Thesis (MScIng)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--University of Washington, 1994. / Vita. Includes bibliographical references (leaves [141]-148).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Supervisor: Mircea D. Driga. Vita. Includes bibliographical references. Available also from UMI company.

Thesis (M.S.)--University of Michigan, 1977.

Thesis (M.S. in Physics) Naval Postgraduate School, December 1995. / "December 1995." Thesis advisor(s): Xavier K. Maruyama. Includes bibliographical references. Also available online.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 142-146).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 186).

This study was initiated in an attempt to investigate dithiocarbamic acid accelerated sulfur vulcanisation. This was, however, found impossible due to the innate instability of dithiocarbamic acids. The focus of the study was then shifted toward thiuram disulfide accelerated sulfur vulcanisation, with emphasis being placed on a rate comparison. Three groups of accelerators were investigated, namely the aromatic, linear aliphatic and cyclic aliphatic thiuram disulfide adducts. The analysis methods that were employed were conventional rubber (cis-1,4-polyisoprene) techniques coupled to model (squalene) compound investigations. The data that was collected consisted of rheometrical torque vs. time data in the rubber system while the data obtained in the model compound study consisted of sulfur and accelerator concentration data as determined by means of high performance liquid chromatography (HPLC). The aromatic accelerators were synthesised in our labs by means of an addition reaction between the aromatic amine and CS2 in basic medium and subsequent oxidation with K3Fe(CN)6, all in a 1:1 molar ratio. The reaction yield was low due to the instability of the dithiocarbamate intermediates and a sluggish oxidation reaction. In the rate constant determination a first order mathematical approach was used for the rubber system as crosslinking is considered to roughly obey first order kinetics. The model compound data was also found to more accurately fit the first order rate law, with an initial slopes method also being applied to the system to determine secondary rate constants and relative rates for the system. The determination of vulcanisation rate constants in the cis-1,4-polyisoprene system was a success, while the rate data determined by means of the squalene model was more related to the rate of accelerator and sulfur consumption as opposed to the rate of crosslinking as is the case with the rubber rate data. The sulfur first order rate data mirrored the rate data derived from the rubber system more closely than the corresponding accelerator rate data, the relative rate data determined by means of initial slopes method, proved that the homolytic cleavage of thiuram disulfides and the subsequent formation of accelerator polysulfides were not limiting steps. This is seen in the similar relative rate data derived from both the raw sulfur and accelerator data in systems that exhibit vastly different vulcanisation rates. Squalene was deemed a suitable model for the cis-1,4-polyisoprene system, although one should consider the extent of charring and solution effects in the individual systems to account for possible incongruities that may be observed between the rubber and simulated system. The lack of agreement between the rubber and model compound rate constant data lies in the fact that the rate of crosslinking is not simplistically related to the rate at which accelerator and sulfur is consumed, this being especially true for the rate at which the accelerator is consumed. Thus the discussion over the acceleratory rates in the various accelerator systems was limited to observations made in the rubber system, with the model compound data was used exclusively to elucidate mechanistic processes. It was discovered that the groups of accelerators examined, namely linear, cyclic and aromatic thiuram disulfide adducts, produced vastly varied rate data. The aromatic thiuram disulfide adducts had only a slight acceleratory effect on the rate of vulcanisation as compared to the unaccelerated sulfur system. The morpholine adduct had a moderately larger rate of acceleration followed by tetramethyl and tetrethylthiuram disulfide, with N’N-dicyclopentamethylenethiuram disulfide having the fastest rate of acceleration.

An ion accelerator has been constructed which, is capable of accelerating very intense monoenergetic beams of protons or deuterons up to 50 KEV energy. Total ion currents of 500 µ amps containing 30 to 40% atomic ions have been obtained. The intensity and high definition of the beam makes it possible to collimate after magnetic analysis, 50 µ amps of protons or deuterons at 30 KEV energy into a 1/16 inch diameter spot on a target. This deuteron beam incident on a heavy ice target is capable of producing a neutron flux of 3 x 10⁸ neutrons/sec from the "D on D" reaction at 50 KEV bombarding energy or the equivalent of the neutrons from 20 curies of radium used in a Ra-Be source. The intrinsic interest of the D-D reactions to nuclear physics had prompted the construction of a scattering chamber to be used in conjunction with the accelerator. An experimental arrangement has been designed and constructed for the measurement of the energy dependent characteristics of the companion reactions, D(d,n)He³ and D(d,p)H³, which has a potential accuracy considerably greater than previously reported. As well, the extension of studies to much lower energies has been made possible by the large ion currents available. / Science, Faculty of / Physics and Astronomy, Department of / Graduate