Indian Journal of Engineering & Materi als Sciences Vol. 6. AUgU51 IlJ99. pp. 206-2 12

Tribological evaluation of N-phenylformamidino-N/-alkylthiocarbamides and their Mo-S complexes as EP lubricant additives

A K Tripathia, A Bhattacharya", R Singh", N Prasadb & V K Verma"

"Cent re for Tri bology. Department of Applied ChemistrYI hDepartment of Metallurgical Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221005, India

Received 8 Jun e 1998; accepted 20 April 1999

The tTibological properties of 0.5% solutions of N-phenylfo rmamidino-N'-alkylthio-carbamides and their Mo-S complexes. i.e.. Il-hydroxo-Il-(N-phenylformamidino-N'-alkylthiocarbamido)-bis-(dioxohydroxo molybdenum VI ) in paraffin oil were evaluated in a four-ball test. In particul ar, Il-hydroxo-Il-(N-phenylformamidino-N'rethylthiocarbamido)­hi s-[ dioxohyd roxo molybden um VI] was found to exhibit an appreciab le increase in the load carrying capaci ty and values of nash temperature parameter, load wear index and pressure wear index and a decrease in the values of coeffi cient of fr iction. However, the Mo-S additives did not marked ly improve anti-wear characteristics in the wear tests. A comparative EP evaluat ion of Il - hydroxo- Il-(N-phenylfo rmamidino-N'-et hylthi~'carbam ido)-b i s- (dioxo hydroxo molybdenum VI) usi ng steel balls of different compositions, indicated its suitability of replacing all oy steel ball s with cheaper carbon steel balls. The topograph y of the wear scars on the used steel ball specimen was studied by SEM.

The lubricants containing oi l soluble Mo-S complexes have been used as EP lubricants l

-6 in automoti ve

hypo id gears , meta l cutting and forming operations. Particularly , molybdenum dithiocarbamates and molybdenum dithi ophosphates have been known to fu ncti on as. ex treme pressure additives , antioxidants and friction modifi ers in lubricating oil s and greases7

. II

In view of the ongoing search for novel Mo-S complexes and efforts6

.lo in the development of better

and more effecti ve EP additives, a number of ary lformam idino-alkylthiocarbamides and their Mo-S complexes were synthesized to study the ir EP and anti -wear properties and to ascertain the possibilities of replacing all oy steel bearing balls with cheaper low carbon all oy steel ball s using an appropriate additive in a four ball test.

Experimental Procedure

Materials

Commercially available 12.7 mm diameter ball of the following compositions and hardness were used:

Specimen I Specimen II

C % Mn % Cr % Fe % Hardness (VHN)

1.06 0.25

0.35 1.76

1.16 0:26

97.43 97.73

918 617

The base fluid

The base fluid was paraffin oil (b.p . 400-41O°C) of the following physical characteristics:

Specific gravity Viscosi ty

Cloud point Pour point Flash point Fire point

Additives

= 0 .8 1 at 25°C

= 116.8 cP at 25°C

5 .02 cP at 100°C

= - 2°C

= - 8°C

= 185°C

= 201 °C

The additives, N-phenylfom1amidino-N'-alkylthiocarbamides (DI - 0 4) were prepared by treating appropriate 5-alkylimino-3-imino-l ,2,4-dithiazol idine hydriodide with aniline in ethanol on a boiling water bath for 30 min12.

H

I /~

RN=i 1= NH,HI + C~H5NH2 ~ EtOH

S --s RNH-C-NH-C-NHC6HS + S +HI

II II S NH

I ...,..

-~

TRIPATHI et at.: TRIBOLOGICAL EV ALUATION OF N-PHENYLFORMAMIDINO-N'-ALKYL THIOCARBAMIDES 207

where R= methyl- , ethyl-, n-butyl- and dimethyl­groups.

11-H ydroxo-Il-(N -pheny Iformam:idino-N' -alky Ithiocar­bamido)-bi s-[dioxohydroxo molybdenum (VI)] additives (A I-A4) were prepared by reacting an ethanolic solution of an appropriate N-phenylform­amidino-N '-alkylthi ocarbamide with an aqueous solution of sodium molybdate in an ice bath for 60

. 11 H 2 nun - at p .

