Water sorption in amorphous poly(ethylene terephthalate)

The water sorption characteristics of poly(ethylene terephthalate) (PET) amorphous samples of 250 μm thickness have been studied at various temperatures in a saturated atmosphere. Concerning diffusivity, one can distinguish the following two domains characterized by distinct values of the activation energy: E_D ≈ 36 kJ mol⁻¹ at T > 100°C, and E_D ≈ 42 kJ mol⁻¹ at T < 60°C, with a relatively wide (60–100°C) intermediary domain linked to the glass transition of the polymer. The crystallization of this latter occurs in the time scale of diffusion above 80°C but doesn't change the Fickian character of sorption curves. The equilibrium concentration m_∞ is an increasing function of temperature, but the solubility coefficient S decreases sharply with this latter, with the apparent enthalpy of dissolution ΔH_s being of the order of −28 kJ mol⁻¹ at T < 80°C and −45 kJ mol⁻¹ at T > 80°C. Density measurements in the wet and dry states suggest that water is almost entirely dissolved in the amorphous matrix at T < 80°C but forms partially a separated phase at T > 80°C. Microvoiding can be attributed to crystallization-induced demixing. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1131–1137, 1999     

Solubility of potassium ferrate in 12 M alkaline solutions between 20°C and 60°C

The solubility of potassium ferrate (K₂FeO₄) was measured in aqueous solutions of NaOH and KOH of total concentration 12 M containing various molar ratios of KOH:NaOH in the range 12:0 to 3:9. Several analytical methods were tested for the determination of ferrate concentration. The final method chosen consisted of potentiometric titration of the ferrate sample with an alkaline solution of As₂O₃. The assumption was made that ferrate dissociates in concentrated KOH solutions predominantly to KFeO₄⁻. The solubility constant, S, defined as the product of the molar concentration of the potassium ion, K⁺, and the ferrate anion, KFeO₄⁻, was found to be 0·044 ± 0·006 mol² dm⁻⁶ for 20°C, 0·093 ± 0·004 mol² dm⁻⁶ for 40°C and 0·15 ± 0·09 mol² dm⁻⁶ for 60°C. From these results the heat of dissolution of K₂FeO₄ was calculated as −14·3 kJ mol⁻¹. At 60°C the enhanced decomposition of the ferrate at the higher temperature led to a greater deviation in solubility values compared with data for either 20°C or 40°C.     

Kinetics of leaching of tunisian phosphate ore particles in dilute phosphoric acid solutions

Van der Sluis et al.'s model was used to determine the rate of the partial dissolution of a Tunisian phosphate rock with dilute phosphoric acid (1.5 mass% P₂O₅). When the temperature rises from 25 to 90°C, for a given particle size, the mass-transfer coefficients, k_L°, vary from 3 × 10^?3 to 8 × 10^?3 m ·s^?1. The corresponding diffusion coefficients, D, lies between 6 × 10^?7 and 27 × 10^?7 m²·s^?1. Activation energy is equal to 14 kJ·mol^?1 and values of k_L°, at 25°C, are in the range of 0.28 × 10^?3 and 4 × 10^?3 m·s^?1 when the agitation speed goes from 220 to 1030 rpm, showing that the leaching process is controlled by diffusion rather than by chemical reaction.     

Calculation of the Detonation Velocities and Detonation Pressures of Dinitrobiuret (DNB) and Diaminotetrazolium Nitrate (HDAT‐NO3)

The enthalpies of combustion (Δ_combH) of dinitrobiuret (DNB) and diaminotetrazolium nitrate (HDAT‐NO₃) were determined experimentally using oxygen bomb calorimetry: Δ_combH(DNB)=5195±200 kJ kg⁻¹, Δ_combH(HDAT‐NO₃)=7900±300 kJ kg⁻¹. The standard enthalpies of formation (Δ_fH°) of DNB and HDAT‐NO₃ were obtained on the basis of quantum chemical computations at the electron‐correlated ab initio MP2 (second order Møller‐Plesset perturbation theory) level of theory using a correlation consistent double‐zeta basis set (cc‐pVTZ): Δ_fH°(DNB)=−353 kJ mol⁻¹, −1 829 kJ kg⁻¹; Δ_fH°(HDAT‐NO₃)=+254 kJ mol⁻¹, +1 558 kJ kg⁻¹. The detonation velocities (D) and detonation pressures (P) of DNB and HDAT‐NO₃ were calculated using the empirical equations by Kamlet and Jacobs: D(DNB)=8.66 mm μs⁻¹, P(DNB)=33.9 GPa, D(HDAT‐NO₃)=8.77 mm μs⁻¹, P(HDAT‐NO₃)=33.3 GPa.     

