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EMISSIVITY X-POINTS IN SOLID AND LIQUID REFRACTORY TRANSITION-METALS
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UNSPECIFIED (1992) EMISSIVITY X-POINTS IN SOLID AND LIQUID REFRACTORY TRANSITION-METALS. METROLOGIA, 29 (4). pp. 261-271. ISSN 0026-1394.
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Abstract
The spectral emissivities of refractory transition metals have been measured form about 2500 K up to temperatures above the melting point T(m). The experimental method adopted is based on multiwavelength pyrometric measurements. where the determination of the spectral emissivity is implicitly related to the evaluation of temperature through the radiation emission law and an assumed relationship between the spectral emissivity epsilon and the wavelength lambda. Heating was produced with a pulsed laser in times of order 100 ms. A specially constructed pyrometer was used which enabled measurements at six different wavelengths to be carried out at time intervals of order 0,1 ms. A model for the evaluation of temperature and spectral emissivities has been developed and its limitations arising from statistical and systematic errors are discussed. Our experiments on the refractory transition metals Hf, Mo, Nb, Re, Rh. Ta. W, V and Zr: (i) confirm the existence of a unique wavelength, lambda(x), for each metal (already well established in the solid state where partial derivative epsilon(lambda)/partial derivative lambda less-than-or-equal-to 0) to which different epsilon(lambda)-isotherms converge for lambda < lambda(x), from which they diverge for lambda > lambda(x), and at which epsilon(lambda) is independent of T, and thus equal, in particular, to its value at T(m); (ii) indicate that lambda(x) is preserved through T(m) and (iii) reveal that at T(m) these metals are effectively "grey", i.e. their emissivity, within the measurement uncertainty, is independent of lambda(partial derivative epsilon(lambda)/partial derivative lambda > 0), while for T> T(m) is partial derivative epsilon(lambda)/partial derivative lambda > 0, that it, opposite to its behaviour at T < T(m).
Item Type: | Journal Article | ||||
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Subjects: | Q Science > QC Physics | ||||
Journal or Publication Title: | METROLOGIA | ||||
Publisher: | BUREAU INT POIDS MESURES | ||||
ISSN: | 0026-1394 | ||||
Official Date: | October 1992 | ||||
Dates: |
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Volume: | 29 | ||||
Number: | 4 | ||||
Number of Pages: | 11 | ||||
Page Range: | pp. 261-271 | ||||
Publication Status: | Published |
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