1. Thermochemical Study of Calciothermy of Scandium Compounds
EMC 2017, Leipzig. June 26th
Thermochemical Study of Calciothermy of Scandium Compounds
M. Sc. Brinkmann, Frederic; Dr.-Ing. Arnold, Alexander;
M. Sc. Milicevic, Ksenija; Prof. Dr.-Ing. Friedrich, Bernd

2. Approach to metallothermic Scandium reduction
1/27
Thermochemistry
Reduction mechanisms
Suitable reducing agents
Scandium compounds
Metal yields
Process parameters
Kinetics
Activation energy
Reaction time
Pressure
Phase separation
Process layout
Crucible material
Furnace layout
Use of reaction enthalpy
Theoretical and experimental investigations

3. Metallothermic Sc reduction processes
2/27
Halide reduction
Oxide reduction
State of the art: ScF3 is reduced by pure Ca at 1550 °C °C [1-3]
Produced Sc metal is contaminated by Ca and Ta or Mo (crucible material)
Further purification includes distillation and sublimation
Zn may be added to lower melting point [1]
Harata et al. [4]:
Sc2O3 reduction with Ca unfeasable
Addition of Al as collector metal leads to Sc reduction and collection in the metal phase

4. Thermochemistry of Scandium - I
3/27
xA +F2 = z AxFy
xA +O2 = z AxOy
Scandium compounds are thermodynamically very stable
Pure substances (a = 1): RE-oxides are more stable than CaO and Al2O3;
RE-fluorides are more stable than AlF3, but less stable than CaF2
-> Metallothermy is unfeasable for pure Sc2O3

5. Sc-Zn phase diagram
4/27
However, Sc melting point is fairly high (1814 K)
Liquidus temperature may be decreased with Zn addition

6. Methodology – „Klärkreuze“
„Klärkreuze“ method: Proposed by W. Guertler almost 100 years ago [5]
Determining the reaction outcome within a ternary (or quarterny) system
Draw connections between all known compounds on the ternary system frame
5/27 B A X
B2X BX AX

7. Methodology – „Klärkreuze“
6/27
Determining intersection points
Determining which line shows equilibrium at intersection point
Example: Intersection 1
A – B2X or B – AX?
Experiment or
thermochemical simulation
2 B + AX = B2X + A
Therefore, the connection
B – AX may be cancelled B A X
B2X BX AX 1 2 3

8. „Klärkreuze“ - Example
7/27 B
B2X BX
A + B + B2X
AX + B2X + BX
AX + BX + X
A + AX + B2X A X AX

9. Thermochemical simulation tool „FactSage 7.0“
8/27
FactSage 7.0 uses thermochemical databases that contain parameters for
Compounds (Gibbs energy as a function of T and p)
Solutions (Gibbs energy as a function of T, p and composition)
By minimizing the Gibbs energy of a system that is determined by a given set of constraints, equilibrium conditions are calculated

10. FactSage 7.0 results
9/27
Databases used:
FactPS
FToxid
FTlite

11. Sc-Ca-Zn-F system – triangulation at 1300 K
10/27
ScF3 can be reduced by Ca but not by Zn
Ca-Zn can be considered to lower alloy melting point

12. Sc-Ca-Zn-F system – tetradration at 1300 K
11/27
Ca-Zn alloys as reducing agent: reduction path always passes CaF2 – ScZn sub system
Thus, reduction results in a ScZn alloy

13. Summary ScF3 reduction by Ca/Zn
12/27
Ca consumption is always 0.59 g / g ScF3
Sc yield is at 100 %
Sc product is diluted by Zn

14. Sc-Ca-Zn-O system – triangulation at 1300 K
13/27
Sc2O3 cannot be reduced by Zn nor Ca
However, intermetallic compounds in the system Ca-Sc-Zn exist
Possible reduction in the quaternary system – tetraedration needed

15. Sc-Ca-Zn-O system – tetradration at 1300 K
14/27
Sc2O3 cannot be reduced by Zn nor Ca
Ca-Zn alloys are candidates for reduction
Reduction outcome is a ScZn alloy

16. Summary Sc2O3 reduction by Ca/Zn
15/27
Reducing alloy
Ca consumption
Zn consumption
Sc in product [wt.-%]
[g/g Sc2O3] Ca -
Ca3Zn
1.744
0.949
26.37
Ca5Zn3
0.970
37.74
Ca0,6Zn0,4
0.872
40.74
CaZn
1.420
31.432
CaZn2
2.840
18.64
CaZn5
7.101
8.4
Diluted by Zn and Ca
Diluted by Zn
Minimum Ca consumption is g / g Sc2O3
At least g Zn is necessary for complete oxide reduction
Highest Sc content in metal product is wt.-%

17. Sc-Ca-Al-F system – triangulation at > 1150 K
16/27
ScF3 can be reduced by Ca and Al
Pure Sc can only be achieved by Ca
Al3Sc is the reduction product of ScF3 and Al:
ScF3 + 4 Al = Al3Sc + AlF3

18. Sc-Ca-Al-F system – tetradration at > 1150 K
17/27
Reduction with Al-Ca alloys: ScF3 is reduced by Ca
Al addition yields Al-Sc compounds
Compounds depend on Al addition (Ca:Al ratio)

19. Sc-Ca-Al-O system – triangulation at 1300 °C
18/27
No thermochemical data for AlScO3
In order to understand the Al-Sc-O system. tetraedration is necessary

