Silicon carbide (SiC) ceramic powders were synthesized by carbothermal reduction in specific geopolymers containing carbon nanopowders. Geopolymers containing carbon and having a composition M 2 OÁAl 2 O 3 Á4.5SiO 2 Á12H 2 O+18C, where M is an alkali metal cation (Na + , K + , and Cs + ) were carbothermally reacted at 1400°C, 1500°C, and 1600°C, respectively, for 2 h under flowing argon. X-ray diffraction and microstructural investigations by SEM/EDS and TEM were made. The geopolymers were gradually crystallized into SiC on heating above 1400°C and underwent significant weight loss. SiC was seen as the major phase resulting from Na-based geopolymer heated to ≥1400°C, even though a minor amount of Al 2 O 3 was also formed. However, phase pure SiC resulted with increasing temperature. While a slight increment of the Al 2 O 3 amount was seen in potassium geopolymer, Al 2 O 3 essentially replaced cesium geopolymer on heating to 1600°C. SEM revealed that SiC formation and a compositionally variable Al 2 O 3 content depended on the alkaline composition. Sodium geopolymer produced high SiC conversion into fibrous and globular shapes ranging from~5 lm to nanosize, as seen by X-ray diffraction as well as SEM and TEM, respectively.
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