To understand the applicability of

To understand the applicability of LPS to UCS Stage II we should determine whether or not a thin liquid film can be retained at the interparticle region, as shown in Figure 10. LPS cannot take place without the said liquid film because the film provides the pathway for atomic diffusion. Referring to the work by Kwon and Messing [39] the interparticle liquid film is subjected to two contrasting effects. The first is the squeezing of the liquid under the effect of the external pressure which tends to decrease the liquid film thickness (d in Figure 10). The second effect is the material removal induced by sintering (which tends to increased, as it removes the solid from the flat neck surfaces, for details see Ref. [39]). When the effects balance eachother an equilibrium thickness can be defined (deq). In order to determine deq, we should first be able to calculate the sintering kinetics. Our strategy, reductio ad absurdum, will therefore be the following: we will determine the LPS equations applicable to UCS Stage II (we assume a priori that the liquid film exists), then we will compare them with the liquid squeezing velocity. Then by considering the predicted film-thickness – and whether this is conducive to enabling the LPS to take place in the first place – we will assess the applicability of LPS to UCS Stage II in the case of porosity not completely filled by water. A short derivation of the LPS equations is reported below, with detailed calculations in the attached ’Supplementary Material’.