Evaporation Rate of Copper from Molten Iron by Urea Spraying under Reduced Pressure

Abstract

Experiments were done by spraying urea (NH₂CONH₂) as its pyrolysis gases at the intervals of 5min onto molten iron containing 0.4 mass% Cu at 1600°C under reduced pressure. If urea amount per each spraying was more than 0.4g, the molten iron was suddenly splashed and slopped over the top of crucible during the experimental run, so that 0.3g of urea was sprayed in the subsequent experiments. Nitrogen concentration of the molten iron increased with increasing the number of urea spraying and the pressure of gas phase. It was 5 to 8 times higher than the concentration in equilibrium with nitrogen gas.
The following relationships were found between the rate constant (k) of copper evaporation and the pressure (P in Pa) : In the case of urea spraying, log k = -log P-0.762; without urea spraying, log k = -log P-0.996. These results show that even in the case of urea spraying the evaporation rate of copper was controlled by mass transfer through gaseous film on the surface of the molten iron. It was concluded that acceleration of copper evaporation by urea spraying may be mainly due to the evaporation as Cu(N₃)₂which has higher vapor pressure than metallic copper. The evaporation rate of copper somewhat decreased in the case of the molten iron containing 0.34 mass% C, because some part of urea was probably consumed by the formation of iron cyanide. Sulfur had little influence on the evaporation rate.