Direct detection of calcium carbonate scaling via a pre-calcified sensitive area of a quartz crystal microbalance

In an industrial cooling circuit supplied with raw river water, the scaling phenomenon can reduce cooling efficiency and even lead to the shut down of the power plant. During the last twenty years, various methods have been developed in order to estimate the scaling propensity of natural waters, which involve the precipitation of calcium carbonate (CaCO3), the main component of scale. The FCP (Fast Controlled Precipitation) is a non2 electrochemical method which consists in CO2 degassing from water by a moderate stirring. FCP allows quantifying the scaling propensity for natural water. However, FCP is not well adapted in the case of waters with low scaling propensities, or for in situ measurements. In this study, a quartz crystal microbalance with a pre-calcified sensitive electrode or SQCM (Scaling Quartz Crystal Microbalance) was developed. The sensitive surface of this gravimetric sensor could be used as an adsorption layer for calcium carbonate nuclei present in water. Thus, SQCM method is able to detect the phenomenon of scaling, even if the water does not precipitate, due to its high gravimetric sensitivity. This method is described in details in this paper, and was successfully applied to evaluate the scaling propensity of synthetic waters. SQCM could be used in situ to assess the efficiency of humic substances in synthetic water towards scaling.