J. Marine. Sci. Appl. (2009) 8: 71-76 DOI: 10.1007/s11804-009-8008-1

Tribological effects of oxide based nanoparticles in lubricating oils GU Cai-xiang*, ZHU Guan-jun, LI Lei, TIAN Xiao-yu and ZHU Guang-yao Merchant Marine College, Shanghai Maritime University, Shanghai 200135, China Abstract: In order to enhance the tribological properties of lubricating oil, suitable surfactants such as Tween-20, Tween-60, Span-20 and Sodium sodecylbenzenesulfonate were selected and lubricating oils containing CeO2 and TiO2 nanoparticles were prepared. The morphology and size of CeO2 and TiO2 nanoparticles were examined with a transmission electron microscope (TEM). The tribological properties of the oils were tested using an MRS-1J four-ball tribotester. The research results show that when the proportion by weight of CeO2 nanoparticles to TiO2 nanoparticles is 1:3, and the total weight fraction is 0.6%, the lubricating oil has optimal anti-wear and friction reducing properties. The addition of CeO2 nanoparticles reduces the required amount of TiO2 nanoparticles. Keywords: nanoparticles; surfactants; lubricating oil; tribological properties Document code: A Article ID: 1671-9433(2009)01-0071-06 CLC number: TE626.3

1 Introduction 1 With the rapid development of marine diesel engine to new and large models, the consumption of fuel oils has been considerably increased whereas the economic effectiveness decreased, the operation cost of ship company has been increased correspondingly. So the inferior fuel oils are used in many marine diesel engines to enhance the economic effectiveness. However the use of inferior fuel oils has inevitably put a higher demand for the quality of lubricating oils in the process of the design and the management of marine engine. The lubricating oils are the blood of the machine’s operation, and the service life and economic effectiveness of the machine are relative to the quality, performance and reasonable use of the oils[1-2]. Nanoparticles put into lubricating oils can improve the properties of extreme pressure, anti-wear and friction reducing. Efficiency and service life of the machine were also improved[3]. In recent years, many scientific researchers have dedicated themselves to studying lubricating oil additives as an important project. These lubricating oil additives have good properties of anti-wear, friction reduction and high load-bearing capability. In addition, they can fill in and repair the worn surfaces with environment-friendly characteristics[4]. The lubricating oils containing CaCO3 nanoparticles were prepared. They have good properties of extreme pressure, anti-wear and friction reducing[5]. The lubricating oils containing the combination of CaCO3 nanoparticles and Received date: 2008-03-11. Foundation item: Supported by the Shanghai Municipal Education Commission(06FZ008); Shanghai Municipal Education Commission Key Disciplines(J50603). *Corresponding author Email: [email protected]

rare earth nanoparticles were prepared too; they have better properties of anti-wear and friction reducing than that containing only one kind of nanoparticles[6]. These lubricating oils containing nanoparticles as mentioned above have been patented. In this research, the combination of CeO2 and TiO2 nanoparticles was put into the lubricating oils for further studying the effect of the combination of different nano-materials as additives in the lubricating oils. It is of theoretical and practical significance to expanding the application range of nanoparticles and to further understanding the mechanism of nanoparticles as additives in the lubricating oils.

2 Experimental study 2.1 Selection and measurement of nanoparticles CeO2 is a kind of light rare earth oxide. The CeO2 nanoparticles have good properties of wear resistance, chemical erosion resistance and good polishing effect as abrasive[7]. Some researchers discovered that CeO2 nanoparticles could restrain the reunification among particles and strengthen the stability of nanoparticles in the organic liquid phase[8]. Shao Xin[9] et al discovered that TiO2 nanoparticles filled to poly (phthalazine ether sulfone ketone) (PPESK) composite materials could remarkably improve the tribological properties. The structure, shape and diameter of nanoparticles play an important role in the lubricating oils as additives. In

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GU Cai-xiang, et al. Tribological effects of oxide based nano-particles in lubricating oils

this paper, the morphology and size of CeO2 nanoparticles and TiO2 nanoparticles were examined by Hitachi H-600 Transmission Electron Microscope (TEM). The detailed measurement methods were given in the references[10]. 2.2

