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A.c. impedance method

Electrochemical tests This group includes the various electrochemical tests that have been proposed and used over the last fifty or so years. These tests include a number of techniques ranging from the measurement of potential-time curves, electrical resistance and capacitance to the more complex a.c. impedance methods. The various methods have been reviewed by Walter . As the complexity of the technique increases, i.e. in the above order, the data that are produced will provide more types of information for the metal-paint system. Thus, the impedance techniques can provide information on the water uptake, barrier action, damaged area and delamination of the coating as well as the corrosion rate and corroded area of the metal. However, it must be emphasised that the more comprehensive the technique the greater the difficulties that will arise in interpretation and in reproducibility. In fact, there is a school of thought that holds that d.c. methods are as reliable as a.c. methods. [Pg.1080]

Conventional electrochemical techniques including CV [1-7], current-scan po-larography [13-15,34,35] and a.c. impedance method [36,37] have so far been used for the study of ET at O/W interfaces. However, recent development in microtechnology brought to an introduction of SECM in this field [16-23]. Our group has also developed a few devices for characterizing ET reactions at O/W interfaces [38,39]. In this section, new methodologies recently introduced in this field are described. [Pg.175]

The a.c.-impedance method described in the previous chapter is often employed to characterize the electrical properties of solid proton conductors. The method gives a rapid answer to the question does the material under investigation conduct electricity and the method is not critical with respect to size, shape and quality of the sample used. [Pg.418]

If the a.c.-impedance method shows that the material is a conductor there still remain the following questions. [Pg.418]

W. I. Archer and R. D. Armstrong [1980] The Application of A. C. Impedance Methods to Solid Electrolytes, Electrochemistry, Chemical Society Specialist Periodical Reports 7, 157-202. [Pg.542]

The development during the last three decades of laboratory methods for investigation of the kinetics of electrode reaction[44,45,46] e.g. of relaxation techniques (potential step, current step, A.C. impedance methods, etc.), of cyclic voltammetry and, most recently of the use of electrodes of very small dimensions, has led to a marked increase in our level of understanding of these processes. The value of these techniques has been greatly enhanced by the development of computer based methods of data analysis. [Pg.276]

When the analysis, using a microelectrode to pass the current, was extended to striated muscle by Katz (1948), it became clear that muscle was anomalous in that the membrane capacity was substantially larger than in nerve fibres. In frog sartorius muscle fibres appeared to be about 5 yF/cm of fibre surface. In time it became clear that this was due to the extensive membranes of the transverse tubular system in muscle fibres. Several studies using A.C. impedance methods were undertaken to define the equivalent circuit of the morphologically complex membranes in a muscle fibre (Falk Fatt, 1964 Schneider, 1970 Valdiosera, Clausen Eisenberg, 1974). [Pg.50]

Inoue, T., Kamimae, J.-L, Ueda, M. et al. (1993) Ionic and electronic conductivities of LaCoOs- and LaMnOs-based perovskite-type oxides measured by the a. c. impedance method with electronblocking electrodes. /. Mater. Chem.,... [Pg.877]

Developments in electrochemical methods since 1976 for measurement of corrosion have been rapid. Research and development has produced several new techniques, e.g. a.c. impedance and electrochemical noise. These methods require corrosion expertise for both operation and interpretation. Industry generally prefers instrumentation that can be operated by process... [Pg.1129]

A renewal of interest in the other rate-controlling processes started in those groups who were developing the impedance method [49, 53] and the a.c. polarographic method [12, 25], probably because it was found that, in many cases, Randles equivalent circuit did not hold and also because the appropriate mathematics are more tractable in the frequency domain. Still, it is recommended that the a.c. studies are combined with the diagnostic results which can be obtained from steady-state techniques and/or cyclic voltammetry. [Pg.281]

In studying a system by a nonlinear impedance method, use is made of the system s nonlinear characteristics. A variant of the nonlinear impedance method called the amplitude demodulation method was first applied in the electrochemistry of semiconductors, in particular to diamond electrodes, in [83] (see the quoted paper for the theory of the method and the experimental set-up). A perturbing current signal of a high frequency oo, modulated in amplitude at a low frequency 2, is applied to electrochemical cell the demodulated low-frequency voltage signal is to be measured at the frequency 2. In accordance with the theory of the method [83], under the condition of formation of a depletion layer in a semiconductor electrode, the in-phase component of the cell response Re h is inversely proportional to d(C 2)/dE. Hence, for the acceptor concentration in the semiconductor we have [compare Eq. (1)] ... [Pg.232]

