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Effect of ethylene glycol on polyacrylic acid based combustion process for the synthesis of nano-crystalline nickel ferrite (NiFe2O4)
Materials Letters 58 (2004) 2717 – 2720 www.elsevier.com/locate/matlet
Effect of ethylene glycol on polyacrylic acid based combustion process for the synthesis of nano-crystalline nickel ferrite (NiFe2O4) S. Vivekanandhan, M. Venkateswarlu 1, N. Satyanarayana * Raman School of Physics, Pondicherry University, Pondicherry 605 014, India Received 1 December 2003; accepted 26 February 2004 Available online 15 June 2004
Abstract Nano-crystalline nickel ferrite (NiFe2O4) was synthesized using combustion process with metal nitrates as Ni and Fe ion sources and polyacrylic acid (PAA) as a chelating agent. The effect of ethylene glycol (EG) addition to polyacrylic acid on the synthesis of nanocrystalline NiFe2O4 powders was investigated through DSC, FTIR, SEM and XRD measurements. Thermal behavior, structural coordination, microstructure and crystalline phase formation of as prepared and also calcined polymeric intermediates were, respectively, obtained from the analysis of DSC, FTIR, SEM and XRD results. The crystallite size was calculated using XRD data and Scherrer’s formula. The smallest crystallite size is found to be 14 nm for the phase pure NiFe2O4 powder obtained from the polymeric intermediates, calcined at 450 jC for 12 h, synthesized by PAA based gel combustion route with the total metal ions to EG ratio (M/EG) of 1:0.5. D 2004 Elsevier B.V. All rights reserved. Keywords: Gel combustion; Nano-crystalline; Spinel nickel ferrite; DSC; FTIR; SEM; XRD
1. Introduction Spinel nickel ferrite (NiFe2O4) is a popular magnetic material having wide range of applications [1]. Magnetic materials with nano-structure exhibit unexpected physical and chemical properties because of smallest crystallite size [2,3]. Synthesis of nickel ferrite by conventional solid state reaction method involves higher operating temperature lead to the formation of inhomogeneity, poor stoichiometry and higher crystallite size [4]. Wet chemical methods such as co-precipitation, sol – gel, hydrothermal, gel combustion, etc., are used for the synthesis of multicomponent oxide materials in nanocrystallite size at relatively lower temperatures [5– 8]. Among the wet chemical methods, gel combustion process using hydroxyl carboxylic acids (citric acid, tartaric acids, etc.) as chelating agents, is known to be simple and cost effective [9 –11]. The basic principle of gel combustion process is to distribute metal ions throughout the polymeric network and to inhibit their segregation and precipitation * Corresponding authors. Tel.: +91-413-2655991-99x404; fax: +91413-2655265/2655211. E-mail address: [email protected] (N. Satyanarayana). 1 Present address: Department of Chemical Engineering, NTUST, Taipei, Taiwan. 0167-577X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2004.02.030
[10]. In gel combustion process, hydroxyl carboxylic acids are used to chelate metal ions as well as to form polymeric network through esterification of hydroxyl and carboxylic groups. Recently, Chen and He [12] prepared NiFe2O4 spinels by sol –gel method using Polyacrylic Acid (PAA) as a chelating agent. In the present work, we have investigated an interesting new process by adding ethylene glycol (EG) to PAA, which resulted in lowering the ignition temperature for the formation of pure crystalline NiFe2O4 phase. Also, a comparative study was made on the effect of EG addition to PAA in the synthesis of nano-crystalline NiFe2O4 powders and it was investigated through DSC, FTIR SEM and XRD measurements.
