Fig. 7. (A), (B) and (C) XPS signals of Al 2p, Al 2s, and O 1s of the printed samples at different sintering temperatures, respectively. (D) Schematic of the oxygen-propane flame burning experiment. (E) Picture of the flame, the Al₂O₃/Al composite sample before burning, during burning, and after burning. (F) Printed samples in other forms. The samples can be designed in any desired shape to fit any application. (G) Mass-produced Al₂O₃/Al composite crucibles. (H) Schematic of the composite under a high temperature condition. The sample is still electrically conductive and can be used as a refractory conductor. The shape can be designed in a computer program and fabricated without a mold or without handcrafting.