UNCLASSIFIED

AD NUMBER

AD293981

NEW LIMITATION CHANGE

TOApproved for public release, distributionunlimited

FROMNo foreigh

AUTHORITY

NRL ltr., 31 Aug 1999

THIS PAGE IS UNCLASSIFIED

UNCLASSIFIED

AD 293 981

ARM ED SERVICES IE jA ItCAL INFORMATION AGENCYARLIN(;TON HALL STATIONARLINGTON 12, VIRGINIA

S•.NCLASSH] EEDi

iI

NOTICE: When govermnent or other drawings, speci-fications or other data are used for any purposeother than in connection with a definitely relatedgovernment procurement operation, the U. S.Government thereby incurs no responsibility, nor anyobligation whatsoever; and the fact that the Govern-ment may have fonmulated, furnished, or in any waysupplied the said drawings, specifications, or otherdata is not to be regarded by implication or other-

wise as In any manner licernsing the holder or anyother person or corporation, or conveying any rightsor permission to manufacture, usc or sell anypatented. Invention that nmny in any way be relatedthereto.

V

t 293 981- 293981 NRL Report 5794

ANTIOXIDANT ACTION OF METALSAND ORGANOMETAL COMPOUNDS IN FLUOROESTERS

AND POLYPHENYL ETHERSH. Ravner, E. R. Russ, and C. 0. Timmons

Surface Chemistry BranchChemistry Division

December 5, 1962

I !

U. S. NAVAL RESEARCH LABORATORY

Washinqton. D.C.

CONTENTS

Abstract iProblem Status ii

Authorization ii

INTRODUCTION 1

EXPERIMENTAL PROCEDURE 2

OXIDATION SlUDIES 2

Fluorinated Esters 2

Polyphenyl Ether.s; 6

I)IS( USSION 10

SUMMARY 11

ACKNOWLEDGIMENT 12

IKFEHEEN({ES 13

ABSTRACT

Aircraft gas turbine engines in the Mach 2 to 3 range, now in thedevelopment stage, will require lubricants considerably more stable tooxidation (to 5001F) than present jet engine lubricants. Fluoroestersand polyphenyl ethers are among the potential high-temperature lubri-cants being considered for this application. It has been discovered atNRL that a high degree of oxidation stability can be imparted to thesefluids by a variety of metals and organometal compounds.

Thrce fluoroesters and a polyphenyl ether [ bis(phenoxy-phenoxy)-benzene] wcs'c subjected to oxidizing conditions at repltively high tem-peratures (4370to 650 0 FJ in the presence and absence of the metals andorganometal compounds, and data were obtained to show the oxidationinhibition due to the additive. These data included viscosity change at100"F, neutralization number increase, evaporation loss, corrosivity tometals, and sample appearance.

At 437'F copper and steel improved the stability of the fluoroalcohol(4/'-alkyl) esters of 3-methylglutaric and camphoric acids. At 4820F,the camphorate was substantially stabilized by copper, barium, monel,and chromium; by toluates or benzoates of barium, nickel, chromium,cobalt, manganese, praseodymium, titanium, ytterbium, and strontium;by cerium disalicylalpropylene diamine and cerium (ip'-heptyl) hydrogen-3-methylglutarate; and by the cooper salts of perfluoroundecanoic acid,(ip' -heptyl) hydrogen 3-methylgiutarate, toluic acid, and phenylstearicacid.

Bis(iP'-amyl)2,2'-dipbenate possessed generally high inherent sta-bility up to 617%F. Some JIF was evolved, however, which was greatlyreduced by the presence of copper. At 642(F the ester underwent exten-sive pyrolysis, which the inhibitors did not prevent.

The polyphenyl ether, bis(pheuoxy-phenoxy)benzene, was effectivelyprotected from oxidation at 600"F by copper, cupric toluate, and cericidetate. Fit Etfciau';i "e ;ý2:Ualtrrlacor benzoates or uarium, manganese, cerium, nickel. lead, praseodymium,

cobalt, chromium, titanium, and ytterbium.

The degree of stability given to these fluids increases interest inthem as potential high-temperature lubricants for aircraft gas turbinesin the Mach 2 to 3 range.

PROBLEM STATUS

'This is an interim report; work on this problem is continuing.

AUTIIORIV'lION

NUT, Problems C02-01 and C02-02Project-; RAP 4 .-JOOl/SG6-1/VO12.03.O0b

a..d P I 00' 08.44-5500

Mvanw; .-:,ip I subm u, 0 A p-l 9(' Z 9 ,2

ANTIOXIDANT ACTION OF METALS AND ORGANOMETAL COMPOUNDSIN FLUOROESTERS AND POLYPHENYL ETHERS

INTRODUCTION

Power requirements for jet aircraft have increased manyfold since World War II,concomitantly imposing more stringent demands on engine lubricants. One propertycritical to the satisfactory performance of these lubricants is resistance to oxidation.

Experience with petroleum oils and aliphatic diester fluids has taught that if metalshave any effect on lubricant stability, it is generally adverse. Certain metals, copperbeing a notable example, are considered to be particularly deleterious in this respect.It is customary, therefore, for laboratory tests which attempt a realistic measure of theoxidation stability of lubricants to specify the inclusion of the metals of construction per-tinent to the application for which the fluid is to be used.

