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The Effect of Ultrasonic Treatment on the Particle Size and Specific Surface Area of LaCoO3
Available online at www.sciencedirect.com Available online at www.sciencedirect.com
Procedia Engineering
Procedia Engineering 00 (2012) 000–000 Procedia Engineering 32 (2012) 1012 – 1018 www.elsevier.com/locate/procedia
I-SEEC2011
The Effect of Ultrasonic Treatment on the Particle Size and Specific Surface Area of LaCoO3 S. Sompecha*, A. Srionb, A. Nuntiyac a
Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand b National Metal and Materials Technology Centre, Klong Luang, Pathum Thani 12120, Thailand c Department of Industrial Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand Elsevier use only: Received 30 September 2011; Revised 10 November 2011; Accepted 25 November 2011.
Abstract It is well known that the properties of the materials depend on the synthesis process. The controlled synthesis concern particle size and specific surface area of LaCoO3 material is necessary in many applications, such as catalysis and gas sensitivity. Since the activity of a catalysis strongly depends on the particle size and specific surface area. In this study, LaCoO3 powder was synthesized by grinding, heating and washing operations. Firstly, mixture powder of starting materials, LaCl3, CoCl2 and Na2CO3 was ground by using a planetary ball mill grind at speed 300 rpm for 2 h. Secondly, the ground sample was calcined at 600oC for 90 minutes. Finally, the sample product was washed with distilled water under ultrasonic for different treatment times to remove the NaCl phase. The ultrasonic bath was sonicated at a frequency of 40 kHz with a total nominal output power of 95 W for 0, 2, 4 and 6 minutes. All prepared samples were characterized by XRD, particle size analyzer, BET and SEM analysis. XRD patterns clearly showed the complete formation of LaCoO3 with a single-phase of perovskite structure from this synthesis. Moreover, it was found that increasing of the sonication treatment time increases the specific surface area of the prepared samples while decreasing the average particle size D[4,3]. In addition, SEM micrographs also revealed that the morphology is significantly influenced by the sonication time of treatment.
© 2010 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of I-SEEC2011 Keywords: LaCoO3; Planetary ball mill; Ultrasonic treatment; XRD; BET; SEM
* Corresponding author. Tel.: +66-53-943-401; fax: +66-53-892-262 E-mail address: [email protected].
1877-7058 © 2012 Published by Elsevier Ltd. doi:10.1016/j.proeng.2012.02.047
2
S. Sompech et al. / Procedia Engineering 32 00 (2012) 1012 – 1018 S. Sompech et al. / Procedia Engineering (2012) 000–000
1. Introduction The automotive exhaust gas that exits from the engine contains poisonous components, such as carbon monoxide (CO). These harmful components convert to inert gases, such as carbon dioxide in catalytic converters, before the exhaust gas emitted to the atmosphere. The catalytic converters are reactors that consist of monolithic honeycombs skeleton, made of ceramic or metallic materials [1]. This structure is then coated by a ceramic substrates impregnated with Pt, Pd and other platinum group metals (PGM), as the active catalytic sites [2-3]. However, due to the rising cost of PGM, many researchers have been searching for alternative materials as the active catalytic phase. One of the promising active phases for the environmental applications is the perovskite group of materials (ABO3), where A and B are cations of different sizes. The catalytic properties of perovskite-type oxides basically depend on the nature of A and B ions and on their valence state [4]. LaCoO3-based has many practical applications for catalytic converters owing to its excellent physical and chemical properties which show high catalytic activity for oxidation of carbon monoxide. In addition, it also used for oxidation of hydrocarbons, methane, hexane, and toluene [5-7]. Thus, it can be used as the catalyst for combustion, automobile exhaust and waste gas purification [3, 8-9]. Moreover, it could be used as electrode materials for solid-electrode fuel cells and gas sensors [10-11]. LaCoO3 have been achieved by many methods such as the conventional method and chemical solution methods. These methods have different of advantages and disadvantages. To overcome these disadvantages or drawbacks and improve the catalytic activity, many researchers have been searching about synthetic methodology in order to synthesis of LaCoO3 with a large specific surface area, small particle size and distribution as well. Recently, mechanochemical method has been used for the synthesis of ultrafine powders. In this method