Daniel William Gorkiewicz

Role of sulfur in the production of carbon fibers in the vapor phase

Abstract Iron particles do not grow filaments in a methane atmosphere profusely enough to make a continuous reactor practical. Adding small quantities of sulfur to the iron vastly increases filament formation. We show that this is because the sulfur liquefies the iron particle, enhancing filament nucleation. With continued increases in sulfur, the number of filaments produced continues to increase, but quality, measured by length and straightness, decreases. We attribute this to higher sulfur concentration in the catalyst particle moving the melting point above the eutectic, thus decreasing the efficiency of filament lengthening.

A new reactor for growing carbon fibers from liquid- and vapor-phase hydrocarbons

Abstract We describe an apparatus for continuous growth of carbon fibers designed to minimize thermophoretic and convective losses while maximizing nucleation of filamentous carbon. A high vapor pressure liquid hydrocarbon (hexane) dissolves a suitable organometallic source of iron catalyst particles, ferrocene. This solution is efficiently vaporized by incorporating it in a flowing gas stream containing some hydrocarbons and air. This feedstock flows through a tube of relatively low diameter and debouches into a larger tube maintained at 1100°C. A quantity of sulfur approximately equal to the quantity of iron catalyst material is vital to rich filament nucleation and is flowed in with the other reactants. The liquid feedstock flow rate should be rapid enough that it exactly saturates the gas stream to which it is added. This condition limits the throughput of reactants, and hence, the production rate of the fibers.

Physical properties of vapor-grown carbon fibers

Abstract Vapor-grown carbon fibers (VGCF) are produced by depositing a layer of pyrocarbon from the vapor phase on a catalytically grown carbon filament. This morphology determines many properties of the fiber, since the filament is more graphitic than the pyrocarbon. In this paper we compare VGCF produced by a continuous process with those grown on a substrate. Fibers having thicker pyrocarbon layers are less graphitic as measured by X-ray diffractometry, electron diffraction and Raman spectroscopy. The bulk density of the fibers, near 2.03 g/cm3, is relatively high for carbon fibers; it decreases slightly as the pyrocarbon thickness increases. The surface area of the fibers determined by N2 adsorption is not larger than the calculated geometric area, indicating that the surface is relatively smooth and free of pores. Each of these measurements indicates that fibers produced by a continuous process are comparable to those grown on substrates, with respect to graphitization and surface properties.