January 1948
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
esting to note that D is apparently increasing with increasing per cent relative humidity for these two polymers. The permeation process has been found to be only slightly temperature dependent for nylon, polyvinyl butyral, cellulose acetate, and polyvinyl alcohol (Figure 6). For these polymers, all of which sorb considerable quantities of water, the heat involved in the solution process is counterbalanced by the activation energy requirements for .diffusion, which are lower than for the waterinsensitive polymers. LITERATURE CITED
(1) Barrer, R. M., “Diffusion in and through Solids,” New York. MacMillan Co., 1941. (2) Bull, H. B., J . Am. Chem. SOC.,66, 1499 (1944).
111
(3) Charch, W. H., and Priridle, K. E. (to E. I. du Pont de Nemows & Co.) U. S. Patent 1,737,187 (Nov. 26; 1929). (4) Charch, W. H., and Scroggie, A. G., Paper Trade J . , 3-11 (Oct. 3, 1935). (5) Doty, P. M., Aiken, W. M. and Mark, H., IND.ENQ. CHEM., ANAL.ED., 16, 686 (1944). (6) International Critical Tables. (7) King., G., Trans. Faraday SOC.,41, 479 (1945:. 18) Mark, H., Am. Sci., 31, 97 (1943). (9) Pauling, L., J . Am. Chem. SOC.,67,555 (1945). (10) Rouse, P. E., Ibid., 69, 1068 (1947). (11) Simril, V. L., Ph.D. Thesis, Univ. of N. C. (1942). (12) Simril, V. L., and Smith, S.,IND.ENG.CHEM.,34,226 (1942). (13) Swnington, F. S., and Burroughs, It. F., Fiber Containers, 28, NO. 4, 107-9 (1943). RXCEIVEDOctober 7. 1946.
Stabilization of Chlorinated Diphenyl in Paper Capacitors L. J. BERBERICH AND RAYMOND FRIEDMAN Westinghouse Research Laboratories, East Pittsburgh, Pa. Experimental results show that the life of a paper capacitor can be prolonged by substantial amounts, tenfold or more, when c&tain compounds are added to the chlorinated diphenyl impregnant, without affecting power factor or resistibity of the capacitor. Data are presented showing tests of stabilizing effectiveness of forty-one compounds. Among the best of these are azobenzena, azoxybenuene, anthraquinone, benzil, dinitrobenzil, dinitrotoluene, o-nitrodiphenyl, and sulfur. Lack of availability at a low price and other factors may, however, place a restriction on the commercial use of some of these compounds. The stabilizing behavior of azobenzene and benzil are reported here for the first time. Experimental studies of the mechanism of capacitor stabilization are described, and’a theory of stabilization involving electron donor and electron acceptor molecules is proposed.
T
HE most important class of capacitors now in use consists essentially of aluminum foils separated by dried and impregnated paper. The performance of these capacitors, when impregnated with chlorinated diphenyl, chlorinated ethylbenzene, or chlorinated naphthalene, may be tremendously improved, tenfold or more, by addition of suitable materials t o the impregnant or paper ( 1 , 8 4 , 1.9, 16-90). Materials of this nature which have been described in the literature may be divided into six classes, as follows: (a) quinones (anthraquinone, ,%chloroanthraquinone) added in low concentrations to the impregnant (16) ; ( b ) nitroaromatic compounds (pnitrochlorobenzene) added in low concentrations t o the impregnant (4); ( c ) maleic anhydride or its derivatives added in low concentrations to the impregnant (6); ( d ) sulfur or selenium (elemental) added in low concentrations to the impregnant ( 9 ) ; (e) a salt of a strong base and a weak acid (calcium gluconate, gum arabic) incorporated into the paper (18); and (f) a substance capable of removing acids directly by adsorption, precipitation, or base exchange (silver, lead, or mercuric compounds, fullers’ earth, calcium bentonite) incorporated into the paper (16,17). The additives for chlorinated impregnants previously reported cover a variety of chemical compounds possessing various structures. The work described in this paper makes possible the addition of two new classes t o those just cited-namely, (9)
