Effects of the orientation of smectite particles and ionic strength on diffusion and activation enthalpies of I and Cs ions in compacted smectite

The apparent diffusion coefficients (D_a) for I⁻ and Cs⁺ ions in compacted Na-smectite which is a major constituent clay mineral of bentonite were studied as a function of smectite's dry density (0.9–1.4 Mg/m³), ionic strength ([NaCl] = 0.01, 0.51 M), temperature (22–60 °C) and diffusion direction to the orientated direction of smectite particles. The Na-smectite was prepared by ion-exchanging with Na⁺ ions a Na-bentonite, Kunipia-F®, of which smectite content is over 99 wt.%. The D_a-values for both ions showed a tendency to be higher in the parallel direction than in the perpendicular direction to the orientated direction of smectite particles at a low-ionic strength of [NaCl] = 0.01 M. The D_a-values for I⁻ ions showed different trends depending on diffusion direction and dry density at a high-ionic strength of [NaCl] = 0.51 M. Namely, although the D_a-values for I⁻ ions showed a tendency to be higher in the parallel direction than in the perpendicular direction to the orientated direction of smectite particles at a high-dry density of 1.4 Mg/m³, these showed a reciprocal tendency at dry densities of 0.9–1.0 Mg/m³. The D_a-values for Cs⁺ ions uniformly increased with an increase of ionic strength in both diffusion directions. Considering electrostatic effect from smectite surface and the change in tortuosity on dry density, ionic strength and diffusion direction to the orientated direction of smectite particles, I⁻ ions are considered to mainly diffuse in interstitial pores. While, Cs⁺ ions can diffuse in both interlayer and interstitial pores, and the D_a-values are considered to have elevated by competing with Na⁺ ions. The activation enthalpies (ΔE_a) for I⁻ ions, slightly higher (ΔE_a = 19.8−20.0 kJ/mol) than that of the diffusion coefficient in free water (D^o) for I⁻ ions (ΔE_a = 17.36 kJ/mol) at a low-ionic strength of [NaCl] = 0.01 M, decreased with an increase of ionic strength, became of similar level to that of the D^o at a high-ionic strength of [NaCl] = 0.51 M, increased with an increase of dry density. On the contrary, the ΔE_a-values for Cs⁺ ions, clearly higher (ΔE_a = 25.6−28.4 kJ/mol) than that of the D^o for Cs⁺ ions (ΔE_a = 16.47 kJ/mol) even in low-dry density over the ionic strength, increased with an increase of dry density. The ΔE_a-values for Cs⁺ ions are considered to be due to the decrease in the activity of porewater in addition to the effect of ion exchange enthalpy between Cs⁺ and Na⁺ ions in smectite.     

The Softness Parameters of Ions. Prediction of the Occurrence of Miscibility Gaps in Molten Salt Mixtures

Softness parameters σ_M for cations and σ_X for anions, have been calculated as dimensionless quantities for approx. 90 cations and 18 anions. They are given by σ_M = [σ_A (M^m+) - σ_A(H⁺)]/σ_A(H⁺) and σ_X = [σ_B(X^a?) - σ_B(OH^?)]/σ_A(H⁺) where σ_A = [σI_i(M) + ΔH⁰_h(M^m+)]/m and σ_B = [-E_a(X) + ΔH⁰_h(X^a?)]/a are Ahrland's parameters. The new normalized and comparative (to the test ions H⁺ and OH^?) softness parameters are positive for soft ions and negative for hard ones. These parameters, obtained independently, are used with a four-coefficient equation to calculate coordinate bond energies for metal halides with acceptable accuracy. Considerations of the average coordination in reciprocal molten salt mixture lead to an expression for the metathesis energy change as proportional to the product of the differences in softness parameters of the two cations and the two anions. An empirical one-coefficient equation involving the softness parameters is proposed to deal with next-nearest-neighbor interactions in binary common-ion molten salt mixtures. These relationships are then used with Blander and Topol's equation to predict the occurrence of irascibility gaps in uni-univalent reciprocal salt mixtures. The gaps found in other systems are also discussed in terms of the softness of the constituent ions.     

