INDUSTRIAL AND ENGINEERING CHEMISTRY
H.5 1944 100
zao
90
eo
70
I
I
0 UPPCR
eo
PERCENT LIMIT
so
ao
zo
IO
I
I
I
I
NOlNlCOTINE
0
4Tl
The melting point is taken without recrystallization, which would tend t o eliminate the minor alkaloid. The presence of picric acid accounts for the spread in the melting points of pure nicotine picrate and pure nornicotine picrate (Table I). Although the picrate melting point is not intended t o be a quantitative procedure, the close agreement between the percentage composition and the melting point of the steamvolatile alkaloid picrate obtained from tobaceo with the values obtained from the known solutions is striking. LITERATURE CITED
(1) Bowen, C. V., and Barthel. W. F., IND. ENG. CHEM.,ANAL.ED.,15, 596 (1943). (2) Ibid., 15,740 (1943). (3) Markwood, L.N., J. Assoc. O f l c h l Aor. Chem., 26,283-9 (1943). (4) Markwood, L. N.,and Barthel, W. F., Ibid., 26, 280-3 (1943).
Figure 2. Area of Melting Point Spread Accordin to the Markwood and Barthel Classification iri Relation to Data for known Mixtures in Figure 1
OXIDATION OF LUBRICATING OILS Effect of Natural Sulfur Compounds and of Peroxides N ACTUAL service the oxiG. H. DENISON, JR. present, suah as sulfur comdation of a lubricating oil Standard oilCompany of sm F ~ ~ pounds.~ The most ~ obvious~poinof attack in studying compositakes place in highly complicsted systems. For example, in tion, a t least for oxidation ret an internal combustion engine, catalysis by metal surfaces and search, consists in determining whether the hydrocarbons or the metal soaps as well as complex variations in temperature and oilnonhydrocarbons control the oxidation characteristics. air agitation throughout the oil stream markedly affect stability. HYDROCARBON FRACTlON T o investigate the mechanism of oxidation in such a complicated There are two general methods by which the composition of a system without adequate knowledge of the oxidation in simple mixture such as lubricating oil can be determined or, more litersystems does not appear sound. The aim of the present paper is ally, approximated. These methods might be termed “analytic” to aid in establishing a basic mechanism of oil oxidation under as and “synthetic”. I n the analytic method the mixture is sepasimple conditions as feasible; when adequate knowledge has rated by physical and chemical processes into its components, been obtained, effect of service variables and catalysts may be which are analyzed and compared with known substances. I n dealt with as perturbations on the reactions taking place in simple the case of lubricating oils this process is exceedingly difficult besystems. cause of the complexity of the mixture. The synthetic method Before lubricating oil oxidation can be discussed, a picture of employs the procedure of preparing compounds similar t o those oil constitution must be established. A finished lubricating oil consists of a multitude of d z e r e n t hydrocarbons, which make up expected t o be present in the mixture and comparing the properties of the synthesized substances and their blends with those of from 80 t o 98% of the stock. I n addition, there are 2 to 2070 the l+ricating oil. This method is simpler than the analytical sulfur compounds, 0.08 t o 0.3% nitrogen compounds and some method, but definite proof of composition is never established. oxygen compounds. These materials may so perturb the oxidaBoth of these methods have been applied by Mikeska (7)and by tion of one another as t o mask completely any similarity of the oxidation mechanism t o those of the pure, low-molecular-weight many others. I n applying the analytic method t o the present problem, the compounds in the literature. technique adopted a t the National Bureau of Standards was The resistance of oil t o deterioration varies with the source of followed and the finished lubricating oil separated into narrow the crude and the treatment it receives. Simultaneously, with fractions by solvent extraction in a Fenske column, as described this variation in stability, the oil varies both in its major fraction, hydrocarbons, and in the small percentage of nonhydrocarbons by Mair and Schicktanz (6).
