Mass transfer in annular electrolytic cells with gas stirring

Mass transfer towards the inner electrode and the wall electrode was studied in an annular cell stirred with an inert gas bubble flow. Experimental data obtained for the wall electrode follow the relationship found previously for circular cells; namely $$Sh = 0.231(ScGa)^{1/3} (L/D_e )^{ - 0.194_\varepsilon0.246}$$ Study of the influence of gas hold-up on the mass transfer rate towards the inner wall electrode has yielded the following relationship: $$Sh_\infty= 0.315(ScGa)^{1/3_\varepsilon0.231}$$      

The mechanism of manganese electrodeposition

The mechanism of manganese electrodeposition from a sulphate bath on to a stainless-steel substrate has been studied by using current efficiency data to resolve the totali-E curves. A simple, two-step electron transfer mechanism: $${\text{Mn}}^{{\text{ + + }}} + {\text{e}}\xrightarrow{{{\text{r}}{\text{.d}}{\text{.s}}}}{\text{Mn}}^{\text{ + }} $$ $${\text{Mn}}^{\text{ + }} + {\text{e}} \to {\text{Mn}}$$ is proposed to explain the following experimentally obtained parameters: cathodic and anodic transfer coefficients, reaction order and stoichiometric number. The mechanism also explains the effect of pH oni _o,Mn and on the corrosion currents.     

Mass transfer characteristics of gas-sparged fixed-bed electrodes composed of stacks of vertical screens

Mass transfer rates at a gas-sparged fixed-bed electrode made of stacks of vertical screens were studied by measuring the limiting current for the cathodic reduction of potassium ferricyanide. Variables studied were air flow rate, physical properties of the solution and bed thickness. The mass transfer coefficient was found to increase with increasing air flow rate up to a certain point and then remain almost constant with further increase in air flow rate. Increasing bed thickness was found to decrease the mass transfer coefficient. Mass transfer data were correlated by the equation $$J = 0.2(ReFr)^{ - 0.28} ({L \mathord{\left/ {\vphantom {L d}} \right. \kern-\nulldelimiterspace} d})^{ - 0.28} $$ For a single vertical screen electrode the data were correlated by the equation $$J = 0.187(ReFr)^{ - 0.26} $$      

Comportement electrochimique de NbCl5 en milieu NaCl-KCl pur et additionne d'ions fluorure

Dans le domaine de température 700–800°C, les solutions d'ions niobium obtenues par addition de NbCl₅ dans le melange équimolaire NaCl-KCl, sont réduites jusqu'au métal en une seule étape: $${\text{Nb(IV) }} + {\text{ 4e}}^ - \Leftrightarrow {\text{Nb(o)}}$$ Cet échange est réversible, il lui correspond le potentiel standard apparent: $$E_{Nb(IV)/Nb}^{'0} = - 0.64V(Ag - AgCl) \pm 0.01V$$ Les espéces Nb(iv) sont oxydées selon le processus réversible: $${\text{Nb(IV)}} \Leftrightarrow {\text{Nb(v)}} + {\text{e}}^ -$$ Le potentiel standard apparent associé est: $$E_{Nb(IV)/Nb}^{'0} = - 0.74V(Ag - AgCl) \pm 0.05V$$ L'ajout d'ions fluorure déstabilise le complexé NbCl₆ ^2? au profit du complexe NbF₆ ^2? . Ceci se traduit par un déplacement du pie cathodique vers des potentiels plus cathodiques mais le mécanisme de réduction comporte toujours une seule étape mettant en jeu quatre électrons. Dans ces milieux des dépôts de niobium métallique ont eté obtenus caractérisés par rayon X. In the 700–800°C temperature range, NbCl₅ solutions in equimolar NaCl-KCl mixtures are reduced to the metal through a single step: $${\text{Nb(IV)}} + 4{\text{e}}^ - \Leftrightarrow {\text{Nb(o)}}$$ This exchange is reversible and the corresponding apparent standard potential is: $$E_{Nb(IV)/Nb}^{'0} = - 0.64V(Ag - AgCl) \pm 0.01V$$ The Nb(iv) species are oxidized according to the following reversible process: $${\text{Nb(IV)}} \Leftrightarrow {\text{Nb(v)}} + {\text{e}}^ -$$ The associated apparent standard potential is: $$E_{Nb(IV)/Nb}^{'0} = - 0.74V(Ag - AgCl) \pm 0.05V$$ The addition of fluoride ions destabilizes the NbCl₆ ^2? complex and yields the NbF₆ ^2? complex. The cathodic peak potential moves toward more cathodic potentials, but the reduction mechanism still involves a single step with four electrons exchanged. In these media, metallic niobium deposits have been obtained, and characterized through X-ray analysis.     

