EFFECTS OF ELECTRODE MATERIAL ON CHARGE INJECTION AND TRANSPORT IN HIGHLY PURIFIED WATER.

Extensive Kerr electrooptic field mapping and voltage/current measurements have been carried out with highly purified water over the temperature range of T equals 0-30 degree C using parallel plane electrodes with average field strengths up to 160 kV/cm. The Kerr constant of water, B, was measured to be B congruent 3. 4-3. 6 multiplied by 10-**1**4m/V**2 for free space light wavelength of 590 nm; it varies only slightly with temperature over the measurement range. For a step high voltage, there is no volume space charge at t equals 0// plus . For times greater than 500 mu s, 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 charges. Thus, by an 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 caused by the space charge shielding. Although injected space charge increases the stored electric energy over the capacitive space charge free energy, (1/2)Cv**2, for unipolar drift dominated conduction the energy delivered to a resistive load is reduced because of internal dissipation as the charge migrates to the electrodes.