Processing, adhesion and electrical properties of silicon steel having non-oriented grains coated with silica and alumina sol–gel

Silicon steels having non-oriented grains are usually coated with a series of inorganic or organic films to be used in electrical applications. However, the commercially available coatings have several disadvantages that include poor adhesion to the substrates, low values of electrical resistance and degradation at higher temperatures. In this work, silica and alumina sol–gel films were deposited onto silicon steel in order to evaluate the possibility of replacing the commercially available coatings by these sol–gel derived materials. Silica and alumina sol–gel coatings were prepared by dipping silicon steel samples into hydrolyzed silicon or aluminum alkoxides. Samples coated with sol–gel films were studied by scanning electron microscopy, energy dispersive spectroscopy and infrared spectroscopy. Adhesion between silicon steel and sol–gel films was measured by using several standard adhesion tests. Electrical properties were evaluated by the Franklin method. Results showed that homogeneous sol–gel films can be deposited onto silicon steel. Thicknesses of the films could be easily managed by altering the speed of deposition. The structure of the films could also be tailored by introducing additives, such as nitric acid and N,N-dimethyl formamide. Adhesion tests revealed a high level of adhesion between coatings and metal. The Franklin test showed that sol–gel films can produce coated samples with electrical resistances suitable for electrical applications. Electrical properties of the coated samples could also be manipulated by altering the structure of the sol–gel films or by changing the thickness of them.