Monitoring of water uptake in anti-corrosion organic coatings using a quartz crystal oscillator sensor

Water absorption is an essential parameter to define the protection properties of anticorrosive paints. This parameter is often evaluated by means of the dielectric capacitance of the coating. The presence of water in the coating increases its dielectric constant. The semi-empirical Brasher-Kinsgbury equation [1] allows the estimation of a coatingpsilas water uptake through capacitance measurements. However, the capacitance of a coating depends, at least, on both the amount of water (volume fraction) and the shape of the water inclusions [2]. Brasher-Kingsbury approximations may result in highly inaccurate values. Therefore, it is interesting to have a direct measurement of the mass increment of the coating together with the time evolution of its dielectric capacitance. A stable quartz crystal oscillator sensor for measuring the water uptake in organic coatings was designed. The phase noise performance of the oscillator has been investigated in order to characterize the oscillatorpsilas resolution during the water uptake process. The result is a quartz crystal microbalance (QCM) sensor able to determine the rate and amount of water absorbed into anticorrosion cataphoretic coatings with a resolution of 360 pg/cm² for one second sampling interval.