Melting lithium alloys

Attention has been given for some time to the use of lithium alloys as an alternative to elemental lithium. Groups working on batteries with molten salt electrolytes that operate at temperatures of 400-450 °C, well above the melting point of lithium, were especially interested in this possibility. Two major directions evolved. One involved the use of lithium-aluminium alloys [5, 6], whereas another was concerned with lithium-silicon alloys [7-9]. 

Bismuth forms an alloy with melted lithium the conversion is dangerous because of its exothermicity. The aluminium/bismuth mixture combusts spontaneously in air. The same goes for a cerium/bismuth mixture. 

The Other Five Candidates. All the molten salt SBs reviewed above have either a Li anode or a lithium alloy, one in which Li prevails quantitatively. As to the other 5 light metals they are seldom mentioned in the literature as candidates for anodes in these SBs, except Al. In (82) it is stated that molten salt batteries with Ca or Mg anodes yield only a small proportion of their theoretical energy because (a) Ca anodes react chemically with the electrolyte, and (b) both Ca and Mg anodes are passivated at high current drains, becoming coated with resistive films of solid salts. In a melt containing Li salts, Ca replaces Li ions by the displacement reaction Ca + 2LiCl = CaCl2 + 2Li. 

In these cells readily available substances are used as active materials -molten sodium and sulfur working in contact with a solid electrolyte (sodium beta-aluminate). Sulfur-sodium storage cells show rather large values of specific electrical energy. Their working temperature is 350 C, i.e. before use they must be heated up to this temperature. Storage cells with electrodes from iron sulfide and lithium alloys with a melt of chlorides as electrolyte exhibit similar properties. The working temperature of these cells is about 400°C. 

LiAl and Li(Si) alloys are processed into powders, which are cold-pressed into anode wafers or pellets that range in thickness from 0.75 to 2.0 mm. In the cell, the alloy pellet is backed with an iron, stainless steel, or nickel current collector. Lithium alloy anodes function in activated cells as solid anodes, and must be maintained below melt or partial melt temperatures. Forty-four weight percent Li(Si) alloy will partially melt at 709°C, while a, 13-LiAl will exhibit partial melting at 600°C. If these melting temperatures are exceeded, the melted anode may come in contact with cathode material, allowing a direct, highly exothermic chemical reaction and cell short-circuiting. 

No fewer than 14 pure metals have densities se4.5 Mg (see Table 10.1). Of these, titanium, aluminium and magnesium are in common use as structural materials. Beryllium is difficult to work and is toxic, but it is used in moderate quantities for heat shields and structural members in rockets. Lithium is used as an alloying element in aluminium to lower its density and save weight on airframes. Yttrium has an excellent set of properties and, although scarce, may eventually find applications in the nuclear-powered aircraft project. But the majority are unsuitable for structural use because they are chemically reactive or have low melting points." ... 

Steels and austenitic stainless steels are susceptible to molten zinc, copper, lead and other metals. Molten mercury, zinc and lead attack aluminum and copper alloys. Mercury, zinc, silver and others attack nickel alloys. Other low-melting-point metals that can attack common constructional materials include tin, cadmium, lithium, indium, sodium and gallium. 

Numerous compounds are observed in the Li-Ag phase diagram. The alloys are heated under Ar and cast in mild steel crucibles for metallographic examination, with homogeneity achieved by remelting under vacuum. Similar procedures were employed in an earlier study, except that H2 was used in place of Ar. An Ar cover gas was also employed to prepare the brasslike yj phase in the Li-Ag system for structural study. The silver and lithium were melted together in an iron crucible for 15-30 s before cooling without quenching to minimize the loss of lithium-. ... 

With very electropositive metais this oxide is reduced very violently following thermite type of reactions. Vioient reactions of this type happen with lithium, magnesium, aluminium and the Al-Mg-Zn alloy. The iron formed is melted due to the exothermicity of this reaction. This experiment is not recommended for lectures. 

Li-Al alloys may be prepared electrochemically, generally by coulo-metric deposition of lithium from a molten salt bath, or pyrometallurgically by heating lithium and aluminium at a temperature above the alloy melting point of 720°C. Practical electrode configurations are constructed by ... 

Interesting support to the belief that the compound Pd2Pb can exist is afforded by the results of experiments 5 to determine the difference of potential between various alloys and pure lead in a normal solution of lead nitrate. The alloys were prepared by melting the palladium and lead under a mixture of lithium chloride and either potassium or barium chloride. Alloys containing less than 33 per cent, of palladium have a potential practically identical with that of pure lead, whilst those containing more than this amount of palladium exhibit a higher potential, which at first rapidly increases with the palladium. Between 20 and 90 per cent, of palladium the alloys are harder than the individual components, a maximum occurring with 65 per cent, of palladium. 

The use of lithium as a solid compound, a pure melt, or a molten alloy is required for tritium breeding in at least the first generation of fusion reactors. Three fusion reactor concepts are discussed with emphasis on material selection and material compatibility with lithium. Engineering details designed to safely handle molten lithium are described for one of the example concepts. Tritium recovery from the various breeding materials is reviewed. Finally, two aspects of the use of molten Li-Pb alloys are discussed the solubility of hydrogen isotopes, and the influence of the alloy vapor on heavy ion beam propagation. 

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