DESENVOLVIMENTO DE FILMES HIDROFÓBICOS POR PLASMA CC PULSADO PARA ISOLADORES ELÉTRICOS DE PORCELANA

Abstract

Ceramic electric insulators are fundamental support devices for electric energy distribution due to its mechanical resistance and dielectric properties. The presence of atmospheric humidity and pollutants can reduce the dielectric property. To achieve an auto cleaning surface or hydrophobic properties, the insulator must have low contact angle and low hysteresis with water. Although, the insulator vitreous surface layer possess great interaction affinity with environmental water. At the present work, aluminum nitride thin films were deposited on the vitreous protective layer of ceramic electric insulators. For this, a pulsed magnetron sputtering plasma was employed, with direct current (DC), and moisture of argon and nitrogen gases. An aluminum target with 99.999% purity was used as precursor. Continuous films deposited produced with Ar and N2 presented about 2 μm thickness, while the films produced with 100% N2 presented around 1 μm, both for the same treatment time. Low exposure times lead to depositions on surface defects and porosity of the insulator vitreous body and showed nanosize island growth (166, 155, 100 nm). The films thickness and surface characterization was performed with field emission scanning electron microscopy (FEG) and atomic force microscopy (AFM). Raman spectroscopy and X-ray diffraction showed the formation of an amorphous aluminum nitride film. The continuous film produced with 100% N2 presented 82.7° water drop contact angle, while the non-continuous film presented in average 67°. According to ASTM D7334-08, these films are hydrophobic. Roughness was not a determinative parameter for surface wettability, but the deposited film surface energy. To measure the contact angle a goniometer was developed. A four point probe was used to measure the electric resistivity for a semi-infinite surface. The Ar and N2 continuous film surface resistivity was 656/. For the nanosize films the surface resistivity was about M/.