An expert panel replies to questions on lead-acid technology and performance asked by delegates to the Ninth Asian Battery Conference. The subjects are as follows. Grid alloys: effects of calcium and tin levels on microstructure, corrosion, mechanical and electrochemical properties; effect of alloy-fabrication process on mechanical strength and corrosion resistance; low dross-make during casting of lead–calcium–tin alloys; future of book-mould casting. An expert panel replies to questions on lead-acid technology and performance asked by delegates to the Ninth Asian Battery Conference. The subjects are as follows. Grid alloys: effects of calcium and tin levels on microstructure, corrosion, mechanical and electrochemical properties; effect of alloy-fabrication process on mechanical strength and corrosion resistance; low dross-make during casting of lead–calcium–tin alloys; future of book-mould casting; effect of increasing levels of silver; stability of continuously processed grids at high temperature. Negative-plate expanders: function of lignosulfonates and barium sulfate; benefits of pre-blended expanders; optimum expander formulations. Valve-regulated batteries: effect of oxygen cycle; optimum methods for float charging; charging and deep-cycle lifetimes; reliability testing.••ChargingExpanderGrid alloyLead-acid batteryPerformanceValve-regulated1.1. Question: How do calcium and tin levels in the lead alloy affect the microstructure and properties of grids? (C.S. LAKSHMI)1.2. Question: How does the structure of continuous-cast/rolled and expanded-metal grids differ from that of gravity-cast grids? What effect will this have on their mechanical strength and corrosion resistance? (C.S. LAKSHMI)There are several continuous grid-production techniques, as follows:•(i)In the wrought strip expansion method, lead–calcium–tin alloy is rolled into a strip and the rolled sheet is slotted and expanded to form a continuous ribbon of grids.•(ii)In the cast-expansion method, a continuous strip is cast slotted, and then expanded to produce the grids.•(iii)In the Conroll™ technique, molten metal is fed to a casting shoe which slides on a rotating drum. The continuous grid strip is subsequently rolled to obtain very thin grids.•(iv)A stamped grid is made by stamping or punching the grid from a continuous sheet of either a rolled or a continuous-cast lead material.1.3. Question: What are the means for achieving low dross-make during the casting of lead–calcium–tin alloy grids? (C.S. LAKSHMI)Dross is a product of oxidation of calcium and molten lead in the grid casting o. 2.1. Question: What are the functions of lignosulfonates and how do they work? (D.P. BODEN)Expanders are used in every lead-acid battery produced in the world. Despite this, they are often regarded as mystery substances and knowledge about how they perform their function, the materials used in their production and the correct formulation for a particular battery application is meager.Lignosulfonates exert physical, chemical and electrochemical effects on negative pastes and active materials. They affect the plasticity of the paste and increase its flow characteristics. This permits less water to be used during paste mixing. Insufficient lignosulfonate will result in a paste that is too stiff, while too much can result in a paste that is sloppy. Depending on the type and quantity of lignosulfonate in the paste, the water ratio may have to be adjusted to achieve the desired paste density and plasticity.The principal chemical function of lignosulfonates is to inhibit the formation of tetrabasic lead sulfate (4BS) in the paste during mixing and in the plates during curing. Consequently, cured negative plates, regardless of curing conditions, contain no 4BS crystals.The electrochemical functions of lignosulfonates are as follows:•(i)Lignosulfonates beneficially improve the electroreduction process during plate formation and thus cause the production of small, finely divided, lead crystallites with high su. 3.1. Question: How does the oxygen cycle affect float and cyclic charging of valve-regulated lead-acid batteries? (R.F. NELSON)The effects are different for float and cyclic charging but, in both cases, oxygen transport from the positive to the negative plate makes charging of VRLA batteries more difficult than for flooded lead-acid products. In flooded batteries, grid corrosion and water breakdown at the positive with the generation of oxygen gas have no effect upon the negative plate, as virtually all of the oxygen escapes as vented gas. In other words, both plates charge independently of each other and the efficiency of charging depends mostly upon mass balance and the charge efficiencies of the plates.Due to the partially-saturated nature of the glass-mat separator in VRLA batteries, oxygen transport to the negative takes place—and increasingly so, as the battery ages. This creates problems in charging because the reduction potential for oxygen is well below (i.e. less negative) than the equilibrium potential of the negative electrode. Thus, when oxygen reaches the negative plate in significant amounts, the normal overcharge process of hydrogen evolution is shut off and the plate potential is lowered. In extreme cases, the negative-plate potential can be drawn down to values below open-circuit and the plate becomes partially sulfated. This may be to only a minor degree, but it will be cumulative and will lead to reduced disch.
