- Email: [email protected]
Pt composites
Accepted Manuscript Title: Fracture toughness and surface morphology of Al2 O3 /Pt composites Author: Dong-Jin Lee Heung-Soap Choi Fan-Long Jin Soo-Jin Park PII: DOI: Reference:
S1226-086X(14)00514-0 http://dx.doi.org/doi:10.1016/j.jiec.2014.10.025 JIEC 2266
To appear in: Received date: Revised date: Accepted date:
16-8-2014 1-10-2014 13-10-2014
Please cite this article as: D.-J. Lee, H.-S. Choi, F.-L. Jin, S.-J. Park, Fracture toughness and surface morphology of Al2 O3 /Pt composites, Journal of Industrial and Engineering Chemistry (2014), http://dx.doi.org/10.1016/j.jiec.2014.10.025 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Graphical Abstract
Fracture toughness and surface morphology of Al2O3/Pt composites
ip t
Dong-Jin Lee, Heung-Soap Choi, Fan-Long Jin, Soo-Jin Park
Ac ce p
te
d
M
an
us
cr
The fracture surface showed an intergranular mechanism of fracture, typical of ceramic materials, at low Pt content, and a transgranular mechanism at high Pt content.
Page 1 of 19
ip t
Manuscript number: JIEC-D-14-01573
cr
Fracture toughness and surface morphology of Al2O3/Pt composites
b
Nano Technology Inc., 289-20 Daehwa-dong, Daedeok-gu, Daejon 306-801, Korea
an
a
us
Dong-Jin Lee a, Heung-Soap Choi b, Fan-Long Jinc,d, and Soo-Jin Park *,d
Department of Mechanical and Design Engineering, Hongik University, Sejong 339-701,
c
M
Republic of Korea
Department of Polymer Materials, Jilin Institute of Chemical Technology, Jilin City 132022, People’s Republic of China
d
Department of Chemistry, Inha University, Nam-gu, Incheon 402-751, South Korea
Ac ce p
te
d
* Corresponding authors.
Phone: +82 32-8767234. Fax: +82 32-8675604. E-mail: [email protected] (S. J. Park).
Page 2 of 19
ABSTRACT: In the present study, Al2O3-based composites with dispersed Pt particles were prepared by using a reduction-precipitation method. Particle distribution, fracture toughness, and morphology of
ip t
the prepared Al2O3/Pt composites were studied. Crystal structure of the composites was evaluated by analyzing Pt characteristic peaks in the X-ray diffraction spectra. Transmission
cr
electron microscopy images indicated that the Pt particles were uniformly dispersed in the Al2O3
us
powder. The fracture toughness of the Al2O3 matrix was improved by the addition of Pt particles, since these particles effectively resisted crack propagation in the Al2O3/Pt composites. Scanning
an
electron microscopy images indicated that the fracture of the composites followed an
d
mechanism occurred at high Pt content.
M
intergranular mechanism, typical of ceramic materials, at low Pt content, whereas a transgranular
Ac ce p
te
Keywords: Al2O3, Pt, Composites, Fracture toughness, Morphology
Page 3 of 19
1. Introduction
Al2O3 is as a typical representative of engineering ceramics. It has been extensively
ip t
employed for structural applications in automotive, aerospace, and biomedical fields because of
cr
its high hardness, good wear resistance, and other outstanding mechanical properties. However, Al2O3 is brittle and is prone to accidental damages; thus, it has limited use as an advanced
us
engineering material for the production of cutting tools, cylinder liners, and piston rings in automotive engines [1-5].
