To overcome the limitations of differential thermal analysis (DTA)

No abstract

To determine the effect of F ions on the structure of the molten alkali silicate systems, quenched Na 2 OSiO 2 -NaF systems were investigated by Raman spectroscopy and molecular dynamics simulation. The systematic increase of 1 100 cm Ϫ1 band intensity in the Raman spectra of the silicate melts accompanying the replacement of O by F provides the evidence for concomitant polymerization of melts. From the molecular dynamics simulation, it was confirmed that most of substituted F was mainly coordinated to Na ϩ ions but not Si 4ϩ ions at least up to 12.5 mol% of F ion content. A small amount of F was found to be coordinated to Si as a non-bridging ion from the molecular dynamics simulation, although there was no recognizable evidence from Raman spectroscopy. These results were consistent with the mechanism in which F associated with otherwise network-modifying Na rather than with network-forming Si. Since F was associated to Na ϩ ions, the replace of O ion by two F ions promote the polymerization of silicate melts.KEY WORDS: fluorine; molten flux; slag structure; molecular dynamics simulation; Raman spectroscopy. much information on the structural details such as bond angle distributions or pair functions that are difficult to obtain by Raman measurements. 5) So, in this investigation, the molecular dynamics simulations were also employed to investigate the structural role of F Ϫ ions in molten alkali-silicate melts and simulated results were compared and discussed with the measured Raman spectra. Actually using the molecular dynamics simulation for these structural analyses has a great advantage, since it is generally difficult to carry out the precise experiments for the melts with high F content due to their high volatilization rate, Raman Spectroscopy MeasurementsThe detail of Raman spectroscopic measurements was described previously. 14) Appropriate portions of reagent grade Na 2 CO 3 , SiO 2 and NaF powders were mixed together in an agate mortar in air and placed in a Pt crucible. The mixture was heated at 1 073 K for 10.8 ks to decarbonate and then fired in a muffle furnace at 1 673K for 7.2 ks. The melted mixture was quenched into a water-cooled copper flat mold and then ground to form a powder. The prepared powder was melted again as a bead (only about 5 mg) at 1 673 K on a Pt-Pt alloy thermocouple wire loop in air and quenched. Quenching was achieved by switching off the power to the hot thermocouple. The initial compositions of the samples are presented in Table 1 and also in Fig. 1. In the table and figure, Na 2 F 2 is used instead of NaF, since it is convenient to consider the substitution of 2F Ϫ to O 2Ϫ (2F Ϫ → O 2Ϫ ). As shown in Fig.1 and Table 1, the SiO 2 contents in the alkali-silicate samples were fixed to 33 and 50 mol% and 2F Ϫ → O 2Ϫ substitution was done along the lines parallel to Na 2 O-Na 2 F 2 join. Namely, total number of Si and Na cations and (2F Ϫ ϩO 2Ϫ ) anions in the samples on this join were constant but only 2F Ϫ /O 2Ϫ ratio was changed.After the samples were prepared, their conte...