Dielectric behaviour of hot pressed AlN ceramic exposed to inorganic acid vapours

Abstract

Dielectric behaviour of hot pressed AIN ceramic is studied before and after exposing the samples to inorganic acid (HCl and HNO₃) vapours with a specific aim to study the effect of these vapours on the dielectric constant (ɛ′) and dissipation factor (tan δ). Four samples having different volume percentage of porosity (0.2 to 15%) are selected for this study. Dielectric dispersion increases after exposing the samples to the above acid vapours. Tan δ also increases quite appreciably; the increase being more at higher porosity. Recovery studies show that the exposure effect is reversible. The exposure time dependence of ɛ′ and tan δ indicates that these parameters show a maxima at a particular exposure time. However, no such maxima is observed in the gravimetric measurements. The increase in dielectric parameters after exposure to acid vapours is explained in terms of the ionic conduction due to the dissociation of these vapours in the presence of moisture. The porosity dependence of this effect is discussed in terms of closed and open porosity reported by other workers.