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
The hydrocarbon fraction of refined lubricating oils is shown to consist of naphthenes in admixture with homologs of benzene and naphthalene. By removing natural sulfur compounds without appreciably affecting other constituents, this hydrocarbon fraction is shown to possess negligible resistance to oxidation. Thus, the few per cent of natural sulfur compounds present in a finished lubricating oil appear to determine the oxidation characteristics. This control of stability is interpreted as resulting from the fact that the hydrocarbon fraction oxidizes at a rate controlled by the concentration of organic peroxides, and the latter are reduced by reaction with the natural sulfurcontaining inhibitors residual in the refined lubricating stock. In addition to controlling the rate of oxidation of an oil, the organic peroxides determine the rate o f corrosion of bearing metals. Such corrosion is shown to result from the ability of peroxides to convert metal into metal oxide, the latter subsequently dissolving by reaction with acidic constituents developed during oxidation.
Vol. 36, No. 5
the aromatic rings themselves. A value for this contribution may be estimated by assuming linear additivity of the effects due to aromatic rings and nonaromatic residues as indicated by the formula: aY 98.4b = S (1)
+
where
a = fraction of aromatic rings 6 = fraction of nonaromatics Y = sp. dispersion contribution of aromatic rings 98.4 = sp. dispersion contribution of nonaromatics S = measured sp. dispersion of sample
The results of such a treatment appear in Figure 1, as well as similar analyses of a Pennsylvania oil (B) and a Gulf Coastal oil (C). The values shown as horizontal lines for naphthalenes and benzenes were obtained by taking the average of several results caalculated according to the above formula from data on known pure homologs. The solid lines represent the original data for the extract fractions, as calculated on a basis of the Vlugter, Waterman, and van Westen ring analysis. The broken lines correspond to values roughly correrted to fit the Deanesly and Carleton ( I ) ring analysis. That tho aromatics present in finished
Eavh fractio1i was analyzed as follows: The ring analysis devised by Vlugter, Waterman, and van Weaten (8) was employed to estimate the percentage of different types of hydrocarbon groups (paraffinic, naphthenic, and aromatic) present in the base oils and in the fractions produced by the solvent treatment. Since many types of aromatic nuclei are possible in a lubricating oil, and inasmuch as the type of aromatic nucleus will affect stability, a classification of aromatic fractions was desirable. For this purpose a chart published by Mair, Willingham, and Streiff (6) was used. They (*orrelatedthe number of carbon atoms per PPO molecule with the specific dispersion of a large number of hydrocarbons, and were able thereby to classify unknown aromatic I 2 3 4 5 6 7 0 0 1 0 1 1 I2 I 3 1 4 1 : bodies. The result of such a n analysis on a n S. A. E. 30 oil (A, EXTRACT -NUMBER Table I), prepared by moderate refinement of a California naphthenic crude, is shown in Table 11. Since the quantity of each Figure 1. Characterization of Aromatic Fractions fraction decreased as the extraction progressed, it was necessary from Lubricating Oils after removal of the first six to combine the succeeding fractions into pairs; thus fraction 7 was in reality fraction 7 plus fraction 8. lubricating oils of various origins are fundamentally benzene and As was to be expected, the successive fractions decreased in spenaphthalene homologs appears evident. Therefore to evaluate cific dispersion and per cent aromatic rings. the stability of the hydrocarbon fraction of a lubricating oil, a To use directly the specific dispersion chart of Mair, Willingstudy of the stability of blends of naphthalene, benzene, and ham, and Streiff, the number of carbon atoms per molecule for each fraction was approximated by dividing the molecular weight riar .thene hydrocarbons should suffice. The oxidation characteristics of such lubricating-oil-like hydroby 13.5. Plotting these specific dispersion values for the excarbons has already been reported by Larsen, Thorpe, and Armtracts did not furnish much information on composition. The field (4), and present work along this line is in complete accord. points on such a plot started close to the alkyl naphthalene line It suffices to say that alkyl naphthenes, including petroleum and followed down to that of almost pure naphthenes. Such bewhite oil, oxidize autocatalytically and are extremely