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Viscosity-Structure Relationship of
Molten Slags and Glasses
(고온 세라믹 융체의 고온점성 측정 및 원자단위 구조와의 상관성 규명 연구 )
Viscosity-structure relationship of alkaline earth silicate melts containing manganese oxide and calcium fluoride
(Kim and Park: J. Am. Ceram. Soc., 2019, vol.102, pp.4943-4955)
BaCO3 (or BaO) has been proposed as a fluxing additive for producing ultra‐low phosphorus ferromanganese alloys under oxidizing conditions because BaO‐based fluxes have relatively higher phosphate capacity than conventional CaO-based fluxes. BaO‐ and MnO‐containing slags could be produced when BaO‐based fluxes are added during the dephosphorization reaction. Thus, slags containing MnO and BaO could be used as a Mn source for producing silicomanganese alloy via chemical reaction with Si‐rich metals in duplex processing.
Little experimental work to understand the effect of CaF2 addition on the viscosity of MnO‐containing barium silicate melts has been carried out, although some experimental efforts have sought to understand the viscosity of MnO‐containing calcium silicate systems. In the present study, we investigate the viscosity of MnO‐containing barium silicate melts to clarify the effect of CaF2 on the viscous flow and structure of alkaline earth silicate melts at high temperature using Raman spectroscopy.
Viscosities of the BaO-SiO2-42MnO-9MgO-CaF2 (BaO/SiO2 = 0.4, mol%) melts as a function of temperature with different CaF2 contents.
NBO/Si ratio of MO-SiO2-MnO(-MgO)-CaF2 melts (M = Ca or Ba) as a function of CaF2 content with different MnO contents.
Structure-Viscosity Relationship of Low-silica Calcium Aluminosilicate Melts
(Kim and Park: ISIJ Int., 2014, vol.54, pp.2031-2038)
It is necessary to remove the inclusions from molten steel to enhance the cleanliness of steel products in secondary refining processes. There are following consecutive processes for the removal of inclusions, viz. (i) flotation of inclusions to the steel melt-slag interface, (ii) separation into the slag phase and (iii) dissolution into the slag phase, among which the final step was reported to be a rate controlling process for the removal of inclusions.
Even though a few reports on the structural changes in the low-silica calcium aluminosilicate melts have been published by glass scientists and chemical geologists, the relationship between the viscosity and the structure of the melts, which potentially correspond to the secondary refining ladle slags, is not fully developed yet. Therefore, in the present study, the structure-viscosity relationship of the low-silica (SiO2 ≤ 10 wt%) calcium aluminosilicate melts was investigated by employing the rotating-cylinder viscosity measurement in conjunction with the Raman spectroscopy measurement for linking the macroscopic thermophysical property and molecular (ionic) structural information. Furthermore, the influence of CaF2 on the structure-property relationship was discussed
Typical deconvolution result for the CaO-Al2O3-8%SiO2-5%MgO-10%CaF2 (CaO/Al2O3=1.2) system.
Identification of Q_Al and Q_Si structural units at specific Raman scattering wavenumbers.
Structure-Property relationship of CaO-MgO-SiO2 system: Quantitative analysis of Raman spectra
(Park: Metall. Mater. Trans. B, 2013, vol.44B, pp.938-947) ; Marcus Grossmann Awarded paper [link]
Knowledge of the structure of silicate melts is of great importance in metallurgical processes. The structure of silicate melts is the dominant factor affecting the transport properties, such as viscosity, conductivity, density, etc. Therefore, there have been numerous attempts to measure and/or predict these macroscopic thermophysical properties as a function of the composition of silicates based on the microscopic view of structures.
In the current study, the effects of CaO/SiO2 ratio, SiO2 content, and Ca-Mg substitution on the distribution of silicate anionic species in the CaOSiO2-MgO slag system were investigated by micro-Raman spectroscopic analysis of melt-quenched glass samples. Furthermore, the relationships among the structural and physicochemical properties of silicate melts were evaluated.
Equilibrium phase diagram of the CaO-SiO2-MgO slag and the composition of glass samples prepared in the current study.
Raman spectra of CaO-SiO2-20 mol pct MgO system with CaO/SiO2 ratio ranges from 0.3 to 1.0.
Effect of Silicate Structure on Thermodynamic Properties of Calcium Silicate Melts: Quantitative Analysis of Raman Spectra
(Park: Met. Mater. Int., 2013, vol.19, pp.577-584)
In the present study, calcium silicate glass samples containing MnO or MgO were prepared by batch melting and quenching method. Recently, Park unveiled that the sulfide capacity of the CaO–SiO2–MnO slag is strongly dependent on the effect of CaO and MnO on the depolymerization behavior of silicate networks.
