“…There are several manufacturing processes for the latter, among which are highlighted: the electron beam melting process [16], creep expansion of argon-filled pores [17], directional aqueous freeze casting [18], rapid prototyping techniques [19], laser-engineered net shaping [20], electric current activated/assisted sintering techniques [21,22], conventional powder metallurgy [23] and space-holder techniques [24]. In this last process, most of the space-holders (ammonium bicarbonate [25][26][27][28], carbamide [29] and PVA [30]) are completely evaporated at low temperatures, whilst others (e.g., sodium chloride [31][32][33][34][35]) are removed by a dissolution process, generally in water.…”