Effects of electrode material on charge injection, transport, energy storage and dissipation in highly purified water

Extensive Kerr electro-optic field mapping and voltage/current measurements have been taken with highly purified water over the temperature range of T=0–30°C using parallel plane electrodes with average field strengths up to 160kV/cm. The Kerr constant of water B was measured to be B≃3.4–3.6×10⁻¹⁴m/V² for free space light wavelength of 590nm and only slightly varies with temperature over the measurement range. For a step high voltage, there is no volume space charge at t=0+. For times greater than 500µs, stainless steel and copper electrodes generally inject positive charge, although under some conditions with mixed electrodes they injected negative charge; aluminum electrodes only inject negative charge; while brass electrodes can inject either positive or negative charge. Thus, by appropriate choice of electrode material combinations and voltage polarity, it is possible to have uncharged water, unipolar charged negative or positive, or bipolar charged water. Generally, the bipolar case allows a higher applied voltage without breakdown, presumably due to the lower electric field strengths at the electrodes due to the space charge shielding. Although injected space charge increases the stared electric energy over the capacitive space charge free energy, (1/2)Cv², for ohmic conduction the energy delivered to a resistive load is reduced because of internal dissipation in the capacitor. Volume space charge makes no contribution to the load energy but increases the dissipation in the capacitor.