Kinetic analysis of the crystallization processes in the glasses of the Bi–As–S system

Kinetic analysis of the crystallization process in Bi₄(As₂S₃)₉₆ and Bi₆(As₂S₃)₉₄ glasses was performed based on DSC curves recorded under non-isothermal measurement conditions. Samples were thermally treated at different heating rates in the temperature range 300?C770?K. The activation energy of crystallization E and the pre-exponential factor K ₀ are determined by the Kissinger method and the characteristic crystallization parameters m and n of investigated glasses by the Matusita method. For both crystallization processes the glass with 4 at.% of Bi is characterized by the mechanism of volume nucleation, which is manifested in the form of two-dimensional growth at the first crystallization process, and as three-dimensional at the second one. On the other hand, in the sample with 6 at.% Bi, the average value of the parameter m is close to one, which indicates one-dimensional crystal growth. Compatibility of the values of the parameters m and n suggests that this sample has a large number of crystallization centers, which do not increase significantly during the thermal treatment.     

Anomalies in the Change of Volumetric Parameters of the Diels–Alder Reaction in Solution

In this article negative values of the activation volume in retro-Diels–Alder reactions are interpreted in terms of the different possibilities of penetration of the solvent molecules into the sterically branched structures of the adduct and activated complex. Empty spaces, inaccessible to penetration of solvent molecules, lead to increases of the molar volume of the screened adducts in solution and, consequently, to a less negative value of the Diels–Alder reaction volume. The values of partial molar volumes of anthracene, maleic anhydride and the adducts cyclopentadiene–maleic anhydride, anthracene–maleic anhydride and anthracene–tetracyanoethylene, in several solvents, were calculated from the solution density data.     

Thermal diffusion in Lennard–Jones fluids in the frame of the law of the corresponding states

This work is related to the definition of a reduced thermal diffusion coefficient thanks to numerical microscale molecular dynamics simulations. This cross transport process, also called Soret effect, couples mass flux and thermal gradient and is still largely misunderstood. For this study, we have applied a boundary driven non-equilibrium molecular dynamics algorithm on Lennard–Jones spheres mixtures. Simulations have been performed at a constant reduced supercritical state, using a van der Waals’ one fluid approximation in order to fulfil the law of the corresponding states. In binary mixtures, we have studied the molecular parameters and the molar fraction influences on thermal diffusion separately and then combined. It is shown that, on pressure and on thermal conductivity, the corresponding states law is fulfilled for a wide range of molecular parameters ratios. In this frame, we have then constructed simple correlations which relate thermal diffusion factor to the mixture parameters. Combining the relations obtained, a reduced thermal diffusion factor taking into account all the various contributions has been defined. Finally, it is shown that this relation enables us to estimate thermal diffusion in various binary and ternary mixtures of Lennard–Jones spheres representing alkanes with a maximum deviation of 15%.     

Formation of the layering boundary in the water–benzene–perfluorobenzene system

The dynamics of the interface between liquid phases in the water–benzene–perfluorobenzene system was studied in a natural experiment. The interfacial tension was found to depend on the density of the organic layer. The range of interfacial tensions in which inversion of the organic and aqueous phases takes place was determined, and the working range of a separating flask as an element of the separation scheme for the mixture was revealed.     

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.     

Thermodynamics of the solubility of sulfamethoxydiazine in organic solvents in the range 293.15–323.15 K

The solubilities of sulfamethoxydiazine in methanol, ethanol, 1-propanol, 2-propanol, acetone, and chloroform have been determined in the range 293.15–323.15 K by a static equilibrium method. The calculated results show that the correlation of the Apelblat equation for measured systems has less deviation than that of the λh equation. The positive Δ_sol H and Δ_sol S for each system revealed that sulfamethoxydiazine being dissolved in each solvent was an entropy-driven process.     

Manifestation of the Even–Odd Effect in the Spectral Properties of Solvated Electron and in the Probability of Positronium Formation in Alcohols

A change in the energy E _max of the solvated electron, which corresponds to the maximum intensity of its optical absorption spectrum in the homologous series of alcohols seems to be alternating in character. The effect is retained upon elevation of pressure up to 2 kbar but disappears in alcohols frozen at 77 K. Probably, the effect also holds for amines. The alternating character of variation is also observed for the intensity Y ₁ of the narrow components of the angular spectrum of -photons generated upon positron annihilation in alcohols and normal alkanes. The nature of alternation of E _max is associated with the mutual elimination of electric fields induced by the dipole moments of two neighboring CH₂ groups in each solvent molecule, including also the molecules forming the solvation shell of an excess electron. That fact that the E _max value correlates to Y ₁ led to the conclusion that Y ₁, rather than the intensity I ₃ of the long-lived component of the annihilation time spectrum generally used for the purpose, more adequately characterizes the positronium formation probability.     

