Accumulators

ACCUMULATORS (from Latin accumulatio — accumulation), or secondary cells, are apparatuses serving for the accumulation of electrical energy by converting it into chemical energy. The first accumulator was built in 1860 by Planté, who discovered that during the electrolysis of a weak aqueous solution of sulfuric acid between lead electrodes, energy accumulates in the system and that, after disconnecting the latter from an external current source, the system itself can serve as such a source. Planté's accumulator consisted of two lead sheets (60 cm in length, 20 cm in width, and 1 mm in thickness) isolated from one another by rubber strips and rolled into a tube. These sheets were immersed in a vessel with a weak aqueous solution of H₂SO₄. When a current was passed through such a system, a layer of PbO₂ was deposited on one plate, and the other was freed from oxides usually covering lead. After this first charge, the accumulator could already produce an electric current, with the plate covered by PbO₂ turning out to be the positive pole, and the clean plate the negative one. The discharge did not last long, and upon its completion, the PbO₂ layer at the anode was reduced to PbO, and the lead at the cathode was oxidized to the same oxide PbO. After the first charge and discharge, the accumulator was charged again, with the compound PbO₂ forming again at the positive electrode, and the oxide PbO being reduced to loose, spongy lead at the negative electrode. By repeating this charging and discharging many times, Planté loosened the surface of the electrodes and thereby achieved the appearance of large quantities of lead oxides participating in the process. The lengthy process of accumulator "forming" did not allow, however, for achieving particularly large capacities, and therefore Faure was the first to propose applying to the lead electrodes beforehand those oxides that would participate in the charging process. These oxides (red lead on one electrode and lead litharge on the other) are mixed with a binder and applied in the form of a paste to the lead electrodes, which are nowadays given the shape of grids. A major disadvantage of such accumulators is their inability to withstand prolonged overload: at high current densities, which can always arise during short circuits, the plates warp and the mass falls out of the pockets. The electromotive force of a freshly charged accumulator reaches 2.3–2.4 volts. Upon discharge, it drops very quickly to 2 volts and maintains this value for a long time, after which it begins to drop slowly. When discharging an accumulator, one should never allow the electromotive force of each cell to drop below 1.8–1.9 volts, since further discharge has a harmful effect on the plates. The charging and discharging process of lead accumulators can be represented by the following reversible reaction (according to recent works by Féry): Pb + H₂SO₄ + Pb₂O₆ ⇄ PbSO₄ + 2PbO₂ + H₂O; here free lead (Pb₂), after charging, appears at the cathode, and lead peroxide (Pb₂O₅) at the anode. If an accumulator filled with solution stands for a long time in an uncharged state, both electrodes become covered with a layer of lead sulfate (PbSO₄), which renders the accumulator unusable. Sulfation of the electrodes proceeds, according to Féry, according to the following formulas: at the cathode — Pb₂SO₄ + H₂SO₄ + O = 2PbSO₄ + H₂O; at the anode — Pb + H₂SO₄ + O = PbSO₄ + H₂O; the cause of this destructive phenomenon turns out to be oxygen dissolved in water and getting there from the atmospheric air. Féry combats this by placing the cathode in a horizontal plane at the very bottom of the vessel. A major disadvantage of lead accumulators is their significant weight (for every accumulated watt-hour in large accumulators, the weight is equal to 0.1 kg and even in portable ones — no less than 0.03 kg). To eliminate this disadvantage, Edison and Jungner proposed accumulators with iron and nickel electrodes, which possess a significantly lower weight for the same capacity. Unfortunately, these accumulators suffer from another drawback: their coefficient of useful action (efficiency) does not exceed 52%. The electrolyte in them is an aqueous solution of caustic soda or caustic potash. The electromotive force developed by them is less than in lead accumulators, and equals 1.4 volts at the beginning of discharge. During discharge, it drops slowly, and one should never let it decrease below 1.15 volts. Individual accumulators are connected into batteries in the exact same way as ordinary galvanic cells: the negative pole of the subsequent one is connected to the positive of the preceding one. The strength of the charging, as well as the discharging current, must not exceed a certain defined limit.

