Calcium containing lead alloys

Lead alloys containing 0.09—0.15 wt % calcium and 0.015—0.03 wt % aluminum are used for the negative battery grids of virtually all lead—acid batteries in the United States and are also used in Japan, Canada, and Europe. If the molten alloy is held at too low a temperature, the aluminum precipitates from solution, rises to the surface of the molten alloy as finely divided aluminum particles, and enters the dross layer atop the melt. 

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. 

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). 

Demand for high performance SLI batteries has led to the development of smaller, lighter batteries that require less maintenance. The level of antimony is being decreased from the conventional 3—5% to 1.75—2.75% to minimise the detrimental effects. Lead alloys that contain no antimony have also been introduced. Hybrid batteries use a low antimony—lead alloy in the positive plate and a calcium—lead alloy in the negative plate. 

This bismuth—calcium—magnesium dross also contains lead that must be removed. The dross is heated in a ketde to free any entrapped lead that melts and forms a pool under the dross. This lead is cast and returned to the bismuth separation cycle. The dross is then melted and treated with chlorine and/or lead chloride to remove the calcium and magnesium. The resulting molten metal is an alloy of bismuth and lead, high in bismuth which is then treated to produce refined bismuth metal. 

Lead alloys containing small amounts of calcium aie formed by plunging a basket containing a 77 or 75% calcium—23—25% A1 alloy into a molten lead bath or by stirring the Ca—A1 alloy into a vortex created by a mixing impeUor (19). 

The raw material should contain at least 50 per cent, of Ca3P208 and be as free as possible from sesquioxides. It may be ignited if high in organic matter, reduced to a fine powder, and fed continuously into tanks lined with wood or hard lead alloy, where it meets on the counter current principle hot sulphuric acid of about 5 per cent, concentration. The reaction is quickly completed and the precipitated calcium sulphate is allowed to settle and filtered off continuously through filter presses. This sulphate is phosphatic gypsum and contains 3 to 4 per cent, of phosphoric acid of which 1 per cent, is soluble in water. The solution is evaporated in wrought-iron pans up to a concentration of 50 per cent, phosphoric acid, which may be further refined for use in pharmaceutical products or foods. 

Frary metal. A lead-based bearing metal containing 97-98% lead alloyed with 1-2% each of barium and calcium excellent for low-pressure bearings at moderate temperatures. 

Tin additions to lead-calcium alloys change dramatically the method of precipitation and age-hardening from discontinuous precipitation of PbsCa to a mixed discontinuous and continuous precipitation of PbsCa and (PbSn)3Ca and, finally, to a continuous precipitation of SnsCa. Such precipitation reactions have been described for alloys that contain low tin contents [45,48,68-70]. The reactions are not influenced or modifled by impurities in the lead alloys [71,72]. A ternary phase diagram has been proposed [41], which sets the areas of stability of PbsCa, SusCa, and mixed (PbSn)3Ca precipitates, and this is shown in Fig. 2.5. The phase diagram has been conflrmed [73]. 

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... 

Lead-alloys containing calcium were introduced in 1935 by Haring and Thomas of Bell Laboratories [5] to reduce water loss and ventilation requirements. These designs are often called low-maintenance batteries, because water additions are not required and now are often prevented by battery manufacturers to minimize electrolyte contamination. Some of the lead alloys in these designs have lower levels of... 

The traditional anodes for base metal electrowinning from sulfate solutions have been lead alloys containing calcium-tin, silver, or similar combinations. One potential concern with the lead anodes is the incorporation of lead corrosion products lowering the cathode purity. 

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. 

Bullion commonly contains np to two per cent arsenic. Arsenic is preferentially oxidised in the softening or Harris processes, bnt more readily than antimony. Conseqnently when softener slag is reduced to form an antimonial lead alloy, arsenic can be retained in the residual slag from where it can be extracted by leaching and precipitation as arsenic trioxide or as calcium arsenite. Alternatively it can be extracted from canstic slags from the Harris process by leaching and precipitation with lime as calcium arsenite, which can contain around 20 per cent As. 

This lead storage battery contains calcium-lead alloy grids for electrodes.This alloy resists the decomposition of water.so the battery can be sealed. 

In modern maintenance-free batteries, the lead alloy often contains calcium or other alkaline earth elements to make the lead stiffer. Calcium is added to the lead in the range of 0.03 to 0.20 wt% depending on the different battery manufacturers. The current trend is to lower the calcium level to 0.03% to 0.05% for better corrosion resistance. Tin has been added to the lead-calcium alloy to enhance the mechanical and corrosion-resistance properties in the range of 0.25 to 2 wt%. Some battery manufacturers have substituted strontium for calcium. The other type of lead alloy is a quaternary alloy that contains lead, calcium, tin, and aluminum. Aluminum is used to stabilize the dressing loss of calcium while molten. 

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