On transport properties of hot liquid and supercritical water and their relationship to the hydrogen bonding

The dynamic viscosity η of water at temperatures along the saturation line is fitted with an expression taking into account the relative void volume, the enthalpy of vaporization, and the hydrogen bonding, the latter through the Kirkwood dipole orientation correlation parameter, g_K. A similar expression is given for the fitting of viscosity data of supercritical water, except that the explicit temperature dependence of ln η on 1/RT is now negative. The self-diffusion coefficients D of water along the saturation line up to the critical point are shown to depend on the fractions of non- and singly hydrogen-bonded water molecules. The high pressure (110 MPa) values of D of supercritical water are a smooth extension of the values for lower temperature water at the same pressure.     

Chromatographic mass of a polymer and its use for determining the molecular mass characteristics

The method has been proposed for determining the molecular characteristics of flexible-chain polymers that obey the universal calibration principle and for which there are available experimental data on the intrinsic viscosity. This method is based on studying the dependence of the hydrodynamic volume M _n[η], M _w[η], M _z[η], and M _η[η] on parameter a in the Mark-Kuhn-Houwink equation. It has been found that, for parameter a varying in the range from 0.5 to 0.8, the weight-average hydrodynamic volume M _w[η] remains almost unchanged. This allows estimation of M _w based on a single intrinsic viscosity value. The notion of the chromatographic mass of a polymer is advanced and is employed for determining other molecular mass parameters.     

Variation of polymer chain dimensions with temperature below the theta point

The temperature dependence of the intrinsic viscosity [η] for the system polystyrene-cyclohexane in the interval ?20 < (T ? ψ) ≤ 0 near the ideal temperature ψ has been investigated. The observed diminution in size of the molecular coil with decreasing temperature is attributable to attractive net polymer-solvent interactions, denoted by negative values for the excluded volume parameter z. The data thus comprise an interesting selection for comparison with the predictions of various excluded volume theories. Among the approximate, closed-form expressions the functional relationship of Flory (x⁵ ? α³ ～ z) appears to describe best the variation of [η] with temperature in the region examined. The behavior of the Huggins constant k′ derived from the intrinsic viscosity plots is also examined, in accordance with the Peterson-Fixman model, suitably extended to the temperature region below ψ.     

The dependence of the lattice parameter and density of Zn1−xMnxTe on composition

The lattice parameter of the diluted magnetic semiconductor Zn_1?xMn_xTe has been determined as a function of composition. This material crystallizes in the zinc-blende structure for values of x below about 0.75. The results show that for this range of composition the lattice parameter satisfies Vegard's law and is given by a(x) = (6.103 + 0.237x) Å. This result corrects earlier published values of a(x) for this material (Juza et al., Z. anorg. allg. Chem.285, 61 (1956)), which are in considerable error. Because of its rather pronounced dependence on x, the lattice parameter provides an excellent method for determining sample composition. By extrapolating the expression of a(x) to x = 1, the results also provide a value of 6.340 ± 0.005 Å for the lattice parameter of the hypothetical zinc-blende phase of pure MnTe. The strong dependence of the lattice parameter of Zn_1?xMn_xTe on x is responsible for most of the variation of its density with composition.     

Modification of hydriding properties of LaCo5 by partial substitutions (LaCo5−xMx with M = Al,Ga)

By partial substitution of Co in LaCo₅ by nontransition metals such as Al, an increase in H capacity (z) vis-a-vis LaCo₅ is achieved at pressures on the order of 100 atm at room temperature. Lower equilibrium pressures, P_e, have been previously observed when compounds such as PrCo₅ and LaNi₅ were partially substituted on transition metal sites by nontransition metals such as Al, Be. This fact, coupled with the existence of the high-pressure phase LaCo₅H_z with z ? 9, suggests that the increased z is due to a lowering of P_e of the high-pressure phase to more modest conditions in temperature and pressure. The actual P(z) curves are, however, complex and reflect phenomenology often observed with pseudo-binaries.     