From these previous works, the quantitative information on the structure of the CaO–SiO2–MO (M=Mn and Mg) slags and the interrelationship between structure and thermodynamic properties are still highly necessitated. Consequently, in the present study, not only a distribution of silicate anionic species but also a chemical speciation of free oxygen, non-bridging oxygen and bridging oxygen in the CaO–SiO2–MO (M=Mn and Mg) slags are investigated by employing micro–Raman spectroscopic analysis for melt–quenched samples. Furthermore, the thermochemical properties such as sulfide capacity and excess free energy of mixing of oxide components are evaluated using a concentration of free oxygen as well as a degree of polymerization of silicate melts.
Relationship between the partial molar excess free energy of mixing of CaO, MnO, MgO and SiO2, and the degree of polymerization, Q3/Q2 ratio in the CaO–SiO2–MO (M=Mn and Mg) melts at 1600 oC.
Composition-structure-property relationships of CaO-MO-SiO2 (M=Mg2+, Mn2+) systems derived from micro-Raman spectroscopy
(Park: J. Non-Cryst. Solids, 2012, vol.358, pp.3096-3102)
Knowledge of the structure of silicate melts and glasses is of great importance for both earth sciences and materials sciences, such as metallurgical processes and glass sciences. The structure of silicate melts and glasses is the dominant factor affecting the transport properties, such as viscosity, conductivity, density, etc. Therefore, there have been numerous attempts in the fields of chemical geology, metallurgy, and glass science to measure and/or predict these macroscopic thermophysical properties as a function of the composition of silicates based on microscopic view of structures.
Viscosity is of particular importance because it controls the rate of transport of matter and thus, of energy. Generally, the largest changes in the viscosity of silicate melts are found when metal oxides, MO (where M=alkali, alkaline earth, transition metals, etc.) are added to SiO2. The associated variation in activation energy follows a similar trend. As the MO content increases, the microheterogeneous structure transforms gradually to discrete polyanions, and finally to isolated [SiO4]4– ions.
Over limited temperature intervals, electrical conductivity or resistivity follows an Arrhenius-type law, as does viscosity. The activation energy has been shown to decrease slightly with increasing MO content.
Vibrational spectroscopy, specifically Raman spectroscopy was originally used to probe the local anionic structure of silicate glasses. The bands assigned to antisymmetric stretching of Si–O– (non–bridging oxygen; NBO) and Si–O0 (bridging oxygen; BO) bonds occur in the 850–1200 cm–1 region, whereas Si–O–Si bending modes are found between 500 and 700 cm–1. The frequencies of the stretching modes decrease with decreasing degree of polymerization of the glass, viz. increasing NBO/Si. There are several types of units, such as SiO2 (fully polymerized), Si2O5 (sheet), SiO3 (chain), Si2O7 (dimer), and SiO4 (monomer). Based on a nuclear magnetic resonance (NMR) spectra of silicate glasses, the stoichiometric notations for each unit were replaced by the so–called Qn concept as follows: Q4 (NBO/Si=0), Q3 (NBO/Si=1), Q2 (NBO/Si=2), Q1 (NBO/Si=3), and Q0 (NBO/Si=4).
In the present study, calcium silicate glasses containing MgO or MnO were prepared by batch melting and quenching. Recently, Park reported that sulfur absorption ability, viz. the sulfide capacity of the CaO–MnO–SiO2 melts, is strongly dependent on the effect of CaO and MnO on the depolymerization of silicate networks. Consequently, in the present study, the effect of Mn2+ and Mg2+ ions on the distribution of silicate anionic species in calcium silicate systems was investigated by micro–Raman spectroscopic analysis of melt–quenched samples. Furthermore, the relationships among the structural and thermophysical properties of silicate melts, such as viscosity, density, and conductivity were evaluated.
Typical deconvolution of the Raman spectra obtained for the 2CaO×3MgO×5SiO2 glass.
Relationship between the viscosity and the Q3/Q2 ratio of CaO–MO–SiO2 (M=Mn, Mg) melts at 1500 and 1600 oC. Activation energy of the viscous flow of melts as a function of the Q3/Q2 ratio.
Structure–Property Correlations of CaO–SiO2–MnO Slag derived from Raman Spectroscopy
(Park: ISIJ Int., 2012, vol.52, pp. 1633-1642)
Even though there have been several studies on the physicochemical properties of the CaO–SiO2–MnO slag due to its importance in smelting and refining processes for the production of manganese ferro–alloys as well as high manganese steel grades, the systematic and fundamental approach on the structure of this slag system is scarcely found.
