LATEXBATTERY SEPARATORS Preparation and Properties H. W. GREENUP AND L. E. OLCOTT The Firestone Tire & Rubber Company, Akron, Ohio
minal voltage under a load of 300 amperes, of batteries containing latex separators, is higher than that of those containing wood separators. Results of the life test showed the latex separators to be more durable than wood separators.
The preparation of storage battery separators from latex is described. The electrical resistance of latex separators is lower than that of wood separators, especially at temperatures in the neighborhood of 0“ F. (- 11.8” C.), and the ter-
T
vitrified bonding material ( I ) , cloth coated with celluloid (4), bird feathers treated with sodium sulfite ( I @ , cork or wood bound with latex (IO),pyroxylin and sodium silicate mixtures ( I I ) , etc. As far as the present writers know, none of these materials have been used extensively. Rubber, especially ebonite, has been much more successful than any other material as a substitute for wood in battery separators. I n 1915 Willard (18) prepared “thread rubber” separators by plying up layers of fabric or cords coated with hard rubber stock, slicing in a direction perpendicular to the cords, and curing the slices. The use of sheets of perforated hard rubber in conjunction with wood separators has been common in the industry for several years in some types of batteries. Wilderman (17) prepared hard rubber separators with fine pores either by binding hard rubber dust with a hard rubber cement and curing the resulting product under light pressure, or by curing semi-cured hard rubber dust under light pressure without a binder. Recently, the commercial production of porous ebonite separators from latex has been started (3, 7, 9). I n 1915 Schidrowitz ( I S ) discovered.that a porous product could be obtained by vulcanizing coagulated latex under such conditions that the serum was retained in the coagulum during vulcanization. The latex coagulum has a reticulated structure; that is, both serum and rubber are continuous phases.
HE commonly used electrical storage battery consists of alternate negative plates of sponge lead and positive plates of lead peroxide immersed in an electrolyte, sulfuric acid; the whole is enclosed in a hard rubber or bituminous composition case. These plates are ordinarily separated from one another by ribbed sheets of wood called “separators.” The separators prevent short circuiting of the plates caused by actual contact of the plates with each other or by “treeing” (formation of lead crystals between the plates). The separators must be thin, in order to make the battery as compact as possible, and yet must be durable. It is necessary that they be highly porous so that their electrical resistance will be low, but the pores must be sufficiently fine so that “treeing” does not take place.
Wood separators are ordinarily made of Port Orford cedar. They are usually given a preliminary treatment in warm, dilute sodium hydroxide solution to swell them, thus increasing their porosity, and to remove injurious substances which cause self-discharge and corrosion of the plates. Wood separators have the advantage of being inexpensive and of having fairly low electrical resistance, but they are not so resistant to the action of sulfuric acid and the oxidizingaction in the cell as is desirable. They are, in many cases, the first part of the storage battery to fail and must then be replaced if the battery is to give further service. Many materials have been used as substitutes for wood in battery separators. Among them are finely divided, fritted glass ( I d ) , thin sheets of wood coated with rubber ( B ) , asbestos and zinc dust molded with a phenolic condensation product and treated with acid to remove the zinc (6),sliced tripoli (W), cloth or paper impregnated with synthetic gum (16), Filtros treated with hydrous silica ( 1 4 , aluminum oxide with a
The same thing was observed by Hopkinson ( 8 ) , who vulcanized a plastic, highly compounded latex mixture in open steam to form a product which was porous when cured. By using sufficient sulfur, a porous ebonite product may be obtained by the Schidrowitz process. It is a product of this type that is used for battery separators. 192
FEBRUARY, 1937
IXDUSTRIAL AND ENGINEERING CHEMISTRY
Preparation of Latex Separators
193
RUWBER
WOOD
For the purpose of comparing latex and wood separators, the former were prepared from a mixture of the following composition (in grams): 166.6
MerOautobenaothiqrole
25% diphenylguanidineBUspsiiaiDn Water
90 5 5
1.0 7.1
15.5 % 2
6
The sulfur and diphenylyanidme suspensions, which contained glue as the protective colloid, were ground in a pebble mill. The zinc oxide suspension, which contained Saprotin (a commercial dispersing agent), was also ground in the pebble mill. This mixture was poured into a mold having the shape of a battery weparator and cured in open steam until a t least 90 per cent of the sulfur present was combined.