2. Experimental Stoichiometric amounts of nickel nitrate (MERCK India, Extra Pure) and ferric nitrate (SD-Fine, AR grade) solutions were added to PAA and EG mixture under constant stirring condition. Total metal ions to PAA ratio was kept constant as 1:2 and EG was added to metal nitrate and PAA mixture by keeping total metal ions to EG ratio of 1:0.5 and it was named as M/EG = 1:0.5. The resulting transparent brown colour solution was evaporated at 90 jC under constant
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stirring condition and continuous evaporation lead to the gel formation. Resulting black colour gel was heated at 150 jC for 12 h in static air. Obtained porous solid mass was called as polymeric intermediate and it was calcined at different temperatures (300 and 450 jC) for 12 h in air ambient to obtained nano-crystalline NiFe2O4 powder. NiFe2O4 was also prepared without EG for comparison purpose and it was named as M/EG = 1:0. Each composition of polymeric intermediate of i2 mg was heated in static air between 30 and 500 jC at the rate of 10 jC min 1 and measured the DSC curves using Mettler Toledo Stare System, Module: DSC 821e/500/575/414183/ 5278. FTIR spectra were recorded, using FTIR-8000 spectrometer of Shimadzu, Japan, between 400 to 4000 cm 1 for as prepared and also calcined polymeric intermediates with KBr powder as diluter. Scanning electron micrographs were taken using Hitachi-450 model scanning electron microscope for the polymeric intermediates. Powder XRD spectra were recorded using a Rigaku X-ray powder diffractometer equipped with graphite monochromater employing Cu Ka radiation for as prepared as well as calcined polymeric intermediates at two different temperatures (300 and 450 jC). Crystallite size was determined using the Scherrer’s formula [13]. NBS silicon standard was used for the estimation of instrumental broadening.
Fig. 2. FTIR spectra of polymeric intermediates (M/EG = 1:0; and M/ EG = 1:0.5) obtained at 150 jC for 12 h.
Fig. 1a, observed exothermic peak between 280 and 400 jC is attributed to the combustion of polymeric intermediate, which may lead to the formation of NiFe2O4. From Fig. 1b, DSC curves for M/EG = 1:0.5 exhibits an exothermic peak in three steps between 225 and 390 jC, which may be due to
3. Results and discussion Fig. 1 shows DSC thermograms of polymeric intermediates prepared with the M/EG ratio of 1:0 and 1:0.5. From
Fig. 1. DSC thermograms of polymeric intermediates heated at 150 jC for 12 h: (a) M/EG = 1:0; (b) M/EG = 1:0.5.
Fig. 3. FTIR spectra of polymeric intermediates (M/EG = 1:0 and 1:0.5) calcined at 300 and 450 jC.
S. Vivekanandhan et al. / Materials Letters 58 (2004) 2717–2720
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well defined peaks at 1715 and 1311cm 1 are due to the presence of aliphatic ester, which confirms the bond formation between PAA and EG through the esterification reaction and it was not observed in the sample prepared with M/ EG = 1:0. Observed IR bands for the sample prepared with M/EG = 1:0.5, at 1515 and 1324 cm 1 are, respectively attributed to asymmetric and symmetric vibration of the chelating COO- groups from the metal carboxylates, which confirms the chelation of metal ions [17]. Thus, the FTIR spectra confirm that the addition of EG formed a bridge network between two PAA polymers, which indicates the formation of the better polymeric nature of the intermediate and it is further confirmed by SEM analysis. Fig. 3 shows the FTIR spectra for the polymeric intermediates calcined at two different temperatures (300 and 450 jC). From Fig. 3a, IR spectrum showed the formation of three new peaks at 1084, 884 and 604 cm 1 for the polymeric intermediates calcined at 300 jC. Peaks at 1084 and 884 cm 1 are attributed to carbonates (CO3 ) [9] and the peak at 604 cm 1 is assigned as the vibrations of Fe2O4 groups [15],
Fig. 4. SEM micrographs of polymeric intermediates: (a) M/EG = 1:0; (b) M/EG = 1:0.5.
stepwise decomposition of PAA and EG derivatives. From Fig. 1a and b, DSC thermograms of polymeric intermediates, it is concluded that the addition of EG not only reduces the ignition temperature from 280 to 225 jC but also increased the heat evaluation due to better combustion, which may result to the formation of highly pure NiFe2O4 powders. Further, it was confirmed by FTIR and XRD measurements. FTIR spectra of polymeric intermediates are shown in Fig. 2. The broad peak observed at 3395 and 3431 cm 1, respectively, for the M/EG = 1:0 and M/EG = 1:0.5 is attributed to the vibration of O – H groups, which indicates the adsorbed moister [14]. From Fig. 2, for both the polymeric intermediates, the observed bands at 2918 and 2852 cm 1 are, respectively, ascribed to asymmetric and symmetric vibration of -CH2- group present in the PAA [15]. The FTIR spectrum for the polymeric intermediate with M/ EG = 1:0 shows two bands at 1549 and 1401 cm 1 are, respectively, assigned to asymmetric and symmetric vibrations of the -COO ion, respectively, which confirm the presence of metal carboxylates (chelation of metal ions by PAA) [16,17]. The sharp peak at 1738 cm 1 for M/EG = 1:0 could be assigned to the CMO stretching vibration of carboxylic group. From Fig. 2, the IR spectrum for the polymeric intermediate with M/EG = 1:0.5 shows two new
Fig. 5. XRD spectra of as prepared and calcined polymeric intermediates (M/EG = 1:0 and 1:0.5) at 300 and 450 jC.
