Role of organic additives on non-aqueous tape casting of SiAlON ceramics

Suspensions consisting of precursor α/β SiAlON forming powders, azeotropic solvent mixture of 60 MEK/40E, dispersant, binder, and plasticizer were optimized for tape casting by rheological measurements and tape properties. Sodium tripolyphosphate (STPP) was introduced as a dispersant for low temperature applications of α/β-SiAlONs. Optimum STPP amount was determined as 0.012 g/m2 (of the particle surface) for stable α/β-SiAlON suspensions. Different amounts of binder/plasticizer mixtures were added to the slurries and the effects on rheological and green tape properties were investigated. Green tapes with dibutyl phthalate (DBP), and plasticizer mixture, poly(ethylene glycol) (PEG) and DBP, exhibited centered cracks with high plasticity, on the other hand, polyvinyl butral (PVB) and PEG showed no crack but low plasticity. Therefore, many different parameters were found to be effective on final tape properties. In addition, tapes were prepared with 6 vol% PVB + PEG, sintered at 1800 °C for 2 h and exhibited almost 97%TD in room temperature applications of α/β SiAlONs.