Study of insulation layer formation on electrical steel surfaces by x-ray photoelectron spectroscopy and electron microprobe analysis

Abstract

The crystallographic orientation of grains (so-called Goss texture) in electrical steel sheets, which are made from an ironsilicon alloy (3 wt.-% Si), is essential for their ferromagnetic properties [1]. For applications an electrical insulating coating system consisting of a glass layer and a phosphate layer on both sides of the sheets is necessary to reduce the eddy current losses. Furthermore, the tension stress induced in the core material by the coating reduces the magnetostriction. The coating system is developed by a three step annealing process. For a reproducible and defect-free development of the layers, it is necessary to keep the process parameters extremely constant [1-4]. To control the process, it is important to know the mechanisms of the layer formation in detail. Therefore, the analysis of the final product only is not sufficient and the structure of the composition of layers after different process steps were analyzed. The oxide layer and the interface metal/metaloxide were investigated by x-ray photoelectron spectroscopy (XPS) combined with Ar ion sputtering, the glass film and the phosphate coating by electron microprobe analysis (EMA).