The mixture was then poured into a

The mixture was then poured into a : a) 10.0 mm diameter Inconel die with pistons equipped with a Teflon gasket in order to maintain the system closed for the hydrothermal sintering (Fig. 2a), or b) 12.7 mm diameter stainless steel die and uniaxially pressed using a Carver Model M press for the cold sintering (Fig. 2b). In both cases, the mixture was first pressed under 320 MPa at room temperature for 10 min to allow further particle rearrangement,then the temperature was increased to 155 °C with a 10 °C.min−1 heating rate average.