Growth of oxide layers on platinum electrodes in molten alkali nitrates

The formation of oxide layers on Pt anodes and on Pt cathodes in each of the molten alkali nitrates, LiNO₃, NaNO₃ and KNO₃, has been investigated under galvanostatic and potentiostatic conditions at 340°C.The coverage by oxygen on the anode increased with the polarization potential and time and reached a limiting value of about 2·6 oxygen atoms per apparent surface platinum atom. No cation effect on the anodic formation of the oxide film was observed.Thick multilayer oxide films grew very rapidly on the “cathode” in the KNO₃ melt and slowly on that in the NaNO₃ melt. In the KNO₃ melt and also in the NaNO₃ melt, the growth rate of the multilayer oxide reached a maximum at ?1.65 V (vs a Ag 0.1 M Ag⁺ in 1 kg KNO₃ reference electrode) and rapidly fell at more negative potentials because of the dissolution of the oxide into the melt. Above ?2.0 V, neither the formation of the multilayer oxide nor corrosion of the electrode was observed. In the LiNO₃ melt, no multilayer oxide film was formed at any potentials.     

Ion Exchange in Molten Salts. II: The Occlusion of Lithium,Sodium, Potassium and Silver Nitrates in the Respective Forms of Zeolite A.

The occlusion of lithium, sodium, potassium and silver nitrates from the anhydrous melts in the respective zeolites has been studied by measuring the gain in weight and by direct analysis. The results in moles of occluded nitrate per formula weight of zeolite M₁₂^I[(AlO₂)₁₂(SiO₂)₁₂] are 11.7 for LiNO₃, 10 for NaNO₃ and 10 for AgNO₃ and essentially zero for KNO₃. A model is proposed for the structure of the occlusion compound Na₂₂[(AlO₂)₁₂(SiO₂)₁₂(NO₃)₁₀], in terms of four Na_I⁺ ions and four [Na_I - NO₃ - Na]⁺ groups at the apexes of the cubic unit cell and four [Na_II - NO₃ - Na]^+1/3 groups coordinated with two [NaNO₃]^?2/3 groups at the faces, to explain the properties of the occluded zeolites.     

Acides forts dans le dimethylsulfoxide

Dissociation of acids in dimethylsulfoxide has been studied by conductometry. Trifluoromethanesulphonic acid is completely dissociated. Dissociation constants of the other acids are: picric acid 10^+0·3, methanesulphonic acid 10^?1·76, hydrochloric acid 10^?2·01, trifluoroacetic acid 10^?3·45 and sulphuric acid ? 10^?1·41. The proton ionic conductivity is “normal”. The acids dissociation is compared in dimethylsulfoxide and other solvents.     

Faradaic rectification study of the metal/metal ion reactions

The kinetic parameters for Ag⁺/Ag and Cu²⁺/Cu reactions at the equilibrium potential and in the absence of dc polarisation have been obtained using the faradaic rectification method at audio frequencies. The values of transfer coefficients, ion exchange current densities and apparent rate constants, obtained for the two reactions at 27°C using 1·0mM of each of the Ag⁺ and Cu²⁺ in 1·0M KNO₃, are respectively 0·22; 7·3mA/cm²; 3·6·10^?3 cm/s and 0·45; 10·7 mA/cm²; 1·1×10^?4cm/s. These data are comparable to those reported in the literature. For obtaining reliable and reproducible results for the studies with metal/metal ion reactions suitable experimental conditions have been described.     

Equilibrium Distribution Coefficients of Some Nitrate Impurities in Sodium Nitrate from Zone Refining

Abstract

The equilibrium distribution coefficients of 10 impurities (Li, K, Rb, Cs, Ag, TI, Mg, Ca, Sr, and Ba) in sodium nitrate were determined from the measured values of the effective distribution coefficients obtained by zone refining. The equilibrium distribution coefficients obtained are as follows: LiNO₃, 9.2 × 10^?2; KNO₃, 3.0 × 10^?1; RbNO₃, 2.2 × 10^?2; CsNO₃, 1.3 × 10^?3; AgNO₃, 7.8 × 10^?1; TlNO₃, 5.2 × 10^?1; Mg(NO₃)₂, 7.4 × 10^?2; Ca(NO₃)₂, 1.5 × 10^?2; Sr(NO₃)₂, 3.0 × 10^?2; and Ba(NO₃)₂, 2.1 × 10^?2. These values are in favorable agreement with those estimated from the phase diagrams and/or those calculated from the heat of solid solution.     

