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Liquid Alkali Metals 671

TABLE VIII Some Products of Corrosion ways. Chromium reacts to form the ternary oxide NaCrO 2
(chromite), and this reaction takes place at virtually all
Product
oxygen concentrations in the sodium. The iron compo-
In liquid sodium In liquid lithium
Container nent does not develop an iron oxide film; nickel shows no
metal Oxides Nitrides Carbides reaction, but has a relatively high solubility in the liquid
metal and is preferentially dissolved relative to the other
Fe — Li 3 FeN 2 Fe 3 C
alloying elements. The net result is that a surface layer
Cr NaCrO 2 Li 9 CrN 5 Cr 3 C 2 , Cr 23 C 6
of NaCrO 2 forms on the stainless steel. In time, the sur-
V NaVO 2 VN, Li 7 VN 4 V 2 C
face reaches an equilibrium composition and the rate of
Nb Na 3 NbO 4 Nb 2 N Nb 2 C
corrosion decreases.
Ta Na 4 TaO 4 Ta 2 N Ta 2 C
Ti Na 4 TiO 4 Ti 2 N Ti 2 C
Zr Na 2 ZrO 3 Li 2 ZrN 2 — SEE ALSO THE FOLLOWING ARTICLES
Mo — MoN Mo 2 C
BATTERIES • CHEMICAL THERMODYNAMICS • NUCLEAR
POWER REACTORS

oxygen usually remains in liquid lithium, nitrogen and car-
bon impurities are more readily transferred from solution BIBLIOGRAPHY
to the solid metal container surface. This is because the
◦
◦
− G values for Li 3 N and Li 2 C 2 at 625 C are only 45
f Addison, C. C. (1984). “The Chemistry of the Liquid Alkali Metals,”
and 178 kJ/mol, respectively, compared with 455 for Li 2 O.
Wiley (Interscience), New York.
In practice, therefore, nitrogen and carbon in lithium may Borgstedt, H. U., and Mathews, C. K. (1987). “Applied Chemistry of the
play a corrosive role similar to that of oxygen in sodium, Alkali Metals,” Plenum, New York and London.
and some examples of the nitrides and carbides formed at Charnock, W., Haigh, C. P., Horton, C. A. P., and Marshall, P. (1979).
“C.E.G.B. Research,” Berkeley (UK).
the surface of various metals are given in Table VIII.
Foust, O. J., ed. (1972). “Sodium-NaK Engineering Handbook,” Gordon
The corrosion rates are normally quite slow (often
and Breach, New York.
not more than a few milligrams per square centimeter Gruen, D. M. (1972). “The Chemistry of Fusion Technology,” Plenum,
per year) and the solid metal surfaces tend to develop New York.
a layer that is resistant to further corrosion. Most re- Mausteller, J. W., Tepper, F., and Rodgers, S. J. (1967). “Alkali Metal
Handling and Systems Operating Techniques,” Gordon and Breach,
search has been carried out on stainless steel in liquid
New York.
sodium, and this provides an interesting illustration of the
Ohse, R. W., ed. (1985). “Handbook of Thermodynamic and Transport
effect. The steel components iron, chromium, and nickel Properties of Alkali Metals,” I.U.P.A.C. Chemical Data Series No. 30,
react toward liquid sodium containing oxygen in different Blackwell, Oxford.