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By Zbigniew Moroń and Tomasz Grysiński


Abstract − The four-point probe method, elaborated by van der Pauw, can be applied also in absolute measurements of electrical conductivity of electrolyte solutions. Conductance cells designed and used according to the method have their cell constant dependent on a single geometrical dimension only – the height. One of such designs, with electrodes located in chambers separated from the measuring space of the cell by narrow gaps, has especially advantageous properties as a calculable cell. This was presented in the previous works of the main author of this paper. The analysis performed there indicates that the consistency between theoretical and experimental results is limited by non-ideal properties of applied instrumentation rather than by the principle of the method. This paper presents later experimental examinations of the cell, carried out in the measuring arrangement improved on the basis of the conclusions presented in the former works. Absolute determinations of electrolytic conductivity of 0,01 and 0,1 kmol/m 3 NaCl solutions were performed. The results obtained confirm the hypothesis that the cell constant of such a cell can be determined from its height with uncertainty of the order of a few hundredths percent. circumference (fig. 1), can be calculated from a simple formula: K = ln2 / (π h) (1) where h is the height of the cell and κ is the electrical conductivity of the liquid filling the cell [2][4]. The shape of the cross-section of the cell may be arbitrary but the height must be uniform in the whole cell. When the electrodes are located asymmetrically, the cell constant can be calculated from the full van der Pauw equation: exp ( AB, CD BC, DA = −π hR κ) + exp ( −πh

Year: 2009
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