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EMISSIVITY XPOINTS IN SOLID AND LIQUID REFRACTORY TRANSITIONMETALS
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UNSPECIFIED (1992) EMISSIVITY XPOINTS IN SOLID AND LIQUID REFRACTORY TRANSITIONMETALS. METROLOGIA, 29 (4). pp. 261271. ISSN 00261394.
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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 lessthanorequalto 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  

Subjects:  Q Science > QC Physics  
Journal or Publication Title:  METROLOGIA  
Publisher:  BUREAU INT POIDS MESURES  
ISSN:  00261394  
Official Date:  October 1992  
Dates: 


Volume:  29  
Number:  4  
Number of Pages:  11  
Page Range:  pp. 261271  
Publication Status:  Published 
Data sourced from Thomson Reuters' Web of Knowledge
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