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which confirmed the formation of NiFe2O4 structure with carbonate impurities. From Fig. 3b, the FTIR spectra for the polymeric intermediates calcined at 450 jC for 12 h showed only one IR peak at 604 cm 1, due to Fe2O4- group and the IR peaks at 1084 and 884 cm 1, which corresponds to carbonates, disappeared, which indicates the formation of pure NiFe2O4 structure compound. Whereas, in Fig. 3a, the observed less intense IR peak indicates the incomplete combustion of intermediate for the M/EG = 1:0. Scanning electron micrograph of the intermediates with two different total metal ions to EG ratios are shown in Fig. 4a and b. From Fig. 4a, the SEM picture for the polymeric intermediates with M/EG ratio of 1:0 showed a cluster structure, which indicates the segregation of metal carboxylates. From Fig. 4b, the SEM picture for the polymeric intermediate with M/EG ratio of 1:0.5 shows polymeric structure with large voids, which may be attributed to the formation of high polymeric network between PAA and EG. SEM and FTIR confirmed that the addition of EG lead to the formation of bridging network between PAA and EG through the esterification, which lead to the formation of high porous polymeric intermediate. Fig. 5 shows the X-ray diffraction patterns for as prepared and also calcined polymeric intermediates at two different temperatures (300 and 450 jC) for 12 h, along with JCPDS standard. From Fig. 5a, peak free XRD spectra confirmed the amorphous nature of polymeric intermediates. From Fig. 5b and c, the XRD spectra for the calcined polymeric intermediates show the crystalline peaks, which indicate the spinel NiFe2O4 phase begun to form at 300 jC and the complete phase was obtained at 450 jC. Formation of crystalline spinel NiFe2O4 phase was confirmed by comparing the obtained XRD pattern with JCPDS standard, which is shown in Fig. 5. The average crystallite size, of the calcined polymeric intermediates at 450 jC, is calculated by using Scherrer’s formula with Lorentz fit XRD data of (311) peak at 35j43Vof 2h values. The obtained crystallite size is 16 and 14 nm for the NiFe2O4 powders obtained from the polymeric intermediates, calcined at 450 jC, synthesized, respectively with M/EG = 1:0 and M/EG = 1:0.5, which confirm that the addition of EG reduces the crystallite size of the prepared NiFe2O4 powders. From the DSC, FTIR, SEM and XRD results, it is clearly observed that the addition of EG to PAA not only helps to form high porous polymeric intermediate, reduce the ignition temperature and lower the crystallite size but also helps to prepare pure NiFe2O4 powders.
4. Conclusions Effect of ethylene glycol with polyacrylic acid in the synthesis of nano-crystalline spinel NiFe2O4 powders was
studied. SEM and DSC investigations, respectively, showed that the addition of EG to PAA lead to the formation of highly porous polymerized intermediates and also reduced the ignition temperature. FTIR results showed that the addition of EG forms a bridge between PAA molecules, which lead to the better polymerization and it was confirmed by SEM results. Crystalline NiFe2O4 phase was confirmed by comparing the observed XRD spectra with the JCPDS standard. The high pure and smallest crystallite size of 14 nm for NiFe2O4 powders obtained from the polymeric intermediates, calcined at 450 jC for 12 h, synthesized with M/EG = 1:0.5. Hence, the newly developed EG assisted PAA based gel combustion process is useful for the synthesis of high pure nano-crystalline oxide materials at lower temperature than the direct PAA based route.
Acknowledgements Authors gratefully acknowledge DRDO, CSIR and DST for utilizing the research facilities available from the major research projects. The authors also thank Dr. T. Gnanasekaran, and Rajesh Ganesan, MCD, IGCAR, Kalpakkam for their help in this work.
