ApplicationofNanotungstenDisulfideParticulatesinGreenMotorOil.doc

1、application of nano-tungsten disulfide particulates in green motor oilapplication of nano-tungsten disulfide particulates in green motor oil*shi chen, mao da-heng(school of mechanical and electrical engineering, central south university, changsha 410083, china)20 abstract: green motor oil is easily

2、oxidized and loses its good antiwear properties, in order to solve this problem and lengthen the service lifetime of green motor oil. nano-tungsten disulfide particulates whose surfaces had been treated are applied in green motor oil. tribology properties of the oils were tested in four-ball machine

3、. the results showed that nano-tungsten disulfide could improve the base oils anti-friction, anti-pressure, and anti-wear property obviously, also make the oxidized base oil under high temperature still keeping good anti-wear properties. lubricating mechanism of tungsten disulfide in oil was discuss

4、ed through auger electron energy spectrum analysis and depth analysis, using phi550eaca/sam electron energy spectrum instrument and its incidental argon ion sputter technology. the results showed that the nano-tungsten disulfides lamina structure, the adsorption film, and fes film formed on the fric

5、tion surface can reduce the friction surfaces abrasion observably. finally, a full formulated green motor oil including nano-tungsten disulfide was prepared, after contrast study with the famous motor oil overseas, the results showed that the green motor oil prepared had better anti-wear, anti-frict

6、ion, anti-pressure property and property of viscosity versus temperature.key words: tungsten disulfide particulates; green motor oil; lubricating mechanism*acknowledgements: the work was supported by huajing powder material science & technology co. ltd and key laboratory of tribology and lubrica

7、tion of nonferrous metals of china, and the fund of mittal steel scholarship at csu (no. 07mx02).corresponding author: shi chen (1982- ), male, ph.d., candidate; research fields: tribology and lubrication. e-mail: shichenmail.1. introductionnowadays, considered as the blood of automobile industry, m

8、otor oil has been advancing with the development of automobile industry. in the developed country, the wastage of motor oil occupies 50% of that of all the lubricating oil. therefore, the research and development of motor oil has become the most interesting item in the lubricating oil industry. howe

9、ver, most of traditional motor oils base oil are mineral oil, and because of leakage using, motor oil inevitably enter the environment directly, while the mineral motor oil has bad biodegradability and its accumulation in environment will pollute the ecological environment. by report, about (500-100

10、0)×104 t petroleum chemical substances enter the biosphere all over the world every year, even though in the countries those have high reprocessing and utilization ratio of lubricant (>60%), there still are 4%-10% lubricant entering environment, which endanger our living environment badly1,2

11、. therefore, most of the petroleum corporations start to develop environment friendly green motor oil, instead of the traditional mineral motor oil.at the same time, for the increasingly lacking petroleum resource, engine technology is developing towards the direction of mixed fuel engine. when the

12、fuels burning inside the engine will be sufficient increasingly and the work temperature inside the engine will increase3,4, which will call for higher high temperature performance of motor oil. but most of the green motor oils have unsaturated bonds in their components, which lead to the green oils

13、 easy oxidation under high temperature and shorten their service lifetime. so in course of developing green motor oil, improving the antioxidation under high temperature is the uppermost problem.presently, the researchers in overseas and in china have done lots of jobs in the way of developing high

14、temperature antioxidation or change the structure base oil to improve the high temperature antioxidation of green motor oil. and some researchers added solid lubricating materials into the oil to lengthen the service lifetime of motor oil under high temperature. for example, the petrolmoly company i

15、n america prepared a new type of motor oil named petrolmoly, which contains the solid lubricative grain molybdenum disulfide, after traffic test, the results showed that compared with traditional motor oil, petrolmoly could decrease the nox emission by 73% and decrease the oil wastage by 37%, increa