unstable as havior results from the fact that, as a result of variation in mocompared to straight lubrirating oils. Alkyl benzenes and alkyl lecular weight and in the nature of the paraffin side chains, the various extracts are necessarily blends of aromatics and nonaromatics TABLE I. INSPECTIONS OF OILS STUDIED rather than pure alkyl aromatics. Oil Flash Viscrjsity, Saybolt Pour Conradson Considerably inDesig- Gravity, Point, Univ. Set. Viscosity ZOint, A.S.T.M. Neutralization Carbon, BIllfU, nation A.P.I. a F. 100' F. 210° F. Index F. Color No. % % formation on the nature 0.08 0.63 3 0.04 20 56.5 8 A 21.3 385 627 0.15 0.03 3 0.07 100 5 45.5 30.3 425 183 B of the extract fractions is 0.20 0.03 2 0.02 1: 57.5 34 21.9 410 585 C 0.22 0.02 0.03 obtained if the per cent 90 1]/a 424 68.1 480 29.4 D 0.48 0.04 0.10 20 6 102 66.4 2 8 . 2 445 530 E aromatic rings and specific 0.00 0.03 25 Water-white 0 . 0 1 61 5 1 . 0 27.0 395 343 F 0.01 0.02 0.12 1- 15 25 51.3 52 405 363 26.8 G dispersion are used to 0.14 0.10 0.18 21/r 54.2 93 29.2 435 342 H 0.06 0.82 0.02 calculate the specific dis10 350.9 0 20.2 380 455 K persion contrihution of
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I N D-US T R I A L A N D E N G I N E E R IN 0 C H E M I S T R Y
May, 1944 em
I
0.1yosulfur as a nonaromatic organic compound gives, in general, an apparent rise of 1% in aromatic rings. Thus any apparent decrease in aromaticity can, within the experimental error of the ring analysis, be attributed t o the removal of sulfur compounds. A s Figure 2 shows, these desulfured oils exhibited instability of a degree similar to the white oils. Some question might be raised as t o whether in this experiment the difference between the original and treated stock was solely due t o sulfur compounds. However, since phenolics were eliminated by the results of the sodium distillation and since t h e Waterman analyses and specific dispersions afforded fair proof of an unvaried hydrocarbon content, natural sulfur compounds seem t o be the agents responsible for the stability of straight mineral lubricating oils. This fact would seem t o be the major key t o a simplification of the research on lubricating oil oxidation. The problem of oxidation mechanisms can then be best approached by first carefully studying the oxidation mechanism of a n idealized sulfur-free oil and then the perturbing effect of sulfur compounds on these reactions.
DUULCURLD CALIFORNIA PARAVINIC 400NEUTW
DCIULNRED CALIFORNIA NAPHTHCNIC
IAI. SO
C A L I W U NAPWTHCNIC S A L . 30
I
8
HOURS AT 340.F.
Figure 2.
479
Ef€ect of Desulfurization upon Stability of Lubricating Oils
TABLE11. HYDROCARBON ANALYSISOF CALIFORNIA NAPHTHENIC-TYPE LUBRICATINQ OIL BY SOLVENTEXTRACTION IN diphenyls are also extremely unstable. Alkyl naphthalenes, on FENSKE COLUMN the other hand, can be extremely stable and even more resistant NaDh- Paraffin to oxygen absorption than the best lubricating oils. Aromatio thine Side Yield, Sp.DisC A t o m Rings, Rings, Chains, I n spite of this extreme stability of alkyl naphthalenes, if an atFractions % persion per Mol. % % % tempt is made to blend them with naphthenes in such proportions 18 1 3.8 189 20.1 64 18 3.3 21.4 2 15 30 174 55 as t o obtain a n aromatic content comparable t o t h a t of lubricating 2.3 22.0 47 3 18 166 35 oils, blends are obtained with stabilities relatively little better than 2.0 166 22.6 45 20 4 35 1.5 159 22.6 41 23 36 5 that of medicinal white oil. Therefore, in spite of the tempta2.2 23.1 38 39 6 156 23 3.5 162 23.9 39 23 7 38 tion t o give undue credit to the alkyl naphthalenes, the hydrocar3.1 39 143 24.0 24 8 37 bon fraction of a lubricating oil cannot have much t o do with its 3.1 145 24.5 9 31 41 28 2 . 5 24.5 30 28 42 138 10 resistance t o oxidation. Larsen et al. came to the same conclu2.4 43 130 26.1 30 11 27 2.3 25.0 12 23 42 133 35 sion. 2.2 129 23.8 39 19 43 13 Since the hydrocarbon fraction of a lubricating oil does not con43 2.0 124 25.1 37 14 20 1.6 114 27.6 41 12 47 15 trol its stability, a n investigation of the next most abundant frac101 28.7 44 Raffinate 62.1 0.7 55 Original oil .. 