Effect of A cation size on structural,magnetic and electrical properties of K2NiF4-type oxide LaSrFeO4

K₂NiF₄-type oxides La_0.8R_0.2SrFeO₄ (R=La, Nd, Gd, Dy) have been synthesized by Pechini method and their structures were established by Rietveld refinements of the XRD data in the space group I4/mmm. Analysis of cell parameters shows that the decrease in the c from La to Dy compound is much larger than that in a. All the samples show antiferromagnetic behavior with increase in value of Θ with decreasing average <La/R/Sr> site radius. For all compounds, semiconducting behavior persists in the whole temperature range and can be expressed by two conduction mechanisms – Arrhenius model and polaron hopping model. The results suggests that the transport properties are dominated by the adiabatic small polaron hopping mechanism. Both activation energy (E_a) and polaron hopping energy (E_p) decrease with decreasing average ionic radius of rare earth ion at A-site.     

Studies on the temperature dependence of extinction oxygen index values for cellulosic fabrics. II. Commercial quality flame-retarded cotton

Extinction oxygen index (EOI) and the derived value at zero ignition time [EOI]_o have been determined for a series of commercial quality flame-retarded cotton fabrics in the temperature range 20 to 200°C. The flame retardants used were Proban-CC (Albright and Wilson Ltd.) and Pyrovatex-CP (Ciba-Geigy). For all the flame-retarded cotton fabrics studied, EOI and [EOI]_o decreased with increase in temperature. The influence of conditioned area density M at a given temperature can be predicted via the linear relationship Substitution of moisture correted area density data had negligible influence on the calculated values of E_o and E₁. The dependence of [EOI]_o on area density, E₁, has a negative temperature dependence. The similarly temperature dependent term E_o is the “intrinsic oxygen-index,” which is independent of ignition and area density variables. For a given flame retardant this represents the fabric properties where maximum access of oxygen is possible. In all cases studied, E_o > E₁ and so the temperature dependence of [EOI]_o is largely determined by E_o. Values obtained for the fractional increase in E_o, with respect to its value at 20°C, with increasing temperature indicate that the temperature sensitivity of the burning behavior of cotton is greater than that of Proban-CC-treated cotton, which itself is greater than that of Pyrovatex CP-treated cotton. It is inferred that effective flame-retardants should not only function under ambient conditions but also reduce the temperature sensitivity of the inherent fibre-burning behavior at elevated temperatures.     

Kinetic study of the polymerization of dimethyldiallylammonium chloride and acrylamide

The kinetics of the polymerization of dimethyldiallylammonium chloride (DMDAAC) and acrylamide (AM) with different monomer molar ratios initiated by an ammonium persulfate–sodium bisulfate redox complex in an aqueous solution were studied. The polymerization rate (R_p) equation, the activation energy (E_a), and the reactivity ratio were measured. The results show that when the n_DMDAAC:n_AM values were 1 : 9, 2 : 8, 3 : 7, 4 : 6, and 5 : 5, the copolymerization rate equation were R_p1 = k[M]^2.61[I_O]^0.51[I_R]^0.52, R_p2 = k[M]^2.70[I_O]^0.50[I_R]^0.53, R_p3 = k[M]^2.73[I_O]^0.50[I_R]^0.56, R_p4 = k[M]^2.77[I_O]^0.51[I_R]^0.59, and R_p5 = k[M]^2.84[I_O]^0.51[I_R]^0.61 (where [M] is the total monomer concentration, [I_O] is the oxidant concentration, and [I_R] is the reductant concentration), respectively when the temperature was 45°C. The E_a values were E_a1 = 79.10 kJ/mol, E_a2 = 81.39 kJ/mol, E_a3 = 85.15 kJ/mol, E_a4 = 88.88 kJ/mol, and E_a5 = 90.61 kJ/mol in the temperature range 35–55°C, respectively. The reactivity ratios of DMDAAC and AM were r_DMDAAC = 0.14 and r_AM = 6.11 when the temperature was 45°C. The structure of PDA was characterized by Fourier transform infrared spectroscopy and ¹H-NMR. The results of the kinetic parameters explained the differences in the copolymerization rate and intrinsic viscosity of PDA with different cationicities. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Zur Rolle von EDA-Komplexen bei kationischen Polymerisationen. VIII. Zur Charge-Transfer-Wechselwirkung von bπ-Donatoren mit organischen Kationen in Lösung