Diffusion coefficients of ions through ion excange membrane in Donnan dialysis using ions of different valence

Donnan dialysis with an ion exchange membrane was investigated for ions of different valence. The effective diffusion coefficients (D_e) of various kinds of ions in the membrane were obtained by fitting of the equation derived from the Nernst–Planck equation to three or more sets of experimental data for Donnan dialysis. It became apparent that the value of D_e/D_s of monovalent ions (e.g., K⁺ or Na⁺ ions) at z_A=1 and z_B=2 (feed ions are monovalent ones and driving ions are bivalent ones) remained constant at ca. 1/210 and that of bivalent ions (e.g., Ca²⁺, Cu²⁺, or Mg²⁺ ions) remained constant at ca. 1/526 where D_s denotes the diffusion coefficient of ions at infinite dilution in water calculated from the Nernst–Einstein equation, and z_A and z_B represent the valences of the feed and driving ions, respectively. D_e/D_s of monovalent ions (e.g., H⁺, K⁺, or Na⁺ ions) at z_A=2 and z_B=1 (feed ions are bivalent ones and driving ions are monovalent ones) was constant at ca. 1/23.3 and that of bivalent ions remained constant at ca. 1/58.4. It was proved that D_e/D using D_e at z_A=1 and z_B=2 was constant at 1/3.0 and that at z_A=2 and z_B=1 remained constant at 3.0 where D represents the diffusion coefficient of ions in the membrane at z_A=z_B (the valences of both feed and driving ions are equal). Therefore, it was found that a large flux of ions could be obtained using the monovalent driving ions in Donnan dialysis. On the other hand, the small flux can be obtained using bi- or higher-valent driving ions.     

Phase separation characteristics of (U,Nd)O2 solid solutions by high temperature oxidation

The phase separation characteristics of the Nd element from SIMFUEL (simulated spent fuel) by high temperature oxidation was investigated in terms of the temperature range between 1,150 and 1,300 °C and the initial concentration of Nd (x) in the pellets of (U_1?x Nd _x )O₂ with x = 0.03, 0.037 and 0.09. The XRD and SEM results indicate that an increase of the heat treatment temperature increases the amount of the Nd-rich (U_1?y Nd _y )O_2+v phase, while decreasing that of the Nd-poor (U_1?z Nd _z )₃O_8?w phase after heat treatment. Since the solubility of Nd in the (U_1?z Nd _z )₃O_8?w phase was almost constant regardless of the heat treatment temperature, the decrease of the Nd concentration in the Nd-rich (U_1?y Nd _y )O_2+v phase with increasing heat treatment temperature seems to be due to a diffusion of the U ions from the Nd-poor (U_1?z Nd _z )₃O_8?w phase to the Nd-rich (U_1?y Nd _y )O_2+v phase. The phase separation ratio of Nd was not nearly affected by the heat treatment temperature, but was increased with an increase in the initial concentration of Nd (x) in the pellets of (U_1?x Nd _x )O_2.00. However, the phase separation ratio of U was slightly decreased with an increase in the heat treatment temperature and was strongly decreased with an increase in the initial concentration of Nd (x) in the pellets of (U_1?x Nd _x )O_2.00.     

Synthesis, structural features, and color of calcium-yttrium hydroxyapatite with copper ions in hexagonal channels

Copper-containing calcium phosphates Ca_{5 ? z} Y _z (PO₄)₃Cu _x OH_{1 ? x ? z ?δ}, where x = 0, 0.1, 0.3 and z = 0, 0.5, with an apatite structure and a partial substitution of yttrium for calcium have been synthesized by a solid-phase method at a temperature of 1100–1150°C. The compounds have been characterized by X-ray powder diffraction and diffuse reflectance spectroscopy. It has been established that yttrium substitutes for calcium only in the Ca(2) position, and the occupancy of this position corresponds to the yttrium content z = 0.4–0.43. The substitution by yttrium slightly decreases the unit cell parameter of the compound (by ～0.3%) and much more considerably (by 3%) reduces the diameter of a hexagonal channel formed by Ca(2) atoms. The predominant fraction of doping copper intrudes into hexagonal channels in both unsubstituted and yttrium-substituted calcium phosphates. Unsubstituted copper-containing phosphates are pink-crimson colored, whereas their yttrium-substituted analogues have much more pale colors from nearly white to greeny beidge. The absorption bands typical for a copper-containing calcium hydroxyapatite observed in diffuse reflectance spectra are strongly suppressed in yttrium-substituted samples probably due to a decreased average oxidation number of copper.     

