Thermodynamics of ionization of some fluorinated β-diketones

Thermodynamic ionization constants, TpK_a, of several fluorinated β-diketones, viz. 2-furoyltri-fluoroacetone, heptafluorobutrylpivaloyl methane, hexafluoroacetylacetone, 2-thenoyltrifluoroacetone and trifluoroacetylacetone have been determined pH-metrically in 0-70vol.% dioxane-water mixtures at 25 and 35±0.01°C applying an empirical pH correction for mixed hydro-organic media. The pK_as in aqueous medium (at 0% dioxane) are obtained following the method of extrapolation and least-squares. All of them are very weak monoprotic acids. TpK_as do not vary linearly with the reciprocal of dielectric constant of the medium, but a plot of TpK_avs the mole fraction of dioxane is linear at a given temperature. The “true constant” K′_a and solvation number, n, in the expression (H⁺)(A⁻)/(HA)=K′_a(S)ⁿ=K^*_a for these reagents have been evaluated by analysing the experimental data mathematically. Values of ΔG°, ΔH° and ΔS° are also computed. Positive values of ΔH° found in aqueous-dioxane media for the above fluorinated derivatives, except HFOD, indicate the endothermicity of the proton enolization reactions. Temperature, medium as well as substituent effects are briefly discussed.     

Faradaic rectification studies of two electron charge transfer redox couples at the metal (solid) interface

The Faradaic rectification studies of the two electron charge transfer processes, cationic and anionic redox couples, have been carried out. The mechanism of the iodide—iodine reaction through single charge transfer comprises the following steps, of which reaction (b) is the slowest and controls the rate of overall reactions.

The values of the transfer coefficient and rate constant are obtained for the second step, which is rate determining in both the directions. The values of the parameters obtained when the concentration of the electrochemical species (I₂) is much less in comparison to that of iodide, are α_c = α_a = 0·5 and k^O_a of the order of 5 × 10^?5 cm/s. The parameters for the iodide—iodine reaction, using 1·0 M KNO₃ as supporting electrolyte, are α_c = 0·49, α_a = 0·51 and k^O_a of the order of 5 × 10^?3 cm/s. For the stannous-stannic reaction either of the two steps appears to be rate determining in both directions and the values of the parameters obtained are α_c = 0·48, α_a = 0·52 and k⁰_a = 2·1 × 10^?3 cm/s.     

Multiplicity,stability and dynamics for isothermal autocatalytic reactions in CSTR

Multiplicity, stability and dynamics for autocatalytic reactions of the type A? → rR + ? with overall rate expression r_A = kC_A^mC_Rⁿ in a continuous stirred tank reactor (CSTR) are studied. Exact multiplicity criteria are defined in the parameter space. Stability analysis shows that no periodic oscillation is possible for the system. When multiplicity occurs, some minimum of R present initially in the reactor is required in order for the high steady state to be achieved. Loci of transient extreme for product are also investigated. Multiplicity and uniqueness criteria are further compared with reported experimental data in literature.     

Solid acid catalysts based on supported tungsten oxides

Supported WO _x clusters are active and stable catalysts for isomerization, dehydration, and cracking reactions. Brønsted acid sites form on WO _x clusters when a lower valent element replaces W^{6 +} or when W^{6 +} centers reduce slightly during catalytic reactions. WO _x clusters of intermediate size provide the balance between reducibility and accessibility required to maximize the number of surface H⁺ species in WO _x –ZrO₂, zirconium tungstate, and oxygen-modified WC catalysts. H₂ is involved in the generation and maintenance of Brønsted acid sites during catalytic reactions on WO _x clusters.     

An experimental study of air entrainment at a solid/liquid/gas interface

Some data from an experimental study of air entrainment into a fluid bath by a continuous moving plane tape is presented. The separate effects of surface tension and viscosity are described and the various modes of air entrainment are given in the context of fluid properties. The velocity of air entrainment is found to be a function of surface tension and viscosity for viscosities less than 4.65 poise. For viscosities greater than this value, the air entrainment velocity tended to a constant value of 9.5 cm sec^?1 independent of surface tension. Relationships of the form: We = k Re^a and We = c (Bo + 1)Re^d, are suggested by analogy to describe air entrainment data without and with buoyancy effects. Data from studies on four tapes and nine fluids gave a very high correlation when plotted in the above form. The data is in substantial agreement with that from similar studies, and shows that the condition Ca = We/Re = constant is not a global criteria for air entrainment by a plunging surface. The experimental data shows that air entrainment velocity may be estimated from the relationship V_AF = 67.679 (μ√(g/ρσ))^?0.672 for the normally plunging plane tapes studied.     

