Accession Number : ADA307394

Title :   Ablative and Insulating Properties of Outgassed Boron Nitride and Boron Nitride Composite.

Descriptive Note : Technical note,

Corporate Author : NATIONAL AERONAUTICS AND SPACE ADMINISTRATION MOFFETT FIELD CA AMES RESEARCH CENTER

Personal Author(s) : Okuno, Arthur F.

PDF Url : ADA307394

Report Date : OCT 1966

Pagination or Media Count : 22

Abstract : Hot-pressed boron nitride that had been outgassed in vacuum ablated with negligible spalling when exposed to a jet of arc-heated air. The measured heats of ablation ranged from 30 to 35 MJ/kg for an enthalpy potential range of 16 to 23 MJ/kg. No ablation occurred in nitrogen at enthalpies up to 26 MJ/kg. A composite of boron nitride and phenolic resin, produced in an attempt to reduce thermal conductivity, was evaluated in both arc-heated air and nitrogen at enthalpy potentials from 8 to 15 MJ/kg and from 15 to 21 MJ/kg, respectively. Poor high-temperature bonding characteristics reduced the heats of ablation to approximately half those of hot-pressed boron nitride. The insulation efficiencies of the composite, pyrolytic boron nitride, boron nitride, and phenolic nylon, were studied at cold-wall convective heating rates of 1.4 to 2 MJ/sq meters-sec in arc-heated air and 1.9 to 2.5 MJ/sq meters-sec in arc-heated nitrogen. When compared on the basis of the total cold-wall heat input per initial pound of material for a back-face temperature rise of 167 deg K, the composite was twice as effective as either pyrolytic boron nitride or hot-pressed boron nitride.

Descriptors :   *ABLATION, *COMPOSITE MATERIALS, *INSULATION, *BORON NITRIDES, *OUTGASSING, AIR, HIGH TEMPERATURE, NYLON, VACUUM, HOT PRESSING, NITROGEN, THERMAL CONDUCTIVITY, BONDING, ENTHALPY, PYROLYSIS, ABLATIVE MATERIALS, PHENOLIC PLASTICS, ARC HEATING.

Subject Categories : Inorganic Chemistry
      Physical Chemistry
      Laminates and Composite Materials
      Miscellaneous Materials

Distribution Statement : APPROVED FOR PUBLIC RELEASE