T ibological p ope ies o g aphene nanopla ele s o bo on ni ide
nanopa icles as addi i es o a polyalphaolefinbaseoil
José M. Liñei a del Río, En ique a R. López, Jose a Fe nández⁎
Labo a o y o The mophysical and T ibological P ope ies, Na oma G oup, Depa men o Applied Physics, Facul y o Physics, Uni e si y o San iago de Compos ela, 15782 San iago de Compos ela,
Spain
abs ac a icle in o
A icle his o y:
Recei ed 3 Feb ua y 2021
Recei ed in e ised o m 4 Ma ch 2021
Accep ed 11 Ma ch 2021
A ailable online 16 Ma ch 2021
Keywo ds:
Polyalphaolefin
Nanoaddi i es
S abili y
F ic ion
Wea
In his wo k, an i ic ion and an iwea capabili ies o hexagonal bo on ni ide nanopa icles (h-BN) o g aphene
nanopla ele s (GnP) as addi i es o a polyalphaolefin nea oil (PAO 40) we e s udied a pu e sliding condi ions.
Fo his pu pose, eigh PAO 40 nanodispe sions we e p epa ed: ou nanodispe sions wi h h-BN and ou o he s
based on GnP. The mass concen a ions o hese dispe sions a e 0.25, 0.50, 0.75 and 1.00 w % o h-BN and 0.05,
0.10. 0.25 and 0.50 w % o GnP, ha ing all o hem a good s abili y agains sedimen a ion (a leas 96 h). T ibolog-
ical assays we e ca ied wi h p epa ed nanolub ican s as well as wi h PAO 40 base oil a 20 N load. All
nanolub ican s based on h-BN o GnP showed lowe ic ion coe ficien s in compa ison o he non-addi i a ed
nea oil, wi h a maximum dec ease in ic ion o 21% o he 0.50 w % GnP nanodispe sion. Rega ding he p o-
duced wea , all disks lub ica ed wi h nanolub ican s showed lowe wea han hose lub ica ed using PAO 40.
The g ea es wea educ ion in wea ack wid h (22%) was also achie ed o he 0.50 w % in GnP nanolub ican .
Mo eo e , h ough he con ocal Raman mic oscopy and oughness analyses o wo n disks i can be concluded
ha he wea educ ions a e due o he su ace epai ing and ibofilm o ma ion mechanisms.
©2021Else ie B.V.All igh s ese ed.
1. In oduc ion
Nowadays, almos a qua e o he o al ene gy consumed wo ldwide
is due o ic ion and wea ha occu s be ween ibological con ac s [1].
Gi en his pe spec i e, i is necessa y o de elop mo e e ficien lub ican s
so as o minimize hese ene gy losses. These educ ions can also lead o
longe machine li e imes and a dec ease in g eenhouse gas emissions. A
lub ican is a mul icomponen mix u e o di e en lub ican bases and ad-
di i es in a a io a ound 90% base oil and 10% addi i es. Fo his eason,
many esea che s ha e conside ed di e en echnologies o disco e ing
no el p ocedu es o eplace adi ional en i onmen al ha m ul addi i es
ha o igin ad e se emissions and include sul u o phospho ous ( o in-
s ance zinc dialkyldi hiophospha e) wi hou comp omising on iendly
en i onmen al addi i es like nanopa icles o e en ionic liquids [2–5].
