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Preparation of expanded graphite with 160 μm mesh of fine flake graphite
Materials Letters 60 (2006) 746 – 749 www.elsevier.com/locate/matlet
Preparation of expanded graphite with 160 μm mesh of fine flake graphite Ji-hui Li ⁎, Li-li Feng, Zhi-xin Jia Department of Chemistry, Hebei Normal University, Shijiazhuang 050091, R.P. China Received 24 January 2005; accepted 3 October 2005 Available online 21 October 2005
Abstract Expanded graphite was prepared using the fine flake graphite that could go straight through 160 μm mesh as raw material, using acetic anhydride as inserting agent and potassium dichromate as oxidant. The best process conditions are as follows: m (fine graphite):m (acetic anhydride):m (concentrated sulfuric acid):m (potassium dichromate) = 1:1.0:3.1:0.6, reaction time is 50 min and reaction temperature is 45 °C. The expanded graphite prepared using the fine flake graphite that could go straight through a 160 μm mesh has many good qualities, such as low mass, small pellet, resists high temperature and resists pressure. The expanded graphite is also an excellent material for antistatic and antielectromagnetic. © 2005 Elsevier B.V. All rights reserved. Keywords: Graphite; Intercalation compounds; Expanded graphite; Oxidation
1. Introduction Expanded graphite was invented in the US by Carburet Company in 1968, and it was exploited in China for less than 30 years. Due to its excellent properties, such as compatibility, spring-back, flexibility, heat conducting, anti-acid, anti-base, and so on [1], it is widely used in many industry sectors. For example it is used in chemical industry, mechanism, space flight, military affairs, etc. A lot of scientific research institutions and industries use 50 mesh size or 80 mesh size flake graphite to make expanded graphite, its expandable volume is usually from 150 to 300 ml/g. Few people use fine flake graphite to make expanded graphite, just because its expandable volume is too small. But in some special field, expanded graphite made by fine flake graphite is better than that made by 50 mesh size or 80 mesh size flake graphite. For example, using it could make antistatic coating, antielectromagnetic material, and infrared shield material. Using the expanded graphite made by 50 mesh size flake graphite is not as good as this is. We had found the method to use the fine flake graphite that could go straight through the 160
⁎ Corresponding author. Tel./fax: +86 311 626 3269. E-mail address: [email protected] (J. Li). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.10.004
μm mesh to make expanded graphite. We also had used the expanded graphite in making antistatic coating, and it is very successful. 2. Experiment 2.1. Raw materials Nature flake graphite taken from inner Mongolia province (diameter ≤ 160 μm) are concentrated sulfuric acid (AR), acetic anhydride (AR), potassium dichromate (AR). 2.2. Preparation of fine flake expanded graphite According to the preparation of low sulfur content expansible graphite with potassium bichromate as oxidant [2], the method to make fine flake expanded graphite is as follows. A fixed quantity of nature flake graphite (diameter ≤ 160 μm), concentrated sulfuric acid and potassium dichromate were stirred in the flask. Acetic anhydride was slowly dripped into the flask. After 50 min, the GIC was prepared. It was then washed in water to neutrality, dehydrated and dried at a temperature of 60 °C. Then the GIC was rapidly heated in a tubular furnace kept at 1000 °C for 5 s for expanding.
