Alternating Current Technique

From the experimental standpoint, the use of a.c. techniques offers many advantages. Sensitivity is much higher than in d.c. measurements, since phase-sensitive detection can be used and very small probe signals can be employed ( 5mV). The technique is therefore a truly equilibrium one, unlike cyclic voltammetry. An alternative approach to the commonly used sinusoidal signal superimposed on the selected d.c. potential is to use a potential step and to employ Laplace transform methods. Instrumentally, this is rather more demanding and the advantages are not clear [51]. Fourier transform methods have also been considered and their use will have advantages in terms of the time-scale for an experiment, especially at very low frequencies. 

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Electrochemical impedance data give information on the kinetics and mechanism of the corroding system. Alternating current techniques have some advantages over DC techniques ... 

The special case of square-wave voltammetry (SWV) is worth noting separately from other alternating current techniques because it is both more rapid and more sensitive than DPP/DPV. In SWV, the applied potential waveform is a staircase with constant step height on which is superimposed an asymmetrical forward and reverse voltage pulse of constant amplitude and very short duration, typically less than 10 ms. Thus, the entire polarogram may be run in about approximately 1 s, with the enhanced sensitivity of the method owing to sampling of the current at the end of both the forward and reverse directions of the pulse. 

M. P. Dare-Edwards, A. Hamnett, and P. R. Trevellick, "Alternating-Current Techniques in Semiconductor Electrochemistry," Journal of the Chemical Society, Faraday Transactions, 79 (1983) 2111-2124. 

The alternating current technique is essentially a variant of the permeation method [48]. The current measured at the output side varies sinusoidally in response to the alternating cathodic current. The diffusivity can be determined from both the phase difference of the alternating current between the two sides and the amplitude of the alternating current at the output side. 

Electrochemical corrosion techniques are essential in predicting the service hfe ofmetal-hc components used in chemical and construction industries. They measure the corrosion rates, the oxidizing power of the environment, and evaluate the effectiveness of corrosion protection strategies. The following direct current dc electrochemical methods are discussed in this chapter linear polarization technique, Tafel extrapolation, and open circuit potential (OCP) vs. time measurements. Electrochemical impedance spectroscopy (EIS) is introduced as an alternating current technique ac. This technique uses alternating current to measure frequency-dependent processes in corrosion and estimates the change of polarization resistance. 

Electrochemical impedance spectroscopy An alternating current technique that measures the impedance of an electrochemical system. The resulting spectra can be used to estimate the various components of an equivalent circuit that represent an electrochemical cell. 

ADifferential/integral. Because of the widespread use of alternating current techniques for measuring impedances (admittance and impedance being the generic notions in electrodynamics encompassing these constitutive properties), it is not... 

Smith, D.E. (1964) Theory of the faradaic impedance. Relationship between impedances for various small amplitude. Alternating current techniques. AnaL Chem., 36 (6), 962-970. 

The ratio 1/A) is also called the cell constant or shape factor and has units of cm or m. A variant of the electrochemical cell shown in Fig. 5.7 is commonly used to evaluate the conductivity of a solution between two electrodes by using an alternating current technique. 

This technique is called the four-point dc technique. An alternative that may be nsed to overcome polarization problems is the use of alternating current techniques using a wide... 

Ohmic overpotential. The ohmic drop caused by the electrolytic resistance between two electrodes can be measured by using an alternating current technique (see Sec. D.1.2, Electrolyte Conductance) or minimized by measuring the potential as close as possible to the working electrode. In any case the ohmic overpotential is a simple function described by the product of the effective solution resistance and the cell current, or iR. 

Eckhard, K., Schuhmann, W. Alternating current techniques in scanning electrochemical microscopy (AC-SECM). Analyst 2008, 133, 1486-1497. 

Experimental data for random dispersions of spheres of unequal sizes come from DeLaRue who, using the same techniques discussed in the previous section, experimented with multisized dispersions of glass spheres. The data used in this comparison also include data previously discussed and other data for which the size distribution was not specified. Clark experimented with foams and thus obtained data at very high void fractions. He used alternating current at 1 kHz in the experiments. Slawinski used alternating current techniques to measure the conductivity of dispersions of castor oil in a mixture of gum arabic and O.OS N KCl. Because his data deviate from the other data and do not follow Maxwell s equation at low void fractions, they must be suspect. Neale and Nader investigated conduction through packed spheres... 

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