The e o e, he u iliza ion o nanopa icles as lub ican addi i es is a possi-
ble solu ion o hese p oblems, owing o hei ou s anding chemical and
physical cha ac e is ics [6]. Fu he mo e, sui able nanopa icles as addi-
i es a e less chemically eac i e han adi ional addi i es because hei
films a e p oduced mechanically, he e o e hey will eac less wi h
o he addi i es and consequen ly be mo e du able [7]. In u h, low quan-
i ies o nanopa icles as lub ican addi i es can imp o e he ibological
pe o mance, since nanopa icles p esen be e ibological p ope ies
ha adi ional solid lub ican addi i es, owing o hey migh inse in
he ibological con ac egion and enhance he beha io o ibofilm
[8,9]. This ibological imp o emen is due o he nanoaddi i es h ough
di e en lub ica ion mechanisms ha can be summa ized in fi e ypes:
ibofilm o ma ion, ans o ma ion o mic os uc u e, olling bea ing e -
ec , syne gis ic e ec as well as su ace epai ing e ec . In he fi s mech-
anism, due o he big specific su ace nanopa icles a ea, a p o ec i e film
can be p oduced on he con ac su aces by chemical eac ion o physical
in e ac ions, a oiding he di ec con ac me al-me al. As ega ds he
ans o ma ion o s uc u e mechanism, he ini ial mic os uc u e o
some nanopa icles is changed due o he high-le el p essu e and he
hea gene a ed in he ic ion p ocedu e. These mic os uc u e changes
may esul in he a ia ion o ibological beha io . Rolling bea ing e ec
appea s when sphe ical-shaped nanopa icles oll be ween ic ion su -
aces aspe i ies and ans o ms sliding o olling ic ion. Fu he mo e,
he syne ge ic e ec occu s when nanopa icles coope a e wi h o he ad-
di i es o achie e a be e ibological pe o mance. Rega ding he su ace
epai ing mechanism, due o hei na u e, nanopa icles can epai he
con ac su ace impe ec ions educing he su ace oughness and en-
hancing he ibological pe o mance [10].
Many s udies confi med ha he use o nanopa icles in lub ican s has
impo an e ec s on he ic ion and wea enhancemen [1,4,11–13].
Nowadays, he e a e se e al ypes o nanopa icles, which a e mainly
classified in o se e al ca ego ies a ending o hei chemical s uc u e
[4]: ca bon-based ma e ials, me als, me al oxides, among o he s.
Jou nal o Molecula Liquids 333 (2021) 115911
⁎Co esponding au ho .
E-mail add ess: jose a. e [email protected] (J. Fe nández).
h ps://doi.o g/10.1016/j.molliq.2021.115911
0167-7322/© 2021 Else ie B.V. All igh s ese ed.
Con en s lis s a ailable a ScienceDi ec
Jou nal o Molecula Liquids
jou nal homepage: www.else ie .com/loca e/molliq
G aphene nanopla ele s (GnP) a e ca bon-based nanoma e ials,
which ha e been analyzed as lub ican addi i es, obse ing ha can im-
p o e bo h ic ion and wea beha io s in compa ison o se e al oils
wi hou addi i es [14–19]. In ac , esea che s ha e p o en ha li le
quan i ies o 0.02–0.5 w % o GnP ha e enhanced bo h ic ion and
wea lub ican p ope ies [20,21]. Fo ins ance, Om ani e al. [14] ob-
ained ic ion and wea educ ions o 26% and 83%, espec i ely, using
canola oil wi h an ideal mass pe cen age o 0.07 w %, whe eas Zhang
e al. [15] obse ed o a syn he ic oil addi i a ed wi h GnP a maximum
ic ion educ ion o 17% o 0.02% GnP concen a ion, whe eas he bes
GnP concen a ion o wea educ ion (14%) is 0.06%., espec i ely.
Nanolub ican s ha con ain hexagonal bo on ni ide (h-BN) ha e
also led o imp o ed an i ic ion and an i-wea pe o mances in com-
pa ison o hose o se e al base oils [22–27]. This may be due o he
qui e so an de Waals o ces be ween loosely packed h-BN laye s,
esul ing in excep ional lub ica ion p ope ies [28]. Se e al s udies con-
fi m hese good ibological p ope ies, o ins ance Çelik e al. [29]ob-
se ed ha a SAE10W engine oil addi i a ed wi h h-BN nanopa icles
imp o e bo h he ic ion and he wea p ope ies in compa ison o
nea oil, wi h educ ions o 14% and 65%, espec i ely. Fu he mo e,
Wan e al. [30] concluded ha nanolub ican s o med by a 15 W-40
oil wi h h-BN nanopowde s conside ably enhanced he an i ic ion pe -
o mance o nea oil wi h ic ion educ ions up o 77%. Besides, h-BN
nanoma e ials a e e y in e es ing because o hey a e conside ed an
en i onmen ally iendly ma e ial [24].