J. Li et al. / Materials Letters 60 (2006) 746–749
747
3. Experimental results and analysis
Table 3 The influence of potassium dichromate amount on expandable volume
3.1. The best process condition
m (fine graphite):m (potassium dichromate) Expanded volume (ml)
3.1.1. The influence of acetic anhydride The data in Table 1 shows that when the amount of acetic anhydride is too large or too small, the expandable volume is not so large [3]. When the amount of acetic anhydride is too large, the consistency of oxidants is cut down, so large expandable volume GIC could not be acquired. When the amount of acetic anhydride is too small, the layers of flake graphite could not be inserted by acetic anhydride completely, so the amount of acetic anhydride is not enough or the flake graphite could not be saturated by the liquid, thus, it could not react thoroughly. 3.1.2. The influence of concentrated sulfuric acid In the table, the expandable volume of GIC firstly increases with the amount of concentrated sulfuric acid, but then it decreases with it. The data in Table 2 shows that when the amount of concentrated sulfuric acid is 1:3.1, the large expandable volume GIC was achieved. Concentrated sulfuric acid could also insert into the layers of the flake graphite, the concentrated sulfuric acid was first used as an acid to provide an acidic environment in the system. It was also used as an inserting agent. But after getting its largest expandable volume, it was used just as an acid and it could oxidize the graphite excessively. 3.1.3. The influence of potassium dichromate It demonstrates that the expandable volume of GIC firstly increases with the amount of oxidant amount, but then it decreases [4]. When the amount of oxidant is not enough, the graphite layers could not be opened thoroughly. The acetic anhydride could not be inserted into the layers completely. The expandable volume is not large when the amount of oxidant agent is far more than the general amount, it could oxidize the fine flake graphite excessively or the distance of two layers is too largely opened by the oxidant that the inserting reagent may escape from it (Table 3). 3.1.4. The influence of reaction temperature The data in Table 4 shows that the best reaction temperature is 45 °C. Low temperature may decrease the velocity of the reaction, but this reaction is exothermic. High temperature may not be suitable to form intercalation compounds. In addition, if
Table 1 The influence of acetic anhydride amount on expandable volume m (graphite):m (acetic anhydride) Expanded volume (ml)
1:0.6 50
1:0.8 57
1:1.0 60
1:1.2 55
1:1.4 45
Table 2 The influence of concentrated sulfuric acid amount on expandable volume m (fine graphite):m (concentrated sulfuric acid) Expanded volume (ml)
1:0.3
1:1.7
1:3.1
1:4.5
1:6.0
20
50
60
54
55
1:0.08
1:0.34
1:0.6
1:0.86
1:1.1
30
45
60
50
40
Table 4 The influence of reaction temperature on expandable volume Reaction temperature (°C) Expanded volume (ml)
25 35
35 53
45 60
55 50
65 43
temperature is too high, it may reduce volatilization of acetic anhydride quickly. 3.1.5. The influence of reaction time The data in Table 5 display that expandable volume increases slowly in 30–40 min, and the largest one is noted at 50 min. The expandable volume decreases when reaction time is extended. It is possible that the structure of intercalation compounds was destroyed. 3.1.6. The influence of expanding temperature Table 6 displays that if the expanding temperature is not high enough, intercalated reagent in the GIC could not get enough energy. The expandable volume would not be large. But if the expanding temperature is too high, for example, higher than 1000 °C, the expandable volume would increase slowly or decrease. The best expanding temperature is selected at 1000 °C. 3.2. Conclusion of the best process condition Through the experimental data above, the best process condition of the reaction could be concluded as follows: m (fine graphite):m (acetic anhydride):m (concentrated sulfuric acid):m (potassium dichromate) = 1:1.0:3.1:0.6, reaction time is 50 min and reaction temperature is 45 °C, expanding temperature is 1000 °C. The largest expandable volume of this method is 60 ml/g. 4. Several analysis of the GIC or expanded graphite 4.1. Ultraviolet spectral analysis The expandable graphite (60 ml/g) is soaked in distilled water, and the liquid was measured by UV-2000 ultraviolet Table 5 The influence of reaction time on expandable volume Reaction time (min) Expanded volume (ml)
30 40
40 53
50 60
60 50
70 44
Table 6 The influence of expanding temperature on expandable volume Expanding temperature (°C) Expanded volume (ml)
700 30
800 49
900 55
1000 60
1100 61
1200 58
1300 55
748
J. Li et al. / Materials Letters 60 (2006) 746–749
the peak of acetic anhydride in the particular condition. And the ultraviolet spectra could also identify that the acetic anhydride had inserted into the layers of the flake graphite. 4.2. Scan electron microscope analysis The expanded graphite is observed by scan electron microscope. The expanded graphite has lots of pores that looks like worms (Fig. 2). 4.3. Transmission electron microscope analysis
Fig. 1.
spectrophotometer. The Fig. 1 displays that the acetic anhydride molecules had intercalated into the graphite layers. Plunge 1 g expandable graphite made by the best react conditions in 50-ml distilled water. After 10 h, test the liquid under ultraviolet spectrophotometer. In Fig. 1, one absorbing peak appears at 204.7 nm. Then test the acetic acid standard solvent under ultraviolet spectrophotometer; absorbing peak was at 204.7 nm. The peak of the expandable graphite immersing liquid fits the acetic acid standard peak completely. In water solvent condition, acetic anhydride molecule could not exist, it would hydrolyze. The hydrolyzed product is acetic acid molecule. So it proves that the absorbing peak of 204.7 nm is
Fig. 2.
