 melts at 400°C. The -Ag6S3O4 phase crystallizes in a monoclinic system and has the following parameters of the unit cell:a = 2.09616 nm, b = 0.53118 nm, c = 1.49885 nm, = 102.78°, V = 1.62753 nm3, Z = 8, dx = 6.59 g/cm3. -Ag6S3O4 also undergoes an irreversible, endothermic polymorphic transition at 221°C. The heat of this transition amounts 7.65 × 10–3 J/mol. A high-temperature form, -Ag6S3O4, melts at 390°C. 相似文献
3.
Studies have been made of the non-ohmic behaviour of the system ZnO-Nb2O5, as a function of composition, in the range 0.1 to 0.5 wt % of Nb2O5 and sintering temperature varying from 900 to 1300° C. It is found that the non-linearity coefficient varies with composition and sintering temperature. The maximum value of ( 8) is achieved for the samples containing 0.2 wt% Nb2O5, sintered at 1100°C. These results are interpreted in terms of the variation of barrier height with composition. 相似文献
4.
P. S. Sklad C. J. McHargue C. W. White G. C. Farlow 《Journal of Materials Science》1992,27(21):5895-5904
Single crystals of -Al2O3 were implanted with iron ions at room temperature to fluences ranging from 4×1016 Fe cm–2 to 1×1017 Fe cm–2. The microstructure and composition in the implanted region were examined using analytical electron microscopy techniques. Special emphasis was placed on monitoring the microstructural changes which take place during post-implantation annealing. Clusters of metallic -Fe were identified in the specimen after implantation to a dose of 1×1017 Fe cm–2. Analytical electron microscopy of implanted specimens annealed in oxygen revealed the redistribution of the implanted iron and the formation of surface precipitates of -Fe2O3, subsurface precipitates of various forms of spinel, and, in some cases, subsurface precipitates of iron, depending on the annealing temperature. Examination of implanted specimens annealed under reducing conditions revealed the presence of precipitates of -Fe. 相似文献
5.
Various sialon materials have been prepared by pressureless sintering at 1775 and 1825 °C using Y2O3 and/or Ce02 as sintering aids. Constant molar amounts of the oxide mixtures were added in the ratios Y2O3/CeO2: 100/0, 75/25, 50/50, 25/75, 0/100 corresponding to 6.0 and 9.25 wt% for the pure Y2O3 and pure CeO2, respectively. Only one of the compositional series reached full density at 1775 °C with cerium replacing yttrium, whereas at 1825 °C all compositional series except one became dense. The samples sintered showed that yttrium but not cerium stabilizes the sialon phase in these ceramics. The dense cerium-sialon ceramics sintered at 1825 °C have as good hardness and indentation fracture toughness as the corresponding yttrium-sialon ceramics, or even higher for the sialon type of materials. For the mixed - sialon materials the hardness decreased as the amount of a sialon phase decreased by increasing cerium-doping. 相似文献
6.
Effects of Y2O3 contents on the microstructure and electrical properties of Pr6O11-based ZnO varistor have been studied. The varistor voltage (V1mA) and the nonlinear exponent () increased with increasing Y2O3 contents, whereas the dielectric constant decreased. Y-rich phase segregated at nodal points in grain boundaries. The average grain size decreased with increasing Y2O3 content. The specimen with 4.0 mol% Y2O3 sintered at 1285 C exhibited the highest nonlinear exponent ( = 77) with the dielectric constant, ~352 at 1 kHz. 相似文献
7.
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
8.
The oxidation behaviours of iron powders, ca. 100 m in diameter, in 5–50 m NaOH, 5–40 m KOH and 5–40 m LiOH solutions at 373–573 K were investigated in the absence and presence of oxygen, where m is molality. The oxidation of iron proceeded noticeably above 423 K to form Fe3O4, -Fe2O3, -NaFeO2, -Fe2O3, Li
x
Fe3–xO4 and -LiFeO2 depending on the reaction conditions. The rate of oxidation in LiOH solutions was much slowerthan those in NaOH and KOH solutions. 相似文献
9.
