LIQUID DIELECTRICS Chemical, Physical, Electrical Properties of Systems Containing Lead or Copper Soaps in Liquid Paraffin As part of a study to determine which of the types of products that may be formed by the service degradation of insulating oils cause serious dielectric losses in insulating oils at 60 cycles and which do not, properties of systems composed of liquid paraffin and a cupric or lead soap of the following acids have been investigated: 1,lO-hydroxystearic, stearic, palmitic, myristic, lauric, capric, pelargonic, caprylic, cyclohexanecarboxylic, undecylenic, erucic, and abietic acids. In the preparation of these soaps, some of which were crystalline, possible adsorption of alkali ions was avoided by treating the acetates with the above acids rather than with their alkali soaps. Most of the systems containing lead soaps, in concentrations of 0.15 per cent by weight, became cloudy as they were being cooled. A t temperatures immediately above the point of separation, the systems had high power factors and dielectric constants. Certain mixtures of lead soaps set to translucent gels or greases on cooling. The systems containing cupric soaps of individual acids had low power factors and conductivities at all temperatures, including those near which the soaps separated from solution. Systems containing mixed soaps, prepared from cupric abietate and certain acids or other soaps, however, had high power factors, conductivities, and dielectric constants a t certain temperatures, even though these systems did not become cloudy on cooling. The dielectric properties of the systems are believed to be related to the state of dispersion of the soaps in the oil.
JOHN D. PIPER, A. G. FLEIGER, c. C. SMITH, AND N. A. BERSTEIN The Detroit Edison Company, Detroit, Mich.
insulating oils with the metals used in the construction of high-voltage cables, and the deleterious effect of these soaps as judged by comparing the metallic content of insulation with its dielectric properties were discussed by Wyatt (17). Inasmuch as other kinds of materials in various quantities are formed simultaneously with metallic soaps during the reaction of metals or their oxides with insulating oils in the presence of oxygen, it seemed desirable to learn what effect the soaps themselves produced on the power factor of insulating oil. After the field had been surveyed by some preliminary work, a number of lead and copper soaps were prepared in a highly purified state, and each was added to an oil of low loss under conditions designed to exclude or minimize any reaction between the soap and the oil. Electrical measurements were then made on the mixtures.
Preliminary Experiments Investigators working in different laboratories on one of the deteriorated oils discussed by Wyatt (17) found considerable evidence that the copper or copper compounds existing in that oil were present in the colloidal state. I n view of Ostwald’s prediction (7) that plots of various dielectric properties of suspended materials against the degree of their dispersion may exhibit maxima or minima in the colloidal range, an attempt was made to determine approximately the state of dispersion of synthetical copper soaps in oils.
T
HE work here described is part of an investigation to determine which of the types of products that may be formed by the serviced degradation of insulating oils cause serious dielectric losses in insulating oils at 60 cycles, and which do not. The types of deterioration products considered in this paper are certain lead and copper soaps. The formation of these soaps through the interaction of
1 The four papers which follow (pages 307 t o 338) were presented before the Division of Industrial and Engineering Chemistry a t the 96th Meeting of the American Chemical Society, September 5 t o 0 , 1938.
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TABLEI. DIALYSIS TESTSON COPPER SOAPS --Cupric
Solvent
Stearatea-
Hours tested
Temp.,
335
65
I
..
..
O
c.
Cupric Oleate-
c -
Permeable or impermeable
Hours tested
T:mp., C.
--Cupric Permeable or impermeable
Hours tested
NaphthenatebPermeable or Temp., imperc. meable
Collodion Membraneso Liquid paraffin Heavy insulating oil Petroleum ether Benzene Xylene Oleic acid Naphthenic acids
... ... 8 8
...
...
..
65 65
.. ..
..
I I
.. ..
100 100 40 40 40
100
...
65 65 25 25 25 65
100
65 65 25 25 25
I I I P P..
100
65
I
... ... ..* ...
25 25 25 25
I
100 100
.... .. ...
..
..
Cellophane Membranesd
... ...
Benzene Xylene Alcohol Ether
...
...
.. .. ,.
..
.. .. .. ..
*.. ... 40 ...
.. ..
25 25
.. ..
I P
I
P P
Prepared as subsequently described. b Contained an excess of the parent acid. e Films made by allowing the solvent t o evaporate from an ether-alcohol (3 vol. to 1 vol.) solution of collodion. d Modified for uae in each solvent by the method of McBain and Kistler ( 0 ) .
a
For this purpose dialysis tests were used. Copper soaps were enclosed in a vessel made partially of a collodion or cellophane membrane, and the vessel was placed in a colorless solvent. Whether or not the soaps dialyzed through the membrane was indicated by noting whether a green color developed in the solvent. I n cases where the soaps did not dialyze, the permeabilities of the membranes were tested with a suitable indicator, usually o-toluene-azo-o-toluene-azo-pnaphthol. I n order to reduce the viscosity of some of the oils and, in the case of cupric stearate, to keep the soap in solution, some of the experiments were run a t elevated temperatures. The materials used, the conditions employed , and the results obtained are indicated in Table I. I n only a few cases, none of which involved insulating oils, did the soaps dialyze through the membranes, although the indicator did so readily. This seemed to indicate that cupric soaps in oils are probably in the colloidal state.