aromatic azo compounds (azobenzene, p-dimethylaminoazobenzene, azoxybenzene, Sudan IV) added in low concentrations t o the impregnant; and (h) diketones (benzil) added in low concentrations t o the impregnant. A mechanism for the action of stabilizers in chlorinated capacitor impregnants has been reported by McLean and Egerton (6, 18). This mechanism, however, does not appear to explain all of the observed behavior. Therefore, another mechanism is presented in this paper together with some experimental evidence in support of it. The stabilizing action of forty-one compounds, including those investigated by others, was determined in capacitors impregnated with chlorinated diphenyl. CRITERIA FOR STABILIZER
It has been shown (14, 19) that the deterioration reaction in chlorinated aromatic impregnated paper capacitors under direct-current stress is closely related to the action of the aluminum electrode surface. The theory has been proposed that traces of hydrogen chloride are formed, which react with the electrode surface to produce aluminum chloride; this in turn catalyzes further decomposition, so that a short life results for the stressed capadtor, especially when operated at elevated ambient temperatures (70” to 100” C.), The stabilizer, if present in concentrations of 1% or less, inhibits the decomposition, so that capacitor life under direct-current stress may be prolonged in this manner by a factor of ten or more. While the life of a capacitor under severe direct-current stresses and temperatures is comparatively short, this is not true when alternating-current stresses of comparable magnitude are applied. Stabilizers, however, are effective for alternating- as well as direct-current applications, but they prolong alternating-current life by a smaller factor than is the case with direct current. This difference in behavior may be ascribed to the greater electrochemical action in the case of the latter. The criteria for the ideal stabilizer for this application appear to be the following: 1. The compound should produce a substantial prolongation of capacitor life without affecting the metals and other materials of construction used in the capacitor. 2. The compound should not adversely affect power factor or resistivity of either the impregnant or the impregnated capacitor.
INDUSTRIAL AND ENGINEERING CHEMISTRY
118
TABLE I. STABILIZ.4TION
Stabilizer
Concn.,
70
None
OF
Anthraquinone Anthraquinone Benzalacetophenone Benzil Benzil Benzoic anhydride Benzophenone Benzophenone Benzyl benzoate Dibenzofuran Dibenzvl ether
Diphenyl carbonate Diphenyl ether Hydroquinone 1,S-Kaphthalic anhydride p-Acetyldiphenyl Phthalic anhydride Phthalic anhydride Pyrogallol Tetrachlorohydroquinone
0.1 0.5 0.1 0.1 0.5 0.1 0.1 0.5 0.1 0.1 0.1 0.1 0.35 1.0 0.1 0.5
0.1 0.1 0.1 0.1 0.2 0.1 0.1
CHLORINATED DIPHEXYL-IMPREGNATBD CAPACITORS AT 85' C.
(bluminum foil, 1000 volts per mil direct-current stress) Yo Power Factor a t 8 5 O C. Capacitors, 190 v.p.m., Life of Individual Units, Liquid, 100 cycles 60 cycles Days
0.04-0.2 0.14 0.04 0.04 0.08 0.05
0.15 0.04-1.2 0.18 0.035 0.07 0.07 0.07 0.05 0.05 0.04 0.1-0.2
......