The study of phase transition of KHF2 doped with sodium ions with Raman intensities of the lattice modes as the order parameter

The phase transition of doped K_1-xNa_xHF₂ is studied with the K⁺ translatory mode and the HF⁻₂ librational mode, which are Raman active in the low temperature phase while inactive in the high temperature phase, as the order parameter. Particular attention is paid to the elucidation of the critical exponent β which is defined as the parameter relating the lattice Raman intensity to the temperature near T_c through (T_c - T)^β. β values for various dopings are interpreted to understand the dynamics of the phase transition in the critical region. The analysis shows that a very small amount of doping results in a drastically large effect in the critical region. Further doping does not induce further a critical effect in a proportional way. This enables one to define the undoped and doped systems with a very small amount of dopant as two distinct states.     

Density,Viscosity, and Glass Transition of an Ethylenediamine–Ethylene Glycol Binary System

Densities ρ and viscosities η were measured for the binary mixtures of ethylenediamine (EDA) and ethylene glycol (EG) in the temperature range 288.15–323.15 K for ρ and at 273.15–323.15 K for η, both of which are broader temperature ranges than those reported previously. The value of ρ monotonously decreases against the mole fraction of EDA, x _EDA, and increasing temperature. The concentration dependence of η exhibits a maximum in the intermediate concentration range at all temperatures measured. The glass transition temperature, T _g, for samples with x _EDA < 0.7 was measured using differential scanning calorimetry. The measured T _g values show a peak in the intermediate concentration range, which is a behavior similar to that of η; however, the peak concentrations for η and T _g did not precisely align because of a deviation in the maximum hydrogen-bond density. The partial molar volumes for EDA and EG and the thermal expansivities, α, were obtained from ρ. Results in the present study are discussed in terms of the extensively increasing hydrogen-bond density for polyamine–polyhydric alcohol systems.     

Unperturbed dimensions of poly-p-chlorostyrene

Viscosity measurements on poly-p-chlorostyrene (PPCS) in benzene-methanol mixtures have been carried out at their corresponding theta temperatures determined by the phase separation method. Viscosity measurements were also run in benzene at the same temperatures. The Stockmayer-Fixman extrapolation method was applied to the data to obtain the chain unperturbed dimensions. K_θ. It was found that these, for PPCS in benzene, decrease with increasing temperature and that, both in benzene and in binary mixtures, they decrease with increasing values of the parameter a from the relationship [η] = KM^α. PPCS theta temperature in benzene was 8.     

Structural properties of LaxSr2−xFeO4±δ at high temperature and under reducing conditions

A series of materials, La_xSr_2−xFeO_4±δ (x=0.6-1.0), have been investigated structurally using neutron and X-ray diffraction techniques as well as Mössbauer spectroscopy as a function of temperature and composition. These materials adopt the I4/mmm K₂NiF₄-type structure over a wide range of temperatures (25-1200°C) and oxygen stoichiometries. In particular, it was observed that at a critical composition of x>0.8 there was a significant shift in the lattice parameters. This was attributed to changes in the Fe³⁺ content and the resultant effect of this on the d_z² orbitals giving a lengthening of the Fe-O bonds. On heating, completely linear behavior in both the a and c cell constants was observed, masking underlying bond length changes.     

