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Time effects in evolution of structure and rheology of highly concentrated emulsions

Thesis (DTech (Chemical Engineering))--Cape Peninsula University of Technology, 2005. / The subject of this study is highly concentrated emulsion explosive (HCEE). These emulsions
are dispersions of an aqueous phase (up to 90 v-%) in an oil phase. The dispersed droplets
consist of an aqueous solution of nitrate salts, which is supersaturated at room temperature,
comprising less than 20% of water by mass. Compounds of this kind are thermodynamically
unstable and their instability is related to the coarsening of emulsion (coalescence) and phase
transition (crystallization) of dispersed phase. However it is demonstrated that the dominating
mechanism is slow crystallization inside the super-cooled droplets. The main goal of this
thesis is a phenomenological study of the dependence of structural parameters, such as droplet
size and volume fraction, as well as the ageing processes, on the rheological properties of
these emulsions.
The results of the measurements include the flow and viscoelastic properties of the materials.
The rheological parameters are correlated with the kinetics of structural changes during
ageing, as a function of emulsion formulation. The emulsions under study are non-Newtonian liquids. Experiments in shear rate sweep mode
demonstrate that the upward and downward branches of the flow curves coincide above some
specific shear rate value. The upward experiments show the existence of a low shear
Newtonian asymptote, while the effect of yielding is observed in the downward curve. Wall
slip is investigated and shown to be negligible.
Date January 2005
CreatorsKharatiyan, Ellina
ContributorsMasalova, I, Slatter, PT, Cape Peninsula University of Technology. Faculty of Engineering. Dept. of Chemical Engineering.
PublisherCape Peninsula University of Technology
Source SetsSouth African National ETD Portal
Detected LanguageEnglish

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