Structural and Preliminary Explosive Property Characterizations of New 3,4,5‐Triamino‐1,2,4‐triazolium (Guanazinium) Salts

Two new highly stable energetic salts were synthesized in reasonable yield by using the high nitrogen‐content heterocycle 3,4,5‐triamino‐1,2,4‐triazole and resulting in its picrate and azotetrazolate salts. 3,4,5‐Triamino‐1,2,4‐triazolium picrate (1) and bis(3,4,5‐triamino‐1,2,4‐triazolium) 5,5′‐azotetrazolate (2) were characterized analytically and spectroscopically. X‐ray diffraction studies revealed that protonation takes place on the nitrogen N1 (crystallographically labelled as N2). The sensitivity of the compounds to shock and friction was also determined by standard BAM tests revealing a low sensitivity for both. B3LYP/6–31G(d, p) density functional (DFT) calculations were carried out to determine the enthalpy of combustion (Δ_cH (1) =−3737.8 kJ mol⁻¹, Δ_cH (2) =−4577.8 kJ mol⁻¹) and the standard enthalpy of formation (Δ_fH° (1) =−498.3 kJ mol⁻¹, (Δ_fH° (2) =+524.2 kJ mol⁻¹). The detonation pressures (P (1) =189×10⁸ Pa, P (2) =199×10⁸ Pa) and detonation velocities (D (1) =7015 m s⁻¹, D (2) =7683 m s⁻¹) were calculated using the program EXPLO5.     

Extraction of zinc from ammoniacal/ammonium sulphate solutions by LIX 54

The extraction of zinc from ammoniacal/ammonium sulphate aqueous media using LIX 54 has been studied. The metal extraction rate has been examined and also the effect of temperature on the extraction of zinc (ΔH° = −8·8 kJ mol⁻¹). The effect of the aqueous pH, and therefore zinc ammine complex formation, on the extraction of zinc was studied. Stripping of the metal from loaded organic phases was carried out at various rates, temperatures (ΔH° = 3·2 kJ mol⁻¹) and sulphuric acid concentrations. The results obtained were compared with others obtained from the literature wherein different extractants were used. © 1998 SCI.     

Role of Sulfur and Its Diffusion in Silicate Glass Melts

Sulfur diffusion D_S is reported on a technical alkali-poor barium alumoborosilicate glass melt at 900–1400°C and on three further Na₂O-modified glass melts at 900°C, using a radioactive tracer method. Whereas D_S for the base glass melt amounts to ≈1 × 10⁻¹⁵m²/s at 900°C, it increases nearly exponentially with increasing Na₂O content from 0 to 15 mol% by almost three orders of magnitude. Similar to other glass melts, the sulfur diffusion obtained in these melts is also closely related to the Eyring diffusivity D_n derived from viscosity. The diffusion controlling species in oxidized melts seems to be SO₄²⁻, in reduced melts S²⁻. SO₃²⁻ does obviously not play any role in this transport process.     

Molecular transport characteristics of a chlorosulfonated polyethylene geomembrane in the presence of aromatic esters

Results of a study on sorption and diffusion of chlorosulfonated polyethylene geomembrane with methyl benzoate, ethyl benzoate, methyl salicylate, iso-butyl salicylate, phenyl acetate, and diethyl phthalate in the temperature range 25–60°C are presented. A gravimetric sorption method is used to calculate the diffusion and permeation coefficients from the Fickian relationship. The diffusion results are dependent on penetrant–membrane interactions, temperature, and on penetrant concentration. The values of diffusion coefficients range from 0·02 × 10^?7 cm² s^?1 for diethyl phthalate at 25°C to 1·81 × 10^?7 cm² s^?1 for ethyl benzoate at 60°C. The activation energies for diffusion range from 21 to 50 kJ mol^?1. The values of heat of sorption ranged between 2·2 and 6·4 kJ mol^?1. Sorption results are also analyzed using a first-order sorption kinetic equation. Experimental results and calculated parameters are used to discuss the transport behavior. None of the esters used have shown any chemical attack toward the geomembrane.     

