Conductivity

Conduction or electrical conduction is the mechanism by which charge flows or the movement of electrically charged particles through a transmission substance (electrical conductor). This movement of charge constitutes an electric current and the physical parameters governing this transport depend upon the substance.

Therefore, conductivity (electrical conductivity or specific conductivity) is a measure of the ability of a substance to conduct an electric current. In solutions, current is carried by free moving ions (positive and negative). A conductive solution is known as an 'electrolyte' and includes solutions of ionic salts or of compounds that ionize in solution (e.g. acids and bases).

Conductivity is the reciprocal (inverse) of electrical resistivity and has the SI units of siemens per metre (S•m^-1). Electrical conductivity is commonly represented by the Greek letter σ.

The conductivity of a solution of water is highly dependent on its concentration of dissolved salts and sometimes other substances which tend to ionize in the solution. Therefore, electrical conductivity of water samples can be used as an indicator of how salt-free or impurity-free the sample is. The conductivity decreases as the purity of the water increases.

Electrical conductivity is also strongly dependent on temperature. For example, electrical conductivity decreases in metals with increasing temperature.

The conductivity, σ is defined as the ratio of the current density J to the electric field strength E:

J = σ E

LabChart
LabChart software (for Windows and Macintosh) combines the familiar simplicity of a traditional strip chart recorder with the powerful analysis features of a digital acquisition system. LabChart software and a PowerLab data acquisition unit provide data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Acquisition and analysis capabilities can be further increased with LabChart Extensions and LabChart Modules. LabChart Modules are available as part of LabChart Pro and LabChart Extensions are free for download from the website for existing LabChart users.

GLP and 21 CFR Part 11
For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.

Signal Conditioners

ML307 Conductivity Pod
This Conductivity Pod is used with conductivity cells for monitoring solution conductance. The Pod measures the alternating current (being positively and negatively charged) across a suitable conductivity cell by applying an AC potential across the pair of platinum plate electrodes that comprise the cell. The output is proportional to the conductivity of the solution. The signal is scaled to read in µS or mS, depending on the range, 5 µS to 20 mS, selected.

The following electrodes are suitable for use with the Conductivity Pod via a BNC connector:

• MLT908 Flow-Thru Conductivity Electrode
• MLT916 Flow-Thru Conductivity Electrode
• MLT915 Dip-In Conductivity Electrode

Electrodes

• MLT908 Flow-Thru Conductivity Electrode - is for monitoring the conductance of continuous streams of water, urine, physiological fluids etc.
• MLT916 Flow-Thru Conductivity Electrode - is for monitoring the conductance of continuous streams of water, urine, physiological fluids etc.
• MLT915 Dip-In Conductivity Electrode - is for measuring the conductivity of samples such as water, urine and physiological fluids

Inhibition of lithium dendrites by fumed silica-based composite electrolytes

X-W Zhang, W Li, S A Khan and R S Fedkiw, Journal of the Electrochemical Society, A1257-A1263, 2004

Polyethylene glycol dimethyl ether (PEGdm, Mw 250, Aldrich) was dried over 4 Å molecular sieves for at least 1 week. Lithium bis(trifluoromethylsulfonyl) imide [LiN(CF3SO2)2 , LiTFSI, 3M] was dried in a vacuum oven at 100°C for 24 h before use. Two types of Degussa fumed silicas with differing surface groups were used in this study: A200 (hydrophilic) fumed silica contains native surface hydroxyl groups, and R805 (hydrophobic) fumed silica contains octyl surface groups at ~48% coverage and hydroxyl at ~52% coverage. Both fumed silicas were dried under vacuum at 120°C for 1 week. The water content of solvents, fumed silicas, and salt was below 50 ppm, as determined by Karl-Fisher titration. The liquid electrolyte was made by dissolving LiTFSI into PEGdm in a fixed mole ratio 1:20 (Li:O) to obtain the highest conductivity.15 The composite electrolytes were prepared by dispersing known quantities of fumed silica into the liquid electrolyte using a high-shear mixer (Tissue Tearor, model 398, BioSpec Products). The mixtures were subsequently centrifuged (IEC HN-SII centrifuge, Damon/IEC Division) to remove gas bubbles but without disrupting the fumed silica network. All electrolyte preparations were carried out in an argon-filled glove box. Two-electrode lithium cells were assembled in a glove box using the composite or liquid electrolyte. Two lithium electrodes were placed in a nylon holder attached to a glass slide, and electrolyte was placed between the electrodes. The area of the lithium electrode facing the electrolyte was 5.08 mm2 (10 X 0.508 mm). The distance between the lithium electrodes was 1.0 ± 0.2 mm. Two copper foil current collectors were used to connect the electrodes to a galvanostat. The glass cover provided a transparent window allowing microscopic observation of dendrite formation. The cells were tightly clamped and transferred out of the glove box. GOOP adhesive and sealant (Eclectic Products, Inc.) was used to seal the cells. Three-electrode cells were also assembled for impedance measurements. In these cells, a small lithium film reference electrode was placed adjacent to the two electrodes but isolated electronically from them. Electrochemical measurement and dendrite observation.— Constant-current charging of the cells was conducted at different current densities using an EG&G model 173 potentiostat. The voltage between the two electrodes was recorded using a PowerLab/4s (ADInstruments) controlled by Chart software (ADInstruments). Simultaneously, the evolution of lithium dendrites was monitored by a NTSC camera fitted on a Fisher Micromaster microscope. Pictures were digitized with a PIXCI SV5 FrameGrabber (EPIX, Inc.) and recorded on a PC. Charge-discharge cycling was also carried out with the EG&G model 173 potentiostat. The same PowerLab/4s was used to control the charge-discharge process and monitor cell voltage. Visual images of dendrite formation during cycling were recorded.

High conductivity molten salts based on the imide ion.

D.R. McFarlane, J. Sun, J. Golding, P. Meakin, and M. Forsyth, Electrochimica Acta, 1271-1278, 2000

Electrochemical investigation of the molten salts was carried out by cyclic voltammetry (scan rate 100 mV/s) using a MacLab, ADInstruments Potentiostat and EChem software.