Sulfur partial pressure

The influence of temperature on the sulfidation kinetics of Ni36Al at a constant sulfur partial pressure of 6.4X10-7 bar is shown in Fig. 3a. The sulfidation kinetic follows the parabolic rate law over the whole temperature range and the sulfidation rate increases with increasing temperature. From the Arrhenius plot of the parabolic rate constants for sulfidation of Ni36Al in Fig. 3b we calculate an apparent activation energy of 58kJ/mol. 

The cross-section in Fig. 6 shows a scale formed in H2-l vol.% H2S. This mixture corresponds to a sulfur partial pressure which is not sufficient to form an outer Ni3S2 scale. Consequently the scale consists of NiAl35S5 5 only. The Al-depleted metal surface zone is thicker now probably due to Ni-diffusion backwards into the matrix. 

El-Dahshan ME, Whittle DP and Stringer J, Effect of presulfidation on the oxidation behavior of Co-based alloys. Part I. Presulfidation at sulfur partial pressures above the dissociation pressure of cobalt sulfide. 

For zinc sulfide concentrate, sulfur is fixed by reduced iron present in the Fe-S-O matte while zinc is volatilized. For the oxide feed, zinc oxide is reduced by iron present in the Fe-S-O matte. From the Fe-S phase diagram (1), the sulfur partial pressure in equilibrium with molten stoichiometric FeS matte is in the range of 10 to 1.0 atm depending on the temperature, which is obviously too high to avoid the back reaction ... 

Nevertheless, certain conclusions may be drawn from even a brief perusal of this work. These include the necessity of positively identifying electrochemical waves by methods such as the standard addition technique. Moreover, there is a clear need to control the sulfur partial pressure over melts. Lastly, more attention must be given to the role of solvent and solute cation composition, since many of the apparent disagreements in the literature have arisen because authors have employed different alkali and alkaline earth sulfides. 

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