UNTESTED
Electrical Characteristics of Latex and W o o d Separators Since starting and lighting batteries are required to furnish discharge currents of az high as 300 to 500 amperes, low internal resistance, and therefore low resistance of the separators, is of great importance. I n this work the resistances of latex separators, Port Orford cedar separators (soaked in acid for 3 weeks), and a combination of Port Orford cedar and pcrforated hard rubher sheets were determined The sheets were 0.015 inch (0.38 mm.) thick and contained small diamond-shaped perforations which gave them a porosity of approximately 48 per cent. Tho method described by Vinal ( 1 6 ) was used in making the measurements. A hard rubber battery case, containing two diaphragms approximately 2 mm. apart, was filled with sulfuric acid of 1.250 specific gravity (26.6' C.). The diaphragms contained circular holes over an area of 10 squarc inches (64.5 sq. em.). Current and potential electrodes were placed on each side of tkie double diaphragm, and the potential difference set up by the current electrodes was measured by means of a Kelvin bridge equipped with an alternating current galvanometer. The separator was placed between the two diaphragms, and its effect upon the potential difference measured. Figure I shows the results obtained at 80" 2'. (26.7' C.), 40' F. (4.4OC.),1OoF.(-12.2aC.),00~.(-17.80C.j,and -10°F. (-23.3' C,). The difference in electrical resistance between iatex and wood, or wood and perforated rubber sheets, increases aa the temperature becomes lower. The effect of this difference in electrical resistance upon the perfonnanceof a battery, aa measured by terminal voltage, is shown in Figure 2. Three-cell, thirteen-plate batteries, containing positive plates 53/8 inches (13.65 em.) high, 5% inches (14.29 em.) wide, and 0.100 inch (2.54 mm.) thick, and negative plates 5 3 / ~inches high, F/8inohes wide, and 0.90 inch (2.29nim.) thick, were insulated with the three types of separators. The batteries were placed under a load of 300 amperes, and their terminal voltages were measured 5 seconds after the start of the discharge. The batteries were cooled in a mechanical refrigerator for the tests made a t temperatures below 80" F. (26.7' C.). The lower electrical resistance of the latex separators, especially a t law temperatures,
TESTED
is demonstrated by the higher voltage of tlic battery containing tlrern. To detenninc just how much this higher voltage of the battery containing latex separators would mean in actual service, the speed a t which batteries containing the thrac types of insulation would turn an automotive starting motor, under constant load, was determined. AProny brake was connected to a starting motor taken from one of the popular lightweight cars. The tests were conducted on batteries cooled to 0' 17. since starter speed hecomcs important a t low temperatures. In making tho tests, the brake tension on the starting motor was adjusted to cause a load of 300 amperes on the battery. The results obtained are as follows:
Lstex Port Oiioid eedsi Port Orioid cedar ~ I U Iperlorated bard rubber sheeta
4.57 4.20
380 278
3.85
220
Service Life of Latex and Wood Separators S o matter how good the electrical characteristics of a separator are, it is worthless if i t will not withstand the action of the sulfuric acid and the oxidizing action of the positive plates of lead peroxide. The separator must neither soften in service, m it would then be cut through by the plates, nor swell and prevent proper circulation of the electrolyte. These properties are usually determined by the life test, which
INDUSTRIAL AND ENGINEERING CHEMISTRY
194
is run in the following manner on batteries containing the separators to be tested:
Literature Cited
1. Charge at 10 amperes for 6 minutes and 25 seconds. 2. Allow to rest for 3 minutes. 3. Discharge at a rate of 300 amperes for 5 seconds. 4. Allow to rest for 30 seconds.
This cycle is repeated continuously for 6 days. On the seventh day a capacity test is made on the battery and the battery is recharged. The cycle is again repeated continuously for 6 days, and the test is continued in the same manner as long as desired. As the battery attains a temperature of 110' to 120" F. (43.3' to 48.9' the test becomes quite severe. Figure 3 shows sections of latex and of Port Orford cedar separators removed from standard thirteen-plate batteries after a life test of twelve thousand cycles. The battery containing the wood separators had failed, but the One containing the latex separator had not* Life tests Of twenty-four thousand Cycles have resulted in disintegration of the plates without failure of the latex separators.