Reaction in the silver zinc cell

An adiabatic calorimeter was used to measure the thermodynamics of the silver zinc cell. The charge and discharge reactions were shown to take place in two stages involving the production of argentous oxide and argentic oxide respectively. No thermal evidence was found to suggest the existence of a higher oxide of silver. The cell reactions were (1) $$2{\text{Ag + ZnO}} \leftrightharpoons {\text{Ag}}_{\text{2}} {\text{O + Zn, }}\Delta {\text{H = 158}} \cdot {\text{7 kJF}}^{ - {\text{1}}}$$ (2) $${\text{Ag}}_{\text{2}} {\text{O + ZnO}} \leftrightharpoons {\text{Ag}}_{\text{2}} {\text{O}}_{\text{2}} {\text{ + Zn, }}\Delta {\text{H = 176}} \cdot 1{\text{ kJF}}^{ - {\text{1}}}$$ If the cell was left on open circuit for a long period, or the positive electrodes heated, reaction (2) was suppressed and the discharge took place via reaction (1), without any reduction in capacity.     

Determination of equilibrium silver sulphate concentration in the system Cu-H2SO4-CuSO4-H2O-Ag2SO4-Ag as a function of composition

The value of the ratio \(\gamma _{{\text{Cu}}^{{\text{2 + }}} } /\gamma _{{\text{Ag}}^{\text{ + }} }^2 \) ( \(\gamma _{{\text{Cu}}^{{\text{2 + }}} } ,\gamma _{{\text{Ag}}^{\text{ + }} } \) -are the mean activity coefficients of copper and silver ions, respectively) was calculated from the measured emf of the cell $${\text{Cu(Hg)|H}}_{\text{2}} {\text{SO}}_{\text{4}} {\text{ (}}c_{\text{x}} {\text{)}} - {\text{CuSO}}_{\text{4}} {\text{ (}}c_{\text{y}} {\text{)|Hg}}_{\text{2}} {\text{SO}}_{\text{4}} {\text{, Hg}}$$ and the solubility of Ag₂SO₄ in H₂SO₄ (c _x) and CuSO₄ (c _y) solutions. The concentration of H₂SO₄ in the solution was varied from 0.5 to 2.1 mol dm^?3 that of CuSO₄ from 0.4 mol dm^?3 to saturation. The results were presented as a function: $$\frac{{\gamma _{{\text{Cu}}^{{\text{2 + }}} } }}{{\gamma _{{\text{Ag}}^{\text{ + }} }^2 }} = a_0 + a_1 c_{\text{x}} + a_2 c_{\text{y}} + a_3 c_{\text{x}}^{\text{2}} + a_4 c_{\text{x}} c_{\text{y}} + a_5 c_{\text{y}}^2 .$$ This function allows the estimation of the equilibrium silver ion concentration \(c_{{\text{Ag}}^{\text{ + }} }^{{\text{eq}}} \) in solutions containing both H₂SO₄ and CuSO₄ in the presence of metallic copper. The function is also very useful for the estimation of the \(c_{{\text{Ag}}^{\text{ + }} }^{{\text{eq}}} \) near a working copper electrode.     

Packed-bed reactor with continuous recirculation of electrolyte

A comparison of calculated and experimental parameters for the packed-bed reactor working with recirculation of the electrolyte is given. A simple mathematical model was applied and the applicability of the relation $$c = c^0 {\text{ exp(}} - k_1 At/V{\text{) for }}V_c \ll V_R $$ was tested. For the investigated reactor a dimensionless relation has been established from experimentalI-E curves for the single pass mode $$(Sh) = 0 \cdot 5(Re)^{0 \cdot 7} (Sc)^{0 \cdot 33} .$$ For pure practical engineering requirements these two equations together give us a satisfactory way of predicting the concentration-time dependence.     

