Repulsive Capillary Force between two Plates Linked by a Concave Molten Slag Bridge

Abstract

In the previous papers, 1,2) the relaxation tests of molten alumonosilicate slags were carried out to evaluate the mechanical properties of molten slags. Namely, molten slag (35mass%CaO-35mass%SiO 2 -30mass%Al 2 O 3 ) drop of about 0.05 g was kept at 1 723 K between two Pt disks (6.5 mm dia.) and then was compressed at various compression rates until particular displacement distance, then the compression process was stopped and the stress relaxation with time was measured. The details of the experiment can be found elsewhere.1) The observed typical stress relaxation test is shown in Fig. 1. The stress relaxation curve was consisted of 3 stages. The force became maximum at maximum stress (Stage I). After this, the force decreased sharply (Stage II). Then the force was decreased gradually and asymptotically approached to the constant value (Stage III). Intriguingly, the molten slag showed the existence of the repulsive residual force even without the compression force.In the previous paper, 1) we supposed that the origin of this residual force was due to the structural rearrangement difficulty of the aluminosilicate molten slags. Namely the original structure of slags was changed to differently configurated structure during the compression process. After the elimination of compress force, it tried to return to the originally configurated structure. The structural relaxation should to involve breaking and making of the bonds between ions or silicate and aluminate units. The bending or distortion of silicate or aluminate units can be easily restored to the original state, however, the whole structural rearrangement among silicate and alumina units by the interatomic or intermolecular breaking and making of bonds can be difficult. Thus, the deformed structure may stay at the meta-stable configurated structure. This meta-stable structure could possess higher energy than that of original structure. This causes the repulsive residual forces. Now we realize, however, that the meta-stable structure may not the main reason of the repulsive force.Initially we excluded the effect of surface tension because the molten slags after the compression showed the concave liquid bridge as shown in Fig. 2. Generally speaking, two wetted surfaces can stick together with great strength if the liquid wets them with an angle qϽp/2. The q angle is defined in Fig. 3. Namely, the existence of the concave liquid bridge between two plates suggests the attractive force between two plates. The Laplace pressure within liquid bridge between wetted two plates can be ex- (1) where q is the wetting angle, g is the surface free energy, H is the plate to plate distance, and R is the radius of the liquid bridge, and all these parameters are shown in Fig. 3 As long as qϽp/2, DP can be negative or the force F between the plates can be attractive and the force can be expressed by Vol. 49 (2009), No. 11, pp. 1814-1815 Note Fig. 1. Schematic description of stress relaxation curve for the molten aluminosilicate slag.