Accession Number : ADA019133

Title :   An Investigation of Reaction Sintered Silicon Nitride as a Radome Material.

Descriptive Note : Final rept. 1 Mar-31 Aug 75,


Personal Author(s) : Harris,Joe N.

Report Date : OCT 1975

Pagination or Media Count : 59

Abstract : Eleven reaction sintered silicon nitride radomes were prepared by slip casting silicon blanks and reaction sintering in nitrogen to; determine the repeatibility of electrical transmission characteristics, examine methods of sealing porous radomes, investigate possible flight attachment systems, and prepare a radome with attachment for rain erosion sled testing. Only two of fifteen castings were lost in the mold. Dry density varied from 1.58 to 1.89 gm/cu cm due to variation in viscosity and particle size distribution of the slip. Final densities of radomes completing the reaction sintering cycle varied from 2.55 to 2.76 gm/cu cm. Electrical transmission patterns were made on six of the radomes using swept frequency techniques. At the frequency representing a half-wave wall thickness for the particular density of each radome, transmission losses were of the order of a few dB. Weight gained gained during nitriding was not a good indicator of electrical transmission capability. Acceptable transmission patterns were made on radomes with apparent weight gains as low as 50 percent. Radomes sealed against moisture by impregnating or surface coating with silicone resin were not degraded in electrical performance by the sealing. A dense reaction sintered silicon nitride attachment ring was self-bonded into a lower density reaction sintered silicon nitride radome as a demonstration of the feasibility of this approach for attachment systems. Low expansion carbon composite rings tailored to match the expansion of silicon nitride were also considered for attachment rings.

Descriptors :   *Silicon nitrides, *Radomes, Fabrication, Electrical properties, Activated sintering, Slip casting, Nitrogen, Moistureproofing, Materials

Subject Categories : Ceramics, Refractories and Glass
      Active & Passive Radar Detection & Equipment

Distribution Statement : APPROVED FOR PUBLIC RELEASE