Corrosion Testing of Thermally Sprayed Aluminium

Corrosion rate determination is often based on linear polarisation (LPR) technique, carried out on small specimens in a controlled environment. The current is measured when the specimen is polarised away from its corrosion potential and the polarisation resistance alone with the current gives the corrosion rate using Faraday's law. An important parameter is the specimen area exposed. When testing rough, porous specimens such as thermally sprayed aluminium (TSA), the geometrical surface area does not represent the real surface area and hence the corrosion rate is not the actual corrosion rate. To measure the actual corrosion rate aluminium was thermally sprayed onto glass and the surface was characterised using a confocal microscope. These specimens were exposed to seawater at 25, 50 and 100°C, and the linear polarisation resistance was determined using a potentiostat at room temperature. This was converted to a corrosion rate based on geometric and the actual surface area.