Using Moving Electrode Impedance Spectroscopy to Monitor Particle Sedimentation

Nikolaus Doppelhammer,Bernhard Jakoby,Christine E. A. Kirschhock,Nick Pellens,Erwin K. Reichel

doi:10.1109/jsen.2020.3004510

Nikolaus Doppelhammer, Bernhard Jakoby + Show 3 more

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https://doi.org/10.1109/jsen.2020.3004510

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Abstract

We have devised a method that employs moving electrode electrochemical impedance spectroscopy to monitor the sedimentation of particles in conductive suspensions. In contrast to standard electrochemical cells with a fixed geometry, our cell has a flexible design with a movable counter electrode that allows precise adjustment of the electrode distance. Measuring the electrical impedance at various electrode spacings and utilizing the linear dependence of this function on the electrode displacement enables probing of a small section of the sample. This has considerable advantages when heterogenous liquids (e.g., suspensions) are to be analyzed. We applied our moving electrode approach to various test cases and obtained the following results: (i) We demonstrated by experiment that the bulk conductivity can be measured correctly even if particle sediments cover the electrode surface. (ii) We studied monodisperse suspensions of various compositions and investigated the effect of particle concentrations and size on conductivity. (iii) We monitored the particle sedimentation process and, by combining experimental and theoretical results, identified a correlation between the growing mass of the sedimentation layer and the impedance measured. The intended application of our approach is to monitor crystallization processes in ionic liquids for use in zeolite synthesis.

Highlights

T HE conductivity of a liquid sample is usually measured by means of a cell with immovable electrodes
In this work we present a method – hereafter referred to as moving electrode electrochemical impedance spectroscopy (MEEIS) – which overcomes this problem by using a flexible
The value of the effective sample cross-section area Ae = 0.799 cm2 in Eq 2 was determined by calibration with a commercially available conductivity standard (1 M KCl, Thermo Fisher Scientific, Chlemsford, USA)

Summary

Introduction

T HE conductivity of a liquid sample is usually measured by means of a cell with immovable electrodes. The simplest setup are two electrodes immersed in the test liquid. The specific conductivity can be determined, for instance, by using electrochemical impedance spectroscopy (EIS) [1]. Manuscript received January 28, 2020; revised June 6, 2020; accepted June 14, 2020. Date of publication June 23, 2020; date of current version March 17, 2021. This article was presented in part at the IEEE Sensors 2019 Conference, Montreal. The associate editor coordinating the review of this article and approving it for publication was Dr Rolland Vida.

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