Browsing by Subject "membrana jonoselektywna"

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Access status: Open Access ,
Metoda elementów skończonych w elektrochemii
(Data obrony: 2010-01-22) Szyszkiewicz-Warzecha, Krzysztof
Wydział Inżynierii Materiałowej i Ceramiki
Potentiometric ion sensors function on ion-selective membranes. Layer interacts with the target analyte to produce electric potential. By measuring this response we can determine the concentrations (activities) of involved species. Thesis pertains to modelling of this potential. In the time-dependent NPP membrane model we use: electric field, components concentrations. The aim is to obtain dependency of the membrane potential on: activities of components in touch with membrane, physic-chemical parameters of membrane (e.g. diffusion coefficients, charge numbers, heterogeneous rate constants). The finite elements method was applied to solve the nonlinear NPP system with time. Problem was reformulated into the so called variational form. Next a family of basis functions was selected to expand approximate solution. The NPP model was expanded in to include the Darken drift velocity concept. According to this idea an internally generated convection may appear in system as the result of the total concentration constancy. Numerical modelling proved that the impact of Darken's drift is negligible in the limit of dilute solutions. However, in the case of more concentrated solutions this impact may be significant, so not including this drift may lead to errors. Thesis also dealt with a problem set forth in the paper by Perram, Stiles to determine steady-state diffusion potential in membrane. Difficulty is posed by the fact that in this problem the values of the electric field on boundary are not given and must be calculated (concentrations are given on boundary). The numerical software in this case was implemented in Mathematica.