chemical precursors undergo reaction, either during milling or during subsequent low temperature heat treatment, to form a composite powder consisting of fully dispersed ultrafine particles embedded within a soluble salt by-product. The ultrafine powder is then recovered by removing the salt by-product with a simple washing procedure [12-15]. In addition, Franco F. et al [16] have studied the effect of ultrasonic treatment on the particle size and specific surface area of powder. The results of their studies showed that the particle size reduction can be controlled through different variables such as power of ultrasonic processor, amount of sample and time of treatment. When the particle size of powder was reduced, the specific surface area have been increased. Thus, the main purposes of this study were to synthesize of LaCoO3 by mechanochemical method (this process includes grinding, heating and washing operations) and to study the effect of ultrasonic treatment on the particle size and specific surface area. 2. Experimental The starting materials were LaCl3 (Fluka, 99.0%), CoCl2 (Sigma-Aldrich, 97%) and Na2CO3 (Fluka, 99.0%) and mixed in the molar ratio 1:1:2.5 to be starting mixture for milling. A planetary ball mill (Retsch, PM 100) was used to mill the starting mixtures at 300 rpm under atmospheric condition. Twenty grams mixture was put in a stainless steel pot of 250 cm3 inner volume with fourteen stainless steel balls of 20 mm diameter and milled for 2 h. The ground sample was calcined at 600 oC with a heating rate of 10 oC/min for 1.5 h, followed by washing with distilled water to remove NaCl phase, in this process used the ultrasonic bath sonicated at a frequency of 40 kHz with a total nominal output power of 95 W for 0, 2, 4 and 6 minutes in order to disperse the powder. Then, the all samples were dried in an oven at 110 oC for 2 h. The treated samples were characterized by X-ray diffraction analysis (Philips X’Pert), using Cu-Kα radiation in an angular range from 2θ = 5o to 80o, to identify the phases existing in the product. The particle size was determined using a laser diffraction method fitted with a wet sampling system
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(Mastersizer S, Malvern). The particle diameters reported was calculated using volume distribution (D[4,3]). The specific surface area of the samples were measured by a nitrogen gas adsorption instrument (Quantachrome, Version 1.11) based on the BET method. Morphology of the sample was observed by scanning electron microscope (JSM-6301F, JEOL). 3. Results and Discussion The XRD patterns of unground mixture in Fig. 1(a) show only peaks of the three starting materials; LaCl3, CoCl2 and Na2CO3 with their the peak intensity decreases gradually and vanished with an increase in milling time. Fig. 1(b) clearly shows the new peaks of NaCl phase that correspond to JCPDS file No. 05-0628 after ground for 2 h. The appearance of the NaCl phase indicated that displacement reactions between chlorides and Na2CO3 occurred during milling and other phases, e.g., various types of carbonate and possibly unreacted starting compounds, are present in the form of amorphous or minor phases in the ground product. This reaction occurred indicated that the mechanochemical (MC) solid-state reaction can be proceeded by grinding mixture of starting materials powder using a high-energy ball mill at room temperature [17]. NaCl CoCl2 Na CO 2 3 z
z
z
Intensity [a.u.]
}
z
(b)
z
z
}
(a)
20
LaCl3
30
}
40
2θ [deg]
50
60
70
Fig. 1. XRD patterns of the prepared samples; (a) unground sample and (b) sample ground for 2 h
Fig. 2(a) reveal that the phases of LaCoO3 and NaCl after the calcined at 600 oC. The appearance of LaCoO3 phase at this temperature indicated that the mechanical activation by mechanochemical processing leads to the formation at low temperature [18]. Normally, LaCoO3 has been synthesized from the constituent oxides as starting materials by heating at around 1000 oC [19]. In comparison with this, the temperature about 600 oC in the present work is extremely lower than as usual. This may be due to the MC effect induced by the grinding. From this results demonstrated that the LaCoO3 powder can be synthesized successfully through this process. However, Fig. 2(b) show only peaks of LaCoO3 are present, suggesting that the NaCl compound in the product was removed out by the washing and filtration operations. Furthermore, the XRD patterns of all peaks of LaCoO3 correspond to JCPDS file No. 25-1060 with perovskite-type structure and EDS spectrums as shown in Fig. 3 illustrate peaks of La, Co and O which accord to chemical elements in LaCoO3. While the dominant spectrum of Au was obtained due to receive from process of Au coated.
