View
215
Download
0
Category
Preview:
Citation preview
1
Challenges of carbothermic route of solar silicon synthesis
M.A. Arkhipov, A.B.Dubovskiy, A.A. Reu,V.A. Mukhanov, S.A. Smirnova
Quartz Palitra Ltd.
1, Institutskaya St., Alexandrov, Vladimir Region 601650, Russia
Email: arkh8@yahoo.com
2
Traditional route for silicon synthesis
MG: SiO2 + 2C = Si+ 2CO 2N, B, P = 20-40 ppm
Si + 3HCl = SiHCl3 + H2
SiHCl3 + H2 = Si + 3HCl 9N, B, P = 0.001–
0.1 ppm
SOLAR
&
SEMI
3
World production of solar grade silicon
Production: 25 000 -30 000 tonnes/year
Demand: over 50 000 tonnes/year
Booking up to Y 2019
Main drawbacks
• Ecoligical threats – due to chlorine use
• Machinery - absence of “turnkey” suppliers.
4
Alternative route
SiO2 + 2C = Si + 2CO 4N, B, P ~ 1 ppm
Purification by Direct Solidification and Chemical etching to 6N, B, P = 1 ppm
5
MG carbo process
Solar carbo process
Quartz Quartzite 2N-3N Quartz 4N5
Carbon Charcoal, coke 2N-3N
Thermal black
4N
Electrode Carbon 4N Graphite 4N
6
Si SiC
Si drops
Electrode
Arc furnace before stocking
Raw materialOxide lining
Carbon lining
7
1. SiO2 + C = SiO + CO2. SiO + 2C = SiC + CO3. SiC + SiO = 2Si + CO4. 2SiO = SiO2 + Si5. 2SiC + SiO2 = 3Si +2CO6. 2SiO2 + SiC = 3SiO + CO
8
Equilibrium SiO pressures after Schei, Tuset and Tveit.
9
SiO +2C = SiC +CO2SiO = SiO2 +Si
10
For carbon important: pores, surface area diffusivity
Ideal: upper zone SiC formation
lower zone SiC → Si
11
SiO2 + C(1+x) = x Si + (1-x)SiO + (1+x)CO
x – yield
x = 0.8-0.9 for MG silicon
x = 0.6-0.85 for solar silicon
12
Silicon move in high temperature zone
T
X
Si
Energy stored inliquid-solid surface isdecreased strongly with temperature rise
13
Si SiC
SiC + quartz chargeArc is strong
Silicon is collectedunder electrode
14
Si SiC
SiC + quartz
current
Too big concentrationof SiC or too highconductivity of charge
Uniform heating
Silicon remains atsintering place
15
AC arc DC arc
t1 – arc absent because of low voltage
16
+_
High electrode consumptionand contamination
17
High puritymaterials
Low reaction ability
SiC formation near bottom
SolutionCatalyst thatcan be removed during process
18
Carbon-powderCharcoal-foam use glue
Briquette: quartz, carbon, glue
Quartz 10% - 75% weight
19
Reaction in briquette (upper zone)
1. SiO2 + C = SiO + CO
2. SiO + 2C = SiC + CO
Sources SiO: a) reaction#1 b) from bottom zone
20
Optimum gas flow inside briquette
Stage 1: SiC formation
Stage 2: binder lose cementing ability
21
Weak cementing force or low density briquette
C
CC
SiO2SiO2
SiO SiO
22
Strong cementing force or high density briquette
CC SiO2
SiO2
C
SiO2
SiCC
C
SiO
SiC
23
150 kW DC arc furnaceV = 28-65 VI = 1500-3600 AGraphite liningGraphite electrode
24
25
26
27
28
29
30
Average batch purity: 99.98%
B = 0.4 ppmP = 2 ppmNa = 20 ppmAl = 60 ppmCa = 10 ppmTi = 15 ppmFe = 50 ppmMn = 1 ppmMg =1.5 ppmCu = 1.5 ppmZr = 2 ppm
Main impurities
31
Maximum batch weight: 15 kg
Energy consumption: 35 kW*h/kg
32
CONCLUSIONS:
1. Carbothermic arc technology presuppose SiC sintering below 1900 °C.To meet the requirement with high purity components efficient to use catalyst.
33
2. DC arc furnace is more efficient than AC:a) less electrode consumption (if electrode is cathode)b) less contaminationc) less loss of energy through electrode
34
3.Binder (cement), chemical composition of briquette and method of its preparation are to guarantee:
a) SiC formation in upper zone
b) High resistivity
35
4. After SiC formation it’s important to avoid losing SiO by reaction:
SiC + 2SiO2 = 3SiO + CO
36
5. Important to keep top of furnace “cold” and bottom “hot” to provide condensation of SiO gas to get capsulation of crater.
37
The present work was done under the contract with Big Sun Energy TechnologyCo., Ltd.
Recommended