USE OF VIBRATIONAL SPECTROSCOPY TO DETERMINE OXIDE CONTENT OF ALKALI-METAL FLUORIDE-TANTALUM MELTS

Infrared and Raman spectroscopic measurements on a series of quenched alkali metal fluoride (Flinak) melts containing tantalum and oxide hav e led to the development of new methods of oxide analysis, which have an important use in the field of molten fluoride chemistry, The tantal um concentration was maintained at 2.7 mol %, with the oxide concentra tion varying from 0 to 5.4 mol %, over 22 samples. The oxide content o f a melt can be determined to within +/-0.1 mol % from the intensity r atio of-two vibrations, For example, a melt consisting of purified Fli nak, after addition of K2TaF7 and heating to 700 degrees C for 5 h for equilibration, was shown by infrared. spectroscopy to contain 0.3 +/- 0.1 mol % oxide and by Raman spectroscopy to contain 0.2 +/- 0.1 mol %. The frequency and relative intensities of the bands enable the assi gnment of Ta-F and Ta-O bands for both fluorotantalate and oxofluorota ntalate entities, In addition a new, dimeric, species with a Ta-O-Ta u nit is postulated. Raman spectra of molten samples showed bands of the same frequency and relative intensities, indicating that crystal effe cts were not important and that the equilibrium melt species were reta ined on quenching.