SYNTHESIS OF SUBMICRON/NANO SIZED CaB_6 FROM CARBON COATED PRECURSORS

摘要

Calcium Hexaboride has been successfully synthesized at the laboratory scale using carbon coated precursors. Carbon coating is performed via pyrolysis of propylene at 550°C in a coating reactor on precursors. Various sets of precursors have been prepared where the starting materials include Calcium Carbonate, two different sources of Boron, and Carbon-black. An effort has been made to study the effects of various amounts of coatings on different combinations of starting materials to form the precursor material, and characterize the CaB_6 formed following the carbothermal reduction of these carbon coated powders under continuous argon flow at a maximum temperature of 1600°C with a holding time of 4 hours. XRD analysis shows that single phase CaB_6 can be successfully formed using carbon coated precursors while employing either boron source. TEM imaging and BET surface area measurements indicate that carbon coated precursors provides CaB_6 powders with fine particles and uniform morphology. The results and discussion provide emphasis on approaches for preparing carbon coated precursors depending on the boron source.