Showing papers on "Phase (matter) published in 1968"

The effect of temperature on the phase equilibria and the types of dispersions of the ternary system composed of water, cyclohexane, and nonionic surfactant

Abstract: The phase diagrams of water-cyclohexane systems containing 3 and 7 wt. % of polyoxyethylene (9.7) nonylphenylether have been determined as a function of temperature. In addition to solubilized regions in aqueous and in nonaqueous solutions, the importance of the three-phase realm (water, hydrocarbon, and surfactant phases) has been emphasized. The characteristic temperature at which the mutual solubility of oil and water increases markedly by the aid of nonionic surfactant is closely related to the phase inversion temperature in emulsions. The marked increase in mutual solubility may result from the sandwich-like structure of surfactant, water, and oil layers. The dispersion types of the system have been determined over a wide temperature range. Besides the usual W O type and O W type, W D , D W , D O , O D , and (W+O) D types have been observed, where D represents the surfactant phase. Except for the extreme volume fraction range, the water phase is continuous at low temperature, the oil phase is continuous at high temperature, and the surfactant phase is continuous at a medium temperature near the phase inversion temperature.

Dynamical Theory of the Phase Transition in KH2PO4-Type Ferroelectric Crystals

Abstract: Dynamical aspects of the ferroelectric phase transition in KH 2 PO 4 -type crystals are elucidated on the basis of the coupling between the proton tunneling mode and the optical mode vibration of the [K-PO 4 ] complexes along the c-axis. Two coupled modes are obtained within the framework of a linear theory. The mode in which both systems oscillate in phase is shown to be responsible for the ferroelectric phase transition. The isotope effect in the Curie point is explained qualitatively and the Curie constant is estimated.

An approach to the study of phase separation in ternary aqueous systems.

Abstract: 1. Simple thermodynamic expressions are used to describe the properties of uncharged binary and ternary polymer solutions, in particular the sedimentation equilibrium of binary systems and the osmotic pressures and ‘incompatible’ phase separations of ternary systems. 2. Sedimentation-equilibrium experiments were performed on four samples of dextran and two of polyethylene glycol. The critical points of the phase diagrams were determined for the mixed solutions of polyethylene glycol–dextran–water and of polyethylene glycol–bovine serum albumin–0·2m-sodium chloride solution. Osmotic pressures were measured on a single-phase mixed solution of a polyethylene glycol and a dextran. By use of the simple thermodynamic expressions consistent values of second virial and interaction coefficients for the materials used were obtained from these experiments. 3. The interpretation of the values of the second virial and interaction coefficients, on the basis of three models of molecular interaction, is discussed.

High flow membrane

Abstract: AN ANISTROPIC HIGH FLUX LOW PRESSURE POLYMERIC MEMBRANE CAPABLE OF BEING DRIED WITHOUT LOSS OF BENEFICIAL MECHANICAL AND PROCESSING CHARACTERISTICS, AND HAVING IN A CONTINUOUS POLYMER PHASE A BARRIER LAYER CONTAINING PORES FROM 1 TO 1000 MILLIMICRONS IN DIAMETER AND AN OPEN POROUS SUPPORT LAYER, THE POLYMER ABSORBING LESS THAN 10 PERCENT MOISTURE AT 100 PERCENT RELATIVE HUMIDITY AT 25*C.

Formation and stability of the platinum and rhodium oxides at high oxygen pressures and the structures of Pt3O4, β-PtO2 and RhO2

Abstract: The systems Pt-O and Rh-O have been investigated at high oxygen pressures (up to 3500 atm) and temperatures ranging from 400 ° to nearly 900 °C. Three platinum oxide phases were found: the hexagonal α-PtO2, already described in the literature, a new phase, β-PtO2 (CaCl2 structure), and Pt3O4 (NaxPt3O4 structure). β-PtO2 andPt3O4 are black, highly insoluble solids, which can be easily synthesized in bulk at high oxygen pressures. The tetragonal PtO phase reported by Moore and Pauling was not encountered in this study and neither was the b.c.c. Pt3O4 found by Galloni and Roffo . In the system Rh-O we found (besides the already-known, two Rh2O3 polymorphs) a new RhO2 phase with the rutile structure. RhO2 is a black, easily synthesized solid, which is highly insoluble even in hot aqua regia. “Goldschmidt radii” were derived for Pt4+ and Rh4+ and found to be 0.66 A and 0.64 A, respectively.