References [1] G. Economos, J. Am. Ceram. Soc. 42 (1959) 628. [2] A.H. Morrish, K. Haneda, J. Appl. Phys. 52 (1981) 2497. [3] A.S. Albuquerque, J.D. Ardisson, W.A.A. Macedo, J.L. LoH pez, R. Paniago, A.I.C. Persiano, J. Magn. Magn. Mater. 226 – 230 (2001) 1379. [4] Y. Shi, J. Ding, X. Liu, J. Wang, J. Magn. Magn. Mater. 205 (1999) 249 – 254. [5] G. Ting-Kuo Fey, K. Chen, J. Power Sources 81 – 82 (1999) 461. [6] F. Li, K. Hu, J. Li, D. Zang, G. Chen, J. Nucl. Mater. 300 (2002) 82. [7] W. Liu, G.C. Farrington, F. Chaput, B. Dunn, J. Electrochem. Soc. 143 (1996) 879. [8] S. Sundar Monoharan, N.R.S. Kumar, K.C. Patil, Mater. Res. Bull. 25 (1990) 731. [9] S.W. Kwon, S.B. Park, G. Seo, S.T. Hwang, J. Nucl. Mater. 257 (1998) 172. [10] S.K. Saha, A. Pathak, P. Pramanik, J. Mater. Sci. Lett. 14 (1995) 35. [11] S. Vivekanandhan, M. Venkateswarlu, N. Satyanarayana, Mater. Lett. 58 (2004) 1218. [12] D.-H. Chen, X.-R. He, Mater. Res. Bull. 36 (2001) 1369 – 1377. [13] H.P. Klug, L.E. Alexander, X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials, Wiley, New York, 1954. [14] C.-H. Lu, S.-J. Liou, Mater. Sci. Eng., B, Solid-State Mater. Adv. Technol. 75 (2000) 38. [15] G. Socrates, Infrared and Raman Characteristic Group Frequencies, Wiley, New York, 2001. [16] X. Zeng, Y. Liu, X. Wang, W. Yin, L. Wang, H. Guo, Mater. Chem. Phys. 77 (2002) 209. [17] G.V. Rama Rao, D.S. Surya Narayana, U.V. Varadaraju, G.V.N. Rao, S. Venkadesan, J. Alloys Compd. 217 (1995) 200.
Effect of ethylene glycol on polyacrylic acid based combustion process for the synthesis of nano-crystalline nickel ferrite (NiFe2O4) S. Vivekanandhan, M. Venkateswarlu 1, N. Satyanarayana * Raman School of Physics, Pondicherry University, Pondicherry 605 014, India Received 1 December 2003; accepted 26 February 2004 Available online 15 June 2004
Abstract Nano-crystalline nickel ferrite (NiFe2O4) was synthesized using combustion process with metal nitrates as Ni and Fe ion sources and polyacrylic acid (PAA) as a chelating agent. The effect of ethylene glycol (EG) addition to polyacrylic acid on the synthesis of nanocrystalline NiFe2O4 powders was investigated through DSC, FTIR, SEM and XRD measurements. Thermal behavior, structural coordination, microstructure and crystalline phase formation of as prepared and also calcined polymeric intermediates were, respectively, obtained from the analysis of DSC, FTIR, SEM and XRD results. The crystallite size was calculated using XRD data and Scherrer’s formula. The smallest crystallite size is found to be 14 nm for the phase pure NiFe2O4 powder obtained from the polymeric intermediates, calcined at 450 jC for 12 h, synthesized by PAA based gel combustion route with the total metal ions to EG ratio (M/EG) of 1:0.5. D 2004 Elsevier B.V. All rights reserved. Keywords: Gel combustion; Nano-crystalline; Spinel nickel ferrite; DSC; FTIR; SEM; XRD
1. Introduction Spinel nickel ferrite (NiFe2O4) is a popular magnetic material having wide range of applications [1]. Magnetic materials with nano-structure exhibit unexpected physical and chemical properties because of smallest crystallite size [2,3]. Synthesis of nickel ferrite by conventional solid state reaction method involves higher operating temperature lead to the formation of inhomogeneity, poor stoichiometry and higher crystallite size [4]. Wet chemical methods such as co-precipitation, sol – gel, hydrothermal, gel combustion, etc., are used for the synthesis of multicomponent oxide materials in nanocrystallite size at relatively lower temperatures [5– 8]. Among the wet chemical methods, gel combustion process using hydroxyl carboxylic acids (citric acid, tartaric acids, etc.) as chelating agents, is known to be simple and cost effective [9 –11]. The basic principle of gel combustion process is to distribute metal ions throughout the polymeric network and to inhibit their segregation and precipitation * Corresponding authors. Tel.: +91-413-2655991-99x404; fax: +91413-2655265/2655211. E-mail address: [email protected] (N. Satyanarayana). 1 Present address: Department of Chemical Engineering, NTUST, Taipei, Taiwan. 0167-577X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2004.02.030