0.04 0.06 0.08
0.04 0.4 0.4
Vol. 40, No. 1
0 42-0.53
3a,5 , 5,5 , 5, 5,5l/z, 6,6,6,6,8,8
O X Y G E NCOMPOUNDS 0.39-0. GO 8,10,11, 12,15,15,15,I. 5 , 23 0.51-0.61 Sa, Sa,118,135,135,153 0.43-0.52 7,7,8 0.40-0.43 6a, 17,18,20 0,44-0,55 70,85,98 0.67-0.74 1" 3a 10 11 0.40-0.58 31)2Q,'lO,'Il,12,12. 19 0.52-0.64 8 , 9,10 0,40-0.44 10, 10, 11 0.45-0.56 2a,3a,g1/2,9'/z 0.46-0.62 20,8,8,8 0.37-0.47 11, 12,12 0.43-0.51 E , 8,8 0.47-0.52 ,, 8 , 11 0.54-0.62 9,10, 11 0.47-0.56 4'/& 5l/z, 6l/2 0.38-0.43 5,8 0.50-0.58 12,17,20 0.34-0.41 7,8,8 0,50-0.66 28,30,33 0.62-0.69 loa, 23,39 1.1 -1.2 6 , 7,8 0,83-0.86 10,11, 14
RC (1000 \'.P.Xf., 8 5 O C.), Av, Life,
Days
5.9
Megohm-Microfarads Initial Half life
21-60
14.0 135.0 7.3 18.3 84.3 10.5 12.8 9.0 10.3 9.5
16-30 21-33 30-50 20-33 30-33 19-20 33-43 23-30 30-38
8.0
27-33 27-43 25-33 20-30 23-30 30-33 21-30 25-30 20-37 16-17 13-17 10-13 16-33
11.7 8.0
8.7 10.0 5.5 6.5 16.3 7.7 30.3 31.0 7.0 11.7
50
19-43 21-25 30-33 19-60 25-50 33-38 6-14 25-43 19-33 2n-33 43 25-28 27-38 23-30 21-30 21-33 50
19-21 25-43 30-33 12 13-18 25-43
NITROQES COMPOUNDS Azobenzene Azobenzene Azobenzene Azobenzene Azoxvbenzene AaoxGbenzene Benzalaniline 8-Naphthoquinoline &Naphthylamine Diphenylamineb Diphenyl piperazine Dimethylaminoaaobenzene $Ilhenyl: a-naphthylamine b Succinonitrile Sudan IV Triphenylamine
0.1 0.2 0.5 5.0
0.1 0.5
0.5 0.1 0.1
0,1-0.3 0.04 0.04 0.05 0.02 0.05 0.09 0.14 15.0
0.1 0.1 0.1 0.1
0.5
0.5
0.6
0.1 0.1
4.0 0.3 1.9 0.20 0.4
0.38-0.39 0.43-0.51 0.42-0.56 0.41-0.44 0.41-0.45 0.42-0.48 0.67-0.71 0.44-0.60 0.78-0.80 0,35-0.41 0.91-0.99 0.55-0.62 0.34-0.39 0.62-0.81 0.44-0.50 0.36-0.44
22,26,26 30,41,46 41,54,60,87 59a,315,350 2",24,31,32 33,67,76 9,10,10 15, 18,20 25,5,7 7;7: 7 19,22,23 5,'6)'6 Sa,15,15,16 5, 6
24.6 39.0 G0.5
332,O 29.0
58.7 9.7 17.7 6.0
1.2b 7.0 21.3 3.0b 5.7 15.3 5.5
MIBCELLANEOUS COMPOVNDS 8.0 0.1 0.09 Chromium acetylacetonate 0.49-0.54 7,8,9 8.7 0.46-0.49 35, 8 , 8. 10 Diphenyl sulfone 0.1 0.04 9.3 0.48-0.51 2",6, 11, 11 Fluoranthene 0.1 0.05 6.7 0.59-0.60 5,5 , 7,10 Stilbene 0.1 0.10 4 N o t included in averages because of premature failure probably due to mechanical defects. b These capacitors were impregnated in glass tubes a n d life-test'ed a t a 1ow.r voltage. T h e lives shown are calculated values.
3. The compound, a t its maximum effective concentration, should be soluble in the impregnant over the complete range of capacitor operating temperatures. 4. The compeund should be sufficiently nonvolatile so that excessive loss from the hot impregnant under vacuum will be avoided. 5. The compound should be commercially available a t a low price.