Recently, Park unveiled that the sulfide capacity of the CaO–SiO2–MnO slag is strongly dependent on the effect of CaO and MnO on the depolymerization behavior of silicate networks. From these previous works, the quantitative information on the structure of the CaO–SiO2–MnO slag is still highly necessitated.
Consequently, in the present study, the effects of lime to silica ratio, silica content, and Ca–Mn substitution on the distribution of silicate anionic species in the CaO–SiO2–MnO slag are investigated by employing micro–Raman spectroscopic analysis for melt–quenched samples. Furthermore, the relationships among the structural information, thermophysical properties such as viscosity, density and electrical conductivity are developed.
Equilibrium phase diagram of the CaO–SiO2–MnO slag and the composition of glass samples prepared in the present study.
Raman spectra of CaO–MnO–50mol% SiO2 system with Mn/(Mn+Ca) ratio ranges from about 0 to 0.8. and Abundance of structural units and Q3/Q2 ratio as a function of Mn/(Mn+Ca) ratio.
Schematics of the structural modification by network–modifying role of Ca2+ and Mn2+ ions in the 50mol% SiO2 system.
Novel Approach to Link between Viscosity and Structure of Silicate Melts via Darken's Excess Stability Function: Focus on the Amphoteric Behavior of Alumina
(Park, Kim, and Min; Metall. Mater. Trans. B, 2008, vol.39B, p.150)
The relationship between thermophysical properties and the structure of silicate melts is of importance to understand the microscopic origin of the thermodynamic properties not only in the metallurgical community but also in chemical geology. The viscosity, which determines the working temperature and process kinetics of the system, CaO-SiO2-Al2O3-MgO melt, has been measured by many researchers. The structure of the subsystems with mainly binary and ternary was investigated with the aid of various experimental techniques. Further, we can find some reports on the measurement or optimization of thermodynamic activities of each component in this quaternary system at high temperatures. Furthermore, there has been considerable interest in the amphoteric behavior of alumina, which acts as a network modifier or network former according to the composition of aluminosilicate melts.
Although there are several studies on viscosities, structures, and thermodynamic properties of CaO-SiO2-Al2O3-MgO slag, comprehensive explanations integrating all three factors together at a given system are still insufficient. Park et al. measured the viscosity and Fourier transform-infrared (FT-IR) transmitting spectra of CaO-SiO2-Al2O3(-MgO) melts and glasses and revealed the amphoteric behavior of alumina based on the changes of activity coefficient of alumina and silica.
In the present study, in line with previous works, the effect of alumina on the relationship between viscosity and structure of the CaO-SiO2-Al2O3-15mol%MgO ((mol%CaO)/(mol%SiO2), B=1.2) system is investigated by employing a viscometer using the rotating cylinder method and FT-IR spectra, respectively. In addition, the original Darken's excess stability function was introduced in order to understand the thermophysical phenomena and the role of alumina based on thermodynamics.
FT-IR transmittance of the CaO-SiO2-Al2O3-15mol%MgO (B=1.2) glasses as a function of wave numbers.
Changes of excess stability of alumina in the CaO-SiO2-Al2O3-15mol%MgO (B=1.2) melts at 1773 K with the concentration of alumina.
Structural Assessment of Fluorine in Calcium Silicates: Focusing on the Viscosity of CaO-SiO2-CaF2 System
(Park, Min, and Sasaki; ICS2008, October 2008, JAPAN; ISIJ Int., 2007, vol.47, p.1368)
Because the viscosity of the CaO-SiO2-CaF2 system is very important in primary and secondary refining as well as continuous casting processes, several researchers measured the viscosity of this slag system. Recently, Park et al. had an attempt to interrelate the viscosity with the structural analysis by applying the rotating cylinder method for molten slags at temperatures from 1473 to 1823 K. The characterization of structural analysis was operated by the Fourier-transform infra-red (FT-IR) spectra for quenched samples. The authors observed that a decrease of the viscosity as well as the activation energy for viscous flow of the slags (B=1.0 and 1.3) in a Newtonian flow region is originated from a decrease in the degree of polymerization due to a network modifying role of F- ions in silicate melts. Although the role of F- ions in the (de)polymerization reaction of silicate melts is still in a room for further discussion based on various analytical methods such as FT-IR, Raman, X-ray photoelectron spectroscopy (XPS), and 19F nuclear magnetic resonance (NMR) spectroscopy, it is simply believed that the existence of F- ions decreases the viscosity of silicate melts, as noted by Sasaki et al.
Newly proposed iso-viscosity contour in the CaO-SiO2-CaF2 system at 1873 K.