Topological model of alkali germanate glasses and exploration of the germanate anomaly

Germanate glasses are of particular interest for their excellent optical properties as well as their abnormal structural changes that appear with the addition of modifiers, giving rise to the so-called germanate anomaly. This anomaly refers to the nonmonotonic compositional scaling of properties exhibited by alkali germanate glasses and has been studied with various spectroscopy techniques. However, it has been difficult to understand its atomic scale origin, especially since the germanium nucleus is not easily observed by nuclear magnetic resonance. To gain insights into the mechanisms of the germanate anomaly, we have constructed a structural model using statistical mechanics and topological constraint theory to provide an accurate prediction of alkali germanate glass properties. The temperature onsets for the rigid bond constraints are deduced from in situ Brillouin light scattering, and the number of constraints is shown to be accurately calculable using statistical methods. The alkali germanate model accurately captures the effect of the germanate anomaly on glass transition temperature, liquid fragility, and Young's modulus. We also reveal that compositional variations in the glass transition temperature and Young's modulus are governed by the O–Ge–O angular constraints, whereas the variations in fragility are governed by the Ge–O radial constraints.     

A study of viscous dissipation in the calendering of power-law fluids

A finite difference procedure was used to solve the equation of conservation of energy with the lubrication approximation. The temperature profiles due to viscous dissipation in the gap formed by a pair of equal sized rolls rotating at the same speed exhibit two maxima in the vicinity of the roll surfaces. The maximum temperatures also exhibit two local maxima and a minimum in the direction of flow. The calculated temperature distributions across and along the flow field reveal the possibility of excessive local heating which might be detrimental for certain temperature sensitive materials such as poly(vinyl chloride) and rubbers.     

High-Temperature Density Determination of Boron Oxide and Binary Rubidium and Cesium Borates

Density determinations of pure B₂O₃ and binary rubidium and cesium borates have been made in the temperature ranges 450° to 1300°C and 500° to 1100°C respectively. The density of B₂O₃ can be represented between 600° and 1000°C as d = 1.3388 + 228 (1/T) and for temperatures above 1000°C as d = 1.3947 + 157.9 (1/T), where d is in grams per milliliter and T is in °K. The volume expansion (dV/dT) in the alkali borate systems at 800°C increases with an increase of alkali oxide when the alkali concentration is more than 18 mole %. This increase in the volume expansion follows the order Cs > Rb > K > Na > Li. In the range 15 to 20 mole % alkali oxide a break in the volume expansion was observed. This break suggests a possible change in the structural configuration of the alkali borates.     

Effect of mixed methyl ketones on the catalyzed resorcinol based oscillatory reaction at different temperatures

The present investigation establishes a comparative trend on the single, binary and ternary reaction systems having resorcinol as main substrate, inorganic bromate as oxidant and different metal ions as catalysts. However, in binary system, acetone has been added (v/v) to the skeletal (single) reaction system as co-substrate and in the ternary system, acetone with butanone, pentanone; hexanone and acetylacetone have been added (v/v) to the skeletal system in order to monitor the oscillatory parameters in presence of mixed methyl ketones at different temperatures. It is found that the temperature; the enolization constant and the hydrophobic interactions influence the oscillatory behavior as well as the formation of the end products in both binary and ternary reaction systems under investigation. The interpretation of the kinetic data revealed that the rate of bromination reaction increases with a decrease in the enolization constants of methyl ketones leading to a decrease in the time period of the oscillations.     

Constitution and Microstructure of Some Binary Alkali Halide Mixtures

The constitutions of binary alkali halide systems are considered for the fluorides, chlorides, and bromides of lithium, sodium, and potassium. These systems are divided equally into those that are simple binary systems having a common ion and those that are capable of double decomposition into reciprocal salt pairs, AB + CD ⇌ AD + BC. The simple binary systems having been examined previously, the present work was principally concerned with the constitution of the pseudobinary systems. Using thermal analysis, X-ray methods, and microscopy, the liquidus and temperature horizontals were determined for 18 such systems and the equilibria were interpreted with reference to quaternary systems. The tendency of a given salt pair to precipitate the reciprocal salts may be related to the relevant lattice energies. Microscopic examination of directionally frozen specimens revealed that true binary eutectic mixtures freeze with regular two-phase distributions very similar to those observed in metallic eutectics; these distributions are illustrated.     