Sodium molybdate RNH-C-NH-C-NH-C6H5

" II

~ EtOH . pH - 2

S NH M020.j(OH)3(RNH-C-NH-C-NHC6HS)

II II S NH

where R= methyl-. e thyl-. n-butyl- and dimethyl­groups.

The resulting compounds were repeatedly washed with water and hot ethanol and the purity of the compounds was confirmed by TLC technique. The charac teri zation of the compounds 0 1-0 4 and A I-~

was carried out by e lemental analys is and IR spectra " ·14 (Table I)

The addit ives (0 .5% wt./vo l. ) were dissolved 111

paraffin oil by stirring and heating at 60°C to homogeni se the so lution .

Rig Test

A variable speed four-ba ll lubricant testing machine operating at 1500 rpm was employed to conduct a se ries of 60 s EP test [ASTM 2783] until the welding poi nt was reached . One hour duration wear tests were perfo rmed at 40 kgf load .

Results and Discussion

0.5% w/v solutions of N-phenylformamidino-N'­alkylthiocarbamides and their Mo-S complexes in paraffin oil were eva luated as potential EP additives by using specimen I alloy steel balls and determining different parameters, viz., wear-scar diameter (d) and coefficient of fri ction (11) at initial seizure load (ISL) and just before weld load (JBWL), 2.5s seizure delay load (SOL) and weld load (WL), fl ash temperature parameter (FIP), load wear index (L WI) and pressure wear index (PWI). The results were compared wi th plain paraffin oil and its admixture with dioxo bis-(N­phenyldithiocarbamato) molybdenum VI reference additive and are recorded in Tables 2 and 3.

Fig. I shows the variati on between the log wear­scar diameter and log loads fo r the paraffi n oil without and with N-phenylformamidino-N'­alkylthi ocarbamide additi ves (0 1 - 0 4). All the additives affo rd very much higher values of ISL and weld load, and comparatively lower scar diameter va lues than the pl ain paraffin oil. Table 2 also clearly indicates that the additi ves afford lower values of coefficient of fri c tion at ISL and JBWL and higher va lues of FTP, L WI and PWI. T his shows that the use of N-phenylformamidino-N'-a lky lth iocarbamides enhances the anti -wear and load-carrying characteri stics and reduces the coeffi cient of friction in comparison to the plain paraffin o il. Fig. 2 depicts the re lati onship between log load and log wear-scar diameter va lues using admixtures of paraffin oil and Il-hydroxo-Il-(N-phenylformamjdino- N'-alkylthio­carbamido )-bis- [ dioxohydroxo molybdenum VI] complexes (A I-A4). This graph also shows much higher va lues of ISL and weld load and corresponding lower values of wear-scar diameter in comparison to plain paraffin oil. Table 3 unambiguously confirms that the additi ves (A I - A4) show quite low values of

.~. • • ____ • __ ••••••• _ ••••• • _ •••••••••••••••••••••• _._ • ••• _ •• ____ •• _ •••• ___ •• _ •••••••••••••••••• _. ___ • • •• _ ••••• H. _____ ._ ,. ___ ._ ••• _ ........... __ • __ •••• ____ •••• __ • __ •••••••••• _ ••• __ •••• _. ______ _

Table I-Preparation of ligands and their Mo-S complexes as additi ves

Code Add itive name

0 1 N- Phenylrormamidi no-N'- methylthiocarbamide

0 1 N- Phcnylrormamidi no-N'-cthylthiocarbamide

O} N-Phcnylrormamidi no-N'-butylthiocarbamide

0 4 N- Phcnylrormamidino-N '-dimethylthiocarbamide

AI Jl -Hydroxo- Jl -(N- phenylrormami dino-N'- methylthi ocarbamido)- bi s-[dioxohydroxo molybdenum VI]

AJ Jl -H ydroxo-Jl- ( N-phenyl rormamid ino-N'-ethyl thiocarbamidol-bi s-[ dioxohydroxo molybdenum V I]

A} Jl -H ydm xo-Jl- ( N- pheny! ro rmamidino-N'-butylthiocarbamido)-bi s- [ dioxohydroxo molybdenum VI]

A4 Jl -Hydroxo-Jl-(N- phenylformami dino-N'-dimethylthiocarbamidol-bis-[dioxohydroxo molybdenum VI]

