Solubility and dissolution mechanism of nitrogen in molten slags by N_2 gas ro silicon nitride ceramics.

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The solubilities of nitrogen in CaO-SiO_2-AI_2O_3 and Na_2O-CaO-SiO_2 slags were measured using N_2-H_2 gas or silicon nitride ceramics. Moreover Vickers hardness and XPS analysis of the quenched slags was measured. Based on these results, the dissolution mechanism of nitrogen into the slags was discussed.The nitride capacity measured by an equilibrium between N_2-H_2 gas and slag under a given partial pressure of oxygen decreased with increasing SiO_2 content. This result suggested that nitrogen dissolved in the slags by exchanging reaction between oxygen ion and nitrogen. On the other hand, the nitride capacity by an equilibrium between silicon nitride ceramics and slag was 10^2 to 10^4 times larger than that from gas-slag equilibrium. Although the nitride capacity was calculated assuming that silicon nitride decomposed, it was not in agreement with that from gas-slag equilibrium. Therefore it was estimated that the dissolution mechanism of nitrogen using silicon nitride ceramics was different from that obtained by nitrogen gas.Vickers hardness of the solidified slag after silicon nitride dissolution decreased with increasing SiO_2 content and this tendency was the same as the influence of silica on nitrogen solubility. This suggested that network formation in the slag 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. The results of XPS analysis supported these estimations.