Friction and Wear Behaviors of Nano-Silicates in Water

Scientific ResearchFriction and Wear Behaviors of Nano Silicatesin WaterChen Boshui; Lou Fang; Fang Jianhua; Wang Jiu; Li Jia(Dept. of Petrochemistry, Logistical Engineering University, Chongqing 400016)Abstract: Nano-metric magnesium silicate and zinc silicate with particle size of about 50- -70m were prepared in water bythe method of chemical deposition. The antiwear and friction reducing abilities of the nano-silicates, as well as their compos-ites with oleic acid tri ethanolamine (OATEA), were evahuated on a four ball fiction tester. The topographies and tibochemicalfeatures of the wom surfaces were analyzed by scanning electron microscope (SEM) and X-ray polectron spectroscope(XPS). Results show that nano silicatcis alone provide poor antiwear and friction reducing abilities in water, but exhibitsexcellent synergism with OATEA in reducing friction and wear. The synergism in reducing friction and wear between nano-silicates and OATEA does exist almost regardless of particle sizes and species, and may be atributed, on one hand, to theformation of an adsorption film ofOATEA, and, on the other hand, to the formation of tribochemical species of silico dioxideand iron oxides on the friction surfaces. Tribo reactions and tribo adsorptions of nano silicates and OATEA would producehereby an efctive composite boundary lubrication flm, which could eficienty enhance the anti-wear and fitioreducingabilities of water.Key words: nano silicate; water, oleic acid mi ethanolamine; friction; wear1 Introduction2 ExperimentalNano-particles, because of their unique physical and chemi-2.1 Preparation and characterization of nano-silicatescal behaviors, have been extensively investigated and widelyNano-silicates dispersed in an aqueous medium were pre-employed in many scientific and technological fields. In thepared by the method of chemical deposition. An 1.0 % so-past few years, an ever increasing attention has been attacheddium silicate aqueous solution and a certain amount of dis-to nano-particles used as additives for lubricating oils andpersant and pH regulators were added into a three-neckedgreasesll41. Nano-particles have been proven to be outstand-flask reactor. Henceforth, a 1.0% magnesium sulfate solu-ing in reducing friction and wear when they are formulatedtion was added dropwise into the reactor at a rate of 2 mlinto lubricating oils and greases. But unfortunately, the studyper minute at room temperature under intensive stirring.on nano-particles as lube additives for water has so far beenThereafter, a colorless transparent bydrosol solution withcomparatively less reported, although some studies havewell dispersed nano-metric magnesium silicate (hereinaftershown that nano-paricles provide exelleat anti-wear and abbreviated as sol-MgSiO,) was obtained afterfriction-reducing capacities in water's91. Indeed, intensivecentrifugation.study on nano-particles as lube additives for water is like-wise of theoretical and practical significance, not only forBy substituting magnesium sulfate solution with zinc sul-understanding their tribological behaviors in water, but alsofate solution, a hydrosol solution with well dispersed nano-for developing new water-based lubricants. The present pa-metric zinc silicate (abbreviated bereinafter as sol-ZnSiO)per aims at exploring the possibility of the in-situ prepara-could also be obtained by the similar procedures as describedtion of inorganic nano-particles in an aqueous medium andabove.understanding their friction and wear behaviors in water.The sol-MgSiO, and sol-ZnSiO, were characterized by aNano-metric magnesium silicate and zine silicate in hydro-transmission electron microscope (TEM). Figure 1 showssol solution were prepared by chemical deposition and theirthe 1中国煤化工l-ZnSiO, which dis-tribological behaviors in water were preliminarily studied. closeYHCN M H Cricles in solMgSiO,31China Petroleum Processing and Petrochemical TechnologyNo.2, June 2009obvious symergism with nano-particles MgSiO4 and ZnSiO,in resisting wear. Results listed in Table 2 also show that thedifference in wear resistance between sol-MgSiO, and sol-ZnSiO, fortified with OATEA could not be clearlydistinguished, indicating that the synergism in resisting wearprovided by OATEA and the nano-silicates was almost