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NATIONALMIVISORYCOMMI’ITEEFORAERONAUTICS

TECHNICALNOTE2460

FORMATIONOFSULFIDEFILMSONSTEELANDEFFECTOF

SUCHFILMSONSTATICFRICTION

ByErvaC. Levine;andMarshallB. Peterson

LewisFlightPropulsionLaboratoryClevbmd, Ohio

Washington

September1951

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TECHLIBRARY~Bm NM

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NATIONALADVEQRYCoMMmmmFORAERONAUTICS

‘IX0BNICflLIW!l!132460

FORMATIONOF SULFIDEFILMSON STEELANDEFFECTOF

SUCHFILMSON 6TATICFRICTION

ByErvaC.LevineandllashallB.Peterson

)SUMMARY

Experimentalstudieswereconductedto evaluatetheformation,undertransienttemperatureconditions,.ofsulfidefilmsonheatedsteelspecimenshmersedin solutionsoffreesulfurin cetaneandtoestablishthenecesssrysulfide-filmthicknessforeffectivelubricationunderstatic-frictionconditions.

Withtheparticularsteelspecimensusedintheseexperiments,theminimumtemperaturesatwhichironstiideisformedontheheatedspecimensin cetanesolutionscontaining0.1to 1.0percentfreesulfurby weightwerefrom,700°to 375°F, respectively.By establishingthecoolingratesofhotspecimensinsertedin coolsolutiohs,amountsofreactionproductformedatvarioustemperatureswithvariedconcentra-tions,andtime-temperaturerelationsinallexperiments,itwaspossi-bleto calculatetherateofformationofthereactidnfilm. Thecalcu--latedrateoffilmformationon steelina solutionof0.5perceptfreesuUurin cetanewasapproximately1.8x105Angstromunitspersecondinthetemperaturerangefroril.lOOOto 1000°F.

Static-frictiondatawereobtainedwithcleandrysteel(coeffi-cientof staticfriction,0.79).andforsteelcoatedwithsulfidef-ilmsofm“iousthiclmess.Dryfilmthicknessesof 5000AngstromUnitsorgreaterwerefoundnecessarytopreventsurfaceweldingcompletelyandto producerelativelylowfriction(coefficientof staticfriction,0.32to0.39).Weldingwasappreciablyreduced,however,withfilmthick-nessesaslowas 3400Angstromunits,-althoughfrictionwasreducedonlyslightly.Thisresultindicatedthatthinsulfidefilmsweresomewhateffectiveeventhoughcompletepreventionofweldingwasnotobtained.

INTRODUCTION. “

Experimentalstudiesby numerousinvestigators(references1 to5)haveestablishedtheconceptthattheeffectivenessof so-calledextreme-pressurelubricantadditivesisdependenton chemicalreactionbetweentheadditivesandthelubricatedsu@acestoproducea solidsurfacefilmhavingdesirablelubricatingproperties.HighsurfaceItemperaturesarenecessaryfortheproperfunctioningofextreme-pressure

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2 NACATN 2460

lubricants.Bow&n andRidler(reference6)havedemonstratedthatsurfacetemperaturesoccurringon effectivelyltiricatedslidersmaybeabove600°C (1112°I?)andthat,inmanycases,localizedsurface-temperatureflashesapproachthemeltingpointofoneoftheslidermaterials. WithcontinuedmQtIonof sliders;a seriesoflocalizedtemperatureflashesoccurswiththetotalsmountofheatenergy(butnotnecessarilythemaximumtemperatureofthesurface)beingdependentontheloading.As suggestedinreference5, “extremetemperature”lubricantsmightbe a moreaccuratenamebecausetheysreprimarilytemperatureactive.

Thecompletemechanismofactionofthetemperature-activelubri-cantsisnotknown because of itscomplexity.However,theactioniSdependentonthecompositionandstructureof slidermaterials,thecompositionoftheatmosphere,andthephysicalconditionsof slidingaswellasthecompositionoftheMbricants.A seriesofpossiblechemical.reactionsthatmightoccurwithsulfuradditives(amongothers)isout13nedinreference1;thelubricatingfilmthatisformedon steelsurfaceswasfoundtobe ironsulfide.

