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1.
Atsumi Nitta Terumi Miura Takayuki Komatsu Kazumasa Matusita 《Journal of the American Ceramic Society》1989,72(1):163-165
Glass-forming regions, valence states, and viscosities in SiO2 –PbO systems containing various transition-metal oxides as a third component were investigated. The glasses were prepared by melting in an open atmosphere. The glass-forming regions ranged as follows: MnO≡ZnO > FeO1.5 >NiO. The ratios Fe2+ /(Fe2+ + Fe3+ ) and Mn3+ / (Mn3+ + Mn2+ ) in the glasses were determined by chemical analysis. The Fe2+ / (Fe2+ + Fe3+ ) ratio in SiO2 –PbO–FeO1.5 glasses ranged from 0.016 to 0.050. The Mn3+ / (Mn3+ + Mn2+ ) ratio in SiO2 –PbO–MnO glasses ranged from 0.056 to 0.30. The fraction of manganese (III) ions in the glasses varies considerably with the glass composition. The effects of transitionmetal oxides on the viscosity are discussed. 相似文献
2.
Taizo Sano Masamichi Tsuji Nobuyuki Gokon Hiroshi Kaneko Yutaka Tamaura 《Journal of the American Ceramic Society》2000,83(10):2509-2514
Oxygen uptake and release of (Li,Mn) ferrite [LMF; (Li0.60 Mn1.20 Fe1.20 )1−δ O4 ; δ= 0.007 to 0.033] was investigated concerning the relations between redox reactions of ferrite and cation migration. Mössbauer spectroscopy and X-ray diffractometry showed that some of the Li+ and Fe3+ ions migrated from the A sites to the B sites of the spinel-type structure and Mn4+ ions migrated from the B sites to the A sites during oxygen uptake at 573 K. The cation-deficient LMF formed by the oxygen uptake released oxygen molecules in He gas only at 660 K. The cation migration during the oxygen release was in the opposite direction of the movement during oxygen uptake at 573 K. 相似文献
3.
The electrical conductivity and thermopower of Mn3 O4 were measured in the temperature range 920° to 1530°C. Electrical conduction in cubic Mn3 O4 is explained by the small polaron hopping of electron holes between Mn4+ and Mn3+ on octahedral sites. The concentrations of Mn4+ and Mn3+ are governed by the disproportionation equilibrium 2Mn oct 3+ ⇄Mn oct 4+ + Mn oct 2+ . This model also explains the electrical behavior of NiMn2 O4 and CuMn2 O4 . 相似文献
4.
W. D. JOHNSTON 《Journal of the American Ceramic Society》1964,47(4):198-201
The oxidation-reduction equilibrium between ferrous and ferric iron in Na2 O · 2Si02 glass melts was studied by equilibrating melts with various oxygen partial pressures. Exceedingly long equilibration times were required to obtain meaningful results. The reaction appears to be diffusion-controlled and may be expressed as 202- + 4Fe3+ $4 4Fe2+ + O2 . Data are presented in which the valence of iron varies from predominantly +3 to predominantly +2. 相似文献
5.
Effect of Acceptor and Donor Dopants on the Dielectric and Tunable Properties of Barium Strontium Titanate 总被引:1,自引:0,他引:1
Xiaofeng Liang Zhongyan Meng Wenbiao Wu 《Journal of the American Ceramic Society》2004,87(12):2218-2222
The effects of different concentrations of Mn2+ , Mg2+ , Al3+ , Fe3+ , La3+ , and Nb5+ on the dielectric and tunable properties of Ba0.6 Sr0.4 TiO3 ceramics were investigated. It was found that doping in small amounts with acceptor ions such as Mg2+ , Fe3+ , and Al3+ could meliorate the dielectric properties clearly. Decrease of dielectric loss was attributed to the formation of compensating defects originating from acceptor substitution. It was concluded that the tunability was linked to both the dielectric constant and the grain size. A higher figure of merit was obtained by doping the ceramics with smaller ions of Al and Fe, compared to Ti. 相似文献
6.