120 27.0 33 16 52 tion was undertaken some years ago. An attempt was made t o desulfur lubricating oils completely without appreciably changing the hydrocarbon fraction. At first a simple vacuum distillation from sodium metel was tried. The distillate, however, contained about 90% of its original sulfur and was still EXPCRIMLNTU 0. ABSORPTION stable; in fact, many oils so treated increased 0. ABSORPTION CALCULATED FROM in stability. One conclusion t o be drawn from 5.2IJOtodt this experiment is t h a t natural acidic. or phenolic bodies which would be removed by ..,OXYGEN ABSORPTION such a treatment play no appreciable part in stabilizing the lubricating oil. Desulfurization was finally accomplished by contacting the oil for several hours with sodium metal a t 500" F. under 200 pounds per square inch hydrogen pressure. After washing and mild clay treatment the oil contained 0.07% sulfur in one run and 0.0370in a check run, a marked reduction from the original 0.53Q/, sulfur. As indicated by bromine number, no olefinization occurred. Since such a treatment might otherwise affect the hydrocarbons, the specific dispersion was measured and a Waterman analysis was made. The results of these andyses after treatment of this moderately refined naphthenic stock (oil A) and of three other lubricating oils from various sources are shown in Table 111. Actually, the drop in per cent aromatic rings as indicated by this analysis is known to be excessive since experiments with synthetic sulfur Figure 3. Dependence of Oxygen Absorption on Peroxide Concentration compounds have shown t h a t the addition of (Oil F)
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Vol. 36, No. S
INDUSTRIAL AND ENGINEERING CHEMISTRY
480
oxidized white oil and 12% finished lubricating oil were % Aromatic % Naphthene 0 Paraffin Epeci5c heated at 250’ F. under nitro% Sulfur Rings Rings &le Chains Diapermion gen. The reduction of perOil Invaatigated Orig. Final Orig. Final Orig. Final Orig. Final Orig. Final oxides by reaction with com52 53 Moderately refined Calif. naph0.53 0.07 15 14 33 33 I2O 12’ ponents of the lubricating oil thenio, S.A.E. 30 (A) 0.22 0.06 1 1 Calif ara5nic 400 neutral (D) 32 27 27 35 58 72 72 58 11, 106 iib is obvious. The results of Gulf ’ d a s t a l lub., S.A.E. 30 (C) 0.20 0.04 10 7 Penn. lub. S.A.E. 30 (E) 0.10 0.01 7 4 16 20 77 76 111 110 such a test with various concentrations of the lubricatinc oil are shown in Figure 5. Here loge (P,/P) rather than DEPENDENCE OF OXIDATION RATE P is plotted, where Po represents the initial peroxide concenO S PEROXIDE CONCENTRATION tration and P the concentration a t time 1. For each set of data No attempt will be made to consider more than the initial steps loge (P,/P) is a straight-line function of time. Moreover, theslope of each line divided by the concentration of added lubricating of the oxidation reaction since this suffices to depict the role of oil is fairly constant throughout; its average value of 0.064 indithe sulfur compounds. If the oxidation of a highly refined oil is cates the relation: continued beyond the initial stage and into the region where the oxidation rate degrildtks to a slower linear reaction, results are d3 (perox.) -0.064 (perox.) (% lub. oil) (4) obtained as shown in Figure 3 for oil F. The absorption of oxydt gen, as measured in the Dornte ( 2 ) type apparatus, proceeds a t Thus the rate of decomposition is directly proportional to peroxide an ever increasing rate up to a point of infiection, then slows concentration and to the concentration of the natural inhibitor. down, and eventually approaches a relatively constant rate. SiTherefore in the oxidation of a typical lubricating oil, peroxides multaneously the peroxide concentration as measured by Wheelappear to be formed in the same manner as they are in a white er’s method (9)rises to a maximum which is reached as the oxyoil; but because of a rapid reaction with certain natural sulfur gen absorption curve passes the inflection point. The peroxides compounds, peroxide concentrations can build u p only to that then rapidly decrease, eventually tending toward a steady state. point a t which the rate of formation and reduction become equal. Such behavior suggests that the rate of oxygen absorption is This mechanism, then, in addition to the peroxide reduction by possibly proportional to the peroxide concentration. To test highly oxidized products formed in the oxidation, maintains this possibility-namely, that peroxide a t a n approximately steady value; its concentration depends upon the rapidity with which the oil forms peroxide and d(Os) = k (peroxide) dt the efficiency of its inhibitors in reducing peroxide. I n one sense the peroxide concentration, while the natural inhibitors are still it is mechanically simpler to prove the integrated relation, present, is determined by a sort of pseudo equilibrium between (02)= -k f (peroxide) dt (3) these two rates. I n certain oils this concentration is immeaaurably low. Since the over-all oxidation rate is dependent upon since a planimeter may then be applied to integrating under the