Kaolinite under pressure at audio frequency range and its electrical features

Abstract

ABSTRACT Electrical features of a humid kaolinite specimens was measured at various pressures and at various frequencies . Surface impedance is supposed on kaolinite particle surfaces (from humidity), chemical reaction and charge transport along surface hydroxyls of kaolinite edges besides the permanent negative charges. Classic mixture laws do not support the interpretation of electrical properties, especially, at high pressures. Accordingly, interpretation was made with percolation threshold theories. Pressure increase causes decrease in pore spaces and accordingly increases possible connections of pore distances filled with humidity to total pore spaces after applying pressure. With pressure increase, the pore voids between particles decrease and water conducting paths increase. Also, dielectric constant and conductance increase with increase of pressure. On the other hand, at a certain pressure, at low frequencies, a noticeable increase of capacitance with pressure increase, that tends to reach constant value, for relatively high pressures. The diffusion and interfacial mechanisms was suggested to interpret samples with increase of pressure and frequency. The latter mechanism acts simultaneously with surface chemical reaction mechanism (Debye behavior) to give a depressed arc (relaxation time distribution). Finally, the pressure and frequency are effective factors on electrical properties.