EXPERIMENTAL STUDIES OF NUCLEATION PHENOMENA WITHIN THERMAL BOUNDARY LAYERS—INFLUENCE ON CHEMICAL VAPOR DEPOSITION RATE PROCESSES

In carrying out partial vapor condensations using actively cooled surfaces it is known that 'mist' formation can occur within thermal boundary layers (Rosner and Epstein, 1968), dramatically modifying total deposition fluxes. Using a combination of flash-evaporation (Rosner and Liang, 1986) and laser probing techniques, we report new experimental results on binary alkali salt (K₂SO₄ + Na₂SO₄) deposition from combustion gases showing that the deposition rate of potassium sulfate first increases with the addition of sodium sulfate until the concentration of Na₂SO₄ reaches a (target surface temperature dependent) 'threshold' value. Further increases in the concentration of Na₂SO₄ dramatically decrease the total deposition rate of K₂SO₄, implying that potassium sulfate-containing microdroplets are formed within the thermal boundary layer, which, despite their thermophoretic drift toward the target, are not collected as effectively as the 'parent' K₂SO₄-vapor species. Laser light scattering measurements clearly reveal that suspended particles exist near the deposition surface under these conditions. Our experimental results on mass transfer rate and light scattering are consistent with those predicted using laminar boundary layer theory (Castillo and Rosner, 1989b) coupling both binary salt vapor deposition with particle vapor scavenging and deposition. Comparisons of our observed mist onset conditions (implying critical supersaturations near unity) with those expected using homogeneous nucleation theory suggest that the binary alkali sulfate mist nucleation mechanism is, instead, heterogeneous, even in our relatively 'clean' combustion products. Because of the; well-known vapor pressure reduction phenomenon associated here with the formation of non-ideal solutions, binary systems are shown to provide convenient 'vehicles' to investigate BL mist formation onset conditions and CVD-rate consequences without requiring the more extreme surface coolings characteristic of unary condensible vapor systems. An understanding of this dramatic phenomenon, obtained via such laboratory experiments and calculations, will allow its inclusion in future deposition rate calculations of engineering importance.     

Investigation of the Phase Diagram of the Na2O–B2O3–SiO2 System by the Small-Angle X-ray Scattering Technique

Sodium borosilicate melts containing 60 mol % SiO₂ are investigated in the temperature range T _g–1100°C by the small-angle X-ray scattering (SAXS) technique. The temperature dependences of the SAXS intensity for the studied melts consist of two linear portions. A change in the slope of these portions is observed at temperatures that coincide, to within the accuracy of the SAXS experiment (±5–10 K), with the liquidus temperatures, which are usually determined to approximately identical accuracy. The change in the slope is associated with the change in the temperature coefficients of the isothermal compressibility upon transition from a liquid state to a supercooled liquid state. Similar results were obtained earlier for binary melts in the sodium borate system and a number of other systems. On this basis, it is assumed that the transition from a liquid state to a supercooled liquid state for melts in any glass-forming system can be revealed from the temperature dependences of the SAXS intensity, and the SAXS technique can be used to determine the liquidus temperatures, primarily for glass-forming melts with a low crystallization ability.     

