Friction and wear performances of borates and lanthanum chloride in water

Available online at www.sciencedirect.comoURIAL.OF: ScienceDirectRARE EARTHSEL SEVIERJOURNAL OF RARE EARTHS, VoL 26, No.4, Aug.2008, p.590www.cejoumal.comFriction and wear performances of borates and lanthanum chloride in waterCHEN Boshui (陈波水), FANG Jianhua (方建华), WANG Jiu (王九),L1Jia (李嘉), LOU Fang(娄方)(ogistical Enginering Universiy, Chongqing 40016, China)Received 11 October 2007; revised 20 December 2007Abstract: The antiwear and friction-reducing performances of sodium borate, potassium borate and lanthanum chloride in water were evalu-ated on a four ball friction tester. The topographies, element distribution and chemical characteristics of the wom surfaces were investigatedby scanning electron microscope (SEM), energy dispersion of X-ray (EDX) and X-ray photoelectron spectroscope (XPS). The results indi-cated that sodium borate, potassium borate and lanthanum chloride increased extreme pressure, antiwear and friction-reducing capacities ofwater to a certain extent, of which potassium borate was the best candidate. Combination of lanthanum chloride with sodium borate and po-tassium borate respectively further improved antiwear and friction-reducing capacities. Scratches of worm surfaces lubricated with water con-taining borates and lanthanum chloride were less severe than those lubricated with water containing borates alone. A tribochemical flmmainly composed of oxides of lanthanum, boron and iron reduced friction and wear for water lubricant formulated with both borates and lan-thanum chloride.Keywords: borate; lanthanum chloride; water; friction; wear; rare earthsIt has been proven that lube additives based on boric com-compounds exhibit good synergism with organic borate es-pounds are promising due to their high load-carrying capac-ters in reducing friction and wear. The present paper aimsity, good thermal and oxidative stabilities, and lowat understanding the friction and wear behaviors of sodiumeco-toxicity, etc. Indeed, many boric compounds, e.g. or-borate, potassium borate and a rare earth compound, lan-ganic borate esters, inorganic borates such as sodium borate,thanum chloride, in water.and even nanometric borate particles, have been verified tobe excellent in reducing friction and wear when formulated1 Experimentalinto lubricating oils and greasesl-s. Since last decades, theinterest in boron based lube additives for lubricating oils andgreases has increased and many efforts have been made. But1.1 Additives and apparatusthe studies of boric compounds as lube additives mainly fo~Additives: sodium borate Na2B2O+ 10H2O), potassiumcused on their behaviors in oils and greases, although someborate (K2B2Or5H2O), lanthanum chloride (I aCl3.* 7H2O).investigations conceming the tribological performances andAll additives are chemically pure.applications of borate esters in water based lubricants haveApparatus: MQ 800 Four-ball Friction Tester; MMW-1Pbeen reported69), which have shown that boric compoundsUniversal Four-ball Friction Tester; CSM-950 Scanningare also attractive lube additives for water. Therefore, inten-Electron Microscope (SEM); Energy Dispersion of X-aysive study of tribological behaviors of boron based lube addi-(EDX); PH1-5100 X-ray Photoelectron Spectroscope (XPS).tives in water is likewise of important theoretical and practicalsignificance, not only for understanding their friction and1.2 Procedureswear behaviors in water, but also for developing new waterThe anti-wear and friction-reducing abilities of the addi-based lubricants, especially environmentally friendly ones.tives in water were evaluated on friction testers. In particular,Rare earth compounds as lube additives have also beenthe maximum non-seizure loads (PB) and welding loads (PD)widely reportedl0-1)]. Studies have shown that many rareof lubricants were tested on MQ-800 Four-ball Frictionearth compounds carry out excellent tribological performn-Tester, while the wear scar diameters (WSD) and frictionances in lubricating oils, greases, pastes, and even coatings.coefficients were tested on MMW-1P Universal Four-ballStudies by the authors also indicated that some rare earthFrict中国煤化工。