Tracer diffusion of131I− ions in a few 1–2 electrolytes in agar gel

Tracer diffusion of¹³¹I^– ions is studied at different temperatures /20°C–50°C/ in 2.5% agar gel containing sodium and potassium sulphate solutions over a wide range of concentrations. The results are in qualitative agreement with the theoretical values in the concentration range 10^–6–10^–1M. Agar gel shows an obstruction effect to diffusional flow. The activation energy for tracer diffusion was found to be of the order of 16.3 kJ mol^–1.     

Electrolyte diffusion of ZnCl2 and self-diffusion of Cd2+ ions in agar gel medium at different temperatures

The values of activation energy required for the diffusion of ZnCl₂ and for Cd²⁺ ions in Cd/Ac/₂ are reported in agar gel medium at 5×10^–5 and 0.001M concentration, respectively. These values are compared with the previously reported values in the same systems at different concentrations. The decrease in activation energy with concentration of electrolyte is in agreement with the Wang's model.     

Diffusion of zinc sulphate in agar gel medium

The activation energy for the diffusion of ZnSO₄ as a function of electrolyte concentration is computed by least squares fitting of the diffusion coefficient data obtained at various temperatures in the Arrhenius equation. It is observed that the activation energy decreases with increasing concentration of the electrolyte. This observation is accounted for on the basis of Wang's model. Further, the obstruction effect caused by the agar macromolecules in the diffusion path of ZnSO₄ uis also determined at these concentrations by varying the gel concentration at 25°C., The obstruction effect expressed in terms of a found to decrease with ZnSO₄ concentration and explained on the basis of competitive hydration of diffusing ions and agar molecules.     

Tracer diffusion of Co2+ ions in agar gel containing multi-electrolyte systems

Tracer diffusion coefficients of cobalt ions have been measured in the supporting medium containing multi-electrolyte systems of alkali bromides. The electrolyte concentration was varied between 10^–6-0.1M at 25°C and the diffusion coefficients were determined by zone-diffusion technique using agar gel medium. The trend in the theoretical values of diffusion coefficients is accounted for by considering the relative contribution of mobility function, ionic strength as well as ion size parameter to the theoretical value in different systems. While the deviations between theoretical and experimental values of diffusion coefficients are explained on the basis of various co-occurring effects in ion-gel-water system.     

Tracer-diffusion of cobalt ions in sodium and potassium nitrates in agar gel

Tracer-diffusion of Co²⁺ ions is studied in agar gel in the presence of sodium and potassium nitrates at 25°C. The diffusion coefficient values at various electrolyte concentrations are compared with the corresponding theoretical values computed on the basis of Onsager's theory. The deviations from the theory are attributed to the various co-occurring effects in the diffusion medium. The activation energy for the process of diffusion of Co²⁺ ions in presence of above electrolytes is also reported.     

Tracer diffusion of Co2+ ions in some transition metal sulphates in agar gel

Tracer diffusion of Co²⁺ ions is studied in agar gel medium in the presence of some transition metal sulphates using the zone diffusion technique. A comparison between the experimental and theoretical values of diffusion coefficients computed on the basis of Onsager's theory shows a divergence between them. These deviations are explained on the basis of various effects in the iongel-water system.     

Electrolyte-diffusion of cobalt sulphate in agar gel medium at 25 °C

The diffusion of cobalt sulphate is studied in 1% agar gel over a concentration range of 10^–5 to 0.2M at 25 °C. The experimental values of the diffusion coefficient at various concentrations determined by the zone-diffusion technique are compared with the theoretical values of diffusion coefficinets computed on the basis of Onsager-Fuoss theory. The observed deviations are interpreted in terms of relative contributions of diffusion-enhancing and diffusion-retarding interactions occurring in the water-gel-electrolyte system.     

Diffusion studies of cobalt ions and their salts in agar gel medium: Obstruction effect and gel hydration

The obstruction effect in the electrolyte diffusion of cobalt halides and in tracer diffusion of Co²⁺ ions in the presence of different supporting electrolytes at various concentrations has been studied at 25 °C using the zone diffusion technique. It has been observed that obstruction effect expressed in terms of increases with concentration and is higher for electrolyte diffusion than in tracer diffusion. Further, for a given concentration it is found to decrease with increasing charge density of an anion. These observations are explained on the basis of competitive hydration between ions and agar molecules.     

Isotope exchange of iodine between sodium iodide [Na131I] and [4-127I]iodoantipyrine via organic medium

The present investigation deals with a study of the isotope exchange reaction of iodine between sodium iodide [Na¹³¹I] and [4-¹²⁷I]iodoantipyrine in organic medium, using different iodinating radioiodine reagents of different carrier-iodine concentration. A maximum saturation yield over 90% of pure [4-¹³¹I]iodoantipyrine has been obtained by performing the isotope exchange reaction in ethanol at 80°C in 30 min. The same yield has been obtained using the same concentrations by performing the reaction at room temperature (17–20°C) for 3 h. Also the rate of the isotope exchange reaction was found to be carrier-iodine dependent as well as time and temperature dependent. According to these results and reaction conditions, a kit form method was elaborated for the synthesis of [4-¹³¹I]iodoantipyrine as well as [4-¹²³I]iodoantipyrine.     

