In Situ Ultraviolet Raman Study on the Phase Transition of Hafnia up to 2085 K

We have recently demonstrated that the Raman scattering through ultraviolet (UV) excitation is eminently well suited for in situ investigation of materials at high temperatures up to 1773 K. Here we report successful Raman measurements of HfO₂ up to 2085 K, using only a 100 mW power of UV laser line. The monoclinic-to-tetragonal transformation finished around 2080 K on heating, while the monoclinic phase appeared at 2018 K on cooling.     

Comparative Lattice-Dynamical Study of the Raman Spectra of Monoclinic and Tetragonal Phases of Zirconia and Hafnia

An interpretation of the Raman spectra of monoclinic ZrO₂ and monoclinic HfO₂ is made by analyzing the results of the zirconia–hafnia substitution jointly with a lattice dynamical treatment of both structures. The Raman spectra of tetragonal ZrO₂ and tetragonal HfO₂ are also interpreted. Emphasis is put on their relations to the spectrum of the parent cubic structure and on the position of the soft mode. The band assignment proposed earlier by other researchers is critically reconsidered.     

Subsolidus Phase Relations and Transparent Conductors in the Cadmium-Indium-Tin Oxide System

Subsolidus phase relations have been determined in the CdO–InO_1.5–SnO₂ system at 1175°C. A cubic-bixbyite solution In_{2−2 x} (Cd,Sn)_{2 x} O₃ (0 < x < 0.34), a cubic spinel solution (1− x )CdIn₂O₄– x Cd₂SnO₄ (0 < x < 0.75), and an orthorhombic-perovskite solution Cd_{1− x} Sn_{1− x} In_{2 x} O₃ (0 < x < 0.045) having the GdFeO₃ structure have been discovered. The CdO phase field exists over a small range of InO_1.5 (<3%) and SnO₂ (<1%). Orthorhombic Cd₂SnO₄ (Sr₂PbO₄ structure) and rutile SnO₂ appear to be point compounds with negligible solubility. The vertical section between spinel CdIn₂O₄ and orthorhombic Cd₂SnO₄ was determined between 900° and 1175°C. The spinel phase field (1− x )CdIn₂O₄– x Cd₂SnO₄ was found to extend between x = 0 and x = 0.75 at 1175°C or x = 0.78 at 900°C. All of the phases in this system appear to allow small excess quantities of the donors In and/or Sn (vs cation stoichiometry) which may be the source of the electrons that give these oxides their n-type character. The electrical and optical properties of bulk and thin-film specimens in this system are compared and contrasted with each other and the relative merits of each are assessed.     

Phase Equilibria in the Hafnia–Yttria–Lanthana System

The HfO₂–Y₂O₃–La₂O₃ system was studied in the wide range of temperatures (1250°–2800°C) and concentrations by methods of X-ray analysis at 20°C, petrography, differential thermal analysis in helium at temperatures to 2500°C, thermal analysis in air using a solar furnace at temperatures to 3000°C, and electron microprobe X-ray analysis. The complete phase diagram was constructed. The liquidus and solidus projections, crystallization paths for the alloys, isothermal (1250°, 1600°, and 1900°C) and polythermal sections are presented. The structure of the boundary binary systems defines the phase equilibria in the ternary system. No ternary compounds were found. Ternary solid-solution regions were determined based on constituent oxides and intermediate phases.     

Biomolecules under Pressure: Phase Diagrams,Volume Changes,and High Pressure Spectroscopic Techniques

Pressure is an equally important thermodynamical parameter as temperature. However, its importance is often overlooked in the biophysical and biochemical investigations of biomolecules and biological systems. This review focuses on the application of high pressure (>100 MPa = 1 kbar) in biology. Studies of high pressure can give insight into the volumetric aspects of various biological systems; this information cannot be obtained otherwise. High-pressure treatment is a potentially useful alternative method to heat-treatment in food science. Elevated pressure (up to 120 MPa) is present in the deep sea, which is a considerable part of the biosphere. From a basic scientific point of view, the application of the gamut of modern spectroscopic techniques provides information about the conformational changes of biomolecules, fluctuations, and flexibility. This paper reviews first the thermodynamic aspects of pressure science, the important parameters affecting the volume of a molecule. The technical aspects of high pressure production are briefly mentioned, and the most common high-pressure-compatible spectroscopic techniques are also discussed. The last part of this paper deals with the main biomolecules, lipids, proteins, and nucleic acids: how they are affected by pressure and what information can be gained about them using pressure. I I also briefly mention a few supramolecular structures such as viruses and bacteria. Finally, a subjective view of the most promising directions of high pressure bioscience is outlined.     