R Oioxohi s-(N-phcnyldi thi ocarbarnatol molybdenum VI

Molecul ar fo rmul a

CyHI2N4S

CWHI4N4S

C I2HIX N4S

C WHI4N4S

CyH I3N4S07Mo2

CwH 15N4S07Mo2

CI2HlyN4S07Mo2

C WHIS N4S07Mo2

CI4HI2N2S40 2Mo

m. p. °C

160

190

175

147

205

215

210

188

178

208

'­<U 0-x '" '" .::; '­o C '" E E :::l Vl

I "" '" :0

~-o '~ '" _ 0

"' -c~ o <U

':::; :?: '" > <U '- '-<U,£ '" <U o J:)

'" r- 2 '" u

10 :::l

_J

'. ::l

-. ::l

* E ""'" E

'. E ""'" E

V"l 00

o o ""

o 00 o 6

V"l V"l

6

o 00

o V"l V"l 1\

o 0\ o 6

V"l o 6

r-0\

o V"l V"l 1\

o V"l V"l

"" 'D o 6

o V"l V"l 1\

o V"l V"l

o V"l o 6

INDIAN 1. ENG, MATER. SCI. . AUGUST 1999

o 0\

o V"l V"l 1\

"" o

6

o V"l V"l

o 8 6

V"l

6

coefficient of friction at ISL and JBWL and higher values of Frp, L WI and PWI. These results indicate that the additives, J-l-hydroxo-J-l-(N-phenylformami­dino-N'-alkylthiocarbamido )-bis-[ dioxohydroxo mo­lybdenum VI] were found to be quite effective compared with N-phenylfonnamidino-N'­alkylthiocarbamides, plain paraffin oil and the reference additive. In particular, the additive, J-l­hydroxo-J-l-(N-phenylformamidino- N'-ethylthiocarba­mido)-bis-[dioxohydroxo molybdenum VI] (A2) gives remarkably high values of FrP (447), LWI (103) and PWI (54) and shows lower values of wear-scar diameter and coefficient of friction at ISL (112 kgf) and JBWL (550 kgf).

In order to explore the possibility of replacing the costly chrome steel bearing balls with cheaper low carbon and chromium steel ball, 0 .5 % (w/v) solution of J-l-hydroxo-J-l-(N-phenylformamidino- N'­ethylthiocar-bamido )-bis-[ dioxohydroxo molybdenum VI] (A2) 10 paraffin oil was evaluated by usmg bearing ball specImen of different composittons (Sped men I and II) in a four ball test. The additive was found to be quite effective on chromium alloy steel as well as low carbon and chromium steel bearing balls (Table 4). From the Table 5, it is clear that the admixtures of Mo-S additives in paraffin oil and plain paraffin oil providing similar values of wear-scar diameter in the wear test, did not show marked improvement in the anti-wear property.

Thus, it is obvious that at lower loads, these Mo-S complex additives remain dormant and may not be effective; however, at higher loads and temperatures these additives may decompose on contact with hot spots of the touching metal surfaces to form a mixed lubricating layer of molybdenum disulphideh ron sfllphide/iron oxide. This mixed layer prevents metallic contact between the sliding surfaces and brings the coefficient of friction values to a lower level and exhibits higher load-carrying capacity.

Surface topography Topography of the wear-scars produced on the steel

balls was examined by uSlOg Scanning Electron Microscopy (SEM). Figs 3 and 4 depict the SEM micrographs of wear-scar for plain paraffin oil and its admixture with J-l-hydroxo J-l-(N-phenylformamidino­N'-ethylthiocarbamido )-bi s-[ dioxohydroxo molybde­num VI]. The loads selected for study were ISL and JBWL. The flow pattern at the leading edges indicates that the lubricant flowed from left to right. The micrographs appear to indicate adhesive wear. The

Table 3-Summary of the ex perimental results obtained with ~ - hydroxo-~ - ( N-phenylformamidino-N '-alkylthiocarbamido)- bi s- [dioxoh ydroxo molybdenum (VI») as EP additives using bearing ball specimen-I

Lubri cant Initi al Observati on at ISL 2.5 s Observati on at just Weld Fl ash Load Pressure Seizu re seizure before weld load load Temperature Wear Wear

Load d* ~ * delay kgf Parameter Index Index (lSL) mm load Wear d* ~* (FTP)(max) (LWI) (PWI ) kgf (2.5s load mm kgf

