Influence of the grain-size and chemical composition of a MgO coating on the structure-phase state and elemental composition of the ground layer formed on an electric steel surface

The surface morphology, phase state and elemental composition, and substructure of the ground layer of anisotropic electric steel (AES) samples have been studied via scanning electron microscopy, atomic force microscopy, transmission electron microscopy, electron probe microanalysis, and x-ray diffractometry. High-temperature annealing of MgO coatings with different grain-size distributions and chemical compositions was found to lead to formation of a single-phase layer of forsterite (Mg₂SiO₄) on the AES surface. It has been revealed that the morphology and substructure of a forsterite layer depend on the grain-size distribution and chemical composition of magnesium oxide and the conditions used in preparation of MgO suspensions. When added to MgO suspensions, TiO₂ and Na₂B₄O₇ impurities promote formation of a denser coating substructure. The increased mixing speed used in suspension preparation improves the surface homogeneity of a ground layer only if a suspension contains MgO grains of different size.