S. Sompech et al. / Procedia Engineering 32 00 (2012) 1012 – 1018 S. Sompech et al. / Procedia Engineering (2012) 000–000
4
z
dd
NaCl
d LaCoO3 d
Intensity [a.u.]
d
(b)
d d
d
d
dd
dd
z z dd d
(a)
20
d
z d
d d
z
30
40
dd
50
2θ [deg]
d
60
z
dd
70
Fig. 2. XRD patterns of the prepared samples; (a) after heating at 600 oC and (b) after washing with distilled water
Fig. 3. EDS spectrums of LaCoO3 after heating and washing
Fig. 4 show the average particle size of LaCoO3 powder after sonicated at different treatment times. In this work, it was found that the average particle size (D[4,3]) of LaCoO3 powder depend on a function of treatment times. The average particle size of untreated powder only shows the presence of particle about 4.90 μm. While the average particle size of powder treated with ultrasonic bath was decreased when increased the ultrasonic treatment times, that is the average particle sizes are 3.24 μm, 2.89 μm and 1.74 μm after treatments for 2, 4 and 6 mins, respectively. The decreasing in size of LaCoO3 powder after sonicated for different treatment times indicate that the ultrasonic can be used for activated deagglomeration of primary particles of powder due to weak agglomerate of particles [16, 20-21]. Fig. 5 show the specific surface area (SSA) of LaCoO3 powder was obtained with different treatments, as a function of sonication times in treatment. This figure clearly reveals that sonication produces a remarkable increase in the SSA with the treatment times. The increasing of the SSA is continuous evidence due to deagglomerate of primary particles after treatment. The SSA increases from 19.89 m2/g to 24.63 m2/g, 27.21 m2/g and 36.68 m2/g after treatment for 0, 2, 4 and 6 mins, respectively.
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Average Particle Size [D4,3] (μm)
S. Sompech et al. / Procedia Engineering (2012) 1012 – 1018 S. Sompech et al. / Procedia Engineering 00 32 (2012) 000–000
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5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 0
2
4
6
Treatment time (min)
Fig. 4. Average particle size [D4,3] of LaCoO3 powder after different treatment times
2
Specific Surface Area (m /g)
40
35
30
25
20
0
2
4
6
Treatment time (min)
Fig. 5. Specific surface area of LaCoO3 powder after different treatment times
Fig. 6 show SEM images of the LaCoO3 powder were obtained after prepare by mechanochemical method and activated with the ultrasonic at different treatment times in the washing process. SEM micrographs of all samples can be clearly seen that the morphology of primary particle and agglomeration of those particles. In all conditions, the mean particle size was in the nanoscale range, between 200-300 nm. In addition, it was found that the degree of agglomeration and dispersion of particles depended on a function of treatment times, this resulted indicate that degree of agglomeration and dispersion of particles can be improved by increasing the sonication treatment times. SEM micrograph in Fig. 6(a) shows the highest agglomeration of sample before sonication, and also show the lowest dispersion of particles. However, degree of agglomeration of particles were decreased and well dispersed after treatment with the ultrasonic bath and sonicated at a frequency of 40 kHz for 2, 4 and 6 mins, this results is shown in Figs. 6(b), 6(c) and 6(d), respectively. Furthermore, in this work found that sonication for 6 min showed the lowest agglomeration and well dispersion as shown in Fig. 6(d).
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S. Sompech et al. / Procedia Engineering 32 00 (2012) 1012 – 1018 S. Sompech et al. / Procedia Engineering (2012) 000–000
Fig. 6. SEM micrograph of the LaCoO3 powders before and after treatment at different times; (a) untreated; (b) for 2 min; (c) for 4 min and (d) for 6 min
4. Conclusion LaCoO3 powder was successfully synthesized by mechanochemical method. The XRD patterns illustrated that the phase of LaCoO3 with perovskite-type structure. However, the particle size reduction of powder can be improved by using the ultrasound treatment and in process controlled by variable of treatment times. Therefore, the average particle size D[4,3] of prepared samples were decreased when increased the treatment times, while the specific surface area was increased. Moreover, SEM micrographs also revealed that the morphology is significantly influenced by the sonication time. Acknowledgements I would like to thank the Commission on Higher Education, Thailand for supporting by grant fund under the program Strategic Scholarships for Frontier Research Network for the Ph.D. Program Thai Doctoral degree for this research. Also, I would like to thank the Faculty of Science and Graduate School of Chiang Mai University for partial financial support.
