On the Growth of Metal Whiskers by Hydrogen Reduction of Halides

Observations have been made of the pressures of hydrogen and hydrogen halide gases prevailing during growth of a variety of metal whiskers by hydrogen reduction of volatile metal halides. The orders of magnitude of the maximum metal activities observed are only 1 to 100 rather than the maximum thermodynamically feasible values of 104 to 106 that might be attained in these reactions. This result is more in accord with current theories of whisker growth. It appears that the reduction of metal halide occurs primarily on the whisker surface and that metal halide vapor rather than metal vapor provides most of the vapor-phase mass transport during whisker growth by this process.