thesame regardless of their particle size and species.400m.20mmTo further investigate the efect ofOATEA on antiwear abili-(2(b)ties of nano-silicates in water, the antiwear abilities of differ-Figure 1 TEM images of sol-MgSiO, and sol-ZnSiO,ent contents of nan-metric magnesium silicate with OATEA(间)- 8ol-MgSiO(umit length: 40m); (b)- sol-ZnSiO,(unitwere tested. Different contents of nano-metric magnesiumlengh: 20mm)silicate were obtained by diluting a certain amount of sol-MgSiO, with various amount of dstiledl water. In the presentand sol-ZnSiO, were spherical, with the grain diameter equat-study, three quantified sol-MgSiO, samples, being 100 mLing to around 70 nm and 50 nm, respectively.apiece, was diluted with 200 mL, 500 mL and 1000 mL ofdis-tllel water, respectively. Each diluent was formulated with2.2 Friction and Wear Performancesthe addition of 1.0 % OATEA and its antiwear ability was2.2.1 Anti- wear abilites of nano-silicates in watertested on a four-ball friction tester. The antiwear performancesThe anti-wear abilities of nano-silicates in water were evalu-of diluted sol-MgSiO, are given in Table 3.ated on a four-ball friction tester. The maximum non-seizureThe results listed in Table 3 indicate that the antiwear abilityloads (P), welding loads (P) and wear scar diameters (WSD)of sol-MgSiO, fortified with OATEA was slightly reducedof sol-MgSiO, and sol-ZnSiO, were tested and compared withwith a decreasing content of nanoparticles in water.those of ditiled water, as shown in Table 1.Table 1 Anti-wear performances tested on a four-ball frictionIt can be seen from Table 1 that although sol-MgSiO, and sol-testerZnSiO, exhibited better anti-wear performances than ditilleldTest samples P，N Pp,N WSD(59N, 30min), mmDisilled water983140.46water, their anti-wear abilities are not prominent.Sol-MgSiO。118920.382.2.2 Effect of 0ATEA on anti-wear abilities of [Sol-ZnSio,127900.41nano-silicatesTable 2 Effect of OATEA on anti-wear abilities of nano-silicatesOleic acid tri ethanolamine (OATEA) is an efectiveTest samplesP,N PoN WSD(59N, 30min), mmand widely used lube additive for water-basedDistilled water+1.0 m% OATEA 530 9810.63lubricants. To examine the effect ofOATEA on anti-Sol-MgSi04+1.0 m % OATEA| 834 19610.48Sol-ZnSi04+1.0 m% OATEA883 19610.51wear performances of MgSiO, and ZnSiO,nanoparticles, OATEA was added into sol-MgSiO,Table 3 Antiwear performance of diferent contents of nan-silicateand sol-ZnSiO, respectively, and the anti-wear ca-with OATEApacities of the formulated lubricants were tested.P,N T Pp N | WSD(59N, 30min), mmTable 2 gives the anti-wear abilities tested on a four-| 100mL of sol-MgSiO, diluted wihball machine. It can be seen from the results given in 200 mL of water+1.0% OATEA784 15690.53Table 2 that by comparing the data listed in Table 2100 mL of sol-MgSiO, diluted withwith those listed in Table 1 OATEA not only could 500 mL of wate中国煤化工0.56significantly enbance the anti-wear abilities of water, 100 mL of sol-Msol-MgSiO, and sol-ZnSiO, but also could provide 1000 mL ofwatMHCNMHG0.58Scientific Research2.2.3 Effect ofOATEA on friction reducing abilities of nano-diluting 100mL of sol-MgSiO, with diferent amount of water,silicatesas mentioned before.Figure 2 shows the changes in friction coeffcients of sol- It can be seen from Figure 3 that the friction coefficients ofMgSiO, with 1.0% OATEA and sol-ZnSiO2 with 1.0% the tested samples fluctuated obviously, especially in theOATEA, respectively, in relationship to the test duration initial 900 seconds of test duration. The friction reducingunder a load of 490N.ability of nano-silicate to some degree did not depend onVariations of friction ceoffcients in relationship to testthe concentration of nanoparticles, although samples with adurations, as shown in Figure 2, indicate that the frictionlow content of nanoparticles, e.g. the sample diluted withreducing abilities of nano-metric magnesium silicate and1000 mL of water, provided excellent friction reducing ca-zinc silicate in water were comparable, although the fric-pacity in the final stage of the test duration.tion coefficient of nano-metric magnesium silicate was Figure 4 shows the friction coffcients of sol-MgSiO. withidentified to be slightly smaller in the whole range of test 1.0% OATEA in relationship with the test duration underduration.different