Spectral emissivity of 99.7% aluminium between 200 and 540°C

P. M. Reynolds

Results are given for surfaces of roughness 3 μ in., 115 μ in. and anodized aluminium within the wavelength range 1 to 14 μ. The spectral emissivity varied strongly with surface roughness and oxidation, but only slightly with temperature. Typical values at wavelengths 2 and 8 μ respectively were 0.09 and 0.04 for polished, 0.30 and 0.24 for roughened, 0.30 and 0.20 for anodized aluminium. Natural oxidation slightly increased the spectral emissivity at all wavelengths below 9 μ and had a marked effect between 10 and 12 μ. An anodic oxide film increased the spectral emissivity beyond 10 μ to greater than 0.70. The significance of these variations to radiation pyrometry is briefly discussed.

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Materials
Curve 1
Temperature K: 599 Wavelength Range, μ: 1.8-12.5 Geometry θ°: ~0° Reported Error, %: ±20 Composition (weight percent), Specifications and Remarks: 99.7 Al, 0.11 Fe, 0.11 Si, 0.01 Cu, 0.01 Mg, < 0.01 Mn, Ni and Zn; cylindrical tube; heated at 467 K for 15 hrs; polished with Carnu on Selvyt cloth; surface roughness 3 microinches (center line average); data extracted from smooth curve; error given in the wavelength range 2 to 10 μ.
Curve 2
Temperature K: 697 Wavelength Range, μ: 1.7-14.0 Geometry θ°: ~0° Reported Error, %: ±20 Composition (weight percent), Specifications and Remarks: Above specimen and conditions except heated at 697 K for 20 hrs before measurement.
Curve 3
Temperature K: 805 Wavelength Range, μ: 1.7-14.0 Geometry θ°: ~0° Reported Error, %: ±20 Composition (weight percent), Specifications and Remarks: Above specimen and conditions except heated at 805 K for 15 hrs before measurement.
Curve 4
Temperature K: 599 Wavelength Range, μ: 1.7-12.5 Geometry θ°: ~0° Reported Error, %: ±20 Composition (weight percent), Specifications and Remarks: Above specimen and conditions.
Curve 5
Temperature K: 462 Wavelength Range, μ: 1.8-14.5 Geometry θ°: ~0° Reported Error, %: ±10 Composition (weight percent), Specifications and Remarks: 99.7 Al, 0.11 Fe, 0.11 Si, 0.01 Cu, 0.01 Mg, < 0.01 Mn, Ni and Zn; tube; heated for 25 hrs at 462 K; roughened and knurled with grade 180 silicon carbide paper; surface roughness 115 microinches (center line average); data extracted from a smooth curve; error given over the wavelength range 2 to 10 μ.
Curve 6
Temperature K: 599 Wavelength Range, μ: 2.0-14.0 Geometry θ°: ~0° Reported Error, %: ±10 Composition (weight percent), Specifications and Remarks: Above specimen and conditions except heated at 598 K for 22 hrs before measurements.
Curve 7
Temperature K: 715 Wavelength Range, μ: 1.25-14.5 Geometry θ°: ~0° Reported Error, %: ±10 Composition (weight percent), Specifications and Remarks: Above specimen and conditions except heated at 715 K for 27 hrs before measurement.
Curve 8
Temperature K: 803 Wavelength Range, μ: 3.5-14.5 Geometry θ°: ~0° Reported Error, %: ±10 Composition (weight percent), Specifications and Remarks: Above specimen and conditions except heated at 787 K for 17 hrs before measurement.
Curve 9
Temperature K: 461 Wavelength Range, μ: 3.0-14.0 Geometry θ°: ~0° Reported Error, %: ±10 Composition (weight percent), Specifications and Remarks: Above specimen and conditions.
Curve 1
Temperature, K: 461 Wavelength Range, µm: 2.0-14.0 Geometry θ': ~0° Reported Error, %: ±10 Composition (weight percent), Specifications, and Remarks: 99.7 Al, 0.11 Fe, 0.11 Si, 0.01 Cu, 0.01 Mg, <0.01 Mn, Ni, and Zn; anodized for 30 min at 1 amp dm⁻² in 4N analar sulphuric acid at 293 K and sealed for 30 min in boiling distilled water; thickness of anodic film 2.54 µm; heated at 456 K for 15 hrs; data extracted from smooth curve.
Curve 2
Temperature, K: 575 Wavelength Range, µm: 1.6-14.0 Geometry θ': ~0° Reported Error, %: ±10 Composition (weight percent), Specifications, and Remarks: Above specimen and conditions except heated at 575 K for 8 hrs before measurement.