Characterization and continuous extrusion of isotropic and anisotropic poly(p-phenylene terephthalamide)/sulfuric acid solutions to form ribbons and blown film

An experimental characterization and processing study of redissolved Kevlar® and poly(p-phenylene terephthalamide)/sulfuric acid solutions is reported. Polarized light microscopy studies show the development of an anisotropic phase. When two phases coexist, negatively birefringent spherulites are observed. At higher concentrations, a single phase of coalescing spherulites is seen and following melting and subsequent cooling, nematic (threadlike) structures are observed. Viscosity and normal stresses were measured at various concentrations and temperatures. A yield stress is exhibited at room temperature. Both room temperature and 60°C viscosity vs concentration curves display maxima. The solution in concentration ranges from 2 to 12 percent have been extruded as ribbons and as annular blown tubular film. Processing variables and problems are discussed. Wide angle X-ray scattering patterns of films show orientation. Tensile properties have been measured on films.     

煤催化气化工艺中内蒙王家塔烟煤灰烧结温度的影响因素分析

煤催化气化工艺中碱金属催化剂的引入加剧了气化炉的结渣,直接影响了流化床气化炉结渣的正常操作。煤灰的烧结特性是流化床气化炉结渣的主要影响因素之一,通过摸索工艺条件使煤气化在烧结温度以下运行,可有效避免流化床气化炉内出现结渣问题。利用压差法测定烧结温度,结合灰渣的XRD分析结果系统研究了钾基碱金属催化剂的添加量、操作压力、反应气氛对王家塔烟煤低温灰化煤灰烧结温度的影响。结果表明,碳酸钾催化剂的添加明显降低了煤的灰熔点及烧结温度。0.1～3.5 MPa下,烧结温度随压力增大而降低,而且压力对烧结温度的影响在高压区更为明显,具体影响规律与煤种灰成分及钾基碱金属催化剂的添加有关。空气、CO₂氧化性气氛下的烧结温度较高,N₂惰性气氛下次之,还原性气氛下较低,而蒸汽的加入显著降低了烧结温度。烧结温度的变化与不同气氛下铁离子存在状态及钾的存在形态密切相关。蒸汽气氛下,钾更多以KOH等低熔点化合物形态存在,而且含钾物相在蒸汽气氛下更容易同煤灰中的硅铝、铁钙等矿物质反应,生成低共融点化合物,致使灰熔点及烧结温度大幅下降。     

High temperature elasticity measurements on oxides by Brillouin spectroscopy with resistive and IR laser heating

Knowledge of single crystal and aggregate elastic moduli of materials at high temperature is important in the development of high-temperature structural ceramics as well as for other areas of material sciences. Sound velocities, and hence elastic moduli, can be readily measured on micro-crystals, polycrystalline aggregates and amorphous materials using Brillouin scattering. We have developed techniques for determining the elastic moduli at high temperatures, using both electric resistive heating (to 1800 K) and CO₂ laser heating (to T > 2500 K). The full set of elastic constants of transparent oxides at high temperatures can be measured on samples with dimensions of 100 × 100 × 20 μm or even smaller. Compact resistance heaters of our design were used to study the temperature dependence of the elastic moduli of a variety of crystalline oxides and glasses, and can be used to observe high-temperature phase transitions involving elastic softening. The combination of Brillouin scattering with CO₂ laser heating allows measurements of the elastic moduli of oxides at even higher temperatures, approaching the melting points of refractory materials. The acoustic velocities of single-crystal MgO were measured to a maximum temperature exceeding 2500 ± 100 K. Both Brillouin and Raman measurements were performed on CO₂ laser-heated samples of single-crystal α-Al₂O₃ to temperatures exceeding 2000 ± 100 K. Our results show that Brillouin scattering coupled with CO₂ laser heating is a viable means of performing sound velocity measurements at temperatures significantly higher than those readily made using resistance heating.     

