mentaince of lead acid battery
Answers
Answer:
Maintenance of Lead Acid Battery. Action of sediment-at the bottom of the cell container. Due to loss of acid by spray during charging. Inadequate treatment after the removal of short circuit. Due to excessive sulphation on the plates.
Explanation:
The lead–acid cell can be demonstrated using sheet lead plates for the two electrodes. However, such a construction produces only around one ampere for roughly postcard-sized plates, and for only a few minutes.
Gaston Planté found a way to provide a much larger effective surface area. In Planté's design, the positive and negative plates were formed of two spirals of lead foil, separated with a sheet of cloth and coiled up. The cells initially had low capacity, so a slow process of "forming" was required to corrode the lead foils, creating lead dioxide on the plates and roughening them to increase surface area. Initially this process used electricity from primary batteries; when generators became available after 1870, the cost of production of batteries greatly declined. Planté plates are still used in some stationary applications, where the plates are mechanically grooved to increase their surface area.
In 1880, Camille Alphonse Faure patented a method of coating a lead grid (which serves as the current conductor) with a paste of lead oxides, sulfuric acid and water, followed by curing phase in which the plates were exposed to gentle heat in a high humidity environment. The curing process caused the paste to change to a mixture of lead sulfates which adhered to the lead plate. Then, during the battery's initial charge (called "formation") the cured paste on the plates was converted into electrochemically active material (the "active mass"). Faure's process significantly reduced the time and cost to manufacture lead–acid batteries, and gave a substantial increase in capacity compared with Planté's battery. Faure's method is still in use today, with only incremental improvements to paste composition, curing (which is still done with steam, but is now a very tightly controlled process), and structure and composition of the grid to which the paste is applied.
The grid developed by Faure was of pure lead with connecting rods of lead at right angles. In contrast, present-day grids are structured for improved mechanical strength and improved current flow. In addition to different grid patterns (ideally, all points on the plate are equidistant from the power conductor), modern-day processes also apply one or two thin fibre-glass mats over the grid to distribute the weight more evenly. And while Faure had used pure lead for his grids, within a year (1881) these had been superseded by lead-antimony (8–12%) alloys to give the structures additional rigidity. However, high-antimony grids have higher hydrogen evolution (which also accelerates as the battery ages), and thus greater outgassing and higher maintenance costs. These issues were identified by U. B. Thomas and W. E. Haring at Bell Labs in the 1930s and eventually led to the development of lead-calcium grid alloys in 1935 for standby power batteries on the U.S. telephone network. Related research led to the development of lead-selenium grid alloys in Europe a few years later. Both lead-calcium and lead-selenium grid alloys still add antimony, albeit in much smaller quantities than the older high-antimony grids: lead-calcium grids have 4–6% antimony while lead-selenium grids have 1–2%. These metallurgical improvements give the grid more strength, which allows it carry more weight, i.e. more active material, and so the plates can be thicker, which in turn contributes to battery lifespan since there is more material available to shed before the battery becomes unusable. High-antimony alloy grids are still used in batteries intended for frequent cycling, e.g. in motor-starting applications where frequent expansion/contraction of the plates needs to be compensated for, but where outgassing is not significant since charge currents remain low. Since the 1950s, batteries designed for infrequent cycling applications (e.g., standby power batteries) increasingly have lead-calcium or lead-selenium alloy grids since these have less hydrogen evolution and thus lower maintenance overhead. Lead-calcium alloy grids are cheaper to manufacture (the cells thus have lower up-front costs), and have a lower self-discharge rate, and lower watering requirements, but have slightly poorer conductivity, are mechanically weaker (and thus require more antimony to compensate), and are strongly subject to corrosion (and thus a shorter lifespan) than cells with lead-selenium alloy grids.
The open circuit effect is a dramatic loss of battery cycle life which was observed when calcium was substituted for antimony. It is also known as the antimony free effect