During the past five pears the writers have investigated the behavior of hundreds of experimental 0.25-microfarad capacitors, impregnated with chlorinated diphenyl, to which were added low percentages of various substances in an effort to obtain insight into the mechanism of capacitor stabilization, and to determine what type of stabilizer best sitisfies the stated criteria. This work was limited to the chlorinsted diphenyl impregnant which is supplied by the Monsanto Chemical Company as 1254 Aroclor. This material, containing 54% chlorine, has an estrernely high order of thermal stability and is a widely used capacitor impregnant. COMPARATIVE EVALUATION O F STABILIZERS
Tables I and I1 show power factor, resistivit'y, and directcurrent life under accelerated conditions of capacitors containing forty-one compounds in various concentrations. All capacitors were made with aluminum foil separated by three sheets of 0.4mil kraft paper, each unit being in a soldered t,in can. All units Tvcre vacuum-dried a,ccording t o a standard procedure and then vacuum-impregnated with a purified chlorinated diphenyl solution of the various stabilizers. Most of the compounds were
40 30-50 37-50 37-43 50-100 23-25. 21-25 GO
25-27
....
25 21-27 ,...
33-43 33-43 27 21-27 37-43 33-60 27-33
30-33 19-GO 27-30 37:+5 17-19 17-18 11-14 8-19 +i5 5- 8
...
33 21-27 20-30, 23-33 43-50 30-60
38
obtained from Eastman Kodak Company. Comparable results were obtained with azobenxene, anthraquinone, benzil, and a few others when commercial grades were substituted for Eastman grades without further purification. Life tests were made a t 1200 volts direct current (1000 volts per mil) and a t various temperatures from 40' t o 100" C., in forced circulation ovens. The life testing procedure and some of the earlier results obtained with st,abilizers have been described in a previous paper (1). Life test results in Table I were obtained a t 85" C., whereas those in Table I1 were obtained at 100" C. Some of these results, as.mell as those obtained a t lower temperatures, are plotted in Figure 1. The capacitor resistivities are reported in terms of RC values, the RC value being t,he product of megohms X microfarads. Tables I and I1 show that certain families of compounds have common characteristics. For example, each compound shown which contains an azo group (azobenzene, azoxybenxene, Sudan IV, and p-dimethylaminoazobenzene) has a definite stabilizing power. Each of the anhydrides (phthalic anhydride, benzoic anhydride, and 1,s-naphthalic anhydride) shows stabilizing effectiveness, but RC values t,end t o be low and power factors somewhat high. Fbrthermore, solubility is limited for this class of compounds. None of the esters (benzyl benzoate, dibutyl phthalate, diphenyl carbonate), ethers (diphenyl ether, dibenzofuran, dibenzyl ether) or simple ketones (benzophenone, p-acetyldiphenyl, benzalacetophenone) show any great effectiveness, although none have any adverse effect.% It is surprising that benzil is an effective stabilizer, in view of the lack of effec-
119
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1948
tiveness of benzophenone. Future tests are planned with diphenyl triketone. Nitro compounds (0-nitrodiphenyl, dinitrotoluene) are effective. Primary and secondary amines (p-naphthylamine, diphenylamine, phenyl-a-naphthylamine) are seen to be undesirable. It is known that compounds of this type raise the power factor of chlorinated diphenyl by ionization of the amine group. Tertiary amines have but slight effect on power factor but have no stabilizing action. These results are in contrast with the stabilizing effectiveness of amines for aliphatic chlorinated hydrocarbons. Finally, Table I1 shows that a combination of two effective stabilizing molecules (azobenzene-anthraquinone mixtur.e) or two effective functional groups in the same molecule (l-nitro-2methylanthraquinone) results in slightly less effective stabilization than what would be obtained with the best component used alone in each case. Dinitrobenzil, however, is an exception, since it is considerably more effective than benzil. More combinations will have to be investigated