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Economical synthesis of Al2O3 nanopowder using a precipitation method
Materials Letters 63 (2009) 2274–2276
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Economical synthesis of Al2O3 nanopowder using a precipitation method S.A. Hassanzadeh-Tabrizi, E. Taheri-Nassaj ⁎ Department of Materials Science and Engineering, Tarbiat Modares University, PO Box 14115-143, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 19 May 2009 Accepted 16 July 2009 Available online 23 July 2009 Keywords: Powder technology Nanomaterials Alumina Precipitation method
a b s t r a c t Al2O3 nanopowder was synthesized by the precipitation method using inexpensive AlCl3·6H2O and Al powder as raw materials. The dried precipitate was heat treated in the range of 60–1200 °C. The influence of heat treatment on crystallization and phase transformation of the precipitate was investigated using X-ray diffractometry (XRD), thermogravimetry and differential thermal analysis (TG–DTA) and Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) reveals that the particle size of the powders lies between 30 and 95 nm. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Alumina is an important material in industrial applications and it has a significant importance from the technological point of view. Alumina nanopowders are utilized in many areas of modern industry such as electronics, metallurgy, optoelectronics and fine ceramic composites [1,2]. Conventional processes for synthesizing ceramic nanopowders involve mechanical synthesis [3], vapor phase reaction [4], precipitation [5], combustion [6] and sol–gel [7] methods. Among these methods, chemical processes produce fine particles of high purity and high specific surface area. Precipitation is a simple and fast chemical route which is used for synthesis of nanopowders. Recently Shojaie-Bahaabad and Taheri-Nassaj [8] have prepared alumina nanopowders by an economical and new sol–gel process using low cost Al and AlCl3·6H2O powders as raw materials. In this work, Al2O3 nanopowders were synthesized via a new precipitation method using the same precursor solution as for the sol–gel process [8], and NH4OH as precipitant agent. The price of aluminum isopropoxide (250 g) provided from Aldrich and Fluka is 408.36 and 580.76 Euro [8], respectively. In the present work, raw materials were Al and AlCl3·6H2O powders (21.75 and 20.25 Euro, respectively, Merck. 1 kg [8]), therefore it can be practical to produce a low cost and economical alumina nanopowder. 2. Materials and methods The Al2O3 nanopowder in this work was obtained via precipitation method using AlCl3·6H2O (Merck), Al powder (M.A. University), HCl (Merck) and NH4OH (Merck). The Al powder has a spherical shape with an average diameter about 37.5 µm. Aluminum chloride hexahydrate ⁎ Corresponding author. E-mail address: [email protected] (E. Taheri-Nassaj). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.07.035
was first dissolved in aqueous HCl. The Al powder was then gradually added to the solution. The ratio of the raw materials was chosen under the conditions that were found to be the optimum in the work of ShojaieBahaabad [8]. According to their work, the molar ratios of Al/AlCl3 and HCl/H2O were 1.81 and 0.18 respectively. The precursor solution was then continuously stirred at 100 °C for 4 h to completely dissolve the starting materials. NH4OH was added to solution and the pH value of the solution was adjusted at 9. The obtained precipitate was washed using distilled water to remove the anion impurities, and finally dried at 80 °C for 48 h. The obtained dried precipitate was ground into powder, and then the powder was calcined at different temperatures. For more comparison, one specimen was prepared via sol–gel method. The crystalline structure of the samples was determined by X-ray diffraction (XRD), using Philips X-pert model with Cu K-α radiation. Differential thermal analyses (DTA) and thermogravimetry (TG) were used with a rate of 10 °C/min with the STA 1460 equipment. The powder morphology was investigated using a Phillips XL30 scanning electron microscope (SEM). Fourier transformation infrared spectroscopy analysis (FTIR) was carried out in a Nicolet Nexus 6700 for studying the chemical groups of the dried precipitate and calcined powder. 3. Results and discussion The synthesis mechanism may be described by the following reactions. Reaction (1) shows that the Al powder reacts with HCl to produce aluminum chloride and therefore Al can be used as a source of AlCl3. 2Al + 6HCl→2AlCl3 + 3H2
