Growth Rates of Aluminum Etch Tunnels

Growth rates of aluminum etch tunnels, formed by anodic dissolution in hot aqueous chloride solutions, have been measured by a new technique in which ac signals of about 1 Hz were superimposed on the dc applied current. SEM photomicrographs indicated that the superimposed current caused the tunnel widths to oscillate during etching. Local metal dissolution rates were thus obtained by dividing the wavelength of the width oscillations by the period of the current signal. It was found that growth velocities were constant with increasing tunnel length, and were independent of the frequency of the signal. An Arrhenius dependence of the growth rate on temperature, with an activation energy of 15 kcal/ mol, was obtained.