Evaluation of unusual change in contact angle between MgO and molten magnesium

The wetting of MgO by molten magnesium was measured between 973 and 1273 K using an improved sessile drop method. In this method, molten magnesium was set around the sample droplet to prevent oxidation of the magnesium droplet. A significant volume loss of the droplet was observed over 1073 K due to the high vapor pressure, and the contact angle was underwent an unusual change over 1173 K. The contact angle first decreased and then increased. This phenomenon occurred due to the pinning of the three-phase line at deep ditch. This change in the contact angle is an apparent change in contact angle. The intrinsic contact angle should be decided using the initial value or the maximum value just before the disappearance of the droplet. For any high vapor pressure system, such a change in contact angle can be observed at high temperatures.