an
The fracture toughness of Al2O3-based materials can be improved by the incorporation
M
of metallic particles with a plastic behavior into the Al2O3 matrix [6-10]. In previous studies Al2O3-based composites were prepared to realize outstanding fracture toughness and excellent
d
physical properties. Mishra et al. studied the microstructure, hardness, and fracture toughness of
te
Al2O3/ZrB2 composites with different percentages of titanium as the diluent [11]. The fracture toughness increased significantly with increasing titanium content due to the formation of
Ac ce p
different phases in the composites, which improved the material resistance to crack propagation. Maiti et al. investigated the influence of sintering temperature and soaking time on the fracture toughness of Al2O3-based ceramics [5]. The study of fracture surface reveals that Al2O3-based ceramics present a mixed mode of fracture−intergranular and transgranular−with the former mode being in greater proportion. Schlenther et al. studied the fracture toughness and corrosion behavior of steel particle-reinforced Al2O3 composites [12]. The authors attributed the increase in crack propagation resistance to the behavior of the metallic matrix phase, which remained intact behind the propagating crack front. Yao et al. developed novel thermal barrier coatings based on Al2O3-Y2O3/Pt composites [13]. These thermal barrier coatings improve the resistance
Page 4 of 19
of the composites to oxidation at high temperatures and also provide excellent resistance to cracking owing to their sealing effect. In the present study, Al2O3/Pt composites were prepared to realize outstanding fracture
ip t
toughness. The structure of the composites was characterized using X-ray diffraction (XRD) spectra. The particle distribution and the morphology were studied using transmission electron
cr
microscopy (TEM) and scanning electron microscopy (SEM), and the mechanical properties
us
were evaluated using a universal testing machine.
M
an
2. Experimental
Hexachloroplatinic(IV) acid, hydrazine monohydrate, and α-Al2O3 powder were
d
purchased from Sumitomo Chemical Co. Ltd. Nitric acid was supplied by Kojima Chemical Co.
te
Ltd.
Pt-dispersed Al2O3 powders were prepared using a reduction-precipitation method.
Ac ce p
Hexachloroplatinic acid and hydrazine monohydrate were used as the Pt solvent and reduction agent, respectively. The Pt solution was prepared by dissolving between 0.6−1.2 g of hexachloroplatinic acid in 50 mL of deionized water, and the hydrazine solution by dissolving 0.4 g of hydrazine monohydrate in the same quantity of deionized water. Then, the two solutions were mixed in a 1:1 ratio. Finally, 3 g of α-Al2O3 powder were added to the solution. For an hour, the temperature was maintained at 85oC and the pH was kept at 1 by adding nitric acid when necessary, in order to bring about the reduction of Pt and the subsequent precipitation. Al2O3/Pt composite samples were given the final shape by pressing the obtained powder in a specific equipment.
Page 5 of 19
The structure of Al2O3/Pt composites was investigated using XRD (XRD, Rint-2000, Rigaku). The particle distribution in the Al2O3 matrix was investigated using TEM (JEOL, JSM6330F). The grain size of Al2O3 and Pt was calculated from TEM images by using computer
ip t
programs. The fracture toughness was measured by performing the three-point bending flexural test, which was performed on a universal testing machine (Instron Model 1125) using single
cr
edge-notch bending specimens. The surface morphology of the composites was investigated by
us
scanning electron microscopy (SEM, JEOL JXA840A).
M
an
3. Results and discussion
Fig. 1(a) shows the XRD data of the Al2O3/Pt composites prepared by the reduction-
d
precipitation method. Broad peaks of Pt are evident at 39.8o, 46.3o, and 67o, indicating the
te
presence of nanosized Pt particles. The intensity of the Pt peak associated with the amorphous halo pattern increased significantly with increasing Pt content [14-17].
Ac ce p
Fig. 1(b) shows the XRD data of Al2O3/Pt composites treated at 1450oC for 2 h. The Pt
peaks became sharp after heat treatment, and the peak size increased with increasing Pt content from 4 wt% to wt12%.
