Direct current measured results

Jones (1971,1972), based on kinetic considerations, postulated the adoption of a criterion for a permissible corrosion rate on the basis of a polarization characteristic of a given corrosion system determined beforehand. In order to determine the corrosion rate at polarisation potential CP> knowledge of the course of the partial curve of the anodic reaction is necessary. The first steps in the analysis of partial currents of corrosion systems were made by Stern and Geary (1957), who described the method of determination of the Tafel coefficient of the anodic reaction on the basis of direct current measurement results of the cathodic polarization curve. Extrapolation of the linear section of this curve to a corrosion potential Ej-orr allows reproduction of a fragment of the anodic polarization partial curve at chosen potential values, as a difference between the polarization current and the partial cathodic current. 

Conductance of a solution is a measure of its ionic composition. When potentials are applied to a pair of electrodes, electrical charge can be carried through solutions by the ions and redox processes at the electrode surfaces. Direct currents will result in concentration polarization at the electrodes and may result in a significant change in the composition of the solution if allowed to exist for a significant amount of time. Conductance measurements are therefore made using alternating currents to avoid the polarization effects and reduce the effect of redox processes if they are reversible. 

The conductance (s) obtained from the resistance was plotted against temperature in Fig. 14. The conductance obtained from the long DNA film was 10 Scm which is consistent with the result obtained by direct current measurements in Fig. 12a, and was independent of temperatures in the range 20 to 60 °C. On the contrary, the conductance of the short DNA film... 

In the 1960s to 1970s, numerous direct current measurements in the Black Sea were performed at 175 mooring stations, of which 86 were 4 to 29 days long. Their results were generalized in [7] in the form of a schematic that... 

Electrochemical and Electrical Methods. Electrochemical and electrical methods for studying film properties and corrosion phenomena have been extensively reviewed (29-31). Comparisons of corrosion test results with direct current measurements of conductivity suggest that visible corrosion is associated with film resistance less than about 1 Mohm/cm, but this condition may well correspond with the occurrence of virtual pores in the film allowing development of local conductive pathways. In studies of the equivalent alternating current resistance as a function of frequency, Kendig and Leidheiser (44) found that the development of a region of slope -1 on a log permittivity versus log frequency plot... 

In order to measure cross sections, a beam of electrons of known energy is directed through a gas sample of known pressure and the resulting ion and electron currents measured.63 If mass selective ion detection is used, then partial ionization cross sections oz may be determined. These cross sections correspond to the production of z electrons and an ion or ions having total charge +ze. Some instruments allow the counting cross section oc, also known as the ion production cross section, to be determined ... 

The basic instrumentation for conductimetric measurements is a Wheatstone bridge arrangement (Figure 4.17). An alternating rather than direct current is used in order to prevent polarization of the solution (i.e. anions moving to the anode and cations moving to the cathode) and any electrolysis that might result from this polarization. 

Kilbride et al. (2002 Andriotis et al., 2003) measured the alternating current (ac) and direct current (dc) conductivities of polymer-SWCNT composite thin films such as PMPV and polyvinylalcohol (PVA), the result showed that the ac conductivity... 

Sample Temperature Rise Owing to Irradiation. A temperature rise of 2.9°C. during irradiation was found at the center of 0.033-inch thick water-cooled polystyrene samples for a beam current of 10 fxa. This temperature was measured several times, using thermocouples compression-molded into the center of the samples. The thermocouple leads entered the sample from the direction shown in Figure 1. Several different thermocouple junction sizes were used, with the same measured results. 

Direct current (DC) amperometry is used for the analysis of catecholamines, phenols, and anilines, which are easy to oxidize. A single potential is applied, and the current is measured. The current resulting from the oxidation or reduction of analyte molecules is dependent on many factors, including the concentration of the analyte, temperature, the surface area of the working electrode, and the linear velocity of the flowing stream over the surface of the working electrode. 

The electron pulses (Raman signal) from the PM tube may be processed by the direct-current (dc) amplification or a photon-counting method. In the former, the electron pulses from the PM tube are averaged over time, and the resulting dc current is amplified directly and measured by a picoammeter or electrometer. However, this method is no longer used because the photoncounting method gives much better sensitivity. 

Polarization experiments on a corrosion system are carried out by using a potentiostat. The experimental arrangement of the cell consists of a working electrode, reference electrode and a counter-electrode. The counter-electrode is used to apply a potential on the working electrode both in the anodic and the cathodic direction, and measure the resulting currents. The electrochemical cell is depicted in Figure 1.26. 

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