ThesoMi reactionfilmformedbythetemperature-activelubricantsmustpossessdesirablelubricatingpropertiesunderstaticanddynamicconditions.An investigationofthelubricatingpropertiesof suchfilmsunderdynsmicconditionsisreportedinreference-7.It is suggested,inref~ence7,thatathighslidingvelocitiesthetimeincrementduringwhichmatingsurfaceareasareinintimatecontactis soshortthataneffectivelubricatingfilmcannotbe formed;thishypothesisis sub-stantiatedinreference8. Static-frictionexperimentsto establishtheminimnmfilmthicknessof sulfideon coppersurfacesthatis effectiveinprovidingsolid-filmMibricationarereportedinreferences9 and10.Suchinformationisunavailableforsteelsurfacesanda basisforquantitativelydefiningan effectivelubricatingfilmof sulfideonsteelisneeded.

ThepreSentinvestigationwasconductedattheNMA Letislaboratory:(1)to studychemicallytheformationof sulfidefilmson steel,and(2)to establishby a frictioninvestigationthesulfidefilmthicknessnecesssryforeffective’lubricationunderstaticconditions.

Thedataonfilmformationwereobtainedundertransienttempera-tureconditionswithheatedsmalJsteelspecimensinsertedin solutionsoffreesulfurdissolvedin cetane.Theeffectof sulfidefilmthick-nesson lubricationwasdeterminedwitha static-frictionapparatus.

APPARATUSANDPROCEDURE

Theseparatephasesofthisstu~’”(chemicalandstatic-frictioninvestigations)willbe discussedindependently.

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NAC.ATN 2460 3

ChmiicalInvestigation

Method.- Theapparatususedfortheformationofironsulfidefilmsonrectangularspecimens.is showninfigure’1.-!lhisequipmentconsistedprims.ril.yofa smallelectricfurnaceandtwoweighingbottles,whichcontainedthelubricantsolutions,allmountedonaturntablewithina coveredglasschaiber.Thechaniberwasprotidedvithanatmosphereofhelium,externalcontrolsforrotatingtheturntable,anda meansforraisingorloweringthesteelspectienintothefurnaceandthesolutiou. ,

Thespecimenandspecimenholder(fig.l(b))werefirstloweredintothefurnaceandheatedto a predeterminedtemperature,whichwasmeasuredby a contactthermocouplepressedintoan indentationatthetopofthespecimen.Withthethermocoupleinthisposition,the-bulktemperatureofthematerialratherthanthesurfacetemperature-measured.Theheatedspecimenwasthenraisedfromthefurnace,theturntablewasrotatedtotheproperposition,andthe”hotsteelspecimenwasinsertedinthecool(roomtemperature)solutionoffreesulfurincetane.Theconcentrationof sulfurin cetanewasvariedfrmnO.1to1 percent.Afterbeingtakenfromthefurnaceandwhileinthesolution,thespecimentemperature.wasobsemedaqdrecordedusinga reco+ingoscillograph,whichgavea sensftiyerecordoftemperatureasa f,uqctionoftimeo Thetemperature“sensitivityof-&lOOF-isdependenkfuthe ~cyclicalfrequencyoftherecordingequi~entandthemdmlJm.cQolin$jrate. Theinstantof contactandthetemperatureof.thespecimenat‘contactwiththesolutionwasestablishedby theabruptchangeinthecoolingrateofthespecimen,as indicate!onthetime-temperaturerecord.Theexperimentswererepeateda nmiberoftimesto,obtaindataattheinitialtemperaturesdesired.

Withtms apparatus,exp%tientswereconductedto establishtheminimumtemperatureatwhichdetectable(bymeansof chemicalspottest)ironsulfidefilmswouldbe formedinsolutionsoffreesuMurin cetane.Thisminimmtemperaturewastakenasthattemperaturebelowwhichanegligibleamountof s~ide isformed;thetotals.mountof sulfideformedonthespecimenat eachinmersiontemperaturewas Obtaimd W quantitativechemicaltests.Ifthesmountof sulfideformedperunitareaatvarioustemperaturesandthetime-temperaturerelationsareknown,theamountofstiideformedpersecondandconsequentlythestiide-filmthicknessformedpersecondcanbe determined.