Phase Relationship between 3C- and 6H-Silicon Carbide at High Pressure and High Temperature

The phase relationship between 3C- and 6H-SiC is investigated in the pressure range 2.5–6.5 GPa and the temperature range 400°–2500°C, by analyzing recovered samples, using X-ray diffractometry and Raman-scattering techniques. The phase transition from 3C- to 6H-SiC occurs at 2200°C and 2.5 GPa. In the pressure range >4.5 GPa, 6H-SiC transforms to 3C-SiC at 2500°C, via an intermediate state, as indicated by broadening peaks in the X-ray diffraction profile. Thermodynamically, 3C-SiC appears to be the low-temperature stable form, and the temperature of transition to 6H-SiC, which is stable at high temperature, appears to increase with pressure.     

Phase Relations and Thermal Expansion Studies in the Ceria–Yttria System

The synthesis, characterization, and bulk and lattice thermal expansions of a series of compounds with general composition Ce_{1– x} Y _x O_{2– x /2} (0.0 ≤ x ≤ 1.0) are reported. The XRD pattern of each product was refined to learn the solid solubility limit and the homogeneity range. The solid solubility limit of YO_1.5 in CeO₂ lattice, under the conditions of slow cooling from 1400°C, is represented as Ce_0.55Y_0.45O_1.775 (i.e., 45 mol% of YO_1.5). The subsequent compositions were biphase. There was no solubility of CeO₂ into the lattice of YO_1.5. The bulk thermal expansion measurements from ambient to 1123 K, as investigated using a dilatometer, revealed that the α_l (293–1123 K) values, within the homogeneity range, decreased on increased Y³⁺ content. A similar trend was observed for average lattice thermal expansion coefficient, α_a (293–1473 K), as investigated using high-temperature XRD. No ordered phases were obtained in this system under the used conditions. These studies on Ce_{1– x} Y _x O_{2– x /2} (0.0 ≤ x ≤ 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu_{1– x} Y _x O_{2– x /2} (0.0 ≤ x ≤ 1.0), because CeO₂ is widely used as a surrogate material for PuO₂.     

Pu, U, and Hf Incorporation in Gd Silicate Apatite

Trivalent Pu can be incorporated in the silicate apatite structure to form Ca₂Pu₈(SiO₄)₆O₂ by sintering under reducing conditions, while the incorporation of tetravalent Pu in the Ca/rare earth sites in oxidizing or neutral conditions is limited to only 0.6 formula units (f.u.). The d -spacings and intensities of the X-ray pattern of hexagonally structured Ca₂Pu₈(SiO₄)₆O₂ after firing at 1250°C are given, and the a and c lattice parameters are 0.9561₁ and 0.7028₁ nm, respectively. The respective solid solubility limits of U and Hf in Ca₂Gd_{8– x} (U/Hf) _x (SiO₄)₆O₂ apatite samples were 0.3 and 0.2 f.u.     

Lead Hafnate (PbHfO3) Perovskite Powders Synthesized by the Oxidant Peroxo Method

Perovskite lead hafnate (PbHfO₃, PH) nanoparticles that were free from halides and organics were synthesized via the oxidant peroxo method. Stoichiometric amounts of hafnium nitrate (HfO(NO₃)₂) and lead nitrate (PbHfO₃) were dissolved in a diluted hydrogen peroxide (H₂O₂) aqueous solution, which was slowly added to a solution of H₂O₂ and ammonia (NH₃) (pH 11). The lead–hafnium precipitate obtained was filtered and washed, to eliminate all nitrate ions. The precipitate was dried, ground, and calcined at temperatures of 400°–900°C. A tetragonal intermediate phase was identified using X-ray diffractometry and Raman spectroscopy during the calcination process, followed by the crystallization of the orthorhombic PH phase at ∼700°C.     

Negative Thermal Expansion in (HfMg)(WO4)3

A single-phase material (HfMg)(WO₄)₃ with an orthorhombic structure, A₂ (WO₄)₃-type tungstate, has been successfully prepared for the first time by the calcination of HfO₂, MgO, and WO₃, substituting Hf⁴⁺ and Mg²⁺ for A³⁺ cations in A₂(WO₄)₃. The new material shows a negative thermal expansion coefficient of approximately −2 ppm/°C from room temperature to 800°C. The mechanism of negative thermal expansion is assumed to be the same as that of Sc₂(WO₄)₃.     

