Evaporation Mechanism of Cu from Liquid Fe Containing C and S

A number of liquid–gas experiments were carried out in order to elucidate evaporation mechanism of Cu from liquid Fe containing C and S. Rate of Cu evaporation in liquid Fe droplets at 1873 K (1600 °C) was determined using electromagnetic levitation equipment. Evaporation rate of the Cu under various conditions (flow rate of gas mixtures, initial C, and S concentrations) was examined. It was found from a series of kinetic analyses of the experimental data that Cu evaporates in forms of Cu(g) and CuS(g). As was reported for the Sn evaporation from liquid iron (Jung et al. Met. Mater. Trans. 46B, 250–258, 2014), S plays two roles for the evaporation of Cu: accelerating the rate by forming CuS(g) and decelerating the rate by blocking evaporation sites. As a result of these combinatorial effects, the evaporation of Cu is decelerated at low S content, but is accelerated at high S content. Based on the elucidated mechanism, an evaporation model equation for Cu was developed in the present study, which takes into account (1) evaporation of Cu in the two forms (Cu(g) and CuS(g)), (2) surface blocking by S using ideal Langmuir adsorption, and (3) effect of C. The obtained rate constant of a reaction Cu ⁱ  + S ⁱ  = CuS ⁱ (g), k _CuS ^R , is 1.37 × 10⁻⁹ m⁴ mol⁻¹ s⁻¹, and the residual rate constant, k _CuS ^r , is 4.11 × 10⁻¹⁰ m⁴ mol⁻¹ s⁻¹ at 1873 K (1600 °C). Both of them were found to be one order lower than those for Sn evaporation.