Inthechemicslexperiments,a transienttemperaturewasgeneraJJyusedbecauseitapproachestheconditionfoundin slidingsurfacesandbecausea fairlyconstantcoolingrateinthetemperaturerangeofinterestalloweda reasonableunderstandingofthetime-temperaturephenomena.Fortimeincrementswhicharewithinthemeasuringsensitivityoftheinstrumentemployed(0.0083‘see),reasonableapproximationsinrate

4 I?ACAZ!N2460n

offilmformationandcoolipgratecouldbemqde. At thebeginningofthesurfacereaction,therateoffilmformationmaybe an exponential ,

functionoftime;butforthepurposesoftheseexpertientsit isneces-sarywithinsmallthe (ortemperature)incrementsto assumethisrelationtobe linear. N

Specimenpreparation.- Specimenmaterialtithlowsulfurcontentwasselectedtominimizeerrorsinthespottestusedbecauseuntreatedsteelspechenswithhighsulfurcontentgavepositivetestsforsulfide.Untreatedpueiron(NationalBureauof Standards99.8-percentiron)andselectedlow-sulfursteelsgavenegativeresults;accordingly,steelscontaininglessthan0.035percentsulfurwereused. Becauseitwasnotedthatthepresenceofoxhlesonthespecimeninhibitedtheformationof sulfidefilms,a heliumatmospherewasusedtominimizeoxidationofthemetalandthesolution.

Therectangularspectins(1/4by l/4by 3/32in.)werecleanedbyabrasionwithO and3/0metallographicpaperandtheriwashedwithacetoneandbenzene.

Qualitativeandquantitativeidentificationof sulfide.- TheFeiglspottest(reference11)wasusedto establishthepresenceof sulfuras— —stiideonthetreatedspecimensintheexperimentalworkreportedherein.Theidentityofthereactionproductironsulfidewasverifiedin severalcontroltestsby meansof e,lectrondiffraction.TheFeiglspottestissensitiveto lessthan1 partpermillionof sulfyras sulfide;therefore,itwaspossibleto estab~shthepresenceofa sulfidefilmof suchrein-utethicknessthatit.coul.dnotbe detectedbyincreaseinweightorchangeintheappearanceofthesurface.

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Quantitativedeterminationswereobtainedby a modificationoftheFeiglspottest. Standardsolutionsofp-aminodimethylanillnecontainingsulfidehaveeasilydiscerniblecharacteristiccolorsthatvarygreatlywithconcentrationof sulfide.By comparingthecolorofthestandardsolutionshavingknownconcentrationsof stiidewithsolutionspreparedby dissolvingtheSulfidej?ilmfromthespecimens(ina spotplatecon-taining2 ccof solution),itwaspossibleto establishtheconcentrationof sulfuras sulfide.Thecolorofthesulfideandp-amino&hnet~nilinesolutionsisunstableforextendedperiodsoftime,consequently,stand-ardwater-colorsolutionsweremixedverycarefullytomatchthedesiredgradationof sulfidecolors.Thecolorfromthetestedsulfidesolution .washmediatelyvisua13ycomparedwiththestandardwater-colorsolutionsto establishconcentrations.Thesensitivityofthismethodofquanti-tativeevaluationwassufficientforthedetectionofa changeof0.1milligramper100cubiccenttietersintheamountof sulfurfromthesulfideinthetestsolutions.

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NACATN 2460 . 5

Thethicknessesofthefilmswerecalculatedfromsimpleweight,area,anddensityvalues.Thefollowingassumptionsweremadeinthecalculations:

(1) Theincreaseinweightwasentirelyduetotheconibinationofsulfurwiththeironofthespecimen

(2) Thedensityofthe FeS filmwas4.84gramEpercubiccenti-meter

(3) Thefilmthicknessonthespecimenswasuniform

(4) Thecalculatedsurfaceareaofthespecimenwassurfacesxea

thereal

Therealsurfaceareaisappreciablygreaterthantheapparentarea;andbecauseaccuratedeterminationoftherealsurfaceareaisdifficult,thea~arentareawasusedinthecalc~tions.Therealfilmthick-nesswasthereforelessthanthatcalculated.

In ordertoverifytheresultsobtainedby themethodjustdescribed,a secondmethodof establishingtheminimumreactiontemperaturewasused.Solutionsofvariousconcentrationsoffreemilfurin cetanewereheatedto specifiedtemperatures.SmalJsteelspecimenswereeachimersedintheheatedsolutionsfora periodof1 minuteandt-henremoved.Theminimumtemperaturesatwhichthesulfidewasformedwereagaindetermined.

