A study of the time-dependence of electrodiffusion in quartz

The time dependence of the each channel reduction and the replacement of the alkali at the aluminum site by hydrogen was measured in AT-cut samples cut from bars of cultured quartz from several sources. Low-temperature infrared measurements were used to monitor the growth of the Al-OH infrared band versus sweeping time. The Al-OH signal increased rapidly for short sweeping times and reached saturation in 1-2 h. First-order kinetics of the form (1-exp(-k₁t)), where t is the time, gave a good approximation to the replacement of the alkali by hydrogen at the aluminum. The sweeping current decreased rapidly during the initial part of the run and then become constant. It is found that, when the current remains constant to within ±2%, the replacement of the interstitial alkali at the aluminum site is complete. After the samples were etched, the etch channels were then counted. The kinetics of the tendency to form etch channels was significantly different from the replacement of the interstitials. Initially, the number of etch channels decayed exponentially with sweeping time. At longer times, the decay shifted to a much slower rate, which may also be exponential. These results suggest that there may be several mechanisms for the removal of the tendency to form etch channels or that there are several types of channels