Measurement of surface resistivity/conductivity of metallic alloys in aqueous solutions by optical interferometry techniques

Optical interferometry techniques was use for the first time to measure the surface resistivity/conductivity of the pure aluminium (in seawater at room temperature), UNS.No305 stainless steel (in seawater at room temperature), and pure copper (in tab water at room temperature) without any physical contact. This was achieved by applying an electrical potential across the alloys and measuring the current density flow across the alloys, during the cyclic polarization test of the alloys in different solutions. In the mean time, optical iterferometry techniques such as holographic interferometry was used in situ to measure the orthogonal surface displacement of the alloys, as a result of the applied electrical potential. In addition, a mathematical model was derived in order to correlate the ratio of the electrical potential to the current density flow (electrical potential/electronic Current flow=resistance) and to the surface (orthogonal) displacement of the metallic samples. In other words, a proportionality constant (surface resistivity or conductivity=1/ surface resistivity) between the measured electrical resistance and the surface displacement (by the optical interferometry techniques) was obtained. Consequently the surface resistivity (ρ) and conductivity (σ) of the pure aluminium (in seawater at room temperature), UNS.No305 stainless steel (in seawater at room temperature), and pure copper (in tab water at room temperature ) were obtained. Also, electrical resistivity values (ρ) from other source were used for comparison sake with the calculated values of this investigation. This study revealed that the measured value of the resistivity for the pure aluminium (7.7x1010 Ohms-cm in seawater at room temperature) is in a good agreement with the one found in literature for the Aluminium Oxide ,85% Al2O3 (5X10 10 Ohms-cm in air at temperature 30C0). Unfortunately, there is no measured values for the resistivity of cupric oxide (CuO), Cuprous Oxide (Cu2O), or even the oxide of the UNS.No304 stainless steel in literature to compared those values with the measured values in this study.