Abstract
We present the results of a part of investigations on the diffusion characteristics of transition elements in the noble metals. In an earlier paper, the work on copper has been reported. The diffusion behaviour of titanium, vanadium, chromium and manganese in silver is reported here. The interdiffusion coefficient of silver-titanium alloys have been determined by Grube’s method in the temperature range between 1051 and 1220 K using (pure Ag)–(Ag-0.23 at% Ti alloy) and (pure Ag)–(Ag-0.45 at% Ti alloy) couples. It is shown that the interdiffusion coefficient is independent of concentration and hence can be regarded as the impurity diffusion coefficient of titanium in pure silver. The impurity diffusion coefficients of vanadium, chromium and manganese in pure silver have been determined by the residual activity method with radioactive tracers 48V, 51Cr and 54Mn in the temperature ranges between 1012 and 1218 K, between 1023 and 1215 K and between 883 and 1212 K, respectively. The temperature dependence of the impurity diffusion coefficients in silver can be expressed by the following equations along with the probable errors:
DTi/Ag=(1.33−0.36+0.49)×10−4exp[−(198±3)kJ mol−1⁄RT]m2⁄s,
DV/Ag=(2.72−1.28+2.40)×10−4exp[−(209±6)kJ mol−1⁄RT]m2⁄s,
DCr/Ag=(3.26−0.91+1.26)×10−4exp[−(210±3)kJ mol−1⁄RT]m2⁄s,
DMn/Ag=(4.29−1.03+1.35)×10−4exp[−(196±2)kJ mol−1⁄RT]m2⁄s.
The difference in the activation energies between the impurity diffusion of the 3d-transition metals and the self-diffusion in silver has been calculated by the electrostatic theory applying LeClaire’s model with the Friedel type oscillating potential about an impurity atom in silver. For all the elements, the calculated values are smaller than the experimental values. However, the atomic number dependence of the calculated values agrees well with that of the experimental values.