Influence of Water, Acid Rain and Bentonite on Ionization Characteristics of Sand under Lightning Impulse Voltage

Change in soil ionization surrounding a ground rod electrode after impulse voltage application with addition of water, acid rain and bentonite to different sized sand is examined. Impulse voltage and current responses in a rod-plane configuration show a characteristic change in sand ionization and breakdown with addition of water and gap length but no effect from voltage polarity. Soil ionization voltage (V₅₀) and time to ionization (t_bd) of sand are found to be increasing with increase in its grain size. Increase in water content in sand decreases the V₅₀ and t_bd indicating increased ionization activity. Acid rain-sand mixture shows approximately the same V₅₀ as water mixed with sand, but a lower t_bd due to increased ion concentration and new functional groups formation, as observed through FTIR patterns. Bentonite-sand mixture shows lower V₅₀ than sand, especially with large grain size due to filled voids. This is attributed to a decrease in permittivity and an increase in plasma temperature after addition of bentonite to sand, as verified by measurements. Modifications of the physico-chemical properties of sand and bentonite are also observed when the samples are subjected to successive impulse voltages; these changes are verified by XRD, FTIR, VSM, LIBS and DRS analyses.