ð1Þ
A precipitate is obtained by adding NH4OH to aluminum chloride hexahydrate solution (reaction (2)). AlCl3 + 3NH4 OH→AlðOHÞ3 + 3NH4 Cl
ð2Þ
S.A. Hassanzadeh-Tabrizi, E. Taheri-Nassaj / Materials Letters 63 (2009) 2274–2276
2275
At the ageing step, Al(OH)3 converts to crystalline boehmite by reaction (3) [9]. AlðOHÞ3 →AlOOH + H2 O
ð3Þ
Transition alumina is produced by calcination of dried boehmite (reaction (4)). 2AlOOH→Al2 O3 + H2 O
ð4Þ
Fig. 1 presents thermogravimetry and differential thermal analysis (TG–DTA) curves of the dried as-precipitated powder. The DTA curve shows an endothermic peak at 240 °C which is attributed to evaporation of absorbed water and dehydration of the dried precipitate. TG curve shows an overall weight loss of approximately 34% up to 500 °C and reveals less change at higher temperature, which can be attributed to the removal of molecular water and dehydration of the precipitate. No significant weight loss occurs after 700 °C. Shojaie-Bahaabad and Taheri-Nassaj [8] reported that the total weight loss of 50% appears in the gel after calcinations. The larger amount of weight loss in the sol–gel method in their work may be due to existence of chloride components. In the precipitation method the product is washed using distilled water and therefore chloride components (e.g. NH4Cl) remove from the precipitate. It may reduce the weight loss in the precipitation method. The XRD patterns of the precipitate heat treated for 3 h at temperature ranges from 60 to 1000 °C are shown in Fig. 2a. It shows the presence of crystalline boehmite as the only crystalline phase in the dried precipitate. The average crystallite size at this temperature was estimated (by X-ray) to be about 9 nm. By increasing the temperature, boehmite is totally converted into η-alumina at 600 °C. In the range from 800 °C to 1000 °C, η and θ-alumina are the identified phases. As temperature increases to 1100 °C, α-alumina appears. α-alumina is the only present phase at 1200 °C. The XRD patterns of the specimens which are prepared by sol–gel method are shown in Fig. 2b. As can be seen, the dried gel and the powders heat treated at 200 and 400 °C do not have any peaks and seem to be amorphous. By increasing the heat treatment temperature, η-Al2O3 and θ-Al2O3 phases are detected in the gel heat treated at 600 °C. By increasing the heat treatment temperature up to 900 °C the intensity of their corresponding peaks increases. Some peaks of α-Al2O3 appear at 1000 °C. Transformation of the transitional alumina phases to the final stable α-Al2O3 takes place at about 1100 °C. According to Fig. 2a and b, it is clear that, in the precipitation method the activation energy barrier for crystallization is lower than that in the sol–gel method. This may be due to the effect of pH on crystallization. Fig. 3 shows SEM image of the powders heat treated at 600 °C. Most of the particles are in the range of 30–95 nm and spherical in
shape. Some agglomerates exist in the powders which are attributed to uncontrolled coagulation during precipitation. Fig. 4 represents the FTIR spectra of the alumina powder heat treated at various temperatures for 3 h. The absorption broad peak at
Fig. 1. DTA and TG curves of the dried precipitate.
Fig. 3. SEM of Al2O3 nanopowder after heat treatment at 600 °C.
Fig. 2. The XRD patterns of a) precipitate and b) sol–gel samples heat treated at various temperatures for 3 h.