On the Role of EDA-complexes in Cationic Polymerization. VIII. The Charge-Transfer-Interaction of bπ-Donors with Organic Cations in Solution The interaction of 25 aromatic bπ-donors with organic cations of the type (RC₆H₄)₃ C^⊕X^⊖ (R =  CH₃,  C(CH₃)₃,  OCH₃,  H,  Cl,  I,  NO₂; X = BF₄^⊖, AsF₆^⊖, SbCl₆^⊖, FeCl₄^⊖) is investigated by means of u.v.-spectroscopy. The influence of the dissociation on the charge transfer energy will be discussed. With the decreasing concentration of the salt the charge transfer band is hardly shifted at longer wave length. The charge transfer energy can be described as a linear function of structural parameters (i.e. σ_p of R; I_p of the donor and reciprocal radius of the anions, respectively). The influence of the solvent is dependent on both the donicity and dielectric factors.     

Electrical and thermal properties of γ‐irradiated nitrile rubber/rice husk ash composites

The effects of both the rice husk ash (RHA) loading and fumed silica (FS) loading on the structure, thermal stability, and electrical properties of acrylonitrile–butadiene rubber (NBR) composites were studied. The filler loading were chosen to be 5 and 20 phr for RHA and 5 and 30 phr for silica. Also, the effect of the γ‐irradiation dose (25 kGy) on these parameters was investigated. The structure and thermal stability were studied with X‐ray diffraction and thermogravimetric analysis techniques. Furthermore, some electrical parameters, such as the direct‐current electrical conductivity (σ_dc), activation energy (E_a), dielectric constant (?′), and dielectric loss (?″), were determined. The incorporation of both RHA and FS resulted in improved thermal stability after γ irradiation at 25 kGy. The loading of FS on NBR was shown to decrease σ_dc, ?′, and ?″ and increase E_a. On the other hand, the loading of RHA showed the opposite trend. Finally, γ irradiation of NBR composites filled with both fillers decreased the values of σ_dc, ?′, and ?″ for all the samples, which followed the trend for the unirradiated composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

AN ELECTROCHEMICAL STUDY OF SOLUBLE COPOLYMER OF ETHYL CARBAZOLE WITH N-METHYL PYRROLE AND 3-METHYL THIOPHENE

Copolymers of N-ethyl Carbazole (ECZ) with N-Methyl Pyrrole (N-MPy) and 3-Methyl Thiophene (3-MTh) were synthesized on platinum substrate and electrochemical investigation of polymeric films was performed. The characterization of homopolymer and copolymer films was performed by electrochemical methods (i.e. polarization curves and cyclovoltammetric measurements), solid-state conductivity measurements and spectrophotometric methods comparatively. A possible scheme for the copolymerization has been suggested. Solid state conductivity of PECz can be improved by inclusion of 3MTh and NMPy into chain. The ionization potentials, I_p, electron affinity, E_a, optical band gap, E_g, peak potentials, E_p, and doping degrees, y, of copolymer electrodes were calculated from these measurements. Copolymer electrodes have lower I_p, E_g, E_p values and better switching properties in accordance with homopolymer electrodes. Presence of alkyl group gives solubility to copolymers obtained both chemically and electrochemically.     

Kinetic rate equation combining ultraviolet‐induced curing and thermal curing. I. Bismaleimide system

