Liquinert quartz crucible - Removal of OH groups in silica crucibles to reduce wetting between the crucible and the silicon melt

When producing monocrystalline silicon ingots for the solar cell industry quartz crucibles are most commonly used. A quartz crucible used in the Czochralski (CZ) process will be used to pull ingots for more than 100 hours. During this time, some of the crucible will dissolve into the melt, along with any impurities in the crucible. To avoid this, the a liquid inert (liquinert) crucible can be used. This master thesis investigate two different crucible types, one fused quartz crucible made from natural quartz, and one crucible made from synthetic quartz. The focus have been on removing hydroxyl (OH) groups from the crucible by heat treatment, and to see how this effects wetting between the crucible and silicon. Some samples were also coated, to investigate the effect of coating and wettability. Samples have been taken from the inner surface of the crucibles, and polished. Heat treatment have been done in three different furnaces, a Sliding Flanges Tube (SFT) furnace, Alumina Tube Furnace (ATF) and in a Thermal Gravimetric Analysis (TGA) furnace, under vacuum conditions. As expected, heat treatment under vacuum conditions reduced the OH content in the samples. When heat treated at temperatures at and above 1450 $\celsius$, a significant amount of cristobalite is formed. The non-coated samples showed a clear negative correlation between the OH content and wetting angle. For the coated samples there were too many uncertainties to identify a correlation between the wetting angle and the OH content. However, the coated samples had a generally higher wetting angle than the non-coated samples. The work done in this thesis did not produce a liquinert crucible, but by reducing the OH content in the crucible, the wetting angle was increased, which may be a step in the direction of creating a liquinert quartz crucible