High-Temperature Contact-Angle Measurement for Molten and Solid Interfaces

A high-temperature contact-angle instrument measures wetting behavior between melts and solids in ceramics, high-temperature alloys, and composites. Specimens are heated to nearly 2,000 °C under vacuum or a controlled atmosphere while the spread profile of a molten drop on a solid substrate is recorded. The measurement locates the liquid–gas–solid contact line. At thermal equilibrium, the contact angle reflects the balance of solid–gas, solid–liquid, and liquid–gas interfacial tensions. In the sessile-drop method, a solid substrate and powdered or bulk melt are placed in a high-purity ceramic or refractory-metal crucible. Molybdenum wire, tungsten mesh, or silicon-molybdenum elements heat the furnace under PID control until the melt forms an axisymmetric drop. A CCD or CMOS camera with a long-focal-length microscope and coaxial blue or white LED illumination images the drop through a quartz window. A narrow-band filter reduces blackbody-radiation interference. Software extracts the left and right profiles with subpixel edge detection and calculates the tangent angle at the three-phase contact point by circle fitting, ellipse fitting, or a Young–Laplace fit. Video recording can track contact angle over the holding period and document interfacial reaction, melt spreading, or substrate dissolution. Applications include wetting of ceramic substrates by metal or glass brazes, liquid-metal or ceramic-melt infiltration of carbon and silicon-carbide fibers, wetting between slag and refractory materials, interaction between metal melts and mold materials, and compatibility studies of nuclear fuel and cladding materials. Atmosphere control is important because oxidizing or reducing gases change surface chemistry and interfacial tension. The system may provide vacuum, inert gas, or reactive gas such as H₂ or N₂.