be in some form different from that of the sols of copper stearate and copper naphthenate. In contrast with the behavior of the copper soaps, only a low concentration of the first lead soap investigated was required to cause the power factor of a mixture of the soap in liquid paraffin to be high. This soap, lead stearate, had been prepared in considerable quantity for other purposes from stearic acid of U. S. P. grade. At temperatures above 92" C., mixtures of this soap in liquid paraffin were clear. No dialysis tests were made t o determine whether the mixtures were solutions or sols because the temperature necessary to keep the material in solution was such that prolonged heating might cause decomposition of the oil. At the lower temperatures the mixtures formed translucent gels. As Figure 2 shows, the maximum power factors of the mixtures were found a t the temperatures corresponding to the transition of the mixtures from sols to gels. These preliminary experiments made it seem worth while to continue the work using concentrations of soaps and temperature ranges selected to cross the transition points between systems which appeared to be homogeneous and systems which appeared to be heterogeneous.
Preparation of Soaps
CONC., % BY WI:
EFFECTOF CONCENTRATIONS OF CUPRICSOAPS ON THE POWERFACTOROF LIQUIDPARAFFIN AT 80' C.
FIGURE 1.
I n order to learn what effect colloidal copper soaps have on the power factor of an insulating oil, cupric stearate and cupric naphthenate were each dissolved in liquid paraffin, and power factor measurements made on the mixtures. The values obtained a t 80" C. for different concentrations of the soaps are shown in Figure 1. (Percentage concentrations given in this paper refer to percentage by weight unless stated otherwise.) As shown, the copper stearate and copper naphthenate did not cause large increases in the power factor of liquid paraffin. It was apparent, therefore, that if the small amount of copper soaps found in insulating oils causes the power factor of the oils to be high, these soaps must
In the usual methods for preparing the soaps of heavy metals-for instance, the method of Whitmore and Lauro (16)-molecular portions of the acids dissolved in alcohol are neutralized with alkali and treated with a small excess of the acetate of the heavy metal in aqueous solution. In an investigation involving dielectric properties, it seemed best to avoid the use of alkali or its salts entirely because alkali ions might become adsorbed on the soaps of the heavy metals. The general method used was as follows: About 4 grams of lead acetate or cupric acetate (Baker's c. P. Analyzed) were dissolved in the least possible amount of hot water, and the solution was diluted with about 100 to 150 ml. of boiling absolute alcohol. Before a precipitate had time to form, slightly less than the theoretical amount of acid (Eastman Kodak Company's Eastman grade except as will be subsequently described) was added in warm (40' C.) absolute alcohol. The solutions were then kept about half an hour at a sufficientlyhigh temperature to prevent precipitation and were cooled rapidly to about 8" C. with stirring; the voluminous precipitate which then formed was filtered with the aid of suction. The recipitate was dissolved in boiling absolute alcohol and was coolei rapidly again, and the reprecipitated material was filtered. This process was repeated with benzene as the solvent; then the adhering solvent was removed under reduced pressure.
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TABLE11. PROPERTIES OF LEADSOAPS --Lead, Weight %Melting Point, C-. Theoretical Visual Appearance Found Reported Found for P b A d Name 5.5> 5.5 112-113.5 112.5-113.5 (6) 20.1 White powder Lead cerotateo 23.18 26.11 White crystalline plates 117-118 Lead 1,lO-hydroxystearateb 27.13, 27.06 26.78 iii-iis ( 5 , 1 e ) White spherulites, agglomerating to glistening plates 115.0-115.5 Lead stearate 29.31, 29.76 28.90 113.0-113.6 113 (16) Sjmilar t o stearate Lead palmitate 31.32 30.71, 3 0 . 6 1 109.6-110.2 Similar t o stearate Lead myristate 34.23, 34.20 34.22 103.s-104.2 ioi'(ie) Similar t o stearate Lead laurate 37.96, 37.89 37.71 Similar t o stearate 96.5-97.0 Lead ca rate 39.74 39.70, 39.59 Similar t o stearate 98.0-98.5 Lead perargonate 42.12, 41.64 82.0-82.8 83 5-84.5 ( 5 ) 41.99 Similar t o stearate Lead caprylate White powder Lead caproatec Lead c clohexanecarboxylated White glass 26:22, 25.58 25:53 14O'(decomposed) 150 '(decomposed) White powder: turns yellow on standing Lead agietatee 23.20, 23.45 23.50 101.5-102.0 About 100 (16) White powder Lead erucate 36.45, 36.55 36.13 75-76 Similar t o stearate Lead undecylenate a Contains free cerotic acid. b Acid prepared by method of DeGroote et al. ( 1 ) : melting point 80-81' C. ( ! 4 ) , 81-82' C. (1). c Insoluble in liquid paraffin: crystallized from ethyl ether solution but not highly purified. d Insoluble in liquid paraffin: very soluble in ethyl alcohol when first formed; precipitated from ethyl alcohol solution by acetone b u t not highly purified. a Abietic acid purified from rosin by method of Steele ( 1 % ) ; melting point, 158' C.; [&I? in alcohol, -53. f A = univalent acid radical. 7 -
...
