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Synthesis of ultrafine Fe3O4 powder by glycothermal process
November 1998
Materials Letters 37 Ž1998. 255–258
Synthesis of ultrafine Fe 3 O4 powder by glycothermal process Dong-Sik Bae
a,)
, Kyong-Sop Han a , Seung-Beom Cho c , Sang-Heul Choi
b
a
b
DiÕ. of Ceramics, Korea Institute of Sci. and Tech., Seoul 136-791, South Korea Dept. of Inorg. Mater. Engineering, Hanyang UniÕersity, Seoul 133-791, South Korea c DiÕision of Materials Research Center, Rutgers UniÕersity, NJ, USA Received 10 February 1998; revised 30 March 1998; accepted 20 April 1998
Abstract Magnetite, Fe 3 O4 , powder was prepared under glycothermal conditions by precipitation from metal nitrates with aqueous ammonium hydroxide. Fine powders were obtained in the temperature range 190 to 2708. The powders were characterized by SEM, BET and XRD. Properties of the Fe 3 O4 powder were studied as a function of reaction temperature. The average particle size and specific surface areas of the synthesized Fe 3 O4 powder increased and decreased, respectively, with increasing reaction temperature. After glycothermal treatment at 2308 for 8 h, the average particle size of the Fe 3 O4 powder was about 70 nm and the particle size distribution was narrow. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Fe 3 O4 ; Ultrafine; Glycothermal process; 1,4-butanediol; NH 4 OH; Magnetite
1. Introduction Recently, there has been an increasing interest in the synthesis of monodispersed metal oxides. Solution synthesis techniques have the potential to meet the increasing demand for the direct preparation of crystalline ceramic powders and offer a low-temperature alternative to conventional powder synthesis techniques in the production of anhydrous oxide powders w1x. Solution synthesis techniques can produce fine, high-purity, stoichiometric particles of single and multi-component metal oxides. Furthermore, if process conditions such as solute concentration, reaction temperature, reaction time and the type of solvent are carefully controlled, ceramic particles of the desired shape and size can be produced w2x.
)
Corresponding author.
Hydrothermal synthesis meets the increasing demand for the direct preparation of crystalline ceramic powders and offers a low temperature alternative to conventional powder synthesis technique in the production of anhydrous oxide powders. Hydrothermal synthesis is considered today a promising way to obtain high-quality ceramic powders. Compared to conventional processing techniques, hydrothermal method has many advantages: Ž1. A crystalline product can be obtained directly at lower reaction temperature. Hence the calcining process, which results in a transformation from the amorphous phase to the crystal phase, can be avoided. It favors a decrease in an agglomeration between particles. Ž2. From a change in hydrothermal conditions Žsuch as temperature, pH, reactant concentration and molar ratio, additive, etc.., crystalline products with different composition, structure, and morphology could be formed. Ž3. The purity of product prepared in appro-
00167-577Xr98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 9 8 . 0 0 1 0 1 - 3
256
D.-S. Bae et al.r Materials Letters 37 (1998) 255–258
priate conditions could be high owing to recrystallization in hydrothermal solution. Ž4. The equipment and processing required are simpler, and the control of reaction conditions is easier, etc. This technique can produce fine, high purity, stoichiometric particles of single and multi-component metal oxides w3x. Some precipitated hydroxides subjected to prolonged boiling under atmospheric pressure in their mother liquor or hydrothermally treated under enhanced pressure at elevated temperatures transform to finegrained oxides of narrow particle size distribution. It has been demonstrated that such powders are composed of much softer agglomerates and sinter much better than those prepared by calcination decomposition of the same oxides w4x. These powders could be sintered at low temperature without calcination and milling steps w5,6x. Furthermore, if the process conditions such as solution pH, solute concentration, reaction temperature, reaction time, seed materials, and the type of solvent are carefully controlled, ceramic particles of the desired shape and size can be produced w7x. The objective of this study was to prepare ultrafine Fe 3 O4 using NH 4 OH under mild hydrothermal conditions.
2. Experimental procedure The process for preparing Fe 3 O4 by glycothermal treatment in 1,4-butanediol solution is schematically illustrated in Fig. 1. Fe 3 O4 precursors were precipitated from 1 M FeŽNO 3 . 3 9H 2 O solution by slowly adding 1 M NH 4OH solution with rapid stirring. The precipitated Fe 3 O4 precursors were washed by repeated cycles of centrifugation and redispersion in deionized water. Washing was performed for a minimum of five times each in deionized water and methanol. Excess solution was decanted after the final washing and the wet precursor was redispersed in 250 ml 1,4-butanediol under vigorous stirring. The resulting suspension was placed in a 1000 ml stainless steel pressure vessel. The vessel was then heated to the desired temperature at a rate of 108rmin. During heating, the autogenous pressure gradually increased to 1 MPa and was usually maintained below 3.5 MPa during the holding period. The reaction products were washed at least five times by repeated cycles of centrifugation and redispersion in
Fig. 1. Procedure for the preparation of the Fe 3 O4 powders in 1,4-butanediol solution.
methanol. The recovered powders were analyzed for phase composition using X-ray diffraction ŽPhillips, PW 1825r00. over the 2 theta range from 10–708 at rate of 2.58rmin. The morphology of the synthesized particles was observed using scanning electron microscopy ŽSEM, Hitachi S-4200.. The specific surface areas were calculated by the BET method ŽMicromeretics ASAP 2000..
