Investigation of the contact angles between various molten metals and substrates of niobium and zirconium. Final report. [Sessile drop technique]

The sessile drop technique was utilized for the determination of the contact angles between droplets of liquid tin, indium, and gallium; and substrates of niobium and zirconium. Contact angles, theta, were measured for various substrate surface roughness and over the temperature range 30 to 650/sup 0/C. Values of theta for all of these systems were found to be greater than 90/sup 0/ i.e., constituting a case of nonwetting between the liquid metals and the substrates. Three characteristic regions of the temperature dependence of contact angles were observed. A steady-state region in which the contact angle is relatively independent of temperature was preceded and followed by regions in which theta decreased rapidly with increasing temperature. For the steady-state or second region, contact angles were found to be independent of time whereas in the third region contact angles showed a decreasing trend with time at constant temperature. In accordance with theoretical predictions for theta greater than 90/sup 0/, increasing roughness of the substrate caused a corresponding increase in theta. Electron microprobe analyses showed that only the Ga--Zr system exhibited evidence of diffusion at the interface. Photographs of the sessile drop of this system over a period of time indicated that the drop had spread over a greater area thus supporting the possibility of a surface diffusion mass-transport process