Fig. 7 shows the comparison of liquid-bridging force and adhesion force for specimens B ~ E. The horizontal axis is the value of liquidbridging force, and the vertical axis represents the adhesion force calculated from both Eq. (5) and Eq. (6). As can be seen, the liquid-bridging force was even higher than the adhesion force, which was attributed to the partial melting of ash particles during the measurement of adhesion force. The adhesion force calculated from either Eq. (5) or (6) was enhanced with the increase of liquid-bridging force. It is clear that the measurement of liquid-bridging force predicts the trend of adhesion force for different kinds of specimens.