The role of sintering time on reversibility of Ni(s)—NiO(s) electrodes for high temperature solid oxide electrolyte galvanic cells

The reversibility of solid electrolyte galvanic cells such as $${\text{Mo/Ni(s)}}--{\text{NiO(s)/CSZ/Fe(s)}}--{\text{Fe}}_{{\text{1}}--\delta } {\text{O(s)/Mo}}$$ has been studied with respect to the sintering time of the active powders. Pellets from short (7h) and long (14h) sintering times have been prepared and assembled to give the above cells. Each of them has been thermally cycled and only the cells containing Ni(s)-NiO(s) electrodes prepared with a long sintering time give emf versus T curves which are independent of cycle. These values are in close agreement with the literature. For the cell reaction $${\text{NiO(s)}} + (1 - \delta ){\text{Fe(s) = Ni(s)}} + {\text{Fe}}_{1 - \delta } {\text{O(s)}}$$ the free energy change $$\Delta G = - (27.85 \pm 0.06) - (0.02157 \pm 0.00004)T{\text{ kJ mol}}^{ - {\text{1}}} $$ has been found in the temperature range 977–1350 K. To check the electrochemical reversibility, cyclic voltammetry has also been used. On the basis of these results and of SEM analysis of the electrode pellets, a mechanism is proposed whereby only at long sintering time would a triple phase contact at the electrode/electrolyte interface be produced.     

Hansen solubility parameters of cellulose acetate butyrate–poly(caprolactone) diol blend by inverse gas chromatography

The specific retention volumes, $ V_{\text{g}}^{0} $ , for adsorption of 21 solute probes on the solid surface of cellulose acetate butyrate (CAB)–poly(caprolactone) diol (PCLD) blend determined in the temperature range by inverse gas chromatography were used to evaluate Hansen solubility parameters (HSP). The effect of plasticizer, PCLD, on the HSP of CAB was investigated. The three components of HSP namely dispersive $ \delta_{2}^{\text{d}} $ , polar $ \delta_{2}^{\text{p}} $ , and hydrogen bonding $ \delta_{2}^{\text{h}} $ of the blend surface were compared with the CAB surface. The $ \delta_{2}^{\text{h}} $ of CAB was increased due to the addition of PCLD, while the change in the dispersive and polar components was found to be insignificant. The three HSP were decreasing linearly with increase of temperature for the blend as well as for pure CAB. The variation of HSP with weight fraction of CAB shown that the $ \delta_{2}^{\text{p}} $ was positively deviating from linearity whereas $ \delta_{2}^{\text{d}} $ and $ \delta_{2}^{\text{h}} $ were negatively deviating from linearity.     

Thermodynamic Properties of Sulfobetaine-Type Surfactants

Sulfobetaine-type surfactants containing a hydroxy group were synthesized by the reaction of long chain monoalkyl dimethyl tertiary amine with 3-chloro-2-hydroxypropanesulfonic acid sodium salt. The structures were characterized by ¹H NMR and ESI-MS. Their critical micelle concentrations (CMC) in aqueous solution were determined by the plate method in the temperature rang from 298.15 to 328.15 K. The thermodynamic parameters of micellization ( $\Delta G_{\text{mic}}^{\theta}$ , $\Delta H_{\text{mic}}^{\theta}$ and $\Delta S_{\text{mic}}^{\theta}$ ) and surface adsorption ( $\Delta G_{\text{ad}}^{\theta}$ , $\Delta H_{\text{ad}}^{\theta}$ and $\Delta S_{\text{ad}}^{\theta}$ ) were calculated from CMC data. The results showed that the micellization and surface adsorption of these surfactants in aqueous solution was a spontaneous and entropy-driven process. The micellization and surface adsorption became easier when the alkyl chain length increased from 12 carbon atoms to 14. The enthalpy–entropy compensation of micellization and adsorption was investigated. The compensation temperature were found to be (311 ± 2) K for both micellization and adsorption. The $\Delta H_{\text{mic}}^{*}$ and $\Delta H_{\text{ad}}^{*}$ decreased, but the $\Delta S_{\text{mic}}^{*}$ and $\Delta S_{\text{ad}}^{*}$ increased with increasing the hydrophobic chain length from 12 to 14.     

