Refining of metallurgical silicon by directional solidification

Martorano, Marcelo Aquino; Neto, João Batista Ferreira; Oliveira, Theogenes Silva de; Tsubaki, Tomoe Oide

doi:10.1016/j.mseb.2010.11.010

Cited by 153 publications

(61 citation statements)

References 29 publications

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“…Therefore, the accumulation of SiC particles at the ingot top can only have occurred during the solidification experiments. For the lowest mold velocities, namely 5, 10, and 20 lm/s, a planar solid-liquid interface is expected, as described by Martorano et al [12,13] The structure of columnar grains aligned in the axial direction observed for these velocities (Figures 3(a) through (c)) is consistent with a planar solid-liquid interface growing upward, pushing the SiC particles to the ingot top and causing the larger carbon concentration in this region (Figure 1). An accumulation of precipitated particles was confirmed at the ingot top for these experiments, as seen in Figures 5(b) and (d).…”

Section: Effects Of Mold Pulling Velocity On Carbon Macrosegregationmentioning

confidence: 63%

Effects of Solidification Rate and Settling Time of SiC Particles on the Macrosegregation of Carbon in Silicon Ingots

Ribeiro

Neto

Martorano

2014

Metallurgical and Materials Transactions E

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The macrosegregation of carbon in silicon was studied aiming for silicon refining for photovoltaic applications. Experiments of directional solidification upward and of settling of SiC particles in the melt were carried out in a Bridgman furnace using electronic grade silicon intentionally contaminated with carbon. Mold pulling velocities in the range between 5 and 80 lm/s and settling time periods of 1 and 6 hours were adopted in the experiments. In the resulting cylindrical ingots, the macrosegregation of carbon along the axial direction was measured and their macro and microstructures revealed and examined. In all directional solidification experiments, the carbon concentration increases to the ingot top as result of an accumulation of SiC particles in this region. For the lower velocities (<40 lm/s), a larger particle accumulation and columnar grains aligned axially and pointing to the ingot top are seen, which is consistent with the pushing of SiC particles by a planar solid-liquid interface. For the settling experiments, the carbon concentration increases from the ingot top to the bottom as a result of the accumulation of SiC particles at the bottom. This accumulation is probably caused by the settling of SiC particles, but an increase in the settling time from 1 to 6 hours have no significant effect in the macrosegregation profile. Finally, in the conditions of the present experiments, the directional solidification of silicon at mold pulling velocities lower than 40 lm/s is more effective to remove carbon from silicon than the settling of SiC particles during times up to 6 hours.

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Section: Effects Of Mold Pulling Velocity On Carbon Macrosegregationmentioning

confidence: 63%

Effects of Solidification Rate and Settling Time of SiC Particles on the Macrosegregation of Carbon in Silicon Ingots

Ribeiro

Neto

Martorano

2014

Metallurgical and Materials Transactions E

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“…However, the PV industry has to face a serious low-cost feedstock supply shortage due to a rapid expansion of the solar cell industry. To lower the production cost of Si solar cells, a promising way is to upgrade metallurgical-grade silicon (MGSi) to solar-grade silicon (SoG-Si) with metallurgical treatments [2][3][4][5] . However, boron (B) element, an impurity in MG-Si, cannot be removed efficiently because of its low vapor pressure (lower than that of Si) [6] and large segregation coefficient (0.8 at 1,414 ºC) [7] .…”

Section: Laboratory Of Special Processing Of Raw Materials Dalian Unmentioning

confidence: 99%

Separation of primary Si and impurity boron removal from Al-30%Si-10%Sn melt under a traveling magnetic field