Synthesis of mullite precursors in molten salts. Influence of the molten alkali nitrate and additives

Silica gel and aluminium salt, in the stoichiometric ratio for mullite (Al/Si=3), have been used to prepare the mullite precursor by reaction in molten alkali nitrates at 450°C. The influence of the nitrate (NaNO₃, KNO₃ or mixture NaNO₃–KNO₃) and the additives (Ca²⁺, Ba²⁺, Bi³⁺) on the phase transformations has been followed between 1000 and 1400°C. It appears that molten NaNO₃ favours the crystallization of cristobalite and α-Al₂O₃ whereas KNO₃ inhibits the formation of silica and mullite. The mixture NaNO₃–KNO₃ seems to be the best choice. Addition of foreign cations improves the mullite formation and favours the synthesis of θ-Al₂O₃, especially in the case of Bi³⁺. But the crystallization temperature of mullite is not changed.     

Effect of Li+ on the acidity of metaphosphate—alkali nitrate melts

The effect of additions of LiNO₃ on the titration behaviour of sodium trimetaphosphate (TMP) in fused KNO₃ is examined. The presence of as low as 2 wt% LiNO₃ in KNO₃ melt at 350°C causes neutralization to occur in a single step consuming one oxide equivalent/equivalent NaPO₃. That the reaction continues step-wise through the formation of P₂O^4?₇ is proved from experiments involving this last acid. LiNO₃ shifts the O₂-electrode potentials in pyrophosphate containing melts to the same values measured in TMP containing melts. Li⁺ ions also affect the stability of TMP in KNO₃ melt. Decomposition occurs at a rate increasing with the rise of both LiNO₃ content and temperature of the melt. These peculiar effects are explained in terms of ion-pair formation and the relative high acidity of Li⁺ ion.     

Ion—solvent interaction: viscosity of ternary electrolytes in dioxane-water mixtures at 35°

The viscosities of the chlorides, bromides and nitrates and perchlorates of Mg²⁺ and Ba²⁺, of the chlorides and nitrates of Ca²⁺ and Sr²⁺, and of the sulphates of Na⁺ and K⁺ at mass fraction of dioxane, 10, 20 and 30% have been measured at 35°. The values of the constant A and B of the viscosity equation indicate ion—ion and ion—solvent interaction respectively. The ion-solvent interaction is found to be of the order NO^?₃ > ClO^?₄ > Br^? > Cl^? and K⁺ > Na⁺.     

Enhancing the electrical conductivity of vanadate glass system (Fe2O3, B2O3, V2O5) via doping with sodium or strontium cations

Novel glass-ceramics of the nominal molar compositions 20Fe₂O₃·20B₂O₃·(60-x)V₂O₅· (xNa₂O or xSrO) (where x?=?0 or 10) were prepared by traditional melt technique. Differential thermal analysis (DTA) was implemented to study the thermal behavior of the prepared glasses. Vanadium pentoxide (V₂O₅), iron vanadate (FeVO₄), sodium vanadate (Na₃VO₄) and strontium vanadate (with different formulae) were crystallized and identified by X-ray diffraction (XRD) analysis under certain conditions of heat-treatment. Further characterization of glass and glass ceramics samples were performed using scanning electron microscope (SEM), density, electrical and dielectric measurements. In conclusion, our study elucidated that the substitution of vanadium by Na⁺ and Sr²⁺ ions enhanced the conductivity at 180?°C from 5.11?×?10^?4 for unmodified glass to 2.93?×?10^?3 and 1.03?×?10^?2?S?cm^?1 for Na- and Sr-modified glasses.     

Comportement electrochimique et reactivite du systeme Ag(II)/Ag(I)-bipyridine dans le carbonate de propylene—III. Etude du mecanisme et de la cinetique de la reaction d'oxydation catalytique de la bipyridine

The electrochemical behaviour of the Ag(II)/Ag(I)-bipyridine system has been investigated in solutions containing bipyridine in excess with respect to the Ag⁺-bipy: 1–2 stoichiometry. The nature of the coupled chemical reaction indicates a chemical catalysis of an electrochemical reaction. The rate constant of the reaction of destruction of the intermediate complex (k₂ = 1.8 × 10^?3s^?1) has been calculated from measurements performed during electrolysis of Ag^I(bipy)⁺₂-bipy solutions.     

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.     

