Effect of the Duration of the Mechanical Activation of Granulated Mixtures of 5Ti + 3Si on the Rate of Combustion Wave Propagation and the Elongation of Samples after Synthesis

The effect the duration of the mechanical activation (MA) of preliminarily granulated mixtures of 5Ti + 3Si with titanium powder of different grades has on the dependences of combustion rates and changes in the length of samples after synthesis is studied. The dependences of the average particle size of a mixture on the duration of activation are established. It is shown that initial mixtures containing titanium of different grades have different combustion rates. It is concluded that mechanical activation leads to equalization of the combustion rates for powder mixtures at MA durations of more than 7 min and for preliminarily granulated mixtures at MA durations of 3 min. For powder mixtures, the combustion rate changes nonmonotonically as the duration of MA grows. For preliminarily granulated mixtures, it first slows and then increases monotonically. An explanation of the observed dependences is proposed. It is shown that in contrast to powder mixtures, there is a sudden increase in the relative length of samples during combustion after the MA of granulated mixtures with a duration of 1 min. This is because with granular MA mixtures, the main evolution of gas from the decomposition of bonds occurs behind the combustion front, in contrast to mixtures without MA. It is shown that the dependences of the relative length of the samples after burning on the duration of MA are close to those of mixtures with both grades of titanium.     

Solvation and cobalt-carbon homolysis of coenzyme B12 in 1-propanol/water mixtures

Summary Solvational changes on the transfer of coenzyme B₁₂ from water to 1-propanol/water mixtures were studied from the temperature dependence of the measured solubilities. These results were combined with calculations using the scaled particle theory. The strong decrease of the Gibbs energy of cavity formation on going from water to 1-propanol is for the smaller mole fractions of 1-propanol (x < 0.3) nearly balanced by a decreasing preferential (peripheral) solvation of the hydrophilic macromolecule by water. Thermodynamic and activation parameters were derived for the thermal homolytic Co-C bond breaking of coenzyme B₁₂ in 50wt% 1-propanol/water and compared with earlier values for the homolysis at 380.6 K in the mixtures. An initial state-transition state dissection of solvent effects for the homolysis reveals that desolvation does not play an important role in activation. The slightly exceptional position of water stems from a stabilization of the initial state.     

Kinetics of oxidation ofcis-, andtrans-chlorobis(ethylenediamine)isothiocyanatocobalt(III)ion with peroxodisulphate in aqueous alcoholic mixtures

Summary The effect of organic cosolvent on the rate constants and activation parameters of oxidation of coordinativelybound thiocyanate with peroxodisulphate was investigated in mixtures of water with methanol,i-propanol andt-butanol. The thermodynamic transfer functions, corresponding to the transfer of reactants and activated complex from water to the solvent mixtures were evaluated from kinetic measurements and from the solubilities of corresponding salts. The experimental results are interpreted in terms of the solvation of both the initial state and the activated complex.     

Reactivity trends in the base hydrolysis of 6-nitro-2H-chromen-2-one and 6-nitro-2H-chromen-2-one-3-carboxylic acid in binary mixtures of water with methanol and acetone at different temperatures

Kinetics of the base hydrolysis of 6-nitro-2H-chromen-2-one (NC) and 6-nitro-2H-chromen-2-one-3-carboxylic acid (NCC) in water-methanol and water-acetone mixtures was studied at temperature range from 283 to 313 K. The activation parameters of the reactions were evaluated and discussed. The change in the activation barrier of the investigated compounds from water to water-methanol and water-acetone mixtures were estimated from the kinetic data. The base hydrolysis of NC and NCC in the water-methanol and water-acetone mixtures follows a rate law with k _obs = k ₂[OH⁻] and k _obs = k ₁ + k ₂[OH⁻], respectively. The decrease in the rate constants of NC and NCC hydrolysis, as the proportion of methanol and acetone increases, is accounted for by the destabilization of the OH⁻ ion. The activation and thermodynamic parameters were determined.     

