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1.
It has been shown that BiVO4 and Pb2V2O7 react with each other, forming a new compound of the formula Pb2BiV3O11 at molar ratio equal to 1:1. This compound has also been obtained from PbO, Bi2O3, and V2O5, mixed at a molar ratio of 4:1:3. It melts congruently at a temperature of 725 ± 5 °C and crystallizes in the triclinic system with unit-cell parameters: a = 0.710076 nm, b = 1.41975 nm, c = 1.42972 nm, α = 134.552°, β = 97.2875°, γ = 89.6083°, and Z = 4.  相似文献   

2.
An isothermal section of the system Al2O3-CaO-CoO at 1500 K has been established by equilibrating 22 samples of different compositions at high temperature and phase identification by optical and scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy after quenching to room temperature. Only one quaternary oxide, Ca3CoAl4O10, was identified inside the ternary triangle. Based on the phase relations, a solid-state electrochemical cell was designed to measure the Gibbs energy of formation of Ca3CoAl4O10 in the temperature range from 1150 to 1500 K. Calcia-stabilized zirconia was used as the solid electrolyte and a mixture of Co + CoO as the reference electrode. The cell can be represented as: From the emf of the cell, the standard Gibbs energy change for the Ca3CoAl4O10 formation reaction, CoO + 3/5CaAl2O4 + 1/5Ca12Al14O33 → Ca3CoAl4O10, is obtained as a function of temperature: /J mol−1 (±50) = −2673 + 0.289 (T/K). The standard Gibbs energy of formation of Ca3CoAl4O10 from its component binary oxides, Al2O3, CaO, and CoO is derived as a function of temperature. The standard entropy and enthalpy of formation of Ca3CoAl4O10 at 298.15 K are evaluated. Chemical potential diagrams for the system Al2O3-CaO-CoO at 1500 K are presented based on the results of this study and auxiliary information from the literature.  相似文献   

3.
The thermodynamic database of the ZrO2-Gd2O3-Y2O3-Al2O3 system is up-dated taking into account new data on lattice stabilities of ZrO2, Gd2O3 and Y2O3 and heat capacity measurements for the monoclinic phase Gd4Al2O9 and phase with garnet structure Gd3Al5O12. New data for the heat capacities of Gd2Zr2O7 (pyrochlore) and GdAlO3 (perovskite) as well as on the enthalpy of formation of fluorite solid solutions (Zr1−x Gd x )O2−x/2 were found to be in good agreement with calculated results. In comparison with the previous assessment, taking into account new experimental data resulted in a change of the melting character of the Gd4Al2O9 phase from a peritectic one to a congruent one in the Gd2O3-Al2O3 system. Correspondently, in the ternary system ZrO2-Gd2O3-Al2O3, the melting character of the three-phase assemblage Gd2O3 (B), Gd4Al2O9 and GdAlO3 changed from eutectic to transition type U. The T 0-lines for T/M and F/T diffusionless transformations and driving force of partitioning to equilibrium assemblage T + F were calculated in the ZrO2-Gd2O3-Y2O3 system.  相似文献   

4.
The microstructure of the coating prepared by reactive plasma spraying Fe2O3/Al composite powders was characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicated that the coating exhibited nanostructured microstructure which consisted of FeAl2O4, Fe or Fe solid solution, Al2O3 and a little FeAl. In the composite coating, spherical Fe particles (tens of nanometers to hundreds of nanometers) were distributed uniformly within the equiaxed and columnar nanograins FeAl2O4 matrix. There were two kinds of Al2O3 phases present in the composite coating. One kind was nano-sized Al2O3 particles uniformly dispersed within the matrix, forming eutectic structure of (FeAl2O4 + γ-Al2O3); the other was 1-1.5 μm Al2O3 particles embedded individually within the matrix. The composite coating had higher toughness than the conventional microstructured Al2O3 coating.  相似文献   

