Some experiments on complex spontaneous emulsification in the system water–benzene–ethanol

The system water–benzene–ethanol was used to illustrate the complexity of spontaneous emulsification, when water-poor emulsions are brought in contact with water. In the first case, an O/W emulsion located close to the plait point in the system was used. The aqueous phase in the emulsion was incompatible with water, and a strong spontaneous emulsification to an O/W between the two liquids took place in the water layer close to the interface between layers. In the second case, a W/O emulsion, also close to the plait point, was brought in contact with water. Now, the spontaneous emulsification between the water and the oil phase of the original emulsion to an O/W emulsion also took place in the water layer forming a distinct emulsion layer beneath the interface.     

On the kinetics of pozzolanic reaction in the system kaolin–lime–water

The kinetics of the pozzolanic reaction of enriched kaolin from the “Senovo” deposit (Bulgaria) with lime is the object of this article. The kaolin contains kaolinite as a major clay mineral as well as admixtures of quartz and illite. The experimental data of pozzolanic activity at temperatures of 100 and 23 °C are obtained for different reaction times. The reaction degrees of kaolinite and lime at 100 °C are determined from the pozzolanic activity data using a powder X-ray diffraction analysis. The kinetic analysis is performed by joint presentation of theoretical and experimental data in dimensionless coordinates having in mind the influence of particle size distribution on the reaction rate. It is found by the kinetic analysis that the rate of entire reaction is limited by the rate of chemical reaction on the reaction surface up to degree of reaction near to 0.4. The rate of penetration of the chemical reaction into the kaolinite particles for this area—from the beginning to degree of reaction 0.4, is determined to be equal to 2.10⁻¹¹ m/s.     

Hydrate formation in the system n-propanol–water

The phase diagram of the binary system n-propanol alcohol–water was investigated with use of differential thermal analysis and powder X-ray diffraction. The phase diagram has three groups of thermal effects, which can be considered as peritectic melting of three different hydrates (?60.0, ?53.5, and ?41.5 °C). At the same time, powder X-ray diffraction data indicate the existence of only one compound in this system (cubic unit cell, a = 12.09 ± 0.01 Å and 12.15 ± 0.01 Å at ?109 to ?66 °C, respectively). The most probable explanation of this contradiction seems to be the existence of several hydrates belonging to the same structural type but different in composition.     

Formation of micro- and nanosized particles of the Fe–Al–Co system in water solutions and its magnetic properties

Samples of the Fe–Al–Co system are obtained electrochemically in a water solution. The kinetic dependences that describe the processes that occur in microparticles of aluminum in water solutions are established. The phase composition of the synthesized samples is determined via X-ray diffraction and Mössbauer spectroscopy. It is shown that the main contribution to the fine magnetic structure of Fe–Al–Co is made by the magnetically ordered structure with a hyperfine field around 348 kOe formed by a mechanical mixture of FeCo and Al.     

On the kinetics of pozzolanic reaction in metakaolin–lime–water system

The kinetics of pozzolanic reaction metakaolin–lime is studied in the present work. Metakaolin is prepared by calcination of enriched kaolin (deposit “Senovo”, Bulgaria) at temperature of 830 ± 10 °C in a labscale muffle oven. The reaction is performed in intensively stirred water suspension at different temperatures in the range 20–100 °C. The kinetics is analyzed by comparing the experimental data with theoretical curves, derived according to appropriate kinetic and diffusion models taking into account the grain size distribution of metakaolin. The macroscopic mechanism and activation energy of the reaction are determined. It is found, that the activation energy decreases gradually from 71 to 45 kJ/mol[Ca(OH)₂] with the increase of the reaction degree from 0.2 up to 0.6, respectively, which is a characteristic for transition regime reactions.     

Bubble points of hydrogen chloride–water–isopropanol and hydrogen chloride–water–isopropanol–benzene systems and liquid–liquid equilibria of hydrogen chloride–water–benzene and hydrogen chloride–water–isopropanol–benzene systems

Bubble points of the HCl–water–isopropanol and the HCl–water–isopropanol–benzene systems and liquid–liquid equilibria (LLE) of the HCl–water–benzene and the HCl–water– isopropanol–benzene systems were measured at 25–85°C and 30–70°C, respectively. The electrolyte nonrandom two-liquid model proposed by Chen et al. [C.-C. Chen, H.I. Britt, J.F. Boston, L.B. Evans, AIChE J. 28 (1982) 588–596] can satisfactorily correlate bubble points and liquid–liquid equilibria of the present mixed-solvent electrolyte systems over the entire range of temperature and concentrations using only binary adjustable parameters.     