In b ie , as can be concluded om he a o emen ioned s udies, GnP
and h-BN nanoma e ials ha e po en ial ibological p ope ies as oil
base addi i es. None heless, he e is s ill no esea ch compa ing he ad-
di ion o wo di e en ypes o nanopa icles o polyalphaolefin(PAO)
base oils in he li e a u e. PAO oils a e e y impo an in lub ica ion,
since hey a e he mos widesp ead syn he ic lub ican s and hey a e
gene ally used in au omo i e applica ions (c ankcase, ansmissions,
gea s) and o he indus ial applica ions ( e ige a ion comp esso s, u -
bines, gea boxes as well as hyd aulic and me al wo king oils) [31].
The e o e, he goal o his esea ch is analyzing he ibological beha io
o wo di e en nanoma e ials: h-BN nanopa icles o g aphene
nanopla ele s as addi i es o PAO 40 base oil a pu e sliding condi ions,
also obse ing he influence o concen a ion o bo h nanopa icles,
ob aining he op imum concen a ion wi h he bes ibological
pe o mance.
2. Ma e ial and me hods
2.1. Base oil and nanoaddi i es
Polyalphaolefin PAO 40, supplied by REPSOL, is syn he ized h ough
1-decene polyme iza ion ollowed by a hyd ogena ion. PAO 40 sample
has a densi y and dynamic iscosi y a 313.15 K o 0.8346 g·cm
−3
and
335.57 mPa s, espec i ely, as well as a iscosi y index o 149.3. An ali-
quo o his PAO 40 was p e iously cha ac e ized by in a ed spec os-
copy (FTIR) wi h no e idence o he p esence o ca bon‑ca bon double
bonds [32].
G aphene nanopla ele s (GnP, CAS numbe 1034343–98-0) wi h a
99.5% pu i y, an a e age pa icle size o 15 μmand11–15 nm hickness
we e supplied by Ioli ec. A sample o his nanoma e ial was p e iously
cha ac e ized using scanning elec on mic oscopy (SEM), T ansmission
Elec on Mic oscopy (TEM), FTIR, Raman as well as X- ay spec oscopy
(EDX) [20]. The cha ac e iza ion showed ha GnPs ha e a bended and
w inkled appea ance wi h a mul ilaye a angemen [20]. Fu he mo e,
hexagonal bo on ni ide nanopa icles (h-BN wi h CAS Numbe :
10043–11-5) wi h a 99.5% pu i y and an a e age size a ound 70 nm
(Ioli ec, GmbH, Ge many, lo MNC018001), we e p e iously cha ac e -
ized by FTIR, SEM and TEM [33]. These analyses p o ed ha he nano-
pa icles ha e a disk-like shaped mo phology and he ypical h-BN
ib a ion mode a ound 1367 cm
−1
[33].
2.2. Nanolub ican s p epa a ion
Nanolub ican s we e o mula ed wi h di e en mass pe cen ages o
GnP (0.05, 0.10, 0.25 and 0.50 w %) and h-BN (0.25, 0.50, 0.75 and 1.00
w %) in PAO 40. Bo h concen a ion anges we e selec ed based on p e-
ious s udies [20,33], in which he op imal concen a ions o bo h
nanoma e ials we e de e mined. In his wo k, a wo-s ep me hod was
employed o p epa e he a o emen ioned nanodispe sions. Fo his
aim, a Sa o ius MC 210P mic obalance (±0.00001 g) was u ilized o
achie e he mass concen a ion o nanopa icles in he oil. As ega ds
nanodispe sions homogeniza ion, an ul asonic ba h (FB11203
Fishe b and), wi h a con inuous sonica ion ime o 4 h and a powe o
180 W a a 37 kHz equency was u ilized. Du ing he sonica ion p ocess
he empe a u e is con olled o a oid o e hea ing o samples.
S abili y o he nanodispe sions was analyzed by bo h sedimen pho-
og aph cap u ing o samples and measu emen o he e olu ion o he
e ac i e index o e ime h ough a Re ac ome e Me le Toledo.
Mo e de ails abou his las echnique we e desc ibed in a p e ious a i-
cle [34].