Figs. 2(a) and (b) show the TEM images of Al2O3/Pt composites with a Pt content of 4
wt%. As shown in Fig. 2(a), circular Al2O3 particles formed large clusters with an average size of 200 nm. Pt particles with a size in the range of 5 to 30 nm were irregularly dispersed in the Al2O3 matrix and combined effectively with Al2O3 particles, as shown in Fig. 2(b) [18,19]. Figs. 2(c) and (d) show the TEM images of the Al2O3/Pt composites with different Pt content. When the Pt content was increased from 4 to 12 wt%, the contrast of the circular, dark
Page 6 of 19
Pt particles against the bright matrix increased significantly. However, the particle size for the composites remained basically unvaried, between 5 and 20 nm, with varying Pt content. Figs. 2(e) and (f) show the TEM images of the Al2O3/Pt composite with a Pt content of
ip t
12 wt% baked at 1450oC for 2 h in air. The grain size of the composites was 1−3 μm. Circular Pt
cr
particles with a size of 30−500 nm were uniformly dispersed inside and outside the Al2O3 clusters. Further, no cracks formed at the interface between Pt and Al2O3, possibly because the
us
nanosized Pt particles and the Al2O3 matrix have similar thermal expansion coefficients [20,21]. Table 1 shows the relative density, hardness, and fracture toughness of the Al2O3/Pt
an
composites. The relative density of the composites increased with increasing Pt content. The Pt
M
particles were uniformly dispersed inside and outside the Al2O3 clusters and were found to be present in the cavities produced because of sintering. This resulted in an increase in the relative
d
density and in the Vickers hardness of the composites from 1685 to 1892 HV when the Pt
te
content was increased from 4 to 12 wt%. The increased Vickers hardness can be explained as follows. At Pt content of 4 wt%, many cavities appeared on the Al2O3 surface, whereas the
Ac ce p
cavities disappeared completely and a compact composite was obtained when the Pt content reached 12 wt%, as shown in Fig. 3. The fracture toughness of the composites increased from 4.7 to 5.5 MPa⋅m1/2 with increasing Pt content, because the Pt particles effectively restricted crack propagation in the Al2O3/Pt composites [22-25]. Fig. 3(a) shows the SEM images of the Al2O3/Pt composite powder before preparation
of the samples as a function of Pt content. Superfine Pt particles were uniformly distributed on the surface of the Al2O3 matrix. For a Pt content of 4 wt%, many cavities were evident on the Al2O3 surface. The number of cavities decreased upon increasing the Pt content to 8 wt%. When the Pt content reached 12 wt%, the cavities disappeared completely, and a compact composite
Page 7 of 19
was obtained. The size of the Pt particles varied between 50 and 250 nm for a Pt content of 4 wt%, and between 70 and 420 nm for a content of 12 wt%. Fig. 3(b) shows the SEM images of the fracture surfaces for the Al2O3/Pt composites.
ip t
Circular Pt particles are uniformly dispersed in the Al2O3 matrix, and increased with increasing Pt content. For a Pt content of 4 wt%, the fracture surface showed the intergranular mechanism
cr
of fracture, typical of ceramic materials. When the Pt content was increased to 12 wt%, the
Ac ce p
te
d
M
an
us
fracture surface varied significantly and showed a transgranular mechanism of fracture [26,27].
Page 8 of 19
4. Conclusions
Al2O3/Pt composites were prepared and their particle distribution, fracture toughness,
ip t
and morphology were studied. The characteristic peaks of the Pt particles appeared at 39.8o, 46.3o, and 67o in the XRD spectra. TEM results indicated that the Pt particles were effectively
cr
dispersed in the Al2O3 powder. The fracture toughness improved with increasing the Pt content,
us
since the Pt particles effectively restricted crack propagation in the Al2O3/Pt composites. The fracture surface showed an intergranular mechanism of fracture, typical of ceramic materials, at a
te
Acknowledgements
d
M
an
low Pt content (4 wt%), and a transgranular mechanism at a high Pt content (12 wt%).