Oxidation of Esculetin,a Model Pollutant Present in Cork Processing Wastewaters,by Chemical Methods

The ozonation of esculetin (6,7-dihydroxycoumarin), a major pollutant present in the wastewater generated in the cork industry, was accelerated at high pH, with apparent second-order rate constants in the range from 3.3 × 10⁴ L/(mol·s) at pH=2 to 8.4 × 10⁷ L/(mol·s) at pH=9. The acid-base equilibrium of esculetin was studied, resulting in a pK_a value of 7.37. Taking into account this pK_a, the rate constants for the reaction between ozone and the un dissociated and dissociated forms of esculetin were 3.0 × 10⁴ and L/(mol·s) 6.67 × 10⁸ L/(mol·s), respectively. Apparent first-order rate constants for the photolysis by UV irradiation were also evaluated, with values between 0.12 × 10^?2 min^?1 at pH=2 and 1.15 × 10^?2 min^?1 at pH=9, while the quantum yields for this photo-degradation reaction varied from 0.99 × 10^?2 mol/Eins to 11.1 × 10^?2 mol/Eins at these pHs. The Fenton's reagent system was used for the generation of hydroxyl radicals, and the rate constant for the reaction between esculetin and these radicals was determined to be 1.06 × 10¹⁰ L/(mol·s). Finally, several chemical oxidation systems were used in the degradation of this pollutant: single oxidants (ozone, UV irradiation) and advanced oxidation processes (Fenton's reagent, UV/H₂O₂, O₃/H₂O₂, O₃/UV, O₃/H₂O₂ /UV, and photo-Fenton system). The results revealed that the most efficient methods in terms of esculetin removal were ozonation among the single oxidants, and the photo-Fenton system among the combined processes.     

Dissociation constants of certain scale forming salts

Dissociation constants of the associated ion pairs CaCO₃^O, CaSO₄^O CaHCO₃⁺, CaOH⁺ and NaSO₄^? in the temperature range 20–98°C were determined. More accurate solubility product values of calcium carbonate and calcium sulfate were obtained. Consideration of the established ion pairs' dissociation constants ensures a more accurate evaluation of the calcium carbonate supersaturation in saline and brackish water, as well as possible evaporation ratios without calcium sulfate deposit formation.     

Kinetics of Estrone Ozone/Hydrogen Peroxide Advanced Oxidation Treatment

Ozone/hydrogen peroxide batch treatment was utilized to study the degradation of the steroidal hormone estrone (E1). The competition kinetics method was used to determine the rate constants of reaction for direct ozone and E1, and for hydroxyl radicals and E1 at three pH levels (4, 7, and 8.5), three different molar O₃/H₂O₂ ratios (1:2, 2:1, and 4:1) and a temperature about 20°C. The average second-order rate constants for direct ozone-E1 reaction were determined as 6.2?×?10³?±?3.2?×?10³ M^?1s^?1, 9.4?×?10⁵?±?2.7?×?10⁵ M^?1s^?1, and 2.1?×?10⁷?±?3.1?×?10⁶ M^?1s^?1 at pH 4, 7, and 8.5, respectively. It was found that pH had the greatest influence on the reaction rate, whereas O₃/H₂O₂ ratio was found to be slightly statistically significant. For the hydroxyl radical-E1 reaction, apparent rate constants ranged from 1.1?×?10¹⁰ M^?1s^?1 to 7.0?×?10¹⁰ M^?1s^?1 with an average value of 2.6?×?10¹⁰ M^?1s^?1. Overall, O₃/H₂O₂ is shown to be an effective treatment for E1.     

Characterization of the Binding Interaction between Poly(Epicholorohydrin‐Diamine) and Reactive Dyes using a Multiple Linear Regression and Quartz Crystal Microbalance Methods

Abstract

The binding processes of Reactive Red K‐2BP (K‐2BP) and Reactive Violet K‐3R (K‐3R) onto poly(epicholorohydrin‐diamine)(PEPIDA) in solution and film were investigated by spectrophotometric and quartz crystal microbalance (QCM) methods, respectively. By using a multiple linear regression technique, the concentrations of the colored components in the mixtures of dye+PEPIDA were measured simultaneously from the absorbance spectra. The binding equilibrium constants for K‐3R and K‐2BP onto PEPIDA in solution were estimated to be 9.31×10⁶ and 1.86×10⁶ L · mol^?1, respectively. The difference in the color removal between K‐3R and K‐2BP by PEPIDA was discussed. The binding processes of K‐3R and K‐2BP onto PEPIDA film were followed by the QCM. The binding equilibrium constants were evaluated to be 1.27×10⁶ and 3.28 ×10⁵ L · mol^?1 for K‐3R and K‐2BP onto PEPIDA film, respectively. They are less than those determined in PEPIDA solutions. The binding rate constants for K‐3R and K‐2BP onto PEPIDA film were estimated to be 1.43×10⁵ and 1.72×10⁵ L · mol^?1 · s^?1, respectively.     

