Unoxidized Graphene/Alumina Nanocomposite: Fracture- and Wear-Resistance Effects of Graphene. on Alumina Matrix

Transcription

1 Unoxidized Graphene/Alumina Nanocomposite: Fracture- and Wear-Resistance Effects of Graphene on Alumina Matrix Hyo Jin Kim,, Sung-Min Lee, Yoon-Suk Oh, Young-Hwan Yang, Young Soo Lim, Dae Ho Yoon, * Changgu Lee, Jong-Young Kim, * and Rodney S. Ruoff #* Icheon Branch, Korea Institute of Ceramic Engineering and Technology, Icheon, Republic of Korea, Energy and Environmental Division, Korea Institute of Ceramic Engineering and Technology, Seoul, Republic of Korea, School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Republic of Korea, Department of Mechanical Engineering and SKKU Advanced Institute of Nanotechnology, Sungkyunkwan Univeristy, Suwon, Republic of Korea, and #Department of Mechanical Engineering and the Materials Science and Engineering Program, The University of Texas, Austin, Texas, USA. AUTHOR ADDRESS jykim@kicet.re.kr CORRESPONDING AUTHOR FOOTNOTE Icheon Branch, Korea Institute of Ceramic Engineering and Technology, 3321 Gyeongchung Daero, Sindun- Myeon, Icheon-si, Gyeonggi-do , Republic of Korea. Tel) Fax)

2 1) TEM images of EG/Al 2 O 3 and EG/LPS-Al 2 O 3 Figure S1. (a) A few-layered graphene nanoplatelet (~2 nm thick) located between grains of the EG/LPS-Al 2 O 3 composite. (b) The enlarged image of Figure 1a, which shows a thin layer of EG (~5 nm) present between grains 1 and 2. 2

3 2) XPS analysis results for the G-O and EG. Figure S2. XPS spectra for (a) graphene oxide (G-O) and (b) exfoliated graphite (EG). 3

4 3) FE-SEM Images of LPS-Al 2 O 3 composites. Figure S3. FE-SEM images for (a) LPS-Al 2 O 3 sintered at 1450, (b) 0.5 vol % GO/LPS-Al 2 O 3 composite, (c-d) 0.5 vol % rgo/lps-al 2 O 3 composite, (e-f) 1.0 vol % rgo/lps-al 2 O 3 composite, and (g-h) 0.5 vol % EG/LPS-Al 2 O 3 composite. The blue arrows in Figure S3h indicate large plate-type particles in the LPS-Al 2 O 3 composites. 4

5 4) Optical microscope images of EG with respect to the centrifuge rpm The EG suspension in DMF was diluted and dried on a slide glass, which was observed by optical microscope. Figure S4. Optical microscope images for the exfoliated graphite separated at the centrifuge rpm of 1000, 5000, and Scale bar is 50 m. 5

6 5) Microstructure and crack profile images of LPS-Al 2 O 3 composites. Figure S5. FE-SEM images for (a-b) LPS-Al 2 O 3 sintered at 1400, (c-d) 0.5 vol % GO/LPS-Al 2 O 3 composite, and (e-f) 0.5 vol % EG/LPS-Al 2 O 3 composite. 6

7 Figure S6. FE-SEM images of cracks on the polished surface created by IF (Indentation Fracture) method for (a) Al 2 O 3, and (b) 1.0 vol % EG/LPS-Al 2 O 3 composite. The evidence of crack deflection was found in Figure S3b (white arrow). 7

8 6) Table S1. The position and intensity of D, G, and 2D bands in the Raman spectra. compound graphene conc. D band G band (vol %) (cm -1 ) (cm -1 ) I D /I G I 2D /I G 2D 1 band (cm -1 ) 2D 2 band (cm -1 ) I 2D1 /I 2D2 graphite G-O rg-o EG* G-O Alumina rg-o EG LPS G-O rg-o Alumina EG * EG was separated by centrifuge at 5,000 rpm. 8

9 7) Table S2. Processing conditions, densities, and fracture toughness for the composites. (solid state: sintering without any added phase, LPS: liquid phase sintering, G-O: graphene oxide, rg-o: reduced graphene oxide, EG: exfoliated graphite) Materials Alumina 0.5 vol% G-O/ 1.0 vol% G-O/ 1.5 vol% G-O/ 0.25 vol% rg-o/ 0.5 vol% rg-o/ 1.0 vol% rg-o/ 0.25 vol% EG/ (5000 rpm) 0.5 vol% EG/ (5000 rpm) 1.0 vol% EG/ (5000 rpm) 1.5 vol% EG/ (5000 rpm) Processing condition Sintering Temp. ( ) Density (g/cm 3 ) Fracture toughness, K IC (MPa m 1/2 ) Solid state ±0.04 LPS ± ±0.04 Solid state ±0.02 LPS ±0.01 Solid state ±0.13 LPS ±0.04 Solid state ±0.10 LPS ±0.15 Solid state ±0.03 LPS ±0.03 Solid state ±0.02 LPS ±0.16 Solid state ±0.02 LPS ±0.01 Solid state ±0.07 LPS ±0.14 Solid state ±0.07 LPS ±0.10 Solid state ±0.12 LPS ±0.04 Solid state ±0.20 LPS ±0.02 9