Surface tension-induced gel fracture. Part 1. Fracture of agar gels

This work involves an experimental investigation of the spreading of liquids on gel layers in the presence of surfactants. Of primary interest is the instability that accompanies the cracking of gels through the deposition and subsequent spreading of a drop of surfactant solution on their surfaces. This instability manifests itself via the shaping of crack-like spreading "arms", in formations that resemble starbursts. The main aim of this study is to elucidate the complex interactions between spreading surfactants and underlying gels and to achieve a fundamental understanding of the mechanism behind the observed phenomenon of the cracking pattern formation. By spreading SDS and Silwet L-77 surfactant solutions on the surfaces of agar gels, the different ways that system parameters such as the surfactant chemistry and concentration and the gel strength can affect the morphology and dynamics of the starburst patterns are explored. The crack propagation dynamics is fitted to a power law by measuring the temporal evolution of the length of the spreading arms that form each one of the observed patterns. The values of the exponent of the power law are within the predicted limits for Marangoni-driven spreading on thick layers. Therefore, Marangoni stresses, induced by surface tension gradients between the spreading surfactant and the underlying gel layer, are identified to be the main driving force behind these phenomena, whereas gravitational forces were also found to play an important role. A mechanism that involves the "unzipping" of the gel in a manner perpendicular to the direction of the largest surface tension gradient is proposed. This mechanism highlights the important role of the width of the arms in the process; it is demonstrated that a cracking pattern is formed only within the experimental conditions that allow S/Δw to be greater than G', where S is the spreading coefficient, Δw is the change in the width of the crack, and G' is the storage modulus of the substrate.     

Self-diffusion of Co2+ ions in CoSO4 in agar gel medium: Concentration dependence of obstruction effect and activation energy

The obstruction effect and activation enerqy for the self-diffusion of Co²⁺ ions in CoSO₄ have been computed using the zone-diffusion technique in agar gel medium at five different concentrations of the electrolyte. Both parameters are found to decrease with an increase in electrolyte concentration. The decrease in obstruction effect expressed in terms of is attributed to the competitive hydration between ions and agar molecules in a diffusion system while the decrease in activation energy is explained by considering the changes in the physical properties of the solution with concentration at microscopic level.     

Effective self-diffusion coefficients of ions in sodium dodecyl sulfate micellar solutions

The effective self-diffusion coefficients of ions in premicellar and micellar solutions of sodium dodecyl sulfate are measured by the NMR self-diffusion method at 40°C. The obtained regularities are explained using a proposed model that takes into account the possible surface diffusion of counterions bound with micelles. This effect is shown to markedly influence the charge transfer in micellar solutions. Based on the results obtained, the self-diffusion coefficients of bound Na⁺ counterions are estimated and the causes and ranges of their variations are indicated.     

Determination of activation energy and the obstruction effect for tracer-diffusion of Co2+ ions in agar gel medium containing transition metal nitrates

Variation of activation energy for tracer-diffusion of Co²⁺ ions in Ni(NO₃)₂, Co(NO₃)₂ and Mn(NO₃)₂ is investigated using 1% agar gel over the temperature range of 25 to 45 °C. The activation energies are obtained by the least square fitting of the diffusion coefficient data obtained at various temperatures through the Arrhenius plots. Further, the extent of obstruction effect by gel macromolecules for Co²⁺ ions in Ni(NO₃)₂, Co(NO₃)₂ and Mn(NO₃)₂ systems at various concentrations of the electrolyte have been determined. The decrease in activation energy is explained by considering the changes in the physical properties of the solution with concentration at microscopic level, while the decrease in obstruction effect expressed in terms of a is accounted for on the basis of competitive hydration between ions and agar molecule.     

Diffusion of rose bengal in agar gel: Variation with the concentration of the diffusant and the gel

The diffusion of Rose Bengal¹³¹I in agar gel is studied in the concentration range of 10^–7 to 10^–5M. In addition, effects due to varying the concentration of the gel and temperature are reported.     

Ammonia-free Birch reductions with sodium stabilized in silica gel, Na-SG(I)

Ammonia-free Birch reduction conditions were developed based upon sodium stabilized in silica gel for a variety of substrates. In general, the yields were similar to those reported for lump sodium in liquid ammonia.     

Production of fission 131I

Summary A method of iodine separation from other radionuclides generated by ²³⁵U fission has been developed in order to explore the possibilities to obtain ¹³¹I as by-product of the ⁹⁹Mo routine production in the Ezeiza Atomic Centre. The experiments were designed to remove this element to gas phase, and the recoveries were investigated both with and without carrier addition. High volatilization percentages were achieved in the presence of iodine carrier. Some other alternatives to increase the iodine displacement to the gaseous phase, namely vacuum distillation, addition of hydrogen peroxide and use of a carrier gas, were also studied. The method developed, which employs a carrier gas stream, without carrier addition, allows the recovery of about 97% of the ¹³¹I, with high specific activity, in a simple and clean way.     

Suspension copolymerization of divinylbenzene in a gel medium

A procedure of suspension polymerization and copolymerization in a medium of thermally reversible gels was developed.