Adsorption of 1,1,3,3-tetramethyl-2-thiourea on the mercury electrode: dependence on the concentration of the base electrolyte

Adsorption of 1,1,3,3-tetramethyl-2-thiourea (TMTU) on a mercury electrode from 1, 0.5, and 0.1 M NaClO₄ is described by means of the adsorption isotherms constants calculated from the surface pressure as a function of electrode charge density and adsorbate bulk concentration. The adsorption parameters for the double-layer were calculated based on the data from the differential capacity-potential curves. The values of the relative surface excess increase with an increase in the concentration of NaClO₄. In each system studied, significantly smaller values of Γ_S for σ_M<0 were obtained, compared with the corresponding values for σ_M≥0. At positive values of σ_M, the values of ΔG° obtained from either the Frumkin or the Flory-Huggins isotherm are similar. However, the values of the parameter A obtained from the Flory-Huggins isotherm are lower.The dependence of Φ^M−2 on the relative surface excess at a constant charge density is nonlinear. The rectilinear segments of these dependences obtained for smaller values of Γ′ were analyzed in order to calculate the electrostatic parameters of the inner layer.     

Knudsen diffusion of various gases through a barium sulphate packed bed

The diffusion coefficients, D_k, of helium, krypton, carbon dioxide and air through a packed bed of barium sulphate calculated from the Knudsen diffusion flow equation were found to be a cumulative parameter obtained from the contribution of the diffusion coefficient through the voids of the packed bed, D_v, and the diffusion coefficient through the pores, D_p, within barium sulphate.The surface area of compacted and uncompacted material obtained from low temperature gas adsorption and the Brunauer, Emmett and Teller equation (BET), together with the void sizes and pore sizes in compacted material obtained by Barrett, Joyner and Halenda (B.J.H.) isotherm analysis, when compared with the surface area values obtained by Knudsen diffusion and permeametry, indicated that the coefficients D_v and D_p evaluate the void and pore areas in compacted barium sulphate, respectively.     

Departure from the Vogel behaviour in the glass transition—thermally stimulated recovery, creep and dynamic mechanical analysis studies

In this work the study of the dynamics of the segmental motions close to T_g of a poly(methyl methacrylate), PMMA, network was analysed by distinct mechanical spectroscopy techniques. Three techniques were employed: dynamic mechanical analysis (DMA), creep and thermally stimulated recovery (TSR). The time-temperature superposition principle was applied to the DMA and creep results, and master curves were successfully constructed. A change from a Vogel to an Arrhenius behaviour was observed in these results. Above T_g it was found a distinct temperature dependence for the retardation times calculated from creep and the relaxation times calculated from DMA. This unexpected behaviour was attributed to the merging of the α and the β relaxations that occurs in PMMA systems. The apparent activation energies (E_a) were also calculated from DMA, creep and TSR experiments. Above T_g the E_a values obtained agreed very well for all the techniques. In addition, the fragility exhibited by this material was investigated by the mechanical spectroscopy techniques referred above and by differential scanning calorimetry (DSC). The obtained values of the fragility index m indicated that the PMMA network is a kinetically fragile system. The thermodynamic manifestation of the fragility was also analysed.     

The equation of catalytic current of the Fe+3H2O2 system with regard to hydroxylation

On the basis of the reaction layer concept, the equation describing the value of i_k/i_d has been introduced with regard to a few chemical reactions responsible for the occurrence of catalytic current. The value calculated have been compared with those obtained experimentally.     

Simultaneous determination of three Flory–Huggins interaction parameters in polymer/solvent/nonsolvent systems by viscosity and cloud point measurements

We propose an integral procedure to simultaneously obtain the three Flory–Huggins interaction parameters in polymer(3)/solvent(2)/nonsolvent(1) systems by carrying out only viscosity and cloud point measurements. First, the interaction parameter between polymer and solvent, χ₂₃, is obtained by applying the Rudin's model which has been well established for various polymer solutions. Then the solvent/nonsolvent interaction parameter χ₁₂ and polymer/nonsolvent interaction parameter χ₁₃ are calculated by combining the Rudin's model and the modified Flory–Huggins free energy for the ternary system, which leads to a group of candidate values of χ₁₂ and χ₁₃. Finally, these values are selected by the best agreement between the calculated binodal curves and the measured cloud points of the ternary system. This procedure has been successfully applied to PES/NMP/H₂O, PAN/DMSO/H₂O, and PAN/DMF/H₂O systems. All the values obtained are comparable to those reported previously. The procedure is simple and easy to follow, with no requirement of complex equipments.     