2.3. T ibological assays
F ic ion es s wi h o a ional configu a ion we e ca ied ou using a
CSM S anda d ibological de ice o he designed PAO 40
nanolub ican s as well as o he base oil, ope a ing in ball-on-disk a
pu e sliding condi ions. The ollowing se ings we e u ilized: oom em-
pe a u e (~23 °C), load o 20 N (2.0 GPa o maximum con ac p essu e),
3 mm adius,340 m slidingdis ance and 0.10 m s
−1
speed. The ibolog-
ical specimens we e s ainless-s eel disks (AISI 52100/535A99, 5 mm a-
dius, su ace finish: Ra < 0.02 μm and ha dness: H 30 190–210) and
ch ome s eel balls (AISI 52100/535A99, 3 mm adius, ha dness: 58–66
Rockwell Scale and oughness <0.05 μm). Bo h s eel balls and disks
we e washed p e iously ibological es s h ough an ul asonic ba h
o ace one so as o emo e any elemen ha could dis u b ou expe i-
men s and a e wa ds d ied wi h ho ai . A e ha , he disks we e lub i-
ca ed wi h each p epa ed lub ican (a ound 0.2 mL). To ensu e a good
epea abili y no less han h ee eplica es we e ca ied ou .
Once he ic ion es s ha e been ca ied ou , be o e analyzing he
p oduced wea , wo n disks we e cleansed in he ace one ul asonic
ba h.Wi h he aim o quan i ying he wea p oduced on he disks an Op-
ical 3D P ofile Senso a S Neox (con ocal mode, 10×) was u ilized.
Thus, wea was analyzed h ough he ollowing pa ame e s: wea
ack dep h (WTD), wea ack wid h (WTW) as well as c oss-
sec ional a ea. Fo his pu pose, hese wea pa ame e s we e measu ed
a h ee di e en zones o he wo n su aces in o de o achie e ep e-
sen a i e alues.
Wo n su aces oughness (Ra) o disks lub ica ed using he p epa ed
nanolub ican s and PAO 40 base oil we e also e alua ed wi h he 3D Op-
ical P ofile o desc ibe he an i-wea capabili y o he nanofluids. Fo
his aim, ISO4287 s anda d (In e na ional O ganiza ion o S anda diza-
ion, Ve nie , Swi ze land) was employed using a Gaussian fil e
(0.08 mm wa eleng h cu -o ). Fi s ly, an a ea inside he scanned
wo n sca is ex ac ed and a e wa ds in his selec ed a ea i is aken a
pe pendicula p ofile o he sliding di ec ion o ibological es s. The
so wa e pe mi s o de e mine he Ra alue o his p ofile. Mo eo e ,
o achie e in o ma ion o he ibofilm composi ion on he wo n ack,
a WITec alpha300R+ con ocal Raman mic oscope was u ilized.
3. Resul s and discussion
3.1. Nanodispe sions s abili y
Nanolub ican s s abili y was e alua ed h ough sedimen pho o-
g aph cap u ing. This echnique consis s o examining he sedimen a-
ion o nanopa icles o e ime. Fig. 1 shows he e is no sedimen a ion
o he mo e and less concen a ed h-BN and GnP nanolub ican s be o e
J.M. Liñei a del Río, E.R. López and J. Fe nández Jou nal o Molecula Liquids 333 (2021) 115911
2
fi s 96 h a e o mula ion o nanolub ican . This s abili y ime is bigge
han ha equi ed o ca y ou he ic ion es s (a ound 4 h pe
lub ican ).
Addi ionally, o e alua e he nanopa icles s abili y in PAO 40 oil, e-
ac ome y me hod was also employed. Thus, nanolub ican s e ac i e
index was e alua ed e e y hou un il 50 h, s udying i s p og ess (Fig. 2)
o bo h 0.05 w % h-BN and GnP nanolub ican s. Guima ey e al. [35]
ha e also analyzed he nanolub ican s s abili y wi h e ac ome y, in
his case Z O
2
nanoaddi i es in a ious base oils. In he a o emen ioned
wo k, he e ac i e index in wo base oils showed a 0.4% inc ease a e
100 h o analysis. P e iously [32], we ha e e alua ed he g aphene oxide
(GO) and educed g aphene oxide ( GO) e ac i e index o PAO 40 and
es e based nanolub ican s. This esea ch e idenced ha a e 50 h o
bo h base oils he e ac i e index inc eased a ound 0.1% and 0.4% o
Fig. 1. S abili y isual obse a ion o PAO 40 nanolub ican s based on h-BN and GnP.