5.
To fabricate an Al-V matrix composite reinforced with submicron-sized Al2O3 and AlxVy (Al3V, Al10V) phases, high energy mechanical milling (HEMM) and sintering were employed. By increasing the milling time, the size of mechanically milled powder was significantly reduced. In this study, the average powder size of 59 μm for Al, and 178 μm for V2O5 decreased with the formation of a new product, Al-Al2O3-AlxVy, with a size range from 1.3 μm to 2.6 μm formed by the in-situ combustion reaction during sintering of HEM milled Al and V2O5 composite powders. The in-situ reaction between Al and V2O5 during the HEMM and sintering transformed the Al2O3 and AlxVy (Al3V, Al10V) phases. Most of the reduced V reacted with excess the Al to form AlxVy (Al3V, Al10V) with very little V dissolved into Al matrix. By increasing the milling time and weight percentage of V2O5, the hardness of the Al-Al2O3-AlxVy composite sintered at 1173 K increased. The composite fabricated with the HEMM Al-20wt.%V2O5 composite powder and sintering at 1173 K for 2 h had the highest hardness.  相似文献   

6.
Al2O3 /xZrO2 (where x = 0, 3, 13, and 20 wt.%) composite coatings were deposited onto mild steel substrates by atmospheric plasma spraying of mixed α-Al2O3 and nano-sized monoclinic-ZrO2 powders. Microstructural investigation showed that the coatings comprised well-separated Al2O3 and ZrO2 lamellae, pores, and partially molten particles. The coating comprised mainly of metastable γ-Al2O3 and tetragonal-ZrO2 with trace of original α-Al2O3 and monoclinic-ZrO2 phases. The effect of ZrO2 addition on the properties of coatings were investigated in terms of microhardness, fracture toughness, and wear behavior. It was found that ZrO2 improved the fracture toughness, reduced friction coefficient, and wear rate of the coatings.  相似文献   

7.
Al2O3/ZrO2/Al2O3 gate stacks were prepared on ultrathin SOI (Silicon on insulator) substrates by ultrahigh vacuum electron beam evaporation and post-annealed in N2 at 450°C for 30 min. Three clear nanolaminate layered structure of Al2O3(2.1 nm)/ZrO2(3.5 nm)/Al2O3(2.3 nm) was observed with a high-resolution cross-sectional transmission electron microscope (HR-XTEM). High frequency capacitance voltage (C-V) characteristics of a fully depleted (FD) SOI MOS capacitor at 1 and 5 MHz were studied. The minority carriers determine the high frequency C-V properties, which is opposite to the case of bulk MOS capacitors. The series resistance of the SOI substrate is found to be the determinant factor of the high frequency characteristics of FD SOI MOS capacitors. This article is based on a presentation in “The 7th Korea-China Workshop on Advanced Materials” organized by the Korea-China Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju Hotel, Jeju Island, Korea on August 24≈27, 2003.  相似文献   

8.
Al2O3/Cu composites were prepared by external addition of Al2O3, and the effect of Al2O3 content on microstructure, density, hardness, electrical conductivity and vacuum electrical breakdown properties was studied. The results show that with increasing Al2O3 addition, the density of Al2O3/Cu composite significantly decreases, the hardness sharply increases and then slowly decreases, but the electrical conductivity invariably decreases. The vacuum breakdown test shows that with increasing Al2O3 addition, the breakdown strength first sharply increases and then decreases when the Al2O3 content exceeds 1.2 wt.%; the chopping current always exhibits a decreasing trend and the arc life first increases and then decreases. According to the morphology of arc erosion and analysis, the arc erosion resistance increases and then decreases sharply. In the range of experiments, the optimal arc erosion resistance of Al2O3/Cu composite can be obtained with the addition of 1.2 wt.% Al2O3.  相似文献   