The expanded graphite is dispersed by supersonic wave, Fig. 3 was taken with transmission electron microscope. In the detection range, its particle size is very small, and these particles conjoint membranes. Place expanded graphite in alcohol solvent, after ultrasonic irradiation, it was tested under transmission electron microscope. From Fig. 3, film layer structure could be found. This can be explained as follows: flake graphite has layer-tolayer film structure; when made into expandable graphite, the distance of the layers raised because of the broken carbon– carbon bond caused by the oxidant. And acetic anhydride had inserted into the layers. When heated at 1000 °C, the insert agent becomes CO2 and H2O gas and escape from the expandable graphite. So the distance of the layers of graphite could be extended further, and the shape of the expanded graphite looked like worms. The structure of the worms is also layer-to-layer, just
Fig. 3.
J. Li et al. / Materials Letters 60 (2006) 746–749
as the strength of the layers becomes very small. Under ultrasonic irradiation, the layers could be peeled off as one layer or small layers, as in Fig. 3. In the transmission electron microscope, Fig. 3 is the one layer of the expanded graphite.
749
resists pressure antistatic and anti-electromagnetic. The expanded graphite has been made to antistatic coating, and the patent has been applied in China. The apply number is 200410009755.4.
4.4. Determination of various technical targets of products References There is no standard of the expanded graphite made by the fine flake graphite that could go straight through the 160 μm mesh, but according to the similar method of GB10698-89 (China standard), various technical targets of products are measured. The moisture, volatile fraction and ash content are 3.7%, 11.5%, and 3.5%, respectively. 5. Conclusion The expanded graphite produced by the fine flake graphite that could go straight through 160 μm mesh has many merits, such as low mass, small pellet, resists high temperature,
[1] Kemin Song, Wenyi Lu, Shuying Gao, et al., Preparation of low-sulfur expansible graphite, Chinese Journal of Applied Chemistry 12 (1) (1995) 94–95. [2] Mei Li, Daqiao Zhang, Jihui Li, Preparation of low sulphur content expansible graphite with potassium bichromate as oxidant, Chinese Journal of Carbon 4 (1997) 46–48. [3] Jihui Li, Qiaoyun Liu, Mei Li, Zhanrong Liu, Preparation of low-sulphur expandable graphite, Fine Chemicals 20 (6) (2003) 341–342. [4] Xiling Chen, Kemin Song, Jihui Li, Jinpeng Liu, Preparation of low sulphur content and expandable graphite, Carbon 34 (12) (1996) 1599–1603.
Preparation of expanded graphite with 160 μm mesh of fine flake graphite Ji-hui Li ⁎, Li-li Feng, Zhi-xin Jia Department of Chemistry, Hebei Normal University, Shijiazhuang 050091, R.P. China Received 24 January 2005; accepted 3 October 2005 Available online 21 October 2005
Abstract Expanded graphite was prepared using the fine flake graphite that could go straight through 160 μm mesh as raw material, using acetic anhydride as inserting agent and potassium dichromate as oxidant. The best process conditions are as follows: m (fine graphite):m (acetic anhydride):m (concentrated sulfuric acid):m (potassium dichromate) = 1:1.0:3.1:0.6, reaction time is 50 min and reaction temperature is 45 °C. The expanded graphite prepared using the fine flake graphite that could go straight through a 160 μm mesh has many good qualities, such as low mass, small pellet, resists high temperature and resists pressure. The expanded graphite is also an excellent material for antistatic and antielectromagnetic. © 2005 Elsevier B.V. All rights reserved. Keywords: Graphite; Intercalation compounds; Expanded graphite; Oxidation
1. Introduction Expanded graphite was invented in the US by Carburet Company in 1968, and it was exploited in China for less than 30 years. Due to its excellent properties, such as compatibility, spring-back, flexibility, heat conducting, anti-acid, anti-base, and so on [1], it is widely used in many industry sectors. For example it is used in chemical industry, mechanism, space flight, military affairs, etc. A lot of scientific research institutions and industries use 50 mesh size or 80 mesh size flake graphite to make expanded graphite, its expandable volume is usually from 150 to 300 ml/g. Few people use fine flake graphite to make expanded graphite, just because its expandable volume is too small. But in some special field, expanded graphite made by fine flake graphite is better than that made by 50 mesh size or 80 mesh size flake graphite. For example, using it could make antistatic coating, antielectromagnetic material, and infrared shield material. Using the expanded graphite made by 50 mesh size flake graphite is not as good as this is. We had found the method to use the fine flake graphite that could go straight through the 160
⁎ Corresponding author. Tel./fax: +86 311 626 3269. E-mail address: [email protected] (J. Li). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.10.004
μm mesh to make expanded graphite. We also had used the expanded graphite in making antistatic coating, and it is very successful. 2. Experiment 2.1. Raw materials Nature flake graphite taken from inner Mongolia province (diameter ≤ 160 μm) are concentrated sulfuric acid (AR), acetic anhydride (AR), potassium dichromate (AR). 2.2. Preparation of fine flake expanded graphite According to the preparation of low sulfur content expansible graphite with potassium bichromate as oxidant [2], the method to make fine flake expanded graphite is as follows. A fixed quantity of nature flake graphite (diameter ≤ 160 μm), concentrated sulfuric acid and potassium dichromate were stirred in the flask. Acetic anhydride was slowly dripped into the flask. After 50 min, the GIC was prepared. It was then washed in water to neutrality, dehydrated and dried at a temperature of 60 °C. Then the GIC was rapidly heated in a tubular furnace kept at 1000 °C for 5 s for expanding.