20. Sc-Ca-Al-O system – triangulation at 1300 °C
19/27
Zacharov (1985):
N = 1 + Mk + Mik + 2 (Ck + Cik)
Here: N = 19 sub systems
Only one tetraedration exists
Sc reduction with Al results in an intermetallic AlxScy phase and AlScO3

21. Summary Sc2O3 reduction by Al/Ca
20/27
Ca/Al ratio [mol/mol]
Sc products
Sc content in product
[wt.-%]
Ca consumption [g Ca/ g Sc2O3]
Al consumption [g Al/ g Sc2O3]
0.5
Al3Sc
35.71
0.872
1.174
0.6
Al3Sc, Al2Sc
39.99
0.978 1
Al2Sc, AlSc
52.62
0.578 2
AlSc, AlSc2
68.96
0.293
100 % Sc yield is possible with the shown ratios
By using Ca and Al as reducing agent, Sc activity in the product is strongly reduced
Intermetallic products depend on Ca/Al ratio

22. Sc-Mg-Zn-F system – triangulation at ≥ 1300 K
21/27
ScF3 reduction with Mg is possible
For every g Sc, g Mg is necessary
2 ScF3+3 Mg = 2 Sc+3 MgF2

23. Sc-Mg-Zn-F system – tetraedration at T ≥ 1300 K
22/27
Subsystems:
ScF3-MgF2-ZnF2-F
ScF3-MgF2-ZnF2-Zn
ScF3-MgF2-Sc-ScZn
MgF2-Mg-Sc-ScZn
MgF2-Mg-MgZn2-ScZn
ScF3-MgF2-MgZn2-Zn
MgF2-MgZn2-ScZn-Zn
Different products are formed when alternating Mg/Zn ratios

24. Sc-Mg-Zn-O system – triangulation at < 1050 K
23/27
Sc2O3 cannot be reduced by either Zn nor Mg
Unclear which compounds are stable in the Mg-Sc-Zn system
Calculations indicate a ternary compound (red dot)
Thermodynamic data for ScZn2 in the temperature range is false
Further calculations are done at T > 1300 K

25. Sc-Mg-Zn-O system – tetraedration at T ≥ 1300 K
24/27
Subsystems:
Sc2O3-MgO-ZnO-O
Sc2O3-MgO-ZnO-Zn
Sc2O3-MgO-MgZn2-Mg
Sc2O3-MgO-MgZn2-Zn
Sc2O3-MgZn2-ScZn-Zn
Sc2O3-MgZn2-ScZn-Mg
Sc2O3-Sc-ScZn-Mg
Sc2O3 reduction with Mg/Zn or Mg is not possible

26. Summary I: Sc2O3
25/27
Sc2O3
Sc2O3 reduction is not feasable with pure substances
Ca-Zn and Ca-Al alloys allow reduction and dilution
100 % yield is thermodynamically possible
Reduction with Al results in intermetallic Al- Sc compounds and AlScO3
Recommended processing
Pure Sc
Al-Sc alloys
Sc2O3 + CaxZny
ScxZny
(Tliq > 748 K)
CaO
(Tliq: 2853 K)
Distillation Sc Zn
AlxScy
(Tliq > 1468 K)
Sc2O3 + Ca + Al
CaO
(Tliq: 2853 K)
Slag additives

27. Summary II: ScF3 ScF3 26/27 ScF3 is not as stable as Sc2O3
Reduction with pure Ca or Mg is possible
Al3Sc is formed during reduction with pure Al
Recommended processing
Pure Sc
Al3Sc alloy
Al-Sc alloys
ScF3 + 4 Al
ScF3 + Al + Ca
ScF Ca / Mg Sc
(Tliq: 1814 K)
CaF2 / MgF2
(Tliq > 1529 K)
Al3Sc
(Tliq: 1593 K)
AlF3
(Tsub: 1533 K)
AlxScy
(Tliq > 1468 K)
CaF2
(Tliq: 1696 K)
AlF3
(Tsub: 1533 K)

28. Outlook 27/27 Results will be used to design reduction experiments
Transfer to „ScAlE“ project
Kinetics and practicability have not yet been considered
Process parameters
Slag design
Co-reduction of Al2O3 and ScF3 / Sc2O3 to be investigated

29. Thank you for your attention!
EMC 2017, Leipzig
Thank you for your attention!

30. Literature
[1] Spedding, F. H.; Croat, J. J. (1973): Magnetic properties of high purity scandium and the effect of impurities on these properties. In: The Journal of Chemical Physics 58 (12), S. 5514–5526.
[2] Beaudry B.J., Gschneidner, JR.: Preparation and basic properites of the rare earth metals. In: Eyring Gschneidner (Hg.): Handbook on the physics and chemistry of rare earths, Bd. 1, S. 173–232.
[3] Daane, A. H.; Spedding, F. H. (1953): Preparation of Yttrium and Some Heavy Rare Earth Metals. In: Journal of the Electrochemical Society 100 (10).
[4] Harata, M.; Nakamura, T.; Yakushiji, H.; Okabe, T. H. (2013): Production of scandium and Al–Sc alloy by metallothermic reduction. In: Mineral Processing and Extractive Metallurgy 117 (2), S. 95–99.
[5] Guertler, G. (1920): Observations of theoretical metallurgy (german). In: Metall und Erz, 17 (8), S. 192–195