“…These techniques can be summarized: i) Reaction Bonding Silicon Nitride (RBSN), ii) Hot Pressing Silicon Nitride (HPSN), iii) Sintering Silicon Nitride (SSN), iv) Sintering Reaction Bonding Silicon Nitride (SRBSN), v) Hot Isostatic Pressing Silicon Nitride (HIPSN), vi) Hot Isostatic Pressing Reaction Bonding Silicon Nitride (HIPRBSN), vii) Hot Isostatic Pressing Sintered Silicon Nitride (HIPSSN) and viii) Hot Isostatic Pressing Sintered Reaction Bonded Silicon Nitride (HIPSRBSN) [20,[22][23][24][25][26][27][28][29][30][31][32][33][34]. It is very difficult to produce pure dense silicon nitride ceramics by means of conventional sintering (simple heating of powder compacts) due to the high degree of covalent bonding between silicon and nitrogen [35].…”