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.     

Utilization of response surface methodology to optimize the culture media for the production of rhamnolipids by Pseudomonas aeruginosa AT10

Pseudomonas aeruginosa AT10 produced a mixture of surface‐active rhamnolipids when cultivated on mineral medium with waste free fatty acids as carbon source. The development of the production process to an industrial scale included the design of the culture medium. A 2⁴ full factorial, central composite rotational design and response surface modelling method (RSM) was used to enhance rhamnolipid production by Pseudomonas aeruginosa AT10. The components that are critical for the process medium were the carbon source, the nitrogen source (NaNO₃), the phosphate content (K₂ HPO₄/KH₂PO₄ 2:1) and the iron content (FeSO₄·7H₂O). Two responses were measured, biomass and rhamnolipid production. The maximum biomass obtained was 12.06 g dm^?3 DCW, when the medium contained 50 g dm^?3 carbon source, 9 g dm^?3 NaNO₃, 7 g dm^?3 phosphate and 13.7 mg dm^?3 FeSO₄·7H₂O. The maximum concentration of rhamnolipid, 18.7 g dm^?3, was attained in medium that contained 50 g dm^?3 carbon source, 4.6 g dm^?3 NaNO₃, 1 g dm^?3 phosphate and 7.4 mg dm^?3 FeSO₄·7H₂O. © 2002 Society of Chemical Industry     

Complex formation in molten salts - IV: Association constants of silver-bromo complexes in molten KNO3Ba(NO3)2 eutectic as solvent

Potentiometric measurements on the molten salt concentration cell: Ag/AgNO₃, KNO₃Ba(NO₃)₂//AgNO₃, KBr, KNO₃Ba(NO₃)₂/Ag were carried out over a wide range of solute concentration and at temperatures in the range 350–410°C to study the association equilibria in dilute solutions of Ag⁺ and Br^? in molten KNO₃Ba(NO₃)₂(89:11 mole %). The results indicated formation of the species AgBr, AgBr^?₂; Ag₂Br⁺ was not formed under the experimental conditions employed. The temperature-dependence of the association constants were, within limits of experimental precision, predictable from the quasi-lattice model.     

Lithium Ion-conducting Blend Polymer Electrolyte Based on PVA–PAN Doped with Lithium Nitrate

A new blend polymer electrolyte based on poly(vinyl alcohol) and polyacrylonitrile doped with lithium nitrate (LiNO₃) has been prepared and characterized. The complexation of blend polymer (92.5 PVA:7.5 PAN) with LiNO₃ has been studied using X-ray diffraction and Fourier transform infrared spectroscopy. Differential scanning calorimetry thermograms show a decrease in glass transition temperature with the addition of salt. The maximum ionic conductivity of the blend polymer electrolyte is 1.5 × 10^?3 Scm^?1 for 15 wt% LiNO₃ doped–92.5 PVA:7.5 PAN electrolyte. The conductivity values obey Arrhenius equation. Ionic transference number measurement reveals that the conducting species are predominantly ions.     

Composition of Polymerized Linseed Oil Bodied by a Molten Eutectic Salt Mixture

Quantities of alkali refined linseed oil, ARLO, were passed through molten eutectic mixtures of salts, KNO₃, NaNO₂ and NaNO₃ or KNO₃ and NaNO₃ in the temperature range of 280° C to 320° C at various flow rates. The oils increased in viscosity. Colour degradation was very slight and the acidity increased to as high as 5 mg KOH/g. The bodied oils were readily separated into two fractions on the basis of solubility in acetone. Acetone solubility decreased with the increase in bodying temperature in the eutectic salt mixture. Both fractions were analyzed for fatty acid composition and structure. Spectroscopic techniques, NMR and chromatographic studies indicated that there was an absence of nitrogen compounds, some degradation (to shorter than 18 carbon atom acids), formation of “oxy” groups and some cyclization in a single acid and in the formation of polymers which were di- and trimeric structures.