Hydrothermal reaction sintering (HRS) is one of the most efficient methods used to obtain very high relative density (e.g. > 99%) ceramic materials. As given in Eq. (I), reaction between highly pure metal (Me) powder or chips and water at a specific temperature (500–1000 °C) and pressure (100 MPa) levels results in the formation of sintered metal oxide (MeO) and hydrogen (H2) gas [53].