The electrical conductance of some molten car☐ylate mixtures

Data are presented for the electrical conductivities in the melt for lead(II) octadecanoate/lead(II) decanoate, lead(II) hexadecanoate/lead(II) decanoate, lead(II) hexadecanoate/zinc hexadecanoate and lead(II) hexadecanoate/cadmium hexadecanoate mixtures over their complete composition ranges. The electrical conductivities are measured as a function of temperature from just above the melting point to just below the decomposition point of the mixtures. The Arrhenius plots for the mixtures are linear in all cases and the activation energies are determined. While the activation energies for lead(II) octadecanoate/lead(II) decanoate and lead(II) hexadecanoate/lead(II) decanoate mixtures are mole fraction independent over the concentration range studied, rendering support to previous models advanced by other workers that the major charge carrier is the free metal cation, the other systems show no such simple behaviour. In these systems there are indications of deviations from ideal behaviour, suggesting that entropy and enthalpy of mixing might be important.     

The Kinematic Viscosity of Binary Liquid Mixtures of n-Nonane with Propan-1-ol,Butan-1-ol,and Pentan-1-ol over the Temperature Range 193.15–313.15 K

The kinematic viscosity of n-nonane mixtures with propan-1-ol, butan-1-ol, and pentan-1-ol was measured over the temperature range 293.15–313.15 K. For all systems, negative deviations of viscosity from additive values were obtained; the deviations increased in magnitude as the temperature and alkan-1-ol hydrocarbon radical length increased. The activation energy of viscous flow was calculated in terms of the Eyring theory and free volume theory in the usual and extended (with the inclusion of molecular association) variants at equimolar mixture compositions. The behavior of the concentration dependences of viscosity and the activation energy of viscous flow in alkan-1-ol-n-alkane mixtures was found to be controlled by molecular association processes.     

Dechlorination of contaminated sediments of Ionian Sea

Natural dredged sediments contaminated by PCBs from the heavy industrialized harbor of Taranto (S. Italy) on the Ionian Sea, previously dechlorinated by mechanical activation in different ball mills (SPEX and AGO-2), together with synthetic mixtures emulating the contaminated sediments, were submitted to thermogravimetric and calorimetric measurements as well as to X-ray powder diffraction in order to clarify the dechlorination reaction mechanism. Both major sediment components, i.e., carbonates and clay minerals, were found to be affected by the mechanical activation. As trace pollutants like PCBs are concentrated in clays, the mechanical activation of sediments increases the release of pollutants yielding a more active decontamination. DSC results were less informative as calorimetric peaks from different thermal events were found to overlap.     

Synthesis of 2-Methoxy-3-pentene in a Liquid Phase over a Sulfoionite Catalyst: II. Kinetic Model of Reactions Occurring in the Synthesis

The kinetics of 2-methoxy-3-pentene synthesis from 1,3-pentadiene isomers and methanol was considered. Reaction rates were measured experimentally, and the compositions of reaction mixtures were determined by chromatography. Reaction rate constants and the activation energy of the main reaction were determined experimentally.     

Physicochemical Properties of Lithium Perchlorate Solutions in Mixtures of Sulfolane with 1,3-Dioxolane

The electrical conductivity, viscosity, and density of sulfolane-1,3-dioxolane mixtures and 1 M lithium perchlorate solutions on their base were studied. The activation energies of viscous flow and electrical conductivity were calculated. Departures of some of the measured values from additivity are demonstrated.     