...
: ...
...
...
OF COPPER SOAPS TABLE111. PROPERTIES
--Copper, Name Cupric cerotate" Cupric 1,lO-hydroxystearate
Visual Appearance
Found
Weight YoTheoretical as C u A d
Liiit' blue powder AA&t insufficiedd >or analysis 10.7, 10.6 10.09 Blue-green powder ( ptd from xylene) LigRt bfue-green powder 13.82, 13.76 13.76 Cupric laurate Cupric caprate Light blue powder 15.74, 15.93 15.66 Cupric caprylate Light blue powder 18.40, 18.32 18.17 Cupric cyclohexanecarboxylateb Blue-green needles retained 19.96, 20.00 20.00 crystalline form a t 275' C. Cupric abietatec Light lavender-blue powder 9.3-9.6 9.54 Light blue fluffy powder 8.60, 8.60 5.62 Cupric erucate Blue-green powder 14.76, 14.83 14.79 Cupric undecylenate a Could not be prepared by metathesis. b Crystallized from benzene: sparingly soluble in organic solvents after crystallization from benzene. c It was necessary t o use 10 per cent excess cupric acetate in the preparation; purified b y diluting the absolute aJcoho1. solution with 40 per cent by volume of cold water. d A umvelent acid radical.
Cupric stearate
-
soap than was the analysis. The melting point of this soap was 5" C. lower than that of lead stearate prepared from pure stearic acid, whereas the lead content was the same. FIGURE2. C ~ ~ A N GINE SPHYSICAL AND DIELECTRIC PROPERTIES DURING COOLING OF A SYSTEM COMPOSED OF 0.15 PER CENT IMPURELEAD STEARATE IN LIQUIDPARAFFIN
The lead soaps prepared are described in Table 11, and the copper soaps in Table 111. Except for lead cerotate, the normal soaps formed in all cases, as the analyses show. In the case of lead stearate a deliberate attempt was made to form other soaps by using the following molecular proportions of lead acetate and stearic acid: 1:2, 1:1, 2:1, and 1:3. Each soap formed was found to have practically the same lead content, melting point, and crystalline appearance. Neither the melting points nor the analyses of the soaps were adequate criteria of their purity in some cases. Lawrence (4) pointed out that the melting points of soaps reported in the literature are too high. The apparent melting points of the copper soaps determined in capillary tubes or over mercury (3) were found to be so high as to be meaningless. The melting points of the lead soaps, many of which were crystalline, are believed to be of some value in indicating the purity of soaps and hence are included in Table 11. An insufficient amount of each soap was available to permit characterizing the soaps by Lawrence's TI and T2. The melting point of the lead stearate prepared from a U. S. P. grade of acid was more reliable in indicating impurity of the
Dielectric Tests In preparing the samples for test, the soap and liquid paraffin were heated and shaken together until the samples appeared homogeneous. The liquid paraffin used, the manner in which the samples were introduced into the cell in which the dielectric measurements were made, and the measuring equipment employed were described previously (10). Power factor measurements were made a t selected temperatures a t 60 cycles and 1,970volts per mm. (50 volts per mil). Dielectric constant values were computed from the data obtained in determining the power factor. Direct-current conductivity measurements were made a t 98.5 volts per mm. (2.5 volts per mil) immediately after the power factor values had been determined a t the same temperature.
Systems Containing Simple Lead Soaps Power factor, dielectric constant, and d. c. conductivity values for four systems, each containing 0.15 per cent of a lead soap of stearic, palmitic, myristic, or lauric acid, are shown in Figure 3. The temperatures a t which these systems appeared homogeneous are to the right or plane side of the half vane shown with each set of curves; the temperatures a t which the systems appeared to be heterogeneous are to the left or feathered side of the half vane. These transition temperatures indicated by the vanes were determined by cooling the systems, contained in glass tubes suspended in a
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FIGURE 4. DIELECTRIC PROPERTIES DURING COOLING OF LIQUID PARAFFIN SATURATED AT 120" C. WITH LEADSOAPS
2/4
2.9
FIGURE5. DIELECTRIC PROPERTIES DURING COOLING OF LIQUID PARAFFIN CONTAINING MISCELLANEOUS LEADSOAPS
2./4
243 aaaa
w
4
I
I
I
I
I 'k--42,/3
0 Sa W 70 80 SO / 0
FIGURE6. DIELECTRICPROPERTIESDURING COOLING OF LIQUID PARAFFIN CONTAINING
PERCENTLEAD HYDROXYSTEAR STEARATE
FIGURE3. DIELECTRIC PROPERTIES DURING COOLING: OF SYSTEMS COMPOSED OF
0.15
PER
CENTLEADSOAPSIN LIQUID PARAFFIN
liquid-paraffin bath, at the rate of from 0.5" to 1' C. per minute. The part of the systems contained between the electrodes of the power factor cell could not be observed while the measurements were being taken. At temperatures well above the visual transition point, the power factors of the systems were considerably below 0.005, except in the case of the laurate system whose power factors were much higher as shown. As the transition temperatures were approached, the power factors rose sharply to maxima
0.06
and then fell nearly as sharply, as the visual transition temperatures were reached. The temperatures a t which the power factors were a t maxima decreased with decreasing molecular weights of the soaps from stearate through laurate, as did also the temperatures a t which the systems became visually heterogeneous. Inasmuch as the power factor measurements were taken a t 5' C. intervals, it is probable that the maxima of some of the peaks were not measured. The absolute heights of the maxima are therefore not sufficiently significant to justify saying that one soap is more potent than the others in causing a high power factor. Attention is called to the similarity in the behavior of the systems rather than to their differences. The dielectric constant and the d. c. conductivity values both passed through maxima a t the same temperatures or
