Properties of Lead Alloys

Hoffmann, W. (1960) Lead and Lead Alloys, 2nd ed. Springer, Berlin Heidelberg New York. 

Properties of Lead and lead Alloys. Lead Industries Association (1984). 

Worcester, A.W. O Reilly, J.T. (1991) Lead and Lead Alloys. In ASM Handbook of Metals 10th. ed, Vol, 2 Properties and Selection Nonferrous Alloys and Special-Purpose Materials. ASM, Materials Park, OH, pp. 543-556. 

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Figure 4.1 presents schematically the basic properties of lead alloys which are essential for their applicability for casting battery grids. These alloy characteristics and their influence on battery performance parameters will be discussed in more detail in this chapter. 

Key properties of lead alloys to be used for casting battery grids. 

Metallic lead has a low melting point (T = 327 °C). This allows diffusion of the alloying elements into the lead matrix at room temperature. These diffusion processes will result in the formation of inter-metallic compounds, which will alter the properties of the lead alloy with time. The changes in mechanical properties of lead alloys during ageing have been extensively studied. Some of the obtained results will be summarised below. 

Antimony, more metallic than arsenic, is an opaque, lustrous, tin-white, brittle solid. Both the element and its compounds are poisonous. Like arsenic, antimony is used to improve the properties of lead alloys. 

Table 1. Mechanical Properties of Lead—Antimony Alloys ...

Rea.ctivity ofLea.d—Ca.lcium Alloys. Precise control of the calcium content is required to control the grain stmcture, corrosion resistance, and mechanical properties of lead—calcium alloys. Calcium reacts readily with air and other elements such as antimony, arsenic, and sulfur to produce oxides or intermetaUic compounds (see Calciumand calciumalloys). In these reactions, calcium is lost and suspended soHds reduce fluidity and castibiUty. The very thin grids that are required for automotive batteries are difficult to cast from lead—calcium alloys. 

Lead—copper alloys are specified because of superior mechanical properties, creep resistance, corrosion resistance, and high temperature stabiUty compared to pure lead. The mechanical properties of lead—copper alloys are compared to pure lead, and to lead—antimony and lead—calcium alloys in Tables 4 and 5. 

Engineering Properties of Zinc Alloys, International Lead Ziuc Research Organization, New York, 1980, pp. 1—36. 

Arsenic added ia amounts of 0.1—3% improves the properties of lead-base babbitt alloys used for beatings (see Bearing materials). Arsenic (up to 0.75%), has been added to type metal to increase hardness and castabiUty (21). Addition of arsenic (0.1%) produces a desirable fine-grain effect in electrotype metal without appreciably affecting the hardness or ductihty. Arsenic (0.5—2%) improves the sphericity of lead ammunition. Automotive body solder of the composition 92% Pb, 5.0% Sb, and 2.5% Sn, contains 0.50% arsenic (see Solders and brazing alloys). 

This example of aluminium illustrates the importance of the protective him, and hlms that are hard, dense and adherent will provide better protection than those that are loosely adherent or that are brittle and therefore crack and spall when the metal is subjected to stress. The ability of the metal to reform a protective him is highly important and metals like titanium and tantalum that are readily passivated are more resistant to erosion-corrosion than copper, brass, lead and some of the stainless steels. There is some evidence that the hardness of a metal is a signihcant factor in resistance to erosion-corrosion, but since alloying to increase hardness will also affect the chemical properties of the alloy it is difficult to separate these two factors. Thus althou copper is highly susceptible to impingement attack its resistance increases with increase in zinc content, with a corresponding increase in hardness. However, the increase in resistance to attack is due to the formation of a more protective him rather than to an increase in hardness. 

The properties of alloys are affected by their composition and structure. Not only is the crystalline structure important, but the size and texture of the individual grains also contribute to the properties of an alloy. Some metal alloys are one-phase homogeneous solutions. Examples are brass, bronze, and the gold coinage alloys. Other alloys are heterogeneous mixtures of different crystalline phases, such as tin-lead solder and the mercury-silver amalgams used to fill teeth. 

Uses. Used in iron and steel production and in non-ferrous metals and alloys. It improves the creep strength of tin and the mechanical properties of lead. Used also in the vulcanization of rubber to reduce curing time and improve its characteristics. 

The applications of arsenic as a metal are quite limited. Meialluigically, it is used mainly as an additive. The addition of from to 2% of arsenic improves the sphericity of lead shot. Arsenic in small quantities improves the properties of lead-base bearing alloys for high-temperature operation. Improvements m hardness of lead-base battery grid metal and cable-sheathing alloys can be obtained by slight additions of arsenic. Very small additions (0.02 - 0.05%) of arsenic to brass reduce dezincdfication. 

On Earth, when a melted alloy solidifies, it forms pine-tree-shaped crystals called dendrites These dendrites play a very important role in determining the properties of the alloy and its subsequent usefulness. Gravity causes fluid Hows in the alloy, leading to the formation of irregular dendrites that weaken the alloy or metal structure. This type nf processing is so complex that it is difficult to measure and predict, and even more difficult to control. In space, gravity-related phenomena such as convection are reduced, thus simplifying the process for study. See also Dendrite. 

Antimony appeared in all notes at a low level and was rubbed off both front and back, indicating its presence in the inks. If it was not added deliberately, it might have been present as an impurity in lead. Antimony frequently is alloyed with lead to increase its strength and to improve the electrical properties of lead plates in storage batteries and often is present in reclaimed lead. 

The methods already described have illustrated the wide applicability of flame atomisation techniques to the analysis of non-ferrous alloys. The introduction of electrothermal atomisation has enabled the direct determination of sub-part per million levels of impurities. The presence of very low levels of lead, bismuth and other low melting point metals is known to have a deleterious effect on the metallurgical properties of nickel alloys. 

While not investigated in depth, the un-reacted ash can be subjected to a mixture of hydrogen and oxygen, with sufficient oxygen to raise the temperature above the melting point of the steel. This will melt the ceramic materials to an ash and allow the recovery of the metals as a peculiar mixture of iron, nickel, chromium, lead, tin, copper, zinc and other metals. The properties of this alloy are not known, but it may be useful in applications where a metal is desired but high quality is not essential. It may also be possible to reprocess this alloy to recover the pure metals. 

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