Conduction in Bi2O3-based oxide ion conductor under low oxygen pressure. II. Determination of the partial electronic conductivity

In order to investigate the partial electronic conduction in the high oxide ion conductor of the system Bi₂O₃-Y₂O₃ under low oxygen pressure, e.m.f. and polarization methods were employed. Although the electrolyte was decomposed when the \(P_{{\text{O}}_{\text{2}} }\) was lower than the equilibrium \(P_{{\text{O}}_{\text{2}} }\) of Bi, Bi₂O₃ mixture at each temperature, the ionic transport number was found to be close to unity above that \(P_{{\text{O}}_{\text{2}} }\) . The hole conductivity (σ _p) and the electron conductivity (σ _p) could be expressed as follows, $$\begin{gathered} \sigma _p \Omega cm = 5 \cdot 0 \times 10^2 \left( {P_{O_2 } atm^{ - 1} } \right)^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} \exp \left[ { - 106 kJ\left( {RT mol} \right)^{ - 1} } \right] \hfill \\ \sigma _p \Omega cm = 3 \cdot 4 \times 10^5 \left( {P_{O_2 } atm^{ - 1} } \right)^{ - {1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} \exp \left[ { - 213 kJ\left( {RT mol} \right)^{ - 1} } \right] \hfill \\ \end{gathered} $$ These values were much lower than the oxide ion conductivity under ordinary oxygen pressure.     

Characteristic velocity and mass transfer in rotating impeller column

The effects of system variables on flow characteristics and mass transfer rate were studied in a rotating impeller column using a ternary system of water (continuous phase)-acetone (solute)-cyclohexane (dispersed phase). The characteristic velocity, Peclet numbers in both phases and mass transfer coefficient between phases were correlated as; $$\begin{gathered} \bar U_o = 6.3(10^2 )(Nd_I )^{ - 2.1} Z_C^{0.83} \hfill \\ \frac{{\bar U_C L}}{{D_C }} = 1.26N^{ - 1.11} d_I ^{ - 2.17} Z_C^{0.59} \bar F_C^{1.9} \hfill \\ \frac{{\bar U_d L}}{{D_d }} = 20.5N^{ - 0.78} d_I ^{ - 1.36} Z_C^{0.25} \bar F_C^{0.09} \hfill \\ \frac{{k_{OC} aL}}{{\bar U_d }} = 13.2N^{ - 1.33} d_I ^{0.74} Z_C^{0.93} \bar F_C^{0.78} \hfill \\ \end{gathered} $$      

Micellization of Some Bile Salts in Binary Aqueous Solvent Mixtures

The micellization behavior of bile salts—sodium cholate and sodium deoxycholate was studied in aqueous methanol, ethanol and ethylene glycol mixtures (10–20 % v/v) over a temperature range (300–320 K) by surface tension and conductivity methods. Critical micelle concentration, extent of counter ion binding (α), interfacial property (A _min, ζ_max, π-CMC, $ \Updelta G_{\text{ad}}^{ \circ } $ ) and thermodynamic parameters ( $ \Updelta G_{\text{m}}^{ \circ } $ , $ \Updelta H_{\text{m}}^{ \circ } $ , $ \Updelta S_{\text{m}}^{ \circ } $ ) for the micellization process are reported and discussed.     