Macroreticular resins. III. Formation of macroreticular styrene–divinylbenzene copolymers

Abstract: Experimental evidence is presented that describes the mechanism of formation of macroreticular styrene–divinylbenzene copolymers in which phase separation occurs during a suspension polymerization. The mode of formation of the macroreticular structure is described as a three-stage process in which each droplet of the organic phase behaves as an individual in a bulk polymerization that results in a bead of copolymer. Macroreticular structure formation is described by changes in copolymer swelling ratios, infrared absorption spectra of vinyl groups pendent to the polymeric matrices, surface area, total porosity, and pore-size distribution. The proposed mechanism of formation is also substantiated by electron micrographs of the copolymers during various stages of the copolymerization.

Enthalpy Changes and Heat‐Capacity Changes in the Transformations from High‐Surface‐Area Amorphous Ice to Stable Hexagonal Ice

Abstract: Amorphous ice prepared by slow condensation of water vapor onto a surface cooled with liquid nitrogen or liquid hydrogen undergoes several exothermal transformations on warming. Thermal analysis by means of warming curves indicates that the heat liberated on warming ice prepared at − 253°C is 8 cal/g from − 253° to − 196°C and 22 cal/g from − 196° to − 120°C.Ice prepared at − 196°C gives up 14 cal/g between − 185° and − 125°C. These enthalpy changes are attributed in part to decreases in the surface area of the amorphous ice. Beginning at − 120°C, 24 cal/g heat is evolved on crystallization to the cubic form (ice Ic). Between − 80° and − 50° an additional 3 cal/g is attributed to recrystallization of the cubic phase to larger crystals. In the cubic to hexagonal (ice Ih) transition between − 50° and − 5°, ΔH is less than ±0.3 cal/g, but a decrease occurs in the low‐temperature heat capacity. The heat capacity of amorphous ice or ice Ic in the range − 170° to − 120°C exceeds that of ice Ih by 27% and the heat capacity of ice Ic between − 120° and − 70°C exceeds that of ice Ih by 12%. The higher heat capacity of ice Ic is attributed to a greater degree of order at low temperature. Heat evolved in the hypothetical transition from amorphous ice at − 253°C to ice Ic at the same temperature is 55 ± 5 cal/g. No glass transition was observed in amprophous ice. Within experimental error, the enthalpy and heat‐capacity changes are the same in D2O as in H2O.

Electric-Field-Induced Phase Change in Cholesteric Liquid Crystals

Abstract: Optically-negative cholesteric liquid-crystal films can be transformed to an optically-positive state by applying high d-c electric fields A phase transformation occurs in which the helicoidal cholesteric structure is converted to either a planar smectic, or a linear nematic, structure The threshhold field for this transformation has been studied as a function of sample thickness, temperature and composition Bulk fields are responsible for the phenomenon It is inferred that the compositional dependences are due to size factors and internal molecular dipole moments

Ice IX: An Antiferroelectric Phase Related to Ice III

Abstract: The dielectric properties of ice III in the frequency range 10−1 to 105 cps have been measured down to − 160°C. There is a gradual transition from the orientationally disordered III to an orientationally ordered and probably antiferroelectric phase, which is designated IX, starting at about − 65°C and reaching completion at about − 108°C. An arrangement of the hydrogen atoms in ice IX is proposed. The amplitude of the orientational polarization decreases continuously through the transformation region although the relaxation time is close to the value extrapolated from previous measurements in the disordered phase. The limiting high‐frequency dielectric constant of the dispersion decreases with decreasing temperature. The cause of this behavior, which is unusual for molecular crystals, is undoubtedly that the polarization of the lattice vibrations contributes a large part of the high‐frequency dielectric constant. This contribution decreases with decreasing temperature because the decreasing anharmonic interaction increases the absorption frequencies. The high‐frequency dielectric constant decreases by about 5.7% at the III‐IX transition although there is little volume change; this decrease might be a valuable way of detecting order‐disorder transitions, particularly if they proceed slowly. The infrared polarizabilities of the various phases are briefly discussed. Ice IX could not be warmed into III because it always transforms to the more stable ice II.

Pinning of flux vortices in type-ii superconductors.