The present investigation is concerned with a study of the oxidative stability of flu-oroesters and aromatic polyethers, both potentially useful as high-temperature jet air-craft engine lubricants, and, more particularly, with the unexpected resistance to oxidationat high temperatures imparted to them by certain metals and salts. The results are remi-niscent of those obtained during a parallel investigation of the high-temperature inhibitionof silicones (4)

There are few data available on the use of organometal compounds as oxidation inhib-itors. Naphthenates of copper and cobalt have been reported to enhance synergisticallythe activity of phenolic antioxidants in lubricating oils (14). Dispersions of inorganicsalts of alkali metals are reported to have antioxidant properties in lubricant compositionscontaining petroleum and synthetic esters (22).

To place in proper perspective the oxidation stability requirements for high-temperature jet engine lubricants, it will be useful to review briefly the development ofboth the engines and the lubricants. Early jet engines, such as the J-33 and J-34, devel-oped thrusts of 3,000 to 6,000 lb. Sump temperatures were of the order 1300 to J 50°F andoil-out temperatures at the bearings were 210o to 260"F. These engines were lubricatedadequately with petroleum oils, grades 1005 and 1010, conforming to military specifica-tions (24). The specification corrosion-oxidation test required that the lubricant be stableat 250°F for 72 hours, which may be taken as an indication of the stability required ofthem under service conditions. In the early 1950's engines (e.g., J-57 and J-79) in theMach I to 2 range, with thrusts of from 10,000 to 16,000 lb came into general use. Theseengines currently power the majority of U. S. firstline fighter aircraft. Sump tempera-tures range from 2300 to 275 0 F, and oil-out temperatures from 3400 to 400°F. The oxi-dative stresses to which the lubricants for these engines arp subjected are of such mag-nitude that petroleum-based fluids cnnnot he employed because of their rapid deterioration.Aliphatic ester-based fluids (2,9,11), however, whon prnperly inhibited with an efficientantioxidant such as phenothiazine (21), have proved to be eminently satisfactory lubricantsfor these engines. The specification (17) covering these fluids requires that they withstanda corrosion-oxidation test at 347 0 F for 72 hours.

Jet engines such as the J-58 and J-93, now-in the development stage, are in the Mach2 to 3 range and have thrusts of from 18,000 to 26,000 lb. Sump temperatures range from3000 to 450°F, and oil-out temperatures may attain 650"F. Although a lubricant specification,6, for• there e a writen, based on trimethylolpropane-type esters, ,iv oi1s

-typeestes, ; oil

2 ~NAVAL RESEAR~CH LAFIOIAYORY

presently qualify undcr it. In tlie original ver-sion of the specifioIatjon, a 500"F eorrosjun**oxidlation test was listed hut proved to be Of no practical value because no oils cotuld befound to meet the stability requirements (6). No corrosion --oxidatien requirement isincorporated in the latest version of this specification (16). In all of the speunficatiunsnoted ablove, the corrosion-oxidation iests provide for various metal specimiens to bepresent, bothi to simulate engine conditions and ,o catalyze oxidative breakdown of tilelubricants.

LXlPEtIME NTAL PROCEl)URF

Because sonme of the experill-ntal1 tlui Is for this study were available only inl limite6quantities, it was nlot feasible to evaluate their corrosion-oxidation stability according tocurrent standar-d methods, which require uip to several hundred minl-li ie i- pr cili. Thbere*fore, cells were- empl))oyed Whuli require sainipt( -volumes of only 210 inl (2 ,23).'T'hc cellswere constructed of borostiijal e glaussu ,i;ni'i itt corrosoni--oxidal ion cells described inmitlif-iry specifications, and were niatOll nitd 'it the tdesired lest tempei~ihirales iiitleniioslalted aluminumo btock fti naCOS. f It iii 'inr I reed Of C0,l)( and1~l 0iio~ii, wiSo btibbledt~hrough thle sanmples at the ju;te ot I cc af"gi' llilieoil Mietat S;lLi'cion 511lrenelli

generatly hail sturface art~iss Of 10 sqiiie i llitti0

'The duoti obtaiiied onl oxidIized iiliý P. ii i ilir iciiid ViSCiOilY change at 10iluF,iut.'italizatiiii imiiin1ber liiruecv:tjI[I;- .,,: lo ;!, !oLrrosivit y toý iiisIcl:;, inod :no nple'ippesranice. IIIii u itimbler1 tf tL1o0)iS' t CUI ii the effluents kvere lia,;13ed into w:-iei fr-.Ps,alter whiiih the fll iiinteild!; 0f the lIl ra iiqi ifl' wcri'- il'cniidy tie ba-id chlorofttuoride11i1l hod.

All ot ilie coiiiii mlitsi cuiii 'ifiy'til ; u iId iti' iV i fI, 11 Alildy Wt"'eiu liisu 'i it llthi lIabii

:-itfs of tile torganic acid anid OWe ihliirid"ill liii Ki-iu1iit (1tid)l. COLA(i- iiiuilte was

proplyJenediiirnine, (i()lI),wsii 1 , e y ovel q icri aiuiiiiioiin uirn Iitu' V11!0nsoiltliniii oltiate; lihe rioitt asic ieric !oluaie was i-.,wti~- with USl'I) tii liiin eerie(1)5']) (3) Even in Ow~ !ow oneuot'ni rt ions emiployedl, none of these additives, was COin -tile tel soltuble in thle tcnt ftlii d!;ý .iwif sV1 ii e i-tIore dift iceti tt ito d~ýI r m ie ai tIme- conrUIosloiofth1le mnajoirity ut. runis wvheth er thie mi s In Iib Icioulc ri Iiou iOUid wan 'iii dis sui ''id additive , orsludge formed dtirl gil, ,,- xi-datloio. ;o it-rt all lthit inialerial was reported as sludge.