et al. 2016

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C rystalline silicon is one of the materials used for solar cells, accounting for over 90% of the photovoltaic (PV) materials [1] . However, the PV industry has to face a serious low-cost feedstock supply shortage due to a rapid expansion of the solar cell industry. To lower the production cost of Si solar cells, a promising way is to upgrade metallurgical-grade silicon (MGSi) to solar-grade silicon (SoG-Si) with metallurgical treatments [2][3][4][5] . However, boron (B) element, an impurity in MG-Si, cannot be removed efficiently because of its low vapor pressure (lower than that of Si) [6] and large segregation coefficient (0.8 at 1,414 ºC) [7] . In recent years, considerable progress has been made in B removal from the MG-Si using hypereutectic Al-Si alloy solidification refining process at low temperatures [8][9][10][11] . In the alloy solidification process, the primary Si initially precipitates from supersaturated melt with decreasing Abstract: Separation of primary Si phase and removal of boron in the primary Si phase during the solidification process of the Al-30%Si-10%Sn melt under a traveling magnetic field (TMF) were investigated. The results showed that the agglomeration layer of the primary Si can be formed in the periphery of the ingot while the inner microstructures mainly consist of the eutectic α-Al+Si and β-Sn phases. The intense melt flow carries the bulk liquid with higher Si content to promote the growth of the primary Si phase which is first precipitated close to the inner wall of crucible with a relatively lower temperature, resulting in the remarkable segregation of the primary Si phase. The content of impurity B in the primary Si phase can be removed effectively with an increase in magnetic flux intensity. The results of electron probe microanalysis (EPMA) clearly indicated that the average intensity of the B Ka line in the α-Al phase region of Al-Si-Sn alloy is higher in the case of solidification under TMF than that of normal solidification condition, suggesting that the electromagnetic stirring can promote the B removal from the primary Si phase. temperature, during which more impurities, especially B, are enriched in the alloy by redistributing the impurities to the solid/liquid (S/L) interface. Adding pure Sn to the hypereutectic Al-Si alloy can effectively expand the crystallization temperature range to promote the growth of the primary Si [12,13] . However, considering the diffusion kinetics of the impurities at the nearby growing Si surface, a more effective enhanced S/L segregation tendency of impurities has not been achieved.In the present study, the traveling magnetic field (TMF) was applied during solidification of the Al-30%Si-10%Sn melt to separate the primary Si. Furthermore, the effect of the electromagnetic stirring on B removal from the primary Si during the solidification of the Al-30Si-10Sn melt was investigated. Experimental procedureCommercial purity Al (99.7 wt.%), Sn (99.99 wt.%) and MG-Si (99.7 wt.%) (all the compositions quoted in this work are in wt.% unless ot...

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“…A formação da macrossegregação na solidificação dendrítica é geralmente atribuída ao transporte convectivo de soluto no líquido ou à movimentação do sólido [1], mas, durante a solidificação direcional com interface sólido-líquido planar, a macrossegregação pode se formar apenas com o transporte difusivo de soluto [2][3][4]. Modelos matemáticos já foram propostos para descrever a macrossegregação induzida pelo transporte difusivo de soluto na interface sólido-líquido planar [5,6,3], nos quais a interface é assumida plana mesmo em condições de solidificação que resultariam em uma zona pastosa com células ou dendritas, o que poderia modificar completamente o perfil de macrossegregação observado [7].…”

Section: Introductionunclassified

Modelo Matemático Unificado Para Micro- E Macrossegregação Em Solidificação Direcional Planar E Celular

Regados¹,

Martorano²,

Lima³

et al. 2018

ABM Proceedings

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ResumoUm modelo para prever a formação da macrossegregação em ligas metálicas binárias foi proposto e implantado a partir das equações macroscópicas de conservação de massa e espécies químicas, resolvidas numericamente em forma adimensionalizada através do Método dos Volumes Finitos para a realização de uma análise paramétrica, na qual se verificou o efeito de parâmetros de processo como o gradiente e a velocidade de solidificação, além de parâmetros do material como o coeficiente de partição de soluto. A análise paramétrica indicou condições nas quais a macrossegregação induzida pela macrodifusão se torna considerável, convergindo para sistemas com interface plana, enquanto altas velocidades de solidificação tornam esse efeito desprezível, aproximando o sistema do perfil de solidificação de Scheil para a fração de sólido. O efeito da reação eutética também foi avaliado, indicando sua influência na formação da segregação de soluto e na estabilidade da interface sólido-líquido planar. Palavras-chave: Macrossegregação; Solidificação direcional; Estabilidade interfacial. UNIFIED MATHEMATICAL MODEL OF MICRO AND MACROSEGREGATION FOR PLANAR/CELLULAR UNIDIRECTIONAL SOLIDIFICATION AbstractA model to predict the formation of macrosegregation in binary metallic alloys was proposed and implemented using macroscopic conservation equations for mass and chemical species. The equations were solved with the Finite Volume Method using a scaled format prepared for a parametrical analysis, in which the effect of process parameters, such as the thermal gradient or solidification velocity, and material properties, like the solute partition coefficient, was evaluated. The analysis pointed conditions where diffusion-induced macrosegregation becomes important until converging to a planar-interface system, while high solidification velocities rendered it negligible, moving it towards the Scheil model. The eutectic reaction's effect was also checked, showing its influence in solute segregation and in the planar interface stability.

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Refining of metallurgical silicon by directional solidification

Cited by 153 publications

References 29 publications

Effects of Solidification Rate and Settling Time of SiC Particles on the Macrosegregation of Carbon in Silicon Ingots

Effects of Solidification Rate and Settling Time of SiC Particles on the Macrosegregation of Carbon in Silicon Ingots

Separation of primary Si and impurity boron removal from Al-30%Si-10%Sn melt under a traveling magnetic field

Modelo Matemático Unificado Para Micro- E Macrossegregação Em Solidificação Direcional Planar E Celular

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