Embed Size (px)
Citation preview
Preparation and tribological properties of Nb1-xTixSe2
micro/nanoparticles
Jiaqing Liang1,a, Changsheng Li1,b*, Hua Tang1,c, Yi Zhang1, Wenjing Li1,
Zhili Hu1, Fen Wang1
1 School of Material Science and Engineering, Jiangsu University, Zhenjiang 212013, PR China [email protected],[email protected], [email protected]
Keywords: Micro/nanoparticles, Solid-state reaction, Nb1-xTixSe2, Tribological properties.
Abstract. Nb1-xTixSe2 (x=0～1) micro/nano-particles have been successfully prepared via solid-state
thermal (750) reaction between microsized Nb, Ti with Se powders under seal environment in a seal quartz tube and characterization by X-ray diffractometer and scanning electron microscopy. It was found that the morphologies of the as-prepared products changed from microplates to micro-nanoparticles or aggregations composed of layer structure with the doping of Ti. And the amount of regular hexagonal microplates evidently reduced and nanoscaled particles increased with the increase of the contents of Ti dopant within a certain limit (1-20 atwt. %). The tribological properties of the as-prepared products as additives in paraffin were investigated by UMT-2 multispecimen tribotester. By the addition of Nb1-xTixSe2 micro/nanoparticles in paraffin, the antiwear ability was improved and the friction coefficient was decreased. The paraffin with Nb1-xTixSe2 micro/nanoparticles showed better tribological properties than that with pure NbSe2. A combination of the molecule-bearing mechanism of sliding friction, and fill in-repair work between the rubbing surfaces can explain the good friction and wear properties of Nb1-xTixSe2 micro/nanoparticles.
Introduction
The transition-metal dichalcogenides MX2 (M = Mo, W, Nb, Ta, Ti, and Zr; X = S, Se) are have a hexagonal layered structure, which is similar to the structure of graphite. Over the past several years, certain MX2 materials(TaS2, TaSe2, NbSe2 etc.) have been studied extensively in bulk because they exhibit interesting temperature-dependent electronic instabilities, such as metal to superconducting or charge density wave (CDW) transitions at low temperature. As member of transition metal dichalcogenide compounds, NbSe2 have been made to be a hotspot as for coexistence of CDW and superconductivity [1,2]. NbSe2 has the similar tribological properties with MoS2 outside, shows some unique performance [3-5]. For example, the resistance rate of NbSe2 is 3.5 × 10-4 Ω · cm, which is far less than that of MoS2 (the resistance rate is 8.5× 102 Ω · cm).
The structure of 2H-NbSe2 (consists of three-lay packets, inside which the layers are ordered in the Se-M-Se sequence with covalent binding between them, whereas the packet is bound by van der Waals coupling. The structure schematic diagram of TiSe2 is similar to that of NbSe2. Recently, researchers had done a lot of research on doping modification of NbSe2, for instance of doping Co, Mn, Cu into NbSe2
[6-8], but they mainly focus on the superconductivity, CDW, photoemission or performance of magnetization[9-12]. Up to date, the relevant reports on modified tribological characteristics of NbSe2 via doping titanium have not been reported[13].
Advanced Materials Research Vol. 619 (2013) pp 536-540Online available since 2012/Dec/13 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.619.536
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 130.126.32.13, University of Illinois, Urbana, United States of America-07/03/13,00:29:03)
In this study, Nb1-xTixSe2 micro/nanoparticles with various structures have been successfully synthesized by a facile solid-state reaction. The results showed the introduction of Ti dopant leaded to an obvious size and morphology changes of the as-prepared products, and the Nb1-xTixSe2 micro/nanoparticles exhibited a better friction and wear property than NbSe2 as additives in paraffin.
Experimental
Synthesis of NbSe2 and Nb1-xTixSe2 micro-nanoparticles
In this experiment, elements of selenium, titanium and niobium powders are all micro-sized and used as received without any further purification. For the preparation of Nb1-xTixSe2 , as a typical case of S2, the mixed powders (molar ratio: Ti: Nb: Se=1: 99: 205, an overdose of 5% Se) is introduced into a quartz tube (Ф6×100mm) at room temperature and then seal it with the acetylene flame rapidly. The quartz tube must be clean and dry before sealing. In order to obtain homogenized powders, we mix the mixture by using mechanical ball milling technique. The uniform mixture is placed into a quartz tube and then seals it. The temperature of the tube furnace is raised to 750°C at a rate of 10°C /min and the heat is maintained at 750°C for 2h. Subsequently the reactor is gradually cooled to room temperature, opened, and the as-prepared powder is obtained. The product is directly characterized without further processing by various analytic techniques. Summary of the samples doped with different amounts of Ti powder are shown in table 1.
Table 1 Summary of the Samples Doped with Different Amounts of Ti powder.