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S.A. Hassanzadeh-Tabrizi, E. Taheri-Nassaj / Materials Letters 63 (2009) 2274–2276
peaks in the lower frequency range (500–1000 cm− 1) are owing to the presence of Al–O (788.34 and 690 cm− 1) infrared vibrations. 4. Conclusions Nano-sized Al2O3 particles with an average size of 30–95 nm have been prepared from low cost AlCl3.6H2O and Al powder via an economical precipitation method. The total weight loss of 35% appeared in the precipitate after heat treatment due to removal of volatile components. Nanocrystalline AlOOH was formed after drying of precipitate at 80 °C. Then, α-Al2O3 was obtained with increasing the temperature up to 1100 °C. Precipitation synthesis decreases the activation energy barrier for crystallization in comparison with sol–gel method. Fig. 4. FTIR spectra of Al2O3 powder heat treated at various temperatures: (a) 100; (b) 300; (c) 500 °C.
−1
−1
3000–3600 cm and absorption peak at around 1650 cm may be attributed to the O–H vibration of water. The two absorption peaks become weaker by increasing the heat treatment temperature. It confirms removing of absorbed water. The absorption peak around 1070 cm− 1 in the precipitate heat treated at 100 °C corresponds to Al– OH bonding mode. As can be seen, this peak disappears by increasing the heat treatment temperature at 300 °C. The broad overlapping
References [1] [2] [3] [4] [5] [6] [7] [8] [9]
Hassanzadeh-Tabrizi SA, Taheri-Nassaj E. J Am Ceram Soc 2008;91:3546. Krell A, Ma HW. J Am Ceram Soc 2003;86:241. Panchula ML, Ying JY. Nanostruct Mater 1997;9:161. Kamata K, Mochizuki T, Matsumoto S, Yamada A, Miyokawa K. J Am Ceram Soc 1985;68:C-193. Li JG, Sun XD. Acta Mater 2000;48:3103. Kingsley JJ, Patil KC. Mater Lett 1988;6:427. Hassanzadeh-Tabrizi SA, Taheri-Nassaj E, Sarpoolaky H. J Alloys Comps 2008;456:282. Shojaie-Bahaabad M, Taheri-Nassaj E. Mater Lett 2008;62:3364. Parida KM, Pradhan AC, Das J, Sahu N. Mater Chem Phys 2009;113:244.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Economical synthesis of Al2O3 nanopowder using a precipitation method S.A. Hassanzadeh-Tabrizi, E. Taheri-Nassaj ⁎ Department of Materials Science and Engineering, Tarbiat Modares University, PO Box 14115-143, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 19 May 2009 Accepted 16 July 2009 Available online 23 July 2009 Keywords: Powder technology Nanomaterials Alumina Precipitation method
a b s t r a c t Al2O3 nanopowder was synthesized by the precipitation method using inexpensive AlCl3·6H2O and Al powder as raw materials. The dried precipitate was heat treated in the range of 60–1200 °C. The influence of heat treatment on crystallization and phase transformation of the precipitate was investigated using X-ray diffractometry (XRD), thermogravimetry and differential thermal analysis (TG–DTA) and Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) reveals that the particle size of the powders lies between 30 and 95 nm. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Alumina is an important material in industrial applications and it has a significant importance from the technological point of view. Alumina nanopowders are utilized in many areas of modern industry such as electronics, metallurgy, optoelectronics and fine ceramic composites [1,2]. Conventional processes for synthesizing ceramic nanopowders involve mechanical synthesis [3], vapor phase reaction [4], precipitation [5], combustion [6] and sol–gel [7] methods. Among these methods, chemical processes produce fine particles of high purity and high specific surface area. Precipitation is a simple and fast chemical route which is used for synthesis of nanopowders. Recently Shojaie-Bahaabad and Taheri-Nassaj [8] have prepared alumina nanopowders by an economical and new sol–gel process using low cost Al and AlCl3·6H2O powders as raw materials. In this work, Al2O3 nanopowders were synthesized via a new precipitation method using the same precursor solution as for the sol–gel process [8], and NH4OH as precipitant agent. The price of aluminum isopropoxide (250 g) provided from Aldrich and Fluka is 408.36 and 580.76 Euro [8], respectively. In the present work, raw materials were Al and AlCl3·6H2O powders (21.75 and 20.25 Euro, respectively, Merck. 