CHEMICAL VAPOR DEPOSITED MATERIALS FOR ELECTRON TUBES.
Abstract
This program was established to investigate chemical vapor deposition as a method of producing materials or coatings for use in vacuum electron devices. Experiments continued with two methods of producing CVDBN, one resulting in a product with isotropic properties, the other with anisotropic properties. The density of the isotropic material is approximately inversely proportional to the deposition temperature between 1400 and 1700 C. A sample of CVD silicon nitride more than 1/4 in. in thickness was prepared. The thermal conductivity of isotropic CVDBN, deposited at 1700 C, is approximately the same as dense beryllia between 300 and 900 C, in spite of its much lower density. Isotropic CVDBN maintains its strength in flexural tests up to temperatures of at least 2200 C, although some plastic deformation is observed at 2000 C and above. Anisotropic CVDBN displayed a superior electrical surface resistance at 90-95% relative humidity and temperatures cycled between 25 and 65C. CVD silicon nitride possessed a bulk electrical resistivity approximating that of very pure alumina at a temperature of 1000 C. Scratch tests indicate that CVD silicon nitride is harder than sapphire, and is at least as hard as hexagonal single crystals of SiC. The degassing properties of several CVD materials have been measured. The chief problem which was encountered in the deposition of the refractory borides and carbides was the excessive growth of large crystals over much of the deposit. Much better depositions were obtained by reducing the temperatures by 50 to 100 C and doubling the linear flow velocity of the vapors over the mandrel.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1966
- Accession Number
- AD0481731
Entities
People
- H. Schilling
- J. Pappis
- L. Hagen
- S. R. Steele
Organizations
- RTX