Interesting paper on nanoparticles in engine oil

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Originally Posted by edwardh1
Needs a 200 word summary


8. Conclusions
The tribological performance of industrially produced WS2 nanoparticles was studied in this part of this
work. The results showed that these nanoparticles (as those produced at the laboratory scale) have
interesting friction reduction and anti-wear properties when tested in PAO base oil in the boundary
lubrication regime, at room and 100°C on both smooth and rough surfaces. However, some
reproducibility problems were observed at 100°C on the smooth surfaces where chemical analysis
revealed important quantities of tungsten in an oxide form. It is then believed that the oxidation of the
nanoparticles may alter their tribological performance due to the in-situ production of tungsten oxide.
On the other hand, the morphological and chemical analyses made on the rough surfaces lubricated by
the WS2 nanoparticles at 100°C revealed the presence of a tribofilm on the wear track that reduced
importantly the roughness of the worn surface. Additionally, it was observed that nanoparticles trapped
on the grooves of the steel can provide proper lubrication in case of nanoparticles starvation in the
contact.
With the aim of using nanoparticles in commercial lubricant oils, their good performance must be
guaranteed in real temperature conditions and in the presence of the additives commonly used in the
industry. Thus, we analyzed the tribological response of WS2 nanoparticles in the presence of a
diphenylamine anti-oxidant, a ZDDP anti-wear and a blend of ZDDP with calcium phenate detergent
additive at 100 °C in boundary lubrication regime. The results showed that the diphenylamine
antioxidant does not have any effect on the tribological behavior of the tungsten disulfide nanoparticles
so it can be used in the formulation of nanoparticles containing lubricants.
Conversely, a better tribological performance was obtained when the nanoparticles were used in
presence of ZDDP additive. Actually not only a stable and low friction coefficient was obtained but also
high reproducibility of the results was observed. The analyses showed the presence of a 50-60-nm-thick
tribofilm protecting the steel surface. The presence of sheets of WS2 observed on the top of the tribofilm
might explain both good friction and wear results. Under the WS2-rich layer a typical ZDDP tribofilm
composed by zinc and iron polyphosphates was found. In this work, synergetic effects between the WS2
nanoparticles and ZDDP anti-wear additive were observed under severe test conditions. Actually, ZDDP
seems to protect WS2 sheets from oxidation, thus leading to improved friction modifier properties, while
the presence of WS2 nanoparticles seems to increase the anti-wear properties of the ZDDP.
On the other hand, when the nanoparticles were tested in the presence of ZDDP anti-wear and calcium
phenate detergent a low and stable friction coefficient was obtained since the very beginning of the test
whereas a certain time was needed to get a friction coefficient reduction for the reference sample (ZDDP
and calcium phenate in PAO without nanoparticles). The results showed that a tribofilm composed of all
the elements from the different additives that were present in the lubricant was present on the steel
surface since the very first cycles. However, it is important to note that the same value of friction
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coefficient and anti-wear behavior was obtained for the ZDDP-calcium phenate blend with and without
the nanoparticles under steady stable conditions. Nevertheless, the most important point to be
remembered is that no antagonism was seen between these additives



12.Conclusion
The use of nanoparticles as lubricant additives in the automobile industry involves the study and
comprehension of their effect into the mechanical parts of a car. In this work, we studied the effect of
WS2 nanoparticles in gearboxes when added to base oil and in the presence of a package of additives.
Results have shown that nanoparticles increase the lifespan of gear drives when added to base oil.
Furthermore, the presence of the package of additives in the base oil seems to increase the action of the
nanoparticles.
The chemical analyses revealed that the nanoparticles are able to form a tribofilm on the steel surface
even in the presence of a commercial package of additives. Different phenomena were observed on the
gears lubricated by the samples. Micropitting, pitting and spalling were observed in the case of the
nanoparticles in base oil, whereas only micropitting was seen in the case of the nanoparticles in base oil
in the presence of the commercial package of additives.
The investigation done on the gear lubricated by the nanoparticles in base oil revealed an important
concentration of tungsten and sulfur in the places where some defects were seen. This nanoparticles
concentration is thought to be able to limit oil seepage inside the cracks which would release hydraulic
pressure and reduce crack propagation. Nevertheless, this cannot be proven with the technology
currently available. Additionally, the chemical analyses revealed not only the presence of a tungsten and
sulfur containing tribofilm in the surface of the tooth, but also that a film formed by the same elements
coming from the nanoparticles (as well as sheets of nanoparticles) were found all along the wall of the
cracks even 100 micrometers below the surface. It has been demonstrated by another research group
that this tribofilm may act as a barrier against hydrogen embrittlement increasing life span of the gear
drive.
Further investigation should be done on the hydrogen permeability of tribofilms produced by tungsten
disulfide nanoparticles in the presence of a commercial package of additives




Even more succinct it is pretty good.
 
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