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near the temperatures a t which the respective power factors passed through maxima. A rough comparison between the d. c. conductivity values and the calculated a. c. conductivity values is indicated in many of the figures in this paper by the ratio between the distances a t which the d. c. conductivity values and the corresponding power factor values, respectively, are plotted above the axes of abscissas. The values of the conductivity maxima for the systems represented in Figure 3 were small in comparison with the values of the power factor maxima. The higher power factors and conductivities of the system containing lead laurate above the transition temperature as compared with those of the systems containing the three other lead soaps shown in Figure 3 made it seem desirable to investigate some lead soaps of the lower fatty acids. That the slightly different effect of the laurate was due to the nature of the soap rather than to an impurity was indicated by the fact that lead laurate prepared from acid freshly distilled a t low temperatures in a small molecular still and crystallized three times from its own mother liquor (melting point 43.2' C.) in the manner previously described (9), formed a system having dielectric properties almost identical with those represented in Figure 3. Lead caprate and lead pelargonate were accordingly prepared, and an attempt was made to put 0.15 per cent of each into solution in liquid paraffin. It was found, however, that upon heating the mixtures, the soaps melted and formed heavy droplets which would not dissolve completely even at 130" C. When the supernatant liquids were decanted from the undissolved soaps, the resulting systems remained clear until they had cooled to the temperatures indicated by half vanes in Figure 4. This figure also shows the dielectric behavior of these systems during cooling. Power factor and conductivity values are plotted on a larger scale than is used in Figure 3, and dielectric constant values on a smaller scale. Curves representing the power factor and conductivity values of the system containing lead caprate had small inflections just above the visual transition temperature; thus they resembled the curves describing the systems containing the lead soaps shown in Figure 3. There was no such inflection in the curves representing these values for the system containing lead pelargonate until a temperature considerably below the visual transition temperature had been reached. Lead undecylenate, a soap of an unsaturated acid, was also prepared and its solubility behavior found to be similar to those of the caprate and the pelargonate. The power factor and conductivity values were found to be very low a t all temperatures investigated on both sides of the visual transition point. The dielectric behavior of a group of miscellaneous lead soaps is shown in Figure 5. As Table I1 indicates, the lead cerotate contained only about one quarter of its theoretical percentage of lead. Inasmuch as the system composed of this material in liquid paraffin had no unusual dielectric properties over the range of temperatures studied on each side of the visual transition point, no effort was made to prepare a more nearly pure product by some other method. Lead abietate in as high a concentration as 0.5 per cent had only a small influence on the dielectric properties of liquid paraffin. The mixture became heterogeneous on cooling, but the temperature of the transition was not determined. When an attempt was made to determine this point about 4 months after the power factor measurements had been made, it was found that the lead abietate, which had been stored in a drawer, had turned slightly yellow and was no longer soluble in liquid paraffin. The instability of this soap to light was reported by Steele (12). The systems containing lead abietate were more unstable towards heat in nitrogen atmosphere than were any of the other systems studied. Applica-
3x1
tion of heat rapidly caused a yellow color to develop and the power factor and conductivity values to rise. The curves of the power factor and conductivity values for a system containing 0.15 per cent lead erucate are nearly flat between 100' and 40" C. Below the visual transition temperature both curves drop sharply. Lead 1,lO-hydroxystearate was prepared to exemplify a lead soap of a hydroxy acid. The dielectric properties of a system containing 0.06 per cent of this soap are shown in Figure 6. The general shapes of the several curves are similar to those for the systems containing lead stearate and related compounds eFcept that the regions of abnormally high values cover a wider temperature range and the maxima appear at temperatures just below the visual transition temperature. The wide temperature range at which the dielectric properties had abnormally high values may have been due to the presence of lead soaps of hydroxy acids isomeric with 1,lO-hydroxystearic acid. According to Steger et al. (IS) isomeric acids are formed when oleic acid is treated with sulfuric acid. The results were not considered sufficiently different from those obtained from systems containing the lead soaps of fatty acids, however, to warrant synthesizing pure 1,lO-hydroxystearic acid by the method of Tomecko and Adams (14).