Structure and Biological Behaviors of Some Metallo Cationic Surfactants

In this study, different cationic surfactants were prepared by esterification with bromoacetic acid of different fatty alcohols, i.e., dodecyl, tetradecyl and hexadecyl species. The products were then reacted with diphenyl amine, and the resulting tertiary amines were quaternized with benzyl chloride to produce a series of quaternary ammonium salts. The metallocationic surfactants were prepared by complexing the cationic surfactants with nickel and copper chlorides. Surface tension of these surfactants were investigated at different temperatures. The surface parameters including critical micelle concentration (CMC), maximum surface excess (Γ _max), minimum surface area (A _min), efficiency (PC₂₀) and effectiveness (π _CMC) were studied. The thermodynamic parameters such as the free energy of micellization ( $\Updelta G_{\text{mic}}^{^\circ }$ ) and adsorption ( $\Updelta G_{\text{ads}}^{^\circ }$ ), enthalpy ( $\Updelta H_{\text{m}}^{^\circ }$ ), ( $\Updelta H_{\text{ads}}^{^\circ }$ ) and entropy ( $\Updelta S_{\text{m}}^{^\circ }$ ), ( $\Updelta S_{\text{ads}}^{^\circ }$ ) were calculated. FTIR spectra and ¹H-NMR spectra were obtained to confirm the compound structures and purity. In addition, the antimicrobial activities were determined via the inhibition zone diameter of the prepared compounds, which were measured against six strains of a representative group of microorganisms. The results indicate that these metallocationic surfactants exhibit good surface properties and good biological activity on a broad spectrum of microorganisms.     

Surface characterization of cellulose acetate propionate by inverse gas chromatography

The purpose of this paper is to study the surface energetics of the polymer excipient cellulose acetate propionate (CAP) in the solid form. The net retention volumes, V _N, for n-alkanes and polar solutes have been measured in the temperature range 353.15–403.15 K by inverse gas chromatography. The dispersive surface free energy, $ \gamma_{\text{S}}^{\text{d}} $ , and Lewis acid–base parameters $ K_{\text{a}} $ and $ K_{\text{b}} $ , have been determined using V _N values. The $ \gamma_{\text{S}}^{\text{d}} $ values are decreased linearly with increase of temperature. The $ \gamma_{\text{S}}^{\text{d}} $ value at 353.15 K is 24.50 ± 1.54 mJ/m², and the temperature gradient was found to be ?0.287 mJ/m²/K¹. The $ K_{\text{a}} $ and $ K_{\text{b}} $ values are 0.410 ± 0.021 and 1.708 ± 0.388, respectively, which suggest that the CAP solid surface contain relatively more basic sites. The K _a and K _b values of CAP are compared with the similar values obtained on the cellulose acetate butyrate solid surface.     

Mass transfer at vertical cylinders under forced convection induced by the counter electrode gases

Mass transfer coefficients were measured for the deposition of copper from acidified copper sulphate solution at a vertical cylinder cathode stirred by oxygen evolved at a horizontal lead anode placed below the cylinder. Variables studied were: oxygen discharge rate, electrolyte concentration and cylinder height. The mass transfer coefficient was found to increase by a factor of 1.8–2.6 depending on oxygen discharge rate and cylinder height. The mass transfer coefficient was related to oxygen discharge rate and cylinder height by the equation: $$K = 65.8 \times 10^{ - 4} \frac{{V^{0.358} }}{{h^{0.29} }}$$      

Surface and Solution Properties of Amphiphilic Drug-Nonionic Surfactant Systems

A surface tension study was performed on mixed amphiphilic drug-nonionic surfactant systems. The drugs used were adiphenine hydrochloride and nortriptyline hydrochloride whereas surfactants were ethoxylated sorbitan esters and polyethylene oxide?Cpolypropylene oxide?Cpolyethylene oxide triblocks. The critical micelle concentration (CMC) and CMC^id (CMC at ideal mixing condition) values suggest nonideal and attractive interactions among the components. The micellar mole fraction $ (X_{ 1}^{\text{m}} ) $ values calculated using Rubingh??s model indicate predominance of the nonionic surfactant in micelle formation. The mole fraction of surfactant in mixed monolayer $ (X_{1}^{\sigma } ) $ values are greater than $ X_{ 1}^{\text{m}} $ values, indicating a greater contribution of surfactant in monolayer formation. Thermodynamic parameters, viz. Gibbs energy of micellization $ (\Updelta G_{\text{m}}^{\text{o}} ) $ , Gibbs energy of adsorption $ (\Updelta G_{\text{ad}}^{\text{o}} ) $ , and excess free energy of mixed micelles $ (\Updelta G_{\text{ex}}^{\text{m}} ) $ and monolayers $ (\Updelta G_{\text{ex}}^{\sigma } ) $ were also evaluated. All these values suggest stable mixed micelle and mixed monolayer formation.     

