A NEW METHOD FOR THE CHARACTERIZATION OF THE WETTABILITY OF POWDERS

The wetting characteristics of fine powders play an important role in a variety of processes. The most important way of characterising the w ettability of a fluid/fluid/solid system is to measure the contact ang le. This paper describes a relatively simple method for the determinat ion of the contact angle on powdery materials. The technique involves the measurement of the dynamic contact angle which is formed when a li quid drop is placed on a horizontal porous surface. On the basis of th e measured dynamic contact angle as a function of time an ''apparent'' static contact angle has been defined, which gives a measure of the w ettability of porous solid systems by analogy with the wetting of non- porous solids. Determinations with glass beads and NaCl-powders as the test materials indicate that the measured value depends on the partic le size of the powder, the porosity and the temperature. It was conclu ded that the capillary penetration of the liquid droplet into the poro us media itself influences the wetting characteristics.