Negative point-to-plane corona discharge in humid air — The effect of gap space on ionic species

A mass-spectrometric study of negative ions, extracted through small orifice in a plane electrode, was carried out in flowing ambient air, having relative humidities within the range of 40% to 50% and pressures from 5 kPa to 30 kPa. The effect of distance between the point and plane electrodes, as well as the effect of discharge current, on the mass spectra has been investigated. A most important observation was the presence of cluster ions CO3⁻·(H2O). Other ions were also found mostly in cluster forms. An unknown cluster ion having e/m = 126 was found, in agreement with earlier reported experiments (de Vries, et. al.). The increase of electrode gap distance caused a reduction of O3⁻·(H2O). groups and an increase of O3⁻·(H2O)i groups of ions as Observed in the mass-spectra. The efficiency of corona treatment of polymer materials in air will also be discussed in relation to the obtained results.