This study was supported by the Carbon Valley Project of the Ministry of Knowledge
Ac ce p
Economy, Korea.
Page 9 of 19
References
1.
Z. Yin, C. Huang, B. Zou, H. Liu, H. Zhu, J. Wang, Material Science and Engineering:
ip t
A 593 (2014) 64.
S. Huang, W. Zhou, F. Luo, P. Wei, D. Zhu, Ceramics International 40 (2014) 2785.
3.
K. Maiti, A. Sil, Ceramics International 37 (2011) 2411.
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B. Dubiel, M. Chmielewski, T. Moskalewicz, A. Gruszczyński, A. Czyrska-
us
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Filemonowicz, Materials Letters 124 (2014) 137.
cr
2.
K. Maiti, A. Sil, Ceramics International 36 (2010) 2337.
6.
A. Nevarez-Rascon, A. Aguilar-Elguezabal, E. Orrantia, M.H. Bocanegra-Bernal,
M
5.
International Journal of Refractory Metals and Hard Materials 29 (2011) 333. M. Masanta, S.M. Shariff, A.R. Choudhury, Material Science and Engineering: A 528
d
7.
9. 10. 11.
S.J. Park, Y.S. Jang, Journal of Colloid and Interface Science 237 (2001) 91.
Ac ce p
8.
te
(2011) 5327.
S.J. Park, K.S. Cho, S.K. Ryu, Carbon 41 (2003) 1437. S.J. Park, K.D. Kim, Carbon 37 (2001) 1741. S.K. Mishra, A. Bhople, S. Paswan, International Journal of Refractory Metals and Hard
Materials 43 (2014) 7.
12.
E. Schlenther, H. Özcoban, H. Jelitto, M. Faller, G.A. Schneider, T. Graule, C.G.
Aneziris, J. Kuebler, Material Science and Engineering: A 590 (2014) 132. 13.
J. Yao, Y. He, D. Wang, H. Peng, H. Guo, S. Gong, Applied Surface Science 286 (2013) 298.
14.
F.L. Jin, K.Y. Rhee, S.J. Park, Material Science and Engineering: A 435-436 (2006)
Page 10 of 19
429. 15.
C. Yang, F. Wang, J. Zhu, H. Jiang, T. Ai, D. Xiao, Material Science and Engineering: A 610 (2014) 154. S. Kim, S.J. Park, Journal of Power Sources 159 (2006) 42.
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S. Kim, S.J. Park, Electrochimica Acta 52 (2007) 3013.
18.
F.L. Jin, C.J. Ma, S.J. Park, Material Science and Engineering: A 528 (2011) 8517.
19.
H.A. beni, M. Alizadeh, M. Ghaffari, R. Amini, Composites: Part B 58 (2014) 438.
20.
F.L. Jin, K.Y. Rhee, S.J. Park, Journal of Solid State Chemistry 184 (2011) 3253.
21.
R. Jamaati, M. Naseri, M.R. Toroghinejad, Materials and Design 59 (2014) 540.
22.
S.J. Park, F.L. Jin, J.R. Lee, Material Science and Engineering: A 374 (2004) 109.
23.
W. Dong, F.L. Jin, S.J. Park, Journal of Industrial and Engineering Chemistry 20 (2014)
cr
us
an
M
d
1220.
O. Ormanci, I. Akin, F. Sahin, O. Yucel, V. Simon, S. Cavalu, G. Goller, Material
te
24.
ip t
16.
Science and Engineering: C 40 (2014) 16.
26. 27.
F.L. Jin, S.J. Park, Material Science and Engineering: A 478 (2008) 402.
Ac ce p
25.
U.O.A. Arıer, F.Z. Tepehan, Composites: Part B 58 (2014) 147. W. Jiang, F.L. Jin, S.J. Park, Journal of Industrial and Engineering Chemistry 18 (2012)
594.
