High-temperature wettability measurements in metal/ceramic systems – Some methodological issues

Methodological differences and inconsistencies in characterizing the wettability in molten metal/solid ceramic systems between different laboratories and research groups are a major source of discrepancy in the measurements of contact angle, θ, surface tension, σlv, and work of adhesion, Wad, reported in the literature. The extreme sensitivity of these parameters to test conditions leads to considerable disagreement between test outcomes for a particular system from different investigators. In this paper, we focus on some methodological considerations that influence the wettability test outcomes in high-temperature systems. In particular, we highlight the role of substrate surface and atmosphere on the contact angle values in ceramic/metal systems. We also identify practical problems in executing the sessile drop wettability test that influence the test outcomes, and argue in favor of increased uniformity and consistency in conducting the tests and greater transparency in reporting the test conditions and test outcomes in order to minimize the current discrepancies in measurements.