Lead-antimony alloys hardness

Lead alloy with 6 % antimony is frequently used in sheet and pipe forms for its superior strength and hardness over soft lead. Lead-antimony alloy is used to make battery plates. Antimony additions increase hardness, tensile strength, and fatigue resistance, and form alloys used in storage batteiy comj)onents. 

Figure 18.9 Natural hardness of lead-antimony alloys (Courtesy of the Swiss Post Office, Bern)...

Excellent antifriction properties and good hardness (qv) make lead—antimony—tin alloys suitable for journal bearings. The alloys contain 9—15 wt % antimony and 1—20 wt % tin and may also contain copper and arsenic, which improve compression, fatigue, and creep strength important in bearings. Lead—antimony—tin bearing alloys are Hsted in ASTM B23-92 (7). 

Trace quantities of arsenic are added to lead-antimony grid alloys used ia lead—acid batteries (18) (see Batteries, lead acid). The addition of arsenic permits the use of a lower antimony content, thus minimising the self-discharging characteristics of the batteries that result from higher antimony concentrations. No significant loss ia hardness and casting characteristics of the grid alloy is observed (19,20). 

Antimony alloys have many commercial applications. The metal makes its alloys hard and stiff and imparts resistance to corrosion. Such alloys are used in battery grids and parts, tank linings, pipes and pumps. The lead plates in the lead storage batteries constitute 94% lead and 6% antimony. Babbit metal, an alloy of antimony, tin, and copper is used to make antifriction machine bearings. Alloys made from very high purity grade antimony with indium, gallium and bismuth are used as infrared detectors, diodes, hall effect devices and thermoelectric coolers. 

The lead-base babbitts are based upon the lead—antimony—tin system, and, like the tin-base, have a structure of hard crystals in a relatively soft matrix. The lead-base alloys are, however, more prone to segregation, have a lower thermal conductivity than the tin-base babbitts, and are employed generally as an inexpensive substitute for the tin-base alloys. Properly lined, however, they function satisfactorily as bearings under moderate conditions of load and speed. 

Antimony (Sb) is used primarily in alloys with other metals, particularly lead. Antimony improves the hardness and corrosion resistance of the metal. 

The first grid alloys used were lead alloys with 11% antimony content called hard lead . These alloys were replaced with low-antimony lead alloys with additions of Sn, As and Ag. Later, battery grid manufacturers switched to lead—calcium and lead—calcium—tin alloys. 

Antimony alloyed with lead improves the hardness of the alloy. The eutectic phase comprises alternating platelets of antimony and lead whieh inerease the hardness of the alloy. Antimony platelets are mueh harder than lead ones. Henee, the overall alloy hardness depends on the content of antimony. 

Bearing metals, used as the bearing surfaces of sliding-contact bearings, are usually alloys of tin, lead, antimony, and copper. They contain small, hard crystals of a compound such as SnSb embedded in a soft matrix of tin or lead. The good bearing properties result from orientation of the hard crystals to present flat faces at the bearing surface. 

Secondary lead is recovered either as soft lead or as hard or antimonial lead. The metallic components of automobile batteries such as plate grids and posts may be made from antimonial lead alloys containing up to ten per cent antimony, but usually less than three per cent. This provides the source of antimony in secondary lead, but it can be controlled to some extent by separately processing metallics and non-metallic scrap. There is a trend to the use of calcium lead alloys in place of antimony for sealed batteries, which significantly reduces the quantity of antimonial lead prodnced by secondary smelters. 

Sodium—lead alloys that contain other metals, eg, the alkaline-earth metals, are hard even at high temperatures, and are thus suitable as beating metals. Tempered lead, for example, is a beating alloy that contains 1.3 wt % sodium, 0.12 wt % antimony, 0.08 wt % tin, and the remainder lead. The German BahnmetaH, which was used ia axle beatings on railroad engines and cars, contains 0.6 wt % sodium, 0.04 wt % lithium, 0.6 wt % calcium, and the remainder lead, and has a Brinell hardness of 34 (see Bearing MATERIALS). 

Type metal, another tin—antimony—lead alloy, is used primarily in reHef or letterpress printing. Antimony is added to increase hardness, minimize shrinkage, permit sharp definition, and reduce the melting point of the alloy. There has been a substantial decrease in the use of type metals as a result of the emergence of less expensive typesetting techniques. 

Antimony is used in many alloys, chiefly for its props of hardening the softer metals, such as Pb. The best known of these alloys are type metal, bearing metal, hard lead and pewter. The powdered Sb is used in some pyrotechnic compns, as a fuel (Ref 9, p 32) and as a source of white light (Refs 3a 8)... 

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