After the formation of green bodies, densification was followed under 95 MPa pressure at RT, followed by the application of 190 MPa pressure at 300℃ for 90 min. The relative densities of natural hydrated, partially hydrated, and added water were found to be around 67%, 63–67%, and 75%, respectively. The study suggested that the addition of water enhances the densification [77]. Apart from those few detailed ones, there are numerous compositions obtained by using HHP as given in Table 1.