Sample Ti-containing Ti:Nb:Se/mole ratio Sample Ti-containing Ti:Nb:Se/mole ratio
S1 0 0:100:205 S6 9% 9:91:205
S2 1% 1:99:205 S7 10% 10:90:205
S3 3% 3:97:205 S8 15% 15:85:205
S4 5% 5:95:205 S9 20% 20:80:205
S5 7% 7:93:205 S10 100% 100:0:205
Characterizations
Power X-ray diffraction (XRD) patterns of the products are performed on a D8 advance (Bruker-AXS) X-ray Diffractometer with Cu Kα = 1.5418 Ǻ radiation. The morphology and microstructure of the synthesized NbSe2 and Nb1-xTixSe2 particles are carried out by scanning electron microscopy (SEM) on a JEOL JXA-840A instrument. All the measurements were carried out at room temperature. Tribological properties of Nb1-xTixSe2 micro-nanoparticles as lubrication additive
The as-prepared products (S1-S9) were dispersed in the paraffin by different percentages with ultrasonic vibration (1800 W power, 2 kHz frequency) for 1 h with span80 as active reagent, and then a series of suspended paraffin samples were obtained. The tribological properties of the base oil containing prepared particles as additive and pure paraffin were investigated on a UMT-2 ball-on-plate friction and wear tester. The friction reduction and wear resistance test was conducted at the rotating speeds of 200rpm with loads of 10 N for 15min.
Advanced Materials Research Vol. 619 537
Results and Discussion
Characterizations of NbSe2 doped with different amounts of Ti
10 20 30 40 50 60 70 80
*
*
* * *
***
Inte
nsity
2-theta(degree)
*--TiySe
x002
10
1
10
2
10
3
10
4
10
5
204
11
0
a
b
c
d
e
f
g
h
i
Fig.2 Wide angle XRD patterns of pure NbSe2 (a) and Nb1-xTixSe2 (b-i) (1, 3, 5, 7, 9, 10, 15, 20
atwt.% ) Ti-doped NbSe2 prepared at 750°C from a 2 h solid-state reaction between micron-sized Ti, Nb and Se elements.
The XRD patterns of NbSe2 and Nb1-xTixSe2 fabricated from a 2 h solid-state reaction between micron-sized Nb, Ti and Se elements at 750°C were illustrated in Fig.2. It can be observed that all the diffraction peaks match well with the standard patterns of pure NbSe2 until the introduction of titanium up to 10 atwt. % in addition to change of intensity of the diffraction peaks. When the doping dosage of Ti exceed 15 atwt.%, there appears some obvious additional reflection line related to TixSey (Fig.2d and e).
The morphological of pure NbSe2 particles and Nb1-xTixSe2 particles is characterization by the HR-SEM. Fig.3a shows that the as-prepared pure NbSe2 particles are composed of relatively regular hexagonal microplates and a thickness of about 100nm~500nm. When introduced 1 atwt.% Ti, uniform regular microplates were obtained, similar to that of pure NbSe2 products (Fig.3b). When 3 atwt.%Ti was introduced in the system, the morphology have a obvious change, the products become aggregates composed of thin layer in addition to regular microplates (Fig.3c). This suggests that the introduction of Ti affected the morphologies of the products due to the rearrangement of atoms during crystallization.
Fig.3 Scanning electron microscopy (SEM) image of a) pure NbSe2, b-j) (1, 3, 5, 7, 9, 10, 15, 20,
100 atwt.%) Ti-doped NbSe2. When doped 5, 7 and 9 atwt.% Ti, the crystallite dimension tend to be larger than the size of
pure NbSe2, and hexagonal plate become less regular (Fig.3d, e and f). Then, with the dopant content increased to 10 atwt.%, a large amount of nanoparticles were obtained along with a small amount of hexagonal plates (Fig.3g). While the doping dosages of Ti exceed 15 atwt.%, the products were mainly composed of plate-like particles besides a small amount of nanoparticles
538 Hydraulic Equipment and Support Systems for Mining
(Fig.3h and i). Fig.3j is the SEM image of pure TiySex. It can be observed that plate-like particles with a size of about 20 µm composed of thin layers and a large amounts of nanoparticles existed on the surface of the plate.
Effect of NbSe2 and Nb1-xTixSe2 micro-nanoparticles on tribological properties
Fig.4a shows the friction coefficient as a function of concentration of the pure NbSe2 microplates from 0 to 7 wt.% at 10N load and 200rpm rotating speed. For the mass fraction <7 wt.%, the friction coefficient of paraffin containing NbSe2 microplates was not always lower than that of the pure paraffin, but decreased to the lowest at 1wt.%. The width of wear scar of plate after rubbing is shown in Fig. 4b. It could be easily be found that the width of wear scars reached to minimum value at 1 wt.% NbSe2.
-1 0 1 2 3 4 5 6 7 8
0.109
0.110
0.111
0.112
0.113
0.114
0.115
0.116
a. Coefficient of friction
b. Width of wear scar
Content of NbSe2 in the parffin suspension(wt%)
Frictio
n c
oeffic
ient
a
b
0.20
0.24
0.28
0.32
0.36
0.40
Wid
th o
f wea
r scar(m
m)
Fig.4 Tribological properties of the paraffin containing 0, 0.5wt.%, 1wt.%, 3wt.%, 5wt.%, 7wt.% of
pure NbSe2 at the load of 10N at a speed of 200r/min.
