Alloys of Strontium

By alloying a little strontium with copper for castings, a harder metal is obtained and blow-holes are prevented. The alloy may be prepared either by adding metallic strontium to the melt, or by electrolysing fused strontium chloride, using a copper cathode. The amount of strontium is not sufficient to affect the electrical conductivity. The alloys with lead, tin, and bismuth, obtained by Caron when attempting to prepare metallic strontium, have already been mentioned. An alloy of strontium and zinc, containing 18 per cent, of the former, can be obtained by heating to redness a mixture of 100 grm. of zinc, 50 of sodium, and 200 of strontium iodide. An alloy with cadmium may be similarly obtained, but since cadmium is more Volatile than zinc the alloy may be enriched up to about 45 per cent, of strontium by heating in vacuo. It takes a fine polish when filed, but quickly tarnishes in contact with air, being apparently not much less reactive than strontium alone. A lead-strontium alloy, of composition Pb₃Sr, and melting at 676° C., has been described.

Strontium amalgamates with mercury, probably with the formation of definite compounds. Davy prepared a strontium amalgam in his efforts to obtain metallic strontium. According to Kerp and Bottger, the only true amalgam has the composition SrHg₁₂, and is produced by electrolysing a solution of strontium chloride, using a mercury cathode, at a temperature below 30° C. By draining the product, hard white crystals, probably monoclinic or triclinic in form, are obtained. The compound begins to break up at 60° C., and is completely molten at 70° C. It is quickly oxidised on exposure to air. Other formulae, however, have been given, for example SrHg₁₄, which, on squeezing under 200 kgm. per sq. cm., is said to form SrHg₁₁ in cubical crystals. By heating these amalgams under special conditions, silver-white crystalline products are obtained, of hardness 2.3, and of composition corresponding to the formulae Sr₂Hg₅ and SrHg₆. The amalgam SrHg₁₁ is apparently unchanged when centrifuged or submitted to a pressure of 5000 kgm. per sq. cm. in an atmosphere of carbon dioxide. The richest amalgam obtainable contains 52 per cent, of strontium. When heated the whole amalgam distils.

An alloy of strontium and iron, containing about 23 per cent, of strontium, may be obtained by heating the two metals together at low redness. The alloy shows a hard, bright, homogeneous surface on filing, but soon tarnishes. It readily decomposes water.

Alloys with lead or tin, for example 5 per cent, of strontium with 95 per cent, of tin, are beginning to find a use commercially as deoxidisers in the purification of metals and alloys.