Phase equilibrium in the system water–acetonitrile–cyclohexene–cyclohexanone

Phase equilibrium in the water–acetonitrile–cyclohexene–cyclohexanone quaternary system and in its binary and ternary constituents was studied using experimental and calculation methods. The parameters were determined for the NRTL equation that adequately describes liquid–vapor, liquid–liquid–vapor, and liquid–liquid–liquid equilibria. The evolution of the three-phase splitting region inside the concentration tetrahedron was studied on the basis of the obtained model, and its transformation into the two-phase region through the critical node was shown. Thermodynamic analysis involving topological representation for the diagram of the phase equilibrium in a quaternary system was performed, and schemes for the complete separation of the reaction mixture were proposed.     

Study of simultaneous solubility of salts in the ammonium nitrate–ammonium chloride–water system

Ternary eutectic of the NH₄NO₃–NH₄Cl–H₂O system at–23.6°С has been found using a set of theoretical and experimental methods. According to the data of visual-polythermal and differential thermal analyses data, crystallization surface of the system has been plotted at–23.6 to 100°С.     

IR spectroscopic study of the hydrogen bond network in the water–3-amino-1-propanol system and its comparison with the spatial network of hydrogen bonds in the water–monoethanolamine system

IR spectroscopy was used to explore the water–3-amino-1-propanol (3AP) system in the range of 400–4000 cm^-1. Based on the stretching vibrations of OH, NH₂ and CH groups and skeletal bending vibrations of 3AP it was concluded that mixed spatial networks are formed in the water–3AP system that predominate at medium 3AP concentrations. The obtained results are similar to the IR spectroscopic data for the water–monoethanolamine system, viz., the networks of both amino alcohols are incorporated into the spatial     

Test of the water adsorption model of organic electrocatalysis in the carbon monoxide–silver system in alkaline medium

A test has been carried out of the model of T. Iwasita, X.H. Xia, H.-D. Liess, W. Vielstich [J. Phys. Chem. B. 101 (1997) 7542], according to which the maximum at about the same potential in both the positive and negative sweeps in cyclic voltammograms (CVs) of small organic molecules on Pt is due to the concurrence of two processes with opposite potential dependences, adsorption of the organic compound and electrooxidation of its intermediates, which decrease and increase, respectively, with increasing potential. In turn, the decrease with increasing potential of the adsorption of the undissociated organic is due to its increasing displacement by molecular water, this competition occurring because the two molecular compounds have similar, low values of the adsorption energy. According to the model of T. Iwasita, X.H. Xia, H.-D. Liess, W. Vielstich [J. Phys. Chem. B. 101 (1997) 7542], with CO on Pt no anodic currents are observed in the negative sweep because of the high adsorption energy of CO on Pt, which precludes its displacement by water. Therefore, the model has been tested with the CO–Ag system, for which anodic currents should be observed in the negative sweep, since the adsorption energy of CO on Ag is very low. Effectively, this has been found to be the case, which indicates that the model is indeed applicable to the CO–Ag system over the tested pH range, 10–14. At pH⩽11 adsorbed CO was displaced from the surface of Ag by N₂ bubbling, while it was not at pH⩾12. However, even at pH⩾12 the adsorption energy of CO on Ag should be rather weak, since anodic currents appeared in the negative sweep in CO-saturated solution over the whole pH range tested, 10–14.     

Small-angle X-ray scattering of the gadolinium triacetate–undecane–water system

By small-angle X-ray scattering a gadolinium triacetate–undecane–water system is studied at hydrotrope concentrations of 0.05-0.5 М on the line of saturation with undecane at 298 K. In the ternary system mixed hydrotrope/undecane lamellar micelles form with lateral dimensions of hydrophilic and hydrophobic plates of 0.4 nm. It is shown that the Gibbs energy of the hydrophobic interaction and the micelle shape are determined by a joint (cooperative) effect of the hydrotrope and hydrocarbon on water.     