1 kg [8]), therefore it can be practical to produce a low cost and economical alumina nanopowder. 2. Materials and methods The Al2O3 nanopowder in this work was obtained via precipitation method using AlCl3·6H2O (Merck), Al powder (M.A. University), HCl (Merck) and NH4OH (Merck). The Al powder has a spherical shape with an average diameter about 37.5 µm. Aluminum chloride hexahydrate ⁎ Corresponding author. E-mail address: [email protected] (E. Taheri-Nassaj). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.07.035
was first dissolved in aqueous HCl. The Al powder was then gradually added to the solution. The ratio of the raw materials was chosen under the conditions that were found to be the optimum in the work of ShojaieBahaabad [8]. According to their work, the molar ratios of Al/AlCl3 and HCl/H2O were 1.81 and 0.18 respectively. The precursor solution was then continuously stirred at 100 °C for 4 h to completely dissolve the starting materials. NH4OH was added to solution and the pH value of the solution was adjusted at 9. The obtained precipitate was washed using distilled water to remove the anion impurities, and finally dried at 80 °C for 48 h. The obtained dried precipitate was ground into powder, and then the powder was calcined at different temperatures. For more comparison, one specimen was prepared via sol–gel method. The crystalline structure of the samples was determined by X-ray diffraction (XRD), using Philips X-pert model with Cu K-α radiation. Differential thermal analyses (DTA) and thermogravimetry (TG) were used with a rate of 10 °C/min with the STA 1460 equipment. The powder morphology was investigated using a Phillips XL30 scanning electron microscope (SEM). Fourier transformation infrared spectroscopy analysis (FTIR) was carried out in a Nicolet Nexus 6700 for studying the chemical groups of the dried precipitate and calcined powder. 3. Results and discussion The synthesis mechanism may be described by the following reactions. Reaction (1) shows that the Al powder reacts with HCl to produce aluminum chloride and therefore Al can be used as a source of AlCl3. 2Al + 6HCl→2AlCl3 + 3H2
ð1Þ
A precipitate is obtained by adding NH4OH to aluminum chloride hexahydrate solution (reaction (2)). AlCl3 + 3NH4 OH→AlðOHÞ3 + 3NH4 Cl
ð2Þ
S.A. Hassanzadeh-Tabrizi, E. Taheri-Nassaj / Materials Letters 63 (2009) 2274–2276
2275
At the ageing step, Al(OH)3 converts to crystalline boehmite by reaction (3) [9]. AlðOHÞ3 →AlOOH + H2 O
ð3Þ
Transition alumina is produced by calcination of dried boehmite (reaction (4)). 2AlOOH→Al2 O3 + H2 O
ð4Þ
Fig. 1 presents thermogravimetry and differential thermal analysis (TG–DTA) curves of the dried as-precipitated powder. The DTA curve shows an endothermic peak at 240 °C which is attributed to evaporation of absorbed water and dehydration of the dried precipitate. TG curve shows an overall weight loss of approximately 34% up to 500 °C and reveals less change at higher temperature, which can be attributed to the removal of molecular water and dehydration of the precipitate. No significant weight loss occurs after 700 °C. Shojaie-Bahaabad and Taheri-Nassaj [8] reported that the total weight loss of 50% appears in the gel after calcinations. The larger amount of weight loss in the sol–gel method in their work may be due to existence of chloride components. In the precipitation method the product is washed using distilled water and therefore chloride components (e.g. NH4Cl) remove from the precipitate. It may reduce the weight loss in the precipitation method. The XRD patterns of