of 1500 r/min at roomFoundation iten: Projer sppored by the National Nanural Science Foundation of ChinExcllal Talents in ChineseUniversity (NCET 04-1002) and Program for lnnovative Groups in ChorCNMHGCorresponding autbor: CHEN Bosbui (E-mll: chenboshui@yahoo.com.cn; Tel: +86 23-68582243)CHEN B s et al, Friction and wear performances of borates and lanthanum chloride in watertemperatures. The tribomates for the present test are GCr15Table 2 shows the anti-wear and fition-reducing abilitiesbearing stel balls 12.7 mm in diameters and 59-61HRC inof sodium borate and potassium borate compounded withhardness. After friction testing, the worm steel balls werelanthanum chloride in water.rinsed with petroleum ether under ultrasonic for 10 min forCompared Table 2 with Table 1, it can be seen that, whensurface analysis. Thereafter, the surface topographies of thelanthanum chloride was incorporated into water containingwom surfaces were observed with scanning electron micro-sodium borate or potassium borate, the maximum non-sei-scope, while the elemental distributions and the tribochemicalzure loads (PB) and welding loads (Po) increase significantly,features were analyzed with energy dispersion of X-ray andwhile the wear scar diameters (WSD) and friction coffi-X-ray photoelectron spectroscope, respectively.cients decrease obviously, indicating that the anti-wear andfriction-reducing abilities of sodium borate and potassium2 Results and discussionborate can be markedly enhanced by lanthanum chloride.Results in Table 2 also indicate that lanthanum chloride ismore powerful in enbancing extreme-pressure performance2.1 Friction and wear performances of borates andof potassium borate than in enhancing that of sodium borate.lanthanum chlorideTable 1 shows the anti- wear and friction reducing abili-2.3 Anti-wear and friction-reducing mechanismties of sodium borate, potassium borate and lanthanum chlo-2.3.1 Surface topography and elemental distributions Fig.1ride in water, respectively.shows SEM images of the worn surfaces lubricated withWhen sodium borate, potassium borate and lanthanumwater containing sodium borate, potassium borate, sodiumchloride are introduced into water, extreme pressure is in-borate plus lanthanum chloride, and potassium borate pluscreased, and anti-wear and friction-reducing capacities oflanthanum chloride, respectively.water is improved to a certain extent, but their capacities toIn Fig.1, severe scratch wear can be observed on surfacesreduce friction and wear differ from each others. Thetested with water containing sodium borate or potassiumanti-wear and friction-reducing abilities of sodium borate,borate (Figs. 1(a)~(b)). Surfaces lubricated with water con-potassium borate and lanthanum chloride in water rank intaining both sodium borate and lanthanum chloride (Fig.1the order of K2B4O>Na2B4O>>LaClz, of which potassium(c) ), or both potassium borate and lanthanum chloride (Fig.borate is the best candidate. It can also draw a conclusion1(d), were less worm and much smoother than those lubri-from Table 1 that the friction and wear performances ofcated with water containing borates alone, especially forformulated water are improved with increasing contents ofsurface lubricated with both potassium borate and lantha-borates and lanthanum chloride.num chloride, as is well correlated with markedly improvedanti-wear and friction-reducing capacities of borates by lan-2.2 Friction and wear performances of compoundedthanum chloride.borates and lanthanum chlorideTable 1 Friction and wear behaviors of borates and lanthanum chloride in waterWSD/mmAverage frictio coefcieantAdditiveConcentration/%PgyNPpN(137 N, 10 min)Disilled water98310.46"0.583°NaB4O+ 10H2O123512360.680.4652.2519610.630.463KzBQO-SH2O1.2553089 .0.650.45522750.590.451LaCly7H2,O01715690.76.4661960.720.458●Note: results obrained under the load of 59 NTable 2 Friction and wear behaviors of compounded borates and lanthanum chlorideAditiveP%N_ PoN WSD/mm (137 N, 10 min)中国煤化工i2% NaB,O-10H20+0.5% LaCly7HO 2943089 0.582% KxBQO-5H2O+0.5% LaCI:7H2O336080 0.45MYHCNMHG592JOURNAL OF RARE EARTHS, VoL 26, No.4, Aug. 2008Fig.2 shows the elemental ditributions of boron, oxygen,tassium borate and lanthanum chloride as lube additives inlanthanum and iron on worm surfaces lubricated with waterwater contributed to reducing frction and wear.containing both potassium borate and lanthanum chloride.2.3.2 Tribochemical characteristics The tribochemicalFrom Fig.2 it can be seen that elements boron, oxygen,features of elements boron, lanthanum, iron and oxygen onlanthanum and iron are well dispersed on the wom surfaces,the wom surfaces were analyzed by X-ray photoelectronbut their contents are different. The existence of elementsSpectroscope (XPS). Shown in Fig.3 are XPS spectra ofboron and lanthanum on the surfaces demonstrated