Diffusion and other kinetic studies of the system cobalt-sulphur
Author(s)
John Richard, Stubbles
Type
Thesis
Abstract
The radioactive isotopes Co60 and S35 have been used to measure the self diffusion coefficients of both the cation and anion respectively in the cubic sulphide Co9S8 between 6OO and 300C. The non-stoichiometry of the phase was controlled by the H2S/H2 atmospheres and temperatures of the diffusion anneals. The cation self-diffusion coefficients have been determined by both a modified sectioning technique and a graphical decrease in surface activity method. Most reliability is placed on results obtained method. delf-diffusion of the anion has by sectioning and counting sulpnide discs by the anion has been determined after exposing them for periods of up to four weeks to circulating radio active atmospheres of H2S/H2 mixtures of constant specific activity. The non-stoichiometry of Co9S8 has been the weight increase of cobalt foils calculated from equilibrated at constant temperatures under constant sulphur pressures. Whilst the anion has negligible mobility in Co9S8, the cation diffuses coefficient decreases with extremely rapidly. It’s the cobalt content of the sulphide, although the relationship is not linear and cannot be expressed by any simple mathematical function. According to the non-stoichiometry data, the general formula of the ions, which constitute phase is Co9+6s8 the excess metal cause only slight expansion of the lattice. The theories of both Wagner and Anderson concerning disorder in binary ionic crystals are confirmed qualitatively. A mechanism of cation self diffusion is proposed, based on the high degree of intrinsic disorder and the unusual structure of the sulphide. Rosenqvist’s equilibrium data for the system Co-S have been verified by using a radiochemical technique in which the specific activity of the radioactive K2S/H2 equilibrium gas mixture (labelled with is proportional to the partial pressure of sulphur Mo--Mo2S3 and Mo2S3-MoS2 equilibria similarly. Debye-Scherrer powder in the system.
Version
Open Access
Date Issued
1957
Date Awarded
01/07/1957
Advisor
Professor P.D., Richardson
Publisher Department
Department of Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)