Síntese e caracterização de vidros silicatos binários SiO2-MoO3 obtidos através do método sol-gel

Abstract

In this work, a binary system glassy SiO2-MoO3 was prepared by the sol-gel method. The advantage of using sol-gel method than the melt-quenching is the fact that it is possible to obtain more homogeneous glasses at room temperature. In addition the no temperature exposure leads to the preservation of desirable components properties. Thus samples were prepared in the binary system by sol gel varying the molecular MoO3 ratio from 0.01% to 10.00%. The TEOS was used as SiO2 precursor and MoOCl4 was the starting material used to obtain the precursor of MoO3. The methods used for MoO3 precursor preparation were the reflux and ultrasound. The samples were prepared as monoliths and characterized in the form of fine powder for the XRD analysis, thermal analysis (DSC and TGA), spectroscopic analysis by infrared attenuated reflection (ATR) and Raman scattering. The precursor solution of MoO3 was studied by absorption spectroscopy in the UV-VIS region and this precursor as powder was analyzed by Raman scattering. Through the XRD results it was possible to demonstrate the amorphous nature of all the prepared samples as well as the formation of MoO3 crystalline phase after heat treatment at 800oC. Even with the crystal peaks of MoO3 after heat treatment, the glasses kept the characteristics of amorphous materials, which is interesting for glass ceramics synthesis. It was also possible to describe some physical-chemical phenomena through thermal analyzes: the TGA curves showed large initial mass losses due to adsorbed organic solvents in gel, demonstrating the importance of heat treatment perform in order to obtain better results while DSC curves showed the possibility of metal incorporation into glassy matrix due to changes in the glass transition temperature (Tg) as consequence of MoO3 molar ratio increments. Infrared analyses identified connections between molybdenum and silica deducting that molybdenum probably is participating in the system by modifying the glass matrix. Raman scattering analysis identified octahedral coordinated molybdenum, most likely to be responsible for the photochromic and non-linear optical properties of glasses. The results suggest therefore the possibility of using the synthesized glasses for photonics or other optical non-linear applications.