J. Li et al. / Materials Letters 60 (2006) 746–749
747
3. Experimental results and analysis
Table 3 The influence of potassium dichromate amount on expandable volume
3.1. The best process condition
m (fine graphite):m (potassium dichromate) Expanded volume (ml)
3.1.1. The influence of acetic anhydride The data in Table 1 shows that when the amount of acetic anhydride is too large or too small, the expandable volume is not so large [3]. When the amount of acetic anhydride is too large, the consistency of oxidants is cut down, so large expandable volume GIC could not be acquired. When the amount of acetic anhydride is too small, the layers of flake graphite could not be inserted by acetic anhydride completely, so the amount of acetic anhydride is not enough or the flake graphite could not be saturated by the liquid, thus, it could not react thoroughly. 3.1.2. The influence of concentrated sulfuric acid In the table, the expandable volume of GIC firstly increases with the amount of concentrated sulfuric acid, but then it decreases with it. The data in Table 2 shows that when the amount of concentrated sulfuric acid is 1:3.1, the large expandable volume GIC was achieved. Concentrated sulfuric acid could also insert into the layers of the flake graphite, the concentrated sulfuric acid was first used as an acid to provide an acidic environment in the system. It was also used as an inserting agent. But after getting its largest expandable volume, it was used just as an acid and it could oxidize the graphite excessively. 3.1.3. The influence of potassium dichromate It demonstrates that the expandable volume of GIC firstly increases with the amount of oxidant amount, but then it decreases [4]. When the amount of oxidant is not enough, the graphite layers could not be opened thoroughly. The acetic anhydride could not be inserted into the layers completely. The expandable volume is not large when the amount of oxidant agent is far more than the general amount, it could oxidize the fine flake graphite excessively or the distance of two layers is too largely opened by the oxidant that the inserting reagent may escape from it (Table 3). 3.1.4. The influence of reaction temperature The data in Table 4 shows that the best reaction temperature is 45 °C. Low temperature may decrease the velocity of the reaction, but this reaction is exothermic. High temperature may not be suitable to form intercalation compounds. In addition, if
Table 1 The influence of acetic anhydride amount on expandable volume m (graphite):m (acetic anhydride) Expanded volume (ml)
1:0.6 50
1:0.8 57
1:1.0 60
1:1.2 55
1:1.4 45
Table 2 The influence of concentrated sulfuric acid amount on expandable volume m (fine graphite):m (concentrated sulfuric acid) Expanded volume (ml)
1:0.3
1:1.7
1:3.1
1:4.5
1:6.0
20
50
60
54
55
1:0.08
1:0.34
1:0.6
1:0.86
1:1.1
30
45
60
50
40
Table 4 The influence of reaction temperature on expandable volume Reaction temperature (°C) Expanded volume (ml)
25 35
35 53
45 60
55 50
65 43
temperature is too high, it may reduce volatilization of acetic anhydride quickly. 3.1.5. The influence of reaction time The data in Table 5 display that expandable volume increases slowly in 30–40 min, and the largest one is noted at 50 min. The expandable volume decreases when reaction time is extended. It is possible that the structure of intercalation compounds was destroyed. 3.1.6. The influence of expanding temperature Table 6 displays that if the expanding temperature is not high enough, intercalated reagent in the GIC could not get enough energy. The expandable volume would not be large. But if the expanding temperature is too high, for example, higher than 1000 °C, the expandable volume would increase slowly or decrease. The best expanding temperature is selected at 1000 °C. 3.2. Conclusion of the best process condition Through the experimental data above, the best process condition of the reaction could be concluded as follows: m (fine graphite):m (acetic anhydride):m (concentrated sulfuric acid):m (potassium dichromate) = 1:1.0:3.1:0.6, reaction time is 50 min and reaction temperature is 45 °C, expanding temperature is 1000 °C. The largest expandable volume of this method is 60 ml/g. 4. Several analysis of the GIC or expanded graphite 4.1. Ultraviolet spectral analysis The expandable graphite (60 ml/g) is soaked in distilled water, and the liquid was measured by UV-2000 ultraviolet Table 5 The influence of reaction time on expandable volume Reaction time (min) Expanded volume (ml)
30 40
40 53
50 60
60 50
70 44
Table 6 The influence of expanding temperature on expandable volume Expanding temperature (°C) Expanded volume (ml)
700 30
800 49
900 55
1000 60
1100 61
1200 58
1300 55
748
J. Li et al. / Materials Letters 60 (2006) 746–749
the peak of acetic anhydride in the particular condition. And the ultraviolet spectra could also identify that the acetic anhydride had inserted into the layers of the flake graphite. 4.2. Scan electron microscope analysis The expanded graphite is observed by scan electron microscope. The expanded graphite has lots of pores that looks like worms (Fig. 2). 4.3. Transmission electron microscope analysis
Fig. 1.