SDL) kgf Paraffi n oi I (without additi ve) 80 0.55 0.080 90 178 2.85 0.430 200 185 27 12 Paraffin oil + Il-hydroxo -Il-(N-phenylformamidino-N'-methyl- 112 0.47 0.051 126 550 1.26 0.080 >550 401 92 58 thiocarbamido)-bis-[dioxohydroxo mol ybdenum (VI») Paraffin oil + Il-Hydroxo-Il-(N-phenylformamidino-N'- 112 0.44 0.042 126 550 1.10 0.063 >550 447 103 54 eth ylthiocarbamido )-bis-[ dioxohydroxo molybdenum (VI») Paraffin oil + Il-Hydr:.o~o-Il-(N-phenyl formamidino-N' -butyl- 126 0.48 0.050 140 550 1.25 0.070 >550 402 90 26 thiocarbamido )-bis-[ dioxohydroxo molybdenum (VI») Paraffin oil + Il-Hydroxo-Il-(N-phenylformll,lllidino-N'- 126 0.49 0.051 140. 550 1.30 0.080 >550 387 95 29 di methylthiocarbamido )-bis-[ dioxohydroxo molybdenum (VI») Paraffin oil + Reference additive [dioxobis-[(N-phenyldithiocarbamato) 112 0.46 0.050 126 550 1.46 0.072 >550 394 79 15 molybdenum (VI»)

d* = Mean wear-scar diameter 11 * = Friction coefficient

~ :a :> -1 :I:

~

~

~ co o § n ~ t'T1 < ~ C

~ o z o 'Tl

* "0 :I: t'T1 Z -< § ~ 3:: :> 3:: 6 Z o ~ " ~ "" -< ~ ~ ~ co

~ 6 t'T1 til

N o \0

210

E E c:

L-.. ... • E a . .0

15 :,t I L-a .. J a-~

z·~ Z·50

Z·OO

1·50

1 .~

1·00

0·80

·0·e5

0·50 ().45 0·1tO 0 ·35

INDIAN J. ENG. MATER. SCI., AUGUST 1999

-- Ploln poroffln oil (without oddltivt ) 0--<> N-Phtny( formomidlno-N'-mtthythiocorbomidCl b----(:;. N -P';'tnyl formomidino -N'- tthyl thiocorbomidt M----K N- Phtnyl formomidlno- N'- butylthiocorbomidc ~ N-Phenyl formomi dino-N'-dimtthytthiocorbom ldt

72 80 90 100 112 126 140156 178 200 224 251 282 315 355 400 450 500 550

log (Iood in kgf)

Fig. I- Vari alion in Ihe log wear-scar di ameter ~ith log load for the paraffin oil wilhout and with N-phenylformamidino-N'­alkylthi ocarbamide addi lives..

E e

. ~ I.. .. ... r a u I.. a :;t I

L-a .. ~

~

2·8e 2·50

2·00

'.50

, .?!!

' ·00 ().80

0·65

()'50

0·40

__ Plain poraffln 011 ~ /ol-Hydrn-.J.L- (N -phenyl formom Idino-N~mtthyl th iocorbomido rBi s-{ diollohydl"OllO moIyt>cXnum (VI)] 0--0 .J.L-~-(N-phcnyl formomidlno-N~ethyl thiocorbomido)-Bi.- [diOllohydr'oxo mottbdCnum (VI)]

lr---l1 ",,-ttydroll~-(N-~yl fo,.momidino-N~butyl thiocorbomidoHII.-{ diollohydrollo molybdenum (Vl)] _ .""-Hydn)llo-,.L-( I+- phttnyl formomidino-N~dimtthyl ttliocOrbomlct.:>)-9is-[ d ioxohydrollO II'IGIybdt!lUm (Vl)]

........ ~.f.,...nce odditlvct

-------I I I I I I I

282 315 355 400 450 500 550

log ( load in kgf)

Fig. 2-Variation in the log wear-scar diameter with log load for the paraffin oil without and with jl-hydroxo-jl-(N-phenylformamidino­N'-alkylthiocarbamido)-bis-[d ioxohydroxo molybdenum (VI)] additives and reference additive.

TRIPATHI el a /.: TRIBOLOGICAL EV ALUATION OF N-PHENYLFORMAMIDINO-N'-ALKYLTHIOCARBAMIDES 211

= -0 C

'" C d.J

E g a. Vl

c;; .D 01) C .... '" d.J .D C o

> E ::::I C d.J

-0 .D >. o E o >< 2 -0 >.