Static-FrictionInvestigation

Appsratus.- Thestatic-frictionexpertientswereperformedwiththeapparatusshowninfigure2. Theprincipalpartsofthe,apparatus(fig.2(b)) weretheriderassembly(containingthreeball.specimensofhardenedsteel;RockwellC-m)’andtheplatespecimen(hardness,RockwellA-HO)whichtheballscontacted.A ballspecimenwassecurelyclampedintheriderat eachoftheverticesofan equilateraltriazigl.e(asshowninfigure2(c))andthetotalloadwasappliedatthecenterofthetri-anglenormalto itsplane.Itwasassumedthatthetotalloadwassupportedequallyonthethreeballs.Theplate(SAE1020)wassecurelyfastenedtothebaseoftheapparatus.Thestatic-frictionforcewasmeasuredwitha dynamometer-ring,strain-gageassanblysimilartothatdescribedinreference12. A photoelectricrecordingpotentiometerwasusedasa friction-forceindicator.Theapparatuswascontainedwithina chamberhavingprovisionsformaintaininganatmosphereof dryair.Preliminaryexperimentsshowedthathumiditiesabove10percentreducedthestatic-frictionforcejtherefore,frictionr~ weremadewithrelativehumiditymaintainedina rangebetweenapproximately7 to10percent.

6 NAOATN2460

Theforcenecess~ to overcomestaticby elasticallyextendinga dynamometerringstraingagesweremounted..Thedynamometer

frictionwasappliedslowlyonwhichtheforceindicating .ringinthestrain-gage

assemblywasconnectedtotheriderassenibl.yby a finewire. Thedis-placementrateof0.0156inchperminuteinthissystemwasproducedbya 1 rpmmotorrotatinga finepitch(64threads/in.)screw.Theinitialmotionoftheriderassemblywasobservedthougha telescopefittedwithcross-hairs.Whenmotionwasobserved,anindicatingmarkwasmadeonthetime-forcerecordinthepotentiometer.

Misalinementresultedindecreasedanderraticfrictionvaluesaswellas skewingoftheriderassenibly.Thisdifficultywasminimizedbya jigplacedovertheplate(fig.2(b)).Thejigcausedtheriderasseniblytobepositioneddirectlyinthelineofforceapplicationandstrainmeasurement.

Specimenpreparation.- Theplatesurfaceswerecleanedby the ‘proceduredescribedinreference12. Thesteelballs(SAE52100)werecleanedby rigorouswashinginl.00-percentalcohol,thenina soiutionof50percentaceteneand50percentbenzene,followedby twowashingsin100-percentalcohol.This procedureremovedallgreasefromthesurface;theabsenceof contaminationwasconfirmedby electrondiffraction.

Forthefrictioninvestigation,ironsulfidefilmswereformedontheballspecimensby heatingandthencooling,bothinanatmosphereofhydrogenslilfide,forpredeterminedperiodsoftime.Thicknessofthefihnwascalculatedfromweightgainandwascheckedbymeansofthemodifiedspottestdescribedearlier.Inmostcases,theresatsagreedwithin10percent.Allweightgainwasassumedtobe causedby’theadditionof sulfurwhichwasstoichiometricaldycombinedwithirontoformironsulfide.

RESULTSANDDISCUSSION

Theseparatephasesofthisstudy(chemicalinvestigations)willbediscussedindependently.

andstatic-friction

ChemicalInvestigation

Minimumreactiont~eratures.- Theminimumreactiontemperatureobtainedinthisinvestigationis definedasthatimmersiontemperature

n)Ew

belowwhichnoironsuHidecouldbedetectedbytheFeiglspot-testonthespecimens.A plotoftemperatureagainstweightconcentrationofsulfurin cetaneshowingtheminimumreactiontemperaturesobtainedbytwomethodsis showninfigure3. Thefirstmethodusedinmostofthe