The anodic dissolution process on active iron in alkaline solutions

Steady state anodic polarization curves were taken for Armco iron and in some experiments for high purity Puratronic iron in KOH solutions in the concentration range 5 x 10^?2-5M. After the 30 min cathodic pretreatment, well reproducible anodic Tafel plots are obtained. The experimentally obtained diagnostic criteria b_a = 67–70 mV dec^?1, n_OH? = 1.1 and nHFeO₂^?= ?0.45 are interpreted by the anodic reaction mechanism in which FeOH_adsand Fe(OH)_2,ads appear as the intermediates adsorbed under Temkin conditions, the primary stable product of the electrode reaction being HFeO₂^?, and the final product Fe (OH)₂, formed by precipitation.     

Synthesis and characterization of alternating poly(amide urethane)s from ε-caprolactam, amino alcohols, and diphenyl carbonate

Alternating poly(amide urethane)s from ε-caprolactam, amino alcohols H₂N-(CH₂)_x-OH (x=2-6), and diphenyl carbonate were prepared by polycondensation of α-hydroxy-ω-O-phenylurethanes 4a-e. The degree of oligomerization was adjusted by the conversion. Oligomers with two or three O-phenylurethane end groups and predetermined molecular weight were prepared by polycondensation of the α-hydroxy-ω-O-phenylurethanes 4a-e in the presence of comonomers with O-phenylurethane end groups in a given concentration. In order to prepare oligomers with hydroxyl and carboxyl groups at both chain ends suitable for coupling reactions, chain analogous reactions were performed with amino acids and amino alcohols. The microstructure of the polymers and the nature of end groups was determined by means of ¹H NMR spectroscopy and the molecular weights were determined by means of gel permeation chromatography. The poly(amide urethane)s 5a-e prepared are semicrystalline materials with melting points between 150 and 200 °C.     

Nanoscale origins of small hysteresis and remnant strain in Bi0.5Na0.5TiO3-based lead-free ceramics

BiAlO₃-doped Bi_0.5Na_0.5TiO₃-Bi_0.5K_0.5TiO₃ (BA-doped BNT-BKT) ceramics are greatly concerned due to their sufficient electric-field-induced strain with small hysteresis and remnant strain for high precision positioning devices and other actuators. In this paper, the structural analysis especially the high-resolution transmission electron microscope (HRTEM) is used to reveal the origin of excellent properties obtained in 0.96(0.75BNT-0.25BKT)-0.04BA, which exhibits a large strain of 0.21% at ～70 kV/cm, a small strain hysteresis of only 24% and a near-zero remnant strain. Using HRTEM, the antiferroelectric nano-domains composited by three variants of in-phase a⁰a⁰c⁺ octahedral tilting coexisted with the remnant ferroelectric nano-domains of anti-phase a^?a^?a^? octahedral tilting are directly identified. Then a continuous tilting model is proposed to interpret the gradually transitional tilting involving nano-domains leading to the small hysteresis and near-zero remnant strain. The findings may pave a way for further optimizing the properties through creating stable antiferroelectric nano-domains in BNT-based ceramics and the analogues.     

A Hirshfeld surface analysis,crystal structure and physicochemical studies of zwitterionic complex: 1-(2-hydroxyethyl)piperaziniumtrichlorozincate (II)

The synthesis, crystal structure and spectroscopic characterization of the novel 1-(2-hydroxyethyl)piperaziniumtrichlorozincate(II) zwitterionic complex are reported. In the atomic arrangement, the ZnCl₃N entities, grouped in pairs, are deployed in rows along the a-axis to form layers parallel to the (a,c) plane. The organic molecules are inserted between these layers through N-H…Cl, C-H…Cl, O-H…Cl and N-H…O hydrogen bonds to form infinite three-dimensional networks. Intermolecular interactions were investigated by Hirshfeld surfaces. The ¹³C and ¹⁵N CP-MAS NMR spectra are in agreement with the X-ray structure. The vibrational absorption bands were identified by infrared spectroscopy. DFT calculations allowed the attribution of the NMR peaks and of the IR bands.     

