The dissolution of lime in iron silicate melts.

A study has been made of the dissolution of lime in iron silicate melts. The experiments were carried out under an inert atmosphere of argon at 1300°C in a vertical tube furnace. A small cylindrical pellet of lime was preheated to the melt temperature before being immersed in the melt contained in an iron crucible. After a preselected period, ranging from 10 seconds to 9 minutes, the pellet and crucible were withdrawn and water quenched for microscopic examination and electron probe microanalysis. The reaction between line and fayalite produced two reaction products, solid dicalcium silicate and a liquid rich in iron oxide. As dissolution proceeded, the precipitated particles of 2CaO.SiO[2] sintered together to form a tenacious layer between the two reactants. The rate of dissolution was calculated from the volume loss of partially dissolved pellets. A kinematic model has been derived to fit the qualitative observations and the quantitative results. The rate controlling step was initially the transfer of lime to the liquid -- 2CaO.SiO[2] interface but later the transport of melt became rate controlling. The effects of manganese oxide, calcium fluoride and boric oxide on the dissolution process were also examined. The presence of manganese oxide in the melt was detrimental to idle dissolution of lime. Even though the 2CaO.SiO[2] particles formed a porous layer, the overall kinetics were retarded by the increased viscosity of the melt. In contrast calcium fluoride and boric oxide accelerated the rate of dissolution by reducing melting points and viscosities. The rate of dissolution was also increased when the pellet was rotated in the melt. With large lime pellets, the dissolution rate was lower than that of corresponding smaller pellets in similar melts. To ascertain whether these results were characteristic only of the dissolution of synthetic hard burnt lime, immersion experiments were carried out using commercially available lime.