J.M. Liñei a del Río, E.R. López and J. Fe nández Jou nal o Molecula Liquids 333 (2021) 115911
3
GO and GO nanolub ican s, espec i ely. In ou s udy, he e ac i e index
e olu ion o e 50 h indica es g ow hs abou 0.1 and 0.2% o bo h 0.05 w %
h-BN and GnP nanolub ican s, espec i ely. These esul s demons a e a
qui e good s abili y o he new o mula ed nanolub ican s.
3.2. T ibological esul s
Fig. 3 and Table 1 show he ic ion coe ficien s (μ) mean alues o
he designed PAO 40 lub ican s, obse ing ha he coe ficien s o ic-
ion ound o all he nanolub ican s a e smalle han ha achie ed o
he non-addi i a ed PAO 40. The bes ic ion pe o mance was
achie ed o he 0.50 w % GnP nanolub ican . This GnP nanolub ican
showed a ic ion coe ficien o 0.064 agains he 0.081 achie ed o
PAO 40 (Table 1), which leads o a 21% maximum ic ion educ ion.
Mo eo e , o h-BN nanolub ican s he bes an i ic ion beha io was
eached o he nanolub ican o 0.75 w % (20% educ ion).
Rega ding he p oduced wea , 3D and c oss-sec ional p ofiles o
wea sca s c ea ed in disks a e he ic ion es s a e shown in Figs. 4.
The alues ob ained o WTW, WTD and he c oss-sec ional a ea o
he wea sca on he disks a e shown in Table 1. I can be obse ed
ha wi h all he nanolub ican s (based on GnP and h-BN) he wea is
smalle han o he PAO 40 in WTW and c oss-sec ional a ea. Fo
such pa ame e s, he maximum educ ions we e ound wi h he 0.50
w % GnP nanolub ican , being 22% in WTW and 19% in c oss-sec ional
a ea. As ega ds h-BN nanolub ican s he bes an i-wea pe o mance
was ob ained wi h he 0.75 w % h-BN nanolub ican wi h educ ions
o hese las pa ame e s o 20 and 13%, espec i ely. These findings
p o e a sui able co ela ion among ic ion and wea pe o mances.
Roughness (Ra) o wo n disks su aces we e also s udied o analyze
he an i-wea nanolub ican s capaci y. Table 2 indica es ha wo n sca s
lub ica ed wi h h-BN o GnP nanolub ican s ha e lowe oughness han
ha wi h PAO 40. Specifically, a Ra o 181 nm was ound o he lub i-
ca ed PAO 40 wo n su ace while o he sca es ed wi h he 0.25 w %
GnP nanolub ican he smalles Ra alue was achie ed (111 nm) i.e. a
39% oughness educ ion. Conce ning h-BN nanolub ican s, he lowes
Ra (131 nm) was ob ained wi h 0.75 w % h-BN.
Raman spec a and elemen al mapping o he wo n acks lub ica ed
wi h nanolub ican s based on PAO 40 and h-BN o GnP wi h he bes i-
bological beha io o each nanoaddi i e we e eco ded wi h a Raman
con ocal mic oscope (532 nm wa eleng h) in o de o iden i y he
ole ha nanoaddi i es has in wea pa ame e s dec ease. PAO 40
Raman spec um is displayed in Fig. S1 obse ing ha cha ac e is ic
peaks o he oil coincide, as expec ed, wi h se e al o hose ound in
he wo n acks lub ica ed wi h nanolub ican s (Fig. 5). Fu he mo e,
Fig. 2. E olu ion o PAO 40 nanolub ican s e ac i e index, n, composed by 0.05 w % in h-
BN o GnP.
Fig. 3. Mean ic ion coe ficien s, μ, ob ained o all he designed lub ican s and o he PAO 40 base oil.
Table 1
Mean ic ion coe ficien s, μ, and mean wo n ack pa ame e s: dep h, WTD, wid h, WTW as well as c oss-sec ional a ea and hei s anda d de ia ions o all s udied lub ican s.