Page 11 of 19
Caption of the Figures
Fig. 1. (a) XRD spectra of Al2O3/Pt composites as a function of Pt content; (b) XRD spectra of
ip t
Al2O3/Pt composites treated at 1450oC for 2 h.
cr
Fig. 2. (a) and (b) TEM images of Al2O3/Pt composites prepared by reduction-precipitation method (Pt content: 4 wt%); (c) TEM images of Al2O3/Pt composites prepared by reduction-
us
precipitation method (Pt content: 4 wt%); (d) TEM images of Al2O3/Pt composites prepared by
an
reduction-precipitation method (Pt content: 12 wt%); (e) and (f) TEM images of Al2O3/Pt composites treated at 1450oC for 2 h (Pt content: 12 wt%).
Ac ce p
te
d
fractured surfaces for Al2O3/Pt composites.
M
Fig. 3. (a) SEM images of Al2O3/Pt composites as a function of Pt content; (b) SEM images of
Page 12 of 19
Table 1 Mechanical properties of Al2O3/Pt composites. Relative density (%)
Hardness (Hv)
Fracture toughness (MPa⋅m1/2)
4
97.8±0.3
1685±10
4.7±0.15
8
98.1±0.3
1788±10
5.1±0.17
12
99.5±0.3
1892±10
cr
ip t
Pt content (wt%)
Ac ce p
te
d
M
an
us
5.5±0.18
Page 13 of 19
30
40
50
60
o
2θ ( )
80
图片 图片
Ac ce p
te
d
Intensity
M
an
组合
70
us
cr
ip t
Intensity 20
20
30
40
50
60
70
80
o
2θ ( )
Page 14 of 19
ip t cr us an
d te
Ac ce p
Intensity
M
(a)
20
组合
30
40
50
60
70
80
o
2θ ( )
图片 图片
Page 15 of 19
30
40
50
60
70
us
cr
ip t
Intensity 20
80
o
Ac ce p
te
d
M
an
2θ ( )
(b)
Page 16 of 19
an
us
cr
ip t
Fig. 1.
(b)
Ac ce p
te
d
M
(a)
(c)
(d)
Page 17 of 19
ip t Ac ce p
te
d
M
an
Fig. 2.
cr
(f)
us
(e)
(a)
Page 18 of 19
ip t cr
M
an
us
(b)
Ac ce p
te
d
Fig. 3.
Page 19 of 19
S1226-086X(14)00514-0 http://dx.doi.org/doi:10.1016/j.jiec.2014.10.025 JIEC 2266
To appear in: Received date: Revised date: Accepted date:
16-8-2014 1-10-2014 13-10-2014
Please cite this article as: D.-J. Lee, H.-S. Choi, F.-L. Jin, S.-J. Park, Fracture toughness and surface morphology of Al2 O3 /Pt composites, Journal of Industrial and Engineering Chemistry (2014), http://dx.doi.org/10.1016/j.jiec.2014.10.025 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Graphical Abstract
Fracture toughness and surface morphology of Al2O3/Pt composites
ip t
Dong-Jin Lee, Heung-Soap Choi, Fan-Long Jin, Soo-Jin Park
Ac ce p
te
d
M
an
us
cr
The fracture surface showed an intergranular mechanism of fracture, typical of ceramic materials, at low Pt content, and a transgranular mechanism at high Pt content.
Page 1 of 19
ip t
Manuscript number: JIEC-D-14-01573
cr
Fracture toughness and surface morphology of Al2O3/Pt composites
b
Nano Technology Inc., 289-20 Daehwa-dong, Daedeok-gu, Daejon 306-801, Korea
an
a
us
Dong-Jin Lee a, Heung-Soap Choi b, Fan-Long Jinc,d, and Soo-Jin Park *,d
Department of Mechanical and Design Engineering, Hongik University, Sejong 339-701,
c
M
Republic of Korea
Department of Polymer Materials, Jilin Institute of Chemical Technology, Jilin City 132022, People’s Republic of China
d
Department of Chemistry, Inha University, Nam-gu, Incheon 402-751, South Korea
Ac ce p
te
d
* Corresponding authors.
