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МЕХАНИКА. ТРАНСПОРТ. МАШИНОСТРОЕНИЕ ©
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He Zhongyi, Xiong Liping, Lu Jinliang,
Ren Tianhui, Zhang Shaoming УДК 621.89
TRIBOLOGICAL STUDY OF A TRIAZINE DERIVATIVE AS LUBRICANT IN RAPESEED OIL
1. Introduction.
During the past 20 years, there has been an increasing interest in "environmentally acceptable" lubricants in Europe and North America. Vegetable oil are potential replacements for mineral oil as base stocks for environment friendly lubricants because they have high biodegradability, low toxicity and their residues can be recycled. Meanwhile extensive effort is being made to find suitable additives that can be used in biodegradable lubricants . Zinc dialkyldithiophosphate (ZDDP) as a traditional EP and AW additive contains Zn, S and P elements which can erode the metal and result to the deposition. The research also indicates that N-containing heterocyclic compound can absorb on the surface of metal and reduce the erosion. Now we design a sort of ashless additives containing S, P, and N elements, which may have good EP, AW capacity and low erosiveness.
In this paper, a triazine derivative which containing active elements such as S, P and N was synthesized, and the tribological behavior as additive in rapeseed oil (RSO) was determined using a four-ball tester.
2. Experimental details.
2.1. base oil and additive.
The base oil in the experiment was the RSO made in Jiali Lipa Co. Ltd.Xi'an, P. R. China. The novel S-P-N type additive were synthesized by the following chemical reaction equation (see the scheme 1). The compound was further confirmed by IR and elemental analysis. The tribological
capability of ZDDP as additives in RSO was also determined as comparison.
2.2. The evaluation of their tribological properties.
The load carrying capacity of the compound in RSO was determined according to Chinese GB3142-82, similar to ASTM D2783. was used to evaluate the maximum non-seizure load, conducted at a rotation speed of 1450 rpm for a test duration of 10sec at room temperature. The friction and wear tests at ambient temperature were examined on a four-ball test machine made in Ji nan Testing Machine Factory of China, conducted at a rotation speed of 1450rpm and different loads for a test duration of 30min. All test balls (012.7mm) used in the test were made of GCr15 bearing steel (%C 0.95-1.05, %Si 0.15-0.35, %Mn 0.20-0.40, %P <0.027, %S <0.020, %Cr 1.30-1.65, %Ni <0.30, %Cu <0.25) with a hardness HRc of 59-61. A microscope was used to determine the wear scar diameters (WSD) of the three lower balls with an accuracy ±0.01mm.
2.3. The surface analysis of worn surface.
-At the end of the four-ball test, the upper
ball were cleaned in petroleum ether (60-90 and then the worn scar was analyzed by XPS while the lower one was analyzed by SEM. XPS was conducted using a PHI-5702 electrometer. The radiation source was Mg Ka line with pass energy of 29.35eV and the binding energy of C1s (284.6eV) was used as a standard value. SEM was conducted by a JEM-1200EX electrometer.
Scheme 1. Chemical reaction equation of the compound DEOP.
ИРКУТСКИЙ ГОСУДАРСТВЕННЫЙ УНИВЕРСИТЕТ ПУТЕЙ СООБЩЕНИЯ
3. Results and discussion.
3.1 Load carrying capacity.
The maximum non-seizure load values (PB value) of the additive in RSO are shown in table 1. It can be seen that DEOP possesses good load carrying capacities in RSO. The PB value of the sample containing 1.0 wt% DEOP is 95.5% higher than that of RSO, and about 48.6% higher than that of ZDDP.
Table 1
Maximum non-seizure load (PB value) of RSO and RSO containing 1.0wt% additives.
Samples DEOP ZDDP RSO
PB / N 1456.4 980 744.8
3.2. Wear and friction properties.
Fig.1 presents the relationship between the wear scar diameter (WSD) and the additive concentration. It can be found that DEOP have better antiwear property than RSO, and the WSD of oil only containing 0.5wt% additive is about 75% of that of RSO, while the effects don't change much when the concentration changes from 0.5wt% to 5.0wt%.
The relationship between WSD and friction coefficient as a function of load are shown in Fig.2.
The antiwear performance of DEOP are similar to that of ZDDP, and much better than that of the RSO. Under load 98N, all WSD is similar, but that of the oil containing 2.0wt% A is worse than others. Despite this, the WSD of lubricating oil containing additive is only about 2/3 of that of the base oil.
