An investigation of the diffusive and electrical properties of porous glass filters

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The transport of ions in a concentration gradient was modeled as an analogy to (1) a classic heat conduction problem and (2) an amorphous semiconductor with an applied electric field. And analytical expression was found for the diffusivity. The Einstein relation was used to calculate the mobilities. The experiments were done on two samples of different permeabilities in a newly developed conductivity cell. The current on the lower concentration side of the cell was measured as a function of time. Using the derived expression for diffusivity and the Einstein relation the mobilities and diffusivities were calculated for zero applied electric field on two samples of different permeabilities. Two different field strengths were applied across one sample and the mobility was determined from the difference in peak arrival times. The results were compared to Copper Sulfate in water. We found good agreement between our experimental values and our theoretical predictions. The behavior of the ions in the filters was shown to be diffusive in nature as electronic transport in amorphous semiconductors at high temperatures.

Diffusion, Porous materials--Electric properties