An investigation of the thermal gradients in silicon during multicrystalline ingot casting

The evolutions of the temperature gradients in both the silicon melt and the solidified silicon crystal during ingot production have been investigated. The casting of a 120 kg multicrystalline ingot has been performed while measuring the temperatures on several locations inside the crucible using a total of nine thermocouples. The thermocouples were placed in groups of three inside quartz tubes, at distances of 0, 8.5 and 14 cm from the crucible bottom. The three quartz tubes were placed one in the centre of the square crucible, one in its corner and the last on the centre of one of its walls. The temperatures were logged throughout the solidification process, giving information about the temperature gradients both in the liquid and the solid parts of the silicon. The temperature readings from the thermocouples at the same distance from the crucible bottom but in different lateral positions allowed for a monitoring of the planarity of the solidification front, which is a result of the degree of unidirectionality of the heat flow. A 1D-model of the heat flow in the system has also been developed.