Ferrosolar UMG Process - Revision history

Marcin at 04:26, 18 February 2022

2022-02-18T04:26:13Z

← Older revision		Revision as of 04:26, 18 February 2022
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	from 3000 Pa to below 5 Pa . In fact, evaporation of phosphorus reaches its maximum rate at pressures from 1 to 5 Pa at the range of temperatures of these treatments. Evaporation lasts between 4 and 8 hours,		from 3000 Pa to below 5 Pa . In fact, evaporation of phosphorus reaches its maximum rate at pressures from 1 to 5 Pa at the range of temperatures of these treatments. Evaporation lasts between 4 and 8 hours,
	depending on the initial phosphorus concentration of the silicon.		depending on the initial phosphorus concentration of the silicon.


	~~Figure 1. Overview of the procedure followed in this study. HPM stands for High Performance~~
	~~Multicrystalline. The starting point is the silicon purification explained in section 2.1. A feedstock:~~
	~~silicon from Ferrosolar´s standard process, B feedstock: same silicon but intentionally mixed with~~
	~~contaminated silicon in the charge of multi growth.~~



	At the end of the evaporation, the furnace is refilled with Ar to an internal pressure of 3000 Pa. Then, it is		At the end of the evaporation, the furnace is refilled with Ar to an internal pressure of 3000 Pa. Then, it is

Marcin at 04:25, 18 February 2022

2022-02-18T04:25:18Z

Marcin: Created page with "Ferrosolar process begins with the crushing of MG Si, to adapt its grain size to subsequent treatments. Crushers have been carefully designed to minimize contamination. The fi..."

2022-02-18T04:24:13Z

Created page with "Ferrosolar process begins with the crushing of MG Si, to adapt its grain size to subsequent treatments. Crushers have been carefully designed to minimize contamination. The fi..."

New page

Ferrosolar process begins with the crushing of MG Si, to adapt its grain size to subsequent treatments.
Crushers have been carefully designed to minimize contamination. The final grain size is 100% less than 1
cm.
Next, this silicon is charged in induction furnaces with a capacity up to one ton of silicon. Ferrosolar uses
reactive slags in graphite crucibles with the objective of a selective removal of certain impurities, including
boron. Once the treatment is finished, the molten silicon is transferred to a suitable vessel and directionally
solidified. The degree of purification in this last step depends on its segregation coefficient of a given
impurity. The overall result of this first stage of slagging and controlled solidification is the reduction of
boron and most of the metallic impurities (Al, Ca, Fe, Ti, etc), as well as the partial reduction of other
impurities like phosphorus (50% reduction) among others.
In the next step, the directionally solidified silicon is grinded bellow 1.5 cm and leached in acid, washed in
deionized water and dried to prepare it for next stage which is a thermal treatment at temperatures in the
range 1550°C – 1700°C under high vacuum (Souto et al. 2014). The main objective of this process is the
removal of phosphorus, given its high volatility under vacuum at high temperatures. Other impurities such
as Al, Ca, K, and Na, are also partially evaporated. In this step, the silicon is firstly introduced into a sealed
chamber equipped with internal atmosphere control. This chamber, acts as the silicon charging system and
is connected to the high vacuum furnace through a valve. Once the silicon has been loaded, the chamber is
purged to reduce its pressure before opening the connection valve with the vacuum furnace. When the purge
has been completed, the internal pressure in the charge chamber is adjusted to 3000 Pa to match that of the
vacuum furnace. When internal pressures on both sides are equivalent the valve opens and the silicon is
transferred into the vacuum furnace, where is placed in a high-density graphite crucible with a capacity up
to 1000 kg of silicon.
When the transfer of silicon has been completed the valve closes, and the vacuum furnace is ready to start
with the thermal treatment. The furnace is equipped with two independent systems to control temperature;
a W-Re thermocouple placed close to the crucible, and an optical pyrometer that measures the temperature
through a quartz crystal window. Internal pressure is initially 3000 Pa, and this pressure is kept constant
until the melting of the silicon has been completed and the temperature stabilized at the chosen setpoint. At
this point, to increase the evaporation kinetics it is necessary to lower the internal pressure in the furnace
from 3000 Pa to below 5 Pa . In fact, evaporation of phosphorus reaches its maximum rate at pressures
Figure 1. Overview of the procedure followed in this study. HPM stands for High Performance
Multicrystalline. The starting point is the silicon purification explained in section 2.1. A feedstock:
silicon from Ferrosolar´s standard process, B feedstock: same silicon but intentionally mixed with
contaminated silicon in the charge of multi growth.
from 1 to 5 Pa at the range of temperatures of these treatments. Evaporation lasts between 4 and 8 hours,
depending on the initial phosphorus concentration of the silicon.
At the end of the evaporation, the furnace is refilled with Ar to an internal pressure of 3000 Pa. Then, it is
connected to a solidification furnace and the purified silicon is casted and directionally solidified. The result
of this evaporation/controlled solidification process is a silicon block of 500-1000 kg depending on the
furnace capacity. Finally, this block is placed in a diamond wire saw machine to remove the laterals, upper
and lower parts where the residual impurities are concentrated. These contaminated parts will be recycled
and re-melted in previous stages of purification. The silicon thus obtained after the cutting step has very
low boron, phosphorus and metals content and is very suitable for photovoltaics.