Kinetic and Thermodynamic Study of the Reduction of 1,1-Diphenylethylene by a Thermally Frustrated Diethyl Ether-BCF Lewis Pair

The reaction enthalpy and rate of reduction of 1,1-diphenylethylene (DPE) by the frustrated Lewis pair formed between tris-pentafluorophenylborane (BCF) and diethyl ether (Et₂O) in dichloromethane have been determined by mixing calorimetry. At 50 °C and 13.6 atm hydrogen, a 0.08 M solution of DPE is reduced to 1,1-diphenylethane, in the presence of 1 equivalent BCF and 0.8 equivalents Et₂O, in 40 minutes. NMR spectroscopy showed>99 % conversion to the reduced product. The rate of conversion of the olefin to the alkane, as monitored by the time-dependent heat flow, showed a linear dependence on the free Et₂O and BCF concentration. Integration of the heat flux provides a measurement of the reaction enthalpy, ΔH, of ca. −116±4 kJ mol⁻¹ for the reaction Ph₂C=CH₂+H₂→Ph₂CHCH₃. The equilibrium constant for dative adduct formation, Et₂O+BCF↔Et₂O−BCF, was determined as a function of temperature by ¹⁹F NMR spectroscopy, and provided an experimental measurement of the enthalpy, ΔH=−54.6±3.3 kJ mol⁻¹, and entropy, ΔS=−154±13 J mol⁻¹ K⁻¹, for dative bond formation in DCM. Extrapolation of the Van’t Hoff plot to 50 °C provides K_eq, which is used to estimate the concentration of free BCF and Et₂O available to activate hydrogen.     

Geminale Substituenteneffekte. VIII. Standardbildungsenthalpien von Acetalen

Geminal Substituent Effects. VIII. Enthalpies of Formation of Acetals The standard enthalpies of combustion ΔH_c° (1 or c) of the α-phenyl-substituted acetals ( 1 ) and diacetals ( 2 ) were measured calorimetrically. The enthalpies of vaporisation or sublimation ΔH_vap or ΔH_sub of 1–2 were obtained from the temperature function of the vapor pressure measured in a flow system, and the standard enthalpies of formation are obtained thereof: ΔH°_f (1 or c) and ΔH_f° (g) (in kJ mol⁻¹) for 1a = −308.40 ± 0.52(1), −248.94 ± 0.88; 1b = −343.48 ± 0.72 (1), −288.5 ± 1.5; 1c = −267.4 ± 1.3 (1), −205.3 ± 1.3; 1d = −343.8 ± 2.1 (c), −261.9 ± 2.2; 1e = −397.02 ± 0.86 (c), −311.3 ± 1.2; 1f = −414.52 ± 0.80 (1), −350.68 ± 0.86; 2a = −564.8 ± 2.4 (c), −467.1 ± 2.5; 2b = −547.6 ± 1.6 (c), −414.9 ± 2.7; 2c = −717.1 ± 7.5 (c), −587.0 ± 8.0. The results are combined into values of two strain free group increments CH[20, C_Ph] = −59.7 and C[20, C_Ph, C] = −71.3 kJ mol⁻¹; and compared to the aliphatic series of acetals.     

Kinetic and rheokinetic study of dicarboxylic fatty acid chain extension using a dioxazoline coupling agent

A kinetic and rheokinetic study of the condensation reaction of a dicarboxylic fatty acid, Pripol®1009 (C36), and a dioxazoline coupling agent (1,3‐Phenylene)‐bis(2‐Oxazoline) (OO) was made. The kinetic study showed a similar reactivity of the two acid groups of C36 and also a similar reactivity of the two oxazoline groups of OO. The reaction kinetics can be described using a second‐order kinetic model. A kinetic constant k = 16.1 × 10⁻⁴ mol⁻¹ s⁻¹ at 156°C with an activation energy E_a = 80.6 kJ mol⁻¹ was calculated. A rheological evaluation of the reactants and the obtained polymers showed that the reactive system had Newtonian behavior during all the reaction times for shear rates lower than 100 s⁻¹. Using this kinetic modeling and measured viscosity evolution of the reactive system at different temperatures, rheokinetic models were proposed for viscosity evolution with the molar mass evolution of the synthesized polymer and the reaction time and conversion. Viscosity evolution of the reactive system during the first 10 min, corresponding to a typical mean residence time in reactive extrusion, were calculated using the proposed rheokinetic model. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1017–1024, 1999     

Partial masking of cellulosic fiber hydrophilicity for composite applications. Water sorption by chemically modified fibers

