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1.
A. K. Nikumbh A. V. Nagawade V. B. Tadke P. P. Bakare 《Journal of Materials Science》2001,36(3):653-662
Six samples of the system Cd1–x
Co
x
Fe2O4 were prepared by the tartarate precursor method with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0. The formation of ferrispinels were studied by X-ray powder diffraction, infrared spectroscopy, electrical conductivity, thermoelectric power, magnetic hysteresis, initial magnetic susceptibility and Mössbauer spectroscopy. The data of the temperature variation of the direct current electrical conductivity showed a definite kink (390°C) except x = 0.0 and 0.2, which corresponds to the ferrimagnetic to paramagnetic transitions. Magnetic properties of the samples with x 0.6 showed definite hysteresis loops. The observed low magnetic moment can be explained in terms of the non collinear spin arrangement. A well defined hyperfine Zeeman spectra are observed for samples with x 0.6 at room temperature and resolved into two sextets corresponding to octahedral and tetrahedral sites. The electrical, magnetic and Mössbauer properties suggest that, a canted spin arrangement upto x = 0.8 and Néel's configuration above this composition. The probable ionic configuration for the system is suggested as
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2.
An isothermal section of the phase diagram of the system Co-Sb-O at 873 K was established by isothermal equilibration and XRD analyses of quenched samples. The following galvanic cells were designed to measure the Gibbs energies of formation of the three ternary oxides namely CoSb2O4, Co7Sb2O12 and CoSb2O6 present in the system.
where 15 CSZ stands for ZrO2 stabilized by 15 mol % CaO. The reversible emfs obtained could be represented by the following expressions.
The standard Gibbs energies of formation of CoSb2O4, Co7Sb2O12 and CoSb2O6 were computed from the emf expressions:
The reasonability of the above data were assessed by computing the entropy change for the solid-solid reactions leading to the formation of ternary oxides from the respective pairs of constituent binary oxides. 相似文献
3.
J. C. Rendón-Angeles Z. Matamoros-Veloza J. López-Cuevas M. I. Pech-Canul K. Yanagisawa 《Journal of Materials Science》2008,43(7):2189-2197
The pseudomorphic replacement of mineral barite (BaSO4) crystals into barium carbonate was investigated in the present work by using carbonated alkaline hydrothermal fluids. Hydrothermal
treatments were carried out over the temperature range from 150 up to 250 °C for intervals between 1 and 192 h, with different
filling ratios (40–70%), and
molar ratios of 1, 5, and 10. The reaction products were characterized by XRD and SEM techniques. The chemical reactivity
of mineral barite crystals was markedly limited at temperatures below 200 °C, and only a tiny BaCO3 layer on the surface of the original BaSO4 crystal was formed on the crystal treated for 192 h. The rate of the pseudomorphic conversion of BaSO4 into BaCO3, was accelerated by increasing the reaction temperature and the molar ratio . Powder X-ray diffraction results showed that under hydrothermal conditions the replacement of ions by ions, in barite crystals was completed at 250 °C with a molar ratio = 10 for an interval of 192 h, resulting in the Witherite structure. The morphology of the completely converted BaCO3 at 250 °C in a Na2CO3 solution for 192 h, showed that the conversion proceed without severe changes of the original shape and dimension of the
original crystal, similar to that observed in mineral pseudomorphic replacement process. 相似文献
4.
Phase relations in the system Cu-La-O at 1200 K have been determined by equilibrating samples of different average composition at 1200 K, and phase analysis of quenched samples using optical microscopy, XRD, SEM and EDX. The equilibration experiments were conducted in evacuated ampoules, and under flowing inert gas and pure oxygen. There is only one stable binary oxide La2O3 along the binary La-O, and two oxides Cu2O and CuO along the binary Cu-O. The Cu-La alloys were found to be in equilibrium with La2O3. Two ternary oxides CuLaO2 and CuLa2O4+ were found to be stable. The value of varies from close to zero at the dissociation partial pressure of oxygen to 0.12 at 0.1 MPa. The ternary oxide CuLaO2, with copper in monovalent state, coexisted with Cu, Cu2O, La2O3, and/or CuLa2O4+ in different phase fields. The compound CuLa2O4+, with copper in divalent state, equilibrated with Cu2O, CuO, CuLaO2, La2O3, and/or O2 gas under different conditions at 1200 K. Thermodynamic properties of the ternary oxides were determined using three solid-state cells based on yttria-stabilized zirconia as the electrolyte in the temperature range from 875 K to 1250 K. The cells essentially measure the oxygen chemical potential in the three-phase fields, Cu + La2O3 + CuLaO2, Cu2O + CuLaO2 + CuLa2O4 and La2O3 + CuLaO2 + CuLa2O4. Although measurements on two cells were sufficient for deriving thermodynamic properties of the two ternary oxides, the third cell was used for independent verification of the derived data. The Gibbs energy of formation of the ternary oxides from their component binary oxides can be represented as a function of temperature by the equations:
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5.