Phone: +82 32-8767234. Fax: +82 32-8675604. E-mail: [email protected] (S. J. Park).
Page 2 of 19
ABSTRACT: In the present study, Al2O3-based composites with dispersed Pt particles were prepared by using a reduction-precipitation method. Particle distribution, fracture toughness, and morphology of
ip t
the prepared Al2O3/Pt composites were studied. Crystal structure of the composites was evaluated by analyzing Pt characteristic peaks in the X-ray diffraction spectra. Transmission
cr
electron microscopy images indicated that the Pt particles were uniformly dispersed in the Al2O3
us
powder. The fracture toughness of the Al2O3 matrix was improved by the addition of Pt particles, since these particles effectively resisted crack propagation in the Al2O3/Pt composites. Scanning
an
electron microscopy images indicated that the fracture of the composites followed an
d
mechanism occurred at high Pt content.
M
intergranular mechanism, typical of ceramic materials, at low Pt content, whereas a transgranular
Ac ce p
te
Keywords: Al2O3, Pt, Composites, Fracture toughness, Morphology
Page 3 of 19
1. Introduction
Al2O3 is as a typical representative of engineering ceramics. It has been extensively
ip t
employed for structural applications in automotive, aerospace, and biomedical fields because of
cr
its high hardness, good wear resistance, and other outstanding mechanical properties. However, Al2O3 is brittle and is prone to accidental damages; thus, it has limited use as an advanced
us
engineering material for the production of cutting tools, cylinder liners, and piston rings in automotive engines [1-5].
an
The fracture toughness of Al2O3-based materials can be improved by the incorporation
M
of metallic particles with a plastic behavior into the Al2O3 matrix [6-10]. In previous studies Al2O3-based composites were prepared to realize outstanding fracture toughness and excellent
d
physical properties. Mishra et al. studied the microstructure, hardness, and fracture toughness of
te
Al2O3/ZrB2 composites with different percentages of titanium as the diluent [11]. The fracture toughness increased significantly with increasing titanium content due to the formation of
Ac ce p
different phases in the composites, which improved the material resistance to crack propagation. Maiti et al. investigated the influence of sintering temperature and soaking time on the fracture toughness of Al2O3-based ceramics [5]. The study of fracture surface reveals that Al2O3-based ceramics present a mixed mode of fracture−intergranular and transgranular−with the former mode being in greater proportion. Schlenther et al. studied the fracture toughness and corrosion behavior of steel particle-reinforced Al2O3 composites [12]. The authors attributed the increase in crack propagation resistance to the behavior of the metallic matrix phase, which remained intact behind the propagating crack front. Yao et al. developed novel thermal barrier coatings based on Al2O3-Y2O3/Pt composites [13]. These thermal barrier coatings improve the resistance
Page 4 of 19
of the composites to oxidation at high temperatures and also provide excellent resistance to cracking owing to their sealing effect. In the present study, Al2O3/Pt composites were prepared to realize outstanding fracture
ip t
toughness. The structure of the composites was characterized using X-ray diffraction (XRD) spectra. The particle distribution and the morphology were studied using transmission electron
cr
microscopy (TEM) and scanning electron microscopy (SEM), and the mechanical properties
us
were evaluated using a universal testing machine.
M
an
2. Experimental
Hexachloroplatinic(IV) acid, hydrazine monohydrate, and α-Al2O3 powder were
d
purchased from Sumitomo Chemical Co. Ltd. Nitric acid was supplied by Kojima Chemical Co.
te
Ltd.
Pt-dispersed Al2O3 powders were prepared using a reduction-precipitation method.
