The solubilities of nitrogen in CaO-SiO2-Al2O3 slags were measured usi
ng N-2-H-2 gas or silicon nitride ceramics at 1823 K. Moreover Vickers
hardness of the quenched slags was measured. Based on these results,
the dissolution mechanism of nitrogen into the slags was discussed. Th
e nitride capacity measured by an equilibrium between N-2-H-2 gas and
slag under a given partial pressure of oxygen decreased with increasin
g SiO2 content. This result suggested that nitrogen dissolved in the s
lags by exchanging reaction between oxygen ion and nitrogen. On the ot
her hand, the nitride capacity by an equilibrium between silicon nitri
de ceramics and slag was 10(2) to 10(4) times larger than that from ga
s-slag equilibrium. Although the nitride capacity was calculated assum
ing that silicon nitride decomposed, it was not in agreement with that
from gas-slag equilibrium. Therefore it was estimated that the dissol
ution mechanism of nitrogen using silicon nitride ceramics was differe
nt from that obtained by nitrogen gas. Vickers hardness of the solidif
ied slag after silicon nitride dissolution decreased with increasing S
iO2 content and this tendency was the same as the influence of silica
on nitrogen solubility. This suggested that network formation in the s
lag was strengthened by the dissolution of silicon nitride, which was
estimated to proceed with the formation of complex network between Si-
N (or Al-N) and oxide.