Tutorial
Graphites
Graphite is a crystalline form of the element carbon consisting of parallel layers of hexagonally arranged carbon atoms in planar condensed ring systems. Natural graphite is a mineral form of graphite that occurs in nature and synthetic graphite is a man-made form produced by heat treating non-graphitic carbons to temperatures above 2500°C. Natural graphite is mined and processed and used in a variety of applications such as lubricants, seals, insulation, fillers, and refractories. The most common synthetic graphites are usually manufactured as composites in which ground petroleum coke is mixed into a paste with a coal tar pitch and then heat treated to around 1200°C - 1400°C in a calcining step to coke the pitch and drive all volatile material from the petroleum coke. Further heating to 2500°C to 3000°C causes an ordering of the carbon atoms to graphatize the mixture into a true graphite. The biggest industrial use of synthetic graphite is in massive electrode used in carbon-arc furnaces to melt steel. Other typical uses of synthetic graphite are in battery electrodes, refractories, nuclear reactors, and even in medical devices such as replacement heart valves. Under the optical microscope the composite nature of this material is evident. The petroleum coke textures and structures described in the petroleum coke section allow the identification of these components set in a coked pitch matrix.
Also included in this section are photomicrographs of carbon anodes used in aluminum production. Pre- baked anodes are composed of ground petroleum coke and a coal tar pitch which have been heat treated to around 1200°C - 1400°C in a calcining step. These a pre-baked are not graphitized . Another variety of carbon anode is made in the Soderburg process is which the anode paste is calcined in the aluminum production process itself. The types of graphite presented in this section are:
| Natural Graphite | ||||||||||||||||||||
| Industrial Graphite | ||||||||||||||||||||
| Battery electrodes | ||||||||||||||||||||
| Crucible | ||||||||||||||||||||
| Machined | ||||||||||||||||||||
| Nuclear | ||||||||||||||||||||
| Anode "Graphite" | ||||||||||||||||||||
| Green Anode Paste | ||||||||||||||||||||
| Baked Anode | ||||||||||||||||||||
| Electrode Graphite | ||||||||||||||||||||
| Baked Electrode | ||||||||||||||||||||
| Graphitized Electrode | ||||||||||||||||||||
REFERENCES
Gray, Ralph J. and Krupinski, Ken C., 1997, Pitch Production: Supply, coking, optical microscopy and applications: in Marsh, Harry, ed., Introduction to Carbon Technologies, Universidad de Alicante, p. 329-423.
Redmount, MelvinB. and Heintz, Edward A., 1997, The manufacture of graphite electrodes: in Marsh, Harry, ed., Introduction to Carbon Technologies, Universidad de Alicante, p. 519-536.
Marsh, Harry and Fiorino, Karen, 1997, The manufacture of carbon anodes for aluminum production: in Marsh, Harry, ed., Introduction to Carbon Technologies, Universidad de Alicante, p. 537-557.