v. Shuleykin. Accumulator manufacturing. From the socio-hygienic point of view, the production of lead accumulators is of the greatest importance; they constitute a battery of galvanic cells in which the cathodes are lead plates, the anodes are plates of lead peroxide, and the electrolyte is sulfuric acid with a strength of 21--23° Baumé. Accumulators of small size are usually housed in glass or ebonite vessels, while large ones are in wooden boxes lined with sheet lead. The main stages of the manufacturing process are as follows. Casting of the plates: lead ingots are subjected to melting at 600°, after which plates are cast from the molten lead either in copper molds (manually) or on presses (mechanically). For better impregnation with sulfuric acid, the plates must have a porous, spongy structure. To this end, the plates during their casting are provided with a large number of lattice-like depressions or grooves, which are filled with a special paste-like composition, the so-called "active substance" or "active mass." This operation, bearing the name of "pasting" of the plates, is preceded by their cleaning, which consists in the worker removing excess lead deposits from the depressions of the plates. The pasting itself consists of the following: red lead, litharge, black lead oxide (and sometimes other powdered substances) are mixed in "glaze mixers" with H₂SO₄ or ammonia into a viscous paste, which is then smeared into the depressions of the plates using wooden spatulas. Next, the pasted plates are subjected to drying in drying ovens, and then to formation: the plates are immersed in vessels with sulfuric acid, their ends ("lugs") are soldered with an electric arc or hydrogen flame, and then under the influence of prolonged passage of an electric current (for 1--3 days) PbO₂ (anode) is formed on some plates, and Pb (cathode) on others. After formation, the plates are unsoldered again, washed in water, and dried. The next operation is the a s s e m b l y of plates into cells and batteries: the plates are arranged in a specific sequence—anodes and cathodes alternate with each other—their lugs, having been previously subjected to c l e a n i n g with a file or on a special machine, are soldered again with a hydrogen flame, the battery is immersed in a vessel with H₂SO₄, the plates are poured over with an insulating material, and subjected, as during formation, to charging with an electric current, which is the final manufacturing operation. To prepare small accumulators, instead of casting small-sized plates, large plates are often cut into pieces of the appropriate size; the cutting of plates is performed with a circular or band saw. Along with the described main manufacturing processes, some auxiliary operations are of serious sanitary and hygienic importance, such as: the manufacture (rolling) of sheet lead for lining vessels, lead-coating of copper parts, repair of casting molds, etc. The dominant hazard of accumulator manufacturing is lead dust released into the air of workrooms, and the direct contact of workers with lead and its compounds. The dustiest jobs are work in the lead mill, pasting, plate cutting, assembly, packing, and cleaning. The dust, especially in departments where one has to deal with lead compounds, is very fine; the diameter of the dust particles here does not exceed 4 µ. Among industries hazardous with regard to lead poisoning, accumulator manufacturing occupies a prominent place. Thus, for example, out of 6,762 cases of lead poisoning in various branches of industry in England for 1900--1909, 285 cases fall on accumulator manufacturing. In 1911--1914, accumulator manufacturing ranked second in the number of lead poisoning cases, alongside the production of white lead. In France for 1922, out of 797 cases of saturnism, 180 (22.5%) fell on accumulator manufacturing, which occupies second place here as well (first place being enameling and glazing); in German saturnism statistics for 1922, accumulator manufacturing occupies first place—53 cases out of 348 (15.3%). Medical examination in 1925 of 341 individuals working in accumulator manufacturing in Leningrad revealed various symptoms of saturnism in 13.5%. The second main hazard constantly present in accumulator manufacturing is the contamination of the air in the forming department with SO₃, released under the influence of the strong current of hydrogen developing in the accumulator liquid (electrolysis). Measures to combat the hazards of accumulator manufacturing: mechanization of production processes, hermetic sealing of equipment, local extraction of dust and vapors, rational general ventilation, isolation of workshops where dusty work is performed, thorough cleaning of workrooms, rational special clothing, and for particularly dusty jobs—

dust respirators, detailed instruction of workers on personal hygiene measures. It is highly desirable to limit the use of lead accumulators by replacing them with alkaline or iron-nickel ones (anode—nickel oxide hydrate, cathode—iron oxide hydrate, electrolyte—potassium hydroxide solution). The most important legislative measures for the protection of labor of those working in accumulator manufacturing in the USSR: 1) a shortened workday (7 hours) when working on the casting and formation of accumulator plates; 2) additional two-week leaves for those working in all main operations—casting, pasting, and formation; 3) prohibition of the labor of adolescents in casting, formation, soldering, and charging.

23V