Experimental Investigation and Thermodynamic Description of the Constitution of the Ternary System Cr-Si-C

The constitution of the ternary system Cr-Si-C is investigated using differential thermal analysis and X-ray diffractometry techniques. Eight invariant reaction temperatures involving the liquid phase are determined. The crystal structures and phase partitions observed for the subsolidus temperature region confirm literature data. Thermodynamic modeling, using a minimum of adjustable ternary parameters and assuming the binary high-temperature phase, β-Cr₅Si₃, to be stabilized toward lower temperatures as ternary D 8₈-type Cr₅Si₃C _x , generally reproduces the measured temperatures within 10 K. The calculated liquidus surface contains four ternary eutectics, three transition reactions, three degenerated reactions, and five (pseudobinary eutectics) maxima. The reaction scheme shows that no solid-phase reactions occur in the Cr-Si-C system at >1000°C, except for the binary transition β-Cr₅Si₃↔α-Cr₅Si₃. The activity diagram along the section Cr-SiC at 1300°C, computed from the optimized data set, agrees with the observed diffusion path.     

Phase behavior of poly(methylmethacrylate) and poly(styrene-co-acrylonitrile) blends

Summary Laser light scattering was used to study the miscibility behavior of PMMA/SAN blends. These systems tend to phase separation at elevated temperatures, Above the lower critical solution temperature (LCST) a regular highly interconnected two-phase morphology is displayed. The region of stability of this structure is determined. Finally, the binary interactional parameter is estimated. It is negative due to the sufficiently repulsive intramolecular interactions relative to the repulsive intermolecular interactions.     

A new kinetic model for interdiffusion at semicrystalline polymer interfaces

A kinetic model has been developed to describe the behavior of semicrystalline polymer interfaces. In these systems, the competition between interdiffusion and crystallization drives the overall transport. The crystallization rate is based on the Avrami equation, in which the Avrami exponent and the crystallization rate constant as a function of temperature and blend composition are determined by in situ optical microscopy and differential scanning calorimetry. The mutual diffusion coefficient is obtained by using the fast mode theory. The predicted density profiles as a function of position are used to extract the interfacial widths, which are affected by molecular weight, equilibrium degree of crystallinity, and temperature. At low temperatures, the crystallization rate is fast, and the crystals present near the interface hinder the interdiffusion, causing the interfacial width to be small. At high temperatures, the crystallization is much slower, and interdiffusion dominates crystallization. The model predictions are compared with interfacial behavior observed by transmission electron microscopy and small angle X-ray scattering in a system composed of polyethylene and isotactic polypropylene and the agreement with the experiments is satisfactory.     

Brillouin scattering study of gelatin gel using a double passed Fabry-Perot spectrometer

The Brillouin spectrum of gelatin gels has been recorded at room temperature as a function of concentration of gelatin, using a double passed Fabry-Perot spectrometer. It was found that both the Brillouin shifts and line-widths increase linearly with concentration. In the case of the line-widths it was shown that the rate of increase was sensitive to the thermal history of the gels, being greater for gels cooled slowly. Explanation of the results in terms of a relaxation phenomenon is improbable. The observations can however be explained in terms of the structure of the gel. Expressing this structure as a number density of crosslinks, which is dependent on the concentration of gelatin, the increase in Brillouin shift is consistent with the change in bulk properties. The increase in line-width is shown to be caused by the crosslinks scattering the sound waves in the gel.     

Material response and reversible cracks in viscoelastic polymers

Deformation processes in viscoelastic polymers are examined in terms of an energy balance involving work, strain energy, viscous dissipation and damage. The concepts of time dependent damage and reversible cracks are presented. The latter, while giving rise to novel mechanical behavior in viscoelastic materials, are important considerations in temperature dependent recovery phenomena of deformed polymers. Constitutive equations are derived for systems with reversible cracks analogous to Maxwell and Kelvin viscoelasticity models. Retractive forces arising from crack closure occur by conversion of surface energies to strain energy and subsequently to mechanical work. This effect is investigated during contraction of hard-elastic polypropylene fibers under constant load at different temperatures.     

