Simulation of Mechanical, Thermodynamic, and Magnetic Properties of Magnesia with Substitutional Elements for Improved Magnetic Core Coating Applications

Abstract

In transformers used in the electrical industry, a coating, such as magnesium oxide or magnesia (MgO), is needed to coat the magnetic ferrite core, such as silicon steel. The coating is to provide electrical insulation of the layers of the ferrite core material, in order to reduce its heat dissipation loss. The coating also separate the layers of the coiled materials to prevent their sticking or welding during high temperature uses. The goal of this thesis is to perform a modeling study to understand the mechanical, thermodynamic, magnetic and thermal properties of pure and M-doped (M stands for Mn, Co, or Ni) magnesia, thus providing a theoretical understanding of the application of this group of coating materials for transformer applications. The study has the following sections. The first section is focused on the mechanical properties of pure magnesia. Using density functional theory (DFT) based calculations, the computed Young’s modulus, Poisson’s ratio, bulk modulus, and compressibility are 228.80 GPa, 0.2397, 146.52 GPa, and 0.00682, respectively, which are in good agreement with the literature data. Using molecular dynamics (MD) simulations, the computed Young’s modulus is 229 GPa. Using discrete element model (DEM) approach, the bending deformation of magnesia is simulated. Finally, using finite element model (FEM), micro-hardness indentation of magnesia is simulated, and the computed Brinell hardness is 16.1 HB, and Vickers hardness is 16 GPa. The second section is on the thermodynamic and physical properties of pure and doped magnesia. Using DFT based simulations, the temperature-dependent thermodynamic properties, such as free energy, enthalpy, entropy, heat capacity at constant volume, and Debye temperature of magnesia, are computed. The X-ray powder diffraction (XRD) spectra of M-doped magnesia are simulated, at the doping level of 1.5%, 3%, 6% and 12%, respectively. The simulated XRD data show that peaks shift to higher angles as the doping level increases. The third section is on the magnetic properties of pure and doped magnesia. Using DFT based simulations, the calculated magnetic moments increase with the doping level, with Mn as the highest, followed by Co and Ni. This is due to the fact that Mn has more unpaired electrons than Co and Ni. The fourth section is on the thermal properties of the pure magnesia. Using the Reverse Non-Equilibrium Molecular Dynamics (RNEMD) method, the computed thermal conductivity of magnesia is 34.63 W/m/K, which is in agreement with the literature data of 33.0 W/m/K at 400 K.