16、sing the fuel economy by about 10%. now petrolmoly has been set down as one of the 125 items of new technology and new product which are recommended to the member countries by un5,6.tungsten and molybdenum both are the vib subgroup elements with the same chemical property. as a new kind of solid lub

17、ricative material, tungsten disulfide also has excellent lubricating properties, but because of the high price, its mostly used as the type of solid film lubrication in the field of spaceflight aviation and military affairs. presently, some researchers used the tungsten disulfide particulates in hig

18、h temperature lubricating grease in china, and got excellent effect7, but few researchers used the tungsten disulfide as the additive of green motor oil overseas and none in china8.in course of preparing high property green motor oil, our research group tried to apply nano-tungsten disulfide particu

19、lates to green motor oil, and have obtained good effect, the addition of nano-tungsten disulfide particulates improved the anti-pressure properties and antiwear properties remarkably, and was able to keep the oils good antiwear properties even when the base oil had lost its primary excellent lubrica

20、ting properties for the oxidation under high temperature. after series of concoction experiments and formula optimization, our research group prepared a kind of fully formulated green motor oil including nano-tungsten disulfide particulates, and finished the contrast research of the prepared motor o

21、il and the foreigner famous motor oil. the results show that the prepared motor oil has better anti-wear, anti-friction, anti-pressure property and property of viscosity versus temperature, compared with the foreigner famous motor oil.2. experimental2.1 experimental materials2.1.1 base oilbase oil u

22、sed was concocted with several kinds of biodegradable green lubricating oil, such as vegetable oil, synthetical ester, synthetical hydrocarbon, whose basal physics parameters are shown in table 1.table 1 basal physics parameters of base oilitemsparameterpour point/-17flash point/290fire point/310she

23、et copper causticity1 classkinematic viscosity/mm2·s-1:4047.251008.72viscosity index1422.1.2 tungsten disulfidetungsten disulfide doesnt dissolve in water, oil, alcohol, grease and other organic impregnants, and doesnt dissolve in ecumenic liquors of acid or alkali, except nitric acid, hydroflu

24、oric acid and the admixture acid of nitric acid and hydrochloric, whose oxygenation abilities are strong. in the atmosphere, tungsten disulfide will be disassembled at 510 and oxygenized rapidly at 539. it can be lubricative for a long time below 425. in vacuum, its disassembly temperature is 1150.

25、tungsten disulfides intensity of antipressure is 21 mpa. tungsten disulfides radio resistance is better than that of graphite and molybdenum disulfide. it has nicer lubricating capabilities, not only applicable to the usual lubricative condition, but also to the rigorous work environment, such as hi

26、gh temperature, high pressure, high vacuum, high load, radioactive and mordant medium9. basal physics parameters of tungsten disulfide used are shown in table 2. the nano-tungsten disulfide particulates are from huajing powder material science & technology co. ltd in changsha of china.table 2 ba

27、sal physics parameters of tungsten disulfideitemsparameterrelative molecular mass247.9density/g·cm-37.4-7.5heat stability/425crystal structurecrystal lattice with six squarescolour and lustregray with lustermohs hardness1-2grain diameter/m0.1for the nano-tungsten disulfide particulates have the

28、 characteristics of small grain size, large surface area, and high surface energy. its very easy for the particulates to agglomerate spontaneously, and stop the oil circuit system. in order to disperse the tungsten disulfide particulates in the base oil well-proportionately, the surfaces of tungsten

29、 disulfide particulates are embellished by surface treating additives and dispersant, then added into the base oil, obtaining a kind of tungsten disulfide suspending oil10, namely tungsten disulfide oil.2.1.3 contrast materialsmolybdenum disulfide (average grain diameter, surface treatment method an

30、d the formulated mode of molybdenum disulfide oil preparation are the same with tungsten disulfide); shell helix ultra motor oil.2.1.4 function additivesconsidering the requirement of environment protection and energy saving, the function additives with low phosphorus, low sulphur and low ash are us

