Raman Spectra Analysis

The Raman spectra fragments of the sample between 400 and 1400 cm-1 are plotted in Fig. 1. The Raman spectra of mold fluxes display two main regions: one between 600 and 700 cm-1 corresponding to Si–O–Si bending vibrations within inter-tetrahedral linkages and the other between 800 and 1200 cm-1 associated with Si–O stretching vibrations of mainly depolymerized silicate species. Moreover, the Raman peak at ∼550 cm-1 in sample 3 is related to the transverse motion of the bridging oxygen within the Al–O–Al linkage. The characteristic peaks for the Raman spectra of the various structural units (Qn) were obtained by typically fitted until an R2 value >99.5% was achieved as listed in Table 2. The typical deconvolution result for the mold fluxes …show more content…
Each Si cation in the center is surrounded by four oxygen anions, and all the tetrahedron SiO44- complexes are connected to each other by Si–O–Si bonds called bridging oxygen (BO). When cations such as Na+ or Ca2+, are added (in the form of Na2O or CaO) to SiO, they break some of the Si–O–Si bonds and form the nonbridging oxygen (O-) NBO, thus de polymerizes molten slag. When Al2O3 is added in mold flux, Al3+ ions are amphoteric and can enter as both the network formers and the network modifiers. When Al3+ ions act as the network formers in the form of [AlO4], a cation must be sited near the Al3+ to provide electrical charge balance (i. e., to form (NaAl4+)). When the mold flux has a low CaO/SiO2 ratio, the network modifiers such as Na2O or CaO, mainly used to break the Si–O–Si bonds and depolymerizes the silicate structure, and the Al3+ ions mainly act as the network modifiers (Samples 1 and 2). When the mold fluxes has a high CaO/SiO2 ratio, there were a lot of the network modifiers in the mold flux. The network modifiers are used to break the Si–O–Si bonds; however they can also promote the form of [AlO4] (Sample 3). The Al3+ ions are absorbed into the silicate structure acting as network former, increasing the complexity of the silicate structure. Mold fluxes usually contain ∼5 wt% Al2O3, but there is typically, a 4 wt% pickup of Al2O3 from the inclusions arising from (i) steelmaking processes and (ii) from the reaction between Al in the steel and the slag pool. The additional increased Al2O3 contents tend to change the mold flux properties in terms of viscosity and crystallization by the silicate structure. This maybe the reason of the mold flux works successfully on a particular caster, but fails to perform on a caster of a similar design utilizing liquid steel. The content of pickup of Al2O3 from the liquid steel by mold flux is different in different steel plants. This leads to different changes in