BxO: Phases Present at High Pressure and Temperature

Boron suboxide compounds are of interest because of their low densities coupled with high hardness. In the present study, we have attempted to determine the nature of the B _x O phases that occur in the field defined by pressures of zero to 1.5 GPa, temperature between 1200° and 1700°C, and the compositional range 2/3 x 24. Amorphous boron powder and boric acid B₂O₃ were the starting reactants for all the runs. The processing of the specimens was carried out in a controlled atmosphere furnace, a hot-pressing assembly, and in a piston—cylinder high-pressure apparatus within quasi-hydrostatic and inductively heated cell assemblies. After processing at elevated temperature and pressure, for compositions over the range 2/3 x 6, B₂O₃ (identical to the hexagonal starting material) and B₆O ( R 3¯ m ) were the dominant phases present. For the compositions 6 x 24, B₆O and rhombohedral B were the primary phases identified. In general, the hardness of the processed composites was dominated by the occurrence of B₆O (approximately equivalent to B₄C). However, there is some suggestion of particularly high values of hardness on a very localized scale in specimens near the B₂₂O composition.     

Pressure and Temperature Dependence of the Raman Spectra of Zirconia and Hafnia

The pressure dependence of the phonon frequencies in the isomorphic materials ZrO₂ and HfO₂, and the temperature dependence of the phonon frequencies of HfO₂, were investigated by Raman spectroscopy in the ranges 0 to 16 GPa and 20 to 800 K. The comparison of the pressure dependence of the Raman spectra of the two materials helps to elucidate the correlation of their vibrations in the intermediate spectral region (240 to 410 cm⁻¹). The high-pressure phase of ZrO₂ is stable up to 16 GPa and of tetragonal symmetry. HfO₂ does not show any pressure-induced phase transition up to 12 GPa, while the temperature effect on the phonon frequencies is similar to that of ZrO₂.     

Phase Formation and Dielectric Characterization of the Bi2O3–TeO2 System Prepared in an Oxygen Atmosphere

Solid-state synthesis of compositions from the Bi₂O₃–TeO₂ system show that, under an oxygen atmosphere, Te⁴⁺ oxidizes to Te⁶⁺ and yields four room-temperature stable compounds: Bi₂Te₂O₈, Bi₂TeO₆, Bi₆Te₂O₁₅, and new a compound with the nominal composition 7Bi₂O₃·2TeO₂. Dense ceramics can be prepared from all these compounds by sintering between 650° and 800°C under an oxygen atmosphere. The permittivity of these compounds varies from ∼30 to ∼54, the Q × f value from 1.100 to 41.000 GHz (∼5 GHz), and the temperature coefficient of resonant frequency from −43 to −144 ppm/K. Bi₆Te₂O₁₅ and 7Bi₂O₃·2TeO₂ do not react with silver, and, therefore, they have the potential to be used for applications in low-temperature cofired ceramic (LTCC) technology.     

高温高压条件下不锈钢的氢损伤

综述了高温高压条件下氢致不锈钢损伤的研究进展情况,重点介绍了不锈钢力学性能和微观结构的变化,并就压力和温度对氢损伤敏感性影响作了简单的讨论。     

高压下甲醇-大豆油液液相平衡数据的测定与关联

为考察高压下制备生物柴油的原料甲醇与大豆油的相互溶解度,采用高压平衡釜和静态法测定了温度为381．2～472．2K,压力为9．79～19．80MPa条件下甲醇一大豆油二元体系的液液相平衡数据,用PR状态方程对所测的液液相平衡数据进行了关联;PR方程中的参数a和b采用van der Wails单流体混合规则。采用单参数vander Waals模型计算交互参数项aij和bij二者各包含一可调参数kij和lij对可调参数kij和lij采用了与温度无关和与温度有关的2种处理方法,并用实验数据估算了可调参数值。采用与温度无关的可调参数时,用PR方程关联实验数据所得按质量分数计的均方偏差和平均偏差分别为0．0499和0．0222;用与温度有关的可调参数时,均方偏差和平均偏差相应为0．0426和0．0193。结果表明：PR状态方程适用于高压下甲醇与大豆油的液液相平衡计算。     

Prediction of Rare-Earth A2Hf2O7 Pyrochlore Phases

Within the series of A₂O₃-HfO₂ phase diagrams (A ranges in cationic radius from Lu³⁺ to La³⁺), only those from Gd₂Hf₂O₇ to La₂Hf₂O₇ are known to exhibit a pyrochlore phase field. For A cations smaller than Gd³⁺, only a disordered fluorite phase field exists. Disorder energies for the entire series of pyrochlore oxides have been determined via atomistic simulation. These energies can be correlated to the order-disorder temperatures from the phase diagrams. Consequently, we predict the existence of hitherto unobserved pyrochlores: Dy₂Hf₂O₇, Ho₂Hf₂O₇, and Er₂Hf₂O₇.     

