Showing papers on "Solid solution published in 1997"
TL;DR: In this paper, XRD and TEM were used to measure the particle sizes of the various phases of the CeO 2 -Zr oxide solid solution and found that the particle size of the supported particulate phase decreased with increasing zirconium loading, but a discrepancy was noted between the XRD results and the TEM results.
241 citations
TL;DR: In this paper, two different forms of the trough model are considered for nickel-base alloys to determine the most applicable model for solid solution strengthening in the system, and the yield stresses of three binary nickel-chromium and three ternary nickel alloys were determined at a range of temperatures.
Abstract: The yield stress of multicomponent nickel solid solution alloys has not been modeled in the past with respect to the effects of composition and temperature. There have been investigations of the effect on the yield stress of solutes in binary systems at a fixed temperature, but the effects on the yield stress of multiple solute elements and temperature changes have not been investigated. In this article, two different forms of the trough model are considered for nickel-base alloys to determine the most applicable model for solid solution strengthening in the system. The yield stresses of three binary nickel-chromium and three ternary nickel alloys were determined at a range of temperatures. The yield stress of the alloys was then modeled using the Feltham equation. The constants determined in fitting the Feltham equation to the experimental data were then applied to other experimental solid solution alloys and also to published information on commercial solid solution nickel alloys. It was found that the yield stress of the nickel solid solution alloys could be modeled successfully using the Feltham equation.
237 citations
TL;DR: In this article, the insertion of trivalent cations into the lattice of Ce0.6Zr0.4O2solid solution improves the oxygen storage capacity at low temperatures by decreasing the temperature of the reduction in the bulk of the solid solution compared to the undoped sample.
218 citations
TL;DR: In this article, the authors studied the catalytic performance of Ni0.03Mg0.97O solid solution catalyst and its bimetallic derivative catalysts which contained small amounts of Pt, Pd and Rh, respectively (the atomic ratio of M/(Ni+Mg) ≈ 0.021%).
Abstract: Reforming of CH4 with CO2 to produce synthesis gas was studied over Ni0.03Mg0.97O solid solution catalyst and its bimetallic derivative catalysts which contained small amounts of Pt, Pd and Rh, respectively (the atomic ratio of M/(Ni+Mg) was varied from 0.007 to 0.032%, M=Pt, Pd or Rh). It was found that there was a significant promotion in both activity and stability due to the addition of noble metals. The optimum loadings of these noble metals were observed at the atomic ratio of M/(Ni+Mg) ≈0.021%. Temperature programmed hydrogenation (TPH) of carbonaceous species formed during the catalytic reaction indicated that the good resistance of Ni0.03Mg0.97O solid solution to carbon deposition was retained on the bimetallic catalysts. Furthermore, we obtained a clear evidence showing the formation of Pt—Ni alloy particles by means of TEM and EDS observation. The kinetic study and temperature programmed reaction (TPR) of CH4 suggest that CH4 decomposition as the rate-determining step on the Ni0.03Mg0.97O is accelerated by the alloy formation. The improved stability was attributed to the promotion in catalyst reducibility.
203 citations
TL;DR: In this paper, a set of experiments, starting with mother solutions of different concentrations, was carried out, and the composition of the solids was analyzed by electron microprobe, which allowed the establishment of the influence of the supersaturation on the distribution of material between solid and aqueous phases.
152 citations
TL;DR: In this paper, a NiO/MgO catalyst prepared by impregnation, which reduced in H2 had very high CO yield and stability in CO2 reforming of methane, was investigated by XPS, XRD, BET and pulse-MS response.
