Thermal Conductivity of the CaO–Al2O3–SiO2 System

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Using a transient hot-wire method, the thermal conductivity of the CaO-SiO2-B2O3 mold flux system was measured. The effects of temperature, BO1.5 concentration and basicity on the thermal conductivity were considered, along with structural investigation by Raman spectroscopy. It was found that the addition of boron oxide caused both a decrement and increment of thermal conductivity, depending on the basicity. These conflicting effects on thermal conductivity were considered to be caused by the following two different behaviors in the oxide melts. Boron oxide is incorporated into silicate networks at a lower basicity, while it tends to form borate networks at higher CaO/SiO2 ratios. In the case of basicity dependency, thermal conductivity initially decreases or remains constant with increasing CaO/SiO2 ratio in regions of low basicity, but increases when the CaO/SiO2 ratio is higher than 1.15. Due to the incorporated state of boron oxide in silicate networks at low basicity, the thermal conductivity is likely to be predominantly affected by the silicate networks. However, at a relatively high CaO/SiO2 ratio, an increase in chain-type metaborate was observed through Raman spectroscopy; this structural change in borate being responsible for the increment in thermal conductivity with higher basicity. Finally, the apparent activation energy of thermal conductivity was calculated, and was found to be reduced by the addition of boron oxide.

Section: Relations Between Activation Energy and Its Molten Structurementioning

confidence: 99%

Relationship between Molten Oxide Structure and Thermal Conductivity in the CaO–SiO2–B2O3 System

Kim

Morita

2014

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“…[2][3][4] The structural unit of aluminate anion is very complicated and thus Al coordination number varies from 4 to 6, viz. AlO 4 , AlO 5 and AlO 6 units.…”

Section: Introductionmentioning

confidence: 99%

Structure-Viscosity Relationship of Low-silica Calcium Aluminosilicate Melts

Kim¹,

Park²

2014

153

The structure-viscosity relationship of the low-silica (SiO2 ≤ 10 wt%) calcium aluminosilicate melts, which represent the secondary refining ladle slag systems, was investigated by employing the rotatingcylinder 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 explored. The viscosity of low-silica calcium aluminosilicate melts decreased with increasing both CaO/Al2O3 and CaO/SiO2 ratios. However, the effect of the former on the viscosity of low-silica calcium aluminosilicate melts was larger than that of the latter. By employing the Neuville's structure model, in which the silicate structural units with various NBO, i.e. Q n Si are located at the boundary of the AlO4 aluminate, and the Raman scattering data of the glass samples, it was demonstrated that the aluminate and silicate units are more effectively modified by increasing the CaO/Al2O3 ratio at fixed silica content. The addition of small amounts of CaF2 (~5 wt%) to the low-silica calcium aluminosilicate melts decreased the viscosity of the melts. From the analysis of Raman scattering data, the liberation of SiO4 4-(Q 0 Si) units from the AlO4 aluminate structure by addition of CaF2 was understood. However, the effect of CaF2 addition on the viscosity became less discernible at higher CaF2 content (≥ 10 wt%) region, where the F ions simply substitute for the non-bridging oxygen ions in AlO4 tetrahedra.KEY WORDS: structure; viscosity; low-silica calcium aluminosilicate; ladle slag; Raman spectroscopy; thermophysical property; non-bridging oxygen (NBO); calcium fluoride (CaF2).

“…54) However, it has also been reported that the thermal conductivity of a molten CaOAl2O3-SiO2 slag exhibits a negative deviation from the expected linearity against 1/T. 7) This disagreement may imply that the theory of heat conduction in crystalline solid as expressed by Eq. (4) is not valid in the molten silicate.…”

Section: Temperature Dependence Of Thermal Conductivitymentioning

confidence: 74%

“…6,[26][27][28] Initially, the Na2O-SiO2 slag system was selected for thermal conductivity measurements, taking advantage of its relatively low melting point. 2,6,26,27,[30][31][32] Soon after, the hot wire method was also established for measuring the thermal conductivity of the CaO-Al2O3-SiO2, 7,[26][27][28] CaO-Al2O3-SiO2-MgO, 31) and CaO-SiO2-FeOx slag systems. 32,33) The fundamental measurement principle of the hot wire method can be described as follows: First, a thin thermoresistor wire is placed vertically in the middle of a molten sample.…”

Section: Non-steady-state Methodsmentioning

confidence: 99%

“…1. 2,5) In spite of a number of integrated studies into the relationship between thermal conductivity and the structure of molten slags, 2,[5][6][7] further clarification is still necessary for a complete understanding. For example, recently reported analyses of the microstructure of various slag systems using Fourier Transform-Infrared Spectroscopy (FT-IR), Raman Spectroscopy, Nuclear Magnetic Resonance (NMR) might provide further insight into the relationship between structure and thermal conductivity.…”

Section: Introductionmentioning

confidence: 99%

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Thermal Conductivity of Molten Slags: A Review of Measurement Techniques and Discussion Based on Microstructural Analysis

Kang¹,

Morita²

2014

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In order to properly interpret the thermal conductivity of molten silicate slags, several different measurement methods are briefly reviewed, along with a discussion as to their respective advantages and limitations. In addition, a large number of thermal conductivity values measured by these methods are assessed, in order to evaluate their dependence on composition and temperature. The behavior of the thermal conductivity of molten silicate slags was found to show good agreement with well-focused analyses into its microstructure. Moreover, with an improved understanding of the microstructure of silicate slags, there is an apparent co-relation between thermophysical properties such as thermal conductivity, viscosity, and so forth.KEY WORDS: thermal conductivity; molten slag; silicate; hot-wire method; laser flash method.