Three dicotyledonous woods of local origin (mango (Mangifera indica), jackfruit (Artocarpus integrifolia) and teak (Tectona grandis)) were transformed by pyrolysis into carbonaceous preforms and subsequently converted into microcellular Si/SiC ceramics by liquid Si-infiltration under vacuum. The pyrolyzed mango, jackfruit and teak were characterized in terms of pyrolysis weight loss, shrinkages, bulk density and microstructures. The end ceramics were found to be 91-98% dense with respect to theoretical densities (T.D.) with porosities in the range of 0.1-4.8%. SEM (in back scattered electron (BSE) mode) imaging confirmed the preservation of microcellular tissue anatomy of the precursor wood structure in the morphologies of the final ceramics. The microc~llular Si/SiC ceramics from mango, jackfruit and teak exhibited excellent oxidation resistance during heating to 1350"C In flowing air, showing a marginal weight gain at the highest temperature. Si/SiC-mango was also characterized in terms of flexural strength, Young's modulus and hardness. These biostructural microcellular Si/SiC ceramics possess application potential in various structural ceramic sectors (e.g. mechanical pump seals, wear inserts, kiln support structures, heat exchangers etc).
Electrical conductivity (σ dc ) of the cellular Si/SiC ceramic composites has been measured over a temperature range 25-1073 K while the thermoelectric power (S) has been measured over 25-300 K. Remarkably, these cellular compounds developed through biomimetic route -where the ceramic system grows within a plant bio-template retaining the imprint of structural intricacies of the native templates -are found to exhibit excellent mechanical, thermal, and electrical properties quite comparable to or even better than those of the systems prepared through conventional ceramic route. The electrical conductivity, measured parallel (σ ║ ) and perpendicular (σ ⊥ ) to the growth axes of the native plants, depicts nearly temperature-independent anisotropy (σ ⊥ /σ ║ ) of the order ~2 while the thermoelectric power is nearly isotropic. The charge conduction across the entire temperature regime is found to follow closely the variable range hopping (VRH) mechanism. The conductivity anisotropy appears to be driven primarily by the unique microcellular morphology of the bio-templates which can be exploited in many electrical applications.
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