Abstract: A NiO/MgO catalyst prepared by impregnation, which reduced in H2 had very high CO yield and stability in CO2 reforming of methane, was investigated by XPS, XRD, BET and pulse-MS response. This catalyst was compared to that obtained by mechanical mixing of powders of the two oxides. It was found that the entire NiO formed a solid solution with MgO in the former catalyst, while only a fraction of NiO formed a solid solution with MgO in the latter one. BET revealed that, in contrast to NiO and MgO, the NiO/MgO catalyst prepared by impregnation had a high stability to sintering, because its surface area hardly changed during calcination from 1.5 to 20 h at 800°C. In the same catalyst, a surface enrichment in MgO, which was greater after than before reduction, was detected. Compared to MgO or NiO, this catalyst had a lower Mg(2p) and a higher Ni(2p3/2) binding energy. This indicates that electron transfer from NiO to MgO took place, which, increasing the binding between the two oxides, might be responsible for the resistance of the solid solution to sintering. Because of the interactions between Ni and Mg, the clustering of Ni, which stimulates carbon deposition is inhibited. This explains the high stability of the CO yield in the CO2 reforming of methane over the NiO/MgO catalyst prepared by impregnation. The pulse-MS response suggested that the decompositions of CO2 to CO and O and of CH4 to C and H are involved in the reaction mechanism of CO2 reforming of methane over the reduced NiO-MgO solid solution catalyst.
128 citations
TL;DR: In this article, the results were discussed in terms of competing mixing and de-mixing reaction rates, which is attributed to a first-order kinetic process involving non-equilibrium vacancies.
111 citations
TL;DR: In this paper, the phase diagram studies with emphasis on the high temperature superconducting phases (2212 phase) and (2223 phase) are reviewed in detail at various temperatures and oxygen partial pressures.
Abstract: Phase diagram studies with emphasis on the high temperature superconducting phases (2212 phase) and (2223 phase) are reviewed in this article. The phase relations of the and the homogeneity regions of the 2212 and 2223 phases have been studied in detail at various temperatures and oxygen partial pressures. However, the Pb-doped system has been investigated less comprehensively. The studies of this system are mostly focused on the 2212 and 2223 phase and the experimental work regarding the 2223 phase is often concentrated on the processing of 2223 samples with high critical current density and not on the preparation of single phase 2223 ceramics. The investigations of the Ag-containing system have just started. Nevertheless, first results show that Ag significantly influences the phase relations and the temperature dependence of the cation solubilities of the 2212 and 2223 solid solutions. These results indicate that the obtained phase diagrams of the system cannot be applied without caution when Ag is present. Therefore, as Ag is widely used as a sheath material for the processing of 2212 and 2223 wires and tapes, the investigation of the entire Ag-containing system is inevitable.
107 citations
TL;DR: In this article, an extended x-ray-absorption fine-structure analysis demonstrates that the Cu-Fe and Ag-Fe systems, both immiscible in equilibrium, exhibit contrasting alloying behavior when subjected to mechanical milling.
Abstract: Extended x-ray-absorption fine-structure analysis demonstrates that the Cu-Fe and Ag-Fe systems, both immiscible in equilibrium, exhibit contrasting alloying behavior when subjected to mechanical milling. While Cu-Fe undergoes atomic-level alloying forming solid solutions, Ag-Fe remains largely unreacted. The alloying behavior observed is explained based on a model for a dynamic system, combining both the effects of externally driven mixing and thermal evolution under the thermodynamic driving force prevailing in a ball-milled mixture.
105 citations
TL;DR: In this paper, the thermal stability of various alumina phases is discussed, and phase change routes of heating for different starting alumina modifications are discussed and a case study of alumina- chromia is presented.
Abstract: Aluminum oxide is a relatively cheap, abundant material that is widely used for plasma- spray applications. This material, however, exists in many crystallographic modifications with different properties. In addition, most of these modifications are metastable and cannot be used in applications employed at elevated temperatures. Usually γ, δ, or other phases form after spraying, while α phase (corundum) is often the most desirable phase due to high corrosion resistance and hardness. This paper first reviews the method of α stabilization in the as- sprayed materials offered in literature. Then, as an example, it summarizes the results of an extensive study of chromia additions to alumina. Chromia was chosen because of its complete solid solubility in alumina and its crystal lattice type, which is similar to that of alumina. It was demonstrated that the addition of approximately 20 wt% chromia results in the formation of one solid solution of (Al- Cr)2O3 in the α- modification. Finally, this paper discusses the thermal stability of various alumina phases. Phase change routes of heating for different starting alumina modifications are discussed, and a case study of alumina- chromia is presented. Both types of as-sprayed structures, a mixture of α, δ, and γ phases, and 100% (Al- Cr)2O3 were annealed up to 1300 °C and the phase composition checked. At lower temperatures and shorter holding times, the amount of α phase decreases while another metastable θ phase appears, and the fraction of γ + δ, if present, increases. At temperature above 1100 °C, the amount of α phase increases again.