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NACATN2460

workreportedhereinconsistedinimmersingof sulfurin cetane.Inthesecondmethod,

7

heatedspecimensin soltiionssolutionsofvariousconcen-

trationsoffreesulfurin cetanewereheatedto specifiedtemperaturesbelowtheboilingpointof cetane.Smallsteelspecimens~pe eachimmersedintheheatedsolutionsfora periodoflminuteandthenremoved.Thedataobtainedaftera l-minuteimmersionofuriheatedsteelspecimensinheatedsolutionschecksthedataobtainedbyinmersingheatedspecimensinroom-temperaturesolutions.Theminimumreactiontemperaturesindicatedforthefirstmethodarethosethatwereobservedattheinstantof contactofthespecimens’withthesolutions.Asexpected,thesedatashowthatas concentrationincreases,minimumreactiontemperaturedecreases;thegreatestdecreaseinminimumreactiontempera-tureoccursat concentrationsup to0.4weightpercent.Veryl.i.ttledecreaseinminimupreactiontemperatureoccurswithincreasedconcen-trationabove0.4weightpercent.As an exsmple,whenthesulfurconcen-trationwasdoubled.(0.8weightpercent),theminimumreactiontemperaturewasdecreasedapproximately35°F. Theminimumreactiontemperaturesobtainedwithpureirontireandtoolsteelwereessentiallythessmeasthedataformildsteel(lowsulfurcontent)presentedinfigure3.

Filmformationcharacteristics.- Thedatareportedinfigure4 showthattherateof stiidefilmformationwasthegreatestwiththeinitialspecimentemperaturesfrom700°to 1.1OOOF forallconcentrationsofsulfursolutions.Aspreviouslymentioned,reference6 indicatesthattemperaturesinthisrangemaybe characteristicofboun~y lubricatedsurfaces.It isthereforeapparentthatthegreatestfilmformationoccursattemperaturesofimportanceinlubrication.

Studyoftheoscillographtime-temperaturerecordsfromthee~eri-mentsthatprovidedthedatapresentedinfigures4 and5 indicatedthattherateof coolingofthespecimenswasessentiallyconstantwithinthetemperaturerangeofinterest.Thetypicalcooling-ratecurvepresentedinfigure5 indicatesthattheaveragetimerequiredfortherectangularspecimensto cool100bF, ina rangeoftemperatures(fromlJOOOto500°F) inwhichchemicalreactionwouldoccur,wasapproximately0.04second.

Forpurposesof evaluation,itisassumedthatittookthespecimen3.04secondto coolfrom1100°to 1000°F, a 100°F increment,ina0.5percentsolution.Theamountof sulfideformedinthatincrementcanbe determinedlyreferencetofigure4. Thedifferencebetweenthequantityformedat1100°F andthequantityformedat1000°F isditidedby thecoolingtimeforthe100°F increment(0.04see).Thiscalculationindicatesthattherateoffilmformationduringthatincrementoftimeandtemperaturewasapproximately1.8x105Angstromunitspersecond.

Forcomparisonpurposes,experimentsweremadewith’scommercialextreme-pressureadditive,dlbenzyldis~ide (reference3))in cetane.

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8, NAOATN 2460.

Theresultswereapproxbnatelythe,sameasthoseobtainedforsimilarsulfurweightconcentrationsoffreesulfur.

Accordingtoreference13,thereactionbetweensti bearingcom- Npoundsandferrousmetalscanbe acceleratedbythepresenceof sodib zstiide I?a$.When Na# isusedasa catalyst,theminimumreactiontemperatureisreducedandtherateoffilmformationisincreased.Sodiumsulfide(0.5weightpercent)andfreesulfur(0.5weightpercent) ‘dissolvedin cetanereducedtheminimumreactiontemperaturetobelow300°F andcausedanappreciableincreaseinrateoffilmformationattemperaturesabove700°F. Theuseof suchcatalystsrequiresmoreextensiveinvestigationbecausetherearemanyobviouscomplicationsinvolved.

Static-FrictionInvestigation

Untreatedsteel.- Theeffectofloadonthecoefficientof staticfrictionforcleandrysteelballsondrysteelplatesis showninfig-ure6,whichisa plotofthedatafromonerepresentativeexperiment.Thesedataaiongwithsubstantiatingunreporteddataestablishthemeanvalueof0.79forcoefficientof staticfriction.Ingeneral,these‘resultsagreewithAmontontslawshowingthatthecoefficientof staticfrictionisindependentofload.Themiiltipledatapointsshow-pinfigure6 forthe300-gramloadwereobtainedat intervalsthroughouttheexperimentafterrunswiththeheavierloads.Surfaceweldingoccurredunderallconditionsofloadingwithcleandrysteel.

