Influence of Different Environement

Volume 5, Issue 4, April – 2020 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165
Influence of Different Environement

on the Tribological Behavior of
Molybdenum Disulfide Mos2
H.S. Bui
Université de Technologie, Ha noi, Viet Nam
Abstract:- Plastic materials are more and more In the previous time, we did not attribute the variation
important in our life. This article measure the thermal of friction coefficient molybdenum disulfide MoS2 in the
properties of some typical plastics materials by using environment around tribocontact [19]. Since 1976, it
the TMA Q400 machine. By comparision of their results demonstrates with the notion of "time stop effect" that there
and their chemical formulas will show their properties. is an influence of water vapor, gases or other contamination
on the friction coefficient. In this paper, we present the
The tribological properties of molybdenite or experimental results obtained in four tribological different
molybdenum disulphide MoS2 depend on the relative gas environments. Then we discuss the reasons which
humidity of gases surrounding the tribocontact. In high change the friction coefficient in the different gaseous
vacuum environments and in inert gases, the friction environments.
coefficient µ of molybdenum disulphide MoS2 is very
low about µ=0,02 and in humid environments, the II. DESCRIPTION OF EXPERIMENTAL TESTS
friction coefficient increases to µ = 0,18.
Tribological tests were done by using one pin-on-disc
The objective of this study is to present the type tribometer as shown in the figure 1. The pin is
experimental results of the tribological properties of hemispherical shape with diameter of 5 mm and length of
molybdenum disulfide MoS2 against steel XC48 in 15 mm. The disc diameter is 70 mm which is covered by a
different gaseous environments (in high vacuum and thin layer of molybdenum disulphide MoS2. Both of them
ambient air). We calculate the potential energy between are made of steel XC 48 and they are localised in the
the gaseous molecules and the surface of adsorption or chamber of tribometer.
between these adsorbed gaseous molecules. We also try
to estimate the interactions between the adsorbed The different gaseous types used for the experimental
gaseous molecules of the gap between the two tests such as dry ambient air. The temperature is nearly
consecutive layers of the crystal molybdenum disulfide stable about 25o C. The relative sliding speed is 0,4 m/s.
MoS2. We discuss the effect of these interactions on the The normal load N is 4,625 N applied with the mass on the
tribological characteristics of molybdenite MoS2. arm carrying the pin.
Keywords:- Molybdenum Disulphide, Water Vapor, To prepare the experimental in high vacuum, the air of
Polarisation, Ionization Energy, Lubrification, Friction the closed chamber is evacuated by a system of pumps. A
Coefficient. primary pump can descend to a pressure of 10 -1 Pa. A
second turbo pump continues descend down to 10 -5 Pa in 24
I. INTRODUCTION hours. Once the high vacuum reached, we can start the
friction tests in high vacuum.
Molybdenum disulfide MoS2 crystal is a hexagonal
structure. It is a solid lubricant lamellar structure of The friction force is recorded by a gauge. The various
alternating layers: layer of sulfur / molybdenum layer / sensors are connected to a central acquisition of
layer of sulfur ... layer of sulfur / molybdenum layer / layer multichannel data. The analog signal is amplified and
of sulfur ... (S / Mo / S ... S / Mo / S ...). Its low friction converted by a conditioner Labview 7.1.
coefficient μ = 0.02 obtained in high vacuum around
tribocontact is due to the weak bonds Van der Waals [1-15]
between two layers of sulfur. However, this low coefficient
of friction can vary and increase to μ = 0.18 in air ambient
around the tribocontact [1-15].
IJISRT20APR413 www.ijisrt.com 478

ISSN No:-2456-2165
Fig 2:- Evolution of friction coefficient of the steel /

molybdenum disulfide / steel in high vacuum (v = 0.4 m / s,
T = 25 ° C, load = 4.6 N)
B. Tribological behavior of molybdenum disulfide in

ambiant air
Under the influence of a mixture of several gases such
as ambient air, the coefficient of friction is not stable
(Figure 3). It varies between the value μ = 0.18 at the start
Fig 1:- The general view of tribometer pion-disc type (disc of the test and μ = 0.12 at steady state and depends on the
support, chamber, vacuum pump) concentration or percentage of the gases in the mixture.
III. RESULTS AND DISCUSSIONS
All the gaseous contamination in the molybdenum

disulfide produced an increase in friction coefficient
compared with the value obtained in high vacuum. Indeed,
it has been shown experimentally in several publications
[1,15].
The contamination by the vapors is probably

