CHEMICAL VAPOR DEPOSITED MATERIALS FOR ELECTRON TUBES.
Quarterly rept. no. 1, 15 May-14 Aug 65,
RAYTHEON CO WALTHAM MA RESEARCH DIV
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This program investigates chemical vapor deposition as a method of producing materials or coatings for use in vacuum electron devices. Experiments have been conducted, one resulting in a product with isotropic properties, the other anisotropic properties. Depositions were made at temperatures ranging from 1350 up to 1900 C. BN deposits 14 in. and more have been obtained on the interior of a 2X2X10 in. graphite box. Experiments were made with various surface finishes of the substrate. Our results indicate that, by following the same general principles which have been developed for pyrolytic graphite, anisotropic BN can be formed after some experimentation into any specific shape whose thickness is not greater than 10 of its radius of curvature. Properties of isotropic CVD BN have been measured. Measurements of its thermal conductivity show it to be about equivalent to nkckel, and its thermal expansion nearly matches that of tungsten. The modulus of elasticity is low, consistent with a high thermal shock resistance. Flexural strengths average about 10,000 psi. X-ray examination showed no prefered orientation. No helium permeation was obtained, and degassing studies demonstrated good vacuum properties at least to 1000 C. Author