Lub ican μσWTW/μmσ/μm WTD/μmσ/μm A ea/ 10
3
μm
2
σ/10
3
μm
2
PAO40 0.081 0.002 442 16 6.04 0.33 2.14 0.12
+ 0.05 w % GnP 0.065 0.002 383 14 5.98 0.27 1.95 0.16
+ 0.10 w % GnP 0.074 0.003 402 12 6.14 0.24 2.12 0.10
+ 0.25 w % GnP 0.065 0.002 369 11 5.88 0.26 1.88 0.14
+ 0.50 w % GnP 0.064 0.003 345 10 5.95 0.37 1.74 0.11
+ 0.25 w % h-BN 0.074 0.004 401 17 6.14 0.32 2.11 0.17
+ 0.50 w % h-BN 0.068 0.003 381 13 6.02 0.43 1.98 0.13
+ 0.75 w % h-BN 0.065 0.002 353 12 5.78 0.23 1.87 0.10
+ 1.00 w % h-BN 0.072 0.002 416 13 5.75 0.26 2.03 0.22
J.M. Liñei a del Río, E.R. López and J. Fe nández Jou nal o Molecula Liquids 333 (2021) 115911
4
Fig. 4. 3D p ofile (10×) and a eas o he wea acks on he disks lub ica ed wi h a) PAO 40, b) PAO 40 + 0.75 w % h-BN and c) PAO 40 + 0.50 w % GnP.
J.M. Liñei a del Río, E.R. López and J. Fe nández Jou nal o Molecula Liquids 333 (2021) 115911
5
GnP nanopla ele s Raman spec um (Fig. S2) displays h ee dis inc i e
bands: D-band o e 1350 cm
−1
, G-band abou 1580 cm
−1
and 2D
band a ound 2690 cm
−1
[20]. h-BN Raman spec um (Fig. S3) shows
he usual band a ound 1370 cm
−1
, simila o g aphene G band [20].
Fig. 5 shows a significan p esence o PAO 40 (g een colo ) in he
wo n sca mapping lub ica ed wi h GnP o h-BN nanolub ican s.
Fig. 5a e idences he p esence o spo s due o g aphene nanopla ele s
( ed colo ) in he wo n ack lub ica ed wi h PAO 40 + GnP
nanodispe sions, whe eas Fig. 5b, co esponding o he pla e lub ica ed
wi h he nanolub ican PAO 40 + h-BN illus a es he bo on ni ide po-
si ion ( ed colo ) in he wo n ack. Bo h Raman spec a (h-BN andGnP)
ob ained in he mapping ag ee wi h GnPnanopla ele s Raman spec um
(Fig. S2) and wi h ha o he h-BN nanopowde s (Fig. S3), espec i ely.
The h-BN and GnP dis ibu ion in he wo n ack is pa allel o ic ion
lines, which shows ha nanoma e ials can enhance he lub ica ion ca-
pabili y o he base oil o ming ibofilms a he su ace con ac . Consid-
e ing ha he wo n su ace a e es s wi h nanolub ican s o h-BN o
GnP a e smoo he han ha wi h he PAO 40 (Table 2), and he co e-
sponding Raman analyses, i can be assumed ha o h-BN and GnP
nanodispe sions he key ibological e ec s a e he su ace epai ing
and he o ma ion o ibofilms due o nanopa icles. Çelik e al. [29]
and Choudha y e al. [36] also de e mined ha he su ace epai ing e -
ec explains he an i ic ion and an iwea p ope ies o some lub ica -
ing oils wi h h-BN and g aphene amily addi i es, espec i ely.
Fu he mo e, in he case o GnP, mic os uc u e changes can also
occu . Zhao e al. [37] s udied he lub ica ion beha io o di e en
g aphene nanoaddi i es wi h se e al ex olia ion deg ees, obse ing
ha he ew-laye g aphene wi h bigge in e laye spacing can enhance
he lub ica ion p ope ies o oil. These au ho s concluded ha ibolog-
ical imp o emen is due o he o ma ion o o de ed g aphene
ibofilms a he ic ion in e ace and owing o he g aphene mic o-
s uc u e changes du ing ibological es s. The e again, olling bea ing
and syne gis ic e ec s a e disca ded due o he ac ha h-BN and GnP
nanoaddi i es p esen non-sphe ical shape and he e is no coope a ion
wi h o he addi i es.