before further generalizations can be made. The best stabilizers in these tables are seen to be azobenzene, azoxybenzene, anthraquinone, benzil, dinitrobeneil, o-nitrodiphenyl, dinitrotoluene, and sulfur. Anthraquinone was studied by McLean and Egerton (19),who showed that the life of a capacitor increases with increasing concentrations up to about 0.5y0by weight. Further additions of anthraquinone result in relatively small increases in life. The solubility of anthraquinone in chlorinated diphenyl is about 1% at 80" C. but only about 0.3% at 25" C. This relatively low solubility results in no serious disadvantage, provided the solution is always maintained at such a temperature that no separation takes place before and during the impregnation of the capacitor. McLean and Egerton pointed out that if greater solubility is desired, this can be obtained without loss of stabilization by use of anthraquinone derivatives, such as a-monochloroanthraquinone, a-monbmethylanthraquinone, and tert-dibutylbenzoquinone. The use of these anthraquinone derivatives, however, may be restricted because of the difficulty of obtaining them in the desired quantities a t a price comparable to that of anthraquinone and azobeneene. Bdth azobenzene and b e n d have no limitations so far as solubility is concerned, since 10% or more of either of these compounds will dissolve in chlorinated diphenyl at 25' C. Furthermore, both of these compounds show pronounced effectiveness in concentrations a t least up to 1 or 2%. Data for benzil in Table I1 show that 1% of this compound results in a markedly longer average life than 0.5% does. Similarly, Table I1 also shows that 2y0 azobenzene results in a capacitor life which is roughly four times that when only 0.5% of this compound is used. Further data on azobenzene in Table I indicate that still
1.0
I
I
1 /
I
1
I
I
C. 0.5 % B E N Z l L D. 0.5 % ANTHRAQUINONE E. 5.0 YoAZOBENZENE
I
I
5,5
,
3.1 RECIPROCAL OF ABSOLUTE TEMPERATURE (DECREES K E L V , N ~ ~ ~ 3 )
2.0
27
2.8
2.9
3.0
Figure 1. Variation of Direct Current Life of Chlorinated Diphenyl Kraft Paper Capacitors with Temperature (1000 Volts per Mil) longer life can be expected when the concentration is increased from 2 to 5%. The solubility and concentration effects of the other compounds were not studied sufficiently t o warrant further discussion. Sulfur is quite interesting, especially since it shows p, marked stabilizing action as compared with the behavior of several sulfur compounds listed in Table 11. The stabilizing action of sulfur has been studied extensively, and the results were recently reported by McLean, Egerton, and Houte (20). These investigators showed that sulfur is effective with lead-tin foils as well as with aluminum foils. They used a precipitated form of sulfur and indicated that a pure form of sulfur is a primary requirement. The sulfur used in this work was a U.S.P. grade
TABLE 11. STABILIZATION OF CHLORINATED DIPHENYL-IMPREONATED CAPACITORS AT 100 O C. (Aluminum foil, 1000 volts per mil direct-current stress)
% Power Factor a t 85O C. Stabilizer None Arobenzene Azobenzene Aeoxybenzene Anthraquinone
Concn.,
% '
O.b 2.0 0.5 0.5
Liquid,
100 Cycles 0.04-0.2 0.04 0.05 0.05 0.04
Capacitors, 1QO v.p.m. 60 cycles 0.42-0.53 0.42-0.56 0.50-0.56 0.42-0.48 0.51-0.61
Life of Individual Units, D a y s 1, 1, 1, 1, 1, 1 1 / 2 , 111'2, 11/z, I ~ / z 11/i, , 21/2 6,7, 8,8, 9, 9, 9, 10 43,50,31,30 9, 11, 14 la, 6, 9, 11, 12, 13, 14
Azobenaene-anthraquinone mixture (50-50) 0.5 0.06 0.42-0.45 6 , 6 , 7 Benzil 0.05 0.44-0.55 5, 5, 7, 9 0,. 5 Benaii 0.05 1 .o . . . . . . . 37,42,38,21, 26 Dibenzofuran 1.0 0.05 0.43-0.47 1, 2, 2,2 Dinitrobeneil 0.1 0.51-0.60 10,10, 11, 12 0.5 4,4'-dinitroaaoxybenaene 0.05 0.47-0.50 5 , 5, 7,8 0.5 Dinitrotoluene 0.05 0.5 13, 14, 14, 16 Diphenyl sulfone 0.07 1.0 0.45-0.48 2 2 2 2 o-Nitrodiphenyl 0.46-0.52 l b , i7' 18,24 0.5 0.05 1-Nitro-2-methylanthraquinone 0.5 0.57-0.58 6,9, d, 11 0.1 0.44-0.56 1, 1. 2,2 0.07 Phenyl sulfide 0.5 Sulfur 0.53-0.58 20 27,28,31 1.0 0.05 T i n tetraphenyl 0.43-0.45 2 , 2,3, 3 0.5 0.2 0 N o t included in averages because of premature failure probably d u e to mechanical defeats.