loads.Figure 3 gives the friction ceoffcients of different con- It can be seen from Figure 4 that the friction cofficient oftents of nano-metric magnesium silicate with 1.0% OATEA nano-metric magnesium silicate in water decreased with anversus test durations under a load of 490N. Different con-increasing load, especially after about 900 seconds oftents of nano-metric magnesium silicate were obtained by testing. It can also be seen from Figure 4 that in the initial900 seconds of test duration, the friction coeffcient ofnano-metric magnesium silicate under each load seemed to.08be smaller than the value obtained after more than 900 sec-onds of testing under the same load.109|0.06 r0.04601 9011201 1501 18010.07Duration, s- 294NFigure2 Friction coffcients of nano silicates with 1.0%一490NOATEA is duration-830N0050190100Duration,sFigure 4 Friction coefficients of sOl-MgSiO vs. duration under0073 Tribological Mechanisms: dluted with 100 mL ofwaterdilated with 200 mL. ofwaterdiluted with 500 mL of water3.1 Surface Topographydiluted wih 1000 mL ofwater0.0530601 9Figure 5 shows the SEM images of worm surfaces lubricatedwith sol-MgSiO. containine 1.0% OATEA and with pureFigure 3 Friction coeffients of dfferent contents ofwater中国煤化工ctively, under a loadsol-MgSiO, vsS test durationYHCNMHG3:China Petroleum Processing and Petrochemical TechnologyNo.2, June 2009gen and carbon - - on the worm surface were analyzed by X-ray photoelectron spectroscopy (XPS). The XPS spectra ofsilicon, iron, oxygen and carbon on the worm surface lubri-cated with sol-MgSiO, containing OATEA under a load of490N for 30 minutes are presented in Figure 6, respectively.(a(bIt can be seen from Figure 6(a) that the peak of silicon spe-Figure 5 SEM images of worn surfacestrum located at a binding energy of 103.6 eV, indicated that(8)- Surface lubricated with sol-MgSiO,+OATEA;(b)- Surfacesilicon existed on the surface in the form of chemical statelubrcated with water+OATEAof SiO2 In Figure 6(b), the peak of iron at a binding energyItcan be sen from Figure s that the wom srt.c lbricaed of 710.8 eV indicated that iron was oxidized to Fe,O, andwith sol-MgSiO, containing OATEA was much smootber than Fe,O, In Figure 6(), the peak of oxygen at a binding en-that lubricated with pure water containing OATEA, on whichergy of 533.0 eV corresponded to the chemical state ofsevere wear scars could be ientified. The smooher wom orxygen in sio, Fe,O。and Fe,O, In Figure 6(d), the peak ofsurface lubricated with sol-MgSiO containing OATEA wellcarbon at a binding energy of 285.0 eV demonstrated thatcoincided with the results that nano-silicates and OATEAorganic alkyl compounds were formed, which were resultedcould provide excellent synergism in reducing friction and from the adsoptions or reactionos of OATEA on the rubbedwear in water.surfaces.3.2 Tribochemical FeaturesIt can be learned from the results of tribological tests andThe tribochemical species of elements一silicon, iron, oxy- suface analyses that the excellent anti-wear and friction re-M1010595974030720Binding energy, eV(间) Silicon, Si,(b) lron, Fe,wmwwmwwM540535535255202952928528027中国煤化工(E)Oxygmn,O,Figure 6 XPS spectra of elements 0JYHCNMHG34Scientific Researchducing capacities of nano silicates in water were closely re- Acknowledgements: The present study is supported by thelated to the presence of a surface active agent, e.g. OATEA. National Natural Science Foundation ofChina No.50275147)The friction and wear reducing mechanisms of nano-sili- and the Program for New Century Excellent Talents in Chi-cates formulated with OATEA in water can be mainly attrib-nese University No. NCET-04-1002).uted on one hand to the formation of a boundary lubricationfilm due to physical and chemical adsorptions ofOATEA onReferencesthe friction surfaces, and on the other hand to the formation[1] Hsu s M. Nano-lubrication: concept and design[]. Tribologyof SiO, derived from tribochemical reactions of nano-Intemnational, 2004, 37(7): 537-545silicates. Superfine SiO2 particles have been proven to be[2] Hudson L K, Eastoe J, Dowding P J. Nanotechnology in action:effective in reducing friction and wear, thanks to their ac-Overbased nano detergents as lubricant oil aditivs[]. Advances intion as“micro-rollers" between friction pairs [1011. 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