Laser applied in glass and glass-ceramics preparation: studies regarding crystal growth and viability for solid-state micro-sensors development

• Grant number: 19/27628-6
• Support type: Regular Research Grants
• Duration: December 01, 2021 - November 30, 2023
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal researcher: Marcello Rubens Barsi Andreeta
• Grantee: Marcello Rubens Barsi Andreeta
• Home Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Assoc. researchers: Oscar Peitl Filho ; Rafael Bonacin de Oliveira

Abstract

The search for new materials that can be used as pH sensors is of great technological importance, especially in the food and medicine industry, where there are large demands for in situ measurements, often impossible to perform due to the mechanical fragility and size of current sensors. The use of ceramic or glass-ceramic-based sensing elements is desired due to the low production costs, and in most cases, the best mechanical properties of these materials. Among the compounds being studied for solid-state pH sensors, lithium-based ionic conductors, especially lithium lanthanum titanate (Li3xLa(2/3)-xTiO3 - known as LLTO, for x H 0.11), have received special attention because they have high ionic conductivity. However, these sensors are not yet a commercial device, mainly due to reproducibility problems related to their microstructure. A possible solution to solve this problem could be in the development of single crystals. However, reports in the literature indicate difficulties in obtaining single crystal samples larger than a few millimeters for LLTO, at a prohibitive cost for large scale production. A new possible route of preparation for this family of compounds, which has not yet been explored, is the production of glass and/or their glass-ceramics (controlled glass crystallization) compounds. With this motivation, this research project proposes the systematic study of glass preparation, and also the crystal growth process in the Li2O- (La,Y,Al)2O3-TiO2-SiO2 system, which includes the composition of the LLTO compound. For this study, from the point of view of materials science, this project aims to contribute to the understanding of crystal growth in glasses of the system to be studied (distribution of crystalline phases, size of crystals and their geometry), through a non-isothermal crystallization. Thus, the scientific aim is to obtain a correlation between the thermal parameters of the crystal growth process with the obtained microstructure and composition, thus enabling a correlation between those parameters with the pH sensitivity of the produced microsensor. From the technological point of view, the correlation between the sensitivity for pH detection with the compound composition and microstructure is expected to allow the preparation of samples that results in the miniaturization of a solid-state pH sensor device. To achieve these objectives, the samples will be prepared in a spherical geometry by laser melting in an aerodynamic levitation system, to be optimized during the execution of this project. After the glass is prepared in small spheres (around 3 mm in diameter and few milligrams), they will be heated in the same aerodynamic levitation system. With this system, it is expected to inhibit an important factor for surface nucleation, which is the substrate influence (one strong factor for heterogeneous nucleation). After controlled crystallization of the glass, it will be cut and polished with optical quality for the study of crystallized phases (to be determined by X-ray diffraction and Raman spectroscopy - this last equipment to be purchased in this research project). The samples produced will also be characterized by thermal analysis, electron microscopy, X-ray fluorescence, as well as pH sensitivity tests. In this way, it is intended to advance in the understanding of the crystallization processes in glasses, as well as in the reproducibility for preparing low-cost and efficient pH sensors, fundamental for the technological development of the national medical and food industries. (AU)