An Ammonium Argentothiosulphate Bromide

A sparingly-soluble ammonium argentothiosulphate bromide salt (called B-salt) has been prepared by the addition of excess silver bromide to an ammonium thiosulphate solution over the concentration range 0·5 M to 2·5 M. Its nearest “simple” empirical formula is (NH₄)₄(AgS₂O₃)₃Br. Chemical and physical properties of the salt are described. B-salt is formed in the practical fixing bath and in the photographic emulsion. The fixation of a bromo-iodide emulsion yields a B-salt containing a small quantity of iodide.     

Application of Salting-Out Agent to Enhance the Hydrophobicity of Weakly Hydrophobic Bacterial Strains

Hydrophobicity is a vital parameter for initial cell adhesion that ultimately leads to biofouling of surfaces and loss of system performance and health issues. The efficiency of a number of biological systems could be improved by increasing the hydrophobicity of concerned bacteria. Here we used ammonium sulfate (salt) to enhance the bacterial hydrophobicity, as measured by a commonly used liquid–liquid partitioning based hydrophobicity assessment assay — the MATH test. We observed successive increases in bacterial hydrophobicity with incremental increase in salt concentration for Gram-negative bacteria. Upon addition of 2 M salt, three closely related E. coli strains were easily distinguishable from one another. Gram-positive bacteria exhibited different trends than Gram-negative strains, with no change in the hydrophobicity of S. salivarius HB cells and a sharp decline followed by an increase in hydrophobicity for D. radiodurans. Cell size measurements revealed that Gram-positive cells exhibited a change in cell size on hydrocarbon exposure, while the Gram-negative cultures remained mostly unaffected. Overall, salt addition was observed to enhance the hydrophobicity of different test strains, especially at the higher concentrations used here of 1.5 and 2 M. Salt addition in conjunction with the MATH test successfully differentiated and quantified otherwise weakly hydrophobic bacteria, thus enhancing the range of this laboratory assay. Our results demonstrate the effectiveness of salt addition in increasing the bacterial hydrophobicity, which could potentially be used in diverse areas, ranging from applied microbiology and engineering to oral care.     

Anisotropy of interfacial free energy in solid-fluid and solid-solid systems

Abstract

A selective discussion is presented of experimental and theoretical wolk on the dependence of interfacial free energy on crystallographic orientation in both solid-fluid and solid-solid systems. Anisotropy of interfacial energy is interpreted in terms of both equilibrium shape and dihedral angle measurements at interfacial junctions.

Résumé

Les auteurs présentent une discussion critique de travaux expérimentaux et théoriques sur l'influence qu'a l'orientation cristal1ine sur l'énergie libre d'interface, dans les systèmes solidefluide et solide-solide. L'anisotropie de l'énergie d'interface s'expliquerait en termes de la morphologie et des angles dièdres des interfaces.     

Controlling factors of microstructural evolution and corresponding deformation behaviour of Al–4Cu alloy in semisolid state

Abstract

The present work describes the microstructural evolution of an Al–4Cu alloy and its deformation response, as measured by the parallel plates technique. Specimens were heat treated to obtain a variety of Al₂Cu dispersions, and deformed by extrusion (1:16 ratio). Results indicated that microstructural coarsening took place initially by particle coalescence, but after 10 min soaking time Ostwald ripening became the controlling mechanism. It was also shown that texture accelerated particle growth rate by increasing the likelihood that chance encounters produced grain boundaries, and hence coalescence events. The mechanism of action of particle stimulated nucleation of recrystallisation was suggested, by observing that the particle growth kinetics of deformed specimens was much higher than that of non-deformed specimens with their larger initial particle size and slower initial growth rate. Finally, rheological experiments showed that deformation behaviour was mainly controlled by particle shape, and to a lesser extent by particle size.