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References [1] Avila P, Montes M, Miro EE. Monolithic reactors for environmental applications: A review on preparation technologies. Chem Eng J 2005;109:11-36. [2] Ozawa M. Thermal stabilization of catalytic compositions for automobile exhaust treatment through rare earth modification of alumina nanoparticle support. J Alloys Compd 2006;408-412:1090-1095. [3] Kucharczyk B, Tylus W. Effect of Pd or Ag additive on the activity and stability of monolithic LaCoO3 perovskites for catalytic combustion of methane. Catal Today 2004;90:121-126. [4] Seyfi B, Baghalha M, Kazemian H. Modified LaCoO3 nano-perovskite catalysts for the environmental application of automotive CO oxidation. Chem Eng J 2009;148:306-311. [5] Cimino S, Landi G, Lisi L, Russo G. Development of a dual functional structured catalyst for partial oxidation of methane to syngas. Catal Today 2005;105:718-723. [6] Szabo V, Bassir M, Gallot JE, Van Neste A, Kaliaguine S. Perovskite-type oxides synthesised by reactive grinding: Part III. Kinetics of n-hexane oxidation over LaCo(1-x)FexO3. Appl Catal, B 2003;42:265-277. [7] Alifanti M, Florea M, Somacescu S, Parvulescu VI. Supported perovskites for total oxidation of toluene. Appl Catal, B 2005;60:33-39. [8] Kirchnerova J, Alifanti M, Delmon B. Evidence of phase cooperation in the LaCoO3-CeO2-Co3O4 catalytic system in relation to activity in methane combustion. Appl Catal, A 2002;231:65-80. [9] Zhu Y, Tan R, Feng J, Ji S, Cao L. The reaction and poisoning mechanism of SO2 and perovskite LaCoO3 film model catalysts. Appl Catal, A 2001;209:71-77. [10] Ohno Y, Nagata S, Sato H. Effect of electrode materials on the properties of high-temperature solid electrolyte fuel cells. Solid State Ionics 1981;3-4:439-442. [11] Shimizu Y, Yamashita N. Solid electrolyte CO2 sensor using NASICON and perovskite-type oxide electrode. Sens Actuators, B 2000;64:102-106. [12] Ding J, Tsuzuki T, McCormick PG Mechanochemical synthesis of ultrafine ZrO2 powder. Nanostruct Mater 1997;8:75-81. [13] Ding J, Tsuzuki T, McCormick PG. Hematite powders synthesized by mechanochemical processing. Nanostruct Mater 1997;8:739-747. [14] Tsuzuki T, Harrison WTA, McCormick PG. Synthesis of ultrafine gadolinium oxide powder by mechanochemical processing. J Alloys Compd 1998;281:146-151. [15] Tsuzuki T, Pirault E, McCormick PG. Mechanochemical synthesis of gadolinium oxide nanoparticles. Nanostruct Mater 1999;11:125-131. [16] Franco F, Perez-Maqueda LA, Perez-Rodriguez JL. The effect of ultrasound on the particle size and structural disorder of a well-ordered kaolinite. J Colloid Interface Sci 2004;274:107-117. [17] Muroi M, Street R, McCormick PG. Enhancement of critical temperature in fine La0.7Ca0.3MnO3 particles prepared by mechanochemical processing. J Appl Phys 2000;87:3424-3431. [18] Ito T, Zhang Q, Saito F. Synthesis of Perovskite-type lanthanum cobalt oxide nanoparticles by means of mechanochemical treatment. Powder Technol 2004;143-144:170-173. [19] Nakayama S, Okazaki M, Aung YL, Sakamoto M. Preparations of perovskite-type oxides LaCoO3 from three different methods and their evaluation by homogeneity, sinterability and conductivity. Solid State Ionics 2003;158:133-139. [20] Caifeng C, Andong W, Lingjuan F. Effects of ultrasonic on preparation of alumina powder by wet chemical method. Adv Sci Lett 2011;4:1249-1253. [21] Lapides I, Yariv S. The effect of ultrasound treatment on the particle-size of Wyoming bentonite in aqueous suspensions. J Mater Sci 2004;39:5209-5212.