0XII)ATIO STUDIES

Fluiornat~ed E~sters

Coimbi nation ol Metals Present I' -cetV" tilsoivelst gat 5Ž1 ii list' ooi iitat ed um lit kAe Stscomi poiyiyasic aries and i iuoroatciL:uu~is kl/ oi) Lti~jilt'O J5eiiJU.tj 1oiueiui5 ICCi 2-'

Clt2 Oft were unou.uiuily!Atabtte ti toxidatbion, 'veil in tihe absence of coivi'it ion-at iinhiibitors(13, 15,19f). In those stutiies the fluids were Ill contact with a icombiination of solni of the1metals oned, iii specificatioi toxidlationi ýcoirosioni test., (16,17), geileratly copper, fateel,aind silver-plated steel. Ii- f'ahte 1, oxidlation expertni _iis under these coiiditions areýumn~ni-i-mz(d for es!te~rs of 3 --metuiylrl ttaric, enamphoiricr, and 2,2' diphienic ac ids. Estersof boti 3,-niiethylglutaric and camphoric acids dci- ouneratech e~xcellent resistance to ou-dation at -43'7"F as evidenced by smnall -viscofiltv iumauge ancaid nimunbers, mhiimumifluoride evoloutionl (reporiod to;- the eaniipho catf.Ž oni Vt iiiclc('liti s-ample appeal-alnce.

At 482"F, oxidative chaingtes ill tWe floblS were ýIudli'n lui'et rfin the mnore stablearoimatic acids are mnore olxidation resistant than Oweir oitialogs3 fromn aln-Ihatie acids.Thuls, after '12 hours ;1t 52F-', tuis(zp"aiyl22 -dncni ;dIf.oxed l;tl ii' degradati xe charige.

NAVAL RESEARCH LABORATORY3

ir o~ E! o

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4 NAVAL RESEARCH LABORATORY

No Metals Present - When, in the course of the present investigation, the experimentssummarized previously were repeated, except that no metals were present, an unexpected andsignificant decrease in the stability of the fluids resulted (Table 1). The more outstandingof these stability changes due to the absence of metals are noted below.

1. (Bis(p'-amyl)3-methylglutarate at 437 0 F for 168 hours. The neutralization num-ber rose from 7.2 to 215.

2. Bis(qp'-heptyl)3-methyglutarate at 437 0 F for 168 hours. The 100°F viscosityincrease rose from 0.5 to 72 percent and the neutralization number from 0.07 to 21. At482 0 F, the viscosity increase rose from 1.8 to 46 percent and the neutralization numberfrom 1.2 to 11. Although the viscosity increase and generation of acids were greater at4370 than at 482 0F, there was much more sludge formed at the higher temperature, apossible indication that the oxidation reactions followed different courses.

3. The camphorate from mixed fluoroalcohols at 437 0 F for 168 hours. The viscosityincrease rose from 5.2 to 64 percent, the neutralization number from 0.06 to 7.7, and theevolved fluoride from 0.19 to 4.1 mg/g sample. (At 437 0 F with the stated metals present,this ester was more stable with regard to viscosity, acidity, and fluoride evolution thanit was at 392 0 F with no metals present.) Exposure to 482°F for 72 hours or longer causedthe camphorate without metals to gel; it was still fluid, however, after 168 hours at thistemperature with the three metals present.

4. Bis(iP'-amyl)2,2'-diphenate at 527OF for 72 hours. The fluoride evolved increasedfrom 0.11 to 5.3 mg/g sample although in other respects no significant diffe-ences werenoted.

individual Metals, or Organocopper Compounds Present - it was apparent from theeesults that the stabilities of the fluoroalcohol esters ofj 3-nethylglutaric, camphoric, anddiphenic acids are measurably improved by contact with the combination of steel, copper,and silver-plated steel. The analogy to be drawn between these results and those fromprevious investigations on the high-temperature stabilization of silicone fluids by bothmetals and organometal compounds was inescapable. Wn these latter studies it was demon--trated thiat the stable i:fe of ightly ph-enylatced polymethyl -l icones was extended sev.r.-..

foid when they were in contact with a combination of chielating agents and certain metals,most notably copper (4). To separate the effects produced in the fluoioesters by each ofthe three metals previously employed in combination, the fluids were subjected to oxida-tion in the presence of the individual metals. Following out the analogy to the silicones,these fluids were also oxidized with organocopper compounds present.

n•I "'able 2 are summarized experimental results demonstrating that both copper metaland copper compounds impart a high degree of oxidation stability to fluoroesters fromboth camphoric and 3-methylglutaric acids; conversely, steel, stainless steel, or organo-cerium compounds have little or no beneficial effects. For comparison, data on the sta-bility of the fluids with neither metals nor salts present are included in Table 2.

M.ask• bed bneficinal .espon.e. to copper w,,ere shown by bis(4i'-.ml)3-nethylglta,±oat 437tF, and by the corresponding bis(ý/'-heptyl) compound at 482°F. After 168 hours.the neutralization number of the former compound in the presence of copper was only0.03 as compared with 215 in the absence of metals. Similarly, with copper present theneutralization number of the latter compound was 0.18 as compared with 11 in its absence,and tWe percent viscosity increase was 4.6 instead of 46. Both copper (ip'-heptyl)3-nethyigfiutarhte and copper phenylstearate stabilized bis(ýp'-heptyf)3--methyglg!,_ta.r.ate, b,,t

not as elfectively as did copper metal.

'iesponse of the campnorate ester to copper metal ivas excellent durhin a 43'7"F, 168-,our run, as evidenced by smail viscosity and acidity increases, minimal evolution of

NAVAL RESEARCH LABORATORY 5

oo

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2I~ ~.C!

