Researchers from Norway and Germany investigated the affect of impurities in fused quartz crucibles utilized in silicon PV ingot manufacturing. The outcomes counsel that the principle components that affect the uniformity of the crucible are the standard of the sand, the particle measurement of the sand, and features of the manufacturing course of.
Researchers from Norway and Germany investigated the affect of impurities in fused quartz crucibles utilized in silicon PV ingot manufacturing, particularly the bodily properties and the uniformity of hydroxyl impurities.
The analysis was completed by infrared microscopy and viscosity testing.
“Understanding the weaker factors of the crucible construction can result in its enchancment,” mentioned corresponding writer Gabriela Kazimiera Warden. pv journal. “We consider that our analysis needs to be of curiosity to crucible producers, as a result of it reveals that some features of the manufacturing course of can affect the ultimate properties of the crucible. It can be essential for them to grasp the standard of the ingot , its contamination and what they will count on from the crucibles throughout use.”
The uncooked materials utilized in Czochralski puller crucibles is pure quartz sand (SiO2) processed to 99.997% purity. The efficiency of a crucible is dependent upon properties, comparable to viscosity, which in flip is dependent upon the presence of impurities, such because the content material of hydroxyl (OH) teams, based on the researchers.
Excess OH results in low viscosity. “It is best for the crucible to have a excessive viscosity, which suggests a higher mechanical stability at excessive temperatures, and thus results in higher stability. This signifies that the crucible can be utilized for an extended time,” they mentioned.
The experimental setup concerned learning half of a fused quartz crucible produced from two kinds of sand. Samples had been faraway from the crucibles and ready for viscosity testing and IR microscopy examination. Usually, OH teams are current in quartz sand used within the fusion course of and water inclusions.
Investigation of the distribution of OH teams within the crucible seeks to establish any doubtlessly weak areas within the crucible. The content material of OH teams was mapped and the viscosity at 1500 C was measured. “Local variations within the teams of OH content material of a median of 26.7 ppm distinction between the highest and backside of the crucible had been discovered,” mentioned the researchers.
Viscosity measurements additional confirmed the crucible’s inhomogeneity with out clear traits or direct correlations with OH teams content material, based on the staff.
In addition, 4 samples originating from 4 completely different crucible sorts had been additionally analyzed. Samples originating from completely different crucibles had been taken and all had been imaged on the identical layer.
The researchers analyzed the variations between the crucibles and attributed them to completely different sand purification remedies. In two of the crucibles, the staff noticed an elevated OH teams content material on the boundary between the bubble-free and the bubble-containing layer, whereas the others confirmed an elevated and most OH teams content material within the bubble- containing layer.
In addition, the hyperlink between sand sorts and the content material of OH teams was confirmed.
“The supply of the native inhomogeneities and the 2 completely different traits of the OH distribution teams are probably because of the high quality of the sand, the scale of the sand particles, and the distinction within the course of of producing, comparable to thermal historical past or sand distribution,” the researchers mentioned.
The variations within the distribution of OH teams are “in all probability” associated to completely different course of situations, together with the thermal historical past, the vacuum and sand distribution, the standard of the sand used, and the scale of the sand particle, they are saying.
An further correlation they discovered was between the kind of sand used to make the crucible and the ultimate content material of OH teams, which they mentioned might affect the viscosity of the crucible.
“Both chemical remedy and variations in chemical measurement had a big impact on the ultimate OH group content material, which was proven to be the bottom within the crucible blended utilizing solely wonderful quartz sand, adopted by a a mix of wonderful and coarse, and the highest of the crucibles produced from coarser sand,” concluded the staff.
And lastly, the researchers emphasised that in “opposite to earlier research,” they didn’t see a transparent correlation between the content material of OH teams and the viscosity values inside OH group content material variations of the samples. “This additional proves that the crucibles should not uniform, and that the viscosity is affected by extra components than the content material of OH teams,” they mentioned.
The analysis is detailed in “Investigation of uniformity of fused quartz crucibles for Czochralski silicon ingots,” revealed in Journal of Crystal Growth.
The staff is from three Norwegian organizations Norwegian University of Science and Technology (NTNU), analysis institute SINTEF Industry, and The Quartz Corp, and the German-based Max Planck Institute for Sustainable Materials
Looking forward, Kazimiera Warden mentioned there’s “much more to discover,” for instance the potential affect of hint parts on the properties of the crucible.
“We hope that our analysis will carry some consideration to the significance of high-quality quartz crucibles for monocrystalline silicon manufacturing. We count on extra teams concerned in analysis on this materials, as a result of we expect it is very important enhance productiveness and due to this fact decrease the price of the ingot, making photo voltaic vitality extra inexpensive, in addition to decreasing the quantity of waste,” he mentioned.
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