← Older revision		Revision as of 04:25, 18 February 2022
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	Crushers have been carefully designed to minimize contamination. The final grain size is 100% less than 1		Crushers have been carefully designed to minimize contamination. The final grain size is 100% less than 1
	cm.		cm.

	Next, this silicon is charged in induction furnaces with a capacity up to one ton of silicon. Ferrosolar uses		Next, this silicon is charged in induction furnaces with a capacity up to one ton of silicon. Ferrosolar uses
	reactive slags in graphite crucibles with the objective of a selective removal of certain impurities, including		reactive slags in graphite crucibles with the objective of a selective removal of certain impurities, including
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	boron and most of the metallic impurities (Al, Ca, Fe, Ti, etc), as well as the partial reduction of other		boron and most of the metallic impurities (Al, Ca, Fe, Ti, etc), as well as the partial reduction of other
	impurities like phosphorus (50% reduction) among others.		impurities like phosphorus (50% reduction) among others.

	In the next step, the directionally solidified silicon is grinded bellow 1.5 cm and leached in acid, washed in		In the next step, the directionally solidified silicon is grinded bellow 1.5 cm and leached in acid, washed in
	deionized water and dried to prepare it for next stage which is a thermal treatment at temperatures in the		deionized water and dried to prepare it for next stage which is a thermal treatment at temperatures in the
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	transferred into the vacuum furnace, where is placed in a high-density graphite crucible with a capacity up		transferred into the vacuum furnace, where is placed in a high-density graphite crucible with a capacity up
	to 1000 kg of silicon.		to 1000 kg of silicon.

	When the transfer of silicon has been completed the valve closes, and the vacuum furnace is ready to start		When the transfer of silicon has been completed the valve closes, and the vacuum furnace is ready to start
	with the thermal treatment. The furnace is equipped with two independent systems to control temperature;		with the thermal treatment. The furnace is equipped with two independent systems to control temperature;
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	until the melting of the silicon has been completed and the temperature stabilized at the chosen setpoint. At		until the melting of the silicon has been completed and the temperature stabilized at the chosen setpoint. At
	this point, to increase the evaporation kinetics it is necessary to lower the internal pressure in the furnace		this point, to increase the evaporation kinetics it is necessary to lower the internal pressure in the furnace
	from 3000 Pa to below 5 Pa . In fact, evaporation of phosphorus reaches its maximum rate at pressures		from 3000 Pa to below 5 Pa . In fact, evaporation of phosphorus reaches its maximum rate at pressures from 1 to 5 Pa at the range of temperatures of these treatments. Evaporation lasts between 4 and 8 hours,
			depending on the initial phosphorus concentration of the silicon.


	Figure 1. Overview of the procedure followed in this study. HPM stands for High Performance		Figure 1. Overview of the procedure followed in this study. HPM stands for High Performance
	Multicrystalline. The starting point is the silicon purification explained in section 2.1. A feedstock:		Multicrystalline. The starting point is the silicon purification explained in section 2.1. A feedstock:
	silicon from Ferrosolar´s standard process, B feedstock: same silicon but intentionally mixed with		silicon from Ferrosolar´s standard process, B feedstock: same silicon but intentionally mixed with
	contaminated silicon in the charge of multi growth.		contaminated silicon in the charge of multi growth.
	~~from 1 to 5 Pa at the range of temperatures of these treatments. Evaporation lasts between 4 and 8 hours,~~
	~~depending on the initial phosphorus concentration of the silicon.~~

	At the end of the evaporation, the furnace is refilled with Ar to an internal pressure of 3000 Pa. Then, it is		At the end of the evaporation, the furnace is refilled with Ar to an internal pressure of 3000 Pa. Then, it is
	connected to a solidification furnace and the purified silicon is casted and directionally solidified. The result		connected to a solidification furnace and the purified silicon is casted and directionally solidified. The result