measured peroxide curve. Integrating and evaluating k from one of the known oxygen absorption values, the curve drawn through the oxygen absorption points of Figure 3 was obtained; t h e validity of Equation 2 is thus established. Moreover, it i s known that peroxides catalyze the oxidation of these oils. These two facts indicate that the rate of oxidation is here determined by the concentration of peroxide, the latter apparently being a fundamental part of the chain reaction which constitutes the oxidation. Therefore the addition of any agent which will reduce peroxide concentration under the conditions of oxidation will reduce over-all oxidation. This action is true of those compounds commonly called “inhibitors”. An exception might be made for HOURS AT 250.F. those agents which, by virtue of an ability to poison catalysts external to the system (such as metals or metal soaps), have unFigure 4. Decomposition of W h i t e Oil Peroxide b y Added Lubricating Oil fortunately come to be called “inhibitors”.
TABLE 111. EFFECTOF SODIUM TREATMENT ON COMPOSITION
-
-
RELATION OF WHITE OIL TO LUBRICATING OIL
Since the 6rst step in the oxidation reaction is controlled by peroxide, those oils (for example, medicinal white oil) which, because of a lack of natural inhibitors, can develop high peroxide concentrations will also develop high oxidation rates. Those lubricating oils which are rich in natural antioxidants-that is, agents capable of rapidly reducing peroxide-will not build up high peroxide concentrations and consequent high oxidation rates. The latter is true only when the natural antioxidants involved are of that ideal type which have no great tendency to absorb oxygen directly. Since the natural sulfur compounds have been shown to be the principal antioxidants in a finished lubricating oil, the reaction between these bodies and peroxide was investigated by observing the rate of peroxide decay when blends of a finished lubricating oil with a sulfur content of 0.5370 (oil A) and B peroxide-rich preoxidized white oil are heated in the absence of air. Figure 4 shows the result when a mixture of SSyo
$1 4e01
a.
P
INITIAL PEROXIDE COHC. WNC. AT t
= KROXIDL
nns.
HOURS AT 250.F.
Figure 5. Effect of Concentration of Added Lubricating Oil on Rate of Decomposition of Peroxides in W h i t e Oil
May, 1944
481
INDUSTRIAL AND ENGINEERING CHEMISTRY
ciently low so t h a t whatever oxidation does occur will not give rise t o too many deleterious agents. CORROSION M4D PEROXIDES
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130
Further investigation of the properties of peroxides brings to light the interesting fact that, in addition t o controlling the rate of oxidation of refined lubricating oils, they are also t h e agents responsible for bearing-metal corrosion. No reference has been made in the literature connecting peroxides with the corrosion of bearing metals. Many articles have been written on bearing corrosion, and the statement is generally made t h a t acidic products of oxidation give rise t o corrosion; yet in all of this work, attempts t o correlate corrosivity with either total acidity or acid strength admittedly failed. Since peroxides were generally known t o exist in oxidized oil, it is surprising t h a t their connection with corrosion has not been treated, especially since Engler and Kneis ($) stated in 1887 t h a t certain metals, particularly lead, in contact with oxidizing turpentine are readily oxidized by peroxides and subsequently by reaction with the acids generated, the lead oxide is converted t o a soluble soap. The application of this reaction in present-day bearing corrosion is readily established. Returning t o the ideal case of white oil, the following experiment was performed: A sample of oil F oxidized to high acid and peroxide values was freed of peroxide by heating to 250’ F. for 2 hours in the presence of 1% moderately refined oil. This sample was called “acid oil”. “Peroxide oil”, low in acid and high in peroxides, was prepared by washing the oxidized white oil several times with cold aqueous caustic. Table IV shows the action a t 275’ and 300’ F. of these samples on cadmium-silver bearing metal in the absence of oxygen. These data show t h a t the acid oil has a negligible effect upon cadmium-silver, whereas peroxide oil causes appreciable cormsion. The variation between a maximum corrosion of 1.6 mg. at 275O F. and 0.0 mg. a t 300’ in the case of acid oil is probably indicative of experimental error. It might be remarked t h a t lead is not corroded a t 340’ F. by naphthenic acids which are free from oxygen and peroxide.