6 NAVAL RESEARCH LABORATORY

fluoride, and satisfactory sample appearance. By way of contrast, steel appeared toaccelerate breakdown of the ester, causing it to gel; silver-plated steel was essentiallyinert, the ester reacting as though no metal or additive were present. Three coppersalts - the phenylstearate, the toluate, and the perfluoroundecanoate - offered substantialimprovement to the stability of the uster. The copper perfluoroundecanoate differedsomewhat from that of other additives insofar as it permitted a larger viscosity increasethan did the other additives but at the same time completely prevented the evolution offluorides.

As already noted, 72 hours at 482 0 F caused gelation of the camphorate. With coppermetal present, however, tHie viscosity increase was only 2.7 percent; even after a i68-hour exposure to this temperature the fluid did not gel, although the viscosity increasewas 215 percent. Substantial improvement in stability with respect to viscosity and acid-ity increases was imparted to the camphorate ester by the following copper salts: per-fluoroundecanoate, (Vp'-heptyl)hydrogen 3-methylglutarate, toluate, and phenylsearate.On balance, the copper (zP'-heptyl)3.-methylglutarate appeared to be the most effective ofthese additives, permitting viscosity and neutralization number increases of only 1.6 per-cent and 1.7 respectively. The effect of copper perfluoroundecanoate at 482OF was similarto that at 4370 F; it permitted a substantial viscosity increase but prevented the generationof volatile fluorides.

The aromatic ester bis(V'-amyl)2,2'-diphenate is inherently so stable that improve-ment with additives is difficult. Even at 617 0 F, after 72 hours the 100OF viscosity increasewas only 12 percent, the neutralization number increase 4.4, and the total fluoride evolved1.8 mg/g sample (Table 2). When copper was introduced into the fluid, fluoride evolution

and acidity decreased, but the viscosity increase was essentially unchanged. Coppertoluate produced similar ambiguous results. When the test temperature was increased to642"F, the compound underwent extensive pyrolysis, as shown by the viscosity decreaseof 92 percent. Pyrolysis also occurred when copper metal was present.

Miscellaneous Metals and Organometal Compounds - In view of these encouragingresults which resembled previous data obtained when silicones were stabilized with vari-

ous metals, metal salts, and metal chelates (4,12). the antioxidant actions of 2 variety ofmetals and of salts in addition to copper were ascertainoed in the camphorate of the flu-oroalcohol. The results are listed in Table 3 and, with those for ceric DSPD excepted,refer to 72-hour runs at 482 0 F. Of the bulk metals studied, barium arid monel were themost effective, with chromium somewhat less so. Nickel apparently had no antioxidantactivity, permitting the fluid to gel. Cobalt was employed in powder form and it could notbe determined whether the tarlike appearance of the fluid after oxidation resulted fromthickening of the fluid due to dispersion of the metal, or deterioration. The effects of thebenzoates or toluates of the following metals were determined: barium, cerium, nickel,chromium, cobalt, manganese, praseodymium, titanium, ytterbium, and strontium. Alldisplayed inhibitory activity, the toluate of barium in 0.1 percent concentration being themost effective, particularly with respect to the cleanliness of the fluid after the run.The salts of praseodymium, lead, chromium, and manganese were relatively the leasteffective. The ceric salts of disalicylalpropylene diamine (437 0 F for 168 hours) and(ip'-heptyl) hydrogen "-methylglutaat. (A59"F fo 72hours) were as.effective prevent-ing a large viscosity increase as were the better toluates.

It is apparent from these data that a variety of metals with either single or multiplevalences, and metal salts, impart significant oxidativestability to fluoroesters fromaliphatic acids.

Polyphenyl Ethers

Among the more attractive candidates for use as high.temperature jet engine oils arethie polyphenyl ethers, which haw boeen reported to have good rto;istsnce 1.0 oxidation,

I

NAVAL RESEARCH LA130RAYORY7

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8 NAVAL RESEARCH LABORATORY

pyrolysis, and radiation (7,8,18,26). These compounds have reasonably good viscosity-temperature characteristics, high-flash points, and low-evaporation rates, provided theirmolecular weights are in the proper range. The meta isomer of bis(phenoxy-phenoxy)-benzene has received much attention because in addition to its possessing the desirableattributes listed above, it is a liquid (pour point of 400 F), in contrast to its ortho and paraisomers, which are high-melting solids. There have been limited data reported on onti-oxidants to improve the stability of the polyphenyl ethers. Some promise has been shownby organotin compounds, oxides of copper, and metal acetylacetonoates (8,26).

For the present study, pulyphenyl ether samples were obtained from two commercialsources. Both were mixed isomers of bis(phenoxy-phenoxy)benzene, with the meta isnomerpredominating. The fluids were equivalent as regards their stability and response toantioxidants. The reactivities of these fluids were not perceptibly affected by percolationthrough adsorbents to remove polar impurities. Results of oxidation stability studies onthese ethers are shown in Table 4. As was the case with the fluoroesters, the organometaladditives were essentially insoluble in the ether.

After 72 hours at 500 0 F, with no metals present, the ether was essentially unchanged.With a test temperature of 572 0 F, the fluid became too thick for a viscosity measurement.The ether was oxidized to a gel when exposed to 600"F for 48 hours.