Investigation of the kinetics of the chain-radical process in the system iron carbonyl–Lewis base

An ESR spectroscopy investigation of the kinetics of accumulation and consumption of iron carbonyl radical anions, Fe₃(CO)₁₂⁻ and Fe₃(CO)₁₁⁻, arising in the reaction of Fe₃(CO)₁₂ with (Et₄N)SEt in THF at 19.5°C, was carried out using the stopped-flow technique. The solution of the inverse kinetic problem showed a satisfactory agreement between calculated and experimental data. This supports the principal idea that chain radical processes including preliminary complex formation followed by one-electron redox-initiation lie at the heart of the interaction of iron carbonyls with Lewis bases, and that the following transformations are due to electron and ligand changes in the coordination sphere of seventeen-electron coordinatively unsaturated species.     

Phase equilibria in the palladium-rich part of the Pd–Au–Cu–Sn quaternary system

The solubility of tin in the phases of Pd–Au–Sn and Pd–Cu–Sn ternary systems and a Pd–Au–Cu–Sn quaternary system with a fixed Pd: Au: Cu ratio of 11.1: 1: 4.6 is studied via microstructural, X-ray diffraction, and energy dispersive analysis. It is found that a quaternary alloy in equilibrium with a solid solution based on Pd, Au, and Sn contains a τ₁ compound with structure which is derivative of the In type. It contains ~15 at % Sn and is a solid solution of the same compounds identified earlier in Pd–Au–Sn and Pd–Cu–Sn ternary systems. In addition, a quaternary alloy with a content of 20 at % Sn also contains a τ₂ compound with the Pd₂CuSn own type and can barely dissolve gold. The obtained data are used to construct a three-dimensional model of the Pd-rich part of the isothermal tetrahedron of the Pd–Au–Cu–Sn system and diagrams of the tin solubility isolines in palladium-rich alloys of the quaternary system at 500°С.     

Synthesis of quasi-crystalline phases in the Al–Cu–Fe–Cr system

Phase equilibria in the Al–Cu–Fe system alloyed with 5% Cr were studied. Based on the data of X-ray powder diffraction analysis, electron microscopy, and differential thermal analysis, the effect of temperature on i ? d phase transitions in alloys Al₆₅Cu₂₅Fe₅Cr₅ and Al₇₀Cu₂₀Fe₅Cr₅. In the Al–Cu–Fe–Cr system, multiphase structures were detected; these structures are mixtures of quasi-crystalline and approximant phases, the contents and morphologies of which depend on the composition of the initial mixture and the crystallization rate.     

Modification of the Pictet–Spengler reaction in the synthesis of fused 2,3-benzodiazocines

A new strategy for the synthesis of the eight-membered heterocyclic skeleton of tetrahydro-quinazolino[3,2-c][2,3]benzodiazocin-15-ones, based on the Pictet–Spengler reaction of 3-amino-2-[2-(3,4-dimethoxyphenyl)ethyl]quinazolin-4(3H)-one with carbonyl compounds in acidic media, is proposed.     

Investigation of the presence of KCl in the structure and morphology of V-amylose–inclusion complexes

Amylose–fatty acid inclusion complexes were prepared using amylose extracted from pea starch and fatty acids with different chain length. To form the complexes, amylose, dissolved in aqueous alkaline solution (0.1 Ν ΚΟΗ), was mixed with fatty acid potassium soap solution and after neutralization the complex was obtained as precipitate. To investigate the structure and morphology of V-amylose–inclusion complexes, a series of techniques such as X-ray diffraction, SEM-microscopy combined with elemental microanalysis, Differential scanning calorimetry and Fourier transform infrared spectroscopy were employed. XRD analysis of complexes, revealed that the complexes displayed the typical V-form pattern, with an extra peak at 2θ?=?28.2°. To identify the origin of that peak the complexes were examined by SEM microscopy combined with elemental microanalysis. The results indicated that the peak was due to the presence of potassium chloride, formed during the preparation of the complexes. Washing the complexes with water was sufficient to remove the salt.     

Variations in Elastic and Viscous Properties in the Course of Nematic–Nematic Transition in the Tetrapalladium Organyl–Pentadecane System

Temperature dependences of elasticity constants and viscosity coefficients for nematic phases of a tetrapalladium organyl–pentadecane system were experimentally studied. At the temperature of the nematic–nematic transition, all the parameters measured were shown to vary in a stepwise manner. For the high-temperature phase N₂, the ratio of elasticity constants K ₃/K ₁ 3, whereas K ₃/K ₁ 10 for the low-temperature phase. The effective viscosity decreases by the order of magnitude in the course of the N₂–N₁ phase transition. On the basis of these results, the conclusion was made that the order parameter and length of columns, structural units of the nematic phases, sharply increase upon the N₂ N₁ transition.     