TABLEIV. RELATIVECORROSIVITY OF ACIDS AND PEROXID 4
a
U
IO
HOURS AT 275” F. Figure 6. Relation of Peroxide to Corrosion of CadmiumSilver and Copper-Lead Bearing Metals
b
peroxide concentration, this results in a low rate of over-all oxidation. I n other lubricating oils, the peroxide concentration may be as high as 10 cc. oxygen per 100 grams oil or even higher, with a consequently higher over-all rate of oxidation. It must be borne in mind that the above remarks apply only t o oils which have been given a normal amount of refining. I n crude distillates, for example, t h e concentration of peroxide reducing cornpounds is exceedingly high. I n fact, no appreciable peroxides are evident, yet the over-all oxidation rate is exceedingly high. This type of reaction apparently does not involve a chain mechanism but consists chiefly in the direct absorption of oxygen by exceedingly reactive molecules. The natural sulfur compounds in a refined oil, in the course of their reduction of peroxides, are themselves oxidized t o deleterious compounds. For example, peroxide reduction experiments carried out in the presence of lubricating oil show a far greater development of resinous compounds than t h a t in the direct thermal decomposition of petroleum peroxides. What other deleterious agents result from the peroxide oxidation of sulfur bodies can be left t o the imagination. However, the refiner is forced t o choose the lesser of two evils; he must maintain sufficient natural sulfur compounds t o prevent the development of appreciable peroxides and consequent high oxidation rate, yet keep them suffi-
Oil Peroxide oil
Time Min.’
276
0 85 230
12.0
85
i :o
Acid oil
276
Peroxide oil
300
Acid oil
300
Oxidized Oil 0
b
Total LOSS of Metal, Peroxide Mg. Contenta
Tq-g.,
300
0
230 0
106 165 0
i:0
i.6 13:o 13.0
105 0:0 165 0.0 0 105 20:o 165 20.0 ex 100 grams oil.
42 1 54 0 0 0
0
413 0 0 0
0
0 443
a
0
weutraiization N0.b
1 .o 2: i 4.4
..
3.5
0.80 1.61 1.62 3.7 2.8 3.0 2.8
.. ..
Expressed as cc 01 Expressed a8 me. K8H per gram oil.
Another series of tests consists of determining simultaneously the loss jn weight of the bearing metal strips, the acidity, and the peroxide number a8 a function of time, again using oil F. A single strip of bearing metal having an alloy area of 4.8 sq. cm. in the case of cadmium-silver and 11.6 sq. cm. in the caae of copperlead was suspended by a glass hook in 200 cc. of the test oil. Oxygen was fed in through a fritted glass plate, sealed close to the base of the cell. The rate of oxygen flow waa such as t o maintain a t least two thirds of the bulk volume as foam. Under these conditions, this rate guarantees saturation of the oil with oxygen. Figure 6 shows the results of such tests. The curve for rate of corrosion, plotted as grams per hour, is parallel to the curve for peroxide number and independent of the curve for acidity; this
INDUSTRIAL A N D ENGINEERING CHEMISTRY
482
Vol. 36, No. 5
Although the parallelism between the peroxide curve and the rate of corrosion curve is not absolute, i t is sufficient to show that, at least within the accuracy of the tests, corrosion rate is proportional to peroxide concentration and independent of acidity, provided some acid is present. It must be borne in mind that these corrosion data are the result of single runs; hence more weight must be placed upon the general agreement and trend than upon the characteristics exhibited by any single curve. Also, the peak on the peroxide curves may be drawn through the experimental points in such a way as to emphasize better agreement than is shown, but the difference between these curves and the worst possible curve through the points is not enough to change the general conclusion. The curves for oils H and K pos0 *-w sibly explain the case frequently encountered where two oils develop similar acidity, yet give rise to markedly different degrees of corrosion. However, Figure 7 shows that peroxide concentration and the absolute rate of corrosion are not definitely and universally interrelated between