Materials Clrcmistry and Physics, 17 (1987) 541-55 1 541 SYNTHESIS AND THERMAL BEHAVIOR OF GEL-DERIVED SnC2_Sb& SEMICONDUCTING GLAZE G.COCC!G and S.ENZG Department of Physical Chemistry,University of Venice (Italy) G.CARTURAN, P.GIORDANO ORSINI and P.SCARDI Department of Engineering,University of Trento (Italy) Received December 18,1986; accepted March 4,1987 ABSTRACT Amorphous xerogels were prepared by the gel route with 3 chemical composition corresponding to the semiconducting glaze of industrial high voltage insulators, i.e. 66% glassy phase - 70% SiO2, 9% Al 0 , _- 23 4,5% (K,Na)20, 9% CaO, 7,5% ZnC - and 33% Sn02cSb 0 2 5 ( Sn02/Sb205 = 97/3). Thermal treatment of the starting xe- rogel separates crystalline SnO 2 dispersed in the glassy phase. Sn02 microcrys- tals are homogeneously dispersed in the matrix and exhibit an average size of ea. 500-800 i, which is one order of magnitude lower than the size of Sn02 - cry- stals obtained in traditionally prepared samples. To follow the structural role of single components up to the final product, the gel-derived samples of pure Sn02,Sn02+Sb205 and the one corresponding to the glass phase were also prepared. X-ray diffraction line broadening analysis, scanning electron microscopy and energy dispersive analysis were employed to investigate the thermal behavior of these samples. The chemical instability of gel-derived semiconductors above llOO°C was investigated and discussed in terms of redox reactions involving Sn and Sb species. INTRODUCTION With the aim of increasing the voltage of power lines , the electrical in- dustry requires new inorganic materials for the manufacture of suitable electri- cal insulators. The control of flashover caused by humidity and pollutant con- densation suggested the use of ceramic insulators coated by a semiconductor glaze, so that the consequent moderate heating causes a positive drying effect. 0 Etsevier Sequoia/Printed in The Netherlands