the precipitate heat treated for 3 h at temperature ranges from 60 to 1000 °C are shown in Fig. 2a. It shows the presence of crystalline boehmite as the only crystalline phase in the dried precipitate. The average crystallite size at this temperature was estimated (by X-ray) to be about 9 nm. By increasing the temperature, boehmite is totally converted into η-alumina at 600 °C. In the range from 800 °C to 1000 °C, η and θ-alumina are the identified phases. As temperature increases to 1100 °C, α-alumina appears. α-alumina is the only present phase at 1200 °C. The XRD patterns of the specimens which are prepared by sol–gel method are shown in Fig. 2b. As can be seen, the dried gel and the powders heat treated at 200 and 400 °C do not have any peaks and seem to be amorphous. By increasing the heat treatment temperature, η-Al2O3 and θ-Al2O3 phases are detected in the gel heat treated at 600 °C. By increasing the heat treatment temperature up to 900 °C the intensity of their corresponding peaks increases. Some peaks of α-Al2O3 appear at 1000 °C. Transformation of the transitional alumina phases to the final stable α-Al2O3 takes place at about 1100 °C. According to Fig. 2a and b, it is clear that, in the precipitation method the activation energy barrier for crystallization is lower than that in the sol–gel method. This may be due to the effect of pH on crystallization. Fig. 3 shows SEM image of the powders heat treated at 600 °C. Most of the particles are in the range of 30–95 nm and spherical in
shape. Some agglomerates exist in the powders which are attributed to uncontrolled coagulation during precipitation. Fig. 4 represents the FTIR spectra of the alumina powder heat treated at various temperatures for 3 h. The absorption broad peak at
Fig. 1. DTA and TG curves of the dried precipitate.
Fig. 3. SEM of Al2O3 nanopowder after heat treatment at 600 °C.
Fig. 2. The XRD patterns of a) precipitate and b) sol–gel samples heat treated at various temperatures for 3 h.
2276
S.A. Hassanzadeh-Tabrizi, E. Taheri-Nassaj / Materials Letters 63 (2009) 2274–2276
peaks in the lower frequency range (500–1000 cm− 1) are owing to the presence of Al–O (788.34 and 690 cm− 1) infrared vibrations. 4. Conclusions Nano-sized Al2O3 particles with an average size of 30–95 nm have been prepared from low cost AlCl3.6H2O and Al powder via an economical precipitation method. The total weight loss of 35% appeared in the precipitate after heat treatment due to removal of volatile components. Nanocrystalline AlOOH was formed after drying of precipitate at 80 °C. Then, α-Al2O3 was obtained with increasing the temperature up to 1100 °C. Precipitation synthesis decreases the activation energy barrier for crystallization in comparison with sol–gel method. Fig. 4. FTIR spectra of Al2O3 powder heat treated at various temperatures: (a) 100; (b) 300; (c) 500 °C.
−1
−1
3000–3600 cm and absorption peak at around 1650 cm may be attributed to the O–H vibration of water. The two absorption peaks become weaker by increasing the heat treatment temperature. It confirms removing of absorbed water. The absorption peak around 1070 cm− 1 in the precipitate heat treated at 100 °C corresponds to Al– OH bonding mode. As can be seen, this peak disappears by increasing the heat treatment temperature at 300 °C. The broad overlapping
References [1] [2] [3] [4] [5] [6] [7] [8] [9]
Hassanzadeh-Tabrizi SA, Taheri-Nassaj E. J Am Ceram Soc 2008;91:3546. Krell A, Ma HW. J Am Ceram Soc 2003;86:241. Panchula ML, Ying JY. Nanostruct Mater 1997;9:161. Kamata K, Mochizuki T, Matsumoto S, Yamada A, Miyokawa K. J Am Ceram Soc 1985;68:C-193. Li JG, Sun XD. Acta Mater 2000;48:3103. Kingsley JJ, Patil KC. Mater Lett 1988;6:427. Hassanzadeh-Tabrizi SA, Taheri-Nassaj E, Sarpoolaky H. J Alloys Comps 2008;456:282. Shojaie-Bahaabad M, Taheri-Nassaj E. Mater Lett 2008;62:3364. Parida KM, Pradhan AC, Das J, Sahu N. Mater Chem Phys 2009;113:244.