Equipment Galvanostat

In such conditions, it is recommended that the T-R be equipped with an electrical control circuit, which primarily keeps the potential constant, and, in exceptional circumstances, also the protection current. These pieces of equipment are potentiostats (for controlling potential) and galvanostats (for controlling current) [8]. 

Figure 19-1 shows the experimental setup with the position of the steel test pieces and the anodes. The anodes were oxide-coated titanium wires and polymer cable anodes (see Sections 7.2.3 and 7.2.4). The mixed-metal experimental details are given in Table 19-1. The experiments were carried out galvanostatically with reference electrodes equipped to measure the potential once a day. Thus, contamination of the concrete by the electrolytes of the reference electrodes was excluded. The potentials of the protected steel test pieces are shown in Table 19-1. The potentials of the anodes were between U(2u-cuso4 = -1-15 and -1.35 V. 

Reference electrodes at the test points may only be needed part of the time, depending on the mode of operation of the protective systems (e.g., for monitoring or for permanent control of potential-controlled protection current equipment). Potentiostatic control is always preferred to galvanostatic systems where operational parameters are changing. 

For a practical realization of the foregoing transient modes, special programming units or signal synthesizers are used which are integrated in the potentiostatic or galvanostatic equipment. 

Electrochemical Equipment. Electrochemical experiments were performed using either a PAR Model 175 universal programmer and a PAR Model 363 potentiostat/galvanostat, or a Pine Instruments RDE-4 bipotentiostat, coupled with a Kipp and Zonen BD 91 X-y-y recorder. The current-time response for the chronoamperometry experiments was recorded with a Nicolet 4094 digital oscilloscope. All potentials were measured vs. a Ag/10"2 M Ag+ reference electrode. 

EG G PAR (USA), Model 273 A, Potentiostat/Galvanostat volt-ammetric analyzer controlled by PC equipped with a data acquisition and treatment software to record the signal generated in the electrochemical cell for DPY measurements. A 25 mL glass cell at 25°C with the carbon paste biosensor, Ag/AgCl (3.0 mol L-1 KC1) reference electrode, and a platinum wire as auxiliary electrode to perform the volt-ammetric measurements. 

The instrumentation for coulometric titrations consists of a galvanostat (a constant-current source), a cell equipped with an endpoint detector, and a timer. 

Apparatus Cyclic voltammetry and amperometric current-time curves were obtained with a Pine Instrument Inc., Model RDE4 bipotentiostat and Kipp Zonen BD 91 XYY recorder equipped with a time base module. All measurements were performed in a conventional single-compartment cell with a saturated calomel electrode as the reference electrode and a Pt mesh as the auxiliary electrode at room temperature. Chronoamperometry was made with EG G Princeton Applied Research potentiostat/galvanostat Model 273 equipped with Model 270 Electrochemical Analysis Software. 

In the case of well-known electrochemical reactions, as well as for electrolyses where larger scales are involved, two-electrode cells (connected to a galvanostat) can be used with continuous feed of the reactant to the working electrode. This type of electrolysis is suitable for industrial purposes where specific devices and cells are utilized. Since electrodes of large areas are necessary, the distance between the anode and the cathode is small and determines the cell geometry (e.g. capillary-gap cell or filter-press cell). The use of cells equipped of porous electrodes (materials like graphite or carbon moss, platinum, nickel) have also been developed to perform electrocatalytic reactions at very large surfaces. Some typical cells used in the laboratory and in industry are presented at the end of this review. 

The second group of electrochemical methods is aimed at measuring any special characteristics of the films, which cannot be directly obtained from standard electrochemical measurements in the potential-current-time (E-i-t) domain. In this case, in addition to a potentiostat/galvanostat, some specialized equipment and suitable electrochemical cells are required. This group of techniques includes ... 

One simplified treatment is for working under galvanostatic conditions. Thus, both the diffusion current density components can be equal to that imposed by the equipment, j ... 

For the measurement of the photopotential and photopotential decay the usual potentio-stat/galvanostat could not be used and special equipment was developed. An example of a photopotential transient measured on n-GaAs is shown in Figure 9.13. 

The equipment is simple (a two-compartment cell with adequate electrodes and a source of current - potentiostat or galvanostat). 

On three-electrode cells, i.e. cells equipped with working electrode, counterelectrode, and reference electrode (WE, CE, and RE) under potentiostatic or galvanostatic control. In this case, the small ac signal is superimposed on a dc polarization. The measurement requires au electrochemical interface (potentiostat or galvanostat) coupled to an FRA (see Section 3.2). 

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