Reduction-oxidation reactions and enhanced wetting or spreading of Na2 Fex Si2 O5+x , and Na2 Nix Si2 O5+x glasses on substrates of Fe, Co, Ni, Ni-Fe, and Ni-Co were observed at 1000°C at low partial pressures of O2 and Na as the O/Si ratio of the glass increased. When the substrate had a higher oxidation potential than the metal of one of the cations in the glass, e.g. CoO-containing glass on Fe, metallic precipitates formed by redox reactions under all conditions. A redox reaction based on reduction of the valence of a cation in the glass, e.g. Fe3+ to Fe2+ , also occurred. Adherence developed between substrates and glasses containing amounts of substrate oxide, either in the starting composition or formed by redox reactions, approaching saturation. 相似文献
7.
High-purity polycrystalline MgO and Al2 O3 were thermally grooved at 1500° and 1600°C. Accurate techniques were developed for following the growth of a single groove. For high-purity samples growth kinetics were essentially similar to those reported in the literature but were determined to be controlled by volume diffusion. Specimens for thermal grooving were prepared from Al2 O3 to which transition metal oxides (Fe2 O39 , MnO, and TiO2 ), which are known to accelerate shrinkage and sintering of Al2 O3 powder compacts, had been added; the rate of groove growth was increased remarkably by minor amounts of these additives. Control of partial pressure indicated that Fe2+ and Ti4+ are the species active in promoting groove growth. Substantial evidence was found for volume diffusion as the mechanism controlling groove formation. 相似文献
8.
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
9.
In barium phosphate glass containing first-row transition metal ions, the ions appear to possess normal oxidation states: Cr3+ , Mn3+ , Fe2+,3+ , Co2+ , Ni2+ , and Cu2+ . Room temperature and 77°K spectra for Cr3+ -, Mn3+ -, Fe2+,3+ -, Ni2+ -, and Cu2+ -containing glasses can be interpreted, on the, basis of octahedrally coordinated metal ions, whereas the spectrum of the Co2+ glass correlates with a tetrahedrally coordinated metal ion. Magnetic moments for the glasses are similar to those for the spin-only values of the various metal ions. 相似文献
10.
Some physical properties okf phosphate glasses con-taining up to about 26 mol% Fe2 O2 were studied. Pronounced changes in properties were observed at compositions containingabout 6, 10, and 13 mol% Fe2 O3 . The X-ray diffraction spectra of devitrified (heat-treated) samples showed new compounds near these compositions. Electron spin resonance and optical studies confirmed the presence of Fe3+ and Fe2+ in both 4- and 6-coordination. An increase in total iron in these samples was associated with a decrease in the ratios Fe2+ 4-coordinated/Fe3+ 6-coordinated 6-coordinated and Fe3+ 4-coordinated/Fe3+ 6-coordinated up to about 2.0 mol% Fe2 O3 , as shown by the intensity of the optical absorption bands at about 2.0 and 1.0 μm and by the intensity of the ESR lines at g⋍4.2 and 2.0, respectively. Samples containing up to 4.3 mol% Fe2 O3 showed an increase in Fe3+ concentration and a decrease in Fe2+ concentration after gamma irradiation. The electrical conductivity and activation energy decreased sharply with increasing Fe2 O3 content. 相似文献
11.
Malahalli S. Vijaya Kumar Kazuhiko Kuribayashi Koichi Kitazono 《Journal of the American Ceramic Society》2009,92(4):903-910
The Yb2 O3 –Fe2 O3 system was studied to investigate the effect of oxygen partial pressure on the formation of metastable phases over a wide range of oxygen partial pressures from 105 to 10−1 Pa. Two kinds of metastable phases, with space groups of P 63 cm and P 63 / mmc , were found through rapid solidification of an undercooled YbFeO3 melt in an atmosphere with reduced P o2 . The crystal structure of the as-solidified samples changed from orthorhombic Pbnm to hexagonal P 63 cm and P 63 / mmc with decreasing P o2 . X-ray diffractometric and scanning electron microscopic results confirmed the existence of various phases in the as-solidified samples. The stabilities of each phase were studied by annealing the bulk sample in the thermogravimetric–differential thermal analysis (TG-DTA) furnace up to 1673 K, and the equilibrium phase diagram was constructed for the Yb–Fe–O system at 1473 K. TG analysis showed an increase of the sample mass during annealing and revealed that the existence of Fe2+ , which has an ionic radius larger than that of Fe3+ , decreases the tolerance factor and therefore destabilizes the perovskite structure. 相似文献
12.
