Lead-calcium-tin

Lead—Calcium-Tin Alloys. Tin additions to lead—calcium and lead—calcium—aluminum alloys enhances the mechanical (8) and electrochemical properties (12). Tin additions reduce the rate of aging compared to lead—calcium binary alloys. The positive grid alloys for maintenance-free lead—calcium batteries contain 0.3—1.2 wt % tin and also aluminum. 

Cast lead—calcium—tin alloys usually contain 0.06—0.11 wt % calcium and 0.3 wt % tin. These have excellent fluidity, harden rapidly, have a fine grain stmcture, and are resistant to corrosion. Table 4 Hsts the mechanical properties of cast lead—calcium—tin alloys and other alloys. 

Wrought lead—calcium—tin alloys contain more tin, have higher mechanical strength, exhibit greater stabiUty, and are more creep resistant than the cast alloys. RoUed lead—calcium—tin alloy strip is used to produce automotive battery grids in a continuous process (13). Table 5 Hsts the mechanical properties of roUed lead—calcium—tin alloys, compared with lead—copper and roUed lead—antimony (6 wt %) alloys. 

Lea.dAnodes. A principal use for lead—calcium—tin alloys is lead anodes for electrowinning. The lead—calcium anodes form a hard, adherent lead dioxide layer during use, resist corrosion, and gready reduce lead contamination of the cathode. Anodes produced from cast lead—calcium (0.03—0.09 wt %) alloys have a tendency to warp owing to low mechanical strength and casting defects. 

Wrought lead—calcium—tin anodes have replaced many cast lead—calcium anodes (14). Superior mechanical properties, uniform grain stmcture, low corrosion rates, and lack of casting defects result in increased life for wrought lead—calcium—tin anodes compared to other lead alloy anodes. 

Lead—tin (1.8—2.5 wt %) is used both as a cable sheathing ahoy (BS 801 ahoy A and DIN 17640) and as a battery connector ahoy ia sealed lead—calcium—tin batteries (15). Tia is generahy added to lead—arsenic cable ahoys ia smah amounts. The arsenic ahoys have excehent creep resistance and mechanical properties, but are unstable and lose arsenic readily by oxidation. The addition of smah amounts of tin (0.10—0.20 wt %) eliminates arsenic loss. Lead ahoys having 0.4 wt % tin and 0.15 % cadmium, which are used for cable sheathing, do not age harden, show excehent corrosion and creep resistance, and are very ductile. 

If the temperature of a molten lead—calcium (tin)—aluminum ahoy is not kept sufficiently high, finely divided aluminum particles may precipitate and float to the top of the melt. These may become mixed with oxides of lead in the dross. The finely divided aluminum particles can react violently with the oxides in the dross if ignited. Ignition can occur if attempts are made to melt or bum the dross away from areas of buildup with a torch. The oxides in the dross can supply oxygen for the combustion of aluminum once ignited. 

Prengaman, R. D. Wrought Lead-Calcium-Tin Anodes for Elecirowinning, AIME Conference, Los Angeles, 28/2/84. 

Lead—calcium—tin alloys beer as dietary source of, 3 588 chemical reactions, 4 525—526 in coal, 6 718... 

Cast lead-calcium-tin alloys, 14 775 Cast-link belt furnaces, 12 289 Cast-mature process, in bar soap manufacture, 22 749 Cast multicrystalline silicon material, 23 40... 

Lead-calcium-silver anodes, 74 777 Lead-calcium-tin alloys, 74 775-776 Lead carbonates, 74 794-795 Lead chalcogenides, 79 157 Lead chloride, 74 785 Lead chromate... 

Rolled lead-calcium-tin alloy strip, 14 115 Rolled lead-copper alloys, 14 116 Rolled zinc alloys, 26 594-598 Roller-hearth furnace, 12 289, 290 Roller mills, 18 65 Roller printing, 9 221 Rollin film, 17 354, 373 Rolling-assisted, biaxially textured substrate (RABiTS) technique,... 