Some improvement in stability was imparted to the ether at 600°F when strips ofeither steel or stainless steel were present in the oxidation cell. In 48-hour runs vis-cosity increases were of the order of 150 to 350 percent and the neutralization numbersapproximately 0.5. More marked reduction of viscosity change was given by copper metal;the neutralization number increases, however, showed little improvement over those runswith only steel present. The very small neutralization number and viscosity increasesobtained with the copper-steel combination might be indicative of syniergistic action, butthe reproducibility of these test results is not sufficiently reliable to justify this conclu-sion. When silver-plated steel was introduced into the fluid, the stability imparted wasof the same order as when copper metal was present.

The effect of individual metals on the stability of the ether at 650OF was determined.In 't8-hour runs, only barium, of the metals investigated, was at all effective; it permitteda viscosity increase of 256 percent and a neutralization number of 1.0. Neither copper,stcmll, nickel, monel, nor chromium prevented gelation of the fluid. With cobalt powderpresent, the fluid presented a tarlike appearance after oxidation, as was the case pre-.viously with the camphorate ester.

At 600)F the ether displayed a significant response to the stabilizing effect of coppertoluate, and copper toluate together with o strip of steel; in 48-hour runs the viscosityincreases and neutralization numbers were remarkedly small, averaging 12 percent and0.17 respectively. However, when the run was extended to 168 hours, the combination ofcopper toluate and steel did not prevent gelation. A marked degree of oxidation stabilitywas likewise imparted to the ether by ceric toluate in 0.05 percent concentration; after48 hours at 600OF the neutralization number increase was of the order of 1.0 and the1000F viscositv incresp. wn. Ri n~rcnt Although very little additionall tluatc appearedto go into solu'tion when the concentration was raised to 0.1 percent, the neutralizationnumber was one-third and the viscosity increase one-half that of the ether with the lowerconcentration of additive.

At 650 0 F, the toluates or benzoates of barium, cerium, nickel, lead, praseodymium,manganese, cobalt, chromium, titanium, and ytterbium each displayed sigpnificant anti..oxidant activity. On balance, manganese benzoate and barium toluate (despite the rela-tively large neutralization numbers that resulted) offered the most substantial protectionto the ether primarily because in both instances the oil was clear and substantially free

of sludge, anddid not incur a large viscosity increase. Of those additives which displayed

IIII

r ~ ~ ~ ~ ~ ~ ~ ~ ~ AA - -EAC LABORATORY______________________

Table 4

rTemp FTeltMedlor Mea-Sl Neal-VA RESEARCH N__ _er _ _Sapl Appearance

50.0 7210 . 0.29 Opqu,k black

570. <1 .0 114 0.41 Opaque, black

800 48 Stel .11.8 1 2 047 Opaque, blacksde

8D 48 Sel.9. 3 .4 Opaque, black9001 48 (T0l).<5)1.0 91 0.99 Opaque, blacklu e

Steel .0.1 01.4 Oele uelled ac

950 48 Copper 3.t 10 1 Celeele

650 48 Steel- ft 3 5. 36ld1 ele

8.9 14 0.17 Opaque, black, sludge

Stel.0.1 G1. Celed G elled

_0 48_ _e( 1)0.5 _s51 1 Oaue lakesug

600 'n~ 48 CheTomin,, 11) 26 0.9 paue aacslug

650 DNS 48 Barium 1.1 256nynpshla 1.0 paqeambe

yb( .8) Y(e(biu5), (ml ;L3o7luOpqeble.lug650 dah 48iue ch ol(01 a4.s9 oele meGeal.

650 48sde Cfz)O ) 3 .8 Opqe abr sug

10 NAVAL RESEARCH LABORATORY

antioxidant activity, lead benzoate and titanium toluate permitted the largest viscosityincreases, 279 and 353 percent respectively. The only toluate which offered no protectionto the ether was that of copper; likewise, barium dinonylnaphthalene sulfonate did not pre-vent gelation of the fluid.

DISCUSSION

Silicones, fluoroesters, and polyphenyl ethers are all so stable that comparativelyelevated temperatures are required to effect their oxidation. Therefore, significant reac-tion products may be so short-lived as to be difficult or impossible to identify. Consider-ation of the well-known oxidative reactions of the aliphatic diesters may serve to illus-trate this latter point (20). The overall reaction rate of these fluids is a function of peroxideconcentration; at any specified temperature the peroxide content rises to a maximum andthen falls off rather sharply as secondary reactions become significant. As the oxidationtemperature is raised, a peak concentration is more rapidly attained and the subsequentdecrease is more precipitate. Finally, a temperature is reached (ca. 450 0 F) above whichperoxides are difficult to detect because they are so rapidly destroyed. In the case ofsilicones, peroxides have been postulated as high-temperature reaction products (1).Nevertheless, at the temperatures at which such peroxides are presumed to form (above500 0 F) they are evidently too short-lived to be detected by conventional chemical methods.The polyphenyl ethers may be an exception to this generalization regarding short-livedhigh-temperature reaction products, since they are reported to generate stable freeradicals above 600OF (26,27). Although these radicals have been detected by electronparamagnetic resonance spectroscopy, their precise molecular configuration has not beendetermined.

The difficulties associated with the identification of the initial high-temperature oxi-dation reaction products of fluoroesters and polyphenyl ethers apply also to the elucida-tion of the mechanism responsible for the inhibition imparted by metals and organometalsalts. Nevertheless, certain assumptions may be reasonably made. For one thing, prob-ably the activities of only the salts are relevant to the inhibition process since, at theelevated temperatures employed in the present investigation, bulk metals undoubtedlyreact with oxidation products of the base fluids. The resulting superficial layers of saltswould be at least slightly soluble in the fluid. It may be further speculated that the usualcatalytic role of metal salts is reversed in the subject fluids and instead of oxidation pro-ceeding by an electron transfer to a metal ion (possibly as a complex) from a hydroperoxide(5), the ion has the general attributes of an energy sump, interrupting the autonatalyticoxidation chain. Thus, the consequent deactivation of the chain-propagating entity (hydro-peroxide, free radical, or energy-rich particle) would drastically curtail the overall oxi-dation rate of the base fluid.