Ac ce p
Hexachloroplatinic acid and hydrazine monohydrate were used as the Pt solvent and reduction agent, respectively. The Pt solution was prepared by dissolving between 0.6−1.2 g of hexachloroplatinic acid in 50 mL of deionized water, and the hydrazine solution by dissolving 0.4 g of hydrazine monohydrate in the same quantity of deionized water. Then, the two solutions were mixed in a 1:1 ratio. Finally, 3 g of α-Al2O3 powder were added to the solution. For an hour, the temperature was maintained at 85oC and the pH was kept at 1 by adding nitric acid when necessary, in order to bring about the reduction of Pt and the subsequent precipitation. Al2O3/Pt composite samples were given the final shape by pressing the obtained powder in a specific equipment.
Page 5 of 19
The structure of Al2O3/Pt composites was investigated using XRD (XRD, Rint-2000, Rigaku). The particle distribution in the Al2O3 matrix was investigated using TEM (JEOL, JSM6330F). The grain size of Al2O3 and Pt was calculated from TEM images by using computer
ip t
programs. The fracture toughness was measured by performing the three-point bending flexural test, which was performed on a universal testing machine (Instron Model 1125) using single
cr
edge-notch bending specimens. The surface morphology of the composites was investigated by
us
scanning electron microscopy (SEM, JEOL JXA840A).
M
an
3. Results and discussion
Fig. 1(a) shows the XRD data of the Al2O3/Pt composites prepared by the reduction-
d
precipitation method. Broad peaks of Pt are evident at 39.8o, 46.3o, and 67o, indicating the
te
presence of nanosized Pt particles. The intensity of the Pt peak associated with the amorphous halo pattern increased significantly with increasing Pt content [14-17].
Ac ce p
Fig. 1(b) shows the XRD data of Al2O3/Pt composites treated at 1450oC for 2 h. The Pt
peaks became sharp after heat treatment, and the peak size increased with increasing Pt content from 4 wt% to wt12%.
Figs. 2(a) and (b) show the TEM images of Al2O3/Pt composites with a Pt content of 4
wt%. As shown in Fig. 2(a), circular Al2O3 particles formed large clusters with an average size of 200 nm. Pt particles with a size in the range of 5 to 30 nm were irregularly dispersed in the Al2O3 matrix and combined effectively with Al2O3 particles, as shown in Fig. 2(b) [18,19]. Figs. 2(c) and (d) show the TEM images of the Al2O3/Pt composites with different Pt content. When the Pt content was increased from 4 to 12 wt%, the contrast of the circular, dark
Page 6 of 19
Pt particles against the bright matrix increased significantly. However, the particle size for the composites remained basically unvaried, between 5 and 20 nm, with varying Pt content. Figs. 2(e) and (f) show the TEM images of the Al2O3/Pt composite with a Pt content of
ip t
12 wt% baked at 1450oC for 2 h in air. The grain size of the composites was 1−3 μm. Circular Pt
cr
particles with a size of 30−500 nm were uniformly dispersed inside and outside the Al2O3 clusters. Further, no cracks formed at the interface between Pt and Al2O3, possibly because the
us
nanosized Pt particles and the Al2O3 matrix have similar thermal expansion coefficients [20,21]. Table 1 shows the relative density, hardness, and fracture toughness of the Al2O3/Pt
an
composites. The relative density of the composites increased with increasing Pt content. The Pt
M
particles were uniformly dispersed inside and outside the Al2O3 clusters and were found to be present in the cavities produced because of sintering. This resulted in an increase in the relative
d
density and in the Vickers hardness of the composites from 1685 to 1892 HV when the Pt
te
content was increased from 4 to 12 wt%. The increased Vickers hardness can be explained as follows. At Pt content of 4 wt%, many cavities appeared on the Al2O3 surface, whereas the
Ac ce p
cavities disappeared completely and a compact composite was obtained when the Pt content reached 12 wt%, as shown in Fig. 3. The fracture toughness of the composites increased from 4.7 to 5.5 MPa⋅m1/2 with increasing Pt content, because the Pt particles effectively restricted crack propagation in the Al2O3/Pt composites [22-25]. Fig. 3(a) shows the SEM images of the Al2O3/Pt composite powder before preparation
of the samples as a function of Pt content. Superfine Pt particles were uniformly distributed on the surface of the Al2O3 matrix. For a Pt content of 4 wt%, many cavities were evident on the Al2O3 surface. The number of cavities decreased upon increasing the Pt content to 8 wt%. When the Pt content reached 12 wt%, the cavities disappeared completely, and a compact composite
Page 7 of 19
was obtained. The size of the Pt particles varied between 50 and 250 nm for a Pt content of 4 wt%, and between 70 and 420 nm for a content of 12 wt%. Fig. 3(b) shows the SEM images of the fracture surfaces for the Al2O3/Pt composites.