..c o >< o :::: Vl

.D

'-o c o ;;; ::::I

c;; > ~

J

c o ;;; C. d.J Vl

.D o

-l Vl

;;; c o ;;; C. d.J

'" .D

o

C d.J _ E

'" .-m ~

a. Vl

* :::l.

* :::l.

-)(. E ;" E

'" o

o V) Ir.

o

o V) V)

N

2; o

N r--

o 0-o c::i

o o

N \D o c::i

o V)

c::i

o 0\

Table 5 - Experimental results of anti-wear studies of additives [AI-A41 using bearing ball of specimen - I.

Paraffin oi I (P)

P

P+A 1

P+A2

P+A3

P+A4

Mean wear scar diameter (mm)

0.96

0.74

0.61

0.84

0.91

Load = 40 kgf. Time = I h. Speed = 1500 rpm .

Fig. 3-Scanning electron micrographs of wear spots using plain paraffin oil at loads :(a) 80 kgf and (b) 178 kgf.

micrographs at higher loads are comparatively smoother than the micrographs at lower loads. This may be due to the formation of a mixed lubricating film, which confirms the effectiveness of the additive at higher loads .

212 INDIAN J. ENG. MATER. SCI. , AUGUST 1999

Fig. 4-Scanning Electron Micrographs of wear spots using the admixture of paraffi n oi l wit h J..l -hydroxo-J..l -(N-phenylformamidino-N'­et hylthiocarbamido)- bi s-[dioxohydroxo molybdenum (VI)] at loads: (a) 11 2 kgf and (b) 550 kgf.

Conclusions The fo ll owing conclusions can be drawn : I. All the additives used were found to be effective

in increas ing the load carrying capaci ty.

2. ~-Hydroxo-~ - (N -phenylformamidino - N'-alkyl­thi ocarbamido)-bi s-[dioxohydroxo molybdenum VI] additives appear to be better EP and anti-friction additives as compared to N-phenylformamidino-N'-alkylthiocarbamide additives.

3. T he above Mo-S compl ex additive do not function as anti-wear additives .

4. T he additive, j..l-hydroxo-j..l-(N-phenylformamidi ­

no-N'-ethy I th iocarbamido)- bi s-[ dioxohydroxo molybdenum VI] appears to be quite effective with bearing ball specimen I and II and proves to be the best EP and anti-friction additive.

Acknowledgement The authors are thankful to the Director, Institute of

Technology, Banaras Hindu University for providing necessary facilities and CSIR for providing an Emeritus Scientistship to VKV.

References

Mitchell PC H, Wear, 10Cl (1984) 28 1.

2 Yamamoto Y & Condo S, Wear, I 12( I) ( 1986) 79.

3 Vcrma V N & Bhatia J, Pmc. Workshop High Pel/orlJl Lllbr. Addit , Kanpur, (1987) I.

4 Sanin P L, Kuzmina G N, Lazovoi Y A & Za movskaya T A, Schmierungstechnick, 18( I 0) (1984) 304; Chem Abstr, (1988) 1088 & 78363 .

5 Zheng E & Xi anglin 0 , Wear, 130 ( 1989) 233.

6 Singh T & Verma V K, Indiall 1 Technol, 28( I) (1990) 649.

7 SinghT&Verma VK , Wear,146(199 1) 3 13.

8 Singh T, Bhatlacharya A & Verma V K, Tribol lilt , 25(6) (1992) 38 1.

9 Verma V K, Bhatlacharya A, Singh R & Tripathi A K, Proc. XI Na tional COil! Indllstr Tribology, New Delhi (1995) 421 .

10 Bhattacharya A, Singh T, Singh A P, Singh R & Verma V K, Lllb Sci, 7( 1) (1994)61.

II Matsuo K J, lSLE, 3 1 (4) ( 1986) 20Cl.

12 Dixit S N, Chemistl)' of Isodithiobiuret5. Dithiobillrets. Dithiazolidines and related systems. Ph D thesis, Banaras Hindu University, ( 1962).

13 Kay A & Mitchell PC H, 1 Chem Soc, A (1970) 2421 .

14 Dyer J R, Applications of Absorption Spectroscopy of organic compounds, (prcntice-Hall India Pvt Ltd, New Delhi), 1989.