widely different oils. For example, as the curve for oil G indicates, considerably 0 IW zoo 54) 400 greater peroxide content causes the same,magHOURS nitude of corrosion as oil H, which exhibits Figure 7. Dependence of Corrosion on Peroxide much lower Peroxide. It is not surprising t o _. find peroxides varying in activity in different oils. Common peroxides are known t o supports the argument that peroxides control corrosion. I n fact, vary considerably in activity. No absolute dependence of corrosion rates on peroxide values for different oils is necessary, the data indicate approximately that however, so long as these two are approximately proportional in $(loss) = --K (peroxide) each separate oil. As long as the second is true, there can be (5) little doubt that peroxides are an appreciable causative factor The parallellism between curves for acidity and for total corrosion in bearing corrosion. This correlation between peroxide concentration and corrolead to the belief that the rate of acid formation is likewise controlled by peroxide concentration. sion is not surprising when we remember that by far the greatest class of corrosion inhibitors are agents which will reduce organic A striking example of the over-all mechanism of corrosion is peroxides-for example, organic phosphites, arylamines, and afforded by a test similar to that just described, where at intervals phenolics. It has been fairly well established that the only corroa pure lead strip was removed for observation. It was found sion inhibitors which are not peroxide-reducing agents owe their that, once appreciable peroxides had formed in the oil but prior effectiveness to the formation of protective coatings on the metals. t o the development of appreciable acidity, the strip was heavily covered with salmon-colored lead oxide. Then as oxidation UTERATURE CITED progressed and appreciable acidity developed, the oxide coat dissolved off and corrosion proceeded. This indicates that at least (1) Deanesly, R. M., and Carleton, L. T., IND.ENQ.CBEM.,ANAL. in highly refined oil, corrosion occurs as a result of the following ED., 14, 220 (1942). (2) Dornte, R. W., IND.ENQ.CHEM., 28,26(1936). reactions : (3) Engler, C.,and Kneis, E., Dingler’s Polytech. J., 263,193 (1887). M A02 = A 0 MO (4) Larsen, R. C.,Thorpe, R. E., and ArmfieId, F. A., IND. ENQ. &EM., 34, 183 (1942). MO 2HA MA2 HzO ( 5 ) Mair, B. J., and Schicktanz, 9.T., J . Research Natl. Bur. Standards, 17,909(1936). where M = metal; AOz = peroxide; HA organic acid ( 6 ) Mair, B. J., Willingham, C. B., and Streiff, A. J., Ibid., 21, 585 (1938). Since these reactions were established in white oil rather than (7) Mikeska, L,.A., IND.ENQ.CnEM., 28,970(1936). in an actual lubricating oil, this proof was extended to commer(8) Vlugter, J. C., Waterman, H. I., and Westen, H. A. van, J . Inst. cial lubricants. Figure 7 shows the result of following peroxide Petroleum Tech., 21,661 (1935). Oil & Soap, 9,89 (1936). (9) Wheeler, D.H., number, neutralization number, and rate of corrosion as a function of time in a typical strip corrosion test. For convenience in plotting, rate of corrosion is expressed as milligrams per 100 hours. These experiments were carried out on various commerBatch Rectification-Correction cial samples in a routine strip-corrosion test. The apparatus consisted of glass tubes, 2 inches in diameter and 20 inches long, Attention has been called to a misprint in my paper on the immersed in a n oil bath whose temperature was automatically above subject, in the April, 1943,issue of ~NDUSTRIAL A N D ENQIcontrolled to 200” * 1O F. Approximately 300 cc. of the oil unNEERINQ CREMISTRY. I n Equation 5, page 408, “q/’ should der test were placed in each tube, and air was bubbled through at be “b)’. the rate of 10 liters per hour. Strips of bearing metal were susR. EDGEWORTH-JOHNSTO pended in the oil. Before each weighing, the strips were washed TBINXDAD LEABEEOLDB, LTD., in petroleum ether and carefully wiped with a soft cotton cloth. B.W.I. POINT-A-PI~RRB, TRINIDAD,
+ +
-
+ +