3. Results and discussion The precipitated powder of the FeŽNO 3 . 3 P 9H 2 O was prepared with NH 4 OH 1 M solution ŽpH s 11.80. was added. The reaction temperature was found to have an effect on the size of Fe 3 O4 particles synthesized in 1,4-butanediol solution. Fig. 2
D.-S. Bae et al.r Materials Letters 37 (1998) 255–258
257
Fig. 2. SEM micrographs of the Fe 3 O4 particles synthesized by glycothermal treatment at reaction temperatures of Ža. 2108C, Žb. 2308C, Žc. 2508C and Žd. 2708C for 8 h.
shows the scanning electron micrographs of the synthesized Fe 3 O4 in the temperature range of 210 to 3008C. Glycothermal synthesis of the Fe 3 O4 from nitrates in NH 4 OH led to nearly spherical and ultrafine particles which were on the order of 50 to 150 nm in size. The reaction temperature affected the size and shape of the Fe 3 O4 particles synthesized in 1,4-butanediol solution. The temperature had a great effect on the grain size of the products and the agglomeration among grains. Lowering temperature yielded smaller grains but agglomeration among grains increased. Increasing reaction temperature changed the size of the Fe 3 O4 particles, as expected.
Specific surface areas of the synthesized Fe 3 O4 powder decreased with increasing reaction temperature ŽFig. 3.. After glycothermal treatment at 230, 250, 2708 for 8 h, BET surface areas of the Fe 3 O4 powders were 42.6 m2rg, 39.83 m2rg, 35.35 m2rg, respectively. A typical XRD pattern of Fe 3 O4 particles synthesized in 1,4-butanediol solution is given in Fig. 4. The sharp diffraction peaks are consistent with the well defined and crystallized particles shown, Fig. 2. The transformation of precursor to Fe 3 O4 in 1,4butanediol did occur in the range of 190 to 2708C and 1 to 3.0 MPa.
258
D.-S. Bae et al.r Materials Letters 37 (1998) 255–258
4. Conclusions
Fig. 3. BET surface areas of the Fe 3 O4 powder vs. glycothermal treatment temperatures.
Ultrafine, nearly spherical, and high purity Fe 3 O4 powder could be prepared by neutralizing the nitrate solutions in NH 4 OH and by glycothermal treatment under mild hydrothermal conditions. After glycothermal treatment at 2308 for 8 h, the average particle diameter of the Fe 3 O4 was about 70 nm. The average particle diameter of the Fe 3 O4 increased with increasing reaction temperature and time. The specific surface areas of the synthesized Fe 3 O4 powders decreased with increasing reaction temperature. The results of this study show that it is possible to control the size of the Fe 3 O4 powders by glycothermal synthesis in 1,4-butanediol solution, if the synthesis conditions such as reaction temperatures and time are carefully controlled.
References
Fig. 4. X-ray diffraction patterns of the raw material and Fe 3 O4 particles synthesized by glycothermal treatment at different temperatures.
w1x S. Hirano, Am. Ceram. Soc. Bull. 66 Ž9. Ž1987. 1342. w2x W.J. Dawson, Am. Ceram. Soc. Bull. 67 Ž10. Ž1989. 1673. w3x S. Komarneni, R. Roy, E. Breval, M. Ouinen, Y. Suma, Adv. Ceram. Mat. 1 Ž1. Ž1986. 87. w4x K. Haberko, W. Pyda, Advances in Ceramics, in: N. Claussen, et al. ŽEds.., Vol. 12, Science and Technology of Zirconia II, Am. Ceram. Soc., 1984, 774-83. w5x M. Rozman, M. Drofenik, D. Kolar, Euro-Ceramics 5 Ž1995. 47. w6x S. Komarneni, E. Freagan, E. Bravel, R. Roy, J. Am. Ceram. Sci. 71 Ž1. Ž1988. C26. w7x S.B. Cho et al., in: J.H. Adair, J.A. Casey, C.A. Randall ŽEds.., Sci. Tech. and App. of Colloid. Susp., Sridhar Venigalla, 1995, pp. 139–150.
