Synthesis and Characterization of Exfoliated Graphite (EG) and to Use it as a Reinforcement in Zn-based Metal Matrix Composites

Transcription

1 Synthesis and Characterization of Exfoliated Graphite (EG) and to Use it as a Reinforcement in Zn-based Metal Matrix Composites

2 Here H 2 SO 4 was used as an intercalant and H 2 O 2 as an oxidant. Expandable graphite was prepared at room temperature by mixing 16 ml of sulfuric acid (98%) and 1.5 ml hydrogen peroxide(30%) with 6 gm of natural flake graphite (60 mesh) having 98% purity. The mixture was placed for 1 h 30 min in a magnetic stirrer. The mixture which was prepared after stirring was washed with water to achieve ph in the range of 5-7. The prepared mixture was then dried at 60 o Cfor30hbefore further heat treatment. Heat treatment was performed by inserting a silica crucible containing the prepared mixture insideid amuffle furnace. Finally the resulting li graphite preparation procedure of expanded graphite compound was subjected to thermal shock at 1000 o Cforabout30 sec in a muffle furnace in air, resulting in the formation of expanded graphite. At such a high temperature the intercalates trapped between the graphite layers decompose and force the layers to separate. The expansion process cause an enormous increase in volume (240 cc/g) and also causes an expansion in the thickness in the c direction of about times. 100 ml acetone was then mixed with 1 gm of the expanded graphite and sonicated in an ultrasonicator followed by simultaneous heating at 80 o C and magnetic stirring. The expanded graphite was treated in an ultrasonicator in order to achieve better exfoliation of graphite having high aspect ratio. It has been found that the sonication exfoliation method aids the preparation for graphene sheets remarkably.

3 (a) (b) (d) (c) SEM of as-received graphite (d) (e) (a) HRTEM and (b) SAD pattern image of as-received graphite The SEM images show several layers of graphene stacked together. The SEM images of the as-received natural flake graphite shows several platelets combining to form agglomerates The hexagonal pattern in the SAD image shows the six fold symmetry of agglomerates. carbon atoms arranged in the graphene plane. This indicates good crystallinity of the graphene sheet.

4 (a) (b) (c) HRTEM and SAD image of expanded graphite The TEM images suggest that the graphene sheets are highly transparent and has folded edges. This also suggests s that the layers have very small thickness. The hexagonal pattern in the SAD image shows the six fold symmetry of carbon atoms arranged in the graphene plane. This indicates good crystallinity of the graphene sheet.

5 (a) (a) (a) (d) At such a high temperature of 1000 o C, intercalates trapped between graphite layers decompose and force the graphite layers to separate. The expansion process causes destruction of graphite crystal structure and an enormous increase in volume (~240 cc/g) and expansion in the thickness or c direction of about 100 times. The expanded graphite looks like sheets of paper and seem to be held together at the edges. The sheets of graphene in expanded graphite are bonded by weak van der Waals forces. The high magnification SEM images show how they are connected.

6 From the AFM analysis detailed information concerned about expanded graphite can be obtained from AFM analysis Thickness of Expanded Graphite was about 69 nm. Considering the space between two carbon layers to be 3.37Å the number of graphene layers in the expanded graphite is around 230.

7 (a) (b) (002) (002) (100)(101)(004) (110) (112) (100)(101) (004) (110) (112) 004 The as-received graphite was expanded. X-ray diffraction of the as-received graphite and the expanded graphite was done. Increased exfoliation in expanded graphite led to remarkable reduction in peak intensity. The distance between the graphite layers has been increased. The layers seem to have separated and there is an apparent increase in the volume. The expanded graphite looks like sheets of paper and seem to be held together at the edges. Both the as-received graphite and the expanded graphite showed highest intensity peak at 26.6 o but the intensity of the peak was much higher in the case of as-received graphite. The less intense peak in the case of expanded graphite clearly indicates that the as-received graphite has been expanded. For the as-received graphite 2θ= o giving the spacing between the carbon layers to be 3.37Å.

8 (a) () (b) %T %T GR /cm EG /cm FTIR plot of as-received and expanded graphite Smaller particles of expanded graphite led to broader peaks and slanted baselines. Broader peaks indicate increase in interaction with the light wave. Expanded graphite being smaller in size than the as-received natural graphite showed broadening in peaks.

9 (a) (b) (e) (c) (d) (f) (a-e) HRTEM of EG (f) SAD pattern HRTEM images of EG in reveal its morphological structure. Here plenty of broken single-layer graphite sheets are observed. It confirmed the production of fully exfoliated graphite. Nevertheless, it has been found that continuous sonication is helpless to give higher yield of graphenes although excessive sonication can lead to destruction of the graphene.

10 (a) (d) (b) (e) (c) (f) It has been found that continuous sonication is helpless to give higher yield of graphene although excessive sonication can lead to destruction of the graphene.

11 The sysntehsis thi of graphene sheets was further confirmed by using Raman spectroscopy. The Raman spectra of the three samples can be clearly distinguished from each other. The sharp and strong G peak and a weaker D peak along with a single 2D peak indicates the presence of graphene having few layers. The D peak at 1346 cm 1 is specific for disorders and defects which arises from the lattice df deformation due to acid intercalation. ti After expansion the intercalated t graphite shows stronger G peak at 1572 cm 1 which is specific for sp 2 carbon and reveals the high quality of the EG. These results suggest that our exfoliation process was effective. The Raman spectrum of the samples show a weak peak around ~2330 cm-1. This band may be assigned to H3O+ vibration. This is a possibly due added for intercalation ti of natural flake graphite. The broad multi-band peaks around 2695 cm 1 1 (2D) are consistent with the multi-layer feature of graphite.the2dbandofthegraphitenano-particlesinthe Raman spectrum becomes intense and symmetric. This indicates that the structural properties of the graphite nano-particles approach those of multi-layer graphene. The D/G intensity ratios for the sonicated sample is very small and nearly equal, 0.07.This ratio indicates thatt the sample is well ordered and has only very few defects. This suggests that the crystal structure of graphene has been preserved.

12 (a) (b) SEM of EG-Zn nanocomposite C Zn O Elemental Analysis of the Nanocomposite

13 Zn-10 wt.% EG Zn-20 wt.% EG Zn-30 wt.% EG

14 1. Exfoliated graphite was successfully synthesized. Exfoliation led to dispersion of graphite nanosheets and as a consequence this led to the best enhancement in mechanical properties over other processing techniques. 2. Zn EG composites with ih different amounts exfoliated graphite (EG) were fabricated through powder metallurgy. The composites were consolidated at approximately MPa and sintered for 2hat300 o Cunderinert atmosphere. Nanocomposites consisting of exfoliated graphite (EG) upto 30 wt% in Zn werefabricated.themicrostructureand mechanical properties of the composites were investigated.