Alan Arias 《Journal of Materials Science》1981,16(3):787-799
Specimens of milled -Si3N4 with 0 to 5.07 equivalent per cent of CeO2, MgO or Y2O3 additions were pressureless sintered at 1650 to 1820° C for 4 h in static nitrogen at 34.5 kPa (5 psi) gauge pressure and while covered with a mixture of Si3N4+SiO2 powders. The density — per cent addition — temperature plots showed maxima which, for all three additives, occurred between 1.2 and 2.5 equivalent per cent. Maximum densities resulted on sintering in the 1765 to 1820° C range and were 99.6 per cent of theoretical with 2.5 equivalent per cent CeO2, 98.5 per cent of theoretical with 1.24 to 1.87 equivalent per cent MgO, and 99.2 per cent of theoretical with 2.5 equivalent per cent Y2O3. Also, densities 94 per cent of theoretical were obtained with as little as 0.62 equivalent per cent additive (1.0 MgO, 2.11 CeO2 or 1.85 Y2O3, in wt%). X-ray diffraction showed that the materials were predominantly -Si3N4 with some or no Si2N2O. Scanning electron photomicrographs showed microstructures of elongated grains with aspect ratios of about 5, with all additives. 相似文献
10.
Si3N4-ZrO2 composites have been prepared by hot isostatic pressing at 1550 and 1750 °C, using both unstabilized ZrO2 and ZrO2 stabilized with 3 mol% Y2O3. The composites were formed with a zirconia addition of 0, 5, 10, 15 and 20 wt%, with respect to the silicon nitride, together with 0–4 wt% Al2O3 and 0–6 wt% Y2O3. Composites prepared at 1550 °C contained substantial amounts of unreacted -Si3N4, and full density was achieved only when 1 wt% Al2O3 or 4 wt % Y2O3 had been added. These materials were generally harder and more brittle than those densified at the higher temperature. When the ZrO2 starting powder was stabilized by Y2O3, fully dense Si3N4-ZrO2 composites could be prepared at 1750 °C even without other oxide additives. Densification at 1750 °C resulted in the highest fracture toughness values. Several groups of materials densified at 1750 °C showed a good combination of Vickers hardness (HV10) and indentation fracture toughness; around 1450 kg mm–2 and 4.5 MPam1/2, respectively. Examples of such materials were either Si3N4 formed with an addition of 2–6 wt% Y2O3 or Si3N4-ZrO2 composites with a simultaneous addition of 2–6 wt%Y2O3 and 2–4 wt% Al2O3. 相似文献
11.
D. Sreenivasu N. Narsimlu G. S. Sastry V. Chandra Mouli 《Journal of Materials Science: Materials in Electronics》1996,7(4):283-284
Electron paramagnetic resonance (EPR) studies have been performed on the glass system (30–x) NaF-xNa2O-50B2O3-20Bi2O3 doped with CuO as a paramagnetic probe. The calculated g values indicate that Cu2+ is in a tetragonally elongated octahedral co-ordination, and the Jahn-Teller character gives rise to anisotropic hyperfine structure. The spin-Hamiltonian parameters and -bonding parameter, 2, are calculated. Varying the fluoride ion concentration and its effect on these parameters is also discussed. 相似文献
12.
I. Z. Babievskaya N. F. Drobot K. S. Gavrichev O. A. Noskova V. A. Krenev S. V. Korostin Yu. V. Permyakov 《Inorganic Materials》2002,38(6):586-596
Using thermodynamic analysis of the Fe–C–NaCl–H2O–O2 system and experimental studies (x-ray diffraction and Mössbauer spectroscopy) of exothermic mixtures containing Fe metal, activated carbon, water, and NaCl, we identified the state of Fe and determined the phase composition of the reaction products at different stages of oxidation with atmospheric oxygen. The calculation and experimental results are in reasonable agreement. Under the conditions of restricted access for air, the main oxidation product is magnetite, Fe3O4. Free access for air leads to the formation of hydrous ferric oxide, Fe2O3 · nH2O. The most stable phase under the conditions of interest is goethite, Fe2O3 · H2O (-FeOOH). Storage of incompletely oxidized samples away from air for 7–14 days leads to partial reduction of iron(III) oxide phases to Fe3O4 and -Fe. 相似文献
13.
