  Metal ion implantation into ceramics has been demonstrated to be an effective
and controllable technique for tailoring the surface electrical conductivity of
the ceramic piece, and this approach has been used in a number of applications.
Importantly, it provides a method for grading the voltage drop across high
voltage insulators, and thereby increasing the maximum operational voltage that
can be applied across the insulator without surface flashover. However a
concern for the use of the method is the long term stability of the
implantation-induced conductivity, this especially so if the implanted metal
species is readily oxidized. Here we report on our examination of the long-term
behavior of the surface conductivity of titanium-implanted alumina. The results
indicate that after an initial drop of as much as 40% in the first few weeks
after implantation, the conductivity shows only a very slow decrease of about
10% over the following year. This degree of change should be quite sufficiently
small to be unimportant for all but the most demanding situations.