.......
.
A.v Life, Days 1.4 8.2 38.5 11.3 10 %8 6.3 6.5 33.0 1.7 10.7 6.2 14.2 2.0 18.8 8.8 1.5 28.7 2.5
RC (1000 V.P,M., 100°C.), Megohm-Microfarads Initial Half life 6.5-11 10 10 1.5-10 10-15 3.3-3.9 8 7-8 8-Q
.....
7 7-8 9-13 8-12 6-7.5 3.2-4 5-6
..... 9-13
5-6 7.5-8 6.7 13
7 ..... 10-15 ..... ..... ..... 4-6
5-8.5 7.5-8.6 4-6
.....7
.....
120
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 40, No. 1
gen chloride, dry aluminum foil (about, 99.97% pure) was added through the side arm, with the SIDE-ARM FOR effect on conductivity shown in Figure 3. Second, FOIL ADDITION one tenth of one per cent of a stabilizer was added, which immediately reduced the conductivity, as DRY H C L . also shown in Figure 3. This effect was observed FROM TANK for azobenzene, anthraquinone, and benzil. Eventually the conductivity would increase again in each case. This could be delayed by further additions of stabilizer. D w l N G TUBE GLASS WOOL CONDUCTIVITY DRYINGTUBE The conductivity of the solution saturated with DUST TRAP CELL hydrogen chloride was about lo-" ohm-' em.-', Figure 2. Conductivity Cell for System Pentachlorodiphenylalt'hough this was not st'rictly After the addition of aluminum, conductivity rose Hydrogen Chloride-Aluminum Foil rapidly to several hundred times this value. According to Thomas (16)and Heldman.(9), this effect is caused by a highly ionized acid, HAICla, formed by of sublimed (sulfur flowers), and good results were obtained interaction of hydrogen chloride and aluminum chloride. When without further purification. Although sulfur has shown a a stabilizer S is added, it may be visualized that two competing beneficial action in laboratory tests, it still remains to be shown reactions occur: that the use of sulfur will not introduce corrosion hazards in some types of commercial capacitors where copper and iron are AlCla HCI @ H+ AlC1,(1) exposed to the impregnant. AICL S Ft (AlC13S) (2)
+
+
+
VARIATION OF LIFE WITH TEMPERATURE
Data have been reported (14, 19) for the variation of directcurrent capacitor life with temperature, and it has been pointed out that the order of magnitude of temperature dependence is consonant with the hypothesis that the deterioration is chemical in nature. The writers have obtained data of this type for kraft paper, aluminum foil capacitors impregnated with chlorinated diphenyl, the most important commercial impregnant and paper, this combination not having been reported upon previously. Figure 1 shows that straight lines are obtained when the logarithm of L is plotted against 1/T, where L is life and 5" is absolute temperature; this indicates a relation of the form L = A X 1OElT, where A and B are constants. If B values are calculated from the slopes of the curves, it is found that B = 5800 for the unstabilized capacitors and somewhat larger values for the stabilized compositions. For example, for chlorinated diphenyl plus 0.5% azobenzene, B = 7500, whereas for chlorinated diphenyl plus 0.5y0 anthraquinone, B = 9100. However, if B values are calculated from data of RIcLean and Egerton (19) for chlorinated naphthalene and kraft paper, it is found that for the unstabilized composition B = 5300, whereas for the liquid plus 0.5% anthraquinone, B = 4200. Since B is sensitive to experimental inaccuracies, it is likely that the variation of B may be explained on this basis. Further work in this direction, however, is indicated. For unstabilized capacitors (curve A , Figure 1) the activation energy E is 26,500 calories per mole. This corresponds to doubling the life for every 6" C. lowering in temperature, in the temperature range 70" to 100' C.
