Author
Abstract
A Pyrolytic graphite (PG) shell was produced by Chemical Vapor
Deposition (CVD) using a new modified vacuum furnace. The deposition
experiments of (PG) were achieved on a substrate of solid rods and slabs of
commercial graphite. This was selected as a miniaturized mandrel for deposition
experiments. 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 chamber
and the PG was deposited by decomposition of the gas at high temperature on
preheated graphite mandrel as previously mentioned. Methane gas was also used
for deposition experiments at high temperature range (1700ºC-2000ºC) and
pressure range of (100mbar-200mbar) .The thickness of the prepared material was
measured as a function of T, P and time. An x-ray diffraction analysis has been
done for the prepared PG shell and compared with standard grid electrode for high
power electronic tubes made of PG. The calculated density of the deposited layer
produced in this work at maximum temperature was about (2.1±0.1 g/cm3) .A high
temperature calibration was achieved using Stephan -Boltzmann's law for
different melting point metals (Cu, Ni, Ta, Mo).In addition an optical pyrometer
was also used for this calibration. Finally, the prepared PG shell of this work was
exposed to a high temperature oxyacetylene burner test at the atmosphere. The test
shows no visual deformation of the external material
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