As indicatedinfigure7 andinvisualstudiesof surfaces,sulfidefilmthiclmessesof4500Angstromunitsorlesswereonlypartlyeffectivein reducingfrictionandpreventingweldingofthesteelspecimens.The !frictionvalueswithfilmthicknessesof3400and4500AngstromUnitswer”egenerallysomewhatlesst~n foruntreatedsteelandshoweda slight’increaseinfrictionwithincreasedloading.ThegeneralincreaseInfrictionwithgreaterloadsforfilmshavingthicknessesof45oOAngstromunitsorlessisa deviationfromAmonton’slawthatmayindicatefurtherprogressivesurfacefailure.Forfilmthicknessesgreaterthan4500AngstromUnits,weldingwaseffectivelyprevented.Static-friction-coefficientvaluesfortheseeffectivefilms(thicknessesgreaterthan4500A)werefrom0.32to0.39. Ingeneral,friction-coefficientvalueswereindependentofloadforallfilmthicknessesgreaterthan4500AngstromUnits.8

Afairedcurveof cross-plotteddatafromfigure7 ispresentedinfigure8,whichshdwsdirectlytheeffectofthiclmesson coefficientofstaticfriction.A criticalfilmthicknesswasestablishedatapproxi-mately5000A,belowwhichfrictionincreasedmarkedlyandweltingoccurred.(Ashilarcriticalsulfidefilmthicknessforcopperwas

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NACATN 2460 9

found.by Campbell,reference9,andby Greenhill.,reference10.) Littlechangeinfrictionwasevidentwithfilmthicknessesgreaterthan5000Angstromuhitsanda markeddecreaseinthescatterofthedataobtainedwithvariousloadswasnotedasthicknessofthefilmwasincreased.

Kinetic-frictiondatawereobtained(reference13)fora steelsphereagainsta steelflatcoatedwitha filmof FeS. The FeS filmreportedinreference14wasbelievedtobe approximately1000Angstromunitsthick=Comparisonoftheresultsofreference14andfigure8showthatkinetic-frictiondataat lowslidingvelocitiesaresomewhatlower(aswouldbeexpected)thanthestatic-frictiondataforthesamethickness,offilm.Thesurfacedsmage(welding)inthekinetic-frictionexperimentsshowedgoodcorrelationwiththatoccurringinthestatic-frictionexperiments;in thekinetic-frictionexperiments,weldingoccurredtiththefilmof1000Angstromunitsthickness.Similarly,inthestatic-frictionexperiments,weldingoccurredwithfi3mthicknessesoflessthan5000Angstromunits.

Threephotomicrographs(XIOO)ofsurfaceconditionsontheflatspecimensaftercontinuedmotionoftheballriderspecimenacrosstheplatearepresentedinfigure9. Thesurfacedisturbanceinfigure9(a)istheresultofmetallicadhesion.Thisadhesionorweldingmaycauseprogressiveincreaseintrackwidth.Theappearanceofthissurfaceme isverys~l= to tht inf@re 9(a)ofreferenceI-2wheresevereweldingandsurfacedsmagetookplacebetweenexperimentsof cleansteelunderconditionsofhighslidingvelocities.Theballspecimencoatedwithan ironsulfidefilm14,400Angstromunitsthickcausedsimplesurfaceabrasionandsmearingofa filmas showninfigure9(b)jno surfacedisturbancecomparablewiththatoffigure9(a)isobserved.Thesmearedfilmisbelievedtobe a transferredironstiidefilm. Thereisnoevidenceofhamd’ulsurfacedisturbanceattheinitial.pointof contact.Figure9(c)showsa trackmadeunderconditionsdmilartothoseoffigure9(b)exceptforan increaseintotalloadfrom2400to4300grams.Inthiscase,considerablymoresmearingcanbe observed;but,.asbefore,noharmfulsurfacedisturbancecanbe discerned.

Photomicr&raphstakenathighermagnific~tion(X270;.fig.10)showsurfacesofboththeweartrackontheflatspecimenandthematingcontactsurfaceontheball. Thesurfaceshownin figure10(a)isthesameoneshowninfigure9(c).Theappearanceofthespecimensathighmagnificationindicatesthatthetransferredtionsulfidehassmearedoversurfacerecessessuchasfinishingmarks.

Thematingrider(ball)surfaceshowninfigure10(b)hasa thickfilmofironsulfide.Thewearareacanbe matchedwiththatshowninfigure10(a).Thewell.definededgesofthecontactsurfaceinfigure10(b)andthestratificationvisibleontheprincipalaccumulations,ofirons~ide infigure10(a)wouldtendto indicatethatfragmentation

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10 MACATM 2460

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ofthefilmmhterialoccurred.Thelightareainfigure10(b)indicateswherethehighloadconditionoccurredonthestablefilm. ThetwowelldefinedspotswithintQelightareaarebelievedtobe loadcarrying

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“build-up‘S“ ofironsulfideandnotareasofharmfulsurfacedisturbance.Nn?

