Structure and Crystallization Kinetics of Glassy CaO-Al2O3-SiO2-CaF2-Na2O Mold Fluxes with Varying Basicity

Li, Jiangling; Yan, Baijun; Shu, Qifeng; Chou, Kuo‐Chih

doi:10.1007/s11663-015-0422-y

Cited by 31 publications

(27 citation statements)

References 30 publications

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Section: Resultsmentioning

confidence: 92%

“…The crystalline characteristics of molten slags correlates well with the structure, where disorder converts into ordered crystal structures during the crystallization process. 36,37 This involves breaking old bonds to form new ones with ion migration in the three-dimension network structure. The chemical bonding energy and the degree of polymerization of the three-dimension network structure determine the difficulty levels in breaking the old bonds and the migration of ions.…”

Section: (3) Structure Of Mold Fluxesmentioning

confidence: 99%

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Effect of Al Speciation on the Structure of High‐Al Steels Mold Fluxes Containing Fluoride

et al. 2016

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To design suitable mold fluxes for the casting of high‐Al steels, the structure of mold fluxes based on CaO–SiO2, CaO–SiO2–Al2O3, and CaO–Al2O3 was examined by Raman spectroscopy and magic‐angle spinning nuclear magnetic resonance. The results showed that Si atoms are replaced by Al atoms as the network formers with the increase in Al2O3 in the mold fluxes. This converts the silicate slags (CaO–SiO2 mold fluxes) into aluminosilicates slags (CaO–SiO2–Al2O3 or CaO–Al2O3 mold fluxes). The F− ions in the mold flux containing Al2O3 are classified into three categories, according to function: Bridging F's, Nonbridging F's, and Free‐F's. The Al3+ ion holds three distinct coordination environments: IVAl, VAl, and VIAl. The addition of F affects the coordination environment of Al3+ to form AlO3F and AlO2F2 that accommodate the network structure of slags. The network structure in the CaO–SiO2 mold fluxes is mainly connected through Si–O–Si linkage. However, the network structure of the mold fluxes containing elevated content of Al2O3 is mainly connected through Si–O–Si, Al–O–Al, Al–O–Si, and Al–F–Al linkages. Hence, the structural characteristics of high‐Al steels mold fluxes must be considered during the designing step of the mold fluxes.

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Section: Resultsmentioning

confidence: 92%

Section: (3) Structure Of Mold Fluxesmentioning

confidence: 99%

Effect of Al Speciation on the Structure of High‐Al Steels Mold Fluxes Containing Fluoride

et al. 2016

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“…It can be concluded that the crystalline phase in the slag film is not affected by the bubbles. Li et al [18] indicated that CaO•SiO 2 formed at high temperatures, while in the lower temperature region, CaO•SiO 2 converted to 3CaO•2SiO 2 •CaF 2 . According to the XRD of A, B1, B2, and B3, the characteristic peak area of wollastonite or cuspidine increased with increasing bubbles content of the mold fluxes A, B1, and B2.…”

Section: Crystal Phasementioning

confidence: 99%

“…Therefore, the higher the content of bubbles, the more Q 1 structure is present. Li et al [18] pointed out that the structure of cuspidine was mainly composed of Q 1 . While, according to Table 2, the content of cuspidine first increased and then decreased with the increase of bubbles, it may be that the nucleation sites were first improved by the bubbles.…”

