Electrical Conductivity and Transference Number Measurements of FeO - CaO - MgO - SiO 2 Melts

Transcription

1 Electrical Conductivity and Transference Number Measurements of FeO - CaO - MgO - SiO 2 Melts Andrew Ducret, Deepak Khetpal and Donald R. Sadoway Department of Materials Science & Engineering Massachusetts Institute of Technology Cambridge, Massachusetts U.S.A.

2 background problems with electrolytic technologies: p unfavorable by-products + Al electrolysis makes CO 2 (½ kg C / kg Al) + Mg electrolysis makes Cl 2

3 a technological response? most metals are found in nature as oxides like dissolves like + molten oxide electrolysis: extreme form of molten salt electrolysis where pure oxygen gas is by-product

4 schematic of prototype cell

5 reaction of US industry? new technology which will eliminate the production of CO 2 which is the unavoidable result of using carbon Through AISI, we have therefore encouraged NSF and other agencies to support Don Sadoway s work as a modest investment towards the steel technology which may be required to match the long term needs of the industrial ecology. Thomas J. Usher, President, U.S. Steel Group from a speech delivered at MIT, November 2, 1993

6 lunar colonization: NASA? breathable oxygen lunar regolith is a multicomponent silicate rich in iron and titanium. ferrites and titantates are liquid semiconductors

7 feasibility assessment p electrical conductivity measurements p transference number measurements p modeling electrical properties p applicability to oxygen generation

8 all-metal, coaxial-cylinder electrode enabling high-accuracy conductivity measurements in the most chemically aggressive melts (does not contact liquid) Mo

9 experimental apparatus conductivity measurements: - impedance spectroscopy - varying immersions + isolate melt resistance

10 experimental apparatus transference number measurements: - stepped-potential chronoamperometry with impedance correction + isolate electronic and ionic components of conductivity

11 solvent compositions FeO additions to S1

12 σ = σ(t) at c = S1 Schiefelbein ln σ / S cm -1 1/T (K)

13 -0.5 effect of FeO addition: σ = σ(t, c) 1425 T(ºC) Ducret ln σ / S cm % 15% S1 10% 5% /T (K) σ / S cm -1

14 FeO greatly raises conductivity σ = X FeO R 2 = σ / S cm T = 1425ºC X FeO in S1

15 FeO acts as an electron donor t e = X FeO R 2 = t e T = 1425ºC X FeO in S1

16 0.45 regression of conductivity data y = x R 2 = σ / S cm T = 1425ºC Khetpal σ = Σ a i *X i σ = *SiO *FeO *(FeO+MgO+CaO)

17 FeO acts as an electron donor T = 1425ºC a FeO *X FeO y = x R 2 = σ = Σ a i *X i Khetpal t e *σ melt

18 applicability to oxygen generation daily oxygen requirement = 2.75 kg Faradaic efficiency = 85% (based on t ionic ) current = 452 A cell voltage = 2 V (2.5 H FeO ) power supply = 904 W current density = 5 A cm -2 electrode area = 90 cm -2

19 in closing high-accuracy electrical conductivity and transference number measurements in molten oxides at extreme temperatures electrolytic production of breathable oxygen not unviable implications for fluxes and slags, e.g., welding, refining, & metallothermic reduction

20 acknowledgments National Aeronautics & Space Administration National Science Foundation Electric Power Research Institute