Graphite formation in abnormal glow discharge

Abstract

Graphite is made up of flat sheets of carbon atoms that form a periodic system of hexagonal rings of six atoms. Along the perpendicular direction of the sheets it has a low electrical conductivity, whereas this is greater throughout them. The possibility of separating the constituent sheets of the graphite and obtaining individual layers of it has led to the current scientific and technological revolution. Graphite can be produced synthetically in the laboratory, with low energy consumption, through the plasma of the abnormal glow discharge in direct current. In this work the abnormal glow discharge graphite formation is reported. The glow was initiated throughout a gaseous atmosphere containing acetylene, utilizing direct current power. In plasma generated in this type of discharge the secondary electrons, coming from the cathode, transfer their kinetic energy to the neutral molecules of the hydrocarbon causing dissociation, ionization and excitation of them. These processes generate active species that react with each other and with the substrate, producing carbon deposits on it. Under controlled conditions of temperature, acetylene content and deposition time, carbon deposits, with the characteristic structure of graphite, in abnormal glow discharge can be obtained. For this purpose, the abnormal glow discharge was established in an atmosphere composed of a mixture of 20% acetylene, 60% argon and 20% hydrogen at low pressure, in a temperature range from 400 °C to 900 °C. Under these conditions, on a copper substrate, a time of 15 minutes was used to obtain the carbon deposits. These deposits were analyzed by infra-red spectroscopy, Raman spectroscopy and scanning electron microscopy, identifying the structure of the graphite and observing the morphology of the deposits on the copper substrate.