Abstract: The superconducting properties of Pb-Bi alloys are reported. Measurements were made on the epsilon phase (a reversible material with K ∼ 12) and the eutectic, which is this epsilon phase with pure Bi precipitates. It is shown that the irreversible properties of the eutectic are consistent with the pinning of vortices in a reversible matrix of epsilon phase. The critical state is shown to be the same in measurements of magnetization, transverse critical currents and zero field critical currents, and it is extended to cover a composite ferromagnetic material. Experimentally it is found that the variation of critical current with flux density, microstructure and temperature is given by the expression J c = 33S v M(rev.)/B1/2 amps/sq.cm. (S v is the phase boundary area per unit volume and M (rev.) the magnetization of the matrix.) There is strong evidence that the irreversibility is due to pinning at the phase boundaries of precipitates and it is found that the surface currents observed in the epsilo...

Isothermal compression of the alloys of iron up to 300 kilobars at room temperature: Iron-nickel alloys

Abstract: The effect of pressure on the crystal structure and the molar volume of iron alloyed with 5 and 10% nickel was determined up to 300 kb at room temperature by means of X-ray diffraction techniques employing a diamond-anvil high-pressure cell. The alloys undergo a reversible bcc-hcp phase transformation, which is accompanied by a volume change of −0.36 ± 0.02 cm3/mole. The crystallographic axis ratio, c/a, of the hcp phase appears to increase with nickel content, whereas it appears to be unaffected by pressure. The bulk moduli calculated from the volume data for the bcc and hcp phases of the alloys do not differ significantly from those for the respective phases of iron. The bulk modulus value for the hcp phase evaluated at zero pressure has been calculated to be 2.06 ± 0.15 Mb and is about 20% greater than that for the bcc phase. The volume of the hcp phase at zero pressure has been calculated from the pressure-volume data by extrapolation. A value of 6.67 ± 0.02 cm3/mole has been obtained for iron and the alloys. The pressure-volume relationship obtained by this work is consistent with the results obtained by R. G. McQueen and S. P. Marsh (1960, 1966) using shock compression techniques.

On the application of phase relationships to complex structures

Abstract: The direct-methods program SAYTAN is applied to data at various restricted resolutions for a small protein. It is shown that useful sets of phases can be obtained even down to 3 A resolution. Conventional figures of merit are not very discriminating for the phase sets developed, but modified figures of merit seem capable of selecting the better phase sets, at least for those generated from 2 A or higher resolution data.

Diffusion during the coagulation step of wet-spinning

Abstract: The coagulation of viscous polymer solutions by diffusional interchange with a liquid bath is the key step to fiber formation by wet-spinning. Model experiments were performed on gelled solutions of an acrylic polymer in dimethylacetamide, to determine the mass-transfer rates of solvent and nonsolvent (water) during coagulation, the rate of movement of a boundary associated with coagulation, and the final equilibrium between the coagulated phase and the bath. Each is given as a function of bath composition and temperature. The data are analyzed by means of various diffusion models, one of them giving quite good agreement. The data and the models are used in conjunction with each other for the elucidation of the mechanism of the processes involved in coagulation.

Subliquidus Immiscibility in Binary Alkali Borates

Abstract: The phase boundaries of subliquidus immiscibility in the lithium, sodium, potassium, rubidium, and cesium borate systems were determined. Two-phase structures were developed in thermal gradients and examined by direct-transmission electron microscopy. No opalescence was observed. Microstructures were of the order of a few hundred angstroms. The extent of immiscibility in each system was determined by the approximate intersection of the immiscible phase boundary with the glass transition region.

A study of optimal phase boundaries: the case of exsolved alkali feldspars

Abstract: A general theory of grain and phase boundaries (the O-lattice theory) is further developed and tested on alkali feldspars with exsolution lamellae, since measurements exist for the structures of the two-phase system (perthitic feldspars) as well as for the orientation of the phase boundary. It is shown that in this case the adaptation of two monoclinic structures is energetically preferable to the adaptation of a monoclinic and a triclinic one. The phase boundary energy is markedly lower in the former case. Thus, a pseudo-monoclinic structure is produced out of the triclinic by periodic submicroscopic twinning. The calculated orientation of the phase boundary is in close agreement with the measurements.

Shrinkage and Thermal Expansion of a Two Phase Material

Abstract: THE problem of deducing theoretically the shrinkage of a two phase composite material in terms of the properties of its components has been considered by Pickett1 and by Hansen and Nielsen2. They were specifically interested in concrete, but the problem has a wider application and is also identical with the problem of deducing the coefficient of thermal expansion for a similar material.