Figure 5a, b shows the friction coefficient and the width of wear scar as a function of content of Ti in Nb1-xTixSe2 from 0 to 20 atwt.% at 10N load, 200rpm rotating speed and the mass fraction of Nb1-xTixSe2 micrio/nano particles was fixed at 1wt.%. For the content of doping Ti <10 atwt.% (except for 1 atwt.%Ti), the friction coefficient of paraffin containing Nb1-xTixSe2 micro/nano particles was lower than that of pure NbSe2 and reduced to the minimum at 10atwt.%Ti. It also can be seen that the friction coefficient become much higher than that of pure NbSe2 when the doping amount exceed 10%. The width of wear scar was the minimum at 10 atwt.%Ti. From the above results, Nb1-xTixSe2 micro/nano particles as lubrication additive could improve tribological properties of the paraffin, and obtained the best performance when the Ti doping content is 10 atwt.%.
0 5 10 15 20
0.104
0.106
0.108
0.110
0.112
0.114
0.116
a. Friction coefficient
b. Width of wear scar
Content of Ti in Nb1-x
TixSe
2 in the parffin suspension(atwt.%)
Fic
tio
n c
oeffic
ient
0.20
0.25
0.30
0.35
0.40
0.45
Wid
th o
f we
ar S
ca
r(mm
)
a
b
Fig.5 Tribological properties of the paraffin containing NbSe2 (S1) and Nb1-xTixSe2 (S2~S9) under a
speed of 200 rpm and at the load of 10N.
Advanced Materials Research Vol. 619 539
Conclusion
The micro/nano Nb1-xTixSe2 flakes are fabricated by solid-state reactions of micro-sized Nb and Se reacting with Ti at 750°C for 2 h. The results reveal that the existence of Ti plays an important influence on the size and morphologies of the as-prepared products. The morphologies of the as-prepared products changed from microplates to the mixture of irregular microplates and nanoparticles to aggregations composed of layer structure with the doping of Ti. The paraffin with the addition of Nb1-xTixSe2 flakes showed the best friction-and-wear properties. Tribological experiments suggested that the effect of Nb1-xTixSe2 flakes as lubrication additive could be attributed to the molecule-bearing mechanism of sliding friction, and fill in-repair work of the both products between the rubbing surfaces. Moreover, the Nb1-xTixSe2 micro-nanoparticles with different morphologies could form a narrower and shallower wear scar on the rubbing surface; as a result, the Nb1-xTixSe2 micro-nanoparticles present a better tribological property than NbSe2.
Acknowledgements
The authors gratefully acknowledge the financial support from the National Nature Science Foundation of China (Grant No.50471051), Jiangsu provincial science and technology enterprises "innovation fund" ( BC2010021), Open Project of Key Laboratory of Tribology of Jiangsu Province (Kjsmcx2011002, kjsmcx1005) and Scientific Research Foundation for Distinguished Scholars, Jiangsu University (Project ID:09JDG009).
References
[1] A. LeBlanc, A. Nader: Solid State Commun. Vol. 150 (2010), p. 1346-1349 [2] I NAIK, A K RASTOGI: Pramana - J. Phys. Vol. 76 (2011), p. 957-963 [3] Bilas P, Romana L, Bade F, et al: Tribol. Lett. Vol. 34(2009), p. 41-48 [4] Li CS, Hao MD, Liu YQ, et al: 2008 3rd Ieee International Conference on Nano/Micro
Engineered and Molecular Systems.Vol.1-3(2008), p. 324-328 [5] Tang H, Li CS, Yang XF, et al: Cryst. Res. Technol. Vol. 46(2011), p. 400-404 [6] M Iavarone, G Karapetrov, J Fedor and D Rosenmann: Supercond. Sci. Technol. 24 (2011), p.
024010 [7] M Iavarone, G Karapetrov, J Fedor, D Rosenmann, T Nishizaki2 and N Kobayashi: J. Phys.
Condens. Matter 22 (2010), p. 015501 [8] Y.Y. Koh, Y.K. Kim, W.S. Jung, G.R. Han, et al: J. Phys. Chem. Solids. Vol.72 (2011), p.
565–567 [9] M. Zehetmayerand H, W. Weber: Vienna University of Technology, Atominstitut, 1020 Vienna,
Austria. 2010 [10] V Sirenko, V Ibulaev, M Shvedun1 and V Eremenko: Journal of Physics: Conference Series
Vol.150 (2009), p. 042186 [11] A. Prodan, V. MarinkoVic, N. Jug, et al: Surf. Sci. Vol. 476(2001), P. 71-77 [12] M. Iavarone, R. Di Capua, G. Karapetrov, et al: Phys. Rev. B.Vol. 78(2008), p. 174518 [13] David C. Johnson, Stephen D. Kevan and Myungkeun Noh: J. Korean Phys. Soc. Vol.
30(1997), p. 575-579
540 Hydraulic Equipment and Support Systems for Mining
Hydraulic Equipment and Support Systems for Mining 10.4028/www.scientific.net/AMR.619 Preparation and Tribological Properties of Nb1-xTixSe2 Micro/Nanoparticles 10.4028/www.scientific.net/AMR.619.536
