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At least 19 recordsLinked to original sources
USGS2002

Employment of Gibbs-Donnan-based concepts for interpretation of the properties of linear polyelectrolyte solutions

Earlier research has shown that the acid dissociation and metal ion complexation equilibria of linear, weak-acid polyelectrolytes and their cross-linked gel analogues are similarly sensitive to the counterion concentration levels of their solutions. Gibbs-Donnan-based concepts, applicable to the gel, are equally applicable to the linear polyelectrolyte for the accommodation of this sensitivity to ionic strength. This result is presumed to indicate that the linear polyelectrolyte in solution develops counterion-concentrating regions that closely resemble the gel phase of their analogues. Advantage has been taken of this description of linear polyelectrolytes to estimate the solvent uptake by these regions. ?? 1991 American Chemical Society.

Journal of Physical Chemistry↗
USGS2002

Interpretation with a Donnan-based concept of the influence of simple salt concentration on the apparent binding of divalent ions to the polyelectrolytes polystyrenesulfonate and dextran sulfate

It has been shown that the apparent enhancement of divalent metal ion binding to polyions such as polystyrenesulfonate (PSS) and dextran sulfate (DS) by decreasing the ionic strength of these mixed counterion systems (M2+, M+, X-, polyion) can be anticipated with the Donnan-based model developed by one of us (J.A.M.). Ion-exchange distribution methods have been employed to measure the removal by the polyion of trace divalent metal ion from simple salt (NaClO4)-polyion (NaPSS) mixtures. These data and polyion interaction data published earlier by Mattai and Kwak for the mixed counterion systems MgCl2-LiCl-DS and MgCl2-CsCl-DS have been shown to be amenable to rather precise analysis by this model. ?? 1985 American Chemical Society.

Journal of Physical Chemistry↗
USGS2002

Vapor-liquid phase equilibria of potassium chloride-water mixtures: Equation-of-state representation for KCl-H2O and NaCl-H2O

Measurements of isothermal vapor-liquid compositions for KCl-H2O as a function of pressure are reported. An equation of state, which was originally proposed by Pitzer and was improved and used by Tanger and Pitzer to fit the vapor-liquid coexistence surface for NaCl-H2O, has been used for representation of the KCl-H2O system from 300 to 410??C. Improved parameters are also reported for NaCl-H2O from 300 to 500??C. ?? 1990 American Chemical Society.

Journal of Physical Chemistry↗
USGS2002

Infrared spectral behavior of fine particulate solids

Transmission and emission spectra of clouds and layers of fine particulate samples of quartz, magnesium oxide, and aluminum oxide in the 6.5-35-??m wavelength range are presented. They demonstrate that the behavior of layers of particles constitutes a good analogue for a cloud of particles; that individual micrometer-sized particles emit most where they absorb most; that as the size of the particle is increased, the emission features reverse polarity and the spectrum approaches that of one obtained from a polished plate; and that as the particle layer-thickness increases, radiative interaction becomes increasingly important so that the emission maximum shifts from the strongest to weaker features, or produces a maximum at the Christiansen wavelength.

Journal of Physical Chemistry↗
USGS2002

Heat capacity from 12 to 305°K and entropy of talc and tremolite

The heat capacities of talc, Mg 3 Si 4 O 10 (OH) 2 , and tremolite, Ca 2 Mg 6 Si 8 O 22 (OH) 2 , have been measured between 12 and 305°K. Smoothed values of heat capacity, entropy, enthalpy, and free energy are tabulated. At 298.15° K. the values of the thermodynamic functions are: talc, C p °= 76.89 ± 0.23 cal. deg. -1 mole -1 , S° = 62.33 ± 0.19 cal. deg. -1 mole -1 , H° - H 0 ° = 11,206 ± 34 cal. mole -1 ; tremolite, Cp° = 156.7 ± 0.6 cal. deg. -1 mole -1 , S° = 131.2 ± 0.5 cal. deg. -1 mole -1 , H° - H 0 ° = 23,335 ± 90 cal. mole -1 . From the equilibrium data of Bowen and Tuttle and the entropy of talc, the heat of formation of talc from MgO, SiO 2 , and H 2 O (liq.) is calculated to be Δ H°f 298 = -43.6 ± 1 kcal.

Journal of Physical Chemistry↗
USGS2002

The addition of iodine to tetramethylammonium iodide

The system tetramethylammonium iodide-iodine-toluene has been studied by the solubility method at 6 and at 25°. The compounds (CH 3 ) 4 NI 3 , (CH 3 ) 4 NI 5 and (CH 3 ) 4 NI 11 were found to be stable phases at both temperatures. In addition, the compound (CH 3 ) 4 NI 10 was found at 6° and the compound (CH 3 ) 4 NI 9 at 25°. The dissociation pressures of the compounds at these temperatures were calculated from the solubility data.

Journal of Physical Chemistry↗
USGS2001

Diamond-anvil cell observations of a new methane hydrate phase in the 100-MPa pressure range

A new high-pressure phase of methane hydrate has been identified based on its high optical relief, distinct pressure-temperature phase relations, and Raman spectra. In-situ optical observations were made in a hydrothermal diamond-anvil cell at temperatures between -40?? and 60 ??C and at pressures up to 900 MPa. Two new invariant points were located at -8.7 ??C and 99 MPa for the assemblage consisting of the new phase, structure I methane hydrate, ice Ih, and water, and at 35.3 ??C and 137 MPa for the new phase-structure I methane hydrate-water-methane vapor. Existence of the new phase is critical for understanding the phase relations among the hydrates at low to moderate pressures, and may also have important implications for understanding the hydrogen bonding in H2O and the behavior of water in the planetary bodies, such as Europa, of the outer solar system.

