Viscosity of Na-Si-O-N-F melts: Mixing effect of oxygen, nitrogen, and fluorine

Sohei SUKENAGA, Masayuki OGAWA, Yutaka YANABA, Mariko ANDO, Hiroyuki SHIBATA

Research output: Contribution to journalArticlepeer-review


Fluorine and nitrogen are important elements of metallurgical slags and fluxes. Studies on their viscosity have often focused on the additive effect of fluoride and nitride compounds (e.g., CaF2 and Si3N4), whereas the influence of anionic composition (i.e., oxygen, fluorine, and nitrogen concentrations) with a fixed cationic composition remains unclear. The present study reports the scarcely quantified viscosity variations due to changes in the anionic composition of a simple sodium silicate system by rotating crucible method under a controlled atmosphere. 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy was used to characterize the structural changes against varying nitrogen and fluorine concentrations in the quenched glassy sample. The observed change in the local silicon structure was consistent with the expected variation from the conventional structural roles of nitrogen and fluorine in silicate glasses: nitrogen atoms tend to bond with silicon atoms, whereas fluorine atoms prefer to exist in surrounding sodium cations. Moreover, nitrogen tends to increase the viscosity, whereas fluorine strongly decreases the viscosity of the sodium silicate melts even with the enhancing effect of the latter on the polymerization of silicate anions. The viscosity of silicate melts has been commonly related to the overall polymerization degree of the liquid. However, the viscosity of fluorine-containing silicates cannot be explained by this conventional scenario. Fluorine ions tend to loosely bond with sodium cations. These sodium-fluorine complexes played a strong lubricant role in the network liquids.

Original languageEnglish
Pages (from-to)2794-2806
Number of pages13
JournalIsij International
Issue number12
Publication statusPublished - 2020 Dec 15
Externally publishedYes


  • 29Si and 19F MAS NMR spectroscopy
  • Glasses
  • Na-Si-O-N-F
  • Silicate melts
  • Viscosity

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

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