A rotating cylinder method for measuring normal spectral emittance of ceramic oxide specimens from 1200 to 1600 K

Abstract

Equipment was designed and constru cted for measuring the spec tral e mittan ce of polycrystalline ceramic oxide specimens in the wavelength region 1 to 15 J-L and at temperatures of 1200, 1400, and 1600 O K. Specimens co nsis ted of small hollow cylinders that were rotated at 100 rpm in a furnace cavity equipped with a water-cooled viewing port. Emittances were determined by comparing the radiance of the specime n to that of a blac kbody at the same te mp erature.A series of six measurements (two measurements eac h on three specimens) was mad e on co mm erciaJJy pure specim ens of alumina, thoria , magnes ia , and zirconia . All four mate rial s show ed similar behavior in that the e mitlan ces were low in th e shorte r wavelength regions and high at th e longer wavelengths. The temperature coeffi cients of spectral em ittance were positive for all four materials, but varied with th e material; those for thoria were appreciably hi ghe r than th e ot he r three. In aJJ cases coeffi cie nts were greater at s hort wavele ngth s than at long.Error sources were in vestigated, and the meas ureme nt un certainti es associated with eac h so urce were e valuated. It was co nclud ed that at 1200 O K the tru e values of e mittance at 2 J-L for th e particular specimens meas ured mi ght be as much as 0.032 lower or 0.012 hi gher th a n th e reported values. Th e data were in good agreement with re Aecta nce meas ure me nt s of the same materia l and with rece ntly repo rted absorption coefficie nt s.

Influence of surface oxidation on the radiative properties of ZrB2-SiC composites

“…That the radiative properties of thermal protection materials are associated with surface temperature has been confirmed by some literatures [12,13,28]; indeed, the emissivities of ZS2 and ZS3, as indicated in Fig. 3 and [15,16].…”