IR Emission Spectroscopy of Molten Salts and other Liquids Using Thick Samples as Reference

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Abstract
The IR emittance of liquids relative to a blackbody is dependent on the reflectivity at the surface of the sample. This dependency leads to distortions in the bandshapes except when the absorption coefficient or the sample thickness is very low. The use of an opaque (i.e. very thick) sample as a reference eliminates the distortions in the bandshapes. A new emittance ε* = (emission of a thin sample)/(emission of an opaque sample) has been introduced. A theoretical analysis as well as experimental work on chloroaluminate melts demonstrate that the emittance ε* gives a better representation of the ideal sample property of interest, i.e., the internal transmittance of the sample, than the usual emittance with a blackbody as a reference.