31、ed, including detersive, dispersantm antioxidant, anticausticon, antipressure and antiwear agent, antirust, pour inhibitor and kilfoam. 2.2 experimental instrument(1) mrs-10a type four-ball machine produced by tsinan experiment machine factory, and the steel balls used are gcr15 bearing steel balls

32、(12. 7 mm) which accord with nation standard ii, whose rigidities are hrc59;(2) electrical resistance furnace;(3) dmi 5000m metallographic microscope, made in leica camera ag;(4) phi550eaca/sam multifunction electron spectrometer, made in perkin-elmer.2.3 experimental method(1) the oil film strength

33、 (pb) and sintering load (pd) of base oil, tungsten disulfide oil and molybdenum disulfide oil were measured by mrs-10a four-ball machine, and their worn spots and variations of friction coefficient with time were tested under 392n, 1450 r/min and 30 minutes. then the worn spots appearances were obs

34、erved and recorded by dmi 5000m metallographic microscope.(2) considering the easy oxidation of base oil under high temperature, while tungsten disulfide can be lubricative for a long time below 425, our research group heated respectively the base oil and tungsten disulfide oil under 250 for 12 hour

35、s in the electrical resistance furnace, and measured each heated oils worn spot diameter tested under the situation of 392 n, 1450 r/min and 30 minutes on four-ball machine, and then observed and recorded the worn spots appearances by dmi 5000m metallographic microscope.(3) in order to research the

36、lubricating mechanism of tungsten disulfide, the balls surfaces which were lubricated by tungsten disulfide oil and had been tested under 392 n,1450 r/min and 30 minutes, were washed by ligarine, and then done auger electron energy spectrum analysis on phi550eaca/sam multifunction electron spectrome

37、ter, analyzing the existent elements on the surfaces, where the analysis situation is as follows: sample rooms vacuum degree is 10-5-10-6pa; the once electron beams voltage of electron guns excitation source (ep) is 3 kv, and its current (ip) is 1µa. then the worn spots surfaces were sputtered

38、by argon ion using multifunction electron spectrometers incidental argon ion sputter technology, analyzing the depth distributing of each element inside the surface, where the analysis situation is as follows: argon ion measuring voltage is 3 kv, and the sputter current is 100 µa/cm2, diameter

39、area of ion guns beam spot is 1mm×1mm, standardized by ta2o5, when the sputter speed is 10 nm/min, the spectrum was recorded by the alternant method of argon snick and data gather, and collected and treated by phi pc-ex-plorer soft, quantitative analyzed by phi multpak soft, which provides the

40、susceptivity gene of elements directly.(4) finally, a fully formulated green motor oil including nano-tungsten disulfide were prepared, and its oil film strength, sintering load, worn spot and variation of friction coefficient with time under 392 n,1450 r/min and 30 minutes were tested on four-ball

41、machine, then they were compared with those of shell helix ultra motor oil.2.4 experimental results and analysistable 3 shows the anti-pressure and anti-wear property parameters contrast of three kinds of oil. in the table, it can be seen that adding tungsten disulfide or molybdenum disulfide doesnt

42、 improve the oil film strength of base oil, but improves the sintering load by 33%, and decreases the worn spot diameter remarkably. furthermore, seen from the contrasting of tungsten disulfide and molybdenum disulfide, tungsten disulfides adding acts a more import part in reducing abrasion, that is

43、 to say, tungsten disulfide has better abilities of improving base oils antiwear properties.table 3 anti-pressure and anti-wear property parameters contrast of three kinds of oilitemsbase oiltungsten disulfide oilmolybdenum disulfide oilpb/n696696696pd/n147019601960worn spot diameter/mm0.4920.4500.4

44、77fig. 1 shows the variation of friction coefficients of three kinds of lubricating oil with time under 392 n. from the curves variation, when lubricated by base oil, the friction pairs friction coefficients rises with time remarkably, which indicates that the organic molecules in base oil generate