Preparation of lubricating oils containing nanoparticles In order to make CeO2 nanoparticles and TiO2 nanoparticles evenly disperse in the lubricating oils, Tween-20, Tween-60, Span-20 and Sodium sodecylbenzenesulfonate were selected. The nanoparticles were treated by these surfactants. The steps of preparing the lubricating oils containing combination nanoparticles are as follows: 1) Evenly mix Tween-20, Tween-60, Span-20 according to the weight proportion of 2:2:1. 2) Adequately blend the mixture above-mentioned with Sodium sodecylbenzenesulfonate according to the weight proportion of 5:1, then add the combination of CeO2 nanoparticles and TiO2 nanoparticles in the mixture (The weight proportions of CeO2 nanoparticles and TiO2 nanoparticles are 0:1, 1:1, 1:2, 1:3, 1:4, 3:1, 2:1, 1:0, respectively). Blend the mixture in electrothermal constant temperature water bath spot for 10 minutes at 70~80℃. 3) Put the nanoparticles treated by surfactants into 500SN base oil (the weight fractions of nanoparticles in the oil are 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, respectively), then put the mixture into the KQ218 ultrasonic vibration instrument to vibrate for 20 minutes so as to disperse the nanoparticles adequately. 4) Put the mixture into the H97-A constant temperature magnetic force mixer, and stir it for about 2 hours at 85℃ while revolutionary speed is 1 300 r/min. Repeat the step 3) and step 4) for many times, the dispersion and stirring time are determined according to the content of nanoparticles. In this paper, 40 kinds of lubricating oils were prepared, according to different weight fractions and different weight proportions of CeO2 nanoparticles and TiO2 nanoparticles. 2.3 Tribological properties of lubricating oils containing nanoparticles The maximum non-seized load PB was examined by MRS-1J four-ball tribotester produced by Jinan Shijin Group Co., Ltd. according to GB/T12583-1998, and wear

spot diameters D of steel balls and friction coefficients μ of lubricating oils were measured and calculated after running for an hour under the load of 392 N. The diameter of the steel ball (GCr15) is 12.7 mm (0.5 in.), and the grade is 25 EP (super light). The steel balls were provided by Shanghai Danan Chemical Grease Co., Ltd. Wear spot diameters D were measured by 15 J microscope produced by Shanghai No.5 Optical Instrument Factory. Wear scar morphology photographs were shot by XTZ-D/E continuously multiple microscope taking CCD visible probe.

3 Results and discussion 3.1

Morphology observation and diameter measurement of nanoparticles Morphology and diameter of nanoparticles were observed and detected by TEM. Fig.1 shows that the shape of CeO2 nanoparticles is spherical and the average diameter measured is about 10.4 nm, while the shape of the TiO2 nanoparticles is grain and the average diameter measured is about 15.2 nm. The shapes of these two kinds of nanoparticles are all uniform and equiaxed. 3.2

Tribological properties of lubricating oils containing nanoparticles Tribological properties of oils are shown in Table 1, Table 2 and Table 3. Wear scar morphology of 500SN base oil and lubricating oils containing nanoparticles are shown in Fig.2. Tables 1~3 show that the properties of extreme pressure, wear spot diameters, and friction coefficients of lubricating oils containing nanoparticles have been considerably improved, compared with 500SN base oils (PB is 362 N, wear spot diameter D is 0.72 mm, friction coefficient μ is 0.124 0). In the case of adding single type of TiO2 nanoparticles into 500SN base oils, the best tribological properties can be obtained when the weight fraction of TiO2 nanoparticles is 0.8%. However, in the case of adding TiO2 nanoparticles and CeO2 nanoparticles into 500SN base oils, only when the weight proportion and the weight fraction of nanoparticles are appropriate can the combination lubricating oils achieve best properties of anti-wear and friction reducing. When ω (CeO2): ω (TiO2)=1:3, ω (CeO2+TiO2)=0.6%; PB can reach 510 N, D reaches a minimum 0.448 mm and μ also reaches a minimum 0.0774. Compared with 500SN base oil, PB is increased by 40.8%. Wear spot diameter D is decreased by 37.7%, and friction factor is decreased by 37.6%. It indicates that the addition of CeO2 nanoparticles can reduce the required amount of TiO2 nanoparticles.

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(a) CeO2 nanoparticles 100000× (b) TiO2 nanoparticles 100000× Fig.1 TEM morphology of nanoparticle Table 1 The maximum non-seized load of lubricating oils containing combination nanoparticles

ω(CeO2 ):ω(TiO2 )

