Synthesis of Ni-Zn ferrites by microwave decomposition of hydrotalcites for the functionalization of porcelain substrates

Abstract

This project describes the development of a ceramic substrate for use in electromagnetic induction plates, which are traditionally made of glass-ceramic material. The glass-ceramic materials used for this type of application are mainly characterised by their high resistance to thermal shock and their high magnetic permeability indexes, which prevent or minimise shielding of the magnetic field. In order to develop such a ceramic material with the magnetic, thermal and mechanical properties required for induction heating technology, a porcelain stoneware composition was doped with mixed ferrites of Ni-Zn. These ferrites are characterised by their low coercivity coefficients, which encourages flow of a high-frequency magnetic field. The ferrites were prepared by different synthesis routes and even ferrite nanoparticles were produced without the need to resort to highly energy-intensive milling processes. Including ferrites in a porcelain stoneware composition generates magnetisation, creating eddy currents that heat the entire mass of the substrate very uniformly by the Joule effect. This leads to a reduced temperature gradient inside the workpiece, unlike compositions with no ferrites, in which heating is by direct conduction. By reducing the temperature gradient in the workpiece, it is possible to reduce the difference in internal stresses between the top and bottom of the plate, which is the main cause of thermal shock fracture. In addition to thermal shock, other essential properties in this type of materials, such as magnetic permeability and mechanical strength, were also improved. The last section of the project was dedicated to studying the potential variables that affect viability in industrial production (dilatometric, thermal and mechanical studies, etc.).