9.
The target of this work was to investigate the phase development in the catalyst system consisting of TiO2 (Anatase) and V2O5 (Shcherbinaite) under several gas atmospheres. Thus a set of V2O5/TiO2 specimens was prepared by ball milling and exposed to subsequent annealing in air and feed gas in the temperature range from 400 to 700 °C. The XRD-results showed that the initial phases Anatase and Shcherbinaite remain stable for all atmospheres containing oxygen. In the temperature range above 525 °C the formation of a Rutile solid solution (Rutile-ss) containing VO x species takes place. However, under reducing conditions (lower oxygen partial pressure) the reduction of V2O5 to V2O3 was found by X-ray diffraction measurements. There is no miscibility up to 1300 °C followed by the formation of V2TiO5 (Berdesinskiite). SEM images underline the reduction by monitoring the change in morphology with respect to the V-containing phases. TiO2 remains without much alteration. The two phases V2Ti7O17 and V2Ti3O9 (Schreyerite) as described in mineralogy have not been observed in these experiments. The knowledge of phase relations helps to find the appropriate processing conditions and to understand the aging phenomena of catalysts.  相似文献   

10.
Phase equilibria in the ZrO2-Nd2O3-Y2O3 system at 1523-1873 K have been investigated by x-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive x-ray spectroscopy (SEM/EDX). Temperatures of phase transformations were determined by differential thermal analysis. Temperatures of invariant reactions in the ZrO2-Nd2O3 system F = A + Pyr and H = F + A were determined as 1763 and 2118 K respectively and thermodynamic parameters of phases were re-assessed. Phase transformations in ternary systems were determined at 1732 K for composition ZrO2-48.46Nd2O3-5.38Y2O3 (mol%) and at 1744 and 1881 K for composition ZrO2-79.09Nd2O3-2.75Y2O3 (mol%). They were interpreted using XRD investigation before and after DTA as Pyr + B → F, Pyr → F and A → B, respectively. The solubility of the Y2O3 in pyrochlore phase was found to exceed 10 mol%. The thermodynamic parameters of the ZrO2-Nd2O3-Y2O3 system were reassessed taking into account solubility of Y2O3 in the Nd2Zr2O7 pyrochlore phase (Pyr). It is assumed that Y3+ substitutes Nd3+ and Zr4+ in their preferentially occupied sublattices. Ternary parameter was introduced into fluorite phase (F) for better reproducing of phase equilibria. Mixing parameters were reassessed for phase A (Nd2O3 based solution), monoclinic phase B and cubic phase C (Y2O3 based solution). The isothermal sections calculated for the ZrO2-Nd2O3-Y2O3 system are in the reasonable agreement with experimental results.  相似文献   

11.
Metal-insulator-semiconductor (MIS) structures containing Ge nanocrystals embedded in both Al2O3 and ZrO2/Al2O3 are fabricated by an ultra-high vacuum electron-beam evaporation method. Secondary ion mass spectroscopy (SIMS) results indicate that Ge embedded in Al2O3 diffuses towards the surface of the Al2O3 layer after annealing at 800°C in N2 ambient for 30 min. Ge embedded in ZrO2/Al2O3 is stable, thus inducing less leakage current. Capacitance voltage studies indicate that annealing can effectively passivate the negatively charged trapping centers. Memory effect of the Ge nanoclusters is verified by hysteresis in the C-V curves in the Al2O3/Ge+Al2O3/Al2O3 and ZrO2/Ge+Al2O3/Al2O3 samples. This article is based on a presentation in “The 7th Korea-China Workshop On Advanced Materials” organized by the Korea-China Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju Hotel, Jeju Island, Korea on August 24–27, 2003.  相似文献   

