| A rotating disc geometry and Zn-Sb alloy powder were used to study the kinetics of cobalt cementation with zinc. In the absence of initial zinc ions and above 55℃, it is considered that the overall cementation rate would be controlled by mass transfer rate through the aqeous diffusion boundary layer, however, below 55℃ the reaction mechanism would be changed. In the presence of 100 gr/l Zn^(2+), the rate of cementation was very slow, which means that the reaction mechanism would be changed. By using Zn-Sb alloy instead of zinc metal as a precipitant, the rate was much increased even in the 100 gr/l Zn^(2+) solution and hence overall reaction rate would be controlled by mass transfer rate above 85℃. The similar phenomenon was found by using powdered Zn-Sb alloy as a precipitant. |
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