LEAD ALKALI METALS
Lead hardened with small amounts of alkali metals used chiefly as bearing metals. Alloys of this type are also called tempered lead and alkali lead. The original alkali lead, known as Bahnmetall, was made under a German patent. It contains 0.73% calcium, 0.04 lithium, 0.55 sodium, and the balance lead, and it is made by electrolysis of the fused alkali salts, using a molten lead cathode. Calcium-lead alloy is made in the same manner and contains up to 1% calcium. The calcium forms a chemical compound, Pb3Ca, with part of the lead, and the crystals of this compound are throughout the lead matrix. The Brinell hardness is 35, and the com-pressive strength 25,000 lb/in2 (172 MPa), being thus superior in strength to the high-tin bearing metals. But the metal is difficult to melt without oxidation and is easily corroded. The melting point is 698°F (370°C), and it retains its bearing strength at more elevated temperatures than babbitts. Calcium lead, with about 0.04% calcium, is used as cable sheathing to replace antimonial lead, giving greater fatigue resistance. It is also used for grids in storage batteries and has a lower rate of self-discharge than antimonial lead. The small amount of lithium in Bahnmetall is intended to prevent the corrosion set up by the calcium. It also increases the compressive strength to about 30,000 lb/in2 (207 MPa). Mathesius metal, another German alloy, contains calcium and strontium to form Pb3Sr crystals. Frary metal, of NL Industries, Inc., is a lead-calcium-barium alloy containing about 1.5% of the alkali metals. These alloys give low friction loss at low temperatures, but they have higher coefficients of friction than the lead-tin alloys at temperatures above 149°F (65°C). A European lead-calcium-barium alloy known as Ferry metal contained 0.25% mercury to decrease the coefficient of friction. Another bearing alloy, Noheet metal, contained some antimony and tin in addition to the alkali metals. B metal, a German alloy, contains 0.73% calcium, 0.66 sodium, 0.05 lithium, and 0.03 potassium.

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