Yan Zhuang Yanzheng Lin Dongyan Zhu Yufang Zheng Zhengfang Yu 《Journal of the American Ceramic Society》1989,72(8):1444-1446
The conductivity and conductivity-temperature characteristics of the Sr(Fe1−x Tix O3−δ system fired in air are studied by means of Mössbauer spectroscopy at room temperature and at 78 K. On the basis of quantitative analysis of the Fe4+ content in the solid solution, the concentrations of oxygen vacancies are calculated and the relationship between Fe4+ content and conductivity is found. It is also found that the turning points of conductivity and material constant B, as well as Fe4+ and the percentage of oxygen vacancies, occur at x=0.7 on the curve. When x=0.7, Fe3+ (II), which has never been reported before, disappears and the lattice parameters no longer vary with x. Besides Fe4+ , Fe3+ (II) is also a factor affecting the conductivity of this system. 相似文献
13.
Samples of basic and alumina brick were examined after service in copper anode furnaces. Copper oxides penetrating the brick had reacted with the chrome grains, with the periclase, and with the alumina. These reactions were studied by examining the stability of the compounds formed when copper oxides were heated with various spinels and oxides. In general, spinels of the series CuO R2 O3 decomposed to the compound CU2 O R2 O3 with the liberation of R2 O3 , when R was Al3+ , Cr3+ , or Fe3+ . With magnesia, cupric oxide formed the mineral güggenit, CuO–MgO, which during heating decomposed with the evolution of oxygen to MgO and Cu2 O. 相似文献
14.
T. Hanzlicek † D. Niznansky J. Dedecek M. Steinerova P. Straka J. Triskova 《Journal of the American Ceramic Society》2007,90(9):2843-2848
The final color of a ceramic body is generally determined by the contents of Fe3+ ions. The Central European market accepts kaolinitic clays for the production of tableware, electro-insulators, and wall tiles only if the Fe2 O3 in chemical analyses of the kaolin does not exceed 1.0 wt%. The chemical analyses calculate the content of all iron components as if they were in the form of Fe2 O3 and then their quantity excludes even good-quality clay from the ceramic industry of white bodies. We found that oxidizing firing of the samples fired at over 1180°C changes the color in cases where the initial Fe3+ component is in the form of hydro ferric oxide [FeO(OH)] or if the ferric ions were added to the white kaolin samples in the form of ferric nitrate [Fe(NO3 )3 ·9H2 O]. The Mössbauer spectroscopy confirms the presence of only diluted Fe3+ ions. The UV-ViS-NIR spectroscopy confirms that even if the concentration of Fe2 O3 is above 3.0 wt%, these ions of Fe3+ in the case of their initial hydro ferric oxide formed in clay are incorporated into the mullitic structure in tetrahedral coordination. The iron-coloring effect depends on the coordination of Fe3+ ions with the studied discoloring effect of fired bodies—the very small and well-distributed particles enter into the formatted mullitic structure. 相似文献
15.
Samples of Sr2 Fe2− x Mo x O6 were prepared by solid-state reaction in air and 5%H2 –95%N2 . X-ray diffractometry was used to identify the phases and evaluate the lattice parameters. It is found that molybdenum ions can dissolve in the SrFeO3 even if the sample is heated in air but the solubility is limited. The solubility can be enhanced by heating the sample in low oxygen partial pressure, which is attributed to the larger ionic radii of Fe3+ and Mo5+ than that of Fe4+ . The degradation of Sr2 Fe2− x Mo x O6 in water and air is also reported. 相似文献
16.