Systems Containing Complex Lead Soaps
As stated previously, systems composed of liquid paraffin and about 0.5 per cent of the lead stearate prepared from the U. S. P. stearic acid formed stiff translucent gels when the clear hot sols were cooled. Systems prepared from lead soaps made from pure stearic acid, however, formed an opaque precipitate which, on standing, settled to the bottom of the containing vessel. The dielectric properties of the systems were also different, as is shown by a comparison of Figures 2 and 3. The region of abnormally high power factor and conductivity covers a broader temperature range in Figure 2 than in Figure 3. The temperature a t which the power factor reaches a maximum is lower in Figure 2 than in Figure 3 and lies nearer the temperature of visual transformation. The power factor above the transition temperature is higher in the case of the former. Interest in the differences in properties of the systems led to an examination of constituents such as might be expected to arise from impure stearic acid. The odor of the U. S. P. stearic acid led us to suspect that it might contain oleic acid or an oxidized oleic acid. After it was found that lead 1,lO-hydroxystearate, used to represent a lead soap of oxidized oleic acid, did not form a gel with liquid paraffin, lead erucate was selected for study. Lead oleate was not used because it is difficult to obtain oleic acid in a pure state. Lepd erucate, some of which was prepared from erucic acid specially purified (melting point, 33.5" C.) in the manner described for lauric acid, did not form a gel with liquid paraffin, a t least in concentrations up to 0.75 per cent. Certain mixtures of lead erucate and lead stearate in liquid paraffin did gel, however. Various proportions by weight of the two soaps were dissolved in liquid paraffin to form clear sols having a given total concentration by weight of lead soap. These clear sols were poured into vials and allowed to cool to room temperature. Figure 7 shows the appearance of these vials when they were tipped in horizontal position and an opaque rod was placed between the vials and the light source. When other factors were equal, the stiffest and most translucent gels were formed when 7 parts of lead erucate and 3 parts of lead stearate by weight were used. Gels freshly made from sols which were rapidly cooled were firmer and transmitted light better than older gels or those made by cooling the sols more slowly.
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the impure lead stearate, rather than sharp as it was in the case with pure lead st,earate and related soaps. As Figure 8 indicates, the power factors well above the transition temperature are rather high for both the mixed soap and the lead erucate. The latter soap, though not especially effective a t lower concentrations in causing high power factors in the systems containing it, became increasingly effective as the Concentration was increased. I n the lower part of Figure 8 are shown the power factors of systems containing 0.15 per cent of mixtures of lead erucate and lead stearate. Small proportions of lead erucate in the systems caused higher power factors than those of the systems in which lead stearate was the only soap. Increasing the proportion of the erucate and decreasing that of the stearate caused the position of the power factor maximum to shift to lower temperatures and its magnitude to decrease. The mixtures which contained lower proportions of the stearate appeared to be much more soluble than those containing higher proportions. It is believed that, as the tomperatures of the systems were reduced, the less soluble stearate was stabilized by the more soluble erncate. This is borne out by the fact that, even at concentrations at which no gel formation took place, the precipitate in systems containing some erucate with the stearate settled out of the oil much more slowly than did the precipitate in the systems in which the stearate was the only soap.
Systems Containing Simple Cupric Soaps FIGURE 8. CHANGE8 IN POWER FACTOR WITH TEMPERATUHE OF
Power factor, dielectric constant, and d. e. conductivity values for several systems containing cupric soaps in liquid Daraffin are shown in Fieure 9. As the preliminary experiments also showed, there was only a small effect on the power factor of Liquid paraffin caused by adding cupric stearate in concentrations much beyond those in which copper soaps are found in badly deteriorated insulation-say, 0.5 per cent. The effects of cupric laurate, cupric caprate, cupric caprylate, cupric undecylenate, and cupric erucate were also small. All of the systems containing these soaps became cloudy when cooled at the temperatures indicated except that containing cupric erucate, which remained clear for several hours at 25' C. before precipitation. I n none of these cases were unusual values of power factor, dielectric constant, or d. e. conductivity observed. When properly prepared, systems containing cupric abietate had dielectric properties similar to those of the other cupric soaps. Complete sets of data for solutions containing over 0.3 per cent are not available. The power factor values a t 100" C . for solutions containing 1.0 per cent of the soap were approximately 0.0025. This soap dissolved in liquid paraffin readily and remained in solution at all the temperatures employed. The effect of cupric 1,lO-hydroxystearate on the power factor and conductivity of liquid paraffin was considerably greater than that of any of the other cupric soaps shown in Figure 9. These values at 120" C., moreover, are greater than those a t
SYSTEMS C ~ N T A I N ~LEAD N I : SmaR A T E AND LEAD &lUCATE Tbe po,, or fac-
tors of several systems containing mixtures of lead erncate and lead stearate are shown in Figure 8. I n the upper part of the figure the power factors of a system containingamixture of 0.60 per cent FIGU~ZE 7. EFFECTOF VARY IN^^ TNE lead erucate and ItATlO OF LEADERUCATETO LEAD 0.15percentIead STEARATE ON GEL-FoRnlINoPaoPERTIE9 stearate are comDared with the power factors of systems containing these soaps separately in these respective concentrations. The power factor of the system containing the mixed soap is very high over a temperature range between that a t which the gel begins to form and that at which the gel sets rather firmly. This temperature range was broad, as i t was in the case of the gel formed from
-
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130' C. It is quite possible, however, that some decomposition took place, for the mixture stood in the cell about an hour between 130" and 120°C. before the 120" measurement was taken. The experiment was not repeated because the supply of both soap and acid was depleted and the results were not sufficiently unique to warrant further study.