Phase Diagrams of H2O and D2O at High Pressures

Abstract: The VIII/VII phase boundaries of solid H2O and D2O were studied by means of differential thermal analysis. The thermal hysteresis of the transition decreases with increasing pressure, but the presumed equilibrium temperatures are independent of pressure to 40 kbar. The transition is of the first order, and the average transition temperature is −3°C in both cases. The ice VI/VII transition pressure at 25°C is 21.39 ± 0.05 kbar, in good agreement with other recent studies, but considerably lower than Bridgman's value. The heavy ice VI/VII and VI/VIII transition lines are located ∼1.4 kbar below the ice VI/VII and VI/VIII transition lines. The heavy ice VI/VII transition at 25°C occurs at 19.90 ± 0.07 kbar. Bridgman's melting curves of ice VI and ice VII are shown to be correct. The melting curve of heavy ice VI is ∼2°C above that of ice VI, but the heavy‐ice VI/VII/liquid triple point is located at 78°C, 20.6 kbar as compared with 81.6°C, 21.97 kbar for H2O. The melting curve of heavy ice VII appears to have a stronger curvature than the melting curve of ice VII.

Electron microscopy of orthorhombic phase in magnetite

Abstract: An electron microscopic observation on a synthetic single crystal of magnetite has been carried out at a temperature range between 77°K and room temperature. It was observed that the ordered phases below the low‐temperature transition appear as finely divided stripes. The diffraction patterns in one of the stripes show the extra spots such as (00½), (100), (010), or (11½) in cubic indices. This indicates that the unit cell of the low‐temperature phase should be twice as large as that proposed by Verwey. The ordering scheme proposed should be more complicated than the Verwey order.

Size and Shape of Montmorillonite Particles Saturated with Na/Ca Ions (Inferred from Viscosity and Optical Measurements)

Abstract: The viscosity and light transmittance of montmorillonite suspensions saturated with Na+, Ca++ and known mixtures of these ions in the adsorbed phase were investigated. Introduction of a small fraction of Na+ (10% – 15%) into the exchange complex of Ca—clay, does not result in the breakdown of the tactoids. The breakdown of the tactoids occurred when the equivalent fraction of Na increased from 0.2 to 0.5. Montmorillonite clay saturated with 50% calcium (and less) exists as single platelets. Combining the structural data with an equilibrium equation based on the diffuse double layer theory indicates that when tactoids are formed, demixing occurred by which Na+ ions are concentrated on the external surfaces of the tactoids and Ca++ ions on the internal surfaces.

Liquid–liquid phase separation in multicomponent polymer solutions. I. Statement of the problem and description of methods of calculation

Abstract: Polymers are complex mixtures that may have widely different compositions even if they contain only components having the same chemical constitution. The effect of the chain length distribution on the phase behavior of polymer solutions in a single solvent is described qualitatively. To obtain a quantitative understanding of these phenomena a numerical calculation method is developed which is based on the Flory-Huggins relation for the free energy of mixing. Some examples are presented, and the accuracy and the reliability of the results are discussed.

Primary and secondary phase separation of sodium silicate glasses

Abstract: The immiscibility curve in the system Na2OSiO2 shows that the amount of Na2O content in the silica rich phase is small at 500°C and hardly changes with temperature up to 800°C but increases sharply in the interval 800–865°C The silica content of the alkali-rich phase increases continuously with temperature The curve is thus extremely asymmetric The electron microscope photographs show that the separate phases (primary phase separation) separate again into two phases during cooling or during a second heating of the glass at a lower temperature This secondary phase separation does not depend upon the duration of the initial heating of the glass It is connected with the asymmetry of the immiscibility curve The alkali-rich phase separates more easily but with the help of a repeated treatment the silica-rich phase can also be caused to phase separate This secondary phase separation is a general phenomenon and must be given attention when discussing the number of phases in the glass Certainly the existence of triple-phase glasses cannot be excluded Phase separation of higher orders can be achieved with the help of heat treatments in several steps

Vibrational Spectra and Force Constants for Isotopic Species of Nitrosyl Chloride

Abstract: From infrared absorption studies in the gaseous phase, fundamental harmonic vibrational frequencies have been determined for 16O14N35Cl, 16O15N35Cl, 18O14N35Cl, and 18O15N35Cl. With the aid of centrifugal‐distortion data from the literature, a unique general quadratic valence‐force‐constant solution was obtained. The resulting values are: FNO = 15.26 mdyn A−1, FNCl = 1.27 mdyn A−1, Fα = 1.32 mdyn A−1·rad−2, FNO,NCl = 1.53 mdyn A−1, FNO,α = 0.1 mdyn rad−1, FNCl,α = 0.12 mdyn rad−1.