15 Jul 1997-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the preparation and characterization of metastable phases of the Al-Fe alloy system by mechanical alloying is reported, and the metastable disordered b.c. solid solution of Fe in Al (up to 1 at.% Fe) is formed.
Abstract: The preparation and characterization of metastable phases of the Al–Fe alloy system by mechanical alloying are reported. In Al-rich (up to 10 at.% Fe) alloys, the supersaturated f.c.c. solid solution of Fe in Al (up to 1 at.% Fe) is formed. Almost complete amorphization is confirmed in the composition range 17–33 at.% Fe. The metastable disordered b.c.c. solid solution of about 10 nm in grain size has also been formed by ball-milling for over 180 h in Fe-rich (above 50 at.% Fe) alloys. Examination of lattice parameter and magnetization have shown that the composition range and degree of disorder are comparable to those formed by crushing and sputter deposition.
TL;DR: In this paper, LiCoO2 and Li2MnO3 were used as a cathode material for secondary lithium batteries, where excess lithium carbonate or lithium hydroxide was added to the mixture on calcination at 900 - 1000 °C to obtain the solid solutions.
Abstract: Lithium-manganese-cobalt oxide, Li(Lix/3MN2x/3Co1−x)O2 (0 ≤ x ≤ 1) was prepared as a solid solution between the two kinds of layer structured end members, LiCoO2 and Li2MnO3. Excess lithium carbonate or lithium hydroxide should be added to the mixture on calcination at 900 - 1000 °C to obtain the solid solutions. The resulting layer structured solid solutions can be used as a cathode material for secondary lithium batteries.
TL;DR: In this article, the Nb3Al phase in these multifilamentary conductors is prepared by phase transformation from supersaturated Nb(Al) bcc solid solution and show high-field critical current densities much larger than those for conventionally prepared Nb 3Al conductors, where the phase is known to be off-stoichiometric.
Abstract: Strain effects on critical current densities have been examined for conductors containing nearly stoichiometric Nb3Al filaments with fine grains. The Nb3Al phase in these multifilamentary conductors are prepared by phase transformation from supersaturated Nb(Al) bcc solid solution and show high-field critical current densities much larger than those for conventionally prepared Nb3Al conductors, where the Nb3Al phase is known to be off-stoichiometric. The degradation of critical current densities with −0.7% intrinsic strain is ca. 20% at 12 T, comparable with those for conventional Nb3Al conductors of high strain tolerance.
TL;DR: In this article, the electrical conductivity and the stability range of compositions in the Gd 2 Ti 2 O 7 Gd 2 Mo 2O 7 pyrochlore solid solution have been investigated to determine their potential as anode materials in solid oxide fuel cells.
TL;DR: In this article, the embedded atom method is applied to study the atomic structure and energy of an f.c.c/b.c phase, where the two phases are oriented in a Kurdjumov-Sachs orientation relationship.
TL;DR: In this article, the micro-structure and chemical composition of the network phase remarkably influenced the electrochemical properties of the V-based alloys, and the cyclic durability was improved by decreasing vanadium content in the TiNi phase by heat-treatment.
TL;DR: The metal particles of an interstitial solid solution of palladium carbide, PdCx (0 < x ≤ 0.15), were synthesized at room temperature in aqueous solution during the reduction of tetrachloropalladat.
Abstract: The metal particles of an interstitial solid solution of palladium carbide, PdCx (0 < x ≤ 0.15), were synthesized at room temperature in aqueous solution during the reduction of tetrachloropalladat...
TL;DR: In this paper, a series of Ba(Ti1−xCex)O3 dielectric ceramic materials was synthesized by the mixed oxide method with x = 0.1.