Phase equilibria in binary subsystems of urea–biuret–water system

Joint results of the differential scanning calorimetry (DSC) and thermogravimetry (TG) experiments were the basis for the fusion enthalpy and temperature determination of the biuret (NH₂CO)₂NH (synthesis by-product of the urea fertilizer (NH₂)₂CO). Recommended values are Δ_m H = (26.1 ± 0.5) kJ mol⁻¹, T _m = (473.8 ± 0.4) K. The DSC method allowed for the phase diagrams of “water–biuret,” “water–urea,” “urea–biuret” binary systems to be studied; as a result, liquidus and solidus curves were precisely defined. Stoichiometry and decomposition temperature of the biuret hydrate identified, composition of the compound in “urea–biuret” system was suggested.     

Individual extraction constants of some organic cations in the two-phase water–nitrobenzene system

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium C⁺(aq) + Cs⁺(nb) ⇔ C⁺(nb) + Cs⁺(aq) taking part in the two-phase water–nitrobenzene system (C⁺ = organic cation; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the individual extraction constants of 15 organic cations in the mentioned two-phase system were calculated.     

Formation of solid solutions in the CdSe–PbSe system under the action of high pressures and temperatures

A method was proposed for producing solid solutions in the CdSe–PbSe systems, which is based on heat and high pressure treatment. X-ray powder diffraction analysis showed the formation of substitutional solid solutions Cd_xPb_1–xSe with the NaCl structure, which contained 20, 40, 60, and 80 mol % cadmium selenide. The solid solutions were characterized by scanning electron microscopy, impedance spectroscopy, gas pycnometry, and Raman spectroscopy.     

Concentration dependences of the physicochemical properties of a water–acetone system

Concentration dependences of the UV spectrum, refractive index, specific electrical conductivity, boiling point, pH, surface tension, and heats of dissolution of a water–acetone system on the amount of acetone in the water are studied. It is found that the reversible protolytic interaction of the components occurs in all such solutions, resulting in the formation of hydroxyl and acetonium ions. It is shown that shifts of the equilibrium between the molecules and ions in the solution leads to extreme changes in their electrical properties. It is concluded that the formation of acetone solutions of water is accompanied by heat absorption, while the formation of aqueous solutions of acetone is accompanied by heat release.     

Phase equilibrium in the ternary system water–ethylene glycol–dimethyl sulfoxide

The ternary system water–ethylene glycol–dimethyl sulfoxide (H₂O–EG–DMSO) was investigated by differential scanning calorimetry in the temperature range of 188–298 K. In the concentration range from ∼10 to ∼50 mol% DMSO, crystallization or glass formation are not observed when the temperature is lowered to 188 K. Significant supercooling of the solution in this composition range is explained by the existence of spatial networks of H₂O and EG.     

Solvation thermodynamics of benzene,nitrobenzene, and aniline in water–acetonitrile mixtures

The enthalpies of dissolution of benzene, nitrobenzene, and aniline in water–acetonitrile mixtures are determined via calorimetry. The concentration dependences of the standard enthalpies of solvation of solutes are calculated. It is found that the concentration dependences of the standard enthalpies of solvation pass through maxima. The height of the observed maxima is shown to depend largely on the nature of the substituent. In the presence of a hydrophilic amino group capable of forming strong hydrogen bonds with water molecules, the value of a maximum falls; in the presence of a nitro group, it rises. The enthalpy parameters of pair interaction between molecules of water and benzene and its derivatives are calculated.     

Individual extraction constants of some univalent cations in the two-phase water–phenyltrifluoromethyl sulfone system

The preparation and characterization of three different phases of zirconium phosphate (ZrP) have been carried out using XRD, SEM, EDX, and FTIR spectroscopy. The phases exchange and sorption properties with three different radioisotope ²³⁴Th, ²³⁸U, and ¹³⁴Cs were investigated.     

Individual extraction constants of some divalent metal cations in the two-phase water–nitrobenzene system

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M²⁺(aq) + Sr²⁺(nb) ? M²⁺(nb) + Sr²⁺(aq) taking part in the two-phase water–nitrobenzene system (M²⁺ = Mg²⁺, Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, ${\text{UO}}_{2}^{2 +} $ , Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the individual extraction constants of the M²⁺ cations in the mentioned two-phase system were calculated; they were found to increase in the following cation order: ${\text{UO}}_{2}^{2 + } $  < Zn²⁺, Ni²⁺ < Cu²⁺, Cd²⁺ < Co²⁺ < Mg²⁺ < Ca²⁺ < Mn²⁺, Fe²⁺ < Sr²⁺ < Pb²⁺ < Ba²⁺.