that po-boron, lanthanum, iron and oxygen on the wom surfaces lu-50 um50um50 μmFig.1l SEM images of wom surfaces(a) Sodium borate; (b) Potassium borate: (c) Sodium borate plus lanthanum chloride; (d) Potassium borate plus lanthanum chloride|(c)I| (山)Fig.2 Elemental dstribuions on wom surfaces (x500)(a)B; (b)O; (c)La; (d)Fe32[(日)20313018291728| MdW15h竹271420019519086050840 830 820Binding energy/eV6T](e43-2-11of897271070040 5352中国煤化工Fig.3 XPS specra of elements c(a) B); ()Lax; (c)Fez;:MYHCNMHGCHEN B S et al, Friction and wear performances of borates and lanthanum chloride in water593bricated with water containing both potassium borate andReferences:lanthanum chloride, respectively.From Fig.3 it can be seen that the peak of boron spectrum[1] Adams J H. Tribological performances of borates as lube addi-in (a) located at the binding energy of 192.0 eV, indicatingtives. Lubrication Engineering, 1977, 33(5): 25. .that boron existed in the form of chemical state of B2O3,. In[2] Liu W M. Xue QJ. A survey on the development of inorganicFig.3(b), the peak of lanthanum at binding energy of 835.1borates as oil aditives. Tribology (in Chin.), 1993, 13(4): 382.eV demonstrated that La2O3 was forned on the wom surface.[3] Abraham H. Molybdenum, Sulfur and Boron Containing LuIn Fig.3(c), the peak of iron at binding energy of 710.8 eVbricating Oil Composition. US Patent 6777378, 2004.indicated that iron was oxidized into FezO4 and Fe2O3. In[4]LiX M, Yang Y Y. The progress of resarch on boric com-Fig.6(d), the peaks of oxygen at binding energies of 532.7,pounds as extreme-pressure, anti-wear and friction-reducinglubricant additives. Lubrication Engineering (in Chin), 2006,533.0 and 530.0 eV correspond to its chemical states in the(9): 197.tribocbemical species of La2O3, B2O3 and FezO4 or Fe2O3,[5] Liu W M, Xue Q J. The anti-wear properties of sodium metalrespectively. From the results of XPS analysis, it can be in-borate as oil additive. Lubrication Engineering, 1992, 48(5):ferred that the anti-wear and friction reducing abilities of29potassium borate and lanthanum chloride as lube additives[6] Huang W J, Chen B s, Dong J X. Study on the tribologicalin water are atributed to the formation of a composite tri-properties of water- soluble borates. Chinese Journal of Me-bochemical reaction flm on friction surfaces mainly com-chanical Engineering (in Chin.), 2001, 37(5):18.posed of oxides of La2O3, B2O3, Fe;O4 and Fe2O3, which[7] Huang W J, Tan Y Q. Developing status of water. soluble lu-have been proven to be good friction and wear reducers.bricating aditives. Lubrication Engineeing (in Chin,), 2002,(1): 72.[8] Zhi乙, Guangqiu s, Yong w. Syothesis, hydrodytic stability3 Conclusionsand tribological properties of novel borate esters containingnitrogen as lubricant additives. Wear, 1998, (22): 135.1. Sodium borate, potassium borate and lanthanum chlo-[9] Stanulov K G, Harhara H N, An opportunity for partial rride increased extreme pressure, anti-wear and fric-placement of phosphates and dithiophosphates in EP packagestion-reducing abilities of water to a certain extent, respec-with boron containing additives. Tribology Intermational,tively, ranking in the order of KzB4O>Na2B4O>LaClz.1998, 31(5): 257.2. The extreme pressure, anti- wear and friction-reducing[10] Zhang ZF, Liu W M. PFriction and wear behaviors of the com-abilities of sodium borate and potassium borate, especiallyplexes of rare earth hexadexylate as grease additive. Wear,the latter one, could be dramatically enhanced by lanthanum1998, (215): 40.chloride.[11] Lian Y F, Yu L G, Xue Q J The efete of cerium dioxide on3. Friction sufaces lubricated with water containing boththe friction and wear properties of flame spraying nickel-basedborate and lanthanum chloride were less scratched. The ex-alloy coating. Wear, 1995, (181): 436.cellent friction and wear reduction performances of com-[12] Xue M Q, Xiong D s, Yan J. Tribological study on rare earthlubricating materials. Chinese Jourmal of Rare Metals (inpounded borates and lanthanum chloride in water were at-Chin), 2004, 28(1): 248.tributed to the formation of a composite tribochemical reac-tion flm mainly composed of oxides of La2O3, B2O3, FeyO4[13] GaoS Y, Yu L G. Progress in tibological study on rare earthlubricating materials. Chinese Rare Earths (in Chin.), 2002,and FexO3,23(6): 57.[14] Chen B s, Dong J X. Synergitic lubrication mechanism of alanthanum-boron composite lube additive. Journal of the Chi-nese Rare Earth Society (in Chin.), 1996, 14(4): 306.中国煤化工MYHCNMHG