Cotton cellulosic fibers have been treated with alkyl isocyanates, modified polypropylene or other aliphatic agents in more or less swelling mediums. Their hydrophilicity can be reduced and this effect is studied by the associated techniques of microgravimetry and microcalorimetry. For the non-treated sample, a sorption mechanism is proposed: two water molecules linked by a double H bond are sorbed per amorphous glucose unit with a high molar energy (–65 to –58 kJ/mol⁻¹) up to P/P_o = 0.85. Above this pressure, the water is sorbed with the liquefaction molar energy (–44 kJ/mol⁻¹). For the treated fibers, the two preceding stages are always observed as a function of P/P_o, but interesting results are obtained for alkyl isocyanate modified samples, with varying lengths of the alkyl chains: C₃H₇₋, C₈H₁₇₋ or C₁₈H₃₇₋. These results show the importance of a critical length of the alkyl chain (between three and eight carbons) for reducing the amount of sorbed water by 25% and modifying the mean diffusion coefficient. These effects would be due to the blocking by the linked agents of some water diffusion paths. © 1996 John Wiley & Sons, Inc.     

Kinetics study of isothermal nicotine release from poly(acrylic acid) hydrogel

The isothermal kinetic of the release of nicotine from a poly(acrylic acid) (PAA) hydrogel was investigated at temperature range from 26°C to 45°C. Specific shape parameters of the kinetic curves, the period of linearity and saturation time were determined. The change in the specific shape parameters of the kinetic curves with temperature and the kinetic parameters of release of nicotine E_a and ln A were determined. By applying the “model fitting” method it was established that the kinetic model of release of nicotine from the PAA hydrogel was [1 − (1 − α)^1/3] = k_Mt. The limiting stage of the kinetics release of nicotine was found to be the contracting volume of the interaction interface. The distribution function of the activation energy was determined and the most probable values of activation energies of 25.5 kJ mol⁻¹ and 35 kJ mol⁻¹ were obtained. Energetically heterogeneity of the interaction interface was explained by the existence of the two different modes of bonding the nicotine molecules onto the hydrogel network by hydrogen bond and electrostatic forces. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Analytical solution using a pore diffusion model for a pseudoirreversible isotherm for the adsorption of basic dye on silica

An analytical solution for a two resistance mass transfer model explaining the adsorption of Astrazone Blue dye (Basic Blue 69) onto Sorbsil silica has been developed. The model includes a film mass transfer coefficient, k_f1 = 80 × 10⁻⁶cm·s−1, and an internal effective diffusivity, D_eff = 18×10⁻⁹cm²·s⁻¹ which controls the internal mass transport processes based on a pore diffusion mechanism.     

Dissolution kinetics of Ca-maleate crystals: Evaluation for biotransformation reactor design

In order to develop a bioreactor for solid to solid conversions the biocatalytic conversion of solid Ca-maleate to solid Ca-D -malate is studied. The dissolution of Ca-maleate is the first step in this process and is described here. A kinetic model, based on the interfacial-barrier theory and the diffusion-layer theory, was developed which describes the increase in Ca-maleate concentration due to dissolution with the help of the time-dependent parameters. According to the model two processes contribute to the dissolution of Ca-maleate·H₂O crystals: (1) the dissolution (and dissociation) reaction of Ca-maleate at the solid–liquid interface, characterized by a time-independent reaction rate coefficient, and (2) the transport of Ca²⁺ and maleate²⁻ across a boundary liquid film, characterized by a time-dependent mass-transfer rate coefficient. In addition, the surface of a crystal and the driving force are time-dependent variables. Since Ca-maleate·H₂O crystals are not uniform, a crystal-size distribution was also used in the model. The effects of stirring speed, temperature, pH, and initial Ca²⁺ concentration on the dissolution rate of Ca-maleate·H₂O crystals were determined experimentally in order to evaluate the model. The model fitted the data well (R²>0·97). In order to determine whether the overall dissolution process was reaction or transport controlled, a method based on overall reaction and transport rates (per unit of driving force) was developed. This showed that the dissolution of Ca-maleate was reaction controlled. Temperature influenced the reaction rate coefficient the most; it ranged from 5·7×10⁻⁶ m s⁻¹ at 10°C to 67×10⁻⁶ m s⁻¹ at 60°C. The reaction rate coefficient was also influenced by the pH and the initial Ca²⁺ concentration, but, as expected, hardly by the stirring speed. Simplifying the model by omitting the time-dependent mass-transfer rate coefficient and by assuming uniform crystals, resulted in only slightly worse fits of the data with R² being at most 0·004 smaller. © 1988 Society of Chemical Industry     

