Donald L. Gerrard

Quantitative determination of thiourea in aqueous solution in the presence of sulphur dioxide by Raman spectroscopy

A method has been developed for the quantitative determination of thiourea in aqueous solutions acidified with sulphuric acid in the presence of sulphur dioxide. The method uses laser Raman spectroscopy and is valid in the presence of high concentrations of sulphur dioxide and inorganic salts. This is particularly important with respect to the use of such solutions for the leaching of gold from ores and concentrates. The method is simple, rapid and accurate to within ±1.2% and has been applied to the study of solutions used in leaching experiments.

Some insights into the microstructure of polypyrrole

Abstract Estimation of the molecular weight between crosslinks and determination of the average conjugation length in polypyrrole are reported. By applying the Flory equation to dimethylsulphoxide-swollen dedoped polymer, it was found that the molecular weight between crosslinks is larger than previously thought and lies in the range of 25–65 pyrrole units. U.v. and resonance Raman spectroscopy indicate that the average conjugation length is short. The upper limit is about 6 pyrrole units.

Degradation of oriented poly(vinyl chloride) films in the presence of metal chlorides

Abstract Films of poly(vinyl chloride) containing added stannous chloride and stretched at 90°C to elongations up to 600% discolour, in shades from purple to grey, when heated at 110°C. The electronic and resonance Raman spectra of such films show characteristic features, which are a function of sample preparation conditions, particularly the time of annealing at 110°C. Resonance Raman spectra show the presence of conjugated polyene sequences, as long as 30 units for the most extensively annealed samples. The electronic spectra are not explicable on this basis, and are probably indicative of a polyene-metal salt complex of the type proposed by Owen and Msayib in the case of poly(vinyl chloride) thermally decomposed in the presence of zinc chloride. Substitution of zinc chloride for stannous chloride with the present degradation conditions gives very similar electronic spectra, though substantially different from those reported by Owen and Msayib. This result is tentatively explained in terms of the very different degradation conditions.