High temperature impedance measurement

An example of the experimental setup for the measuring of extracellular action and resting potentials is shown in Fig. 4. All electrochemical measurements can be conducted at constant temperature inside a Faraday cage mounted on a vibration-stabilized table in a laboratory (Fig. 4). Ag/AgCl electrodes were connected to a voltmeter/pFl meter [Cole Palmer Microcomputer pFl-vision Model 05669-20, Fig. 4(a)] with high input impedance or a programmable electrometer/amplifier [Keithley-2000/20, Keithley-6517, or Keithley-6514, Fig. 4(b)]. An IBM-compatible microcompu-... 

Frequency dependent complex impedance measurements made over many decades of frequency provide a sensitive and convenient means for monitoring the cure process in thermosets and thermoplastics [1-4]. They are of particular importance for quality control monitoring of cure in complex resin systems because the measurement of dielectric relaxation is one of only a few instrumental techniques available for studying molecular properties in both the liquid and solid states. Furthermore, It is one of the few experimental techniques available for studying the poljfmerization process of going from a monomeric liquid of varying viscosity to a crosslinked. Insoluble, high temperature solid. 

Effect of Sample Dilution. To determine the effect of sample dilution on impedance measurements, shrimp samples were stored at >2(y C or for 21 d. Frozen samples were used to mimic fr h shrimp while refrigerated samples were used to represent spoilage over time. Duplicate SO-g samples were removed from storage every 7 d and used for impedance analysis. Each sample was removed from the bags, boiled for 5 min, cooled to room temperature, then transferred to a tared blender jar and diluted either 1 1 or 1 10 with sterile deionized, demineralized water. Samples were homogenized for 2 min on high. Controls consisted of water alone. 

Figure 3.20. AC impedance measurement by TDI RBL 488 load bank and Solartron 1260 [21]. (Reproduced by permission of ECS—The Electrochemical Society, from Tang Y, Zhang J, Song C, Liu H, Zhang J, Wang H, Mackinnon S, Peckham T, Li J, McDermid S, Kozak P. Temperature dependent performance and in situ AC impedance of high-temperature PEM fuel cells using the Nafion-112 membrane.)...

The results also suggest that through AC impedance measurements, the performance drops caused by individual processes such as electrode kinetic resistance, membrane resistance, and mass transfer resistance can be correlated to either reduction or improvement in cell performance. If individual impedances are known, the contribution to the change in performance can be identified, which is very important in the design and optimization of high-temperature MEA catalyst layer components, structure down-selection, and MEA architecture. 

The curves showing the frequency dependence of loss functions [tan 5, G"(g)), or / (to)] permit the detection in the frequency domain, at temperatures just slightly above the glass transition temperature, of a prominent absorption or a process. The unavailability of experimental devices to measure mechanical viscoelastic functions at high frequencies impedes the detection of a fast process or P relaxation in the high frequency region. This latter process is usually detected in the glassy state at low frequencies. 

Example 13.2 Characteristic Frequency Consider an experimental system involving a Pt disk in 0.1 M NaCl solution at room temperature for which impedance measurements are desired to a maximum frequency of 10 kHz. Estimate the maximum radius for a disk electrode that xoill avoid the influence of high-frequency geometry-induced time-constant dispersion. 

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