Phase Equilibria in the Systems Rare-Earth Sesquioxide-Beryllium Oxide

Phase equilibria in systems comprised of a rare-earth or yttrium sesquioxide and beryllia were studied. Two types of beryllates, stable and metastable, with molecular ratios of 1:2 and 3:2, were found: their formation and stability are discussed in terms of crystal chemistry.     

Studies in Germanium Oxide Systems: IV, Phase Equilibria in the System K,O-GeO,

Phase relations in the binary system K₂O-GeO₂ were determined by conventional quenching techniques. Three compounds, K₂O.2GeO₂, 3K₂O.11GeO₂, and K₂O.7GeO₂, exist in the composition range 65 to 100% GeOn. The compound 3K₂O.1lGeO₂ melts congruently at 1055°C, whereas K₂O.2GeO₂ and K₂O.7GeO₂ melt incongruently at 761° and 950°C, respectively. Thermal expansion data for the crystalline compounds are presented. The structure of potassium germanate glasses is discussed.     

金属氧化物半导体气敏传感器的研究和开发进展

综述了近期国内外金属氧化物半导体气敏传感器的研究和开发进展；阐述了半导体气敏材料的气敏作用及机理；展望了今后半导体气敏传感器技术的发展趋向。     

Ultrasonic Technique For Measuring Phase Holdups In Multiphase Systems

An ultrasonic technique is being developed to detect the dispersed phase holdups in multiphase systems. This technique is based on the fact that the transmission time and attenuation of ultrasound in suspensions differ from those in pure liquids. Experiments were carried out at three probe gap spacing, (2.04, 4.27, and 6.31 cm) in a fluidized bed of 7.6 cm diameter. Water was used as the continuous phase and air and 500 μm glass beads as the dispersed phases. The time-averaged amplitude ratio decays exponentially with gas and solid holdups, whereas the transmission time increases slightly with gas holdup but decreases with solid holdup. It is also observed, for the first time, that the fluctuations of the instantaneous ultrasonic signals can be correlated with the solid and gas holdups in a multiphase system. This correlation may provide a basis for the development of a new approach for phase holdup analysis in multiphase flow systems.     

Studies in Lithium Oxide Systems: X, Lithium Phosphate Compounds

As a preliminary to the investigation of the ternary systems Li₂O-B₂O₃-P₂O₅ and Li₂O-SiO₂-P₂O₅ the existence of the previously reported lithium ortho-, pyro-, and metaphosphate compounds was confirmed. A rapid, reversible inversion takes place in Li₄P₂O₇ at 630°C. New data on the melting points, optical properties, and X-ray diffraction patterns of each of the compounds were obtained.     

Synthesis of Precursors of Complex Oxide Systems Using Electrogenerated Reagents

Glass Physics and Chemistry - The scientific foundations for the synthesis of precursors of nanostructured oxide systems Al2O3–ZrO2–MxOy (M = Mg, Y) are developed. The processes...     

Performance Improvement of Double-Gate TFET Using Metal Strip Technique

Silicon - In order to overcome the limitations of a tunnel field-effect transistor (TFET) and to enhance its performance, the use of a low work function live strip (LWLS) in a conventional...     

Preparation of Porous Tin Oxide Nanobelts Using the Electrospinning Technique

The electrospinning method is adopted to prepare utralong PEO/stannic hydroxide composite nanofibers. Tin-oxide nanobelts can be obtained by calcination of the composite nanofibers in an open atmosphere. The nanobelts were characterized by a field emission scanning electron microscope, X-ray diffraction, a transmission electron microscope, a Raman spectromicroscope, and Fourier transform infrared spectroscopy. Microstructural analysis has shown that the nanobelts prepared consist of a continuous network of interconnected SnO₂ grains. As a result, the SnO₂ nanobelts possess a high surface area and continuous porosity, which may be applied for the fabrication of sensitive gas sensors.     

Phase relations in the Barium Titanate—Titanium Oxide System

Phase relations in the BaTiO₃—TiO₂ system were studied at temperatures above 1300°C in air. Quenching experiments were performed with high-purity reagents, and a new equilibrium phase diagram was constructed. Results include redetermination of the liquidus boundaries, the eutectic temperature, the melting or decomposition temperatures of the stable compounds in the system, the cubic—hexagonal transition in BaTiO₃, and the solid solubility of TiO₂ in BaTiO₃.     