The phase diagram of the system BaO-Fe2 03 was determined by X-ray diffraction, melting-point measurement, and microscopic methods. Since the reduction of Fe3+ to Fe2+ was observed by chemical analysis in the samples heated at high temperature, especially in molten samples, the samples were heated at 1 atmosphere pressure of oxygen in the temperature region in which the liquid was in equilibrium; 1 atmosphere pressure of oxygen was su5cient to restrain the reduction of Fe3+ . In the temperature region of solid-solid equilibrium, the dissociation was not observed even when the samples were heated in air. BaO - 6Fe2 O3 formed a solid solution with BaO.Fe2 03 . The BaO:Fe2 03 ratio of the solid solution was BaO.4.5Fe2 03 at 1350°C. and BaO. 5.0Fe2 0a at 800°C. The precipitation micro-structures of each primary solid solution were observed. 相似文献
17.
W. D. JOHNSTON 《Journal of the American Ceramic Society》1965,48(4):184-190
The oxidation-reduction equilibria in molten glasses having a soda/silica ratio of 1/2 and containing small amounts of variable-valence ions of the transition elements titanium, vanadium, iron, cobalt, and nickel, the post-transition elements tin and antimony, and the rare-earth element cerium were obtained by equilibrating the melts with various atmospheres. The simple mass expression
was always applicable. In the expression, n is the number of electrons involved in the valence change of the metal M. The value of n is 1 for all systems except for the ions of antimony and tin where n is 2. The ions found are those generally accepted as existing in glass melts which are Ti3+ , Ti4+ ; Fez+, Fe3+ ; Ce3+ , Ce4+ ; Mn2+ , Mn3 ; Co2+ , Co3+ ; Ni2+ , Ni3 ; Sb3+ , Sb5+ ; and Sn2+ , Sn4+ . Two mass action expressions were needed for vanadium-containing glasses to describe the equilibria between 5+, 4+, and 3 f species. 相似文献
was always applicable. In the expression, n is the number of electrons involved in the valence change of the metal M. The value of n is 1 for all systems except for the ions of antimony and tin where n is 2. The ions found are those generally accepted as existing in glass melts which are Ti
18.
Synthesis of lead tantalate pyrochlores by the reaction of PbO and Ta2 O5 in various molar ratios between 1.5 and 4.0 at low temperatures (500–650°C) has been carried out. It has been shown that when PbO is reacted with Ta2 O5 in various molar ratios at low temperatures, metastable lead tantalate pyrochlore solid solutions having cubic symmetry are formed. X-ray diffraction data give evidence for an increase in the a lattice parameter with increasing PbO content and partial occupancy of Pb in the Ta sites leading to the formula Pb1.5+ x 2+ (Ta2− y Pb y 4+ )O7−δ (0.0 < x < 0.5; 0.0 < y < 0.6) for this phase. It has also been found that the intermediate members of the solid solutions are metastable and tend to segregate into Pb-deficient and Pb-excess compositions leading to significant compositional inhomogeneity for the intermediate members. 相似文献
19.
Ryosuke O. Suzuki Jun-ichi Nagata Daniel Risold 《Journal of the American Ceramic Society》1998,81(9):2493-2496
Phase equilibria in the PbO x -CaO system at oxygen partial pressures of 1.01 105 and 1.01 103 Pa were experimentally investigated. The temperatures of the eutectic reaction between PbO and PbCa2 O4 and of the peritectic melting of PbCa2 O4 were measured via differential thermal analysis at five oxygen partial pressures. The phase transition in air between PbO and Pb3 O4 was not affected by the coexistence of PbCa2 O4 . 相似文献
20.
Junying Zhang Zhongtai Zhang Zilong Tang Yuanhua Lin 《Journal of the American Ceramic Society》2002,85(4):998-1000
A (Ce0.67 Tb0.33 )Mn x Mg1− x Al11 O19 phosphor powder was synthesized, using a simple sol–gel process, by mixing citric acid with CeO2 , Tb4 O7 , Al(NO3 )3 ·9H2 O, Mg(OH)2 ·4MgCO3 ·6H2 O, and Mn(CH3 COO)2 . The phosphor crystallized completely at 1200°C, and the phosphor particle size was between 1 and 5 μm. The excitation spectrum was characteristic of Ce3+ , while the emission spectrum was composed of lines from Tb3+ and Mn2+ . The Mn2+ gave a green fluorescence band, and concentration quenching occurred when x > 0.10. The luminescent properties of the phosphor were explained by a configurational coordinate model. 相似文献