An NMR self-diffusion investigation of water/xylene/alkyl amine solutions

Extensions of the solution phases have been determined and the self-diffusion behaviour investigated in ternary systems containing water/xylene/primary alkyl amine, where the chain length of the amine varied between C₆ and C₁₀. The phase diagrams at 25°C are dominated by a solution phase and a rather large water/xylene miscibility gap which increases slightly in size with increasing chain length of the amine. A lamellar liquid crystalline phase was found in all binary amine/water systems at 25°C, except for hexylamine where the lamellar phase melts below this temperature. The self-diffusion coefficients of all components decrease in a similar way when water is added to a xylene/amine solution. The self-diffusion is rapid and of similar magnitude for all components, which shows that no well-defined inverse aggregates are formed. The data are discussed in terms of hydrogen bonding between the different species in the solution.     

Nucleation from supersaturated water vapors onn-dodecane substrate: A reverse Wilson chamber (RWC) method study

The reverse Wilson chamber method (RWC), developed for heterogencous nucleation investigation is applied to critical supersaturation measurements and determination of the surface concentration of nuclei (droplets) vs. supersaturation dependence in the case of nucleation from supersaturated water vapors onn-dodecane substrate. The experimental results obtained are interpreted in terms of the classical (Volmer) theory of heterogeneous nucleation as well as in the framework of the theory of barrierless nucleation. The several times lower critical supersaturations measured at four different temperatures, covering the range between 20° and 35° C, are explained by taking into account the effect of the negative line tension of three-phase contact. The temperature dependence of line tension for the three-phase systemn-dodecane/water/water vapor is extracted from the data to fir the theory. The results obtained are in complete disagreement with those ones obtained by Wu and Maa for the same system using jet-tensimeter technique, however, in another temperature interval. This discrepancy is discussed in detail in the text.     

Phenanthrene degradation in subcritical water

Subcritical water (<374 °C and <221 bar) has unique characteristics such as dramatically decreased dielectric constant, surface tension, and viscosity with increasing temperature, allowing for dissolution and reaction of organics in high-temperature water to occur. Additionally, the dissociation constant of water at temperatures of 200-300 °C is three orders of magnitude greater than that of ambient water, which may also contribute to the reactivity of subcritical water with certain organic compounds. In this study, the degradation and oxidation of phenanthrene in subcritical water were investigated. Both deionized water and water with 3% hydrogen peroxide were used in the degradation and oxidation studies. The effect of temperature on degradation efficiency has been determined with a temperature range of 100-350 °C. When the temperature was increased from 150 to 350 °C, the amount of phenanthrene degraded varied from 6 to 243 μg in each milliliter of deionized water. However, these quantities were increased to 195 μg at 150 °C and 3680 μg at 350 °C in each milliliter of water with 3% hydrogen peroxide. Several degradation products including phenol, benzoic acid, and ketones were identified by using gas chromatography/mass spectrometry (GC/MS).     

Laser induced breakdown spectroscopy on soils and rocks: Influence of the sample temperature,moisture and roughness

ExoMars, ESA's next mission to Mars, will include a combined Raman/LIBS instrument for the comprehensive in-situ mineralogical and elemental analyses of Martian rocks and soils. It is inferred that water exists in the upper Martian surface as ice layers, “crystal” water or adsorbed pore water. Thus, we studied Laser Induced Breakdown Spectroscopy (LIBS) on wet and dry rocks under Martian environmental conditions in the temperature range − 60 °C to + 20 °C and in two pressure regimes, above and below the water triple point. Above this point, the LIBS signals from the rock forming elements have local minima that are accompanied by hydrogen (water) emission maxima at certain temperatures that we associate with phase transitions of free or confined water/ice. At these sample temperatures, the plasma electron density and its temperature are slightly lowered. In contrast to powder samples, a general increase of the electron density upon cooling was observed on rock samples. By comparing the LIBS signal behavior from the same rock with different grades of polishing, and different rocks with the same surface treatment, it was possible to distinguish between the influence of surface roughness and the bulk material structure (pores and grains). Below the triple point of water, the LIBS signal from the major sample elements is almost independent of the sample temperature. However, at both considered pressures we observed a hydrogen emission peak close to − 50 °C, which is attributed to a phase transition of supercooled water trapped inside bulk pores.     

