NITRIDE CAPACITIES IN CAO-SIO2 AND CAO-SIO2-AL2O3 MELTS

Nitride capacities, C(N3-), defined by (mass-% N) . P(O2)3/4/P(N2)1/2 in the CaO-SiO2 and CaO-SiO2-Al2O3 melts were measured in the temperature range of 1723 to 1923 K by a gas-slag equilibration technique using CaO, Al2O3, and Mo crucibles. Nitrogen content in slag, (mass-% N), was proportional to oxygen partial pressure, P(O2), to the power of -3/4 at constant nitrogen partial pressure, P(N2). The values for C(N3-) increased linearly with increasing temperature and increased with the content of nitride formers, SiO2 and Al2O3, but the effect of SiO2 on C(N3-) value was found to be greater than that of Al2O3. The activity coefficients of Si3/4N in the CaO-SiO2 melts tended to increase with increasing the content of SiO2.