ip t
Circular Pt particles are uniformly dispersed in the Al2O3 matrix, and increased with increasing Pt content. For a Pt content of 4 wt%, the fracture surface showed the intergranular mechanism
cr
of fracture, typical of ceramic materials. When the Pt content was increased to 12 wt%, the
Ac ce p
te
d
M
an
us
fracture surface varied significantly and showed a transgranular mechanism of fracture [26,27].
Page 8 of 19
4. Conclusions
Al2O3/Pt composites were prepared and their particle distribution, fracture toughness,
ip t
and morphology were studied. The characteristic peaks of the Pt particles appeared at 39.8o, 46.3o, and 67o in the XRD spectra. TEM results indicated that the Pt particles were effectively
cr
dispersed in the Al2O3 powder. The fracture toughness improved with increasing the Pt content,
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since the Pt particles effectively restricted crack propagation in the Al2O3/Pt composites. The fracture surface showed an intergranular mechanism of fracture, typical of ceramic materials, at a
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Acknowledgements
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low Pt content (4 wt%), and a transgranular mechanism at a high Pt content (12 wt%).
This study was supported by the Carbon Valley Project of the Ministry of Knowledge
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Economy, Korea.
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Caption of the Figures
Fig. 1. (a) XRD spectra of Al2O3/Pt composites as a function of Pt content; (b) XRD spectra of
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Al2O3/Pt composites treated at 1450oC for 2 h.
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Fig. 2. (a) and (b) TEM images of Al2O3/Pt composites prepared by reduction-precipitation method (Pt content: 4 wt%); (c) TEM images of Al2O3/Pt composites prepared by reduction-
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precipitation method (Pt content: 4 wt%); (d) TEM images of Al2O3/Pt composites prepared by
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reduction-precipitation method (Pt content: 12 wt%); (e) and (f) TEM images of Al2O3/Pt composites treated at 1450oC for 2 h (Pt content: 12 wt%).
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fractured surfaces for Al2O3/Pt composites.
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Fig. 3. (a) SEM images of Al2O3/Pt composites as a function of Pt content; (b) SEM images of
Page 12 of 19
Table 1 Mechanical properties of Al2O3/Pt composites. Relative density (%)
Hardness (Hv)
Fracture toughness (MPa⋅m1/2)
4
97.8±0.3
1685±10
4.7±0.15
8
98.1±0.3
1788±10
5.1±0.17
12
99.5±0.3
1892±10
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Pt content (wt%)
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5.5±0.18
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30
40
50
60
o
2θ ( )
80
图片 图片
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Intensity
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组合
70
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Intensity 20
20
30
40
50
60
70
80
o
2θ ( )
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Intensity
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(a)
20
组合
30
40
50
60
70
80
o
2θ ( )
图片 图片
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30
40
50
60
70
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cr
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Intensity 20
80
o
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2θ ( )
(b)
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cr
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Fig. 1.
(b)
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(c)
(d)
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Fig. 2.
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(e)
(a)
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(b)
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Fig. 3.
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