Acidity measurements at elevated temperatures. VII. Dissociation of water

The self-dissociation of water has been studied over the temperature range from 0 to 300°C and in KCl media from 0.02m to 2.7m. Also, isothermal pressure coefficients of the dissociation quotients have been obtained in these same media up to 250°C. A potentiometric method employing a hydrogen electrode concentration cell with flowing solutions was employed. The estimated accuracy of logQ _w values up to 250°C is 0.02 log units and at 300°C is 0.04 log units. Smoothing functions have been found which fit these data along with the precise potentiometric data of Harned and co-workers at low temperatures, the existing calorimetric data up to 55°C and the recent conductimetric measurements of pure water up to 271°C by Bignoldet al., within about 1.5 times the estimated errors. Thermodynamic quantities for the dissociation reaction have been tabulated for rounded values of temperature and ionic strength at the saturation pressure of water. The isothermal pressure coefficients of log Q_w varies approximately linearly with the square root of the ionic strength. This and the dependence of logK _w on the density of the water is consistent with the assumption that the molal volumes of aqueous ions vary linearly with the compressibility coefficient of water. The heat for the dissociation reaction at infinite dilution is also shown to be strongly dependent on density.     

Partial molar isentropic compressibilities and volumes of selected electrolytes and nonelectrolytes in dimethylsulfoxide

Precision densities and sound velocities for solutions of selected univalent electrolytes and nonelectrolytes in DMSO have been measured at 25°C, and apparent molar isentropic compressibilities and volumes evaluated. The data were extrapolated to infinite dilution to obtain standard state partial molar quantities, K _s,2 ^° , and V ₂ ^° . Values of V ₂ ^° and K _s,2 ^° for alkali metal halides in DMSO are very similar to those in water. The results confirm conclusions derived from data in water and other nonaqueous solvents that K _s,2 ^° and V ₂ ^° for alkali metal halides are strongly dependent on solvent compressibility. K _s,2 ^° becomes more negative and V ₂ ^° decreases as solvent compressibility increases. Attempts to determine ionic K _s,2 ^° values suggest that a significant dissymmetry exists between ₄P⁺ and ₄B^– in DMSO, whereas in water and MeOH, these large ions appear to behave similarly. Ionic V ₂ ^° values support this conclusion. Steric hindrance in the DMSO molecule is believed to be responsible for this dissymmetry.     

The solubility of the noble gases He,Ne, Ar,Kr, and Xe in water up to the critical point

The solubility of the noble gases Ar, He, Ne, Kr, and Xe in pure water was measured from 298 to 561°K. These data in turn were extrapolated to the critical point of water, thus providing a complete set of Henry's law constants from 274 to 647°K when combined with the existing literature data. Equations describing the behavior of the Henry's law constants over this temperature range are also given. The data do not confirm extrapolations of empirical correlations based on low-temperature solubility data.     

Determination of differences in free and bound water contents of beef muscle by DSC under various freezing conditions

The differences in bound water content of beef semimembranous muscle samples obtained from previously chilled (24 h at +4°C) middle-aged beef carcasses were determined by the use of DSC. Initially, samples obtained from fresh, unprocessed meat were frozen at –40, –50 or –65°C to determine their melting peaks for freezable water (free water) content with the use of DSC. The samples were then subjected to an environment with an ambient temperature of –30, –35, –40 or –45°C, with no air circulation, or with an air circulation speed of 2 m s^–1, until a thermal core temperature of –18°C was attained; this was followed by thawing the samples until a thermal core temperature of 0°C was reached. This process was followed by subjecting the samples to the ambient temperatures mentioned above, to accomplish complete freezing and thawing of the samples, with DSC, and thereby determination of the freezable water contents, which were then used to determine the peaks of melting. The calculated peak areas were divided by the latent heat of melting for pure water, to determine the freezable water contents of the samples. The percentage freezable water content of each sample was determined by dividing its freezable water content by its total water content; and the bound water content of each sample was determined by subtracting the percentage free water content from the total. In view of the fact that the free water content of a sample is completely in the frozen phase at temperatures of –40°C and below, the calculations of free and bound water contents of the samples were based on the averages of values obtained at three different temperatures.     

