16 巻 (1979) 9 号 p. 514-520
The thickness of a liquid bridge which induces an adhesive force between powder particles under high water vapor pressures was studied. For this purpose, adhesive force generated at contact points between spherical and plate specimens of Pylex glass was measured by using an electrobalance, then a pore size distribution calculated from an isotherm of water vapor desorption on Vycor glass at 10°C was compared with that obtaind from the nitrogen desorption isotherm at -196°C.
An adhesive force appeared at relative water vapor pressures (P/P0) above 0.4, and it increased considerably in the P/P0 range 0.65-0.75. Moreover, a capillary condensation occurred in a hollow Pylex capillary at P/P0 above 0.6. From the above results, a liquid bridge at contact points between particles is considered to be formed above P/P0 0.6. The thickness of the liquid bridge at P/P0 0.6 is calculated to be 37Å by adding “multilayer thickness” to the “Kelvin radius”. The average radius of the Vycor glass, calculated from a nitrogen desorption isotherm, was 20Å, whereas the average radius calculated from the water vapor desorption isotherm was 30Å. Such difference between the pore radii will be attributed to assumptions that the surface tension for the adsorbed water layer is equal to that for a bulk water and that the angle of contact is zero. Considering these facts, it is estimated that the thickness of the liquid bridge at P/P0 0.6 is within the range of 28-37Å.