Binary interaction coefficients of the Redlich—Kwong equation of state

A direct relationship between the binary interaction coefficients, k_ij and c_ij proposed by Chueh and Prausnitz, and Zudkevitch, for modifying the original mixing rules of the Redlich—Kwong equation of state is presented. Values of k_ij are evaluated by means of two methods for binary vapor—liquid equilibrium data for five systems at a total of thirty-two isothermal conditions. The calculated results from k_ij value obtained by minimizing Σ|ΔP| values are preferable to those obtained by minimizing Σ|Δy| values. The effect of temperature on k_ij for the systems investigated is shown and discussed.     

Degree of polymerization of the CaAl2Si2O8 aluminosilicate glass

The pressure dependence of the refractive index for a glass of the composition 0.50SiO₂ · 0.25Al₂O₃ · 0.25CaO at pressures up to 5.0 GPa is determined using a polarizing interference microscope and an apparatus with diamond anvils. The densities and compressibilities of the glass are calculated from the measured refractive indices within the framework of the theory of photoelasticity. The results are compared with the data obtained earlier for vitreous silica. The lower compressibility of the glass under investigation as compared to the compressibility of fused silica is in agreement with the degree of polymerization that is calculated with due regard for the formation of triclusters from the relationship NBO/T = (2O + 3O _t ? 4T)/T, where NBO (nonbridging oxygen) is the number of nonbridging oxygen atoms; O is the number of gram-ions of oxygen, except for of tricluster oxygen; O _t is the number of gram-ions of tricluster oxygen; and T is the total number of gram-ions of network formers.     

Adsorption of some highly toxic dyestuffs from aqueous solution by chitin and its synthesized derivatives

The adsorption of indigo carmine (IC) and trypan blue (TB) by chitin was kinetically investigated as dependent on temperature and pH. Experimental data obtained at different temperatures for the adsorption of each dyestuff were applied to the pseudo first-order, the pseudo second-order and the intraparticle diffusion rate equations, and the pseudo first-order rate constants (k₁), the pseudo second-order rate constants (k₂) and the intraparticle diffusion rate constants (k_p) at these temperatures were calculated, respectively. In addition, adsorption isotherms of each dyestuff by chitin were also determined at different temperatures. It was seen that adsorption isotherms fitted the H type. Chitin was then modified via ring-opening reaction with cyclic acid anhydrides (succinic, maleic and 1,2,4-benzenetricarboxylic) in lithium chloride/N,N-dimethylacetamide. Chitin derivatives obtained were compared according to their capabilities to adsorb IC and TB. It was determined that IC and TB were more adsorbed by chitin modified with 1,2,4-benzenetricarboxylic anhydride (CBA) and chitin modified with maleic anhydride (CMA), respectively. 31.33% of IC (C_o: 300 ppm) by CBA, and 44.29% of TB (C_o: 200 ppm) by CMA were adsorbed. Then, the adsorption of IC by CBA and of TB by CMA was kinetically investigated as dependent on temperature. The constants k₁, k₂ and k_p related to the adsorption of IC by CBA and of TB by CMA were calculated as stated above.     

Modeling of segregation in magnetized fluidized bed with binary mixture of Geldart-B magnetizable and nonmagnetizable particles

For the magnetized fluidized bed(MFB)with the binary mixture of Geldart-B magnetizable and nonmagnetizable particles,the magnetically induced segregation between these two kinds of particles occurs at high magnetic field intensities(H),leading to the deterioration of the fluidization quality.The critical intensity(H_(ms))above which such segregation commences varies with the gas velocity(U_g).This work focuses on establishing a segregation model to theoretically derive the H_(ms)–U_g relationship.In a magnetic field,the magnetizable particles form agglomerates.The magnetically induced segregation in essence refers to the size segregation of the binary mixture of agglomerates and nonmagnetizable particles.Consequently,the segregation model was established in two steps:first,the size of agglomerates(d_A)was calculated by the force balance model;then,the H_(ms)–U_g relationship was obtained by substituting the expression of d_Ainto the basic size segregation model for binary mixtures.As per the force balance model,the cohesive and collision forces were 1_2 orders of magnitude greater than the other forces exerted on the agglomerates.Therefore,the balance between these two forces largely determined d_A.The calculated d_A increased with increasing H and decreasing U_g,agreeing qualitatively with the experimental observation.The calculated H_(ms)–U_ g relationship agreed reasonably with the experimental data,indicating that the present segregation model could predict well the segregation behavior in the MFB with the binary mixture.     