inherently an impact on the structure of molybdenum
disulfide MoS2 and produces an increase of friction
coefficient rather than the one in high vacuum. In fact, it
has been demonstrated experimentally in a wide range of
publications reported that it increases the friction
coefficient when the two consecutive layers of Fig 3:- Evolution of friction coefficient of the steel /
molybdenum disulfide sliding parallel with the basal planes molybdenum disulfide / steel in ambiant air (v = 0.4 m / s,
of the crystallites. T = 25 ° C, load = 4.6 N)
For each experiment, we must change the new pin and IV. DISCUSSION
the new disc.
The molybdenum disulphide is gray-black in color
A. Tribological behavior of molybdenum disulfide in high and the density is 4800-5000 kg / m3. It is easily
vacuum (10-5 Pa) transmitted to another surface. If it attaches to a surface and
Once the contact pin of steel / molybdenum disulfide / it is difficult to wash. Transfer is easy for all surfaces
steel disc is established is placed, the chamber is pumped because it easily sticks to surfaces. In reality, there are two
by a primary pump for an hour until the residual pressure forms: hexagonal and rhombohedral. We can also list
P = 10-1 Pa and then the secondary pump descends the certain physical properties; the most important ones are:
residual pressure 10-5 Pa in 24 hours.  Melting point: around 1700 ° C under atmospheric
pressure
Our test of the tribological contact steel / MoS2 / steel  Molecular mass: 160.08 g / mol
carried out in high vacuum (P = 10-5 Pa) lead to a friction  Hardness (basic planes): 1-1.5 Moh scale
coefficient μ = 0.018 in steady state (Figure 2).  Hardness (crystal edges) 7-8 Moh scale
 Magnetic properties: diamagnetic
 Sublimation temperature: 1050 ° C under high vacuum
 Dissociation temperature: 1370 ° C

ISSN No:-2456-2165
Some authors use the inorganic fullerene of In order to stabilize the MoS2 molecules, the
molybdenum disulfide in oil to improve its tribological molybdenum and the sulfur are hybridized to sd 4p and the
characteristics and its viscosity. The two families of structure of MoS2 obtained is a hexagonal structure. The
molybdenum disulfide, the rhombohedral structure (rh) and crystal structure of natural molybdenite (molybdenum
the hexagonal structure (hcp), on which the research work disulfide) is hexagonal, with the basic coordination unit of
is based, will be presented. molybdenum disulfide MoS2 is a trigonal prism: the
molybdenum Mo atom is located in the center of the right
Figure 4 shows the crystal resemblances between the trigonal prism and itself is surrounded by six sulfur atoms
rhombohedral (rh) and hexagonal (hcp) structure. The at the vertices of this prism and each sulfur atom is
distances between sheets are different. It is 1.23 nm in the equidistant from three molybdenum atoms. The crystal
hexagonal structure and 0.615 nm in the rhombohedral structure of molybdenum disulphide MoS2 can be
structure (Figure 4). considered as a stack of XMX macromolecules whose
valences are all saturated. Because of the special structure
of the molybdenum disulphide MoS2 due to the sd4p
hybridization of the Mo and S atoms, we have a hexagonal
shape (Figure 5) which is symmetrical and self-balanced.
The consecutive sulfur layers are linked together by

fairly weak forces, while the bonds between molybdenum
and sulfur in each layer are covalent and under the
influence of the different conditions such as ambient air, in
high vacuum, it will be influenced the friction coefficients
of molybdenite MoS2. It has a very large anisotropy of the
crystal and an easy cleavage parallel to the basal plane.
Fig 4:- The two main structures of molybdenum disulfide V. CONCLUSION

MoS2: hexagonal (hcp) and rhombohedral (rh)
Our tests conducted on the tribological couple
Molybdenum disulfide has been widely studied for a acier/MoS2/acier in high vacuum (P = 10-5 Pa), and in
long time. The studies relate to its physical, chemical ambiant air that illustrate the influence of environment
character and also on its tribological behavior. around the tribo-contact tribological behavior of MoS2:
We study the electronic configurations of  Tests under high vacuum demonstrate clearly the
molybdenum atoms and sulfur atoms, so that we can find intrinsic nature of self-lubricating molybdenum
the optimal combination. disulfide μ = 0.02. Disulfide behaves almost as well
as a lubricant fluid.
 The electronic configuration of molybdenum is:
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s1 4d5  The tests carried out under ambient air clearly show the
influence of the properties of different gases on the
 The electronic sulfur configuration is: tribological molybdenum disulfide MoS2.
1s2 2s2 2p6 3s2 3p4
 It is interesting to perform tribological tests in mixtures
If we arrange valence electrons in the 5p orbit 5s 4d of gases (argon + oxygen), (nitrogen + oxygen) ...,
for the molybdenum atom and 3s, 3p for the sulfur atom, (nitrogen + oxygen + water vapor) to determine the
we have arrangements of the electrons in the orbitals and partial pressures at critical transition (low friction /
the overlap of the orbitals (figure 5): friction severe).
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Fig 5:- MoS2 molecular orbitals structures

ISSN No:-2456-2165
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Volume 5, Issue 4, April – 2020 International Journal of Innovative Science and Research Technology

Influence of Different Environement

IJISRT20APR413 www.ijisrt.com 478

Fig 2:- Evolution of friction coefficient of the steel /

B. Tribological behavior of molybdenum disulfide in

III. RESULTS AND DISCUSSIONS

All the gaseous contamination in the molybdenum

The contamination by the vapors is probably

IJISRT20APR413 www.ijisrt.com 479

The consecutive sulfur layers are linked together by

Fig 4:- The two main structures of molybdenum disulfide V. CONCLUSION

[1]. Bui.H.S, Zaidi.H, « Influence de l'environnement sur

IJISRT20APR413 www.ijisrt.com 480

IJISRT20APR413 www.ijisrt.com 481

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