EFFECT OF SURFACE ROUGHNESS ON THE REFLECTANCE OF REFRACTORY METALS
Abstract
The influence of surface roughness on the thermal optical properties (reflectance and emittance) of three refractory materials, columbium alloy, D-36, tantalum and tungsten has been studied. Current data obtained by different investigators for the same materials have varied more than 50 percent. Several investigators studying the interaction of radiation with rough surfaces have developed theoretical approaches to correlate thermal optical properties with the material being studied; however, no predictions have been made as to the magnitude of the surface effects. This report establishes several general trends in this direction. Two surface roughness preparations were used-random sanding and sandblasting. As a typical example of the results, the total hemispherical reflectance of tantalum was changed 26 percent at short wavelengths and 25 percent at longer wavelengths by surface roughness values ranging from 0.192 to 3.0AA microns. The specular reflectance of tantalum changed 56 percent at short wavelengths and 75 percent at long wavelengths for the same range of surface roughness values. Material effects caused a maximum difference of only 16% in the total hemispherical reflectance of these three refractory materials; however, the maximum change in surface roughness caused the total hemispherical reflectance to vary 20 to 40 percent as a function of wavelength. The influence of second order effects has been observed. The degree to which emittance influences the surface temperature and incident heat flux capabilities of materials is discussed.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1966
- Accession Number
- AD0812801
Entities
People
- Donald F. Stevison
Organizations
- Air Force Research Laboratory