A novel and general kinetic rate equation combining ultraviolet‐induced (UV‐induced) curing and thermal curing was successfully derived from the conventional thermal‐kinetic rate equation. This proposed novel kinetic rate equation can be applicable to the curing system either simultaneously or individually by UV‐induced and thermal cure methods. This general kinetic rate equation is composed of the reaction order n, activation energy E_a, curing temperature T, energy barrier of photoinitiation E_Q, intensity of UV radiation Q, concentration of photoinitiator [I], and a few other parameters. The proposed equation was supported by experimental data based on the curing systems of 4,4′‐bismaleimidodiphenylmethane (BMI) and 2,2‐bis(4‐(4 maleimido phenoxy) phenyl propane (BMIP). The BMI and BMIP systems were isothermally cured at various temperatures, or simultaneously cured with varying intensity of UV radiation (wavelength 365 nm). Conversion levels for the various cured samples were subsequently measured with a FTIR spectrometer. The reaction order n = 1.2, activation energy E_a = 40,800 J/mol, and E_Q = 7.5 mW/cm² were obtained for curing BMI system. The reaction order n = 1.3, activation energy E_a = 53,000 J/mol, and E_Q = 9.1 mW/cm² were obtained for curing BMIP system. The values of n and E_a in the same curing system (BMI or BMIP) are irrespective of the curing method (either simultaneously or individually by UV‐induced and thermal cure methods). The salient results of this study show that UV radiation only enhances the initiation rate and UV ration do not influence the activation energy E_a. The experimental results are reasonably well represented by these semi‐empirical expressions.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electrical characteristics of Al/polyindole Schottky barrier diodes. I. Temperature dependence

In this study, the forward and reverse bias current–voltage (I–V), capacitance–voltage (C–V), and conductance–voltage (G/ω–V) characteristics of Al/polyindole (Al/PIN) Schottky barrier diodes (SBDs) were studied over a wide temperature range of 140–400 K. Zero‐bias barrier height Φ_B0(I–V), ideality factor (n), ac electrical conductivity (σ_ac), and activation energy (E_a), determined by using thermionic emission (TE) theory, were shown fairly large temperature dispersion especially at lower temperatures due to surface states and series resistance of Al/PIN SBD. I–V characteristics of the Al/PIN SBDs showed an almost rectification behavior, but the reverse bias saturation current (I₀) and n were observed to be high. This high value of n has been attributed to the particular distribution of barrier heights due to barrier height inhomogeneities and interface states that present at the Al/PIN interface. The conductivity data obtained from G/ωV measurements over a wide temperature range were fitted to the Arrhenius and Mott equations and observed linear behaviors for σ_ac vs. 1/T and ln σ_ac vs. 1/T^1/4 graphs, respectively. The Mott parameters of T₀ and K₀ values were determined from the slope and intercept of the straight line as 3.8 × 10⁷ and 1.08 × 10⁷ Scm^?1K^1/2, respectively. Assuming a value of 6 × 10¹² s^?1 for ν₀, the decay length α^?1 and the density states at the Fermi energy level, N(E_F) are estimated to be 8.74 Å and 1.27 × 10²⁰ eV^?1cm^?3, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of poly(vinyl caprolactone-co-vinyl pyridine) and poly(vinyl imidazol-co-vinyl pyridine) on the corrosion of steel in H<Subscript>3</Subscript>PO<Subscript>4</Subscript> media

The inhibiting effect of two organic copolymers namely poly(vinyl caprolactone-co-vinyl pyridine) (PVCVP) and poly(vinyl imidazol-co-vinyl pyridine) (PVIVP) on the corrosion of steel in phosphoric acid was investigated at various temperatures. The study was carried out by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and weight loss measurements. Inhibition efficiency (E %) increased with polymer concentration to attain 85% at 10⁻⁴ M for PVIVP. Adsorption of polymers on the steel surface in 2 M H₃PO₄ followed the Langmuir isotherm model. EIS measurements show that the dissolution of steel occurs under activation control. Polarisation curves indicate that the tested polymers functioned as cathodic inhibitors. E % values obtained from various methods used are in good agreement with each other. The temperature effect on the corrosion behaviour of steel in 2 M H₃PO₄ in the presence and absence of the inhibitor was studied in the temperature range 298–338 K. The adsorption free energy (ΔG ^o _ads) and the activation parameters (E _a, , ΔS ^o _a) for the steel dissolution reaction in the presence of polymer were determined.     

Studies on the thermal degradation of synthetic polymers: 16. Estimation of the product yield on the basis of intensity function for thermal gasification of polyethylene

The kinetic equation for the pyrolysis gasification reaction of four kinds of polyethylene, differing from one another in average molecular weight, has been established. Differences in the molecular weight of the samples have no effect on the kinetic parameters when the molecular weight is 10⁴ or above. The intensity function, I_F=Tθ^a (K s^a), describing the severity of the decomposition conditions, has experimentally turned out to be a temperature throughout the residence time, θ, for reactions constrained by Arrhenius parameters A and E. The value of the exponent, a, may be found approximately from the kinetic parameters in this experiment. The values of the product yield calculated from the Arrhenius equation, $\text{k = A}\text{exp}\text{(}\text{?E}\text{RI}{}_{\mathrm{F}}\text{)}$, for a particular I_F, agree with the experimental values.     