Systems Containing Complex Cupric Soaps When the first batch of cupric abietate (the second copper soap investigated) was made, the technique of preparing the soaps had not been developed to the degree in which it was later used. I n concentrations of about 1.5 per cent the first batch of cupric abietate made formed a cloudy gel with liquid paraffin when cooled. The power factor of the system so formed was very high a t temperatures near the transition point from sol to gel. After dielectric measurements made on systems prepared from a second batch were found not t o agree with those made on the system prepared from the first, it was discovered that not all of the acetic acid formed by the inFIGURE9. DIELECTRIC PROPERTIES DURING teraction of cupric acetate COOLINGOF SYSTEMS COMPOSED OF CUPRIC and abietic acid was being reSOAPSAND LIQUIDPARAFFIN moved by the process of purification then used. VC'hen the acetic acid was removed by reprecipitating the soap froin the The dielectric proper solvents, cupric abietate which, with liquid paraffin, properties of the $b 26 formed systems having dielectric properties such as are shown svstems to which 0 0 in Figure 9 were prepared. The addition of a small amount the acid was added of acetic acid to such systems caused the power factor to are shown in Figincrease enormously. This accidental discovery led to one ure 10. Symbol of the most interesting phases of the present study. R is used in this At the time the work just described was in progress, the paper to indicate only lead soap which had been investigated was the impure the ratio, moles of FIGURE 10. EFFECT OF ACETICACID stearate which formed a gel on cooling with liquid paraffin. a d d e d acid per ox PROPERTIES OF A SYSTEM CONIt was thought that the high power factor of the system conmole of cupric TAIKINO 0.5 PERCENTCUPRIC ABmtaining cupric abietate as well as that containing lead stearate soap. Even the TATE IN LIQUID PARAFFIN Unlabeled numerals indicate the number Of was due to a gel-forming material. In the case of the system smallest additions moles of acetic acid added per mole of auprio containing cupric abietate, a question arose concerning the of acid caused an abietate constitution of the gel-forming material. If this material increase in t h e were cupric acetate, it was felt that the maximum effect on power factor a t the the dielectric properties would obtain when two moles of higher temperatures. When Rae. was increased to 0.2, a maxiacetic acid were added per mole of cupric abietate. If, on mum appeared at about 35" C. Further increases in Rae. to 0.4 the other hand, this material were cupric acetate abietate, caused the positions of the maxima to shift t o higher temperai t was felt that the maximum effect would obtain when one tures and the values to increase. The power factor values a t mole of acetic acid per mole of cupric abietate was added. 100" C. also increased greatly as is shown. Increasing ratio Anhydrous acetic acid, prepared as described previously Rae. beyond 0.4 caused the power factor values at all tempera(9, I I ) , was therefore added in various molecular quantities tures to drop until, when Rae. equaled 2.0, the power factor to systems consisting of 0.50 per cent cupric abietate in liquid values were nearly as low as those of the system where no acid paraffin. was added. Each set of measurements was made on freshly
0.4 approached those of the initial system. Curves showing t h e square of the refractive indices (n2, Figure 10) of the system where R,,, = 0.0 and that where R a c . = 0.4 are also shown with the dielectric c o n s t a n t values. The two curves are almost identical. Curves of the d. c. conductivity values are of the same general shapes as are the curves of the power factor values, although the d. c. c o n d u c t i v i t y values are in all cases smaller than the calculated a. c. conductivity values. The curves of the d. c. conductivity values, moreover, are not as upturned a t the 100" C. side of Figure 10 as are the curves of the power factor values. The results of the FIGURE 11. EFFECT OF CYCLOtests showed that the HEXANECARBOXYLIC ACID ON maximum effect on the DIELECTRIC PROPERTIES OF A dielectric properties ocSYSTEMCONTAININQ 1.0 PER CENT CUPRIC ABIETATE IN curred, not when Rae. LIQUIDPARAFFIN = 2 or Race = 1, but Unlabeled numerals indicate the when Rae. = 0.4. The number of moles of oyolohexanecarboxylic acid added per mole of results further showed cupric abietate that when Rso.was not greater than 0.4, no gel formed. The viscosity of the system was slightly increased at all temperatures, however, as Figure 10 shows. These viscosity values were determined on the same day with the same Ostwald tube viscometer. When Rae. was made greater than 0.4, a gelatinous suspended precipitate was found in the power factor cell after the dielectric measurements had been made. This material could not be redissolved by heating the system to 100" C. It was found, in fact, that the forma-
