Wetting behaviour and reactivity between liquid Gd and ZrO2 substrate

The wetting behavior and reactivity between molten pure Gd and polycrystalline 3YSZ substrate (ZrO2 stabilized with 3 wt% of Y2O3)were experimentally determined by a sessile drop method using a classical contact heating coupled with drop pushing procedure. The test was performed under an inert flowing gas atmosphere (Ar) at two temperatures of 1362?C and 1412?C. Immediately after melting (Tm=1341?C), liquid Gd did not wet the substrate forming a contact angle of ?=141?. The non-wetting to wetting transition (? < 90?) took place after about 110 seconds of interaction and was accompanied by a sudden decrease in the contact angle value to 67?. Further heating of the couple to 1412 ?C did not affect wetting (?=67??1?). The solidified Gd/3YSZ couple was studied by means of optical microscopy and scanning electron microscopy coupled with X-ray energy dispersive spectroscopy. Structural investigations revealed that the wettability in the Gd/3YSZ system is of a reactive nature associated with the formation of a continuous layer of a wettable reaction product Gd2Zr2O7.