Effect of filler content and surface treatment on the tensile properties of glass‐bead‐filled polypropylene composites

The tensile properties of polypropylene (PP) filled with two A‐glass beads with the same size, PP/3000 (glass bead surface pretreated with a silane coupling agent) and PP/3000U (no surface pretreatment), have been measured by using an Instron materials testing machine at room temperature, to identify the effects of the filler surface pretreatment and its content on the tensile properties of these composites. The results show that the Young's modulus E_c of the composites increases non‐linearly with increasing volume fraction of glass beads ϕ_f, while the tensile yield strength σ_yc and tensile stress at break σ_bc of the composites decrease with an increase of ϕ_f, in the ϕ_f range 0–30%. Furthermore, the values of E_c and σ_bc of the PP/3000 system are somewhat higher than those of the PP/3000U system under the same test conditions, but this is in contrast to the tensile strain at break ε_bc and tensile fracture energy E_bc, especially at higher ϕ_f values. Good agreement is shown between the measured tensile strength and the predicted value by using an equation proposed in previous work. In addition, ε_bc and E_bc reach maximum values at ϕ_f = 25% for both systems. This indicates that there is a brittle–ductile transition for the composites in tension. © 2000 Society of Chemical Industry     

Activity of substrates in the catalyzed nucleation of poly(ethylene terephthalate) melts

The activity, Φ of AgBr, AgI, PbF₂, Ag₂S, LiF, and CaF₂ in the catalyzed nucleation of poly(ethylene terephthalate) (PET) melts was determined using a nonisothermal differential scanning calorimetry (DSC) technique. A comparison with existing experimental data was made. It is established that the higher the melting temperature of the substrate the lower its activity as a crystallization core in the heterogeneous nucleation of PET. The lateral surface energy, σ, the end surface energy, σ_e, the adhesion energy, β, and the difference between the surface energies at the substrate/melt, σ_sf, substrate/deposit, σ^*, and the total energy of misfit dislocations, E_d [i.e., σ_sf - (σ^* - E_d)] were calculated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 349–353, 1997     

Anomalous behavior of electrical conductivity of solubilized collagen solutions with thermal denaturation

The temperature dependence of the electrical conductivity, σ, for a collagen solution was measured in the temperature region including the thermal denaturation temperature, t_d. The σ increased with temperature, t, but decreased at ca. 40°C, and then again increased. In this temperature region, a change of optical rotation, α_D, was observed. The change is due to the thermal denaturation. The differential curve of σ vs. t gave clear deflection points and a large peak at ca. 40°C. The t_d could be estimated from the peak temperature. The t_d decreased with the increase in the concentration of collagen and with the decrease in the heating rate. These measurements were carried out for the collagen prepared by various methods. Some of them showed one peak; others had two peaks. The t_d obtained by the measurement of σ correlated with that obtained by the measurement of α_D. The activation energy of σ, ΔE_a, obtained from the linear relationship between log σ and 1/T, increased with the concentration of collagen, but was unchanged for the heating rate. The ΔE_a obtained for various types of collagen showed a constant value. © 1993 John Wiley & Sons, Inc.     

Polymerization in an electrodeless glow discharge. II. Olefinic monomers

The rates of polymer deposition from various olefinic monomers in an electrodeless glow discharge were studied. The previously found empirical relationship (with styrene in part I) between the rate of polymer deposition R, the monomer pressure p_M, and gas pressure p_x in a steady-state flow system (i.e., R = a(p_M)² [1 + b(p_x)], R being nearly independent of the discharge power) was also found with all monomers investigated. (The effect of gas was examined with nitrogen in this study.) However, it was found that the polymer deposition is controlled by the monomer flow rate and R_o (in pure monomer flow) is proportional to the flow rate of monomer F_w (based on the weight); i.e., R_o = kF_w, where k is a characteristic rate constant of the polymerization. Olefinic monomers can be generally classified into two major groups, i.e., type A monomers which predominantly polymerize, and type B monomers which decompose in a glow discharge. Type B monomers have smaller values of a and k compared to type A monomers. The values of a and k for type A monomers both increase with increasing molecular weight of the monomer. The values of k for all monomers investigated are within roughly an order of magnitude, indicating that the reactivity levels of monomers are very similar in a glow discharge polymerization.     