Thermodynamic calculation of Ms in ZrO2–CeO2–Y2O3 system

The difference of Gibbs free energy between tetragonal and monoclinic phases in ZrO₂–CeO₂–Y₂O₃ as a function of composition and temperature is thermodynamically calculated from the three related binary systems. In 8 mol% CeO₂–0.5 mol% Y₂O₃–ZrO₂, the equilibrium temperature between tetragonal and monoclinic phases, T₀, is obtained as 832.5 K and the M_s temperature of this alloy with a mean grain size of 0.90 μm is calculated as 249.9 K using the approach derived by Hsu et al. [J. Mater. Sci., 18(1983)3206; 20(1985)23; Acta Metall., 37(1989)3091; Acta Metall. Mater., 39(1991)1045; Mater. Trans. JIM, 37(1996)1284], which is in good agreement with the experimental one of 253 K.     

Calorimetric study of ytterbium orthovanadate YbVO4 polycrystalline ceramics

The heat capacity of ytterbium orthovanadate was first measured by adiabatic calorimetry in the temperature range T?=?12.28–344.06?K. No obvious anomalies were observed on the curve obtained. The values of standard thermodynamic functions in the temperature range T?=?0–400 K were calculated. Based on low-temperature calorimetry data obtained, previously published data on the high-temperature heat capacity of ytterbium orthovanadate were corrected. The anomalous contribution to heat capacity for YbVO₄ was compared with the data known for YbPO₄.     

Miscibility of oligomeric poly(dimethyl siloxanes) with long-chain unbranched alkanes: 2. Unsymmetrical cloud point curves

Previously obtained cloud point curves for mixtures of oligomeric poly(dimethyl siloxanes) (weight fraction W₁) with oligomeric polyethylenes have been supplemented by the use of samples of higher molecular weight. Initial flat regions at low-medium W₁ as well as a slight shoulder at extremely high W₁ are now considered to be due to crystallization, since the temperatures at which they occur are the melting points of the oligoethylenes. The actual cloud point curves were of an unsymmetrical dome shape, the form of which could not be simulated by using a concentration-independent interaction parameter g in the Flory-Huggins equation. However, spinodals calculated by assuming a quadratic dependence of g on composition were of the same shape as the experimental cloud point curves. The critical compositions calculated on this basis were also close to the experimental ones.     

Raman spectroscopy study of high-modulus carbon fibres: effect of plasma-treatment on the interfacial properties of single-fibre-epoxy composites: Part II: Characterisation of the fibre-matrix interface

High-modulus carbon fibres from different precursors were submitted to an oxygen plasma-treatment under similar conditions. Single-fibre epoxy composites were prepared from them, and fragmentation tests were performed in order to characterise fibre-matrix interfacial adhesion. Raman spectroscopy has been used in the present work to map the strain along the fibre during tensile loading of the matrix. The strain distributions obtained agreed well with the prediction of analytical models used conventionally to describe load transfer at interfaces. Interfacial shear stress distributions were then obtained from these distributions according to the conventional force-balance concept. The interfacial shear strength (IFSS) and frictional shear stress (τ_f) values were calculated to quantify the degree of fibre-matrix adhesion. It was found that both parameters increased dramatically after the surface treatment, confirming the ability of cold plasma oxidation to improve the adhesion of carbon fibre to epoxy matrices. A dependence of the IFSS on the degree of surface order, as given by the structural order parameter I_D/(I_D+I_G), calculated from the relative intensities of the D and G bands of Raman spectra, was found. This supports the role played by the graphitic structure in fibre-matrix adhesion.     

Linear viscoelastic properties of epoxy resin polymers in dilatation and shear in the glass transition region: 2. Measurement of the glass transition temperature

Measurements of the 20 second creep compliances in dilatation and shear, over a range of temperature spanning the glass transition region, have been made for six epoxy resin polymers. The linear thermal expansion behaviour has been determined in the same temperature range. Shear and dilatational compliances, and the linear thermal expansion properties may all be measured on the same specimen. Values of the glass transition temperature derived from 20 sec shear and bulk compliance data agree well with values obtained from thermal expansion data. When T_g was derived from creep data obtained at longer creep times (in part 1 of this paper), it was found that T_g in dilatation exceeds T_g in shear. It was shown that this is consistent with the difference in activation energies in dilatation and shear obtained in part 1 of this paper. An example is given of how systematic errors of the order of 1°C in temperature measurement may lead to maxima or minima when Poisson's ratio is calculated from measured values of shear and tensile compliances.     