Phase equilibria in the aluminium-rich side of the Al–Zr system

The Al-rich phase equilibria in the Al–Zr binary system were investigated experimentally. The phase diagram for compositions up to 40 at.% Zr was determined experimentally by differential thermal analysis and metallography. Three stable intermetallic compounds exist in this region of the diagram: Al₃Zr₂, Al₂Zr, and Al₃Zr. The peritectic melting of Al₃Zr₂ and the congruent melting of Al₂Zr were confirmed. Al₃Zr, the most Al-rich intermetallic compound, melts peritectically, which contradicts information available in the literature. In addition, the reaction between Al₃Zr and the (Al) solid solution seems to be of eutectic nature, in contradiction with previous results found in the literature. Based on these new experimental evidence, a revised phase diagram is drawn.     

Simulation of the random scission of C–C bonds in the initial stage of the thermal degradation of polyethylene

We performed molecular dynamics simulations to analyze the initial stage of the thermal degradation of polyethylene, which is dominated by the random scission reaction. The simulations were initiated from structures that were taken from previously equilibrated snapshots of the amorphous polymer and of a free-standing thin film. Isolated chains were also used for comparison. Our systems were coupled to a thermal heat bath, and the effect of different coupling constants was studied. Rate of random scission increases as the strength of the temperature coupling increases. Rates of reaction are almost similar in thin films and the bulk, whereas the rates are much faster in isolated chains. Expansion of the free-standing thin film accompanies degradation, producing fragments of various sizes. Chains of higher molecular weights than the initial chains can be produced due to recombination of fragments during the expansion of thin films. The polydispersity index of the resulting fragments is higher in thin films compared to the bulk. The bonds at the low density portion of the thin films have a higher probability of being broken.     

Formation of calcium in the products of iron oxide–aluminum thermite combustion in air

The composition of condensed products resulting from the combustion of thermite mixtures (Al + Fe₂O₃) in air is studied by precise methods. It is shown that during combustion, calcium is formed and stabilized in amounts of maximal 0.55 wt %, while is missing from reactants of 99.7 wt % purity. To explain this, it is hypothesized that a low-energy nuclear reaction takes place alongside the reactions of aluminum oxidation and nitridation, resulting in the formation of calcium (Kervran–Bolotov reaction).     

Counterion effects in the preparation of aldehyde–bisulfite adducts

The identification and development of an aldehyde–bisulfite adduct as an isolable starting material in the synthesis of the CETP inhibitor Evacetrapib are described. The physical properties of the sodium and potassium analogs are compared, and the extension of the scope of this study to include an investigation into the solid state properties of a range of sodium and potassium bisulfite adducts of commonly encountered aldehydes is discussed.     

Use of the Mass Spectrum–Compound Fragment Composition Database in the Determination of the Structure of Organic Compounds

A mass spectral database in which structural formulas are presented as nonisomorphic connected k-vertex fragments (2 k 7) is used for identifying the structure of organic compounds. It is shown with the example of a test sample of 13000 mass spectra of various organic compounds that up to half the fragments of an unknown analyte can be identified in 50% of cases. Relationships between the correctly and erroneously identified data are given.     

Experimental investigation of the formation of double phosphates in the LaPO4–NaF system

In the course of segregation smelting of rare-earth and rare metal raw materials with a fluxing agent (NaF), two immiscible melts form, one of which is a silicate melt and the other is a phosphate–salt melt. The silicate melt is enriched with Fe₂O₃, Al₂O₃, SiO₂, and Nb₂O₅, and the phosphate–salt melt is dominated by P₂O₅, TR₂O₃, Sc₂O₃, and Y₂O₃, and also with Ca, Sr, and Ba oxides. Chemical reactions between lanthanum orthophosphate and sodium fluoride in the LaPO₄–NaF system were studied for developing a technology for processing the phosphate–salt (rare-earth metal) melt. It was found that a metathesis reaction gives double phosphate Na₃La[PO₄]₂ and binary fluoride NaLaF₄. The products of crystallization of melts in the LaPO₄–NaF system decompose in weak mineral acids unlike those in conventional technology for processing monazite raw material.     

Determination of the Activity Coefficients of NaCl in the System NaCl–NH4Cl–H2O

Using ion-selective electrode(s) (ISE) the activity coefficients of NaCl in the system NaCl–NH₄Cl–H₂O at 10, 25, and 40°C were measured by a computer-controlled automatic titration system. The ionic strength fractions of NH₄Cl were 0.2, 0.4, 0.6, and 0.8, respectively. It was found that the influence of the NH₄⁺ cation on the Na glass ISE was small enough to be neglected up to 3.0 mol-kg^-1. The Pitzer equation was adopted to calculate the activity coefficients of NaCl in this system and compared with the experimental data. Comparison of results indicates that the Pitzer parameters correlated from solubility data are suitable for calculating the activity coefficients for this system within the saturated solutions.