Yuan -Jang Sue San -Yuan Chen Hong -Yang Lu Pouyan Shen 《Journal of Materials Science》1991,26(6):1699-1704
Cordierite-based glass ceramics of the 2MgO2Al2O35SiO2 composition with t-ZrO2 (3 mol% Y2O3-ZrO2) and P2O5 addition, was heat-treated isothermally and isochronically for crystallization studies. Major crystalline phases incurred by the heat treatment were t-ZrO2 and -cordierite. Surface nucleation predominated when edge and corner nucleation in these samples were suppressed regardless of their radii of curvature. Crystallization began with the formation of -quartz S.S. and its transformation to -cordierite was followed by prolonged heating. Cellular growth of -cordierite on the surface of the quenched glass plates, gave a linear kinetics. The activation energy for cellular growth was 410 kJ mol–1. 相似文献
14.
Mixed metal oxides in the system Fe2O3-NiO were prepared by coprecipitation of Fe(OH)3/Ni(OH)2 and the thermal treatment of hydroxide coprecipitates up to 800 or 1100°C. X-ray diffraction showed the presence of -Fe2O3, NiO and NiFe2O4 in samples prepared at 800°C. The oxide phases -Fe2O3, NiO, NiFe2O4 and a phase with structure similar to NiFe2O4 were found in samples prepared at 1100°C. Fourier transform-infrared spectra of oxide phases formed in the system Fe2O3-NiO are discussed. Two very strong infrared bands at 553 and 475 cm–1, a weak intensity infrared band at 383 cm–1 and two shoulders at 626 and 441 cm–1 were observed for -Fe2O3 prepared at 1100°C. NiFe2O4, prepared at the same temperature, showed two broad and very strong infrared bands at 602 and 411 cm–1, while NiO showed a broad infrared band at 466 cm–1. Fourier transform infrared spectroscopic results were in agreement with X-ray diffraction. 相似文献
15.
The effect of Y2O3 additive on the properties of hot isostatically pressed silicon nitride was studied. The influence of small additions of Y2O3 on the densification of silicon nitride was investigated. The density and elastic moduli of the product increase with increasing of the Y2O3 additions. The hot isostatically pressed pure silicon nitride consists of -Si3N4, -Si3N4and Si2N2O; phase content of the hot isostatically pressed silicon nitride with 10 wt % Y2O3addition consists of -Si3N4, yttrium silicate and Y2Si3O3N4. The effect of the outgassing of the specimens prior to hot isostatical pressing on the properties of the final material is discussed. 相似文献
16.
Yun -Mo Sung 《Journal of Materials Science》1996,31(20):5421-5427
Crystallization and sintering behaviour of three cordierite (2MgO-2Al2O3-5SiO2) glasses containing different amount of additives were investigated and compared by using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Archimedes method. The stoichiometric 2MgO-2Al2O3-5SiO2 (MAS) glass and the 2MgO-2Al2O3-5SiO2 glass containing 3 wt% of B2O3 and 3 wt% of P2O5 (MASBP) showed two exotherms (one for -cordierite formation from a glass and the other for -cordierite formation from the -cordierite phase), whereas the 2MgO-2Al2O3-5SiO2 glass containing 2 wt % of B2O3, 2 wt% of P2O5, and 2 wt % of TiO2 (MASBPT) showed only a single exotherm representing -cordierite formation. By using Kissinger, Augis-Bennett, Ozawa, and modified Kissinger methods, the activation energy values for -cordierite formation in the MASBP and MASBPT glasses were determined as 310±6 and 326±13 kJ mol–1, respectively, whereas that in the MAS glass was determined as 868±5 kJ mol–1. The MASBPT glass showed the lowest peak temperature value for -cordierite formation (980 °C) amongst the three glasses. Both the MASBP and MASBPT glasses showed excellent sintering behaviour (> 99.7% of theoretical density). 相似文献
17.