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tion of this precipitate was a function of the time and temperature of heating as well as of the concentration of acid. For example, after the viscosity at 100" C. had been measured, the clear sol, in which Rat. = 0.4, was allowed to cool gradually in the viscometer tube. The next morning a fine suspension was observed in the tube. It was found that the viscosity at 100" C. had dropped to a value about midway between the original value and the value of the system in which Rae. = 0.0. I n the systems just described, high power factors and conductivities were produced in an oil by adding it soap, which does not greatly affect these values, and an acid, which was shown (11) to have even less effect, to form a mixture which to all visual appearances is homogeneous. Attention is called to the similarity between such systems and those which obtain in the service degradation of an insulating oil. Under conditions in which soluble soaps form in oil, acids whose soaps are insoluble would probably form also. In the first stages a t least, the systems appear homogeneous. With this similarity in mind, it seemed advisable to determine whether effects similar to those described could be obtained when some other acid was substituted for acetic acid, and also when some other soap was substituted for cupric abietate. The first of these was carried out. In Figure 11 the effect is shown of different molecular proportions of cyclohexanecarboxylic acid on the power factor, dielectric constant, and d. c. conductivity of a system composed of 1.0 per cent cupric abietate in liquid paraffin. Between 100" and 80" C. the power factor values were as low as those of the systems to which no acid was added. Below 80" C. the power factor values rose sharply to maxima which were progressively higher for values of Roy.from 0.4 to 0.8. Below 65" to 67' C., the temperatures at which the maxima appeared, the power factor values dropped sharply at first but flattened out a t about 30°C. When the Roy. values were increased beyond 0.8, the position of the power factor maxima shifted slightly to regions of lower temperature and its magnitude dropped. When Roy.was made 2.0, the maximum disappeared entirely and the values obtained were about the same as those of a similar system containing no acid. Values of the dielectric constant rose sharply at temperatures below 80" C. in all cases where the power factor values also rose. Curves of the d. c. conductivity values resemble closely those of the power factor values except that, whereas 77ME IN W .
FIGURE 12. EFFECT OF CYCLOHEXANECARBOXYLIC ACID ON THE VISCOSITYOF A SYSTEM CONTAINING1.0 PER CENT CCPRIC IN LIQUID c,
lu
IO
PARAFFIN
AND CHANGE OF VISCOSITY WITH TIME IN A RESULTING PRODUCT AT 50" C.
$W
*a
ABIETATE
30 40 50 60 70 8 0 0 0 TEMP,DE6REES C
Unlabeled numerals indioate the number of moles of cyclohexanecarboxylic aoid added per mole of cupria abietate
the power factor curves flatten out a t fairly high values a t the lower temperatures, the d. c. conductivity curves approach the axis of abscissas more closely before flattening. The viscosities of the systems containing various concentrations of cyclohexanecarboxylic acid are shown in Figure 12. The curve for the system in which Rcy. = 0.4 follows that of the system in which Roy. = 0.0 from 80" to 70" C. and then rises abruptly. Figure 11 shows that the power
MARCH, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
factor maximum for this system occurred a t 67" C. At room temperature this system was a clear gel. The curve for the system in which Ray. = 0.8 follows the curve for the system in which Roy. = 0.0 to 67"C., and then the former curve rises abruptly. The power factor maximum for this system, found a t 65" C., was again just below the temperature a t which the gel began to form. The curve for the system in which R a y . = 2.0 appeared to parallel a t slightly lower viscosity the curve for the system in which Rcy, = 0.0. The former system contained very fine particles of suspended matter
.
TIME IN HOURS
FIGURE 13. STABILITY AT 65' C. OF THE DIELECTRIC PROPERTIES OF A SYSTEM COMPOSED OF LIQUIDPARAFFIN, CUPRIC ABIETATE (1.0 PER CENT),AXD CYCLOHEXANEC CARBOXYLIC ACID Roy.
= 0.8
315
abietic acid @ab. = 0.4) was added to the system with the highest copper content. The power factor maximum of the resulting mixture had a value which was only a fraction of that of the original mixture, and the position of the maximum had shifted far to the left, as Figure 14 shows. The gelforming property of the system had also been destroyed. From the results of this experiment it appeared that the reaction between cupric abietate and cyclohexanecarboxylic acid must produce, in addition to a soap which forms a gel with liquid paraffin and causes a high power factor, abietic acid which destroys the gel and lowers the power factor. It was felt that if the abietic acid formed could be removed, the resulting system should have a higher power factor than i t did before the removal. In an attempt to remove the abietic acid, a system composed of cupric abietate, liquid paraffin, and cyclohexanecarboxylic acid ( R a y . = 0.6) was placed within a cellophane membrane of large pore size, and the membrane suspended in liquid paraffin. The gel remained within the membrane, and part of the abietic acid and excess cupric abietate dialyzed away. Because the membrane soon became partially blocked, however, the experiment was abandoned. I n order to try to avoid either the formation or use of any acid, two attempts were made to prepare the gel-forming soap by reacting together cupric abietate and cupric cyclohexanecarboxylate. In one of these, 0.500 gram of the former and 0.048 gram of the latter with 55 grams of degassed liquid paraffin were sealed in an evacuated glass tube and shaken 63 hours a t room temperature. The gelatinous contents were heated to 100°C. and centrifuged in the sealed tube, whereupon the unchanged cupric cyclohexanecarboxyl-
.