Surface Activities, Foam Properties, HLB, and Krafft Point of Some n-Alkanesulfonates (C14–C18) with Different Isomeric Distributions

A homologue series of sodium secondary n-alkanesulfonates (C₁₄, C₁₆ and C₁₈) were obtained by photosulfochlorination process with two different reaction conditions. Different length chains with different isomeric distributions of n-alkanesulfonates are expected to present variations in physicochemical properties. In this investigation, the relationships between their isomeric distribution and their chain length and micellar behaviors were thoroughly explored. Their CMC at different temperatures were determined using specific conductivity and surface tension measurements. Through surface tension isotherms, the surface activities (??_CMC) were obtained. The surface absorption amounts (??_max) and the molecular areas (A _min) were calculated using Gibb??s equation. As expected, these surfactants exhibit good surface properties. It was shown that the CMC values increase with increasing the percentage of secondary isomers, with a surface tension decrease. It was also shown that the CMC values decrease with increasing chain length. The HLB values were calculated for each surfactant and the results obtained suggest that they are O/W emulsifiers. The foam properties of synthesized surfactants were evaluated and compared to those obtained for commercial samples. It was shown that the foamability is influenced both by the length of the hydrophobic moiety and the percentage of secondary isomers. It can be easily concluded that the C₁₄ sulfonates show the best foaming properties independently of their isomeric distribution. The Krafft point values obtained indicate that the micellization and the surfactant solubility mainly depend on the proportion of secondary isomers and the length of hydrophobic moiety.     

Cationic polymerization of acenaphthylene and methyl acenaphthylenes

Cationic polymerization of acenaphthylene was studied both by experimental methods and theoretical calculations. Very pure acenaphthylene was obtained by double sublimation and its polymerization kinetics were studied with SnCl₄ as initiator. Reactivity ratios were determined for methyl-1, methyl-3 and methyl-5 acenaphthylenes, while values of stabilization energies, (ΔE)^s_r, have been calculated. There is good agreement between the trends of the two sets of values. In the case of acenaphthylene, the comparison of results obtained by Hückel's and by Pople's methods has shown the contribution of ring strain to the reactivity of acenaphthylenic monomers.     

Molar mass determination of poly(octadecene-alt-maleic anhydride) copolymers by size exclusion chromatography and dilute solution viscometry

The number average molar mass M_n of poly(octadecene-alt-maleic anhydride) (PODMA) copolymers calculated from data obtained by size exclusion chromatography (SEC) using a polystyrene (PS) calibration was found to be inaccurate. The use of SEC combined with dilute solution viscometry enabled a method to be developed using an iterative approach, which does not require knowledge of the Mark-Houwink constants for PODMA samples. A new calibration curve was constructed as a plot of molar mass M_u for PODMA. True number-average molar masses M_n (true) calculated using the new calibration are approximately twice the apparent molar mass M_n (app) based on a PS calibration for higher molar mass samples (>10?000 g mol⁻¹).     

Electrostatic interactions during the intercalation of Li in Lix TiS2

A model for the electrostatic interactions between the Li⁺ ions and the conducting electrons in the layered compound Li_xTiS₂ is developed. Li_xTiS₂ is considered as a sandwich structure consisting of layers of a homogeneous dielectric separated by conducting planes. The Li⁺ ions intercalated in the van der Waal gaps are treated as point charges in the dielectric and their charges are screened by the conducting planes. By image technique the interaction energy can be calculated as the Madelung energy of an ionic crystal. Assuming an effective dielectric constant of 30 good agreement between the calculated and the experimental emf-x reaction is obtained. On this basis it is concluded that the strong deviations from ideality observed during intercalation of Li⁺ in Li_xTiS₂ are due to electrostatic forces screened by the conduction electrons.     

The pressure effect on the thermodynamic properties of polystyrene—trans-decalin solution

The viscosity of a solution of polystyrene in trans-decalin was measured over pressure and temperature ranges from atmospheric pressure to 400 kg/cm² and 20° to 40°C. The viscosity measurements at elevated pressure were made by the use of a rolling-ball type viscometer, and the validity of this method was confirmed by comparing with the calibrated Ubbelohde viscometer at atmospheric pressure. Values of the interaction parameter, χ, were obtained from the coil expansion coefficients on the assumption of the fifth-power rule of the Flory theory for the expansion of the polymer molecules in the solution. χ₁ increases with increasing pressure. The pressure coefficient of the theta-temperature calculated from the pressure and the temperature derivatives of χ₁ is in good agreement with the result of Schulz et al. The values of χ₁ were compared with those calculated from the new Flory theory and the Patterson theory for polymer solutions. At lower pressure these theories predict the behaviour of χ₁ well, but at higher pressure the prediction becomes inaccurate.