It is apparent from the present study that traditional concepts of factors affectingthe oxidation stability of petroleum or aliphatic diester lubricants may not automaticallybe assumed valid for fluids of different chemical constitution. In particular, the presentlyaccepted level of stability of fluoroesters and polyphenyl ethers, as determined in thespecification tests, would probably not correlate well with their stabilities in an operatinggas-turbine engine. in laboratory tests, copper metal is traditionally present to promotedeterioration of the fluids, whereas for precisely the same reason, copper metal and itsalloys are rigorously limited as materials of engine construction. The ironic fact is that

copper at high temperatures is a potent antioxidant for these fluids and they would displaya higube_ degree of stability in the laboratory where copper is present than in an enginewhere copper is absent.

One then may reasonably speculate whether other experimental conditions for theevaluation of lubricant stability, hitherto taken for granted, should not be rcexamined todetermine their precise effect on the fluid. Among the factors which might merit such

NAVAL R1 SiARAi. ItLABORAl ORY 1

re -examilnationl are thle effect of fighit and the inltiiuiCe1 of glass. For example, the compo--sition of glass containeis hits been sliowii to affect significantly the room temperaturestorage sstability of airriUN af!uels (10).

SUMMARY

The discovery has been made at this Laboratory as to the beneficial effect of certain

metals and organometat salts on the oxidation stabilities of a p olyphenyl ether, and threeiUnurualZolulQ esters ot (Jolybosik, acidsý. Thet fUiaodoCUjeuiiob (ki' --alcohlols) wcre of dhegeneral formula IIktUF 2 -CE2 ) ,ClIOI1.

lIn the absence of metals;, estcrs oif 3niethylgiutaric and camphoric acids were unstableat 43'10F and seriously de~graded at 4t182" Out!;tanding improve ment in the stability of theea;tcrs was obtained at 437"F in the pre!sence ot copper, either atone or together with steeliind silver. plated steel. At -1812"F ft(e response of both fluids to copper was good, bot' steelor silvoc-plated steel showed no inhib~ilo ry eff ect. 11-ao ?oo moodl, and chroi-nium eachprevented at fnificant degradation of flie caisphoin rte a:t 112 'F, the former being the mostit ; f-cive with respIect to ( leilnthies ,; of the flid S. The activity of cobalt was miargins!;

e1(kel Permitted the fluo Sito f "I 'thip st, *ariyl) eater otfitile aroinatic 2,2.'-diphenicx-)vid was; inhierently :5o 51 atle, eveni al 617', thot the only ituprovsmnent imparted to it 1)y

-oprWas :I lessening; of evolved lhini'tde.'s Al 64,!21 the cater uiderwent extensive:1'.' rolys is r -,ardtes a f a Olte ptec si (ci of coppe:r.

V i a oe a colat iveuly insoluble ortaposcitp iti ~h sls na1leim inp roved fthe 48 2,F st abil -,y of bhit IbI'e 3- mcliiylg to a rate and tMe cam11pho rat e fluoroe sterf!. The co pper co mpouinds;ive atig:a ted wvere tie (4'3etl)3ne y1g i;II' t ~ h ty;~o' e nic thyigl Ot d riic,

it i y ate rtet(Iitatce, anid pe rt liorouiiderIaloast c lit the camo ph orate ester, the be ozoate so otuat et of the, ('ltowaig nictals all (tispt):Iycl antioixidanit act ix'itv at '182."F to varytinfg

(lit'lees: hai 41o11, nicac , ch mm iii i, cokt dt, nalanginesae, prose's lym ini0, t itani umi, y tt e rbiu0,aiiu at~roiunit01. tof these the mosat cit ciix ire :iq ha, iton Inmuate. CeYriunm disalicylaipropyl-lie1( dtanilin i 111id ccriloin (pla' i~t y ) h id i'l igeo -.;n l;1eisai also d is ptayedt effect iveiilibitilion in (tie camisior:lt it[ ibisý winooeratlli'i-

rb e p0 iyjphienyl c: hl1it iiutt ied WaS t iY 1 06 IbIi lt of l) his (L~ thIŽ enlxy --phi I Oybi z enle,

0eiio meta ion ier 1b ein g p reiai 1nant . Witllii it, ni;c t as pie senut, die fltold geliled wheni exposedI (30W1I" (or 48 houruls. Altthoiutgt eitther tI'slee )r s;ilver -plated steeli prevenited getatiun ofihe fluid, coopeir, csliprc tolilate, aiid ':vrt lieiual e were imure effective in pr event inn.tihicklciii,' 'if the folu t.At 65~0)F; bar w .11 t)r10V'veltec gelation; coipper, steel, nickel, moiiet,

chromiir'oini, and cobalt had non antioxidant activity. 'the tioluates or- henzoates of cerium,ntickel, lead, praseodymitum, inaugailese, coibalt, clikromnini, Miaiiium, ytterbium, andbaraiii alt displayed !igaulicant antioxidant activity:' the most efftective were maeganese).enzoi~uc and b~ariuLm toluate. Cope 4orate and ba rioui dineonytoaphthalctne sulfanatelathi permnited the ether in 4el.