45、friction decomposition, which increases the tiny protruding bodies of friction pairs direct contact and largen the real contact area, leading to the increase of friction coefficient of friction pairs. when lubricated by tungsten disulfide oil, the rising phenomenon of friction pairs friction coeffic

46、ients with time is not obvious, maybe it results from the effect of generated adsorption film and friction chemistry reaction film in friction process. molybdenum disulfide oil has the similar variation with tungsten disulfide oil, but from the variation trends of the two curves, when lubricated by

47、molybdenum disulfide oil, the friction pairs friction coefficient rises obviously in the end, maybe thats because in the end of friction period the temperature between friction pairs rose remarkably, which led to the decomposition of the film formed by molybdenum disulfide oil and made it lose its g

48、ood antiwear properties. it also indicates that the high temperature-resistant property of molybdenum disulfide is worse than that of tungsten disulfide, and so does the worn spot diameter contrasting in table 3.fig. 1 variation of friction coefficients of three kinds of lubricating oil with time un

49、der 392 nfig. 2 and fig. 3 show respectively the surfaces of worn spots lubricated by base oil or tungsten disulfide oil in normal temperature and base oil or tungsten disulfide oil heated under 250. in fig. 2, the worn spot diameter of base oil is big, on which there are many furrows, but the worn

50、spot diameter of tungsten disulfide oil is small, without any obvious furrows, it can be guessed that fatigue wear and friction burn occur between the friction pairs, and the surfaces of friction pairs are blocked off by friction reaction film and adsorption film. (a) base oil(b) tungsten disulfide

51、oilfig. 2 surfaces of worn spot of steel balls lubricated by base oil and tungsten disulfide oil under normal temperature, tested under 392 n for 30 minutesin fig. 3, after heated under 250 for 12 hours, the base oil is oxidized obviously, so on its worn spot surface, there are many obvious furrows,

52、 and besides, there are some obvious desquamation spots of metal, it can be inferred that tiny cutting and adhesion abrasion occur between the friction pairs, however on the worn spot lubricated by tungsten disulfide oil, there still not any obvious furrows, and only its diameter increases a little,

53、 consequently, even when the base oil is oxidized, tungsten disulfide can form the films on the friction surfaces and reduce the abrasion effectively.consequently, nano-tungsten disulfide particulates can improve the anti-pressure properties and antiwear properties remarkably, and make the oil keep

54、good antiwear properties even when the base oil have been oxidized under high temperature. furthermore, as the similar solid lubricating material, tungsten disulfide has better abilities of improving base oils antiwear properties than molybdenum disulfide.(a) base oil(b) tungsten disulfide oilfig. 3

55、 surfaces of worn spot of steel balls lubricated by base oil and tungsten disulfide oil which have been heated under 250 for 12 hours, tested under 392 n for 30 minutes3. lubricating mechanism discussionour research group have researched and discussed the lubricating mechanism of tungsten disulfide,

56、 from the way of structure analysis and the analysis of worn spot surface formed in rubbing.fig. 4 shows the microcosmic appearance and crystal structure of tungsten disulfide, it can be seen that tungsten disulfide colloidal particulate is lamellar structure, bedding surface is so smooth, length an

57、d breadth size are much greater than thickness, slipping occurs easily between layers; tungsten disulfide crystal is a cell layer that is made up of three s-w-s plane layers, inside which each tungsten atom is surrounded by the sulfur atoms distributing like diamond, linked with each other by strong

58、 covalent bond. the atoms of crystal form the regular hexagon syngony, and buildup reticulation plane structures, which are superposed again and become the layer structure like sandwich, and each layer is linked by vanderwaals force. this weak binding force is easy to be sheared on the middle of layers11,12. (a) particulates microcosmic appearance(b) crystal structurefig. 4 structure of tungsten disulfideconsequently, the tungsten disulfides structure shows that during the lubricating process between friction pair, tungsten disulfide has the characteristic of low friction co