Abstract: The microstructure evolution process of the reaction between silicon oxide and magnesium oxide in oxide layer was observed by focused ion beam microscope(FIB) in simulating the high temperature annealing process of grain-oriented silicon steel in laboratory.Then the distribution of Mg, Al and Si in the near surface layer of the sample section was analyzed by energy dispersive spectrometer (EDS). Finally, the structure of the magnesium silicate glass film was analyzed by transmission electron microscopy(TEM). The results showed that: (1) the diffusion rate of Mg ions is the major factor affecting the reaction of magnesium oxide and silica; (2) Mg ions diffuse firstly along the interface between silica oxide and iron matrix, and gradually coat the silica particles, and then Mg ions begin to diffuse into and react with the silica particles as the further increase of temperature; (3)as the temperature increasing, the Al decomposed by AlN gradually converts the magnesium silicate (Mg2SiO4) at the pinning site into magnesium aluminum spinel (MgO·Al2O3).

Key words: magnesium oxide, silica, high temperature annealing, magnesium silicate, magnesium aluminum spinel