Polarographic behaviour of hansa yellow- like dyes. Reduction mechanism and substituent effects

The electroreduction of a series of 3-phenyl-2,3-dioxopropionanilide 2-arylhydrazones (III) on the dropping mercury electrode (dme) was investigated in ethanolic Britton-Robinson buffers. In each case, the polarographic curves showed two waves, A and B, corresponding to a four- and a two-electron process, respectively. The E_1/2 values for the wave A at pH 8.0 were shown to be a linear function of the Hammett substituent constant σ; -(E_1/2)_A(V) = 0.982 + 0.145 σ (r = 0.989). A mechanism for the polarographic reduction of III is proposed.     

Application of critical state to uniaxial compaction

From the radial stress σ_R and the normal stress σ_A, measured continuously during uniaxial loading and unloading on three compactable (sodium chloride, polyethylene and tartaric acid) and two non-compactable (polypropylene and polystyrene plastics) materials, characteristic compaction profiles of (σ_A ? σ_R) versus (σ_A + σ_R) can be observed. The uniaxial loading stress pathways for both compactable and non-compactable materials validated the assumption that the Coulomb yield criterion, which is usually applicable for the shear testing of soils, can be applied to the uniaxial compression of particulate materials. In addition, the unloading stress profiles for the compactable materials produced two characteristic parameters: a normal stress value at zero shear (σ_A + σ_R)_o and a minimum shear stress value (σ_A ? σ_R)_min. Correlation of (σ_A + σ_R)_o and (σ_A ? σ_R)_min values with either the tensile strength f_c or the Vickers hardness number H_V from the resultant compacts showed a linear logarithmic relationship. No such relationship was found, however, with non-compactable materials.     

Radiopaque epoxy resins

Transparent, X-ray contrast (radiopaque) epoxy resins were obtained by dissolving up to 25 wt % triphenylbismuth in the commercial epoxy resin prepolymers EPON-815, DER-330, DER-383, and DEN-431 which were then hardened with diethylenetriamine. The radiopacities of the mixtures were found to be proportional to the molar concentration of the radiopaque additive. The systems follow the relationship, R = R_o + (R_a ? R_o) V _a M_a where R, R_o, and R_a are the radiopacities of the mixture, the pure epoxy resin, and triphenylbismuth, respectively (expressed in mm aluminum/mm resin); M_a and V _a denote the molar concentration and molar volume of the bismuth compound. R_a for triphenylbismuth was found to be 7.4 ± 0.2 mm Al/mm resin; the average value of R_o for the four epoxies equals 0.16 ± 0.1 mm Al/mm resin. The amount of amine required to harden the radiopaque resins was far less for the epoxy novolac resin DEN-431 than for the three bisphenol-A based epoxies. The concentration of triphenylbismuth required to impart a radiopacity equivalent to that of aluminum measures 14.6 wt % in EPON-815, 14.8 wt % in DER-330, 14.9 wt % in DER-383, and 15.9 wt % in DEN-431. The radiopaque resins remain transparent indefinitely, even when exposed to water. © 1995 John Wiley & Sons, Inc.     

Application of various viscosity theories to the viscosity data of methyl methacrylate-acrylonitrile random copolymers

Values of K_o, Flory constant related to unperturbed dimensions, are evaluated for methyl methacrylate-acrylonitrile random copolymers using Flory-Fox, Kurata-Stockmayer and Inagaki-Ptitsyn methods and compared with the K_o values obtained by Stockmayer-Fixman method. K_o values are seen to be less in solvents which have large a (Mark-Houwink exponent) values. A correlation between K_o and a is developed to arrive at a more reliable estimate of K_o for this copolymer system.