LOW-TEMPERATURE INTERACTIONS BETWEEN MOLECULAR-HYDROGEN AND ZIRCONIA - EFFECTS ON THE COMPOSITION, CHARGE AND WETTABILITY OF THE SURFACE

ZrO2 powders have been subjected to contact with molecular hydrogen at low temperatures T (25-200-degrees-C) and for variable duration (15 min-22 h). X-ray photoelectron spectroscopy determinations showed that the hydrogen treatment, whatever the adopted conditions, did not induce the formation of Zr3+ surface defects. Zr4+ spectra were, instead, found to be modified for treatments performed at T greater-than-or-equal-to 80-degrees-C. The same trend with the temperature of the treatment was observed for the reactivity of the electrical double layer. The values of the point of zero charge of samples treated at T greater-than-or-equal-to 80-degrees-C were observed to shift in the alkaline direction, the more so the longer the length of treatment. Static contact-angle measurements performed on ZrO2 layers deposited on glass platelets indicated that the wettability for water decreased upon H-2 treatment. Possible relations between the different observed effects are discussed.