One of the first applications of HHP was conducted on a mixture of α-quartz and amorphous silica. After addition of NaOH including aqueous solutions, the blend was pressed under 180 MPa pressure. The sample then placed in autoclave which was heated in between 120 and 350℃ under 27 MPa pressure for 30 min [72]. In other studies; CaCO3 [74], and subsequently TiO2 was formed. In the process; TiO2 (800 nm average particle size) was mixed with water, placed in autoclave, compressed by the push rod to 200 MPa pressure while heated to 350℃ for 30 min. The relative density of sintered TiO2 pellet was found to be 71% [75].