'rh e ioppios ite roile.- ptav pd iyv mottat asi -,ci as enopper it ans t sixidant a iii fluorol ati era,poyhey oter, adsfcn, ,., a; pro.idnt' in a at ic and pet roteum oils, call

for mnure careful exaniniiatiiono uthle ir sal: it, tie laiii) latus;' evaluation ot lub~ricanit -;! a-tiility. It will le necessary !, ikInow t lie s~pecific effect of such metals before ihe uinherentstabitity aiid probable service utiltity ofI new lutbricant ftuids (~al. be reliably assessed.

'The result., recpol'tr-o Li-e,'i;doan t't the jnk;Hnal aIid sasd'4high'-temioerat~reantixidnt ropetie ofcer aiui met als and ii 'ganoloetal co-ipoulids in fluoreste 's and

putyphenyvl ethers. A prograu it; no11w iii prg~ to) syutlie ire moioie sotulile compiounds,not only at the metals reported litce(, h)Lt of others being investigated, t(o improve further0- ;iabialit(ties of fklooroctera ,.; ar-ina t ii others, andi othe r tiighl-'temperatulre fluids. Suit --atile studies of the inihibition mnecianitsnis inivoltved may Yield iiuformatiior, icading to the!,election aod tsyi)Lh-ie' o5(f even mnure efiicieiit iint txidants.

12 NAVAL RESEARCH LABORATORY

ACKNOWLEDGMENT

The authors wish to acknowledge the assistance of Marian Goalldsm••h who co,,ndduclmany of the oxidation tests reported in this study.

REFERENCES

1. Andrianov, K.A., "Organic Silicon Compounds," State Scientific Technical PublishingHouse for Chemical Literature, Moscow, U.S.S.R. (1955); Translation F-TS-9191V

2. Atkins, D.C., Jr., Baker, H.R., Murphy, C.M., and Zisman, W.A., Ind. Eng. Chem. 39:491(1947)

3. Baker, H.R., O'Rear, J.U., and Sniegoski, P.J., J. Chum. Euig. Data 7:560 (1962)

4. Baker, H.R., and Singleterry, C.R., J. Chem. Eng. Data 6:146 (1961)

5. Bawn, C.E.H., and Moran, D.P., J. Inst. Petr. 44:290 (1958)

6. Berkey, K.L., "Gas Turbine Lubricants Picture - 1960," Proceedings of the AirForce-Navy-Industry Propulsion Systems Lubricants Conference, Nov. 1960; pp. 41-46,Published Apr. 1961

7. Bolner, G.E., Schmidt-Colterus, J.J., and Weber, J.H., Denver Research Institute,WADC Technical Report 60-282-Part II, July 1961

8. Borsoff, V.N., Kerlin, W.W., Accinelli, J.B., and Beaubien, S.J., "Gear and BearingLubrication in Extreme Environments," Proceedings of the Air Force-Navy-IndustryPropulsion Systems Iubricants Con(crencc, Nov. 1960; pp. 187-200, PublishedApr. 1961

9. Bried. E.M., IKiddev, IP., Murphy, C.M., and Zisman, W.A., Ind. Eng. Chem. 39:484(1947)

10. Christin, A.G., C, (iinlolla, A.J., Johnson, .).E., and Carhart, H.W., Ind. Eng. Chem

50:1153 (1958)

11. Cohen, G.,Murphy, C.M.,O'Rear, J.G., Ravier, If., and Zisman, W.A., Ind. Eng.Chem. 45:1766 (1953)

12. Elliott, J.R., U.S. Patent 2,445,567 (1948)

13. Faurote, P.D., Henderson, C.M., Murphy, C.M., O'Rear, J.G., and Ravner, H., Ind.Eng. Chem. 48:445 (1956)

14. Foehr, E.G., U.S. Patent 3,018,248, Jan. 23, 1962

15. Henderson, C.M., Buhi, P., and Ravner, H., "Laboratory Examination of E.I. duPontde Ncmours Company Fluoroalcobol E'sters of Camphoric Acid," NRL ltr rpt 61 70-284.56 of 20 Dec. 1956

16 "1 .i,'icicating oil, Aircrmft 'Ttibine E~ngine, 4 0 0 U1,p" Milii~try Specification Mil .-9236B

17. "Lubricating Oil, /i•c craft lurbin(l Enine, ,3ynthctic B3a!;ae, Military Specification8. iI,.-) ,v'.:08D)

8.% M~ahoney, ('I),. * I -), mini, F..U., (el, ini W.W., :5,1 i,,,) : l'ean . AU(i .}: 3:33 (19C0))

i4 NAVAl RESEARCH LABORATORY

19. Murphy, C.M., O'Rear, J.G., Ravner, H., Sniegoski, P.J., and Timmins, C.O., J.Chem. Eng. Data 4:344 (1959)

20. Murphy, C.M., and Ravner, H., hId. Eng. Chem. 44:1607 (1952)

21. Murphy, C.M., Ravner, H., and Smith, N.L., lId. Eng. Chem. 42:2479 (19501

22. Norton, J.lt., and Sproule, L.W., U.S. Patent 3,000,819, Sept. 19, 1961

23. "Oil, Lubricating, Instrument (Synthetic)," Bureau of Ordnance Specification 14-0-20

24. "Oil, Lubricating, Jet Engine," Military Specification MIL-O-6081

25. O'Rear, J.G., and Sniegoski, P.J., "New Partially-Fluorinated Compounds," NRLReport 5795, July 18, 1962

26. Smith, J.O., Willson, G.R., McEllhill, E.A., and Stenmiski, J.R., "Research on HighTemperature Additives for Lubricants," 1st Quarterly Progress Report, Air ForceContract No. AF 33(616)-7853, Phase II, Project 1(8-7340) MRC Project No. 2016,Feb. 15 to May 15, 1961