10 8) Fracture toughness measurement methods 8.1) IF method We compared the toughness values measured by IF (Indentation Fracture) method with those measured by direct toughness measurement method (SEVNB, Single-Edge V-Notch Beam). For the IF method, the micro-hardness testing technique was used to induce radial cracking from the corners of the indentation. A mirror-finished surface was indented by a Vickers hardness machine. The indentation loads were 98 N. The fracture toughness was calculated by the Antis equation. K IC E 0.16 H 0.5 P C0 1.5 K IC : Fracture toughness, E: Young s modulus, H: Hardness, C 0 : Crack length, P: Applied load 10

11 Figure S7. Optical images of Vickers indentation sites for (a) EG (1.0 vol %)/Al 2 O 3 composite and (b) for EG (1.0 vol %)/LPS-Al 2 O 3 composite. 11

12 8.2) SEVNB method First, polished rectangular beam-type specimens (3 mm 4 mm 30 mm) were prepared for the purpose of testing fracture toughness at room temperature. A V-shaped notch was then prepared at the surface 3 mm 30 mm of the beams. For this purpose, the beams were glued to a ceramic substrate and a preliminary notch was cut in them with a hard metal blade (200 μm thick). Then, the V-shaped notch ( mm deep) was polished out in the preliminary notch using a sharpened hard metal blade with diamond paste. (grain size: 1 μm) Home-made equipment providing alternating movements was used for reproducible V-notch preparation. In order to measure the notch length and the radius of the notch tip,, optical microscope with magnifications of 50 and 100 were used. The load was measured using a three-point-bending tester. The fracture toughness was determined from the following equation; PS BW α 3F α K IC 1.5 F α α 1.99 α 1 a W 2 α α 2.7α 1 2α1 α 1.5 Hard metal Blade K K IC specimen K IC specimen IC specimen K K IC specimen IC specimen V-Notch Home-made equipment for alternating movements K IC : Fracture toughness (MPa m 0.5 ), S: Support span (m), F max : Fracture load (MN), α: Initial precrack relative length (m), B: Thickness of specimen (m), W: Width of specimen (m), a: Notch depth (m) Schematic geometry of V-notches c a = mm; b ~ 0.5 mm; c > width of blade b a a-b > c; β ~ 30 or as small as possible S: V-notch root S 12

13 Figure S8. (a-b) Low- and higher-magnification V-notch images of Al 2 O 3, (c-d) Low- and highermagnification V-notch images of GO/Al 2 O 3 composite, and (e-f) Low- and high-magnification V-notch images of EG/Al 2 O 3 composite. (notch root radius: ~10 m) 13

14 Figure S9. (a-b) Low- and high-magnification V-notch images of LPS-Al 2 O 3, (c-d) Low- and highmagnification V-notch images of GO/LPS-Al 2 O 3 composite, and (e-f) Low- and high-magnification V- notch images of EG/LPS-Al 2 O 3 composite. (notch root radius: ~10 m) 14

15 Intensity(Arb. Unit) 9) XRD patterns for EG with respect to centrifuge rpm. As centrifuge rpm increases from 1,000 to 13,000 rpm in separation process of EG from asexfoliated suspension, the thickness of EG decreases, which reduces the Bragg peak intensity as shown in Figure S11 below (reference 21). graphite EG 1000 rpm EG 5000 rpm EG rpm-1 EG rpm-5 EG rpm theta Figure S10. XRD patterns for graphite and the exfoliated graphite separated at the centrifuge rpm of 1000, 5000, and

16 Intensity(Arb. Unit) EG 1000 rpm EG 5000 rpm EG rpm-1 EG rpm-5 EG rpm theta Figure S11. XRD patterns for the exfoliated graphite separated at the centrifuge rpm of 1000, 5000, and

17 10) Microstructure of wear tracks for pure Al 2 O 3 and EG/Al 2 O 3 composite Figure S11. Microstructures of EG(0.25 vol%)/al 2 O 3 composite and pure Al 2 O 3. C: composite, P: Pure Al 2 O 3, C/P-1: worn surface, C/P-2: pore, C/P-3: small crack, C/P-4: residues from WC ball. 17