Abstract: A series of Ba(Ti1−xCex)O3 dielectric ceramic materials was synthesized by the mixed oxide method with x = 0.1, 0.2, 0.3, 0.33, 0.4 and 0.5. The phase-forming process, the crystal structure of the main phase, the ceramic microstructure and the dielectric properties were studied. The results show that the compositions with x ≤ 1 3 are mainly single-phase solid solutions of BaTiO3 and BaCeO3. The solubility limit is exceeded for x = 0.4. Permittivity values ranging from 800 to 3700 with dissipation factors between 0.01 and 0.1 were measured at 1 MHz for the solid solutions, and a dielectric relaxation behaviour was observed.
TL;DR: In this paper, the phase equilibria in the system Gd2O3-Al2O-3-SiO2 at 1400 and 1300 °C were determined using X-ray diffraction, SEM-EDX and EPMA.
TL;DR: The microstructures of Fe16Cu84 and Fe60Cu40 (atomic percent) during mechanical alloying (MA) were studied by high resolution electron microscopy (HREM) using a HF 2000 FEG TEM in this paper.
TL;DR: In this article, the formation of a continuous series of solid solutions with spinel structure between the terminal members of the binary systems studied has been established based on the data of x-ray phase and crystal-optical analyses.
Abstract: Phase relations in two binary systems MgAl2O4–ZnAl2O4 and MgAl2O4–Mg2TiO4 have been studied and phase diagrams for them have been constructed. Based on the data of x-ray phase and crystal-optical analyses, the formation of a continuous series of solid solutions with spinel structure between the terminal members of the systems studied has been established. In the MgAl2O4–ZnAl2O4 system the solid solution is stable in the range from room temperature to melting temperature. In the MgAl2O4–Mg2TiO4 system the solid solution decomposes below 1380 °C, yielding the formation of limited regions of homogeneity on the basis of MgAlM2O4 and Mg2+2δ Ti1–δO4. Decomposition of the solid solution is accompanied by crystallization of MgTiO3.
TL;DR: In this article, a solution growth process is employed for the deposition of CdS 1 − x Se x thin film composites with 0 ≤ x ≤ 1.5 and x ≥ 0.8.
TL;DR: In this paper, the ionic conductivity of YSZ solid solutions with titania additions up to 20 mol% was found to decrease with increasing titania content, which is explained by the ability of Ti to achieve a sixfold oxygen coordination.
Abstract: Solid solutions and composites based on YSZ (yttria-stabilized zirconia) with titania additions up to 20 mol% were prepared by solid state reaction. Structural characterization included XRD and Raman spectroscopy. Electroded samples were also studied by impedance spectroscopy in air between 573 and 1273 K. The ionic conductivity of these solid solutions decreases with increasing titania content. A sharp drop in conductivity is observed for specimens with compositions near to the usually assumed solubility limit of titania in the fluorite phase (about 10 mol%). This decrease is of almost one order of magnitude with respect to undoped or lightly doped samples. A smaller composition dependence is observed for higher titania additions (10–20 mol% TiO 2 ). Raman results show that tetragonal short range order is found in the cubic fluoritic phase well below the 10 mol% TiO 2 addition. This short range order is explained by the ability of Ti to achieve a sixfold oxygen coordination. As a consequence, a decrease in the concentration of mobile oxygen vacancies is expected, which is the reason for the electrical conductivity decrease.
TL;DR: In this paper, the authors demonstrate the use of an electric field as a processing parameter in self-sustaining combustion synthesis of nitride composites and solid solutions, and demonstrate that the extent of solubility of each phase into the other increased with increasing field.
Abstract: The synthesis of AlN-SiC composites and solid solutions was achieved through the imposition of an electric field in self-propagating high-temperature reactions. Despite its highly exothermic nature, the reaction Si 3 N 4 + 4Al + 3C = 4AlN + 3 SiC is not self-sustaining without the imposition of a threshold field (E) of 8 Vcm − 1 . At higher fields, the nature of the product depended on the value of the field. At E = 8 and 16.5 V cm − 1 , the product is a composite of AlN-rich and SiC-rich phases. The extent of solubility of each phase into the other increased with increasing field. When E = 25.0 V cm − 1 , the product is a solid solution with the 2H structure. The degree of randomness of the solution increased with a further increase in the value of the imposed field. Compositional analyses of the product phases are in reasonable agreement with the reported tentative phase diagram for AlN and SiC. The work demonstrates the use of an electric field as a processing parameter in self-sustaining combustion synthesis of nitride composites and solid solutions.
