Application of nano-coating technology for the protection of natural lapideous materials

Nowadays, the coating industry offers a wide range of products to protect, decorate, and perform special functions on surfaces of objects such as automobiles, aerospace aircrafts, heavy industrial machines and structures, consumable toys, and many other products. The use of coatings as a corrosion protection agent is of great interest in the research and development industries, acting as a barrier between the material substrate and the corrosive elements. In the present work, we have tested the anti-corrosion performances of three types of protective coatings, derived from calcium-phosphate (CaP) minerals, ethyl silicate (TEOS) and polysilazanes. These coatings have been applied on different lapideous materials that belong to the groups of siliceous and carbonaceous rocks. CaP minerals and TEOS coatings are performed by the immersion of samples in baths of crafted solutions, whereas polysilazanes are applied on surfaces with techniques of spraying and brushing. Raw and coated samples have been analysed by SEM/EDX and FTIR to address their effective functionalization of the surfaces. The coated lapideous samples have been tested with corrosive agents to simulate decay processes in harsh acidic environments. The main results reveal that PHPS treated samples offers a considerable higher level of protection against acidic attack compared to the other protective coatings. Moreover, we highlighted a different behaviour among siliceous and carbonaceous surfaces treated with PHPS, as the former reveals a much longer survivability in acidic environments.