Indian clays are known for their smecticity. One such clay sample collected from Bhuj (Gujarat) was characterised and modified by successive sedimentation processes for different time intervals. The non-plastic components of clay, viz., quartz, illite, iron oxide, CaO, MgO, and organic matter were removed in different steps, as the heavy impurities in the clay-water suspensions, settle down during sedimentation. The free iron oxide present in clay suspension was reduced by giving sodium citrate-bicarbonate-dithionite treatment and iron content was further reduced from 1215 per cent to 57 per cent respectively. The organic matter was removed by sodium acetate-H 2 O 2 treatment. The modified clay so obtained was characterised by thermal analysis, FTIR, and XRD, SEM and TEM. The cation exchange capacities of original and modified clays were determined both by methylene blue method and ammonium acetate method. The cation exchange capacity is found to enhance from 120130 meq/100 g to 135145 meq/100 g. Using the above procedure, 92 per cent smecticity was obtained. Organophilisation of purified clay (smectite) was carried out by intercalation with alkyl ammonium salt. The XRD analysis showed enhancement of interlamellar spacing from 1.294 nm to 2.855 nm.
Ceramic matrix composites are high performance, high temperature materials of scientific as well as technical interest. During the last decade there has been great interest in development of oxide composites for structural as well as electrical applications. Silica/silica composites have been developed using electrophoretic infiltration. Matrix was derived from silica sol and colloidal silica sol having different process routes, solid content (24% -35%), pH (2 -3.5) and viscosity (55 -70 mpoise). The effect of densification parameters such as applied voltage, infiltration time, thickness of preform, viscosity, etc., have been studied and discussed.Composites processed at lower potential difference and under constant current density conditions yield better matrix microstructure and particle bonding, as well as interlaminar bonding. The composites fabricated with colloidal silica sol exhibit 60% sintered density.
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