ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Fundamentals of High Temperature Processes
Crystallisation of Silicate Glasses and Melts with Chemical Compositions in Primary Phase Region of Gehlenite
Masahiro SusaKodai SasakiTakaaki YamauchiTakashi WatanabeRie EndoMiyuki HayashiMasahito Hanao
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2020 Volume 60 Issue 1 Pages 58-64


Crystallisation behaviour has been investigated on samples with two compositions: (A) 42CaO-37SiO2-21Al2O3 and (B) 43CaO-27SiO2-19Al2O3-11CaF2 (all mass%). Composition (A) is within the primary phase region of gehlenite and composition (B) is just between gehlenite and cuspidine on a mass basis. Two types of sample were prepared from glassy and molten states for each composition. These samples were characterised by differential thermal analysis, X-ray diffraction analysis and electron probe microanalysis.

- Crystallised samples A from glassy state:

It contained gehlenite and wollastonite in the XRD profile, and in BE images gehlenite crystals grew more largely than wollastonite, suggesting that gehlenite precipitates in preference to wollastonite.

- Crystallised samples B from glassy state:

It contained cuspidine and gehlenite in the XRD profile. In BE images, cuspidine precipitated but gehlenite was not observed.

- Crystallised samples A from molten state:

It contained only gehlenite in the XRD profile, and in BE images there was dendritic gehlenite developed across the sample.

- Crystallised samples B from molten state:

It contained cuspidine and CaF2 as well as gehlenite in the XRD profile. In BE images, gehlenite comprised the major part, and it is likely that gehlenite crystallises in preference to cuspidine.

It is also likely that the pseudo-binary system of gehlenite and cuspidine forms eutectics and that the eutectic composition is rather closer to cuspidine. Consequently, the increase in Al2O3 concentration would little affect crystallisation of the glassy portion in actual mould fluxes containing CaF2 but strongly affects crystallisation of the liquid portion.

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