Heterocoagulation is a technique, where a homogenised mixture of ceramic and CNT is achieved using colloidal processing.Sun and Gao have used heterocoagulation technique to formMWCNT reinforced alumina and titania powders for SPS.Cationic dispersant (e.g., polyethylenimine (PEI)) or anionicdispersant (e.g., sodium dodecyl sulphate (SDS)) were used toimpart either positive or negative potential on the CNT surface.The zeta potential of the colloids was manipulated by variationof the pH of the suspension. For this purpose either acid oralkali has been added to the mixture. Post heterocoagulation,the powders can also be consolidated by slip casting.
Surfactants are organic compounds, which reduce the interfacial tension between a liquid and solid and thus improve thewettability of the solid surface by the liquid. These moleculesconsist of a long hydrocarbon chain terminated in a polar(cationic or anionic) or sometime neutral functional group.SDS and cetyl triammonium bromide (CTAB) are examplesof common anionic and cationic surfactants, respectively. Theeffectiveness of a surfactant depends on its concentration inthe liquid medium in which it is dispersed. Beyond a concentration level the surfactant molecules form a characteristicagglomerated structure known as micelle. The correspondingconcentration is known as critical micelle concentration (CMC).Beyond CMC the wettability of surfactant molecules onto thesurface of solid particles increases considerably owing to a steepdecrease in surface tension.
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