12.
Corrosion of boilers and heat exchangers is accelerated in the presence of vanadium, sodium, and sulfur from low-grade fuels. Several iron- and nickel-based alloys were immersed in 60 mol% V2O5–40Na2SO4 salt for 1000 h in order to investigate their degradation behavior at 600 °C in air. Materials performance was analyzed by means of substrate recession rate and metallographic characterization. Their corrosion mechanism is characterized by the formation of a sulfide/oxide layer adjacent to the metal, the dissolution of scale oxides in the molten deposit, and their precipitation near the outer surface of the deposit. High Ni- and Cr-containing alloys show the lowest metal loss rates. Al addition was detrimental due to low-melting eutectic AlVO4–V2O5 formation. Fe–Cr-based alloys showed the highest metal loss rates. In such alloys, high Cr additions (above 20%) did not improve the performance due to the negative synergetic effect by simultaneous dissolution of Fe2O3 and Cr2O3. The predominant salt composition at the corrosion front varied from vanadate rich to sulfate rich during the exposure. This change in the attacking salt makes it difficult to find a protective material for mixed sulfate–vanadate-induced corrosion.  相似文献   

13.
Phase formation sequence of the yttrium aluminates in the Y2O3-Al2O3-SiC ternary system as temperature increases were investigated via x-ray diffraction (XRD). Results showed that YAM (monoclinic), YAP (perovskite) and YAG (garnet) were the yttrium aluminates presented in the solid-state reacted samples at a fixed Al2O3:SiC ratio of 1:1. Formation of the yttrium aluminates depended on the temperature. The YAM, YAP and YAG started to form below 1150 °C, at 1300 °C, and at 1450 °C, respectively. Accordingly, two behavior phase diagrams of the Y2O3-Al2O3-SiC ternary system were recognized, one is in the temperature range of 1150-1300 °C and the other is in 1300-1450 °C, respectively. Thereafter, the phase equilibrium was reached in the temperature range of 1450-1700 °C. Effects of SiC on the phase formation processes in the ternary system were discussed.  相似文献   

14.
Electric transport and magnetoresistance characteristics were investigated for Fe3O4-x Fe(x=0, 10, 20 wt.%) samples and Fe3O4-α-Fe2O3 samples sintered at 500°C. For composition dependence of Fe3O4-x Fe samples, the largest room temperature MR, 3.3% at 10 kOe, was obtained from a Fe3O4-10 Fe sample. For the surface heat treatment dependence of Fe3O4 powders, the largest room temperature MR, 4% at 10 kOe, was obtained from a Fe3O4-α-Fe2O3 sample sintered with Fe3O4 powders heated at 200°C in air. It was found that these enhanced MR ratios always appear together with the appropriate excess resistance which is regarded as the tunneling barrier. These enhanced MR ratios of Fe3O4-10 Fe and Fe3O4-α-Fe2O3 samples can be explained by the increased interparticle contact sites and the appropriate thickness of α-Fe2O3, respectively.  相似文献   

15.
The kinetics of low-temperature dissolution of oxides Y2O3 and Fe2O3 in an iron matrix during mechanical alloying has been studied using electron microscopy. It has been shown that the dissolution rate upon deformation of primary coarse oxides Fe2O3 in α iron (and, hence, saturation of the α matrix with oxygen) during treatment in a ball mill for up to 10 h is several times higher than the dissolution rate of Y2O3 oxides. The high-temperature (1100°C) annealing of a mechanoalloyed mixture of Fe + 1.5% Y + 1.35% Fe2O3 leads to the precipitation of 60% (of the total number of particles) secondary oxides 2–5 nm in size and only of 5–7% secondary nanooxides in a mechanoalloyed mixture of Fe + 2% Y2O3.  相似文献   

16.
A glass based on the P2O5-ZnO-Sb2O3 ternary system was modified with various additives, such as RO (R=Ca, Ba and Mn), B2O3 and V2O5, for low temperature and low expansion sealing materials. The glass transition temperature (Tg) and coefficient of thermal expansion (CTE) were monitored and reduced with additive compositions of RO. Additional incorporation of B2O3 at the expense of RO also showed a similar result. Significant improvement was observed when the glass was modified with V2O5. A glass showing Tg<350 °C along with CTE<65×10−7/°C was found, suggesting a high potential for low temperature sealing materials especially for display applications. The role of the quaternary element within the glass is discussed, along with the structural effect using Raman spectroscopy.  相似文献   

