Development of a transparent hydrorepellent modified SiO2 coatings for glazed sanitarywares

Abstract

The formulation of innovative transparent hydrorepellent coatings is strongly motivated in order to satisfy the market request and necessity to improve the cleanability of the sanitarywares. A lot of attention is devoted to the use of cheap precursors, low temperature synthesis process and industrial scalability potentiality. In this framework, in the present paper the set-up of the deposition of modified SiO2 coatings on glazed ceramic supports by spraying technique was reported. Several solutions were formulated using as precursor tetraethylorthosilicate (TEOS) and co-precursor methyltriethoxysilane (MTES) in different molar ratios (i.e. 50:50, 25:75, 75:25), in suitable solvents and mixture of solvents (i.e. H2O, ethanol). The influence of the process parameters (i.e. precursors ratio, solvents, catalyser, annealing temperature) on the properties of the produced coatings was deeply investigated by means of scanning electron microscopy (SEM), simultaneous thermogravimetric and differential analyses (TG–DTA), infrared spectroscopy (FT-IR), X-Ray diffraction (XRD) and Vickers microhardness. Their hydrophobic behaviour was tested by the measurements of the static water contact angles and the chemical and stain resistance by the conformity to some tests of the standard UNI 4543. The obtained coatings were amorphous, homogeneous, uniform, thin (average thickness 300 nm), crack-free, leading to an improved hardness value of the glazed ceramic support (4.47 GPa vs 3.68 GPa for the coated and uncoated substrates, respectively), and allowed to improve both the hydrophobic behaviour and the chemical and stains resistance of the glazed sanitaryware supports, on the basis of the standard UNI 4543. The best hydrophobic performances were revealed in the case of coatings prepared starting from acidic catalysis derived precursor solutions. Moreover, the highest water contact angle values were detected for lower temperatures annealing, due to the methyl groups preservation, in agreement with the FT-IR and TG–DTA findings.