THE ELECTRICAL CONDUCTIVITY OF MOLTEN SLAGS CONTAINING TITANIUM-OXIDE (I)
In order to study the behaviour of TiO2 in molten slags, the electrical conductivity of the Na2O-SiO2-TiO2 system was measured. The measured range of composition was TiO2 0-35 mol% at Na2O/SiO2=0.40, 0.50 and O.61 The conductivity decreases smoothly with temperature. At constant temperature the conductivity remains almost unchanged for the slags containing TiO2 less than 10mol%, but with more TiO2 the conductivity decreases with increase of TiO2.
The conduction mechanism is ionic and the mobile ion is Na+. Ti ion cannot move, because the bonds Ti-O is strong owing to small ionic radius and large ionic valency.
The molar electrical conductivity, which corresponds directly to the mobility of Na+, was calculated. At the range of low TiO2 contents Ti ions distort Si-O network, raising the mobility of Na+, while at the range of high TiO2 contents oxygen ions impede the conduction of Na+, thus lowering the mobility of Na+. The latter behaviour of TiO2 is different from SiO2 or Al2O3, because TiO2 lowers viscosity of sodium-silicate contrary to SiO2 and Al2O3. TiO2 is amphoteric, and it behaves as basic oxide at low contents, while it is like an acidic oxide at high contents.
For the series Na2O/SiO2=0.50 the conductivity of slags containing TiO2 40-50 mol% was measured. In the conductivity-temperature curve an anomalous point appears in the neigh-bourhood of solidifying temperature, suggesting the behaviour of TiO2 as a semi-conductor.
It was summarized that the peculiar behaviour of TiO2 would be ascribed to the following facts:
(1) The bonds Ti-O are strong, and Ti ion has the strong action of "network distortion"
(2) Ti is a transition metal, and TiO2 is a typical semi-conductor.