If both the light intensity and the electrode potential are modulated at different frequencies, information may, in principle, be obtained at the sum and difference frequencies. This method has been little used the complexities of the a.c. impedance analysis in the light have precluded all but... [Pg.226]

A more advantageous method is a.c.-impedance spectroscopy, which has become a standard method for the measurement of ionic conductivities in general. The basic principles have been described many times and the interested reader may refer to the excellent review by Gabrielli. A small applied potential difference allows measurements close to thermodynamic equilibrium. The accessibility of an extended frequency range (typically 1-10" s ) allows the separation of impedance contributions from the sample itself and from the electrode/electrolyte interface using equivalent circuits to assist the interpretation of the data obtained. Unfortunately interpretation is unambiguous only for simple circuits and the different... [Pg.410]

In the following, methods will be reviewed, where the conductivity is measured during an electrolysis (d.c.) experiment. Simultaneous use of a.c.-impedance measurements may be used to identify the contributions from the electrode reactions and grain boundaries. A.c. measurements in combination with a relaxation of the d.c. current may also be used to find out whether concentration gradients have been built up as a result of the passage of current. [Pg.420]

Progress in the understanding of superionic conduction is due to the use of various advanced techniques (X-ray (neutron) diffuse scattering, Raman spectroscopy and a.c.-impedance spectroscopy) and-in the particular case of protons - neutron scattering, nuclear magnetic resonance, infrared spectroscopy and microwave dielectric relaxation appear to be the most powerful methods. A number of books about solid electrolytes published since 1976 hardly mention proton conductors and relatively few review papers, limited in scope, have appeared on this subject. Proton transfer across biological membranes has received considerable attention but is not considered here (see references for more details). [Pg.609]

Large differences between the interfacial properties of ds and ssDNAs observed earlier by capacitance measurements [10, 37] suggested that a.c. impedance measurements could be used to detect DNA hybridization on electrodes [433, 434] (Sect. 12.8.). A three-component ODN system on a gold electrode (involving avidin-biotin interactions) was used to detect specific DNA sequences by means of faradaic impedance spectroscopy [435]. Impedance spectroscopy does not seem, however, to be the most convenient method for the DNA biosensor faster and simpler voltam-metric or chronopotentiometric methods will probably be more convenient. Gon-ductivity of the perfect DNA, contrasting with a loss of conductivity in duplexes with mismatched bases, may be of use in... [Pg.5702]

These expressions are particularly useful for the determination of the transfer coefficient ac by small amplitude perturbation methods such as a.c. impedance. [Pg.81]

Electrochemical methods appear to have distinct advantages in the study of cement hydration. Methods involving potential measurement (including pH, zeta potential, and selected ion potential), conductivity measurement, and a.c. impedance measurement provide useful information related to both ion concentration of pore solution and microstructural change in hydrating cement paste. The early hydration and setting behavior of OPC-CAC and OPC-Hydrated-CAC paste systems can be determined using these techniques. [Pg.370]

The aperture impedance principle of blood cell counting and sizing, also called the Coulter principle (5), exploits the high electrical resistivity of blood cell membranes. Red blood cells, white blood cells, and blood platelets can all be counted. In the aperture impedance method, blood cells are first diluted and suspended ia an electrolytic medium, then drawn through a narrow orifice (aperture) separating two electrodes (Fig. 1). In the simplest form of the method, a d-c current flows between the electrodes, which are held at different electrical potentials. The resistive cells reduce the current as the cells pass through the aperture, and the current drop is sensed as a change in the aperture resistance. [Pg.401]

The ionic conductivity of a solvent is of critical importance in its selection for an electrochemical application. There are a variety of DC and AC methods available for the measurement of ionic conductivity. In the case of ionic liquids, however, the vast majority of data in the literature have been collected by one of two AC techniques the impedance bridge method or the complex impedance method [40]. Both of these methods employ simple two-electrode cells to measure the impedance of the ionic liquid (Z). This impedance arises from resistive (R) and capacitive contributions (C), and can be described by Equation (3.6-1) ... [Pg.109]


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See also in sourсe #XX -- [ Pg.265 ]




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