Reasons for the occurrence of the second reaction will be discussed later. A competing mechanism such as this offers some explanation for the temporary drop in conductivity shown in Figure 3. DECOMPOSITION O F CARBON TETRACHLORIDE
The corrosion of aluminum by carbon tetrachloride and the inhibition of this attack by capacitor stabilizers have been previously described ( 6 ) . It may be assumed that the mechanism of this deterioration is similar, t o some extent, a t least, to the decomposition reaction in a capacitor, although the causes of decomposition are believed t o be different in the two cases. There is a great difference in the relative stability of carbon tetrachloride and chlorinated diphenyl; the former iyill dec6mpose in contact with aluminum after a few minutes at 77" C.,
CONDUCTIVITY PHENOMENA IN CHLORINATED DIPHENYL
A series of experiments was carried out with the conductivity cell shown in Figure 2, by means of which the action of stabilizers is demonstrated in a convenient way. This study was suggested by work originally reported by XcLean ( 1 4 , although the experimental procedure is somewhat different. Anhydrous hydrogen chloride (Harshaw Chemical Company) was passed through calcium chloride and then bubbled through chlorinated diphenyl in the Pyrex cell maintained a t 90" C. by immersion in an oil bath. Direct-current conductivity was measured at 5-minute intervals between the nickel electrodes of a special cell previously described (2). Measurements were made with a General Radio Company type 544-B megohm bridge, a gradient of 22 volts per mil being applied for 20 seconds for each measurement. The order of additions to the cell was as follows: First, after the liquid became saturated with hydro-
Figure 3. Effect of Stabilizers on Conductivity of Chlorinated Diphenyl Saturated with Hydrogen Chlbride and in Contact with Aluminum at 90" C.
INDUSTRIAL AND ENG INEERING CHEMISTRY
January 1948
~ L F Cscw 1-0 be itiiiioat perfectiy cirauisr iiilt.i t h i s suggvsts tbnt the action is initiated at cat.alytically tic points, auhsequmtly spreading out radially from t h w poi W W V ~ W I:WW
2 3
I
0 I 2
4
3
8 9 10 11 12 13 14
No additive Nu additive No additive NO additive
100 49 21 4.9
22 2.0 0.7 !I . 5
:>.n
4.G 0.9 4.6 0.1 8.i
Figure 6 shows an aluminum capacitor mode sftor failure o Iifc 1c.hl. TIic composition of the fluorescent matrriai eau: t l i e spots is not known, but it is obviously a product, of catalyt ic &composition. The resrmhlitnce hct.wccii tla:se s! itnd t.hc corroded arcm of E'igurcs 4 and 5 should be obscrved The porsibility IWS considered that the acbive centixs w l promote decomposition might be associated with inrlusioni inrpuritics on the aluminum surface. A typical a W I l y S k ii follows: M g 0.008%; Cu O.WSY,; Ba 0.004%; Si 0.00: IFpuritim, copper, in particular, could be asmeiatrid with intive cenlws, since the life of B capacitor a i t h copper lid
