Binder burnout and sintering kinetic study of alumina ceramics shaped using methylcellulose

摘要

Ceramic components are generally processed by the techniques such as compaction, extrusion, injection molding, casting etc., and the selection of forming method is generally based on the complexity of the shapes. Additives such as binders, plasticizers, surfactants and lubricants, which are generally organic in nature, play a significant role to ensure the flowability of the mass which is critical in shaping of ceramics. Alumina (alpha-Al2O3) powder was subjected to torque rheometric studies to identify Critical Volume Binder Concentrations (CBVC) corresponding to specific processing regimes. An initial torque value of 3-4N-m for compaction followed by 6-7N-m for extrusion and 2-3N-m for casting regimes were observed. Viscosities of the pre-mixes prepared by the addition of methyl cellulose (C6H7O2 (OH)x(OCH3)y, (where x = 1.0-1.5 and y = 2-1.45) as a binder were also found to exhibit a similar trend in viscosity, corresponding to CBVC torque values and are shaped into green specimens. Green strength of the standard specimens (45 x 4 x 3 mm) was estimated through 3-point bend tests and exhibited a good correlation with the binder content. Binder burnout characteristics were also elucidated by TG/DSC technique and activation energy estimated is 75-110 kJ/mol for the thermal degradation of methylcellulose binder. Activation energy of 883 +/- 45 kJ/mol was estimated through kinetic analysis of sintering by the construction of the Master Sintering Curves (MSC).