Behaviour of ruthenium dioxide particles in borosilicate glasses and melts

Ruthenium–glass systems are formed during the vitrification of nuclear waste. They are also widely used in micro-electronics because of their unique electrical properties. However, the interaction of this element with the glass matrix remains poorly understood. This work focuses on a RuO2 particles-nuclear alumino-borosilicate glass system in which the electrical conductivity is known to vary considerably with the RuO2 content and to become electronic above about 0.5–0.7 vol.% RuO2 [R. Pflieger, M. Malki, Y. Guari, J. Larionova, A. Grandjean, J. Am. Ceram. Soc., accepted for publication]. Some RuO2 segregation was observed in SEM/TEM investigations but no continuous chain of RuO2 particles could be seen. Electron relays between the particles are then necessary for a low-rate percolation, such as the nanoclusters suggested by Adachi et al. [K. Adachi, S. Iida, K. Hayashi, J. Mater. Res. 9 (7) (1994) 1866; K. Adachi, H. Kuno, J. Am. Ceram. Soc. 83 (10) (2000) 2441], which could consist in dissolved ruthenium. Indeed, several observations made here clearly indicate the presence of dissolved ruthenium in the glass matrix, like the modification of the glass density in presence of RuO2 particles or the diffusion-limited growth of RuO2 particles in the melt.