[10]. In gel combustion process, hydroxyl carboxylic acids are used to chelate metal ions as well as to form polymeric network through esterification of hydroxyl and carboxylic groups. Recently, Chen and He [12] prepared NiFe2O4 spinels by sol –gel method using Polyacrylic Acid (PAA) as a chelating agent. In the present work, we have investigated an interesting new process by adding ethylene glycol (EG) to PAA, which resulted in lowering the ignition temperature for the formation of pure crystalline NiFe2O4 phase. Also, a comparative study was made on the effect of EG addition to PAA in the synthesis of nano-crystalline NiFe2O4 powders and it was investigated through DSC, FTIR SEM and XRD measurements.
2. Experimental Stoichiometric amounts of nickel nitrate (MERCK India, Extra Pure) and ferric nitrate (SD-Fine, AR grade) solutions were added to PAA and EG mixture under constant stirring condition. Total metal ions to PAA ratio was kept constant as 1:2 and EG was added to metal nitrate and PAA mixture by keeping total metal ions to EG ratio of 1:0.5 and it was named as M/EG = 1:0.5. The resulting transparent brown colour solution was evaporated at 90 jC under constant
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stirring condition and continuous evaporation lead to the gel formation. Resulting black colour gel was heated at 150 jC for 12 h in static air. Obtained porous solid mass was called as polymeric intermediate and it was calcined at different temperatures (300 and 450 jC) for 12 h in air ambient to obtained nano-crystalline NiFe2O4 powder. NiFe2O4 was also prepared without EG for comparison purpose and it was named as M/EG = 1:0. Each composition of polymeric intermediate of i2 mg was heated in static air between 30 and 500 jC at the rate of 10 jC min 1 and measured the DSC curves using Mettler Toledo Stare System, Module: DSC 821e/500/575/414183/ 5278. FTIR spectra were recorded, using FTIR-8000 spectrometer of Shimadzu, Japan, between 400 to 4000 cm 1 for as prepared and also calcined polymeric intermediates with KBr powder as diluter. Scanning electron micrographs were taken using Hitachi-450 model scanning electron microscope for the polymeric intermediates. Powder XRD spectra were recorded using a Rigaku X-ray powder diffractometer equipped with graphite monochromater employing Cu Ka radiation for as prepared as well as calcined polymeric intermediates at two different temperatures (300 and 450 jC). Crystallite size was determined using the Scherrer’s formula [13]. NBS silicon standard was used for the estimation of instrumental broadening.
Fig. 2. FTIR spectra of polymeric intermediates (M/EG = 1:0; and M/ EG = 1:0.5) obtained at 150 jC for 12 h.
Fig. 1a, observed exothermic peak between 280 and 400 jC is attributed to the combustion of polymeric intermediate, which may lead to the formation of NiFe2O4. From Fig. 1b, DSC curves for M/EG = 1:0.5 exhibits an exothermic peak in three steps between 225 and 390 jC, which may be due to
3. Results and discussion Fig. 1 shows DSC thermograms of polymeric intermediates prepared with the M/EG ratio of 1:0 and 1:0.5. From
Fig. 1. DSC thermograms of polymeric intermediates heated at 150 jC for 12 h: (a) M/EG = 1:0; (b) M/EG = 1:0.5.
Fig. 3. FTIR spectra of polymeric intermediates (M/EG = 1:0 and 1:0.5) calcined at 300 and 450 jC.