(η-Tetraarylcyclobutadiene)(η-formylcyclopentadienyl)cobalt(I) complexes: Facilities to finetune the electron-donating capability in dipolar organometallics

Five different (η⁴-tetraarylcyclobutadiene)(η⁵-formylcyclopentadienyl)cobalt(I) complexes (1a-1e) were synthesized in reasonable yields in a one-pot reaction of CoCl(PPh₃)₃, formylcyclopentadienyl sodium and the appropriate diarylethyne. The aryl groups of the ethyne were modified by various para-substituents X (X = Cl, H, Me, OMe, NMe₂), which were intended to alter the redox potentials of the synthesized cobalt sandwich complexes. A cyclic voltammetry study revealed a linear dependence of the first oxidation potential to the Hammett parameter σ_p. X-ray structure analyses performed for two complexes (X = Me and NMe₂) demonstrate only subtle changes in the solid state structure despite the large differences in electrochemical properties. A theoretical analysis by the density functional theory method has been performed on the geometries and electronic structures of the complex (η⁴-cyclobutadiene)(η⁵-cyclopentadienyl)Co(I), its cation and dication.     

Étude des systémes ternaires polymère-mélanges de solvants: relation entre solvatation préférentielle et viscosité

The preferential solvation of ternary systems of polymer with mixed solvents is characterized by the λ′ parameter which depends on the thermodynamic properties of the system and also on some molecular parameters of the polymer (molecular weight, index of polydispersity, index of branching etc.). The dependence of λ′ on molecular parameters can be illustrated by a unique relation between the λ′ parameter and the intrinsic viscosity [η]:λ′[η] = λ′_∝ [η] + a′ +. This representation is verified for polystyrene and polymethyl methacrylate in several mixed solvents.     

Untersuchungen zur aufklärung des mechanismus des redoxsystems flavinmononucleotid/dihydroflavinmononucleotid: I. Coulometrische bestimmung der elektronenübergangszahl der reduktion von flavinmononucleotid

The reduction of flavinmononucleotide in 0.05 M H₂SO₄ was investigated. The charge number of the electrode reaction was determined coulometrically; it goes through a minimum of z=1.6±0.1, when the degree of reduction, x, is about 1/2; for small and for large degrees of reduction z is equal to 2. The sum of the anodic and cathodic diffusion currents decreases until the degree of reduction, x?0.6. This observation and the minimum found for the dependence of z on x, may be explained by the formation of the complex (FMNH⁺·FMNH₂). It is possible to oxidize this complex within the potential range investigated by us but not to reduce it. The existence and non-reducibility of this complex was confirmed experimentally. Spectroscopic investigations also showed that the complex (FMNH^*·FMNH₂) is formed, for the extinctions at 570 and 900 nm do not obey the relation (E₅₇₀)² ≈ E₉₀₀.     

Optically detected magnetic resonance study of the lowest excited triplet state of aromatic thioketones: Xanthione

The aromatic thioketone xanthione has been investigated by means of the optically detected magnetic resonance (ODMR) technique in a n-hexane matrix at ≈ 1.1 K. It was established that the short-lived red emission, which is characteristic for many thione molecules, is phosphorescence. At high temperatures (77 K) this phosphorescence originates mainly (>80%) from the T₁^z (n, π*) sublevel (k_z^(r) >k_x^(r), k_y^(r). At low temperature (1.1 K) the intersystem crossing following S₂ (π, π*) ← S₀ excitation is a highly spin-sublevel selective process which populates predominantly the T₁^x and T₁^y, levels. Hence, the slow spin—lattice relaxation phosphorescence at low temperature originates from these sublevels. A value of 0.0611 cm^?1 was obtained for the zero-field parameter |E|/hc. A lower limit of 0.66 cm^?1 has been found for the zero-field parameter |D|/hc. This value is considerably larger than those observed for ketones, and it is shown that spin—orbit coupling contributes strongly to the zero-field splitting.     