17.
This paper investigates the high-temperature oxidation of cermet coatings composed of two types of nanosized particles (WC and a mixture of WC and Al2O3) incorporated in nickel and produced by co-electrodeposition. For this purpose, high-temperature oxidation tests were conducted at three temperatures (500, 600, and 700 °C) in dry air with 6 time intervals up to 96 h and mass changes at each specific time interval was measured. Statistical techniques were used to calculate the oxidation rate constants (k) and growth-rate time constants (a) for all coatings. The confidence intervals associated with tests were also calculated. The results showed linear to sub-parabolic oxidation rates for coatings composed of only WC particles and sub-liner to liner oxidation rates for coating with both WC and Al2O3 particles. The reduction in oxidation rates for coatings with both WC and Al2O3 particles were correlated to the addition of Al2O3 particles in the matrix.  相似文献   

18.
The phase relations in the Si-Al-Pr-O-N-C systems, involving SiC-AlN-Pr2O3, AlN-Pr2O3-Al2O3 and SiC-AlN-Pr2O3-Al2O3 systems were determined by XRD phase analyses of the solid-state reacted samples from powder mixtures of SiC, AlN, Pr2O3, as well as Al2O3. Pr2Al(Si)O3N(C) solid-solution (1:1 ss) between SiC and Pr2AlO3N (1:1 compound) was discovered with the limited solubility of 0.6 SiC at 1650 °C. Subsolidus phase diagram of SiC-AlN-Pr2O3 system was presented, SiC was compatible with AlN, Pr2O3 and 1:1 ss, respectively. Two-aluminates PrAlO3 (PrAP) and PrAl11O18 [β(Pr), β-Al2O3 type] were formed when Al2O3 impurity was introduced in AlN powder. They establish the equilibrium relationships respectively with SiC, AlN, Pr2O3 and Pr2AlO3N. Accordingly, the phase relations in the AlN-Pr2O3-Al2O3 ternary system and SiC-AlN-Pr2O3-Al2O3 quaternary system containing four quaternary phases compatible tetrahedrons were presented.  相似文献   

19.
Technologically modified spinel MgO-Al2O3 ceramics were prepared from Al2O3 and 4MgCO3·Mg(OH)2·5H2O powders at sintering temperatures of 1200, 1300, and 1400 °C. Free-volume structural effects in MgO-Al2O3 ceramics and their electrophysical properties were studied using combined x-ray diffraction, scanning electron microscopy, Hg-porosimetry, and positron annihilation lifetime spectroscopy. It is shown that increasing of sintering temperature from 1200 to 1400 °C results in the transformation of pore size distribution in ceramics from tri- to bi-modal including open macro- and meso(micro)pores with sizes from ten to hundreds nm and nanopores with sizes up to a few nm. Microstructure of these ceramics is improved with the increase of sintering temperature, which results in decreased amount of additional phases located near grain boundaries. These phase extractions serve as specific trapping centers for positrons penetrating the ceramics. The positron trapping and ortho-positronium decaying components are considered in the mathematical treatment of the measured spectra. Classic Tao-Eldrup model is used to draw the correlation between the ortho-positronium lifetime and the size of nanopores, which is complementary to porosimetry data. The studied ceramics with optimal nanoporous structure are highly sensitive to humidity changes in the region of 31-96% with minimal hysteresis in adsorption-desorption cycles.  相似文献   

20.
Methods of X-ray diffraction and transmission electron microscopy were used to study the microstructure of dispersion-strengthened Cu-Al2O3 nanocomposites obtained by the method of simultaneous deposition of Cu and Al2O3 from the vapor phase. The effect of the size of particles of the oxide (Al2O3) and of their content on the electrical resistance of the composite has been considered. The results obtained make it possible to suppose that the main structural factor that determines the electrical resistance of the composite are nanodispersed particles of Al2O3 with a size of less than 20 nm.  相似文献   

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