S. Vivekanandhan et al. / Materials Letters 58 (2004) 2717–2720
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well defined peaks at 1715 and 1311cm 1 are due to the presence of aliphatic ester, which confirms the bond formation between PAA and EG through the esterification reaction and it was not observed in the sample prepared with M/ EG = 1:0. Observed IR bands for the sample prepared with M/EG = 1:0.5, at 1515 and 1324 cm 1 are, respectively attributed to asymmetric and symmetric vibration of the chelating COO- groups from the metal carboxylates, which confirms the chelation of metal ions [17]. Thus, the FTIR spectra confirm that the addition of EG formed a bridge network between two PAA polymers, which indicates the formation of the better polymeric nature of the intermediate and it is further confirmed by SEM analysis. Fig. 3 shows the FTIR spectra for the polymeric intermediates calcined at two different temperatures (300 and 450 jC). From Fig. 3a, IR spectrum showed the formation of three new peaks at 1084, 884 and 604 cm 1 for the polymeric intermediates calcined at 300 jC. Peaks at 1084 and 884 cm 1 are attributed to carbonates (CO3 ) [9] and the peak at 604 cm 1 is assigned as the vibrations of Fe2O4 groups [15],
Fig. 4. SEM micrographs of polymeric intermediates: (a) M/EG = 1:0; (b) M/EG = 1:0.5.
stepwise decomposition of PAA and EG derivatives. From Fig. 1a and b, DSC thermograms of polymeric intermediates, it is concluded that the addition of EG not only reduces the ignition temperature from 280 to 225 jC but also increased the heat evaluation due to better combustion, which may result to the formation of highly pure NiFe2O4 powders. Further, it was confirmed by FTIR and XRD measurements. FTIR spectra of polymeric intermediates are shown in Fig. 2. The broad peak observed at 3395 and 3431 cm 1, respectively, for the M/EG = 1:0 and M/EG = 1:0.5 is attributed to the vibration of O – H groups, which indicates the adsorbed moister [14]. From Fig. 2, for both the polymeric intermediates, the observed bands at 2918 and 2852 cm 1 are, respectively, ascribed to asymmetric and symmetric vibration of -CH2- group present in the PAA [15]. The FTIR spectrum for the polymeric intermediate with M/ EG = 1:0 shows two bands at 1549 and 1401 cm 1 are, respectively, assigned to asymmetric and symmetric vibrations of the -COO ion, respectively, which confirm the presence of metal carboxylates (chelation of metal ions by PAA) [16,17]. The sharp peak at 1738 cm 1 for M/EG = 1:0 could be assigned to the CMO stretching vibration of carboxylic group. From Fig. 2, the IR spectrum for the polymeric intermediate with M/EG = 1:0.5 shows two new
Fig. 5. XRD spectra of as prepared and calcined polymeric intermediates (M/EG = 1:0 and 1:0.5) at 300 and 450 jC.
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which confirmed the formation of NiFe2O4 structure with carbonate impurities. From Fig. 3b, the FTIR spectra for the polymeric intermediates calcined at 450 jC for 12 h showed only one IR peak at 604 cm 1, due to Fe2O4- group and the IR peaks at 1084 and 884 cm 1, which corresponds to carbonates, disappeared, which indicates the formation of pure NiFe2O4 structure compound. Whereas, in Fig. 3a, the observed less intense IR peak indicates the incomplete combustion of intermediate for the M/EG = 1:0. Scanning electron micrograph of the intermediates with two different total metal ions to EG ratios are shown in Fig. 4a and b. From Fig. 4a, the SEM picture for the polymeric intermediates with M/EG ratio of 1:0 showed a cluster structure, which indicates the segregation of metal carboxylates. From Fig. 4b, the SEM picture for the polymeric intermediate with M/EG ratio of 1:0.5 shows polymeric structure with large voids, which may be attributed to the formation of high polymeric network between PAA and EG. SEM and FTIR confirmed that the addition of EG lead to the formation of bridging network between PAA and EG through the esterification, which lead to the formation of high porous polymeric intermediate. Fig. 5 shows the X-ray diffraction patterns for as prepared and also calcined polymeric intermediates at two different temperatures (300 and 450 jC) for 12 h, along with JCPDS standard. From Fig. 5a, peak free XRD spectra confirmed the amorphous nature of polymeric intermediates. From Fig. 5b and c, the XRD spectra for the calcined polymeric intermediates show the crystalline peaks, which indicate the spinel NiFe2O4 phase begun to form at 300 jC and the complete phase was obtained at 450 jC. Formation of crystalline spinel NiFe2O4 phase was confirmed by comparing the obtained XRD pattern with JCPDS standard, which is shown in Fig. 5. The average crystallite size, of the calcined polymeric intermediates at 450 jC, is calculated by using Scherrer’s formula with Lorentz fit XRD data of (311) peak at 35j43Vof 2h values. The obtained crystallite size is 16 and 14 nm for the NiFe2O4 powders obtained from the polymeric intermediates, calcined at 450 jC, synthesized, respectively with M/EG = 1:0 and M/EG = 1:0.5, which confirm that the addition of EG reduces the crystallite size of the prepared NiFe2O4 powders. From the DSC, FTIR, SEM and XRD results, it is clearly observed that the addition of EG to PAA not only helps to form high porous polymeric intermediate, reduce the ignition temperature and lower the crystallite size but also helps to prepare pure NiFe2O4 powders.