spectrophotometer. The Fig. 1 displays that the acetic anhydride molecules had intercalated into the graphite layers. Plunge 1 g expandable graphite made by the best react conditions in 50-ml distilled water. After 10 h, test the liquid under ultraviolet spectrophotometer. In Fig. 1, one absorbing peak appears at 204.7 nm. Then test the acetic acid standard solvent under ultraviolet spectrophotometer; absorbing peak was at 204.7 nm. The peak of the expandable graphite immersing liquid fits the acetic acid standard peak completely. In water solvent condition, acetic anhydride molecule could not exist, it would hydrolyze. The hydrolyzed product is acetic acid molecule. So it proves that the absorbing peak of 204.7 nm is
Fig. 2.
The expanded graphite is dispersed by supersonic wave, Fig. 3 was taken with transmission electron microscope. In the detection range, its particle size is very small, and these particles conjoint membranes. Place expanded graphite in alcohol solvent, after ultrasonic irradiation, it was tested under transmission electron microscope. From Fig. 3, film layer structure could be found. This can be explained as follows: flake graphite has layer-tolayer film structure; when made into expandable graphite, the distance of the layers raised because of the broken carbon– carbon bond caused by the oxidant. And acetic anhydride had inserted into the layers. When heated at 1000 °C, the insert agent becomes CO2 and H2O gas and escape from the expandable graphite. So the distance of the layers of graphite could be extended further, and the shape of the expanded graphite looked like worms. The structure of the worms is also layer-to-layer, just
Fig. 3.
J. Li et al. / Materials Letters 60 (2006) 746–749
as the strength of the layers becomes very small. Under ultrasonic irradiation, the layers could be peeled off as one layer or small layers, as in Fig. 3. In the transmission electron microscope, Fig. 3 is the one layer of the expanded graphite.
749
resists pressure antistatic and anti-electromagnetic. The expanded graphite has been made to antistatic coating, and the patent has been applied in China. The apply number is 200410009755.4.
4.4. Determination of various technical targets of products References There is no standard of the expanded graphite made by the fine flake graphite that could go straight through the 160 μm mesh, but according to the similar method of GB10698-89 (China standard), various technical targets of products are measured. The moisture, volatile fraction and ash content are 3.7%, 11.5%, and 3.5%, respectively. 5. Conclusion The expanded graphite produced by the fine flake graphite that could go straight through 160 μm mesh has many merits, such as low mass, small pellet, resists high temperature,
[1] Kemin Song, Wenyi Lu, Shuying Gao, et al., Preparation of low-sulfur expansible graphite, Chinese Journal of Applied Chemistry 12 (1) (1995) 94–95. [2] Mei Li, Daqiao Zhang, Jihui Li, Preparation of low sulphur content expansible graphite with potassium bichromate as oxidant, Chinese Journal of Carbon 4 (1997) 46–48. [3] Jihui Li, Qiaoyun Liu, Mei Li, Zhanrong Liu, Preparation of low-sulphur expandable graphite, Fine Chemicals 20 (6) (2003) 341–342. [4] Xiling Chen, Kemin Song, Jihui Li, Jinpeng Liu, Preparation of low sulphur content and expandable graphite, Carbon 34 (12) (1996) 1599–1603.