TITLE:
Thermally induced gelation of alumina shaping-neutron scattering and rheological measurements
AUTHORS:
Papiya Biswas, Kotikalapudi Rajeswari, Somasani Chaitanya, Roy Johnson, Swapnil A. Prabhudesai, Veerendra K. Sharma, Subhankur Mitra, Ramaprosad Mukhopadhyay
KEYWORDS:
Ceramics; Polymers; Heat Treatment; Molecular Dynamics
JOURNAL NAME:
Open Journal of Inorganic Chemistry,
Vol.3 No.2,
April
30,
2013
ABSTRACT: Thermally induced gelation forming based on methylcellulose
is recently being explored as a simple and environmentally benign process.
Alumina slurry containing 0.1 wt% methylcellulose is subjected to Quasi Elastic
Neutron Scattering (QENS) and rheological measurements in gelation
temperature regimes to evolve a possible mechanism of the forming process. A
reduction in diffusivity of water in the slurry from 2.16 to 1.92 × 10-5 cm 2 ·s-1after exposure to 55°C is
observed with QENS. This is found to be well correlated with a steep increase
in viscosity from 1.2 Pa.s till 50°C to 50,000 Pa.s at 55°C. QENS studies revealed
the diffusion of water occurs by jump diffusion with the jump lengths
distributed randomly. Further, for the entire sample much longer residence time
is found as compared to bulk water, which is due to hydrophilic interaction
of water molecules with the methylcellulose in the slurry. Reduction in
diffusivity of water along with the steep increase in viscosity could be understood as the strong, cross-linked polymer-solvent
irreversible gel formation in presence of alumina which is responsible for the
retention of a consolidated shape of the ceramic green body. Samples maintained
the integrity while heat treatments achieving close to theoretical density
values of3.98 g·cm-3 at 1550°C.