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1.
G. R. TERWILLIGER H. K. BOWEN † R. S. GORDON 《Journal of the American Ceramic Society》1970,53(5):241-251
Polycrystalline MgO and MgO-Fe2 O3 solid solutions (0.10 to 8.08 wt% Fe2 O3 ) were fabricated to almost theoretical density by vacuum hot-pressing. Specimens were creep-tested in air under four-point dead-load conditions between 1000° and 1400°C at stresses between 50 and 550 kg/cm2 . Steady-state creep was never achieved in the experiments, which sometimes lasted more than 50 h. The strain rate vs time ( t ) data were described by an equation of the form = c1 /(t+C2 )p , which is consistent with the assumptions that creep occurs at least in part by a "viscous" mechanism and that grain growth occurs simultaneously. Doping MgO with Fe2 O3 enhanced the viscous contributions to creep and inhibited the nonviscous ones. Creep rates in these specimens increased with increasing Fe2 O3 additions. The occurrence of simultaneous grain growth during the high-temperature creep of magnesiowustite (i.e. MgO-Fe2 O3 solid solutions) was used in establishing the strain rate vs grain size dependence. The results of this study are consistent with a transition between grain boundary and lattice diffusion mechanisms as the grain size increases (4 to 44 μan). The creep of polycrystalline MgO is a mixed process in that viscous and nonviscous (dislocation) contributions are present. 相似文献
2.
WALTER C. ALLEN 《Journal of the American Ceramic Society》1968,51(9):485-490
The characteristics of spinels in the series MgCr2 O4 -MgFe2 O4 were determined. The plot of cell size vs. molar composition is unusual in series showing complete solid solution because an unusually large deviation from Vegard's law was observed. This deviation is caused by changes in spinel structure with composition and temperature, and an equation was derived which applies a correction in terms of the degree of inversion. The effects of temperature on compositions high in MgFe2 O4 include changes in density and refractive index. Solid solution of forsterite in MgCr2 O4 decreases the cell size to 8.329 A but apparently is less than 1%. Changes in composition caused by vapor loss or by dissociation are small enough that this series is essentially binary below 1400° C. 相似文献
3.
Perovskites of the system SrFeO3 -SrTiO3 were prepared, and measurements were made of their magnetic and electrical behavior. Chemical analysis showed that the percentage of Fe4+ varied from 72.5% for SrFeO2.86 to about zero for Sr(Fe0.1 Ti0.9 )O2.95 ; the remainder of the iron was in the Fe3+ state and electrical balance was achieved by oxygen loss. Sr(Fe1- x Ti x )O3 was antiferromagnetic between x = 0 and x = 0.9, with a Néel temperature below 60°K. A parasitic ferromagnetic component developed when these compounds were cooled in a magnetic field, the magnitude of this component being dependent on the cooling field. The conductivity of these perovskites ranged from 10−8 ohm−1 cm−1 for x = 1.0 to 10−2 for x = 0.0 and showed a marked change at x = 0.8. The break corresponded to a change in slope of the lattice parameter and the disappearance of Fe4+ . The Fe4+ content depended on the heat treatment and atmosphere during formation. 相似文献
4.
KE-CHIN WANG LLOYD H. DREGER V. V. DADAPE JOHN L. MARGRAVE 《Journal of the American Ceramic Society》1960,43(10):509-510
The sublimation of chromic oxide, Cr2 O3 , has been observed in vacuum by the Langmuir technique using induction and solar heating. Extensive sublimation did not yield any new phases on the basis of X-ray powder studies, and condensates of Cr2 O3 were always obtained. Flash vaporization and flow experiments in CO or O2 atmospheres and in vacuum indicated no appreciable differences in rates of sublimation. Weight-loss experiments showed that the rate of sublimation was slightly higher than predicted for decomposition to the elements and suggested that small amounts of complex molecules, e.g. CrO and CrO2 , were also present in the equilibrium vapor. 相似文献
5.
