(454d) Synthesis of Vapor Grown Carbon Fibers (VGFs) On Pretreated Metal Foil Using Thermal CVD

Cold rolled metal foil is the simplest form of catalyst for vapor grown carbon fibers (VGFs) synthesis. Using nickel foil as catalyst bypasses the steps of catalyst preparation which has the potential to reduce the cost of production of VGFs. Nickel foil undergoes dusting corrosion during synthesis to form nanoparticles which act as catalysts for VGF growth. However, the catalyst particle diameters are difficult to control and are not uniform. Due to this reason, VGFs lacks diameter uniformity as the catalyst particle diameter determines the VGF diameter. Gases used for synthesis were acetylene (C2H2), hydrogen (H2), ammonia (NH3) and nitrogen (N2) as inert. Faceting pretreatment was optimized to increase the carbon yield. Other synthesis parameters optimized were temperature of synthesis, hydrogen concentration and ammonia concentration. Hydrogen concentration was optimized to keep the catalyst active and increase the yield of carbon. However, the amorphous content of nanofibers did not decrease as observed by SEM. Ammonia concentration was optimized in the inlet gas to decrease the byproducts of amorphous carbon and very fine fibers. The VGFs obtained for optimized conditions were 100-300nm in diameter and contained minimal amorphous carbon. Under reaction conditions used for synthesis of VGFs, ammonia undergoes endothermic decomposition to H2(g) and N2(g). The opposing heats of reaction for exothermic acetylene decomposition and endothermic ammonia decomposition changes the characteristics of catalyst during synthesis. This change of catalyst surface temperature is proposed to reduce the quantity of amorphous carbon and very fine fibers as observed by SEM. Raman spectroscopy, thermal gravimetric analysis (TGA) and TEM were also used to further characterize the VGFs.