Procedia Engineering
Procedia Engineering 00 (2012) 000–000 Procedia Engineering 32 (2012) 1012 – 1018 www.elsevier.com/locate/procedia
I-SEEC2011
The Effect of Ultrasonic Treatment on the Particle Size and Specific Surface Area of LaCoO3 S. Sompecha*, A. Srionb, A. Nuntiyac a
Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand b National Metal and Materials Technology Centre, Klong Luang, Pathum Thani 12120, Thailand c Department of Industrial Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand Elsevier use only: Received 30 September 2011; Revised 10 November 2011; Accepted 25 November 2011.
Abstract It is well known that the properties of the materials depend on the synthesis process. The controlled synthesis concern particle size and specific surface area of LaCoO3 material is necessary in many applications, such as catalysis and gas sensitivity. Since the activity of a catalysis strongly depends on the particle size and specific surface area. In this study, LaCoO3 powder was synthesized by grinding, heating and washing operations. Firstly, mixture powder of starting materials, LaCl3, CoCl2 and Na2CO3 was ground by using a planetary ball mill grind at speed 300 rpm for 2 h. Secondly, the ground sample was calcined at 600oC for 90 minutes. Finally, the sample product was washed with distilled water under ultrasonic for different treatment times to remove the NaCl phase. The ultrasonic bath was sonicated at a frequency of 40 kHz with a total nominal output power of 95 W for 0, 2, 4 and 6 minutes. All prepared samples were characterized by XRD, particle size analyzer, BET and SEM analysis. XRD patterns clearly showed the complete formation of LaCoO3 with a single-phase of perovskite structure from this synthesis. Moreover, it was found that increasing of the sonication treatment time increases the specific surface area of the prepared samples while decreasing the average particle size D[4,3]. In addition, SEM micrographs also revealed that the morphology is significantly influenced by the sonication time of treatment.
© 2010 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of I-SEEC2011 Keywords: LaCoO3; Planetary ball mill; Ultrasonic treatment; XRD; BET; SEM
* Corresponding author. Tel.: +66-53-943-401; fax: +66-53-892-262 E-mail address: [email protected].
1877-7058 © 2012 Published by Elsevier Ltd. doi:10.1016/j.proeng.2012.02.047
2
S. Sompech et al. / Procedia Engineering 32 00 (2012) 1012 – 1018 S. Sompech et al. / Procedia Engineering (2012) 000–000
1. Introduction The automotive exhaust gas that exits from the engine contains poisonous components, such as carbon monoxide (CO). These harmful components convert to inert gases, such as carbon dioxide in catalytic converters, before the exhaust gas emitted to the atmosphere. The catalytic converters are reactors that consist of monolithic honeycombs skeleton, made of ceramic or metallic materials [1]. This structure is then coated by a ceramic substrates impregnated with Pt, Pd and other platinum group metals (PGM), as the active catalytic sites [2-3]. However, due to the rising cost of PGM, many researchers have been searching for alternative materials as the active catalytic phase. One of the promising active phases for the environmental applications is the perovskite group of materials (ABO3), where A and B are cations of different sizes. The catalytic properties of perovskite-type oxides basically depend on the nature of A and B ions and on their valence state [4]. LaCoO3-based has many practical applications for catalytic converters owing to its excellent physical and chemical properties which show high catalytic activity for oxidation of carbon monoxide. In addition, it also used for oxidation of hydrocarbons, methane, hexane, and toluene [5-7]. Thus, it can be used as the catalyst for combustion, automobile exhaust and waste gas purification [3, 8-9]. Moreover, it could be used as electrode materials for solid-electrode fuel cells and gas sensors [10-11]. LaCoO3 have been achieved by many methods such as the conventional method and chemical solution methods. These methods have different of advantages and disadvantages. To overcome these disadvantages or drawbacks and improve the catalytic activity, many researchers have been searching about synthetic methodology in order to synthesis of LaCoO3 with a large specific surface area, small particle size and distribution as well. Recently, mechanochemical method has been used for the synthesis of ultrafine powders. In this method chemical precursors undergo reaction, either during milling or during subsequent low temperature heat treatment, to