A novel model to detect the content of inorganic nanoparticles in coatings used for stone protection

In the field of restoration of cultural heritage, it has been developed coatings containing nanoparticles having multifunctional features, to protect stone materials against environmental degrading agents. Detecting such nanoparticle concentration within the coating, can represent a challenging issue because its monitoring over time can provide insights about the treatment durability. This paper deals with a theoretical basis to develop an instrumental method to fulfil this requirement. The “sample” under consideration consists in marble coated by silica in which nanoparticles are dispersed. The latter have a core–shell structure, in which the shell consists of titania, while different cores have been tested. The technique is based on the measurement of the interaction of the electromagnetic fields with coated surface. It has been shown the possibility to estimate the thickness of the protective coating and the concentration of nanoparticles contained in it, by using the transition matrix method and radiofrequency impedance measurement. The measurement of reflection coefficient of the electric field incident to the coated surface can be carried out with an Horn antenna, by using a frequency of about 350 Ghz. This makes it possible to assess the thickness of the coating. On the contrary, impedentiometry at about 10 MHz, carried out with an open-ended coaxial probe, allows to detect the concentration of the nanoparticles into the coating.