Premium
Novel Coagulation Method for Direct Coagulation Casting of Aqueous Alumina Slurries Prepared Using a Poly(Acrylate) Dispersant
Author(s) -
Prabhakaran Kuttan,
Raghunath Sooraj,
Melkeri Anand,
Gokhale Nitin Madusudhan,
Sharma Suresh Chandra
Publication year - 2008
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2007.02122.x
Subject(s) - dispersant , slurry , coagulation , aqueous solution , chemical engineering , acrylate , materials science , adsorption , dispersion (optics) , casting , particle (ecology) , particle size , chemistry , polymer chemistry , composite material , polymer , organic chemistry , copolymer , psychology , physics , oceanography , psychiatry , geology , optics , engineering
Coagulation of concentrated aqueous alumina slurries prepared using an ammonium poly(acrylate) dispersant by MgO has been studied for direct coagulation casting (DCC). A small amount of MgO (0.2 wt% of alumina) increased the viscosity of the concentrated alumina slurry with time and finally transformed it into a stiff gel. The mechanism of coagulation is proposed such that the time‐delayed in situ generation of Mg 2+ ions from the sparingly soluble MgO forms Mg–poly(acrylate) with the unadsorbed ammonium poly(acrylate) molecules in solution that shift the poly(acrylate) adsorption equilibrium toward the left by depleting the poly(acrylate) molecules adsorbed on the alumina particle surface. This leads to insufficient dispersant coverage on the particle surface and coagulation of the slurry. DCC using MgO is possible only if the slurry is prepared at a dispersant concentration higher than that required for optimum dispersion as the slurries prepared at the optimum dispersant concentration underwent premature coagulation. The gelation time could be tailored within 20 min to a few hours by maintaining the temperature in the range of 70°–30°C. The wet coagulated bodies prepared from 50 vol% alumina slurry showed a compressive strength of nearly 0.05 MPa.