Diffusion of calcium in yttria stabilized zirconia ceramics

Bulk and grain boundary diffusion of calcium in yttria fully stabilized zirconia was studied in air in the temperature range from 1100 to 1400°C. Secondary ion mass spectrometry (SIMS) was used to determine the diffusion profiles as average concentration vs. depth in the B-type kinetic region. The obtained results allowed the calculation of the temperature dependence of the bulk diffusion coefficient D and the grain boundary diffusion parameter D′δs. Activation energies of these processes amount to 333 and 367 kJ mol⁻¹, respectively. Diffusion data of calcium were compared to those of titanium obtained previously using the same zirconia material.     

Complexes of Hydrogen Peroxide with Dioxoactinide(VI) Species in Aqueous Carbonate and Bicarbonate Media. Formation of An(VI)–H2O2 Complexes

The spectra for 1:1 complexes formed between triscarbonatouranium(VI) + H₂O₂ and triscarbanatoneptunium(VI) + H₂O₂ are presented. The respective rates of formation (25°C, 0.05 M NA₂CO₃) are 565 ± 41 M⁻¹ s⁻¹ and (2.19 ± .01) X 10³ M⁻¹ s⁻¹. The corresponding activation parameters are ΔH* = 67.8 ± 3.2 kJ/m, 43.6 ± 2.0 kJ/m, ΔS* = 30 ± 11 J/m °K and −36 ± 7 J/m °K, respectively. The U(VI) complex appears to be stable over a period of months while the Np(VI) complex is formed as a transient species that disappears via a complex process.     

Computed Thermodynamic and Explosive Properties of 1‐Azido‐2‐nitro‐2‐azapropane (ANAP)

Some thermodynamic and explosive properties of the recently reported 1‐azido‐2‐nitro‐2‐azapropane (ANAP) have been determined in a combined computational ab initio (MP2/aug‐cc‐pVDZ) and EXPLO5 (Becker–Kistiakowsky–Wilson's equation of state, BKW EOS) study. The enthalpy of formation of ANAP in the liquid phase was calculated to be Δ_fH°, ANAP(l)=+297.1 kJ mol⁻¹. The heat of detonation (Q_v), the detonation pressure (P), and the detonation velocity of ANAP were calculated to be Q_v=−6088 kJ kg⁻¹, P=23.8 GPa, D=8033 m s⁻¹. A mixture of ANAP and tetranitromethane (TNM) was investigated in an attempt to tailor the impact sensitivity of ANAP, but results obtained indicate that the mixture is almost as sensitive as pure ANAP. On the other hand, ANAP and TNM were found to be chemically compatible (¹H, ¹³C, ¹⁴N NMR; DSC) and a 1 : 1 mixture (by weight) of both components was calculated to have superior explosive properties than either of the individual components: Q_v=−6848 kJ kg⁻¹, P=27.0 GPa, D=8284 m s⁻¹.     

Electrochemical absorption of hydrogen in transition metal oxides—II. Sorption of hydrogen in titanium monoxide TiO

The absorption of hydrogen in titanium “monoxide” was studied electrochemcially by potential-step and ac techniques. The absorption equilibrium obeys the Crandall—Faughnan—Armand isotherm and the chemical diffusion coefficient is a linear function of concentration. The heat of absorption is 80 kJ (g atom H)⁻¹ and the true diffusion coefficient D₀ is 4 × 10⁻¹³ cm²s⁻¹ at 20°C. The absorption occurs in oxygen vacancies.     

The diffusivity of oxygen in dilute alkaline solution from 0° to 65°C

Diffusion coefficients for oxygen in 0·1 M sodium hydroxide solution have been determined from 0° to 65°C using a rotating platinum electrode. The results may be represented with a standard deviation of approximately 1% by the expression:

where D_o = 8·03 × 10^?3cm²s^?1 and the apparent activation energy, Q_D, is 3·49 kcal mol^?1. Between 25° and 65°C the product of the diffusivity and the solution viscosity is essentially constant:

Values for diffusion coefficients for oxygen in pure water have been derived from these data with an absolute error probably less than 4%.Difficulties in obtaining reproducible results at a rotating platinum electrode are attributed to deactivation of the electrode by reduction of a surface oxygen phase. Results at the higher temperatures indicate that methods of determining diffusivities by diffusion through a stagnant layer of solution involve an increasing indeterminate error as the temperature rises, due to convective mass transport.