Calcium-Tin Alloys

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. 

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 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... 

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. 

The changes in mechanical properties, YS, UTS and creep resistance (CR), of fully aged cast lead—calcium—tin alloys with two different Sn concentrations (0.5 wt% Sn or 1.5 wt% Sn) as a function of Ca content are presented in Fig. 4.36. Data from Ref. [66] were used to plot these dependences. The alloys with low-Ca content (0.02 and 0.03 wt% Ca) have low mechanical properties which improve with an increase of the Ca content up to the peiitectic concentration, pass through a maximum and decrease thereafter. All three measured parameters (YS, UTS and CR) have higher values when the alloys contain 1.5 wt% Sn (higher r value) than at the lower 0.5 wt% Sn level. Tin accelerates the precipitation reaction to completion. This holds for the whole range of calcium concentrations but proceeds at different rates. 

Mechanical properties of cast lead—calcium—tin alloys with 0.5 or 1.5 wt% Sn contents. Data from... 

Mechanical properties of wrought (rolled) lead—calcium—tin alloys with three different Ca concentrations. Data from ref [18] are used. 

Lead—calcium—tin alloys with 0.06—0.08 wt% Ca and 0.6—1.5 wt% Sn are used for the manufacture of positive grids for maintenance-free, valve-regulated, automotive and stationary batteries. Cast grids have a coarse-grained structure and ensure stable battery operation. They are highly corrosion resistant and thus can guarantee long cycle life of the battery. 

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