BASAL PLANE EMITTANCE OF PYROLYTIC GRAPHITE AT ELEVATED TEMPERATURES
Abstract
A direct measurement of the total hemispherical emittance of 'as deposited' PG layers on ATJ graphite cylinders in the range from 1200 to 2840C is described. The method consisted of resistively heating these long, thin cylinders inside a cooled, blackened enclosure until the power generated was all radiated and temperature equilibrium ensued. By sighting an optical pyrometer through a window in the enclosure, the apparent temperature of the surface and the true temperature of a cavity inside the samples could be measured. These temperatures, as well as the electrical power supplied to the sample, were recorded for each equilibrium temperature. These data for various sample thicknesses were used to determine the true temperature of the surface, the total hemispherical emittance, epsilon-H, and the normal emittance at 0.65 microns. The electrical resistivity in the ab-plane and the thermal conductivity in the c-direction were also determined. The epsilon-H for PG was approximately 0.6 microns from 1300 to 2600C. Exposure for a few seconds in an inert atmosphere or in a vacuum to temperatures above 2600C, irreversibly altered the surface finish and increased epsilon-H to progressively higher values depending on the time and temperature. The normal emittance values at 0. 65 microns also were significantly affected.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1967
- Accession Number
- AD0660892
Entities
People
- Robert J. Champetier
Organizations
- The Aerospace Corporation