Thermodynamics of Micellization of Sulfobetaine Surfactants in Aqueous Solution

The thermodynamics of micellization of the sulfobetaine (SB) amphoteric surfactants, that is N-alkyl-N,N-dimethyl-3-ammonio-1-propanesulfonate and N-alkyl-N,N-dimethyl-3-ammonio-1-butanesulfonate (the carbon atom number of the alkyl chain is 12, 14 and 16 respectively) in aqueous solution, have been studied by surface tension measurements with the temperature range from 298.15 to 318.15?K. The critical micelle concentrations (CMC) of SB n-3 and SB n-4 surfactants were determined from the drop-volume methods at different temperatures. The obtained results indicated that the values of critical micelle concentration strongly depended on the surfactants species and temperatures. Thermodynamic parameters ( $ \Updelta G_{\text{mic}}^{ \circ } $ , $ \Updelta H_{\text{mic}}^{ \circ } $ and $ \Updelta S_{\text{mic}}^{ \circ } $ ) of the micelle formation were determined. The micellization was found to be enthalpy-driven at lower temperatures, while this process was entropy-driven at higher temperatures. The enthalpy?Centropy compensation were also investigated. The compensation temperature T _c and $ \Updelta H_{\text{mic}}^{*} $ decreased, while $ \Updelta S_{\text{mic}}^{*} $ increased with the increase in the hydrophobic chain length.     

Mass transfer downstream of nozzles in turbulent pipe flow with varying Schmidt number

Local mass transfer rates at the wall of a pipe downstream of constricting nozzles have been measured using the electrochemical limiting diffusion current technique for different electrolyte Schmidt numbers. The familiar peaked axial distribution of mass transfer downstream of the nozzle was verified and the peak mass transfer values were found to agree well with the data of Tagget al. [1]. An overall correlation of the data in terms of both Reynolds number and nozzle expansion ratio produced the equation $$({{Sh_{2P} } \mathord{\left/ {\vphantom {{Sh_{2P} } {Sh_{2FD} }}} \right. \kern-\nulldelimiterspace} {Sh_{2FD} }})({{D_1 } \mathord{\left/ {\vphantom {{D_1 } {D_2 }}} \right. \kern-\nulldelimiterspace} {D_2 }})^{ - 0.7} = 14.39Re_2^{ - 0.182} $$ Limiting current-time traces produced evidence of the highly turbulent flow in the recirculation zone near the position of peak mass transfer.     

Positive polyacetylene electrodes in aqueous electrolytes

Polyacetylene films, contacted with platinum mesh, have been polarized anodically in aqueous H₂SO₄, HClO₄, HBF₄ and H₂F₂ of medium concentrations (30–70 wt%). Two oxidation peaks are observed, the equivalents of which are 1 $${\text{(1) 0}}{\text{.045 F mol}}^{ - {\text{1}}} {\text{ CH (2) 0}}{\text{.23 F mol}}^{ - {\text{1}}} {\text{ CH}}$$ The potential of the Process 1 decreases linearly with increasing acid concentration by 20–40 mV mol^?1 dm^?3, while the potential of Peak 2 exhibits normal Nernst behaviour (about + 60 mV decade^?1. Process 1 is partially reversible, while Process 2 is totally irreversible. From these findings for Process 1 we conclude the reversible insertion of anions into the polyacetylene host lattice, which is primarily oxidized to the polyradical cation, with the co-insertion of acid molecules HA to yield the insertion compound [(CH)⁺·yA^?·vyHA] _x y?4.5% andv=1.5 for H₂SO₄ and HClO₄. In the course of Process 2, the polymer is irreversibly oxidized according to $$( - ^ \cdot {\text{CH}} \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot ^ \oplus {\text{ CH}} - )_{x/2} + 2{\text{H}}_{\text{2}} {\text{O}} \to ( - \mathop {\text{C}}\limits_{\mathop \parallel \limits_{\text{O}} } \cdot \cdot \cdot \cdot \cdot \cdot \cdot \cdot \mathop {\text{C}}\limits_{\mathop \parallel \limits_{\text{O}} } - )_{x/2} + 6{\text{H}}^{\text{ + }} + 5e^ - $$ As this process occurs to some extent even in the potential region of Process 1, a continuous degradation of the host lattice occurs upon cycling.