Additives grid alloying

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. 

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). 

Oxidation of additives such as antimony, in the grid alloy ... 

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. 

Influence of Grid Alloying Additives on the Processes of Anodic Corrosion... 

Table 4.4 summarises the effects of As on the mechanical properties of low-antimony lead alloys [21]. Arsenic improves the hardness and less so the UTS of the alloys. If these data are compared with the required grid alloy characteristics presented in Table 4.1, it can be seen that lead alloys with addition of arsenic meet the requirements of the battery industry with regard to hardness and their tensile strength is close to the required values. 

The above results indicate clearly that grid alloying additives interact with the organic expander. The thus formed organometallic compounds exert an influence on the performance characteristics of negative battery plates. 

If thermopassivation is a result of changes in composition of the corrosion layer, then the grid alloy composition will affect the semiconductor properties of the oxides in this layer through the dopants formed as a result of oxidation of the grid alloying additives. The latter s ions will modify the electrical properties of the oxides in the corrosion layer (Table 13.1) [5,6]. 

Influence of Additives to the Positive Grid Alloy on the Processes During Storage and on the Performance Parameters of Wet-charged Batteries... 

The properties of the corrosion layer, and of its interfaces, depend strongly on the additives to the grid alloy (in this case, antimony). Antimony affects the corrosion layer in such a way that it does not limit the discharge of the active mass, so the latter exhibits its full capacity. This phenomenon is known as antimony-free effect . 

The rate of grid corrosion is influenced by the composition of the grid alloy and the manufacturing process. Selection of appropriate alloying additives is important to reach the desired service fife. 

Table 1.9 Grid alloys for lead acid batteries, their eharacteristic additives, and fields of application. 

The rates of the self-discharge reactions also depend on temperature, additives to the active mass, electrolyte formulation, and grid alloy composition. As the surface of the electrodes is covered by PbS04 (the product of the self-discharge reactions), the state of charge of the electrodes begins to affect the rate of the self-discharge process. 

The problem has been partly solved with the introduction of maintenance-free batteries, with their improved grid alloys and reduced gassing and water loss. The drawback with this type of battery is the extra head space required to provide a reservoir of acid, enabling the battery to last 3-4 years. In addition, there is still the possibility of corrosion from acid spray. 

Selenium acts as a grain refiner in lead antimony alloys (114,115). The addition of 0.02% Se to a 2.5% antimonial lead alloy yields a sound casting having a fine-grain stmcture. Battery grids produced from this alloy permit the manufacture of low maintenance and maintenance-free lead—acid batteries with an insignificant loss of electrolyte and good performance stability. 

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