To understand whether these equatio

To understand whether these equations are applicable to UCS, NaCl was considered as a model system.The diffusion coefficient of electrolytes in water is of the order of 10−9 m2/s[42] and d in liquid phase sintering of ceramics is usually of the order of 1 nm [29]. We can furthermore assume a=1μm, Pext =50–200 MPa, T=300 K, Vs =27cm3/mol[31], and Sf =6mol/kg[34], corresponding to about 0.14 in molar fraction. The obtained sintering curve is reported in Figure 11(a). One can observe that, even assuming a very low value for k1 (i.e. 0.05), the sintering kinetics are irrationally high. These results suggest the non-applicability of LPS to UCS of NaCl, with previous works pointing out sintering times for NaCl+5 wt% H2O of the order of some minutes even at pressures up to 275 MPa [41]. Note that this does not exclude the possibility that LPS could take place inpressure-less conditions, for which the role of the capillarity pressure proposed in Eq. (1) should be properly accounted.