Determination of hydroxyls density in the silica-mesostructured cellular foams by thermogravimetry

Thermogravimetry was applied to determine the surface hydroxyls coverage in the mesostructured cellular foams (MCFs) calcined at different temperatures and then rehydroxylated by contacting with water vapor or liquid. The TG measurements were performed by heating MCFs in air stream using a three-step temperature program: (i) at rate of 5 °C min⁻¹ from 25 to 200 °C; (ii) held at 200 °C for 30 min; and (iii) heating at rate of 10 °C min⁻¹ up to 1100 °C. The hydroxyls content was calculated from weight loss during third step. The hydroxyls density appeared to depend strongly on the calcination temperature and the subsequent contact with water vapor. When MCFs were exposed for a short period (ca. 1 min) to moist air the hydroxyls content increased rapidly, more in the samples calcined at 300 °C than 500 °C, to attain surface densities of 4.75 and 1.6 OH nm⁻², respectively. The 2-h contact with water vapor resulted in slower further increase of hydroxyls densities, to values of 5.45 and 2.9 OH nm⁻², for samples calcined at 300 and 500 °C, but longer contacts had no significant effect. A similar trend was also observed when sample was treated with liquid water.     

The association of aromatic anions in water

Molar conductances of dilute solutions of sodium 2-naphthalenesulfonate at 25°C and of sodium 2-anthraquinonesulfonate have been measured at 25 and 37°C. These data are interpreted to show that the anthraquinonesulfonate anion is dimerized in solution. Dimerization constants and the enthalpy and entropy of dimerization are calculated. Spectrophotometric absorbancies have been measured at 25, 30, 35 and 40°C for a series of aqueous solutions containing both sodium 4-dimethylaminobenzenesulfonate and sodium 3-nitrobenzenesulfonate. Equilibrium constants and enthalpy and entropy changes for formation of the 1 1 complex between these two ions have been calculated from these data. The formation of these complexes between like-charged ions, and of dimers of other aromatic solutes in water is discussed in terms of a two-state model of hydrophobic hydration.     

Limiting interdiffusion coefficients of Tris(acetylacetonato)cobalt(III) in water and in organic solvents

The diffusion coefficients of tris(acetylacetonato)-cobalt(III) in water (5, 15, 25, and 40°C), methanol (25°C), ethanol (15, 25, and 45°C), 1-propanol (25°C), 1-butanol (45°C), acetone (25 and 40°C), 2-butanone (25°C), acetonitrile (25°C), tetrahydrofuran (25°C), benzen (25°C), toluene (25°C), and carbon tetrachloride (25°C) have been measured at concentrations close to infinite dilution. The Stokes-Einstein coefficient (f=kT/Dr) has been calculated for Co(acac)₃ in each solvent and is found to be larger in water than in organic solvents. Furthermore, it increases as the temperature is lowered (or as the viscosity is increased) in water while it decreases with increasing viscosity of organic solvents. The differences are discussed in terms of the enhancement of the water structure by the solute.     

Loss of selenium in water samples at natural levels during storage

Selenium losses in river, ground, snow-melt and tap water samples, and the recovery of selenite, selenate and selenomethionine added to purified water have been studied. In 1-litre high-density polyethylene bottles, tap, river and snow-melt water samples (at Se concentrations of 44.5–138 ng/l) could be stored at 4 °C for up to 15 days without Se losses. In similar samples stored at room temperature Se losses of 13–25% after 15 days were found, except for groundwater, which showed no Se losses during storage for 13 months at room temperature or at 4 °C. Selenite and selenate added to purified water were recovered without losses after 15 days at 4 °C, while 7.5% of selenomethionine was lost. The stability of different chemical forms of Se during storage followed the order: selenate > selenomethionine > selenite. It is recommended that unacidified water samples should not be kept in polyethylene bottles at room temperature for more than 1 week, nor stored at 4 °C for more than 2 weeks, before analysis for Se.     

Determination of enthalpy of ionization of water from 250 to 350° C

The enthalpy changes at zero ionic strength (H°) for the ionization of water (H₂O=H⁺+OH^–) were determined by flow calorimetry from the heats of mixing of aqueous NaOH and HCl solutions in the temperature range 250 to 350°C. Pitzer ion-interaction models developed by other workers were used to calculate enthalpies of dilution of aqueous NaOH, HCl, and NaCl solutions for the extrapolation of H values from the conditions of the experiment to infinite dilution. Equations are derived for thermodynamic quantities (log K, H°, S°, C _p ^° and V°) for the ionization of water using the H° values determined in this study from 250 to 350°C and literature log K and H° values from 0 to 225°C. Smoothed values of log K, H°, S°, C _p ^° , and V° are presented at rounded temperatures from 0 to 350°C and at the saturation pressure of water for each temperature. The equations in the present study provide a better representation of experimental thermodynamic data from 0 to 350°C than the Marshall-Franck equation.     