form a composite powder consisting of fully dispersed ultrafine particles embedded within a soluble salt by-product. The ultrafine powder is then recovered by removing the salt by-product with a simple washing procedure [12-15]. In addition, Franco F. et al [16] have studied the effect of ultrasonic treatment on the particle size and specific surface area of powder. The results of their studies showed that the particle size reduction can be controlled through different variables such as power of ultrasonic processor, amount of sample and time of treatment. When the particle size of powder was reduced, the specific surface area have been increased. Thus, the main purposes of this study were to synthesize of LaCoO3 by mechanochemical method (this process includes grinding, heating and washing operations) and to study the effect of ultrasonic treatment on the particle size and specific surface area. 2. Experimental The starting materials were LaCl3 (Fluka, 99.0%), CoCl2 (Sigma-Aldrich, 97%) and Na2CO3 (Fluka, 99.0%) and mixed in the molar ratio 1:1:2.5 to be starting mixture for milling. A planetary ball mill (Retsch, PM 100) was used to mill the starting mixtures at 300 rpm under atmospheric condition. Twenty grams mixture was put in a stainless steel pot of 250 cm3 inner volume with fourteen stainless steel balls of 20 mm diameter and milled for 2 h. The ground sample was calcined at 600 oC with a heating rate of 10 oC/min for 1.5 h, followed by washing with distilled water to remove NaCl phase, in this process used the ultrasonic bath sonicated at a frequency of 40 kHz with a total nominal output power of 95 W for 0, 2, 4 and 6 minutes in order to disperse the powder. Then, the all samples were dried in an oven at 110 oC for 2 h. The treated samples were characterized by X-ray diffraction analysis (Philips X’Pert), using Cu-Kα radiation in an angular range from 2θ = 5o to 80o, to identify the phases existing in the product. The particle size was determined using a laser diffraction method fitted with a wet sampling system
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(Mastersizer S, Malvern). The particle diameters reported was calculated using volume distribution (D[4,3]). The specific surface area of the samples were measured by a nitrogen gas adsorption instrument (Quantachrome, Version 1.11) based on the BET method. Morphology of the sample was observed by scanning electron microscope (JSM-6301F, JEOL). 3. Results and Discussion The XRD patterns of unground mixture in Fig. 1(a) show only peaks of the three starting materials; LaCl3, CoCl2 and Na2CO3 with their the peak intensity decreases gradually and vanished with an increase in milling time. Fig. 1(b) clearly shows the new peaks of NaCl phase that correspond to JCPDS file No. 05-0628 after ground for 2 h. The appearance of the NaCl phase indicated that displacement reactions between chlorides and Na2CO3 occurred during milling and other phases, e.g., various types of carbonate and possibly unreacted starting compounds, are present in the form of amorphous or minor phases in the ground product. This reaction occurred indicated that the mechanochemical (MC) solid-state reaction can be proceeded by grinding mixture of starting materials powder using a high-energy ball mill at room temperature [17]. NaCl CoCl2 Na CO 2 3 z
z
z
Intensity [a.u.]
}
z
(b)
z
z
}
(a)
20
LaCl3
30
}
40
2θ [deg]
50
60
70
Fig. 1. XRD patterns of the prepared samples; (a) unground sample and (b) sample ground for 2 h
Fig. 2(a) reveal that the phases of LaCoO3 and NaCl after the calcined at 600 oC. The appearance of LaCoO3 phase at this temperature indicated that the mechanical activation by mechanochemical processing leads to the formation at low temperature [18]. Normally, LaCoO3 has been synthesized from the constituent oxides as starting materials by heating at around 1000 oC [19]. In comparison with this, the temperature about 600 oC in the present work is extremely lower than as usual. This may be due to the MC effect induced by the grinding. From this results demonstrated that the LaCoO3 powder can be synthesized successfully through this process. However, Fig. 2(b) show only peaks of LaCoO3 are present, suggesting that the NaCl compound in the product was removed out by the washing and filtration operations. Furthermore, the XRD patterns of all peaks of LaCoO3 correspond to JCPDS file No. 25-1060 with perovskite-type structure and EDS spectrums as shown in Fig. 3 illustrate peaks of La, Co and O which accord to chemical elements in LaCoO3. While the dominant spectrum of Au was obtained due to receive from process of Au coated.
