(Preparation of Pyrolytic Graphite (PG) Shell Using CVD Technique)

Abstract

A Pyrolytic graphite (PG) shell was produced by Chemical VaporDeposition (CVD) using a new modified vacuum furnace. The depositionexperiments of (PG) were achieved on a substrate of solid rods and slabs ofcommercial graphite. This was selected as a miniaturized mandrel for depositionexperiments. The substrate was heated at temperature range of (1500ºC-2300ºC)and a hydrocarbon gas (liquid benzene) was used with a pressure range of(1.5mbar- 2.5 mbar).A flow of hydrocarbon gas was admitted into the chamberand the PG was deposited by decomposition of the gas at high temperature onpreheated graphite mandrel as previously mentioned. Methane gas was also usedfor deposition experiments at high temperature range (1700ºC-2000ºC) andpressure range of (100mbar-200mbar) .The thickness of the prepared material wasmeasured as a function of T, P and time. An x-ray diffraction analysis has beendone for the prepared PG shell and compared with standard grid electrode for highpower electronic tubes made of PG. The calculated density of the deposited layerproduced in this work at maximum temperature was about (2.1±0.1 g/cm3) .A hightemperature calibration was achieved using Stephan -Boltzmann's law fordifferent melting point metals (Cu, Ni, Ta, Mo).In addition an optical pyrometerwas also used for this calibration. Finally, the prepared PG shell of this work wasexposed to a high temperature oxyacetylene burner test at the atmosphere. The testshows no visual deformation of the external material