P. C. HAYES 《Journal of the American Ceramic Society》1980,63(7-8):387-391
The sintering kinetics of submicrometer Fe3 O4 and Fe2 O3 powders were investigated at 300° to 500°C. Using measurements of the rate of reduction of surface area, the coefficients of surface diffusion on the oxides are estimated for a range of oxygen partial pressures. The surface-diffusion coefficients appear to be independent of P O2 for magnetite and only slightly dependent on P O2 for hematite. 相似文献
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R. Todd Hunter Mark Edge Aristotle Kalivretenos Kathy M. Brewer Nancy A. Brock Alice E. Hawkes James C. Fanning 《Journal of the American Ceramic Society》1989,72(6):943-947
The Fe2+ /Fe3+ ratios of 47 simulated nuclear waste glass samples with ratios varying from 0.01 (oxidized) to 1.6 (reduced) were determined by wet-chemical and Mössbauer spectral analyses. The wet-chemical method involved the spectrophotometric determination of Fe2+ and total iron using remote spectroscopy with fiber optic chemical sensing. Interferences from other species present in these glasses were examined and alternative analytical techniques were investigated. Results of wet-chemical and Mössbauer spectral analysis were comparable; however, the wet-chemical method is probably preferable for the analysis of highly radioactive glasses until such glasses have been shown to have satisfactory Mössbauer spectra. 相似文献
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Electron paramagnetic studies showed that Ti3+ and Fe2+ occur in mullites taken from a refractory material which was fused-cast under a reducing atmosphere. Exposure of the mullite samples to temperatures >1600°C caused oxidation of Ti3+ and Fe2+ to Ti4+ and Fe3+ , respectively. 相似文献
10.
Zn2 SnO4 , an inverse spinel, and ZnFe2 O4 , a normal spinel, form a complete series of solid solutions in the system ZnO-Fe2 O3 3nO2 . The variation of cell dimensions with composition varies from 0.8439 nm (ZnS2 nO4 ) to 0.8660 nm (ZnS2 nO4 ) and exhibits a positive deviation from a linear relationship. Mg2 SnO4 and MgFe2 O4 , both predominantly inverse in nature, have only an incomplete series. 相似文献
11.
The electrical conductivity and ion/electron transference numbers in Al3 O3 were determined in a sample configuration designed to eliminate influences of surface and gas-phase conduction on the bulk behavior. With decreasing O2 partial pressure over single-crystal Al2 O3 at 1000° to 1650°C, the conductivity decreased, then remained constant, and finally increased when strongly reducing atmospheres were attained. The intermediate flat region became dominant at the lower temperatures. The emf measurements showed predominantly ionic conduction in the flat region; the electronic conduction state is exhibited in the branches of both ends. In pure O2 (1 atm) the conductivity above 1400°C was σ≃3×103 exp (–80 kcal/ RT ) Ω−1 cm−1 , which corresponds to electronic conductivity. Below 1400°C, the activation energy was <57 kcal, corresponding to an extrinsic ionic condition. Polycrystalline samples of both undoped hot-pressed Al2 O3 and MgO-doped Al2 O3 showed significantly higher conductivity because of additional electronic conduction in the grain boundaries. The gas-phase conduction above 1200°C increased drastically with decreasing O2 partial pressure (below 10−10 atm). 相似文献
12.
Liquidus temperatures are presented for mixtures in the system MgO-FeO-Fe2 O3 -SiO2 . The standard quenching technique was modified for work under controlled atmospheres of varying O2 pressures. Data were obtained for the temperature range 1159° to 1775°C., and with O2 pressures ranging from 1 to 10-8 .9 atm. Approximate compositions of crystalline phases were determined, and paths of equilibrium crystallization were derived for selected mixtures under idealized conditions. Application of the phase diagrams to steel-plant refractories problems is indicated. 相似文献
13.
C. GRESKOVICH 《Journal of the American Ceramic Society》1970,53(9):498-502
The reaction kinetics for NiCr2 O4 formation and the diffusion of Cr3+ ions into single-crystal NiO were studied between 1300° and 1600°C in air. The experimental activation energy for NiCr2 O4 formation was about 83 kcal/mol. After incubation, NiCr2 O4 formed by a diffusion-controlled process. The origin of pores at the NiO/NiCr2 O4 interface is discussed. The concentration profiles of Cr3+ in NiO were linear because the interdiffusion coefficient was directly proportional to the mol fraction Cr3+ . Theoretical considerations indicate that the interdiffusion coefficient equals 3/2 the self-diffusion coefficient of Cr3+ , which is rate-determining. The interdiffusion coefficient at 1 mol% Cr2 O3 can be expressed as =4×10−3 exp (−55,000/RT) cm2 s−1 . 相似文献
14.