ω(CeO2+ TiO2 ) /% 0.2 0.4 0.6 0.8 1.0

ω(CeO2+ TiO2 ) /% 0.2 0.4 0.6 0.8 1.0

0:1 431 461 461 490 490

1:1 431 461 461 490 490

1:2 431 461 490 490 461

1:3 431 461 510 461 461

1:4 431 461 490 461 461

3:1 431 461 461 490 461

2:1 461 490 490 461 490

Table 2 The wear spot diameters of lubricating oils containing combination nanoparticles ω(CeO2 ):ω(TiO2 ) 0:1 1:1 1:2 1:3 1:4 3:1 2:1 0.684 0.661 0.621 0.572 0.703 0.653 0.626 0.571 0.647 0.562 0.497 0.598 0.610 0.571 0.515 0.624 0.512 0.448 0.498 0.586 0.537 0.498 0.598 0.481 0.490 0.554 0.553 0.552 0.558 0.614 0.542 0.522 0.631 0.579 0.587

1:0 461 461 461 461 461

1:0 0.682 0.663 0.639 0.678 0.690

Table 3 The friction coefficients of lubricating oils containing combination nanoparticles

ω(CeO2 ):ω(TiO2 )

ω(CeO2+ TiO2 )

/% 0.2 0.4 0.6 0.8 1.0

0:1 0.113 2 0.101 3 0.085 9 0.079 7 0.099 0

1:1 0.101 8 0.099 6 0.096 1 0.091 6 0.100 1

1:2 0.109 2 0.099 0 0.087 6 0.079 1 0.101 3

1:3 0.089 9 0.083 0 0.077 4 0.083 0 0.093 3

1:4 0.108 1 0.104 7 0.093 3 0.098 4 0.101 8

3:1 0.104 1 0.092 2 0.080 8 0.076 2 0.089 9

2:1 0.112 6 0.101 3 0.091 8 0.101 8 0.101 8

1:0 0.113 2 0.103 3 0.092 2 0.099 0 0.104 1

GU Cai-xiang, et al. Tribological effects of oxide based nano-particles in lubricating oils

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(a) 500SN base oils

(b) ω(CeO2+ TiO2 )=0.2%,ω(CeO2 ):ω(TiO2 )=1:4

(c) ω(CeO2+ TiO2 )=0.6%,ω(CeO2 ):ω(TiO2 )=1:3 (d) ω(CeO2+ TiO2 )= 1.0%,ω(CeO2 ):ω(TiO2 )=1:3 Fig.2 Wear scar morphology of oils (100×)

Fig.2 shows that wear spot morphology of 500SN base oils is extremely not round, and severe adhesive wear and tearing trace can be seen obviously. The wear scars are deeper and wider as shown in Fig.2(a). When the CeO2 and TiO2 nanoparticles were put into the lubricating oils, wear scars have been greatly improved. They are shallower and narrower and have no tearing trace. The wear spot is round and the wear scar is flat as shown in Fig.2(b). These indicate that the nanoparticles have good properties of anti-wear and friction reducing. When ω (CeO2): ω (TiO2) ＝ 1:3, ω (CeO2+TiO2)=0.6%, the wear spot is more round and more flat than any other wear spots. The wear scar is shallow and thin and the wear spot diameter is the minimum as shown in Fig.2(c). But when the weight fraction of CeO2 nanoparticles and TiO2 nanoparticles is 1.0%, wear scar becomes deeper and wider; moreover, the wear spot becomes big and not round as shown in Fig.2(d). It shows that overmany nanoparticles result in reunification among nanoparticles and reducing the effects of anti-wear and friction

reduction. Tribological properties experiments and wear scar morphology observation show that properties of anti-wear and friction reducing of CeO2 nanoparticles and TiO2 nanoparticles are subjected to two factors, weight fraction and weight proportion. On the one hand, the weight fraction should be appropriate to make sure there are enough nanoparticles spreading on the friction surfaces; on the other hand, the proportion of CeO2 nanoparticles and TiO2 nanoparticles should be equally appropriate. Whenω(CeO2 ):ω(TiO2 )＝1:3, ω(CeO2+ TiO2 )=0.6%, the optimal tribological properties can be obtained. In addition, the experimental results show that the weight proportion of surfactants is that Tween-20:Tween-60:Span-20:Sodium sodecylbenzenesulfonate=2:2:1:1, the combination surfactants have better dispersing and stable effects on CeO2 nanoparticles and TiO2 nanoparticles. The reason may be that surfactants and nanoparticles form

Journal of Marine Science and Applicaton (2009) 8: 71-76

microcapsule. In addition, the experimental results also show that the addition of CeO2 nanoparticles can reduce the required amount of TiO2 nanoparticles. To sum up, the study on tribological properties of the combination of CeO2 nanoparticles and TiO2 nanoparticles used as additives in the lubricating oils indicates that they can improve base oil’s properties of extreme pressure, anti-wear and friction reducing. The application of the combination of CeO2 nanoparticles and TiO2 nanoparticles in the lubricating oils plays an important role in improving and reforming the traditional lubricating techniques of marine diesel engines. The lubricating oils containing CeO2 nanoparticles and TiO2 nanoparticles have the characteristics of being simple to prepare, technologically feasible and remarkably effective, which have significant influences on promoting the lubricating performance and prolonging the service life of marine diesel engines.