4. Conclusions Effect of ethylene glycol with polyacrylic acid in the synthesis of nano-crystalline spinel NiFe2O4 powders was
studied. SEM and DSC investigations, respectively, showed that the addition of EG to PAA lead to the formation of highly porous polymerized intermediates and also reduced the ignition temperature. FTIR results showed that the addition of EG forms a bridge between PAA molecules, which lead to the better polymerization and it was confirmed by SEM results. Crystalline NiFe2O4 phase was confirmed by comparing the observed XRD spectra with the JCPDS standard. The high pure and smallest crystallite size of 14 nm for NiFe2O4 powders obtained from the polymeric intermediates, calcined at 450 jC for 12 h, synthesized with M/EG = 1:0.5. Hence, the newly developed EG assisted PAA based gel combustion process is useful for the synthesis of high pure nano-crystalline oxide materials at lower temperature than the direct PAA based route.
Acknowledgements Authors gratefully acknowledge DRDO, CSIR and DST for utilizing the research facilities available from the major research projects. The authors also thank Dr. T. Gnanasekaran, and Rajesh Ganesan, MCD, IGCAR, Kalpakkam for their help in this work.
References [1] G. Economos, J. Am. Ceram. Soc. 42 (1959) 628. [2] A.H. Morrish, K. Haneda, J. Appl. Phys. 52 (1981) 2497. [3] A.S. Albuquerque, J.D. Ardisson, W.A.A. Macedo, J.L. LoH pez, R. Paniago, A.I.C. Persiano, J. Magn. Magn. Mater. 226 – 230 (2001) 1379. [4] Y. Shi, J. Ding, X. Liu, J. Wang, J. Magn. Magn. Mater. 205 (1999) 249 – 254. [5] G. Ting-Kuo Fey, K. Chen, J. Power Sources 81 – 82 (1999) 461. [6] F. Li, K. Hu, J. Li, D. Zang, G. Chen, J. Nucl. Mater. 300 (2002) 82. [7] W. Liu, G.C. Farrington, F. Chaput, B. Dunn, J. Electrochem. Soc. 143 (1996) 879. [8] S. Sundar Monoharan, N.R.S. Kumar, K.C. Patil, Mater. Res. Bull. 25 (1990) 731. [9] S.W. Kwon, S.B. Park, G. Seo, S.T. Hwang, J. Nucl. Mater. 257 (1998) 172. [10] S.K. Saha, A. Pathak, P. Pramanik, J. Mater. Sci. Lett. 14 (1995) 35. [11] S. Vivekanandhan, M. Venkateswarlu, N. Satyanarayana, Mater. Lett. 58 (2004) 1218. [12] D.-H. Chen, X.-R. He, Mater. Res. Bull. 36 (2001) 1369 – 1377. [13] H.P. Klug, L.E. Alexander, X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials, Wiley, New York, 1954. [14] C.-H. Lu, S.-J. Liou, Mater. Sci. Eng., B, Solid-State Mater. Adv. Technol. 75 (2000) 38. [15] G. Socrates, Infrared and Raman Characteristic Group Frequencies, Wiley, New York, 2001. [16] X. Zeng, Y. Liu, X. Wang, W. Yin, L. Wang, H. Guo, Mater. Chem. Phys. 77 (2002) 209. [17] G.V. Rama Rao, D.S. Surya Narayana, U.V. Varadaraju, G.V.N. Rao, S. Venkadesan, J. Alloys Compd. 217 (1995) 200.