Dip coating of silica layer on melt-spun Finemet ribbons: surface morphology and electrical resistivity changes

In this study, melt-spun Finemet ribbons were coated by a thin layer of SiO2 using dip coating method. Amorphous ribbon prepared by melt spinning method and dip coating were done by using a solution of tetraethylen orthosilicate as a SiO2 precursor, ethanol as solvent and distilled water for hydrolysis. Different thicknesses of SiO2 layer, namely 304, 349, 451, 526 and 970 nm were obtained proportional to the number of dipping. Surface morphology and chemical composition of the coatings were analyzed by using Scanning Electron Microscope equipped with an energy dispersive spectroscope. The results clearly verified the presence of Si and O elements and confirmed the presence of silica layer on the surface of all coated ribbons. Microstructure and surface morphology of samples showed a smooth and brittle layer. Electrical resistivity of the samples was measured with a standard four-point probe device. The results confirmed an intense in increase of resistivity. Average value of electrical resistivity for coated samples was around 104 Ω-m compared to 10-6 Ω-m for Finemet ribbons. Capacity of the samples was evaluated by electronic parameter analyzer device in two different frequencies of 100 kHz and 1000 kHz. Impedance measurements of coated samples in 100 and 1000 kHz showed an increase about 70 and 10 times respectively.