SignificanceofChemicalandFrictionInvestigations E

Theminimumreactiontemperatures,fortheparticularspecimensusedinthechemicalstudy,aresufficientlylowsothatthereexistsa considerabletemperatnn?erange(1100°to 700°or3750F) on slidingsurfaceswherea reactionfilmcanbe formedby anadditivesuchasfreesulfur.me rateoffilmformationcalculatedfromthecurvesforboththe0.5and1.0weightpercentsolutionsoffree-suEur incetaneatthemaximumtemperatureswasapproximately1.8X105Angstrcmunitspersecond.

Thefrictionresultspresentedinfigure8 indicatethata filmofironsulfideapproximately5000Angstromunitsthickisnecessarytoobtainminimumfrictionduringunlubricatedsliding.Also,withthisthicknessof50CM)Angstromunitsweltingwascompletelyprevented.Withsulfidefi3mthicknessesaslowas 3400Angstromunits,however,visualobservationindicatedthatweldingwasappreciablyreducedin spiteofthefactthatfrictionwasreducedonlyslightly.Thisresultindicatesthatthinironsulfidefilmscanbe somewhateffectiveeventhroughcompletepreventionofweldlngisnotobtained.TheseresultscorrelatedgeneraJ3ywiththoseofreference14 (forkineticfriction)wherea filmofironsulfideapproxhatel.y1000Angstromunitsthickreducedfrictiononlyslightlywhileappreciablyreducingwelding.Thisreductioninweldingfortheironstiidefi3mas comparedwiththatfordrysteelmaybe observedbycomparison,resepctively,offigure8 ofreference14withfigure9(a)ofreference12.

,,

In analysesofthesedata,it”shouKlbeappreciatedthatmanyfactorscharacteristicofdynamicslidingconditionscanchangetheratesofreaction.Forexemple,therateoffilmformationisappreciablyaffectedby rateof coolingandanychangeinthecoolingratefromthatobtainedwiththespecimensofthisreportwillthuschangetherateoffilmforma-tion.Thereareotherfactorsofconsiderableimportancewhich,becauseof experimentalMmitatio&,havenotbeenincludedintherese=chreportedherein.Onefactoristhatoftheeffectofmaterial.stresses -onrateof reaction.Thereisno doubt%hatthehighcontactstresses

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encounteredinpracticallubricationproblemswillcausea markedincreaseinrateofreactionina mann,ersimilartothemechanicalactivationofchemicalreactionsdescribedinreference15.

.Anotherfactoristh&

under conditionsrequiringextreme-pressurelubrication,surfacetemper-aturesmaybe considerablyabovethevalueof1100°F indicatedinref-emence6. Thedataofreference6 tieforeffectivelyboundary-lubricated

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NACATN 2460 H

surfaces.It isobviousthatadditivesofthetypebeingconsideredwillnotbe necessaryuntilconventionalboundary-lubricatingfluidsareno longeradequate.In suchcases,surfacetemperatureswouldbehigher,possiblyapproachingtheconditionsfordryslitingreportedinreference6 wheremaximumtemperatureswerealmostatthemeltingpointofoneofthematerialsin contact.Highersurfacetemperatureswouldverymarkedlyincreasethereactionrateandconsequentlytherateoffilmformation.Datahavealsobeenobtainedwhichindicatethatmiuimumreactiontemperaturecouldbe reducedandrateofreactionincreasedbytheuseofa catal.yet.

SUMMARYOFRESULTS

Formation,undertransient,taperatureconditions,of sulfidefilmsonheatedsteelspecimensimmersedin cetanecontaini~tissolvedfreesulfurwerestudiedandthestqtic-frictionpropertiesof suchfilmswereinvestigated.Thefollowingresultswereobtained:

1. Miu3mumtemperaturesbelowwhichironsulfideisnotformedonheatedsteelspechnensin cetanesolutions’containing0.1to 1.0percentfreesulfurby weightwerefrom700°to 375°F, respectively.Thecat-alystsodiumsulfideNa2S effectivelydecreasedtheminimumreactiontemperature.

