Influência das variáveis de sinterização nas propriedades mecânicas e elétricas de vitrocerâmicas produzidas a partir de pó de vidro reciclado e adição de Nb2O5

Abstract

The reuse and recycling of end-of-life products are crucial when considering the environmental problems caused by generated waste. Glass-ceramics can be produced from the controlled crystallization of the glass. In this dissertation, glass-ceramics are obtained from glass powder from discarded windshields. In addition to this glass powder, different concentrations of niobium pentoxide were used to act as a nucleating agent and to facilitate crystallization. Four compositions were obtained: without Nb2O5 and with 5%, 10% and 15% of Nb2O5. In the production process, two sintering temperatures, 700°C and 800°C, and two sintering times, 1 h and 3 h, were adopted. It was carried out a study of the microstructural properties, mechanical and electrical, besides the properties of density, porosity and water absorption of the material produced. In addition, the characteristics of the glass powder used for glass-ceramic production were evaluated. To characterize the glass powder, wet particle size analysis, X-ray fluorescence and TG and DTA thermal analyzes were performed. As for glass ceramics, the following were performed: XRD, Archimedes Method, SEM, Linear Retraction of the Diameter, Biaxial Flexural Strength and Diametral Traction. The Dielectric Constant and Electric Conductivity of the produced glass ceramics were also determined. It was found that the use of particles smaller than 1.2 μm, considered too small, would hinder the densification of the material, while the large size distribution favored the packaging of the particles. The use of higher sintering temperatures and longer sintering time increase porosity and reduce density. In contrast, the temperature of 800°C allows crystallization without the use of nucleante agent. The addition of Nb2O5 promoted the crystallization of the material already at 700°C, fact that does not occur without its addition at this temperature. It also allowed the formation of the Isoleucita, perosviskite structure that presents good ferroelectric properties. Thus, the glass ceramics with the highest concentrations of this pentoxide obtained the highest dielectric constants and electrical conductivities, being 63,597 and 4,283 μS / m, respectively, both found in glass-ceramics produced with 15% of Nb2O5, sintered at 700°C for 1 h. On the other hand, there was loss of mechanical resistance in both biaxial flexion and diametral traction, with a decrease of 34.83 MPa to 14.34 MPa in resistance to biaxial flexion. In spite of this, the glass-ceramics produced still present superior resistance to that of structural concretes. In relation to the standard deviation of the mechanical properties, there was an expressive reduction with the addition of the nucleating agent. The obtained results allowed to conclude that the production of glass-ceramics from the windscreen glass is viable, and satisfactory mechanical and electrical properties were obtained.