Wettability of mineral and metallic powders: Applicability and limitations of sessile drop method and Washburn's technique

Characterization of powder wettability is a prerequisite to the understanding of many processes of industrial relevance such as agglomeration which spans from pharmaceutical and food applications to metallurgical ones. The choice of the wetting fluid is crucial: liquid must wet the powder in order for agglomeration to be successful. Different methods for wettability assessment of powders were reported in the literature, however the sessile drop method and capillary rise test remain among the most widely employed because they are easy to perform and inexpensive. In this paper, the application and limitations of sessile drop method and capillary rise test on mineral and metallic surface were discussed. This work provides a collection of wettability measurements using several powders and binders which are involved in the manufacturing process of welding wires. Moreover a new reference liquid for the calibration of capillary rise method was proposed.

Graphical abstractPhotograph of a potassium silicate droplet on Fe–Mn surface using the Photron Fastcam-Pci® video recorder. The apparent contact angle θ, the diameter, D and the height, H of the droplet after the impact on powder are visualized.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Sessile drop and Washburn's tests on mineral and metallic powders are compared. ► Kinetics plays a more important role than thermodynamics in dictating wettability. ► The choice of the best wetting liquid is a critical step in Washburn's experiments. ► A surfactant solution with fluorinated ethers was the best total wetting liquid. ► Washburn's test performs better than sessile drop method for the powders tested.