Reactivity of carbocations from 1,2-dihydroquinolines in binary mixtures of methanol with pentane and acetonitrile

The rate constants and activation parameters of the reactions of the carbocation resulting from 6-ethoxy-1,2,2,4-tetramethyl-1,2-dihydroquinoline photolysis with methanol (k ₁) and the methoxide ion (k ₂) have been measured by flash photolysis in binary mixtures of methanol with inert solvents (nonpolar pentane and polar acetonitrile) in wide composition ranges. The changes in the activation parameters for k ₁ at different solvent compositions show that the increase in the rate constant in the pentane mixtures is mainly deter-mined by the increase in the preexponential factor. The decrease in k ₁ in the acetonitrile mixtures is deter-mined by the decrease in the methanol concentration and by the increase in the activation energy. The different roles of the methoxide ion in the reaction are demonstrated. They depend on the nature of the inert solvent in the mixture. The results of this study are considered in terms of methanol clustering in pentane and acetonitrile, the different solubilities of 6-ethoxy-1,2,2,4-tetramethyl-1,2-dihydroquinoline in the components of the binary mixtures, and the difference in distribution and solvation between the carbocation and the methoxide ion in the mixtures.     

Characterization of Dominant Hydrogen Bonded Complex Structures of Dielectric Polarization and Viscous Flow Processes in Glycerol–Formamide Binary Mixtures

The static permittivity and viscosity of glycerol–formamide (Gly–FA) binary mixtures were measured at eleven concentrations over the entire composition range and at temperatures T=288.15, 303.15, 318.15 and 333.15 K. The excess static permittivity and excess viscosity of the mixtures were determined using the mole-fraction additive mixture law. Results indicated that the molecular dielectric polarization in Gly–FA mixtures is governed by 1:1 complexes with a decrease in number of H-bonded parallel aligned dipolar ordering at all of the investigated temperatures. The 2Gly:FA complexes facilitate the viscous flow process and the number of these complexes decreases with increasing temperature. The apparent activation energy of viscous flow, determined from Arrhenius plots, increases with increases of the Gly concentration in the mixtures. The electric-field-induced increment of the Helmholtz free energy and the entropy of these binary mixtures were determined from the temperature dependence of the static permittivity and its derivative, respectively.     

Thermoanalytical investigation of drug–excipient interaction

Piroxicam–excipient (chitosan or cellulose) mixtures after mechanical activation were investigated using DSC. Crystallization of amorphous piroxicam was detected near 80°C in the mixtures of the components activated separately. If the components in the mixture are activated together, amorphous piroxicam does not crystallize at heating. Both excipients interact with piroxicam, decreasing its melting point and enthalpy of melting. Mechanical activation intensifies the interaction, decreasing the melting point by 8°C and reducing the enthalpy of melting two times.     

The reduced Redlich–Kister excess molar Gibbs energy of activation of viscous flow and derived properties in 1,4-dioxane + water binary mixtures from 293.15 to 309.15 K

The excess molar volume, viscosity deviation and excess Gibbs free energy of activation of viscous flow have been investigated from the density and shear viscosity measurements of water–dioxane mixtures over the entire range of mole fractions from 293.15 to 309.15?K. The results were fitted by the Redlich–Kister equation. Partial molar volume and Gibbs energy at infinite dilution were deduced from four methods, activation parameters and partial molar Gibbs energy of activation of viscous flow against compositions were investigated. The water–dioxane interactions have principally an H-bound character and there are two principal types’ structures limited by 0.08?mole fraction in dioxane. The reduced Redlich–Kister excess properties provide an indication of the intermolecular interactions and for dioxane–water cluster formation as suggested in the literature.     

Temperature Dependent Dielectric Relaxation in Solvent Mixtures at Microwave Frequencies

By the use of time domain reflectometry method, dielectric measurements were carried out on dimethylformamide‐2‐nitrotoluene solvent mixtures in the frequency range 10 MHz‐20 GHz, at various temperatures from 15 °C to 45 °C. These solvent mixtures as well as pure solvents display a Debye type dispersion. Their frequency dependent dielectric properties can be summarized by the three parameters in the Debye equation: a static permittivity, permittivity at high frequency and a dielectric relaxation time constant. The free energy of activation for dipolar relaxation process and the Kirkwood correlation factor were determined using these fitting parameters for these solvent mixtures at various concentrations and temperatures. By using these dielectric parameters, the excess permittivity and excess inverse relaxation time is obtained. The excess permittivity is found to be positive for all concentrations and temperatures whereas the excess inverse relaxation time is negative.     