27. Smith, J.O., Wilson, G.R., MrElhill, E.A., and Stemniski, J.R., "Research on HighTemperature Lubricant Additives," 3rd Quarterly Progress Report, Air Force Con--tract No. AF 33(616)7853, Phase II, Project l(8-7340) MRC Project No. 2016, Aug.15 to N'hv. 15. i96i

I.. ,�

K

L . I

"kit

Date: 31 August, 1999

From: Mary TemplemanCode 5227

To: Dr. MurdayCode 6100

Subj: Distribution Statement of NRL FR Report(s)NRL -FR-5 794

Dear Sir:

Please review the attached report(s) for a distribution statement.

Thank you,

Mary Tempi man(202)767-34 5marytW@iibra _.nrl.navy.mil

CC: CHARLES ROGERSCODE 1;ý

P :_.1 Document Name: untitled

-- 1 OF 1-- 1 - AD NUMBER: 293981-- 3- ENTRY CLASSIFICATION: UNCLASSIFIED-- 5- CORPORATE AUTHOR: NAVAL RESEARCH LAB WASHINGTON D C-- 6 - UNCLASSIFIED TITLE: ANTIOXIDANT ACTION OF METALS AND-- ORGANOMETAL COMPOUNDS IN FLUOROESTERS AND POLYPHENYL ETHERS-- 8- TITLE CLASSIFICATION: UNCLASSIFIED-- 9 - DESCRIPTIVE NOTE: INTERIM REPT.--10 - PERSONAL AUTHORS: RAVNER,H.;RUSS,E.R.;TIMMONS,C.O.;--11 - REPORT DATE: 5 DEC 1962--12- PAGINATION: 14P MEDIA COST: $ 6.00 PRICE CODE: AA--14- REPORT NUMBER: NRL-5794--20- REPORT CLASSIFICATION: UNCLASSIFIED--23 - DESCRIPTORS: *ANTIOXIDANTS, *ESTERS, *ETHERS, AIRCRAFT,

BENZENES, CAMPHORS, FLUORIDES, GLUTARIC ACID, HIGH TEMPERATURE, JETENGINES, LUBRICANTS, METALORGANIC COMPOUNDS, METALS, OXIDATION,PHENYL RADICALS, POLYMERS, STABILITY

--24- DESCRIPTOR CLASSIFICATION: UNCLASSIFIED--25 - IDENTIFIERS: PHENYL RADICALS, CAMPHORS--26- IDENTIFIER CLASSIFICATION: UNCLASSIFIED--27 - ABSTRACT: THREE FLUOROESTERS AND A POLYPHENYL ETHER (BIS(PHENOXY--- PHENOXY)-BENZENE) WERE SUBJECTED TO OXIDIZING CONDITIONS AT 437 TO-- 650 F IN THE PRESENCE AND ABSENCE OF THE METALS AND ORGANOMETAL

-- COMPOUNDS, AND DATA WERE OBTAINED TO SHOW THE OXIDATION INHIBITION-- DUE TO THE ADDITIVE. AT 437 F CU AND STEEL IMPROVED THE STABILITY-- OF THE FLUOROALCOHOL (PSI-ALKYL) ESTER F 3-METHYLGLUTARIC AND-- CAMPHORIC ACIDS. AT 482 F, THE CAMPHORATE WAS SUBSTANTIALLY-- TABILIZED BY CU, BA, MONEL, AND CR; BY TOLUATES OR BENZOATES OF BA,-- NI, CR, CO, MN, PR, TI, YB, AND SR; BY CERIUM DISALICYLALPROPYLENE-- DIAMINE AND CERIUM (PSIHEPTYL) HYDROGEN-3-METHYLGLUTARATE; AND BY-- THE CU SALTS OF PERFLUOROUNDECANOIC ACID, (PSI-HEPTYL) HYDROGEN 3--- METHYLGLUTARATE, TOLUIC ACID, AND PHENYLSTEARIC ACID. BIS(PSI-AMYL)-- 2,2-DIPHENATE POSSESSED GENERALL HIGH INHERENT STABILITY UP TO-- 617 F. AT 642 F THE ESTER UNDERWENT EXTENSIVE PYROLYSIS, WHICH THE-- INHIBITORS DID NOT PREVENT. THE POLYPHENYL ETHER, BIS(PHENOXY--- PHENOXY)BENZENE, WAS EFFECTIVEL PROTECTED FROM OXIDATION AT 600 F-- BY COPPER, CUPRIC TOLUATE, AND CERIC TOLUATE. AT 650 F EFFECTIVE-- INHIBITORS WERE BA METAL, AND THE TOLUATES OR BENZOATES OF BA, MN,-- CE, NI, PB, PR, CO, CR, TI, YB. (AUTHOR)--28 - ABSTRACT CLASSIFICATION: UNCLASSIFIED--30 - ANNOTATION: ANTIOXIDANT ACTION OF METALS AND ORGANOMETAL-- COMPOUNDS IN FLUOROESTERS AND POLYPHENYL ETHERS. POTENTIAL HIGH-- TEMPERATURE LUBRICANTS FOR AIRCRAFT GAS TURBINES IN THE MACH 2 TO 3-- RANGE.--33- LIMITATION CODES: 2 APPROVED FOR PUBLICDate: 8/24/99 Time: 6:17:42PM ---RELEASI DISTfIBIJTI&UII

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