Fig. 3 also shows ha o he ic ion coe ficien o nanolub ican
wi h highes h-BN concen a ion (1.00 w % in h-BN) is qui e highe
compa ed o lowe concen a ions (0.50 w % and 0.75 w %). This ac
may be owing o he nanopa icles agglome a ion a high concen a ion
(1.00 w %), h-BN nanopa icles a e likely no jus o ulfill wo n su ace
alleys bu also gene a e new aspe i ies. These p oduced aspe i ies in-
c ease he oughness o wo n su ace (Table 2) and migh p oduce
Fig. 4 (con inued).
Table 2
Roughness pa ame e alues, Ra, and hei unce ain ies σo wo n su aces lub ica ed
wi h he all he s udied nanolub ican s and PAO 40 using a Gaussian fil e wi h a long
wa eleng h cu -o o 0.08 mm.
Lub ican Ra/nm σ
PAO 40 181 18
0.05 w % GnP 127 10
0.10 w % GnP 121 13
0.25 w % GnP 111 10
0.50 w % GnP 115 12
0.25 w % h-BN 142 15
0.50 w % h-BN 135 13
0.75 w % h-BN 131 14
1.00 w % h-BN 137 10
J.M. Liñei a del Río, E.R. López and J. Fe nández Jou nal o Molecula Liquids 333 (2021) 115911
6
Fig. 5. Elemen al mapping and Raman spec a o he wo n acks es ed wi h he nanolub ican s: a) PAO 40 + 0.50 w % GnP and b) PAO 40 + 0.75 w % h-BN.
J.M. Liñei a del Río, E.R. López and J. Fe nández Jou nal o Molecula Liquids 333 (2021) 115911
7
highe ic ion when hey a e compa ed o nanopa icles wi h sligh ag-
glome a ion [29].
4. Conclusions
The subsequen conclusions we e eached in his wo k:
- Eigh PAO 40 nanodispe sions we e p epa ed, ou nanodispe sions
in hexagonal bo on ni ide nanopa icles (h-BN) and ou o he s
based on g aphene nanopla ele s (GnP), showing s abili y imes o
a leas 96 h.
-Coe ficien s o ic ion achie ed o all henanolub ican s a e smalle
han ha ob ained o PAO 40 wi hou addi i es.
- The bes ic ion educ ion was eached o he 0.50 w % GnP
nanolub ican , wi h a 21% maximum ic ion educ ion wi h espec
o base oil.
- Fo h-BN nanolub ican s he bes an i ic ion beha io was achie ed
o he 0.75 w % nanolub ican , wi h a ic ion educ ion o 20%.
- Fo all he nanolub ican s (based on GnP and h-BN) he p oduced
wea in disks is smalle han o he PAO 40. Specifically, he maxi-
mum educ ions in he WTW and c oss-sec ional a ea we e ound
wi h he 0.50 w % GnP nanolub ican , being 22% and 19% espec-
i ely.
- Fo h-BN nanolub ican s he bes an i-wea pe o mance was ob-
ained o he 0.75 w % h-BN wi h educ ions o 20% and 13% in
WTW and c oss-sec ional a ea, espec i ely.
- Th ough he Raman and oughness analyses, he su ace epai ing
and ibofilm o ma ion mechanisms due o he nanopa icles we e
confi med.
Decla a ion o Compe ing In e es
The au ho s decla e ha hey ha e no known compe ing financial
in e es s o pe sonal ela ionships ha could ha e appea ed o influ-
ence he wo k epo ed in his pape .
Acknowledgmen s
I is a pleasu e o hank Repsol company o supplying us he PAO 40
base oil sample. Au ho s would like o hank he use o RIAIDT-USC an-
aly ical acili ies. This wo k was suppo ed by he Xun a de Galicia
(ED431E 2018/08 and ED431C 2020/10) and by MINECO and he ERDF
p og amme h ough ENE2014-55489-C2-1-R and ENE2017-86425-C2-
2-R p ojec s.
Appendix A. Supplemen a y da a
Supplemen a y da a o his a icle can be ound online a h ps://doi.
o g/10.1016/j.molliq.2021.115911.
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