Galvanic current measurement

Galvanic current Measurement of the galvanic current between two different metals can be easily measured using a zero resistant ammeter ". This method can have specific application, e.g. to provide a signal indicating failure of a protective coating in a process vessel. Commercial probes are available for industrial monitoring. 

Galvanic corrosion test (DIN 50 919) and galvanic current measurement... 

Coating type Immersion test (test period 240 h) Galvanic current (measurement lest period 48 h) ... 

DIN 50 919 Immersion test with short-circuit/ galvanic current measurement 4 5 2 3 2 2 — 1 1... 

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. 

Laboratory galvanic current measurements can be very useful in the pre-screening of materials. For instance, in a study on dental implant bridges it has been reported that silver-palladium, when brazed to titanium, corrodes in vitro (Ravnholt and Jensen, 1991), thus eliminating the need to carry out in vivo tests. 

Tamboli et al. (2009) have used OCP and galvanic current measurements to study PCMPC chemistries for Cu as well as a range of barrier metals including Ta, TaN, Ti, TiN, and Ru. A primary contaminant generated during Cu CMP is the residual species of the dissolution inhibitor BTA regularly used for metal CMP (Yamada et al., 2008 Tran et al., 2012). When present in the CMP slurry, Cu +/Cu+ can form insoluble Cu-BTA complexes, which in turn can lead to unavoidable surface defects in the form of strongly adsorbed (sometimes polymeric) islands and/or scratches on the processed Cu. Electrochemical methods have been proven to be usefiil to study the presence of these Cu-BTA defects as well as their removal chemistries under in situ conditions (Miao et al., 2014). 

When the potentials of two materials in a galvanic couple are widely separated, Faraday s Law can be used to calculate the galvanic corrosion rate from the galvanic current measured between them. This calculation can be done by the procedures in ASTM G 102. 

Comparison of the galvanic current measured between either B or X and pure magnesium in 5% NaCl solution (pH 11). 

Schematic illustration of a setup for galvanic current measurement (based on Song and StJohn (26)). 

A 12 channel ZRA allowed 12 simultaneous measurements, and the standard configuration was that shown in Fig. 12.2. Twelve plates of identical size were used for the galvanic current measurements six plates of Mg and six plates of steel. Each of the metal plates had the following dimensions ... 

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