Evaluation of the effect of column orientation in type-I high-speed counter-current chromatography

The performance of type-I high-speed counter-current chromatography was evaluated by changing the column inclination against the rotating centrifugal force field. The separations were performed with two different solvent systems composed of 1-butanol–acetic acid–water (4.75:0.25:5, v/v) (BAW) and hexane–ethyl acetate–methanol–0.1 M HCl (1:1:1:1, v/v) (HEMW) using dipeptides and DNP-amino acid as test samples, respectively. A set of short coiled columns connected in series is mounted around the holder hub in two different ways: in the parallel orientation, all column units are arranged in parallel to each other and mounted on the holder at various angles against the horizontal plane. In the zigzag configuration, the neighboring units of the same column are mounted symmetrically forming various angles apart. In the parallel configuration, for both the BAW and HEMW systems, Sf (the retention of stationary phase) first increased as the column angle decreased from 90° to 60° and then decreased, as the column angle further decreased from 60° to 0°, while Rs (peak resolution) continually declined over the entire column angle range from 90° to 0°. But, for both solvent systems, with the zigzag configuration, retention of stationary phase and resolution both decreased as the column angle decreased from 90° to 0°. In general, Sf and Rs for separation of dipeptides in the BAW system, from 90° to 15°, is better for the parallel orientation than for the zigzag configuration. However, at 0°, Sf and Rs are better for the zigzag orientation. In the DNP-amino acid separation with the HEMW system, retention of the stationary phase and Rs for the parallel orientation is better than that for the zigzag orientation from 90° to 30°, whereas from 30° to 0° the results are opposite. Over all results of our studies revealed that the formally used column orientation [5] at 90° inclination yields the highest peak resolution in both solvent systems.     

Dissociation constant of protonated tris(hydroxymethyl)aminomethane in N-methylpropionamide and related thermodynamic quantities from 10 to 55°C

The dissociation constant of protonated tris(hydroxymethyl)aminomethane (tris·H⁺) in the solvent N-methylpropionamide (NMP) has been determined at intervals of 5°C from 10 to 55°C by measurement of the emf of cells without liquid junction using hydrogen and silver-silver chloride electrodes. At 25°C, pK _a was found to be 8.831, as compared with 8.075 in water. The standard changes in Gibbs energy, enthalpy, and entropy for the dissociation process have been evaluated from the dissociation constant and its change with temperature. By comparison with similar data for the dissociation of tris·H⁺ in water, thermodynamic functions for the transfer from water to NMP have been derived. The dissociation process is isoelectric, and the solvent dielectric constant is high (=176 at 25°C). Consequently, electrostatic charging effects are expected to be minimal, and the change in dissociation constant depends primarily on solute-solvent interactions. The results, combined with transfer energies for HCl, tris, and tris·HCl from emf and solubility measurements, demonstrate that the decreased acidic strength of tri·H⁺ in NMP is attributable in large part to the fact that NMP is less effective than water in stabilizing tris and its salts.     

Modification of Non-Hydrolytic Sol-Gel Derived Alumina by Solvent Treatments

The effect of wetting non-hydrolytic derived alumina xerogels with water and organic solvents in the 20–70°C range on the alumina's properties was investigated. Wetting with organic solvents does not affect the alumina. However, contact with water was found to change the sharp crystallization at 800°C to a continuous crystallization starting at 450°C. Water treatment for a day at room temperature (RT) followed by second calcination decreased the surface area by 10%. This decrease in surface area is less pronounced with increasing wetting periods. On the other hand water treatment at 50–70°C followed by a second calcination resulted in a surface area increase of up to 15%. Upon water treatment the total pore volume has decreased from 0.65 (cm³/gr) to 0.48 (cm³/gr) and the average pore size decreased from 6.8 nm to 4.1 nm. The Cl content was found to be uneffected by the water treatment, remaining at 2.5% wt. Wetting with water at elevated temperature (70°C) accelerated the morphological changes, eliminating the crystallization peak at 800°C in one hour. A dissolution-reprecipitation mechanism is suggested to explain the results. In addition, Mass-Spectroscopy of the effluent gas during heat treatment revealed the emission of CO₂ and water upon phase transition into -Al₂O₃, at 1150–1300°C.     

