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Direct Coagulation Casting of Alumina Suspension by High Valence Counter Ions Using Ca ( IO 3 ) 2 as Coagulating Agent
Author(s) -
Xu Jie,
Wen Ning,
Li Hexin,
Qi Fei,
Xi Xiaoqing,
Yang Jinlong
Publication year - 2012
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.1551-2916.2012.05239.x
Subject(s) - suspension (topology) , chemistry , zeta potential , dispersant , chemical engineering , coagulation , microstructure , valence (chemistry) , particle size , mineralogy , chromatography , nanoparticle , crystallography , organic chemistry , psychology , physics , mathematics , optics , homotopy , psychiatry , pure mathematics , engineering , dispersion (optics)
A new direct coagulation casting of aqueous alumina suspension was developed via controlled release of high valence counter ions from calcium iodate with increase in the temperature from 55°C to 70°C. The influence of calcium iodate on the rheology of alumina suspension was investigated. A small amount of calcium iodate increased the viscosity of the concentrated alumina suspension at high temperature and finally transformed it into a wet‐coagulated body. The mechanism of coagulation is proposed such as that the solubility of calcium iodate increases with increase in temperature. The high valence Ca 2+ ions diffuse into the double electrical layer of alumina particles surface through electrostatic attraction, reduces the zeta potential, hence decreases repulsive force between particles. Also reaction between Ca 2+ and citrate leads to insufficient dispersant coverage on the particle surface. Both factors contribute to the coagulation of the suspension. The coagulation time was from 1 to 4 h by maintaining the temperature in the range of 55°C–70°C. The wet‐coagulated bodies prepared from 50 vol% alumina suspension showed a high compressive strength of 2.6–3.2 MPa with uniform microstructure. The relative density of sintered sample is 99.4% at 1550 °C for 2 h with perfect microstructure.