Nanoscale origins of small hysteresis and remnant strain in Bi0.5Na0.5TiO3-based lead-free ceramics

BiAlO₃-doped Bi_0.5Na_0.5TiO₃-Bi_0.5K_0.5TiO₃ (BA-doped BNT-BKT) ceramics are greatly concerned due to their sufficient electric-field-induced strain with small hysteresis and remnant strain for high precision positioning devices and other actuators. In this paper, the structural analysis especially the high-resolution transmission electron microscope (HRTEM) is used to reveal the origin of excellent properties obtained in 0.96(0.75BNT-0.25BKT)-0.04BA, which exhibits a large strain of 0.21% at ∼70 kV/cm, a small strain hysteresis of only 24% and a near-zero remnant strain. Using HRTEM, the antiferroelectric nano-domains composited by three variants of in-phase a⁰a⁰c⁺ octahedral tilting coexisted with the remnant ferroelectric nano-domains of anti-phase a⁻a⁻a⁻ octahedral tilting are directly identified. Then a continuous tilting model is proposed to interpret the gradually transitional tilting involving nano-domains leading to the small hysteresis and near-zero remnant strain. The findings may pave a way for further optimizing the properties through creating stable antiferroelectric nano-domains in BNT-based ceramics and the analogues.     

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.     

Solutions of iodic acid in formamide. Thermodynamic properties from electromotive force measurements

Electromotive force measurements on cells without liquid junction have been used to determine pK_a of iodic acid and the standard electrode potentials (E°) of the silver-silver iodate electrode in formamide at 9 temperatures from 5–45°C. The pK_a was evaluated by using the Debye-Huckel theory with an ion-size parameter of 5.5 A°. The change in the standard electrode potentials is given as a function of temperature, t°C by the equation E°_t = 0.2786 - 8.125 x 10^?4(t - 25) - 6.385 x 10^?6(t - 25)² The standard thermodynamic quantities (ΔG°, ΔH°, and ΔS°) for the cell reactions have been evaluated for different temperatures.     

Activity of immobilized Thermomyces lanuginosus and Candida antarctica B Lipases in Interesterification Reactions: Effect of the Aqueous Microenvironment

Lipases are enzymes used in numerous reactions of industrial interest. Depending on their aqueous microenvironment, lipases can catalyze hydrolysis or, conversely, organic synthesis like interesterification. This reaction can be used as a method to modify the physical and chemical properties of fats and oils, a basic process for production of “structured lipids”. For such synthesis reactions, thermodynamic water activity (a_w) of the catalyst is generally the most important parameter to control. Actually, it will directly determine the performance of the synthesis, namely its yield, selectivity and stability. Effect of the a_w on the activity of immobilized Thermomyces lanuginosus and Candida antarctica B lipases in interesterification reactions was studied. Water sorption and desorption isotherms were determined, showing a phenomenon of hysteresis for the Thermomyces lanuginosus lipase. Evaluation of the influence of a_w on reaction yields revealed that the IE activity tends to increase with the water activity of immobilized Thermomyces lanuginosus lipase. In contrast, a_w had little influence in the case of the Candida antarctica B lipase.     

Generalisation de la theorie de l'electrode dite “electrode a disque-anneau’, dans un fluide d'otswald. Calcul des facteurs de collection

Supposing that in the diffusional boundary layer, the tangential component V_x and radial component V_r of the relative fluid velocity are respectively written in the form V_xS₀x^by and V_ra₀r^by (S₀, a₀ are independent coefficient of the normal coordinate y, tengential coordinate x, radial coordinate r;b is a numerical exponent that is expressed in terms of the behaviour law and of the flow), the authors calculate a analytical expression for the collection factor N defined as the quotient, with the sign inverted, of the limiting diffusional flux on the downstream active surface by the limiting diffusional flux on the upstream active surface. This factor N is dependent only on geometrical characteristics of system and on exponent b.     

Reversible autocatalytic reactions in an isothermal CSTR: Multiplicity,stability and relaxation times

In a recent paper, Gray and Scott have considered the autocatalytic reactions: A → B; rate ∝ abⁿ, n = 0, 1 or 2 where a and b are the concentrations of A and B respectively. Interest centred mainly on irreversible systems but for which the catalytic species was not indefinitely stable, decaying instead by a rate proportional to its concentration b. In practice all chemical reactions are to some extent reversible. The present work investigates the effect of reversibility for the cases in which B does not decay. Bounds are established on the ranges of residence-time t_res for which multiple stationary-states are possible. The stability of the different solutions is assessed and the relaxation times t_* characterizing the decay of perturbations are given. For deceleratory reactions reversibility enhances the decay rates (decreases t_*): for autocatalytic systems the decay rates may be unaltered or even reduced by a finite reverse reaction-rate. Also treated is the influence of non-zero inlet concentrations b₀ of the autocatalyst. This may lead to greater changes in the patterns of behaviour possible than those observed in the absence of reversibility. The algebraic analysis remains tractable throughout so the various effects can readily be interpreted in physical terms.     