Section: Structure Of Molten Slagsmentioning

confidence: 99%

Effect of Bubbles on Crystallization Behavior of CaO–SiO2 Based Slags

Wen

Ding

et al. 2019

Metals

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Surface longitudinal cracks are a serious problem and particularly prevalent in the casting of peritectic steel (carbon content between 0.10%C and 0.18%C, non-alloyed). It is usually alleviated by controlling the horizontal heat transfer from the steel shell to the mold through increasing the crystallization performance of slags. In the actual continuous casting process, a large number of bubbles are formed in the molten slags, and the crystallization properties of the mold fluxes are affected by bubbles. Therefore, an investigation of the influence of bubbles on the crystallization performance of mold fluxes was carried out by applying the hot thermocouple technique and it is hoped that surface longitudinal cracks can be solved in this way in the peritectic steel casting process. The continuous cooling transformation (CCT) diagrams and time–temperature transformation (TTT) diagrams were constructed for an analysis of the crystallization kinetics. The results showed that the crystallization ability of mold fluxes was enhanced by adding bubbles through shortening the incubation time of crystallization, increasing the critical cooling rate, and decreasing the activation energy of crystallization. As a result, the crystalline fraction, slag film thickness, and surface roughness of the slag films were improved, but the crystalline phase was not affected by bubbles. With an increase of the bubble content remaining in the molten slag, the growth mechanism of the cuspidine crystal phase changed from a low dimension to a high dimension, and the content of the molten slag’s structure unit (Q1) needed for cuspidine in the molten slag was markedly increased.

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“…Few papers are found for mold flux devitrification. [12,13,23] The present authors investigated traditional glassy mold fluxes [13,24] and glassy fluoride-free mold fluxes based on CaO-SiO 2 -TiO 2 -B 2 O 3 system using DTA. [25] Regarding devitrification of fluorine-free mold fluxes based on the CaO-Al 2 O 3 -B 2 O 3 system, no report was found in the literature.…”

Section: Introductionmentioning

confidence: 99%

Development of Non-reactive F-Free Mold Fluxes for High Aluminum Steels: Non-isothermal Crystallization Kinetics for Devitrification

Shu

Medeiros

et al. 2020

Metall Mater Trans B

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It is necessary to study crystallization from glass (devitrification) for non-reactive F-free CaO-Al 2 O 3 based mold fluxes; this is especially important for the development of mold fluxes for continuous casting of high aluminum steels. To the knowledge of the authors, there is no report in the literature regarding devitrification of F-free mold fluxes based on the CaO-Al 2 O 3-B 2 O 3-Na 2 O-Li 2 O system. Therefore, crystallization kinetics for particular compositions in this system, with different w(CaO)/w(Al 2 O 3) ratios, was investigated by Differential Scanning Calorimeter, Field-Emission Environmental Scanning Electron Microscopy / Energy Dispersive Spectroscopy, and X-ray Diffraction techniques. The first crystal, which precipitates during heating from glass, is Ca 12 Al 14 O 33 , followed by CaO. For the first crystal, which precipitates as plate-like (2-dimensional), it was found that, when using the Matusita-Sakka model, agreement between the calculated Avrami parameters and the micrographs obtained from electron microscope was reached. In the same way, agreement was found for the second event-CaO precipitation-which grows 2-dimensionally or 3-dimensionally, depending on the w(CaO)/w(Al 2 O 3) ratio. The most important event (in terms of energy liberated and amount of crystals) is Ca 12 Al 14 O 33 precipitation. For this event, the effective activation energy for crystallization, E G , decreases with the increase of w(CaO)/ w(Al 2 O 3) ratio. The activation energy for crystallization reflects the energy barrier for crystallization. Thus, it can be concluded that mold fluxes crystallization during heating is enhanced when increasing the w(CaO)/w(Al 2 O 3) ratio, for constant contents of B 2 O 3 , Na 2 O, and Li 2 O.

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Structure and Crystallization Kinetics of Glassy CaO-Al2O3-SiO2-CaF2-Na2O Mold Fluxes with Varying Basicity

Cited by 31 publications

References 30 publications

Effect of Al Speciation on the Structure of High‐Al Steels Mold Fluxes Containing Fluoride

Effect of Al Speciation on the Structure of High‐Al Steels Mold Fluxes Containing Fluoride

Effect of Bubbles on Crystallization Behavior of CaO–SiO2 Based Slags

Development of Non-reactive F-Free Mold Fluxes for High Aluminum Steels: Non-isothermal Crystallization Kinetics for Devitrification

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