The friction coefficient of RSO is much higher than that of oil containing additives, but it becomes lower when the load is more than 490N,
Fig.1. Wear scar diameter (WSD) as a function of additive concentration (Load: 392N).
while that of oil containing additive is more stable, and waves in a range, and it means that the novel S-P-N type triazine derivative has reducing friction property.
3.3. The analysis results of the worn surface.
Fig.3 is the electron micrograph of the wear scar. It shows that there are many furrows in the wear scar only with RSO, while it becomes smoother when lubrication with RSO containing 1.0wt% additive DEOP. The elemental distribution on the wear scar of steel ball in the later experiment was detected using SEM. From these figures, it also can be seen that the surface film contains S and P, and the abundance of S is higher than that of P.
Table 2 is the XPS spectra determining the chemical valence of the typical elements on the worn scar of the upper ball with 2.0wt% DEOP in RSO under 392N applied load for 30min. It is seen that the binding energy of S2p is 168.8eV which corresponds to SO42-, the binding energy of N1s is 407.5eV which corresponds to NO3-, and the binding energy of P2p is 134.4eV which corresponds to PO43-. This is also supported by the
Fig.2. Wear scar diameter (WSD) and friction coefficient as a function of load (concentration: 2.0wt%).
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Fig.3. The micrograph and S, P distribution of the wear scar (294N, 30min, 1450rpm) (Left: RSO; right: RSO with 1.0wt% additive DEOP).
Table 2
Binding energy (eV) of S2p, P2p, N1s and Fe2p elements obtained from worn scar.
Binding energy (eV
C1s S2p P2p N1s Fe2p O1s
284.7, 286.4, 288.8 168.4, 161.6 134.4 407.5 710.2 533.0
binding energies of O1s being around 533.0eV. It was also found that there is FeS according that the binding energy of Fe2p is 710.2eV while the binding energy of S2p is 161.6eV. The binding energy of C1s is 284.7eV, 286.4eV and 288.8eV, which correspond to C-H, CO-, COO- existing in the additive and RSO.
According to XPS data, tribochemical reactions occur between the additives and metal surfaces during the sliding process. The mainly binding energy of N1s is about 400eV, which correspond to C-N bonds and Fe-N bond[10], which indicates that the N element in the additive structure also reacted with the metal face when it was chemisorpted and/or physisorpted in the metal surface. All of these FeS, sulfate, organosulphur compound, phosphate and N-containing compounds contribute to the formation of the complex boundary lubrication film which improves the tribological behavior of the base oil. It is also supposed that the formation of the compounds containing active elements in the boundary film on the rubbed surface is one of the reasons that DEOP as additives in RSO exhibit good load carrying capacity, good antiwar and friction-reducing properties.
4. Conclusions.
(1). DEOP possess excellent load carrying capacity even much more than traditional lubricating oil additive ZDDP at some condition in RSO.
(2) Under boundary lubrication condition, DEOP possesses excellent antiwear property
similar to ZDDP. In addition, DEOP has reducing friction property when load is lower 490N.
(3) DEOP as oil additive could form a boundary film, in which the main states of active elements are SO42-, PO43-, to provide excellent antiwear function and load carrying capacity.
Acknowledgement.
The work reported here were supported financially by Jiangxi Natural Science Foundation of China (Grant No 2007GZH0838) and Jiangxi Education Department Foundation of China (Grant No 2007184) and Science Foundation of East China Jiaotong University(Grant No 04ZKJC11, 05ZKJC15) and Doctor Foundation of East China Jiaotong University
BIBLIOGRAPHY
1. He Zhongyi, Lu Jinliang, etal, Study of the tribological behaviors of S,P-containing triazine derivatives as additives in rapeseed oil Wear 2004, 257, 389-394.
2. He Zhongyi, Xiong Liping, etal, Synthesis and tribology study of bi-alkoxy mono-thiophosphate triazine derivatives as additives in rapeseed oil Chinese Science Bulletin, 2005 50-12, 1174-1179.
3. L. Jiusheng, Z. Yanyan, R. Tianhui, Tribological evaluation of S-(1H-benzotriazole-1-yl) methyl N,N-dialkyldithiocarbamates as additives in rapeseed oil, Wear, 2002;25(3):720-724.