2. Thecalculatedmeanrateofsulfidefilmformationon steelina solutionof0.5percentbyweightfreesulfurin cetanewasapprodmately1.8x105Angstromunitspersecond@iw an ititialt~ incr~entof0.04secondattemperatmesfrom1100to 1000°F. ‘

3. Static-frictiondataobtainedforcleandrysteel(coefficientof staticfriction,0.79)andforsteelcoatedwithsulfidefilmsofvariousthicknessesshowedthat@ filmthicknessesof5000Angstromunitsorgreaterwerenecessarytopreventsurfaceweldingcompletelyandtoproducelowfriction(coefficientof staticfriction,0.32to0.39).Weldingwasappreciablyreduced,however,withfilmthicknessesaslowas3400Angstromunitsalthoughfriction,wasreducedonlyslightly.TMSresultindicatedthatthinsulfidefibs weresomewhateffectiveeventhoughcompletepreventionofweldingwasnotobtained.

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LewisFlightPropulsionLaboratory,NationalAdvisoryCommitteeforAeronautics,

Cleveland,Ohio,J- 8, 1951.

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13EFEm?cEs

1. Prutton,C.F.,Turdmll,David,andDlouhy,George:MechanismofActionofOrganicChlorineandSulfurCompoundsinExtreme+ressureLubrication.Jour.Inst.Petroleum,vol.32,no.266,Feb.1946,pp.90-H8. ,

2. Shard,G.L.,Russell,H.W.jandNelson}H.R.: lRdn=mePress~eLubricants.Film-FormingActionofLeadNaphthenateandFreeSulphur. Ind.andEng.Cha (Ind.cd.)vol.33,no.1-1,Nov.1941,PP.1352-1359.

3. Evans,E.A.: ExtremePressureLubrication.Jour.Inst.Auto.Eng.(London),vol.~, no.1,Ott.1942,pp.1-16.

4. Beeck,Otto,Givens,J.W.,andWilJ_iams,”E.C.:”OntheMechanismofBoundaryLubrication.II. WearPreventioribyAdditionAgents.Proc.Roy.Soc.(London),ser=A,vol.177,1941,pp.103-1.18.

5. Bowden,F.P.,andTabor,D.: TheAreaofContactBetweenStationaryandBetweenMovingSurfaces.Proc.Roy.Sot.(London)zser.A)VO1. 169,1939,p. 411.

6. Bow&n,F. P.,andRidler,K.W. E.: Physical.PropertiesofSurfaces.III.-TheSurfaceTemperatureofSlidingMetals.TheTemperatureofLubricatedSurfaces.Proc.ROYSot.(London),ser.A,vol.154,no.883,May1,1936,pp.640-656;

7. Johnson,RobertL.,%ikert,MaxA.,andAtHighSlidingVelocitiesofSurfacesanAdditive.NACATN1720,1946.

. .

Bisson,EdmondE.: FrictionLubricatedwithsulfuras

8. Bisson,EdmondE.,Swikert,M= A.,andJohnson,RobertL.:E&fectofChemicalReactivityofLubricantAdditivesonFrictionandSurfaceWeldingatHighSlidingVelocities.NACATN2144,19EQ.

9. Campbell,W. E.: StudiesinBoundaryLubrication.Trans.A.S.M.E.,vol.61,no.7,Oct.1939,pp.633-6+%1.

10. Greenhill.,E.B.: TheLubricationofMetalsby CompoundsContainingSulf%r.Jour.Inst.Petroleum(London),vol.34,no.297,Sept.1948,PP.659-669.

SL. Feigl,Fritz:QualitativeAnslysisby SpotTests.Trans.by JanetMatthews.Nor&manPub.Co.,Inc.(NewYork),2dEng.cd.,1939,p. 198.

NJ,

!3”

.

.

.

●

NACATN 2460 13

3.2.Johnson,RobertL.,Swikert,MaxA.,andBisson,EdmondE.:llkictionatHighSlidingVelocities.NACATN 1442,1947..

13. Simonsson,Lennart:CorrosionofFe inS-bearinggases.Chem.Abs.,vol.39,no.4,Feb.20,1945,p. 687. (FromChem.Zentr.,vol.II,1943,p. 1316.)

14. Johnson,RobertL.,Godfrey,Douglas,andBisson,EdmondE.:FrictionofSolidFilmsonSteelatHighSlidingVelocities.NACATN1578,1948.

15● Shaw,M. C.: MechanicalActivation- A NewlyDevelopedChemicalProcess.Jour.A@. Mech.,vol.15,no.1,March1948,pp.37-44.

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