Behavior of Pressure Gradient and Transient Pressure Signals during Liquid‐Liquid Two‐Phase Flow

Liquid‐liquid two‐phase flows are encountered in several process industries, multiphase reactors and oil industries. In each of these applications, identification of flow patterns poses a challenging problem and many efforts are directed towards developing suitable devices for this purpose. In the present work, attempts have been made to use pressure gradient and transient pressure signals to study flow patterns during the simultaneous flow of two liquids through a horizontal pipe. It is observed that the slope of the pressure gradient curves as a function of fluid superficial velocities is a weak function of the flow pattern. However, the variation of the slope with the pattern transition is much more significant when the pressure gradient is normalized with respect to only kerosene flow through the pipe (Δp_TP/Δp_KO). Further attempts have been made to identify flow patterns from transient pressure signals and the statistical analysis of these random signals has been undertaken. The PDF analysis and the wavelet multiresolution technique have been adapted to explain the signals in detail. The flow regimes identified are smooth stratified, wavy stratified, plug flow, ‘three‐layer' flow, ‘oil dispersed in water and water' and ‘oil and water in oil' flow patterns. The signal characteristics are depicted for each flow pattern.     

X-ray Diffraction and 151Eu Mössbauer Spectroscopic Study of the Hf1−xEuxO2−x/2(0 ≤x≤ 1.0) System

Powder X-ray diffractometry (XRD) and ¹⁵¹Eu Mössbauer spectroscopy were performed for samples prepared in the temperature range 1500–1500°C for the hafnia–europia (HfO₂–Eu₂O₃) system Eu _x Hf_{1− x} O_{2− x /2}(0 ≤ x ≤ 1.0). The XRD results showed that two types of solid solution phases formed in the composition range 0.25 ≤ x ≤ 0.725: an ordered pyrochlore-type phase in the middle-composition range (0.45 < x < 0.575) and a disordered fluorite-type phase, enveloping the pyrochlore-type phase on both sides, in the composition ranges 0.25 ≤ x ≤ 0.40 and 0.60 ≤ x ≤ 0.725. ¹⁵¹Eu Mössbauer spectroscopy sensitively probes local environmental changes around trivalent europium (Eu³⁺) caused by the formation of these solid solution phases. In addition to the broad, single Mössbauer spectra observed in this study for the Eu³⁺, the values of isomer shift (IS) exhibited a pronounced minimum in the neighborhood of the stoichiometric pyrochlore phase ( x ≈ 0.5). Such IS behavior of Eu³⁺ was interpreted based on the XRD crystallographic information that the ordered pyrochlore phase has a longer (in fact, the longest) average Eu–O bond length than those of the disordered fluorite phases on both sides or the monoclinic (and C-type) Eu₂O₃at x = 1.0.     

Flame Temperature Calculations at High Temperature and Pressure

In the past, real gas effects on the flame temperature were evaluated using the virial equation of state. Usually, the virial expansion was truncated after the third term. In this work the equation of state for dense gases proposed by Haar and Shenker is considered. The implementation developed for H₂O, CO, CO₂, H₂, and N₂ by Powell, Wilmot, Haar and Klein is used. The contribution of all minor species is assumed to be approximated by a Lennard-Jones gas with ϵ/k = 100 K and σ = 3.0 Å. It is found that the more conventional approach is valid up to a loading density of 0.2 g/cm³. As density increases real gas effects cause the calculated flame temperature to decrease and the calculated pressure to increase. A computer program to perform the calculations has been devised for a personal computer.     

Interfacial Tension of CO2 and Organic Liquid under High Pressure and Temperature

In order to investigate the effect of organic liquid molecular structure and the intermolecular force operating with CO₂ molecules and organic liquid molecules on interfacial tension (IFT) between CO₂ and organic liquid at the first contact, the interfacial tension between CO₂ and hexane, octane, ethanol and cyclohexane at different temperatures and pressures is measured by using the pendant drop method and the axisymmetric drop shape analysis (ADSA). The results show that the interfacial tension between CO₂ and organic liquids is affected by the polarity and the structure of the organic liquid molecule obviously. The intermolecular force operating within CO₂ molecules or organic liquid, and that between CO₂ and organic liquids molecules play a dominate role on the interfacial tension between CO₂ and the organic liquids.