Electronic conductivity in nonstoichiometric cerium dioxide

The electrical conductivity of sintered specimens of nonstoichiometric CeO_2?x was measured as a function of temperature (750–1500°C) and oxygen pressure (1–10^?22 atm). The isothermal compositional dependence of the electrical conductivity of CeO_2?x was determined by combining recently obtained thermodynamic data, x = x(P_O2, T), with the conductivity data. The compositional and temperature dependence of the electrical conductivity may be represented by the expression

$\text{σ=410[x]e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{ohm cm}\text{)}{}^{\mathrm{?1}}$

over the temperature range 750–1500°C and from x = 0.001 to x = 0.1.This expression was rationalized in terms of the following simple relations for (a) the electron carrier concentration

$\text{n}{}_{\mathrm{ce}}\text{′}{}_{\mathrm{ce}}\text{=}\text{8x}\text{a}{}_0{}^3$

where n_Ce′Ce is the number of Ce′_Ce per cm³ and a₀ is the lattice parameter and (b) the electron mobility

$\text{μ=5.2(10}{}^{\mathrm{?2}}\text{)e}{}^{\mathrm{<mtext>?(0.158+x)</mtext><mtext>kT</mtext>}}\text{(}\text{cm}{}^2\text{/}\text{V sec}\text{)}$

.     

Extensional rheology of cellulose/NaOH/urea/H<Subscript>2</Subscript>O solutions

The extensional flow behaviors of cellulose/NaOH/urea/H₂O solution were investigated by using capillary breakup extensional rheometry (CaBER). The effects of temperature, storage time and cellulose concentrations on both the storage modulus G′ and the loss modulus G″ were also analyzed. For 2 wt% cellulose solution, the G′, G″ and filament lifetime remained unchanged after long storage time. While, for 4 wt% cellulose solution, physical gels could form at either higher temperature or for longer storage time, and the filament lifetime, the relaxation time (λ _e ) and the initial extensional viscosity (η _e0) first increased and then decreased with increase of the storage time. The transition points of the filament lifetime shifted to lower storage time with the increase of the temperature. The η _e0 is proportional to λ _e . The results presented suggest that the extensional properties of the cellulose/NaOH/urea/H₂O solution first increase and then decrease during the gelation process, and the spinning time, which decreases linearly with the increase in the storage temperature, must be controlled below the time that η _e0 starts to decrease.     

The determination and assignment of a complete 14N quadrupole coupling tensor in liquid solution

¹⁴N line splittings in the spectrum of nitrobenzene (neat liquid) and metadinitrobenzene (dissolved in benzene), induced by an external electric field, have been used to determine the complete ¹⁴N quadrupole coupling tensor of these substances. Assuming that both molecules are rigid and planar, and that the quadrupole coupling tensors at the ¹⁴N nuclei are identical, the principal components in a local reference frame (x′, y′, z′) are (eQ/h)V_x′ x′ = ±0.34 MHz (eQ/h)V_y′_y′= ±1.18 Hz and (eQ/h)V_z′_z′ = ±1.52. The z′-direction is parallel to the CN bond and the y?direction is perpendicular to the plane of the nitrogroup. With these data the asymmetry parameter η = 0.55.     

Anomalies in the properties of Hf(S2−xTex)1−y and Hf(Se2−xTex)1−y near the metal-insulator transition

The solid solutions Hf(S_2?xTe_x)_1?y and Hf(Se_2?xTe_x)_1?y were prepared to examine changes in the electronic structure in a narrow composition range near the metal-insulator transition. Powder X-ray diffraction analysis and resistivity measurements are presented. The x³ dependence of the hexagonal c parameter for the sulfur solutions is due to large packing mismatches in the layers. In the selenium solutions, anomalous behavior is observed in the composition dependence of the a and c hexagonal lattice parameters in the range 0.05 < x < 0.10, y ～ 0. Between these concentration limits, both lattice parameters show positive deviations from smooth behavior and the diffraction linewidths broaden. The temperature dependence of the resistivity suggests that the Hf(S_2?xTe_x)_1?y solutions have an energy of activation for conduction at room temperature for $\text{0 < x <}\text{7}\text{8}$; the sample of composition $\text{x =}\text{5}\text{8}$ has a metal-insulator transition as a function of temperature below room temperature. The band gap goes to zero with composition for Hf(Se_2?xTe_x)_1?y in the range x = 0.080 to x = 0.095. Nonstoichiometry, phase separation, and changes from covalent to metallic bonding explain the structural and electronic changes observed in the seleno-telluride system near the metal-insulator transition.