三种脂肪酸乙酯声速的实验测量与理论估算

生物燃料作为化石燃料的替代物越来越受到人们的关注,脂肪酸乙酯（FAEEs）是生物燃料中的重要成分。为了获取生物燃料组分的物性参数,补充现有数据不足,利用布里渊散射法对3种脂肪酸乙酯的声速进行了测量,测量温度范围为293.15~473.15 K,压力为0.1 MPa。为方便工程应用,实验数据被拟合成温度的函数,实验值与关联式计算值的相对偏差绝对平均值为：0.13%（己酸乙酯）、0.11%（庚酸乙酯）、0.08%（辛酸乙酯）。实验数据也被用来评估两种生物燃料声速预测方法,结果表明,Wada模型优于Auerbach模型,更适合脂肪酸乙酯的声速预测。     

Formation of AlN-Polytypoid Phases during α-SiAlON Decomposition

Phase transformations from α– to ß–SiAlONs (i.e., from α' to ß') have been recently reported in a number of rare-earth SiAlON systems during postsintering heat treatment. In the present work, this transformation process in a Sm (α+ß)-SiAlON material is studied by using XRD, TEM, and EDS X-ray mapping techniques. It is observed that in addition to the formation of ß' and M' phases, the α'-to-ß' transformation is accompanied by a significant increase in the amount of an AlN-polytypoid phase. The results suggest that some α' phases are thermodynamically unstable at temperatures lower than the material sintering temperature and will decompose when conditions allow. For the composition studied in this work, the α-SiAlON decomposition can be described in general as α'→ß'+ M'+ AlN polytypoid.     

Micro-phase separation and crystallization behavior of amorphous oriented PLLA/PVAc blends during heat treatment under strain

Amorphous oriented poly(l-lactide) (PLLA)/poly(vinyl acetate) (PVAc) 50/50 films were prepared by uniaxial drawing of melt-mixed blends at 65 °C. The morphology development and crystal organization of the blends during heat treatment under strain were investigated using small angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). Equatorial scattering maxima in the SAXS patterns for samples annealed at 75 °C were observed before the appearance of crystal reflections. Further annealing of the samples at higher temperature induced two further discrete meridian scattering maxima. The observations indicated that homogenous oriented PLLA/PVAc film undergoes micro-phase separation first, followed by crystallization of PLLA in the PLLA-rich phase. The micro-phase separated PVAc nanodomains are aligned parallel to the stretching direction, whereas the crystallized PLLA lamellae are oriented perpendicular to the stretching direction (crystal c-axis along the stretching direction). Micro-phase separation was not observed when films were annealed at 120 °C, at which temperature the high crystallization rate of PLLA overwhelmed the micro-phase separation process.     

Control of the Properties of Glazes by the Aid of Eutectics

Published equilibrium eutectics and other low-temperature invariant points were investigated regarding deformation temperatures and rates. Their solubility in dilute acid, alkali, and phosphate solutions was also studied, and the one showing no solubility and the lowest deformation temperature was chosen as the center of the deformation series in each of the alkali-alumina-silica systems. The KAS, LAS, and NAS deformation eutectics were assembled in a triaxial system in which fusion temperatures and rates were determined, and the deformation eutectic was thus determined. Similar data were developed on combinations of the individual alkali eutectics and the lead-alumina-silica deformation eutectic reported in Part I of this study. The deformation eutectic of the combined alkali series and the lead-alumina-silica eutectic were combined in a series and the deformation eutectic was determined.     

A comparison of two theoretical analyses of the elastodynamics of poly(vinyl alcohol) hydrogels

In two recent publications, Brillouin scattering measurements of the hypersonic velocity and attenuation in poly(vinyl alcohol) (PVA) hydrogels were analysed using two different theoretical models. These are the theories of Marqusee and Deutch for Brillouin scattering from gels and of Johnson for the elastodynamics of gels. In this work we take an overview of our previous results and also present new results particularly regarding a pair of important gel parameters. These new aspects enable us to compare critically the results obtained from the two theories and to comment on the suitability of the models to Brillouin scattering from PVA hydrogels.