Study of viscometric properties of L-ascorbic acid in binary aqueous mixtures of D-glucose and D-fructose

The relative viscosities and activation parameters of L-ascorbic acid have been determined in water and binary aqueous mixtures of D-glucose and D-fructose at different temperatures. A and B-coefficients of Jones–Dole equation are determined using density and viscosity data. Gibbs energy of activation of viscous flow per mole of solvent as well as per mole of solute along with activation enthalpy and entropy is also determined using Feakin’s transition-state theory. The obtained results are explained in terms of intermolecular interactions and in this study L-ascorbic acid has been found as structure breaker in binary aqueous mixtures of D-glucose and D-fructose.     

A correlation of gas solubilities and kinetics of hydrolysis in binary aqueous mixtures

A treatment which predicts the solubilities of gases in solvent mixtures is examined in the context of the analysis of kinetic data for reactions in aqueous mixtures. The treatment is qualitatively successful to some extent in resolving the effects of changes in the initial state of the reacting substrate in the activation parameters.     

Physico-chemical properties of binary mixtures of 1-butanol with chloroethanes or chloroethenes at 298.15 K

The densities ρ, speeds of sound u, and viscosities η, of pure 1-butanol, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, trichloroethylene, and tetrachloroethylene and those of their binary mixtures have been measured at 298.15 K and atmospheric pressure over the entire range of compositions. Excess molar volumes V ^E, viscosity deviations Δη, deviation in compressibilities Δκ_s and excess Gibbs energy of activation G*^E, were obtained from the experimental results and those were fitted to Redlich–Kister's type function in terms of mole fractions. Viscosities, speeds of sound and isentropic compressibilities of the binary mixtures have been correlated by means of several empirical and semi-empirical equations. The experimental data are analysed to discuss the nature and strength of intermolecular interactions in these mixtures.     

The thermal stability of copolymers of allyl alcohol with acrylonitrile and methyl methacrylate

Homopolymerization of allyl alcohol (AA) initiated by gamma rays and copolymerization of AA with methyl methacrylate (MMA) and acrylonitrile (AN) were investigated. The thermal stabilities of the homopolymers and copolymers were determined and their degradation activation energies calculated. The copolymers, P(AA/AN), obtained from AA + AN monomers were more stable thermally than those copolymers, P(AA/MMA), formed from AA + MMA monomer mixtures.     

Catalyse multifonctionnelle—VI : Isomerisation de la Δ-5 cholestenone par les melanges phenols-amines

Kinetic study of Δ-5 cholestenone isomerisation in benzene, catalysed by phenols-triethylamine mixtures indicates a transition state with a mole of phenol and a phenol-triethylamine complex. Catalytic activity of phenols-triethylamine mixtures according to versus those complexes association constants in benzene shows a clear maximum for m-nitrophenol. Besides, activation enthalpies are decreasing with phenols acidities, while activation entropies become more negative.     

Viscosities and thermodynamics of viscous flow of some binary mixtures at different temperatures

Viscosities of three non-electrolyte binary mixtures have been determined at different temperatures over the complete concentration range. Excess molar viscosities and excess molar energies of activation for viscous flow for n-butylamine + dichloromethane, n-butylamine + chloroform and n-butylamine + carbon tetrachloride systems at 20°C, 25°C, 30°C and 35°C were calculated. Thermodynamic effect parameters of activation were also calculated. The predictive abilities of some equations for viscosities of mixtures were examined.Presented at the XV Jornadas sobre Investigación en Ciencias de la Ingeneriía Química y Química Aplicada, Neuquén, 1989, R. Argentina.