Structure–property relationship amphoteric oxide systems via phase stability and ionic structural analysis

Abstract The effects of basicity and amphoteric oxides (Al 2 O 3 and Fe t O) on the structure–property relationships of CaO–SiO 2 –(Al 2 O 3 and Fe t O) and CaO–SiO 2 –Al 2 O 3 –Fe t O slags were investigated to determine the constitutional effects on the structure of high‐temperature ionic melts. The proportion of Q n species, which is determined by Raman spectroscopy, and the viscosity measured by the rotating cylinder method are both correlated and shown together with the slag structure index (NBO/T) concept. The NBO/T of CaO‐SiO 2 binary slags showed a linear relationship with basicity (CaO/SiO 2 ), including an inflection point at CaO/SiO 2 = 1.0 resulting from the stability and Q n ‐dominant unit of the melt, which changes close to the wollastonite (CaSiO 3 ) congruent point. This inflection point changes with the increasing amphoteric oxide content (Al 2 O 3 and Fe t O) because of the change in the dominant polymeric unit (Si 4+ –O–Si 4+ →M 4+ –O–Si 4+ ; M: Al and Fe), in accordance with the equilibrated primary phases. As the Al 2 O 3 content increased, the viscosity and activation energy of slags both drastically increased owing to the change in the flow unit (Si–O–Si, Al–O–Si, and Al–O–Al). In contrast, as Fe t O increased, the viscosity and activation energy ( E η ) of slags decreased because of the change in the flow unit (Si–O–Si, Fe–O–Si, and Fe–O–Fe). Ultimately, the flow unit (T–O–T; T = Si, Al, and Fe) and activation energy of the slags were found to be closely related to the solid primary phase on the phase diagram, and the physical‐property–structure relationship was determined from the phase stability.