VOL. 29, NO. 2
(1) Anderson, U. S. Patent 1,458,377 (1923). (2) Baird, Ibid., 1,279,074 (1918). (3) Beckmann, Ibid., 1,745,657 (1930). (4) Benner and Heise, Ibid., 1,484,928 (1924). ( 5 ) Bliss, Ibid., 1,206,983 (1917). (6) Carpenter, Ibid., 1,087,637 (1914). (7) Greenup, Ibid., 1,959,160 (1934). (8) Hopkinson, British Patent 220,591 (1922). (9) Madge, Ibid., 377,751 (1932). (IO) Norris, U. S. Patent 1,567,747 (1926). (11) Pederson, Ibid., 1,732,140 (1930).
!::E
c.),
~ ~ ~ ~ (1915). ~ i (14) Thatcher, u, s. Patent 1,393,467 (1922). (15) Vinal, "Storage Batteries," p. 51, New York, John Wiley & Sons, 1930. (le) u. s. Patent 1 9 3 6 6 7 2 2 3 (lg21)* (17) Wilderman, Ibid., 1,651,567 (1927). (18) Ibid., 1,243,368 (1915). (19) Wood, Ibid., 1,502,455 (1924).
RIUCEIVED September 18, 1936. Presented before the Division of Rubber Chemistry at the 92nd Meeting of the American Chemiaal Society, Pittaburgh, Pa., September 7 t o 11, 1936.
High-Molecular-Weight Alkyl-Aryl Ketones A.
NLY a comparatively small n u m b e r of high-molecularweight alkyl-aryl ketones have
0
been syathesized' The present paper describes the preparation and DroDertiesof a number of
w.
RAMTON AND C. W. CHRISTENSEN Armour and Company, Chicago, Ill.
A number of ketones of the type R-C-R',
where R is an
II
0 aryl and R ' an alkyl radical, have been synthesized. Two genera1 methods of preparation were employed-the Friedel-Crafts using the aliphatic acid chloride and the Grignard reaction employing the aliphatic nitrile. The ketones described are waxlike solids insoluble in water, alcohol, and acetone, and very soluble in solvents such as benzene, toluene, kerosene, and turpentine. Their properties are discussed and several uses indicated.
new CompouAds of this type. With the- exception .. .o- f t h o s e k e t o n e s which are liquid at room tempernture7 new ketones are solids. When highly purified by reDeated recrvstafiieation they still Eetain their waxlike properties. All are characterized by low viscosities in the molten state, high flash and fire points, and resistance to oxidation when heated for prolonged periods a t 350' F. These ketones have the property of adhering to metallic surfaces, forming permanent lubricating and protective films. In reviewing the work of srevious investieators. we find that C h s an2 Hafifelin (2) bepared the fGowin@;by the action of acid chlorides upon the corresponding hydrocarbons : phenyl heptadecyl ketone, m-xYlYl hePtadeCY1 ketone, PXYbl heptadecyl ketone, P-tOIY1 pentadecyl ketone, and (4) prepared P-tO1yl pentadecyl ketone* heptadecyl ketone, m-xylYl PentadecYl ketone, P-ethoxYphenyl pentadecyl ketone, and dimethylresorcyl pentadecyl ketone by a similar method. a-Naphthyl heptadecyl ketone was prepared by Ryan and Nolan (6) bx the action of the corresponding Grignard reagent upon stearamide. The same authors also prepared a-naphthyl pentadecyl ketone and ptolyl pentadecyl ketone using palmitamidem %senmurid and h h f e r t (6)Prepared 3,4-dihYdroX3'PhenJ'l heptadecyl ketone by heating catechol distearate with aluminum
chloride, and Auwers (1) prepared p-hydroxyphenyl pentadecyl ketone by heating p-ethoxyphenyl pentadecyl ketone with aluminum chloride.
Methods of Preparation
if
The writers prepared a number mixed ketones and investigated some of their chemical and physical properties. TWO general methods of preparation, the Friedel-Crafts reaction and the Grignard synthesis, were employed and comparisons made to establish the identity of the products. The synthesis of diphenyl heptadecyl ketone is typical of the preparation of these compounds by the Riedel-Crafta reaction: A 15.4gram (0.1-mole) sample of diphenyl was dissolved in 200 cc. carbon disulfide and 30.2 grams (0.1 mole) stearyl &lo-
ride. This mixture was cooled in ice to approximately 10" C., and 13.3 grams (0.1 mole) aluminum chloride were added slowly over a period of one-half how with constant stirring and refluxed until no further evolution of hydrochloric acid was observed.
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