Gas solubilities in ionic liquids using a generic van der Waals equation of state

A family of modified van der Waals equations of state (vdW EOS) is extremely useful for many industrial applications. For example, the generic Redlich-Kwong (RK) EOS or its modification by Soave (SRK EOS) and Peng-Robinson (PR EOS) are still of popular use in industry to the present day. These two most popular (“cubic”) EOSs are based on modifications [1/(V² + bV), or 1/(V² + 2bV − b²)] of the volume dependence on the attractive part of the original van der Waals EOS [1/V²] and also modifications of the temperature dependence of the attractive “a(T)” parameter of the original EOS (constant a). It is extremely rare in actual EOS applications to use the volume dependence of the original van der Waals EOS. In the present phase equilibrium calculations, we employ such a generic vdW EOS, P = RT/(V − b) − a(T)/V², with our well-tested mixing rule for multi-component mixtures. Using the same form of the “a(T)” parameter and the mixing rule, it has been found that all generic RK, PR, and vdW EOSs can present the phase behaviors (temperature-pressure-composition diagrams) equally well. It is shown that experimental gas solubility data (CO₂, CF₃-CFH₂, SO₂, and NH₃) in room-temperature ionic liquids are well correlated with the present EOS model, and also that the phase behaviors such as LLE (liquid-liquid separations) are satisfactorily predicted.     

Evaluation of the aromaticity in French coals by 13C-1H cross polarization,magic angle spinning and dipolar dephasing nuclear magnetic resonance spectroscopy

The aromaticity factor f_a of various French coals, as determined by ¹³C-¹H cross polarization and magic angle spinning, is reported. The f_a, values, which are estimated after a careful examination of the evolution of the ¹³C magnetization as a function of the contact time, are 0.63, 0.74, 0.82 and 0.85, respectively, for the Gardanne, Vouters, Méricourt and Escarpelle coals. The fraction of non-protonated aromatic carbons, fⁿ_a, as determined by dipolar dephasing experiments seems to decrease with increasing rank until a minimum value is reached for the low volatile bituminous coal from Méricourt, followed by an increase for the semi-anthracite coal from Escarpelle.     

The effect of electrode material on redox reactions of quinones in acetonitrile

Standard heterogeneous electron transfer rates for the one-electron reductions of 1,4-benzoquinone, 1,4-naphthoquinone and 9,10-anthraquinone in acetonitrile solution were measured at Pt, Au and graphite electrodes by rapid scan cyclic voltammetric methods. Observed values of the order, k_s ～ 0.5 cm s^?1 are compared with conflicting earlier results. The quinone reactions conformed with the criteria necessary for simple electron transfer processes and are adequately interpreted in terms of the Marcus theory.     

Effects of impurities on the properties of BaTiO3 synthesized from barium titanyl oxalate

The effects of impurities, such as H⁺/Cl^? and Zr⁴⁺, on the tetragonality (=c/a) of BaTiO₃ were examined to determine their effect on the synthesis of nano-sized particles with a high dielectric constant. The quantity of incorporated impurities was adjusted by controlling the milling and washing processes, which are essential for the preparation of BaTiO₃ using an oxalate method. The tetragonality decreased with increasing impurity concentration, which can be actual proof of the assumption that impurities decrease the tetragonality due to the enhanced internal strain fields. Moreover, the experimental results showing a tetragonality of 1.0068 for a particle size of 119 nm suggest that the dielectric properties of BaTiO₃ prepared by the oxalate route may be comparable with those prepared by solid-state reactions by optimizing the process parameters.     

Thermal expansion and P-V-T equation of state of cubic silicon nitride

We performed in-situ X-ray diffraction measurements of polycrystalline cubic silicon nitride samples at high temperatures under atmospheric pressure and at simultaneous high-pressure-temperature conditions. In air, cubic silicon nitride survives metastably up to 1733 K without oxidation. The temperature dependence of the thermal expansion coefficient was determined to be α(T) = a₁ + a₂T – a₃T⁻² where a₁ = 1.34(6) × 10⁻⁵ K⁻¹, a₂ = 5.06(44) × 10⁻⁹ K⁻², and a₃ = 0.20(10) K. Using all the experimental data obtained under atmospheric and high pressures, a complete set of parameters of the high-temperature third-order Birch Murnaghan equation of state was obtained: K₃₀₀,₀ = 303(5) GPa, K′_300,0 = 5.1(8), and (∂K_T,0/∂T)_P = –0.017(1) GPa K⁻¹, where K₀, K′₀, and (∂K_T,0/∂T)_P are the isothermal bulk modulus, its pressure derivative, and its temperature derivative, respectively. These parameters are necessary to calculate the equilibrium phase boundary between the β and cubic phases in silicon nitride.