Studies in Germanium Oxide Systems: II, Phase Equilibria in the System Na2O—GeO2

Phase equilibrium relations in the system Na₂O-GeO₂ have been determined using standard quenching techniques supplemented by differential thermal analysis. Two congruently melting compounds, Na₂O·GeO₂ and 2Na₂O·9GeO₂, exist; the melting points are 1103°± 15°C and 1073°± 3°C, respectively. The eutectic temperature between GeO₂ and 2Na₂O·9GeO₂ is 950°±f 10°C at 94.5 wt GeO₂. The eutectic temperature between 2Na₂O · 9GeO₂ and Na₂O·GeO₂ is 790° f 10°C at about 75 wt% GeO₂. Both the refractive index and the density of glasses in the system Na₂O-GeO₂ exhibit maximum values at about 16 to 18 mole % Na₂O. The Ge-O-Ge absorption band at 890 cm⁻¹ shifts toward lower wave numbers with the addition of Na₂O.     

Intercalation-induced Esterification over a Layered Transition Metal Oxide

The layered transition metal oxide HNbMoO₆ is demonstrated to catalyze the esterification of lactic acid (a hydroxycarboxylic acid) with activity superior or comparable to conventional ion-exchange resins. Layered HNbMoO₆ also catalyzes the esterification of propionic acid (a carboxylic acid) in the presence of lactic acid, despite exhibiting negligible activity for any carboxylic acid as the sole reactant. X-ray diffraction (XRD) measurements indicate that lactic acid is intercalated into the interlayer structure of the oxide whereas carboxylic acid is not. The intercalation mechanism thus greatly affects the catalytic activity of this layered catalyst.     

Grain Growth in Magnesium Oxide Containing a Liquid Phase

Specimens of magnesia containing 0.1, 1, and 2 cation % V (all as V₂O₅) were prepared and fired at various temperatures and times. The activation energy of grain growth was 62 kcal in all three systems; the grain growth followed the equation, D^a = kt. Electrical conductivity measurements and microscopic examination showed a liquid phase in the 1 and 2 cation % V systems above 1200°C. In the 0.1 cation % V system, no liquid phase was detectable by X-ray, microscopic, or conductivity studies; however, as the kinetics of grain growth were similar to that of the 1 and 2 cation % V sys tems, it was suspected that a liquid phase was affecting the grain growth kinetics. Great care should be taken, therefore, in interpreting kinetic measurements on grain growth of so-called pure oxides.     

Subsolidus Phase Relationships in Si3N4–AlN–Rare-Earth Oxide Systems

The subsolidus phase relationships in Si₃N₄–AlN–rare-earth oxide (Me₂O₃ where Me=Nd, Sm, Gd, Dy, Er, and Yb) systems were studied. Solid-solution regions with the α-Si₃N₄ structure were delineated along the Si₃N₄–"Me₂O₃:9AIN" joins for all of the rare-earth oxide systems studied. The solubility limits of these solid solutions increased with decreasing size of the rare-earth ions.     

Phase Stability and Phase Structure of Ru–Ti–O Complex Oxide Electrocatalyst

Phase stability of (Ru_1?x,Ti_x)O₂ solid solution was investigated via materials computation and X‐ray diffraction phase analyses. The unit cell volume of (Ru_1?x,Ti_x)O₂ was found not increasing monotonously with the fraction of TiO₂, making the volume–composition relationship no longer suitable for the quantitative phase analysis. A monotonous nonlinear c/a–x relation obtained from the ab initio density functional theory (DFT) computation was proved critical to achieving accurate phase analysis results. Gibbs free energy of mixing and its derivatives were determined for (Ru_1?x,Ti_x)O₂ by a combination of DFT and thermodynamic calculations, where approximation of the temperature dependence of the interaction parameter (Ω) played a critical role. It was found that the conventional approximation method of arbitrarily choosing a value & [10,25] kJ (mole of atoms)^?1 for Ω near a critical temperature of a solid solution structure failed to predict the correct symmetry and span of the miscibility gap for (Ru_1?x,Ti_x)O₂. In comparison, Ω calculated from disordered (Ru_1?x,Ti_x)O₂ was found a good approximation at the critical temperature. The calculated miscibility gap for (Ru_1?x,Ti_x)O₂, therefore, showed good agreement with the accurate quantitative phase analysis results for the samples prepared by a sol–gel method.