The stability of the systems just discussed was investigated by both viscosity and dielectric measurements. The change with time a t 50" C. in the viscosity of the system in which Ray. = 0.8 is shown in Figure 12. The viscosity decreased soinewhat with time, but the rate of change diminished with time. The change in dielectric properties with time was determined a t 65" C. The initial dielectric properties were determined as quickly as possible after the temperature of the bath surrounding the power factor cell had been reduced to the desired temperature. Subsequent determinations were made a t intervals. As Figure 13 shows, the values of the dielectric properties rapidly rose to practically constant values and then diminished slowly. The dielectric tests and the viscosity tests both showed that the gels being studied were reasonably stable. Similar tests showed that by raising and lowering the temperature, the physical and electrical properties of the systems could be duplicated reasonably well; that is, the gels were reversible. The effect of abietic acid on the power factor of a system consisting of cupric abietate, liquid paraffin, and cyclohexanecarboxylic acid was indicated when copper-deficient cupric abietate was used in the series of experiments in which various concentrations of cyclohexanecarboxylic acid were added to cupric abietate in liquid paraffin. At the time some of these experiments were performed it was not realized that an excess of cupric acetate was necessary in the method for preparing cupric abietate. The effect of adding cyclohexanecarboxylic acid (ROY.= 0.6) to systems containing 1.0 per cent cupric abietate of various compositions is shown in Figure 14. The nearer the composition of the cupric abietate approached the theoretical percentage of copper, the higher was the power factor maximum and the higher was the temperature a t which it occurred. In the soaps of lower copper content a trace of abietic acid was found. For this reason
FIGURE 14. EFFECT OF ABIETIC ACID ON THE POWERFACTOR OF A MIXTURE OF LIQUID PARAFFIN,CUPRIC ABIETATE (1.0 PER CENT), AND CYCLOHEXANECARBOXYLIC ACID Roy.
-
0.6
ate fell t o the bottom, leaving a clear sol above it. When cooled, this sol formed a soft gel which was decanted into the power factor cell. The residue was washed with hexane, dried, and weighed. About half of the cupric cyclohexanecarboxylate had dissolved to give a system in which the molecular ratio of cupric cyclohexanecarboxylate to cupric abietate was 0.1. The dielectric properties and the composition of the system are shown in Figure 15. The addition of cupric cyclohexanecarboxylate to cupric abietate in liquid paraffin caused power factor and conductivity maxima similar to those caused by adding cyclohexanecarboxylic acid to similar systems. In the experiment just described, no effort was made to remove the excess cupric abietate or to isolate the gel-
INDUSTRIAL AND ENGINEERING CHEMISTRY
316
forming soap in order that its composition could be investigated. I n an effort to do this, the experiment outlined in Figure 16 was conducted. The copper content of one of the soap fractions isolated was above the theoretical copper content (12.9 per cent) of cupric abietate-cyclohexanecarboxylate, and the content of the other was lower. As Figure 16 shows, the soap of higher copper content was lost. The
FIUURE15. DIELECTRIC PROPERTIES OF A SYSTEMCONSISTING OF CUPRIC ABIETATE (0.90 PER CENT), CUPRIC CYCLOHEXANECARBOXYLATE (0.044 PER CENT),AND LIQUIDPARAFFIN power factors of three systems containing the soap of lower copper content are given in Figure 17. The positions of the power factor maxima as well as their heights are shown to depend upon the concentration of the soap. The system containing 1.2 per cent of the soap set to a clear gel on cooling. The change in viscosity with temperature of the system containing 0.52 per cent of the soap is included in Figure 17. The temperature a t which the power factor was a maximum was just a few degrees below the temperature a t which the break in the viscosity curve occurred, as was the case for the systems discussed in connection with Figures 11 and 12.
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Inasmuch as the power factor values were high at temperatures above those at which gel formation began, it seems possible that even when the values were at a maximum they were related to the state of dispersion of the part of the soap that had not started to gel more than to that part which had. On the other hand, the same physical condition which causes gel formation may be the phenomenon which causes the high power factor values, but this effect of the phenomenon may be counteracted by its effect in increasing the viscosity of the system. Whatever the state of dispersion that was chiefly responsible for the high power factor values, the experiments seem to indicate that the material dispersed was a loose combination of an insoluble and a soluble soap to form a combination which, though not soluble in liquid paraffin, could be dispersed in it to form a stable system. The similarity in dielectric behavior of the systems containing cupric abietate and cupric cyclohexanecarboxylate as compared with those containing cupric abietate and acids indicates that the high power factors and conductivities of the latter were due to the physical state of the soaps formed rather than to increased electrolytic dissociation caused by the added acids. Efforts made to find copper soaps which, when substituted for cupric abietate, form systems with interesting dielectric and physical properties such as have been described have not yet been successful. The pairs of soaps and acids which have been tried in liquid paraffin are as follows: cupric laurate and acetic acid, R,. = 2.0 and 0.4; cupric laurate and cyclohexanecarboxylic acid, Roy. = 2.0; cupric caprate and capric acid, Rae. = 2.0; cupric erucate and cyclohexanecarboxylic acid, Roy.= 0.8. I n each case the addition of the acid lowered slightly the power factors of the system to which it was added. One marked difference was apparent between the mixtures containing cupric abietate and those containing the other soaps. The fo
