Processes for Upgrading Metallurgical Grade Silicon to Solar Grade Silicon

Safarian, Jafar; Tranell, Gabriella; Tangstad, Merete

doi:10.1016/j.egypro.2012.03.011

Cited by 102 publications

(53 citation statements)

References 21 publications

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“…The Siemens process in particular is an expensive process with regard to high energy consumption. [2,3] The production of SoG-Si through metallurgical refining processes is more energy efficient and environmentally friendly than the chemical route which in turn may encourage a faster growth of the global PV market. This has been the motivation for the development of several refining processes such as the ELKEM Solar Silicon (ESS) process in Norway, the NS Solar process in Japan, Chinese metallurgical routes such as those of Shanghai Propower and Ningxia, and the Photosil process in France.…”

mentioning

confidence: 99%

“…[1] A majority of SoG-Si and all the EG-Si existing in the market are currently produced from MG-Si through the Siemens process or the newly developed fluid bed reactor (FBR) technology. In these chemical processes, pure silicon is deposited on rods or seeds from a gas phase, which is produced from MG-Si and contains gaseous compounds of silicon such as SiHCl 3 or SiH 4 . The Siemens process in particular is an expensive process with regard to high energy consumption.…”

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confidence: 99%

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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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confidence: 99%

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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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“…The solidification method has also been studied for the purification of Si. 18) However, some elements with large segregation coefficients, such as B and P, are extremely difficult to remove by solidification segregation.…”

Section: Purification Of Si Crystal Using Namentioning

confidence: 99%

Low-temperature synthesis of Si and Si-based compounds using Na

Morito

2014

J. Ceram. Soc. Japan

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Low-temperature solution growth of Si crystals using Na was demonstrated based on the NaSi binary phase diagram. Single crystals, films, porous bulk samples, and helical microtubes of Si crystals were prepared from a NaSi solution by Na evaporation. Dissolution and crystallization of Si in a Na melt reduced the impurity content in the Si crystals. Low-temperature synthesis and morphology control of porous SiC ceramics using Na were also performed and a new ternary compound, Na 8 B 74.5 Si 17.5 , was synthesized.

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“…The most common route to produce SoG-Si from Metallurgical Grade Silicon (MG-Si) is still based around so-called the Siemens technology which includes gasification, distillation and re-deposition of silicon via trichlorosilane, a very energy intensive method which also generates significant amounts of chemical waste. [1] Hence, more cost effective metallurgical processes for making solar grade silicon -with less environmental impact -have been studied and developed in the recent years due to the rapid PV market growth. Boron (B) and phosphorus (P) are the two crucial impurity elements that are most difficult to be removed from silicon, since they cannot be effectively separated by directional solidification, a key process step for removing many 2 impurities such as Fe, Ti, Al, Ca, Mg, etc..…”

Section: Introductionmentioning

confidence: 99%

“…[12] Based on our recent publication, [12] hydrogen existence in the refining gas is crucially important for B removal and there is significant dissolved hydrogen in the system for the chemical reaction (1). It was experimentally shown that the kinetics of B removal by H 2 -H 2 O gas is much higher than that by Ar-H 2 O and N 2 -H 2 O under similar refining conditions.…”

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Mechanisms and Kinetics of Boron Removal from Silicon by Humidified Hydrogen

Safarian

Tang

Olsen

et al. 2015

Metall Mater Trans B

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The removal of boron from silicon by top blowing of humidified hydrogen has been studied in the present work through experimental work, thermodynamic calculations, computational fluid dynamic modeling, and quantum chemistry calculations. The effect of process parameters; temperature, lance diameter, lance distance from the melt surface, gas flow rate, and crucible material on the kinetics of boron removal were studied. It has been shown that the rate of boron removal is decreased with increasing temperature due to the competitive reactions between silicon and oxygen as well as boron and oxygen, which can be confirmed with the increases of p SiO /p HBO in the system. The rate of boron removal is increased with increasing the gas flow rate due mainly to the better supply and transport of the gas over the melt surface, as confirmed by the CFD modeling. Moreover, the rate of boron removal in alumina crucible is the highest followed by that in quartz and graphite crucibles, respectively. Based on the obtained results, it has been proposed that boron removal from silicon melt by humidified hydrogen is controlled both by the chemical reaction for boron gasification and mass transport in the adjacent gas phase.

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Processes for Upgrading Metallurgical Grade Silicon to Solar Grade Silicon

Cited by 102 publications

References 21 publications

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

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

Low-temperature synthesis of Si and Si-based compounds using Na

Mechanisms and Kinetics of Boron Removal from Silicon by Humidified Hydrogen

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