Time-weighted average (TWA), 74 215 concentration, 25 372 exposure limit, for tantalum, 24 334 Time-Zero SX-70 film, 79 303, 305-307 Tin (Sn). See Lead-antimony-tin alloys Lead- calcium-tin alloys Lead-lithium-tin alloys Lead-tin alloys, 24 782-800. See also Tin alloys Tin compounds allotropes of, 24 786 analytical methods for, 24 790-792 in antimony alloys, 3 52t atomic structure of, 22 232 in barium alloys, 3 344, 4 12t bismuth recovery from concentrates, 4 5-6... 

Mechanical properties of cast lead—calcium tin alloys... 

Table 2.3. Mechanical properties of lead-calcium-tin alloys with 1.5wt.% Sn.

Table 2.5. Effect of tin and silver on corrosion resistance of lead-calcium-tin alloys. (Corrosion weight loss in mg cm . )...

Following the studies on pure lead [57,64], a great deal of work has been undertaken to determine the effects of tin on the corrosion layer of lead-calcium-tin alloys, which are the major alloys for VRLA batteries. One study [82] showed that the corrosion rate of lead-calcium alloys was significantly reduced by the addition of tin and the thickness of the a-PbO layer was substantially reduced. It was further found that tin enrichment at grain boundaries in cast alloys induced a high level of tin in the corrosion layer that was able to suppress passivation. Finally, it was suggested... 

Tin has been shown to increase greatly the conductivity of the passive corrosion layer in lead-calcium alloys. The presence of tin can exercise an important influence on the corrosion resistance of lead-calcium-tin alloys, as well as on the thickness and conductivity of the passive layer formed on the alloys [91]. Tin additions of about... 

Fig. 2.8. Segregation of tin in lead-calcium-tin alloys to grain and sub-grain boundaries.

Silver additions to lead-calcium-tin alloys. Silver has been added to lead-calcium-tin alloys to increase the resistance to creep and corrosion, and to prevent growth of the positive grids at elevated temperatures. Valve-regulated lead-acid batteries often operate at elevated temperatures and/or produce high internal... 

Fig. 2.11. Schematic of corrosion product on lead--calcium tin alloy.

Silver has a significant effect in delaying the discontinuous precipitation reaction as well as the overageing of calcium precipitates [90]. Silver also increases the corrosion resistance of lead-calcium tin alloys — particularly under conditions that simulate end-of-discharge (high pH) conditions — and improves the cycle-life and capacity of VRLA batteries. Silver decreases the thickness of the PbO layer but produces a harder, more compact, corrosion layer than tin. Silver does not, however, increase the conductivity of the corrosion layer. 

Silver imparts little improvement to the mechanical properties of lead-calcium tin-(silver) alloys which are fully aged (Table 2.6), but gives lower elongation in both cast and rolled alloys. There is no effect on the microstructure at 0.03 wt.% Ag [51]. Significant improvement in creep resistance has been observed in alloys which contain silver [99]. Significant increases in cycle-life and capacity have been described... 

Table 2.6. Comparison of mechanical properties of lead-calcium-tin-silver alloys.

Silver is reported to segregate to the grain and sub-grain boundaries of lead-calcium-tin alloys [94]. Microprobe analysis of the cross-section of grid wires produced from cast and rolled lead-calcium-tin alloys with a bulk silver content of... 

Gravity casting of grids is usually employed for the manufacture of flat positive plates. Flat positive lead-calcium-tin grids are more sensitive and more prone to corrosion than tubular grids. Nevertheless, it must be pointed out that even for batteries with flat positive plates, corrosion has been only one of the limiting factors during standby applications. 

Fig. 13.1. Accelerated corrosion test of gravity-cast, lead-calcium-tin grids in sulfuric acid (60°C, 1.26 specific gravity, 1.85 V constant potential against SHE). Change of grid weight measured every 3 weeks without removal of corrosion layer ( ) standard alloy/standard casting (A) improved (in terms of calcium and tin content) alloy/standard casting (o) improved (in terms of calcium and tin content) alloy/improved casting.

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