TL;DR: In this paper, the microstructure of Zirconium titanate (ZT) ceramics with compositions in the range of ZrTiO4-Zr5Ti7O24 were prepared via the mixed oxide route, using ZnO and CuO as sintering aids and Y2O3 as stabilizer.
Abstract: Zirconium titanate (ZT) ceramics having compositions in the range of ZrTiO4-Zr5Ti7O24 were prepared via the mixed oxide route, using ZnO and CuO as sintering aids and Y2O3 as stabilizer. Specimens were sintered at 1450°C for 4 h and then cooled at 6°C h-1, 120°C h-1 or air-quenched. All products exhibited densities exceeding 95% of the theoretical values. The amount of ZnO and CuO in the products decreased as the cooling rate decreased and as the content of TiO2 increased. Energy dispersive analytical spectroscopy studies suggested that a grain boundary phase, rich in ZnO and CuO, existed as a continuous layer. Both composition and cooling rate were found to have significant effects on the microstructure of the zirconium titanate ceramics. Transmission electron microscopy showed that as the TiO2 content increased, a superstructure with a tripled a-axis developed, but there was no obvious change in the lattice parameters. As the cooling rate decreased, extra peaks were observed in X-ray spectra and the lattice parameter in the b direction shortened dramatically; both are associated with cation ordering. A short-range commensurate superstructure with a ZTTZZTTZTTZZTT (or ZTTZZTTZTTZZTT) stacking sequence was observed in the ordered ZrTiO4 specimens. All the samples showed poor dielectric properties at microwave frequency (4 GHz). The low dielectric Q values (400–1000) were due to the presence of the structural stabilizer, Y2O3, within the grains. The Q value increased slightly with increasing TiO2 content. The air-quenched samples had the highest Q values (850–1000); slower cooling led to the formation of microcracks within the samples and the reduction of Q values. The relative permittivity was controlled by bulk composition, the presence of a grain boundary phase, microcracks, oxygen vacancies and cation ordering. The ordering of cations and the presence of microcracks reduced the relative permittivity; rapidly cooled samples with higher TiO2 content had higher relative permittivities (with a maximum of 44.3 for air-quenched Zr5Ti7O24).
TL;DR: The ternary system CdZn-Te has been studied by differential thermal analysis, differential scanning calorimetry and X-ray powder diffraction as discussed by the authors.
TL;DR: In this paper, the lattice parameters of NpyU{1−yO2 solid solutions at high temperatures were given in polynomial expressions of temperature, and the thermodynamic capacity, Cp, and heat capacities, of npyU 1−y O2 solvers at high temperature were estimated using the measured thermal expansions and literature data.
TL;DR: In this paper, the oxidation behavior of γ-TiAl based intermetallics has been investigated at 900 °C in an oxygen-argon mixture, where a depleted layer is formed at the scale/alloy interface.
TL;DR: In this paper, Rietveld analysis of neutron powder diffraction data on the sanmartinite (ZnWO4)-cuproscheelite (CuWO 4) solid solution has enabled the comparison of microscopic and macroscopic order parameters associated with the structural phase transition.
Abstract: Rietveld analysis of neutron powder diffraction data on the sanmartinite (ZnWO4)-cuproscheelite (CuWO4) solid solution has enabled the comparison of microscopic and macroscopic order parameters associated with the P2/c-P1 structural phase transition. The macroscopic spontaneous strain, calculated from the lattice parameters, conforms well with a second-order Landau model. Furthermore, this is also true of the symmetry-related atomistic M--O order parameter and the quadratic elongation of the MO6 octahedra. It is clear that the Jahn-Teller effect, associated with the divalent Cu cation, is the driving force for the phase transition and the excess elongation evident in the M--O(2) bond giving rise to the non-symmetry predicted strain element e22. The existence of a large region of order parameter saturation at the copper-rich end of the solid solution is also associated with the MO 6 elongation and the breakdown of the homogeneous strain field of the zinc solute atoms.