Electrochemical noise technologies

The corrosion rate is probably the nearest the engineer will get with currently available technology to measuring the rate of deterioration. There are various ways of measuring the rate of corrosion, including AC Impedance and electrochemical noise (Dawson, 1983). However, these techniques are not suitable for use in the field for application to the corrosion of steel in concrete so this section will concentrate on linear polarization, also known as polarization resistance or LPR, and will discuss various macrocell or galvanic current measurement techniques. 

Huet, F. (2005) Electrochemical noise technique, in Analytical Methods in Corrosion Science and Engineering (eds R Marcus and F. Mansfeld), Corrosion Technology, Taylor Francis, CRC Press, vol. 22, pp. 507-570. 

Very often baseline problems are related to detector problems. Many detectors are available for HPLC systems. The most common are fixed and variable wavelength ultraviolet spectrophotometers, refractive index, and conductivity detectors. Electrochemical and fluorescence detectors are less frequently used, as they are more selective. Detector problems fall into two categories electrical and mechanical/optical. The instrument manufacturer should correct electrical problems. Mechanical or optical problems can usually be traced to the flow cell however, improvements in detector cell technology have made them more durable and easier to use. Detector-related problems include leaks, air bubbles, and cell contamination. These usually produce spikes or baseline noise on the chromatograms or decreased sensitivity. Some cells, especially those used in refractive index detectors, are sensitive to flow and pressure variations. Flow rates or backpressures that exceed the manufacturer s recommendation will break the cell window. Old or defective source lamps, as well as incorrect detector rise time, gain, or attenuation settings will reduce sensitivity and peak height. Faulty or reversed cable connections can also be the source of problems. 

Transducer technologies include electrochemical, piezoelectric, colorimetric, and optical systems. The transducer system must acquire signals that are unique to the probe system and generate low noise signals that can be further processed without degradation to provide a human observer with an indication of probe system activity. 

The veirious types of measurement technologies for assessment of corrosion may be summarized as shown in Tables 2 to 5. These techniques cover both laboratory Jind field use. However, many of the direct methods, particularly the electrochemical methods of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) are generally more suited to laboratoiy evaluation. In the laboratory, test conditions are clean and more controlled. Consequently, more sophisticated measurement electrode systems can be used that take advantage of their more sophisticated measurements technologies. In the field, practicalities of changing process conditions, high flow rates, debris, electrical noise, and electrical safety limit their use. 

Kozlov VA, Safonov MV (2003) Self-noise of molecular electronic transducers. Tech Phys 48 1579-1582 Kozlov VA, Korshak AN, Petkin NV (1991) Theory of diffusion-type transducers for ultralow electrolyte flow-rates. Sov Electrochem 27 16-21 Krishtop VG, Agafonov VM, Bugaev AS (2012) Technological principles of motion parameter transducers based on mass and charge transport in electrochemical microsystems. Russ J Electrochem 48(7) 746-755 Larcam CW (1965) Theoretical analysis of the solion polarized cathode acoustic linear transducer. J Acoust Soc Am 37 664-678... 

---