Single ionic partial molar volumes and solvation of ions

The limiting partial molar volumes of alkali metal halides in water and some other protic solvents have been dissected into individual ionic contributions. The extra-thermodynamic procedure employed assumes independent contributions of ion-solvent and solvent-solvent interactions to this property. The resulting parameters are found to be chemically reasonable and consistent with the molecular properties of the solvents. The limiting partial molar volume of the hydrogen ion has been calculated to be –4.2 cm³-mol^–1 in water at 25°C. Analysis of data for aqueous solutions from 0 to 50°C permits the evaluation of the energy change associated with the transfer of a water molecule from the bulk to the hydration zone. Results from the present work are compared with those obtained from the scaled particle theory.     

Determination of polycyclic aromatic hydrocarbons in aqueous samples by microwave assisted headspace solid-phase microextraction and gas chromatography/flame ionization detection

The novel pretreatment technique, microwave-assisted heating coupled to headspace solid-phase microextraction (MA-HS-SPME) has been studied for one-step in situ sample preparation for polycyclic aromatic hydrocarbons (PAHs) in aqueous samples before gas chromatography/flame ionization detection (GC/FID). The PAHs evaporated into headspace with the water by microwave irradiation, and absorbed directly on a SPME fiber in the headspace. After being desorbed from the SPME fiber in the GC injection port, PAHs were analyzed by GC/FID. Parameters affecting extraction efficiency, such as SPME fiber coating, adsorption temperature, microwave power and irradiation time, and desorption conditions were investigated.Experimental results indicated that extraction of 20 mL aqueous sample containing PAHs at optional pH, by microwave irradiation with effective power 145 W for 30 min (the same as the extraction time), and collection with a 65 μm PDMS/DVB fiber at 20 °C circular cooling water to control sampling temperature, resulted in the best extraction efficiency. Optimum desorption of PAHs from the SPME fiber in the GC hot injection port was achieved at 290 °C for 5 min. The method was developed using spiked water sample such as field water with a range of 0.1-200 μg/L PAHs. Detection limits varied from 0.03 to 1.0 μg/L for different PAHs based on S/N = 3 and the relative standard deviations for repeatability were <13%. A real sample was collected from the scrubber water of an incineration system. PAHs of two to three rings were measured with concentrations varied from 0.35 to 7.53 μg/L. Recovery was more than 88% and R.S.D. was less than 17%. The proposed method is a simple, rapid, and organic solvent-free procedure for determination of PAHs in wastewater.     

Enthalpies of 1,4-Dioxane, 1,2-Dimethoxyethane, and Ethylacetate Solvation in the Water–1-Propanol and Water–Glycerol Binary Mixtures

The enthalpies of 1,4-dioxane, 1,2-dimethoxyethane, and ethylacetate solution in binarymixtures of water with 1-propanol and glycerol were measured at 25°C using a precise isoperibol calorimeter. The enthalpies of the solute solvation were calculated and compared with the experimental data for other solutes. The results obtained were interpreted in terms of universal and specific solute solvation using parameters of a solvent polarity. It was found that the extreme shape of the curve _solv H° vs. X for ethylacetate in the mixtures of water with 1-propanol results from peculiarities of carbotylate-group solvation and appears to be not connected with the influence of alcohol microaggregates in the mixed solvent.     

The mechanism and stability of thermal transitions in hair keratin

Differential Scanning Calorimetry (DSC) has been applied to study the interactions between components of human hair keratin. Keratin is a biopolymeric composite made of several proteins forming basically two phases: amorphous matrix and crystalline microfibrillar phase. Water, the content of which depends on atmospheric humidity, is also an integral part of keratin structure. The following processes are apparent from the DSC: removal of loosely bound water (ca. 70°C), a transition in the amorphous phase (155°C) and melting/denaturation of the -crystalline phase (233°C). The process occurring in keratin at ca. 155°C has an opposite character to a glass transition; we refer to this process as the toughening transition. The area of the -keratin peak increases significantly upon annealing at temperatures from 80°C to 150°C and decreases for higher annealing temperatures. Water affects both the crystalline and amorphous phases of keratin. The process similar in nature to annealing — induced recrystallization in synthetic polymers is strictly correlated with removal of strongly bound fraction of water in keratin.