S. Sompech et al. / Procedia Engineering 32 00 (2012) 1012 – 1018 S. Sompech et al. / Procedia Engineering (2012) 000–000
4
z
dd
NaCl
d LaCoO3 d
Intensity [a.u.]
d
(b)
d d
d
d
dd
dd
z z dd d
(a)
20
d
z d
d d
z
30
40
dd
50
2θ [deg]
d
60
z
dd
70
Fig. 2. XRD patterns of the prepared samples; (a) after heating at 600 oC and (b) after washing with distilled water
Fig. 3. EDS spectrums of LaCoO3 after heating and washing
Fig. 4 show the average particle size of LaCoO3 powder after sonicated at different treatment times. In this work, it was found that the average particle size (D[4,3]) of LaCoO3 powder depend on a function of treatment times. The average particle size of untreated powder only shows the presence of particle about 4.90 μm. While the average particle size of powder treated with ultrasonic bath was decreased when increased the ultrasonic treatment times, that is the average particle sizes are 3.24 μm, 2.89 μm and 1.74 μm after treatments for 2, 4 and 6 mins, respectively. The decreasing in size of LaCoO3 powder after sonicated for different treatment times indicate that the ultrasonic can be used for activated deagglomeration of primary particles of powder due to weak agglomerate of particles [16, 20-21]. Fig. 5 show the specific surface area (SSA) of LaCoO3 powder was obtained with different treatments, as a function of sonication times in treatment. This figure clearly reveals that sonication produces a remarkable increase in the SSA with the treatment times. The increasing of the SSA is continuous evidence due to deagglomerate of primary particles after treatment. The SSA increases from 19.89 m2/g to 24.63 m2/g, 27.21 m2/g and 36.68 m2/g after treatment for 0, 2, 4 and 6 mins, respectively.
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Average Particle Size [D4,3] (μm)
S. Sompech et al. / Procedia Engineering (2012) 1012 – 1018 S. Sompech et al. / Procedia Engineering 00 32 (2012) 000–000
5
5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 0
2
4
6
Treatment time (min)
Fig. 4. Average particle size [D4,3] of LaCoO3 powder after different treatment times
2
Specific Surface Area (m /g)
40
35
30
25
20
0
2
4
6
Treatment time (min)
Fig. 5. Specific surface area of LaCoO3 powder after different treatment times
Fig. 6 show SEM images of the LaCoO3 powder were obtained after prepare by mechanochemical method and activated with the ultrasonic at different treatment times in the washing process. SEM micrographs of all samples can be clearly seen that the morphology of primary particle and agglomeration of those particles. In all conditions, the mean particle size was in the nanoscale range, between 200-300 nm. In addition, it was found that the degree of agglomeration and dispersion of particles depended on a function of treatment times, this resulted indicate that degree of agglomeration and dispersion of particles can be improved by increasing the sonication treatment times. SEM micrograph in Fig. 6(a) shows the highest agglomeration of sample before sonication, and also show the lowest dispersion of particles. However, degree of agglomeration of particles were decreased and well dispersed after treatment with the ultrasonic bath and sonicated at a frequency of 40 kHz for 2, 4 and 6 mins, this results is shown in Figs. 6(b), 6(c) and 6(d), respectively. Furthermore, in this work found that sonication for 6 min showed the lowest agglomeration and well dispersion as shown in Fig. 6(d).
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S. Sompech et al. / Procedia Engineering 32 00 (2012) 1012 – 1018 S. Sompech et al. / Procedia Engineering (2012) 000–000
Fig. 6. SEM micrograph of the LaCoO3 powders before and after treatment at different times; (a) untreated; (b) for 2 min; (c) for 4 min and (d) for 6 min
4. Conclusion LaCoO3 powder was successfully synthesized by mechanochemical method. The XRD patterns illustrated that the phase of LaCoO3 with perovskite-type structure. However, the particle size reduction of powder can be improved by using the ultrasound treatment and in process controlled by variable of treatment times. Therefore, the average particle size D[4,3] of prepared samples were decreased when increased the treatment times, while the specific surface area was increased. Moreover, SEM micrographs also revealed that the morphology is significantly influenced by the sonication time. Acknowledgements I would like to thank the Commission on Higher Education, Thailand for supporting by grant fund under the program Strategic Scholarships for Frontier Research Network for the Ph.D. Program Thai Doctoral degree for this research. Also, I would like to thank the Faculty of Science and Graduate School of Chiang Mai University for partial financial support.
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