Behavior and State of Boron in CaO–SiO2 Slags during Refining of Solar Grade Silicon

Teixeira, Leandro Augusto Viana; Tokuda, Yomei; Yoko, Toshinobu; Morita, Kazuki

doi:10.2355/isijinternational.49.777

Cited by 104 publications

(50 citation statements)

References 7 publications

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“…The region close to SiO 2 saturation is compared with previous works [2][3][4][5][6][7][8] in Figure 3, and the present work is seen to be higher than most other works at SiO 2 saturation. Only in the study by Miki et al [8] they found a higher concentration than in the present work.…”

Section: A the Binary Cao-sio 2 Systemcontrasting

confidence: 35%

“…These values are seen in Figure 1 to be in good agreement with the values found by ICP-MS. The results in the present work are compared with previous works in Figure 2 where it is seen that the calcium concentration in the present work is somewhat lower than in previous works [2][3][4] for slags with high CaO content. An estimate by Schei et al [5] at 1823 K (1550°C) is also included in the figure, and this estimate is seen to be in closest agreement with the present work.…”

Section: A the Binary Cao-sio 2 Systemsupporting

confidence: 32%

“…The MATLAB Surface Fitting Tool was used to fit Eq. [3] to the measured data, and [10] is also indicated as vertical lines.…”

Section: Discussionmentioning

confidence: 99%

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Thermodynamic Activities and Distributions of Calcium and Magnesium Between Silicon and CaO-MgO-SiO2 Slags at 1873 K (1600 °C)

Jakobsson

Tangstad

2015

Metall Mater Trans B

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The distributions of calcium and magnesium between silicon and CaO-MgO-SiO 2 slags have been determined in the present study at 1873 K (1600°C). The distribution equilibria were used to estimate the activities of the slag components in the binary CaO-SiO 2 and MgO-SiO 2 systems. These activities were used to determine the Henrian activity coefficients of calcium and magnesium in liquid silicon at 1873 K (1600°C). The distribution equilibria were also used to estimate the activity of SiO 2 in the ternary CaO-MgO-SiO 2 system. Finally, the activities of CaO and MgO were estimated in the ternary CaO-MgO-SiO 2 system using the determined Henrian activity coefficients in liquid silicon together with the distribution equilibria and the estimated activities of SiO 2 .

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Section: A the Binary Cao-sio 2 Systemcontrasting

confidence: 35%

Section: A the Binary Cao-sio 2 Systemsupporting

confidence: 32%

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Thermodynamic Activities and Distributions of Calcium and Magnesium Between Silicon and CaO-MgO-SiO2 Slags at 1873 K (1600 °C)

Jakobsson

Tangstad

2015

Metall Mater Trans B

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“…Teixeira et al 33) reported that the activity coefficient of BO1.5 in a CaO-SiO2 binary slag system increases with basicity in acidic slag compositions, while decreasing under basic conditions. They explained that at a molar ratio of CaO/SiO2 less than 0.86, boron oxide is incorporated into the silicate network.…”

Section: Effect Of Temperature and Composition On Thermal Conductivitymentioning

confidence: 99%

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

Kim

Morita

2014

ISIJ Int.

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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.

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“…Moreover, slag refining can be performed on a large scale, which makes it more economic than many other process candidates, which are not as scalable. The potential of slags for B removal includes silicate slag compositions such as CaO-SiO 2 , [5][6][7][8][9][10] CaO-Ca F 2 -SiO 2 , [6,8,11,12] CaO-BaO-SiO 2 , [6] CaO-MgO-SiO 2 , [5,6,13] CaO-Al 2 O 3 -SiO 2 , [14] CaO-Na 2 O-SiO 2 , [14,15] Al 2 O 3 -CaOMgO-SiO 2 , [16] Al 2 O 3 -BaO-SiO 2 , [16] and Al 2 O 3 -CaO-MgOSiO 2 . [16] The thermodynamic equilibrium for B distribution between liquid silicon and molten slags has been most studied and the ratio of the concentrations of B in slag and silicon phases, the distribution coefficient denoted L B (L B ¼ pct B ð Þ wt pct B ½ ), has been determined.…”

mentioning

confidence: 99%

Thermodynamic and Kinetic Behavior of B and Na Through the Contact of B-Doped Silicon with Na2O-SiO2 Slags

Safarian

Tranell

Tangstad

2013

Metall Mater Trans B

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Boron (B) is the most problematic impurity to be removed in the processes applied for the production of solar grade silicon. Boron removal from liquid silicon by sodium-silicate slags is experimentally studied and it is indicated that B can be rapidly removed within short reaction times. The B removal rate is higher at higher temperatures and higher Na 2 O concentrations in the slag. Based on the experimental results and thermodynamic calculations, it is proposed that B removal from silicon phase takes place through its oxidation at the slag/Si interfacial area by Na 2 O and that the oxidized B is further gasified from the slag through the formation of sodium metaborate (Na 2 B 2 O 4 ) at the slag/gas interfacial area. The overall rate of B removal is mainly controlled by these two chemical reactions. However, it is further proposed that the B removal rate from silicon depends on the mass transport of Na in the system. Sodium is transferred from slag to the molten silicon through the silicothermic reduction of Na 2 O at the slag/Si interface and it simultaneously evaporates at the Si/gas interfacial area. This causes a Na concentration rise in silicon and its further decline after reaching a maximum. A major part of the Na loss from the slag is due to its carbothermic reduction and formation of Na gas.

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Behavior and State of Boron in CaO–SiO2 Slags during Refining of Solar Grade Silicon

Abstract: Fig. 11.11 B NMR result for sample having a basicity of 0.55 containing around 0.25 % of boron and results simulated by quantum chemical calculation (vertical lines).

Cited by 104 publications

References 7 publications

Thermodynamic Activities and Distributions of Calcium and Magnesium Between Silicon and CaO-MgO-SiO2 Slags at 1873 K (1600 °C)

Thermodynamic Activities and Distributions of Calcium and Magnesium Between Silicon and CaO-MgO-SiO2 Slags at 1873 K (1600 °C)

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

Thermodynamic and Kinetic Behavior of B and Na Through the Contact of B-Doped Silicon with Na2O-SiO2 Slags

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