A number of experiments were performed on iron-containing sodium disilicate melts in air. It was found that it was not possible to obtain an equilibrium between Fe2+ and Fe3+ in platinum crucibles owing to the reaction between platinum and iron, whereas in alumina crucibles the equilibrium was rapidly established. Thermodynamic calculations of the reaction 2FeO (in Na2 O-2SiO2 ) +½O2 (g) = Fe2 O3 (in Na2 O-2SiO2 ) showed that the equilibrium went more and more to the right with increasing temperature. The standard free energy, enthalpy, and entropy for the reaction were calculated. 相似文献
15.
TORAJI NISHIJIMA TOSHIYUKI KAWADA AKIRA ISHIHATA 《Journal of the American Ceramic Society》1965,48(1):31-34
The thermal conductivities of sintered Al2 O3 and UO2 were measured in the ranges 400° to 1700°C and 300° to 2100°C respectively. The conductivity values for Al2 O3 agreed with those reported previously at all temperatures investigated. The conductivity of UO, decreased with increasing temperature to a minimum of 0.0050 cal per cm sec °C at about 1400°C, and then increased with increasing temperature to 0.0105 cal per cm sec °C at 2100°C. 相似文献
16.
Marta Prades Nahum Masó Héctor Beltrán Eloisa Cordoncillo Anthony R. West 《Journal of the American Ceramic Society》2008,91(7):2364-2366
The effect of Mn doping on the cubic to hexagonal phase transition temperature in BaTiO3 has been determined by quenching samples with different Mn contents from a range of temperatures. Under conditions of equilibrating samples in air over the range 1000°–1400°C, cubic solid solutions BaTi1− x Mn x O3−δ form over the range 0≤ x ≤0.015(5), whereas hexagonal solid solutions form for x ≥0.02, depending on the temperature. The results are compared with those on doping BaTiO3 with Fe3+ and observations made concerning acceptor doping with Ti3+ . 相似文献
17.
The control of the microstructure of Ce-doped Al2 O3 /ZrO2 componsites by the valence change of cerium ion has been demonstrated. Two distinctively different types of microstructure, large Al2 O3 grains with intragranular ZrO2 particles and small Al2 O3 grains with intergranular ZrO2 particles, can be obtained under identical presintering processing conditions. At doping levels greater than ∼ 3 mol% with respect to ZrO2 , Ce3+ raises the alumina grain-boundary to zirconia particle mobility ratio. This causes the breakaway of grain boundary from particles and the first type of microstructure. On the other hand, Ce4+ causes no breakaway and produces a normal intergranular ZrO2 distribution. The dramatic effect of Ce3+ on the relative mobility ratio is found to be associated with fluxing of the glassy boundary phase and is likewise observed for other large trivalent cation dopants. The ZrO2 second phase acts as a scavenger for these trivalent cations, provided their solubility limit in ZrO2 is not exceeded. 相似文献
18.
Activity–composition relations in Al2 O3 –Cr2 O3 solid solutions at 1500° and 1600°C were determined by equilibrating members of this solid-solution series with Mo–Cr alloys of known activity–composition relations and a gas phase of known oxygen potentials. The oxide solid solution shows considerable positive deviation from ideality. 相似文献
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20.
Influence of Fe3+ /Fe2+ Ratio on the Crystallization of Iron-Rich Glasses Made with Industrial Wastes
Alexander Karamanov Paola Pisciella Carlo Cantalini Mario Pelino 《Journal of the American Ceramic Society》2000,83(12):3153-3157
The influence of the Fe3+ /Fe2+ ratio on the crystallization of iron-rich glasses was investigated in this study. The glass batches were made from two hazardous industrial wastes: mud (goethite and jarosite) originating from the zinc hydrometallurgical process and electric arc furnace dust (EAFD). Glass compositions were prepared by adding different percentages of carbon powder. The crystallization process was investigated by a combined thermogravimetry/differential thermal analysis technique, in air or nitrogen atmospheres, using powder and bulk glass samples. The crystalline phases formed, i.e., pyroxene and spinels, and their relative ratio were determined by X-ray diffractometry. The experimental results indicated that melting temperature and crystallization behavior were influenced by the initial Fe3+ /Fe2+ ratio and by the amount of carbon added to the glass batch. For goethite and jarosite glass compositions, decreasing the Fe3+ /Fe2+ ratio increased the crystallization rate by favoring magnetite formation. For EAFD glass compositions, the addition of carbon to the batch inhibited chromite–magnetite spinel formation and favored the attainment of an amorphous glassy phase. 相似文献