Osami Abe 《Journal of Materials Science》1990,25(9):4018-4026
The sintering process of Y2O3- and Al2O3-doped Si3N4 has been investigated by dilatometry and microstructural observations. The densification progressed through three processes. The bulk density increased to 85% theoretical without the formation of -Si3N4 in the initial process. The densification once terminated after the second process. The / transformation of Si3N4 and the related formation of prismatic grains reduced the densification rate in the second process, although the grain size and the aspect ratio were very small. The final process was the densification of -Si3N4, where the fibrous grains grew remarkably. The kinetic order for the densification of -Si3N4 indicated a diffusion-rate controlling mechanism with the activation energy of 244 kJ mol–1 (<1450 ° C) and 193 kJ mol–1 (>1450 ° C). The influence of heating rate on the grain growth was characterized by a parameter derived from kinetic parameters. The relationships between grain growth and densification behaviour have also been discussed. 相似文献
18.
U. C. Boehnke P. Heitman M. Krötzsch B. Lippold G. Zahn 《Journal of Materials Science》1993,28(1):111-116
Before investigating the ternary system Bi2O3-CaO-CuO, a revision of the binary bounding system Bi2O3-CaO was first necessary. In the range between 20 and 70 mol % CaO the solid solutions and '1 and the stoichiometric compounds Bi2CaO4, Bi6Ca4O13, and Bi2Ca2O5 were found to exist for 675 °CT780 °C. Above 780 °C a new high temperature compound with the formula Bi6Ca5O14 has been identified. The X-ray powder diffraction data, unit cell dimensions, as well as the space group, have been reported. The ternary system contains no intermediate compounds and also no solubility was found for the binary bounding phases. Below 780 °C all the Bi-Ca oxides mentioned above are in equilibrium with CuO. At 820 °C, a wide liquidus field is dominating so that these quasibinary equilibria disappear. For 780 °C6Ca5O14 forms an equilibrium with Ca2CuO3 and CuO. Other equilibria are deduced. For a fixed ternary composition the reaction path of the sintering process was investigated as a function of time and temperature. 相似文献
19.
High temperature oxidation behavior of Ti-Al-Nb ternary alloys 总被引:1,自引:0,他引:1
Yong Shen Xiaofei Ding Fugang Wang Y. Tan J.-M. Yang 《Journal of Materials Science》2004,39(21):6583-6589
The oxidation behavior of four Ti-Al-Nb ternary alloys with different microstructures were investigated at 1000°C using interrupted oxidation test in air. Alloys with single-phase -TiAl, two-phase -TiAl + 2-Ti3Al, multi-phase -TiAl + 2-Ti3Al + Nb2Al and two-phase 2-Ti3Al + Nb2Al were prepared. The oxidation resistance of the Ti-Al-Nb ternary alloy at high temperature was found to be better than that of the binary Ti-Al alloy. Among the four Ti-Al-Nb ternary alloys, the + 2 two-phase alloy has the best oxidation resistance. The presence of Nb-enriched phase such as Nb2Al and Nb3Al decrease the oxidation resistance at elevated temperature presumably due to the formation of Nb2O5, which would accelerate the exfoliation of oxide. 相似文献
20.
A. M. Sanad I. Kashif A. M. Abou-Al-Azm M. A. Khaled H. Farouk 《Journal of Materials Science》1986,21(1):230-234
A glass system was prepared according to the formula 75 mol % B2O3-(25 –x) mol % BaO –x mol % Fe2O3, wherex = 0, 1, 2.5, 5, 7.5 and 10. The glasses were subjected to heat treatment at 550° C for 2, 6, 12, 18 and 24 h. The glasses were also irradiated using-rays at a dose of 4.805 × 104 rad h–1 for 12, 18 and 24 h. An X-ray diffraction technique was used to identify the separated crystalline phases. The electrical conductivity and activation energy of untreated, heat-treated and irradiated samples were measured and calculated. The rate and the dimensions of crystallization were also calculated by using the Avrami equation. It was found that-Fe2O3 is the separated phase when a sample containing 7.5 mol% Fe2O3 is heat treated for 24h;-Fe2O3 and Fe2O3 are the separated phases when the sample containing 10 mol% Fe2O3 is heat treated for 6, 12 and 18 h, with the addition of BaO when the sample is heat treated for 24 h. A miminum value for the electrical conductivity of glass samples was found to occur around an Fe2O3/BaO ratio of 0.425. The rate of crystallization in the sample containing 10 mol% Fe2O3 is 1.30607 × 10–3 and the geometry of crystallizationn is 1.2238, which indicates that the crystallization was in one dimension. 相似文献