| The kinetics of arsenic cementation with iron was studied by use of rotating disc geometry and using iron powder. The rate of arsenic cementation with iron was very slow owing to the formation of nonconductive thin film of arsenic on the iron disc surface. However, the addition of Cu ions to the system as an activate reagent increased the reaction rate remarkably. The kinetics showed two steps first order reaction, and the initial rate constant was proportional to the square root of agitation speed as suggested from Levich equation, k＝0.62D^(⅔)ν^(-1/6)ω^(½). Above 55℃, the activation energy of initial stage was 3.4 ㎉ while that below 55℃ was 20.9㎉. In the enhanced region, however, the activation energy was 4.1㎉ above and 10.9㎉ below 55℃ respectively. Therefore, the reaction mechanism both in the initial and final stages considered to be changed from diffusion through a boundary layer above 55℃ to surface chemical control below 55℃. The deposit composed of a Cu-As compound and armorpous arsenic was found by the X-ray analysis. In the case of using iron powder the rate can be described in terms of the Fro¨ssling equation, Sh＝2＋0.4Re_p^(½)Sc^(⅓). |
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