LITHIUM AND LITHIUM ALLOYS
This lightest of all metals, symbol Li, has a specific gravity of 0.534. It is found in more than 40 minerals, but is obtained chiefly from lepidolite, spodumene, and salt brines. The dried crude concentrate from the flotation cells contains about 20% Li2O. It may be extracted by solar evaporation from the brines of underground lakes in Nevada and other locations. It occurs also in seawater in lesser concentrations. North Carolina has immense reserves of lithium ores.
Lithium melts at 356°F (186°C) and boils at 2444°F (1342°C). It is unstable chemically and burns in the air with a dazzling white flame when heated to just above its melting point. The metal is silvery white but tarnishes quickly in the air, and a lithium nitride, Li3N, is formed. The metal is kept submerged in kerosene. Lithium resembles sodium, barium, and potassium, but has a wider reactive power than the other alkali metals. It combines easily with oxygen, nitrogen, and sulfur to form low-melting-point compounds which pass off as gases, and is thus useful as a deoxidizer and degasifier of metals. In glass the small ionic radius of lithium permits a lithium ion coupled with an aluminum ion to displace two magnesium ions in the spinel structure. Lithium is also a key constituent in batteries for computers and camcorders and has potential for batteries operating laptop computers, cellular phones, and other devices. For such applications, there are the liquid-electrolyte Li-ion battery and the solid-state Li-ion-polymer (Li-ion-P) battery. The latter contains no metallic lithium and uses a multilayer plastic-laminate structure that permits use with integrated circuits for information storage. Lithium-ion rechargeable batteries are expected to supplant nickel-cadmium as the principal consumer battery.
Lithium cobaltite, LiCoO2, and lithium zirconate, Li2ZrO3, are also used in ceramics. Lithium carbonate, Li2CO3, is a powerful fluxing agent for ceramics and is used in low-melting-point ceramic enamels for coating aluminum. It is used in medicine to treat mental depression.
Lithium metal, 99.4% pure, is produced by the reduction of lithium chloride, LiCl. The salts of lithium burn with a crimson flame, and lithium chloride is used in pyrotechnics. It is also used for dehumidi-fying air for industrial drying and for air conditioning, as it absorbs water rapidly. It is employed in welding fluxes for aluminum and in storage batteries. The anode is lithium, the cathode is a lithium-tellurium alloy, and the electrolyte is a molten bath of lithium salts at 800°F (427°C). Lithium ribbon, of Foote Mineral Co., for high-energy battery use, is 99.96% pure metal in continuous-strip form, 0.02 in (0.05 cm) thick. It comes on spools packed dry under argon. An
anhydrous form of lithium hexafluoroarsenate powder is used as the anode in dry batteries. Aluminum-lithium alloys are basically 2XXX and 7XXX aluminum alloys containing up to about 3% lithium. Because of lithium’s extremely light weight, they provide higher stiffness-to-density and strength-to-density ratios than traditional structural aluminum alloys and thus have potential for aircraft applications.
Because of the low weight, lithium compounds give the highest content of hydrogen, oxygen, or chlorine. Lithium perchloride, LiClO4, is a stable solid used as a source of oxygen in rockets and flares, with lithium chloride as a residue. One cubic foot (0.028 m3) yields 91 lb (41 kg) of oxygen. On a volume basis, it has 29% more oxygen at normal temperature than liquid oxygen at its boiling point. Lithium hydride, LiH, a white or gray powder of specific gravity 0.82 and melting point 680°C, is used for the production of hydrogen for signal balloons and floats. A 1-lb (0.45-kg) can of hydride when immersed in water will liberate 45 ft3 (1.3 m3) of hydrogen gas. It is more stable to heat than sodium hydride, and it provides molecular hydrogen, not atomic hydrogen. Lithium aluminum hydride, or lithium alanate, LiAlH4, is used in the chemical industries for one-step reduction of esters without heat. Lithium metal is very sensitive to light and is also used in light-sensitive cells. Lithium niobate is the key to a pyroelectric radiometer for measuring optical power, radiance, and irradiance in the visible and near and midinfrared wavelength regions at the National Institute of Standards and Technology. Lithium 7, which comprises 94% of natural lithium, is noted for low neutron absorption. The other isomer, lithium 6, has high neutron absorption and is used in nuclear reactors.
Lithium is soluble in most commercial metals only to a slight extent. It is a powerful deoxidizer and desulfurizer of steel, but no lithium is left in the lithium-treated steel. In stainless steels, it increases fluidity to produce dense castings. Cast iron treated with lithium has a fine-grain structure and increased density with high impact value. Not more than 0.01% remains in the casting when treated with lithium-copper. In magnesium alloys, the tensile strength is increased greatly by the addition of 0.05% lithium. The solid solubility of lithium in lead is not over 0.09%, but lithium refines the grain structure of the lead, increasing the strength, and it hardens the lead by the formation of a compound, Pb3Li2. Lithium-treated lead is called alkali lead and is used for machine bearings. Lithium up to 15% is added to magnesium to make alloys.
Lithium-copper master alloys consist of a group of foundry alloys containing usually 90, 95, or 98% copper with the balance lithium, used for deoxidizing and degasifying nonferrous alloys. Lithium combines easily in the molten bath with oxygen, hydrogen, nitrogen, sulfur, and the halides. The compounds formed are stable, of a nonmetallic nature, have low melting points, and volatilize easily so as to pass off as vapors at the pouring temperature of the metals. Lithium copper is a high-conductivity, high-density copper containing a minute quantity of residual lithium, 0.005 to 0.008%, made by treating copper with a 50–50 lithium-calcium master alloy. The conductivity of lithium copper is 101.5% IACS. The tensile strength is 31,500 to 36,500 lb/in2 (217 to 252 MPa), with elongation 60 to 72%. The wrought metal is tougher than phosphorized copper, and it has exceptional deep-drawing properties. Lithium is an excellent desulfu-rizer for nickel alloys. From 1 to 7% calcium may also be included in lithium-copper master alloys. Lithium-calcium alloys usually contain 30 to 50% lithium, with the balance calcium. They are silvery white with a metallic luster and are hard and brittle. The melting range is 446 to 500°F (230 to 260°C). They must be kept in tight containers under kerosene. The alloys are used for treating steel, cast iron, or nickel where no residual copper is to be left. Copper-manganese-lithium contains 60 to 70% copper, 27 to 30 manganese, 0.5 to 5 lithium, and sometimes 5 to 7 calcium. Copper-silicon-lithium contains 80 to 84% copper, 10 to 11 silicon, 2.5 to 10 lithium, and sometimes 2.5 calcium.

Additional comments :