4 Conclusions 1) The weight proportion of surfactants is that Tween-20:Tween-60:Span-20:Sodium sodecylbenzenesulfonate=2:2:1:1, the combination surfactants have better dispersing and stable effects on CeO2 nanoparticles and TiO2 nanoparticles. 2) Whenω(CeO2 ):ω(TiO2 )=1:3, ω(CeO2+TiO2)=0.6%, lubricating oils containing combination nanoparticles have the optimum effects of anti-wear and reducing friction. 3) The adding of CeO2 nanoparticles can reduce the required amount of TiO2 nanoparticles.

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Maritime University Press, 2003, 147-150(in Chinese). [6] GU Caixiang, GU Zhuoming, CHEN Zhigang, et al. Study on application of environmentally friendly nanoparticles as additives in lubricating oils[J]. Journal of Yunnan University (Natural Sciences), 2005, 27(3A): 20-24(in Chinese). [7] YANG Ru, LIU Jianhong, LI Ming. Synthesis of mesoporous ceria using a non-surfactant template approach[J]. Journal of the Chinese Rare Earth Society, 2004, 22(6):739-744(in Chinese). [8] DOU Lixin, GONG liehang, SHEN Jian, et al. Restriction mechanism of nano rare earth compounds to aggregation of ultrafine particles[J]. Journal of the Chinese Rare Earth Society, 2003, 21(Suppl.):67-73(in Chinese). [9] SHAO Xin, TIAN Jun, LIU Weimin, et al. Friction and wear properties of nanometer TiO2 particle-filled poly (phthalazine ether sulfone ketone) composite[J]. Polymer Materials Science and Engineering, 2003, 19(3):208-210(in Chinese). [10] ZHANG Lide. Preparation and application technology of super powder[M]. Beijing: China Machine Press, 2001: 238-239(in Chinese). GU Cai-Xiang was born in 1964. She is a PhD candidate, and an associate professor. Her current research direction: material science and tribology.

ZHU Guan-Jun was born in 1962, and he is a master. His current research direction: material science and tribology.

TIAN Xiao-Yu was born in 1986, and he is a graduate student. His current research direction: material science and tribology.

References [1] STEPHEN M H. Nano-lubrication: concept and design[J]. Tribology International, 2004, 37(7): 537-545. [2] SHAKVOROSTOV D, POHLMANN K, SHERGE M. An energetic approach to friction, wear and temperature[J]. Wear, 2004, 257(1/2): 124-130. [3] QIN Min, CHEN Guoxu, GAO Yongjian. Research process of nano-lubricating additives[J]. Synthetic Lubricants, 2001(4): 9-14(in Chinese). [4] BAKUMIN V N, SUSLOV A Y, KUZMINA G N, et al. Synthesis and application of inorganic nanoparticles as lubricant components review[J]. Journal of Nanoparticle Research, 2004, 6: 273-284. [5] GU Caixiang, GU Zhuoming, WANG Renbing, et al. Study on anti-wearing and friction reducing properties of lubricating oils containing CaCO3 nanoparticles[C]// Modern Ship-Repairing Technology. Dalian: Dalian

ZHU Guang-Yao was born in 1981, and he is a graduate student. His current research direction: material science and tribology.

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氧化物纳米粒子在润滑油中的摩擦学作用 顾彩香，朱冠军，李

磊，田晓禹，朱光耀

（上海海事大学 商船学院，上海 200135） 摘

要：为了提高润滑油的摩擦学性能，选择了吐温-20、吐温-60、司本-20、十二烷基苯磺酸钠作为表面活性剂，制备

了含纳米CeO2和TiO2粒子添加剂的润滑油. 采用透射电子显微镜（TEM）观察、测定了纳米CeO2和TiO2粒子形貌和平均 粒径. 采用MRS-1J四球摩擦磨损试验机测试了含纳米CeO2和TiO2添加剂的润滑油的摩擦学性能. 结果表明，纳米CeO2和 TiO2的复合粒子的最佳添加量为：ω(CeO2):ω(TiO2)=1:3, ω(CeO2+TiO2)=0.6%，该润滑油具有最佳的抗磨、减摩性能. 纳 米CeO2粒子添加可以适当减少纳米TiO2粒子的用量. 关键词：纳米粒子；活性剂；润滑油；摩擦学性能