• norsk
    • English
  • English 
    • norsk
    • English
  • Login
View Item 
  •   Home
  • Fakultet for naturvitenskap (NV)
  • Institutt for materialteknologi
  • View Item
  •   Home
  • Fakultet for naturvitenskap (NV)
  • Institutt for materialteknologi
  • View Item
JavaScript is disabled for your browser. Some features of this site may not work without it.

Removal of Boron from Silicon by Gas refining with Water and Hydrogen

Sulentic, Ines
Master thesis
View/Open
565836_FULLTEXT01.pdf (Locked)
565836_COVER01.pdf (Locked)
URI
http://hdl.handle.net/11250/249051
Date
2012
Metadata
Show full item record
Collections
  • Institutt for materialteknologi [1572]
Abstract
A high demand of silicon for solar cells has lead to a search of an alternative route to solar grade silicon. A suggested method is upgrading metallurgical grade silicon. This thesis focuses on the gas refining of silicon in order to removal boron from the silicon melt. The most documented refining gas is water and has been used in this thesis in a combination with hydrogen. The aim of this work was to determine the optimum water content in combination with hydrogen for boron removal from silicon. In addition to water content investigation, two different crucible materials were examined for this aim. The temperature of the process was 1500 ºC and the furnace in question was a resistance heated alumina tube furnace. The alumina tube cracked several times during experiments and was a source of error during the experimental work. The cracking of the alumina tube is believed to be due to the high cooling and heating rates of the experiments. It was shown that water is possible oxidation agent for boron removal in Si and that addition of H2 increases the boron removal rate. However, a high water content, such as 11 vol% H2O, showed a slow boron removal rate. The best results came from experiments with 3.2 vol% H2O + 50 vol% H2. During a 1.5 hour long experiment, the boron content was decreased from its doping concentration of 170 ppmw to 1.01 ppmw. The mass transfer coefficient, k*, of this experiment, was found to be 5∙10-5 m/s. ICP-MS and resistivity measurements were conducted to determine the boron concentration of the extracted samples during experiments. The reliability of the resistivity measurements is dependent on the size of the sample. The small sample sizes might have caused some uncertainties in the results. EPMA confirmed the presence of SiC and SiO2 phases in the silicon after experiments. It is assumed that these phases may lead to a blockage of the active surface area, which may hinder the boron oxidation. SiC is formed in the silicon due to a C contamination from the graphite crucibles used. It is believed that using a quartz crucible will lower this contamination.
Publisher
Institutt for materialteknologi

Contact Us | Send Feedback

Privacy policy
DSpace software copyright © 2002-2019  DuraSpace

Service from  Unit
 

 

Browse

ArchiveCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsDocument TypesJournalsThis CollectionBy Issue DateAuthorsTitlesSubjectsDocument TypesJournals

My Account

Login

Statistics

View Usage Statistics

Contact Us | Send Feedback

Privacy policy
DSpace software copyright © 2002-2019  DuraSpace

Service from  Unit