Estudo e secagem de argila vermelha utilizando um sensor magnetoelástico

Abstract

An important application of magnetoelastic sensors is in antitheft systems. Because of their excellent performance and their passive wireless nature, they have also been extensively used in environmental sensing of changes in temperature, atmospheric pressure, flow speed of fluid over the sensor surface, density and viscosity of liquids and mass change. The present work investigates the use of magnetoelastic sensors based on Metglas®2826MB3 to study the drying behavior of ceramic materials. Two clays from the Vale do Caí region, the main producer of ceramic materials for the construction industry, were analyzed. Aqueous clay suspensions were prepared and their characterization was performed using traditional techniques that considered the drying kinetics, shrinkage and cracking behavior as a function of the wet weight of the material deposited into an aluminum mold. Subsequently, the suspensions were deposited on the sensor tape surface with a doctor blade device. Applying a variable magnetic field, it was possible to determine the experimental resonance frequency of the sensor. This frequency is inversely proportional to the ribbon length and dependent upon the physical properties of the materials. A mathematical model was used to correlate the resonance frequency with the elastic properties of the coating. Besides the physical properties of the materials, also included in model was the dependence of the tape's elastic modulus on magnetic field, known as the E effect. The stress developed during the drying process may cause cracks and deformations in the material when it is not dissipated. This stress contributes to the magnetic anisotropy which is introduced into the problem through the E effect. The cantilever technique was used to determine the presence of tensions during drying. Measuring the deflection of the substrate, it is possible to determine the stress generated by the suspension. The curves of resonance frequency versus time show several distinct regions. For the region that separates the two main rying stages of the suspension, the frequency measurement proved to be very sensitive to the presence of tension. Therefore, the structures observed in the experimental curves of frequency versus time could be modeled using the experimental distribution of stress and the elastic properties of the sensor and clay suspension. This promising result suggests that the tensions developed during the drying of ceramic materials could be determined by measurements of the resonance frequency of the sensors.