Susumu Ikeno Kenji Matsuda Toshimasa Matsuki Toshiaki Suzuki Noriaki Endo Tokimasa Kawabata Yasuhiro Uetani 《Journal of Materials Science》2007,42(14):5680-5685
The formation mechanism of spinels on Al2O3 particles in the Al2O3/Al–1.0 mass% Mg2Si alloy composite material has been investigated by transmission electron microscopy (TEM) in order to determine the crystallographic
orientation relationship. A thin sample of the Al2O3/Al–Mg–Si alloy composite material was obtained by the FIB method, and the orientation relationship between Al2O3 and MgAl2O4, which was formed on the surface of Al2O3 particles, was discovered by the TEM technique as follows:
At the interface between the Al2O3 and the matrix the MgAl2O4 (spinel) crystals had facets of {111} planes. Spinels were not grown as thin films, but as particles consisting of {111}
planes. They grow towards both the matrix and the Al2O3 particles. 相似文献
6.
M. Rekas T. Bak J. Nowotny C. C. Sorrell Y. Zhao K. Foger E. R. Vance 《Journal of Materials Science: Materials in Electronics》2000,11(9):691-696
The present work reports equilibration kinetics for (La0.8,Sr0.2)CoO3(LSC) and (La0.72,Sr0.18)FeO3(LSF) in the temperature range 876–1114 K using a gravimetric method. Chemical diffusion determined in this way that depends on oxygen partial pressure, can be expressed by the following temperature dependence at low and high O2), respectively, for LSC:
and for LSF:
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7.
This paper defines an effective microwave surface resistance
for the nonuniform distribution of microwave surface resistance R
s in the strip of a microstrip. It is proved that
is equivalent to the expression of R
s used in experiments, and that the
is dominated by the edge part, i.e., the area of width 2/2t from the strip edge, where is the magnetic penetration depth and t is the film thickness. Under the assumption that
where
is the component of rf magnetic field along the film thickness and n is an integer, the ratio of the contributions of the edge part and the rest of the strip to
is calculated by using an approximate analytical expression of the surface current density distribution J
s in the strip and
calculated by the London equation. The effect of film's edge on R
s was studied using a microstrip resonator. It is found that the perfectness of the edge could affect the magnitude of the power dependence of R
s significantly, which agreed with our analysis. 相似文献
8.
The objective of this work was to characterize the interfacial reaction zone in the metal matrix composite system-Al2O3(FP)/Mg (ZE41A). The composite was fabricated by liquid infiltration method. The reaction zone, a result of the reaction between magnesium in the alloy and the alumina fibres, was analysed for its morphology, chemistry, and crystallographic orientation using transmission electron microscopy. The results of this study showed the reaction zone to be, on average, 100nm wide and composed of MgO. The grains of the reaction zone ranged from less than 10 nm at the fibre/reaction zone interface to greater than 100nm at the matrix/reaction zone interface. It is proposed that the growth of the reaction zone was controlled by a seepage mechanism involving infiltration of liquid magnesium between MgO crystalS. Finally, it was observed that the MgO grains have the following crystallographic orientation relationship with the alumina grains from which they grew:
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9.
Single-phase nickel manganite spinels, Ni
x
Mn3–x
O4, with 0.5 x 1, were prepared by a careful thermal processing of nickel-manganese coprecipitated oxalate precursors. Powder X-ray diffraction analysis of the spinel revealed the presence of cubic single spinel phase with parametera which decreases with nickel content. The lattice parameter variation can be explained in terms of the distribution of Ni2+ ions on the octahedral sites. Therefore, a fine analysis of data shows that some Ni2+ ions (forx>0.56) are located in tetrahedral sites. The percentage of nickel in A-sites increases with nickel content (x) following the relation % Ni2+ in A sites =P = – 82.1x
2+192.4x–81.5 and thus the general formula for cation distribution is
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