Journal of Physical Chemistry A↗
USGS2001

Anomalous preservation of pure methane hydrate at 1 atm

Direct measurement of decomposition rates of pure, polycrystalline methane hydrate reveals a thermal regime where methane hydrate metastably `preserves' in bulk by as much as 75 K above its nominal equilibrium temperature (193 K at 1 atm). Rapid release of the sample pore pressure at isothermal conditions between 242 and 271 K preserves up to 93% of the hydrate for at least 24 h, reflecting the greatly suppressed rates of dissociation that characterize this regime. Subsequent warming through the H2O ice point then induces rapid and complete dissociation, allowing controlled recovery of the total expected gas yield. This behavior is in marked contrast to that exhibited by methane hydrate at both colder (193-240 K) and warmer (272-290 K) test conditions, where dissociation rates increase monotonically with increasing temperature. Anomalous preservation has potential application for successful retrieval of natural gas hydrate or hydrate-bearing sediments from remote settings, as well as for temporary low-pressure transport and storage of natural gas.

Journal of Physical Chemistry B↗
USGS2002

The structure of Yb 3+ aquo ion and chloro complexes in aqueous solutions at up to 500 °C and 270 MPa

We report here on X-ray absorption fine structure (XAFS) measurements used to determine the structure of the Yb 3+ ion in aqueous solutions over a range of temperatures from 25 to 500 °C and pressures up to 270 MPa. Fluorescence Yb L 3 -edge spectra were collected separately from nitrate (0.006 m Yb/0.16 m HNO 3 ) and chloride (0.006 m YbCl 3 /0.017 m HCl) aqueous solutions within a hydrothermal diamond anvil cell. The Yb−O distance of the Yb 3+ aquo ion in the nitrate solution exhibits a uniform reduction at a rate of 0.02 Å/100 °C, whereas the number of oxygens decreases from 8.3 ± 0.6 to 4.8 ± 0.7, in going from 25 to 500 °C. No evidence for nitrate complexes was found from measurements made on this solution. The Yb 3+ is found to persist as an aquo ion up to 150 °C in the chloride aqueous solution. In the 300−500 °C range, chloro complexes are found to occur in the solution, most likely of the type Yb(H 2 O) δ - n Cl n +3- n (δ ≈ 7). The Yb−Cl distance of the chloro ytterbium(III) complexes is found to decrease uniformly at a rate of about 0.02 Å/100 °C, whereas the number of chlorines increases from 0.5 ± 0.3 to 1.8 ± 0.2 in the 300−500 °C temperature range. Conversely, the Yb−O distance undergoes a lower uniform reduction at a rate of 0.007 Å/100 °C, whereas the number of oxygens decreases from 8.3 ± 0.5 to 5.1 ± 0.3 in going from 25 to 500 °C in the same solution.

Journal of Physical Chemistry A↗
USGS2003

CO2 hydrate: Synthesis, composition, structure, dissociation behavior, and a comparison to structure I CH4 hydrate

Structure I (sI) carbon dioxide (CO 2 ) hydrate exhibits markedly different dissociation behavior from sI methane (CH 4 ) hydrate in experiments in which equilibrated samples at 0.1 MPa are heated isobarically at 13 K/h from 210 K through the H 2 O melting point (273.15 K). The CO 2 hydrate samples release only about 3% of their gas content up to temperatures of 240 K, which is 22 K above the hydrate phase boundary. Up to 20% is released by 270 K, and the remaining CO 2 is released at 271.0 plusmn; 0.5 K, where the sample temperature is buffered until hydrate dissociation ceases. This reproducible buffering temperature for the dissociation reaction CO 2 ·nH 2 O = CO 2 (g) + nH 2 O(1 to s) is measurably distinct from the pure H 2 O melting point at 273.15 K, which is reached as gas evolution ceases. In contrast, when si CH 4 hydrate is heated at the same rate at 0.1 MPa, >95% of the gas is released within 25 K of the equilibrium temperature (193 K at 0.1 MPa). In conjunction with the dissociation study, a method for efficient and reproducible synthesis of pure polycrystalline CO 2 hydrate with suitable characteristics for material properties testing was developed, and the material was characterized. CO 2 hydrate was synthesized from CO 2 liquid and H 2 O solid and liquid reactants at pressures between 5 and 25 MPa and temperatures between 250 and 281 K. Scanning electron microscopy (SEM) examination indicates that the samples consist of dense crystalline hydrate and 50-300 μm diameter pores that are lined with euhedral cubic hydrate crystals. Deuterated hydrate samples made by this same procedure were analyzed by neutron diffraction at temperatures between 4 and 215 K; results confirm that complete conversion of water to hydrate has occurred and that the measured unit cell parameter and thermal expansion are consistent with previously reported values. On the basis of measured weight gain after synthesis and gas yields from the dissociation experiments, approximately all cages in the hydrate structure are filled such that n ≈ 5.75.

Journal of Physical Chemistry B↗