Although HRS is one of the earliest techniques, it utilizes a metal powder or chips that are oxidized under hydrothermal conditions by supercritical water in a capsule under mild pressures (100 MPa) and mid/high temperatures (1000℃). The process consumes less energy compared to conventional sintering of the same composition, and it enables to sinter materials having high vapor pressure, phase transformation and/or high decomposition rate at sintering temperatures.