The fractionation of the oxygen isotopes in the formation of oxide films on copper has been measured at 0, 25, and 100°C on granular copper and copper foil by determining the O18/O16 isotope ratio in the residual unreacted oxygen gas after a fraction of the oxygen has reacted. An analysis is given of the mixing problem and of the kinetics of the reaction. Two fractionation factors, one of unity or less than unity for an initial rapid reaction and one greater than unity for the slower and (approximately) steady state reaction are required to explain the data. The fractionation factor for the steady state reaction is calculated to be 1.045, 1.042, and 1.037 at 0, 25, and 100°C, respectively. All of these values are greater than the lower limit of 1.029 given by the rate theory of Bigeleisen in contrast to an earlier conclusion of Bernstein.

Topics
Isotopes, Oxides, Transition metals
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© 1957 American Institute of Physics.
1957
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