Materials Letters 37 Ž1998. 255–258
Synthesis of ultrafine Fe 3 O4 powder by glycothermal process Dong-Sik Bae
a,)
, Kyong-Sop Han a , Seung-Beom Cho c , Sang-Heul Choi
b
a
b
DiÕ. of Ceramics, Korea Institute of Sci. and Tech., Seoul 136-791, South Korea Dept. of Inorg. Mater. Engineering, Hanyang UniÕersity, Seoul 133-791, South Korea c DiÕision of Materials Research Center, Rutgers UniÕersity, NJ, USA Received 10 February 1998; revised 30 March 1998; accepted 20 April 1998
Abstract Magnetite, Fe 3 O4 , powder was prepared under glycothermal conditions by precipitation from metal nitrates with aqueous ammonium hydroxide. Fine powders were obtained in the temperature range 190 to 2708. The powders were characterized by SEM, BET and XRD. Properties of the Fe 3 O4 powder were studied as a function of reaction temperature. The average particle size and specific surface areas of the synthesized Fe 3 O4 powder increased and decreased, respectively, with increasing reaction temperature. After glycothermal treatment at 2308 for 8 h, the average particle size of the Fe 3 O4 powder was about 70 nm and the particle size distribution was narrow. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Fe 3 O4 ; Ultrafine; Glycothermal process; 1,4-butanediol; NH 4 OH; Magnetite
1. Introduction Recently, there has been an increasing interest in the synthesis of monodispersed metal oxides. Solution synthesis techniques have the potential to meet the increasing demand for the direct preparation of crystalline ceramic powders and offer a low-temperature alternative to conventional powder synthesis techniques in the production of anhydrous oxide powders w1x. Solution synthesis techniques can produce fine, high-purity, stoichiometric particles of single and multi-component metal oxides. Furthermore, if process conditions such as solute concentration, reaction temperature, reaction time and the type of solvent are carefully controlled, ceramic particles of the desired shape and size can be produced w2x.
)
Corresponding author.
Hydrothermal synthesis meets the increasing demand for the direct preparation of crystalline ceramic powders and offers a low temperature alternative to conventional powder synthesis technique in the production of anhydrous oxide powders. Hydrothermal synthesis is considered today a promising way to obtain high-quality ceramic powders. Compared to conventional processing techniques, hydrothermal method has many advantages: Ž1. A crystalline product can be obtained directly at lower reaction temperature. Hence the calcining process, which results in a transformation from the amorphous phase to the crystal phase, can be avoided. It favors a decrease in an agglomeration between particles. Ž2. From a change in hydrothermal conditions Žsuch as temperature, pH, reactant concentration and molar ratio, additive, etc.., crystalline products with different composition, structure, and morphology could be formed. Ž3. The purity of product prepared in appro-
00167-577Xr98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 9 8 . 0 0 1 0 1 - 3
256
D.-S. Bae et al.r Materials Letters 37 (1998) 255–258
priate conditions could be high owing to recrystallization in hydrothermal solution. Ž4. The equipment and processing required are simpler, and the control of reaction conditions is easier, etc. This technique can produce fine, high purity, stoichiometric particles of single and multi-component metal oxides w3x. Some precipitated hydroxides subjected to prolonged boiling under atmospheric pressure in their mother liquor or hydrothermally treated under enhanced pressure at elevated temperatures transform to finegrained oxides of narrow particle size distribution. It has been demonstrated that such powders are composed of much softer agglomerates and sinter much better than those prepared by calcination decomposition of the same oxides w4x. These powders could be sintered at low temperature without calcination and milling steps w5,6x. Furthermore, if the process conditions such as solution pH, solute concentration, reaction temperature, reaction time, seed materials, and the type of solvent are carefully controlled, ceramic particles of the desired shape and size can be produced w7x. The objective of this study was to prepare ultrafine Fe 3 O4 using NH 4 OH under mild hydrothermal conditions.
2. Experimental procedure The process for preparing Fe 3 O4 by glycothermal treatment in 1,4-butanediol solution is schematically illustrated in Fig. 1. Fe 3 O4 precursors were precipitated from 1 M FeŽNO 3 . 3 9H 2 O solution by slowly adding 1 M NH 4OH solution with rapid stirring. The precipitated Fe 3 O4 precursors were washed by repeated cycles of centrifugation and redispersion in deionized water. Washing was performed for a minimum of five times each in deionized water and methanol. Excess solution was decanted after the final washing and the wet precursor was redispersed in 250 ml 1,4-butanediol under vigorous stirring. The resulting suspension was placed in a 1000 ml stainless steel pressure vessel. The vessel was then heated to the desired temperature at a rate of 108rmin. During heating, the autogenous pressure gradually increased to 1 MPa and was usually maintained below 3.5 MPa during the holding period. The reaction products were washed at least five times by repeated cycles of centrifugation and redispersion in
Fig. 1. Procedure for the preparation of the Fe 3 O4 powders in 1,4-butanediol solution.
methanol. The recovered powders were analyzed for phase composition using X-ray diffraction ŽPhillips, PW 1825r00. over the 2 theta range from 10–708 at rate of 2.58rmin. The morphology of the synthesized particles was observed using scanning electron microscopy ŽSEM, Hitachi S-4200.. The specific surface areas were calculated by the BET method ŽMicromeretics ASAP 2000..
3. Results and discussion The precipitated powder of the FeŽNO 3 . 3 P 9H 2 O was prepared with NH 4 OH 1 M solution ŽpH s 11.80. was added. The reaction temperature was found to have an effect on the size of Fe 3 O4 particles synthesized in 1,4-butanediol solution. Fig. 2
D.-S. Bae et al.r Materials Letters 37 (1998) 255–258
257
Fig. 2. SEM micrographs of the Fe 3 O4 particles synthesized by glycothermal treatment at reaction temperatures of Ža. 2108C, Žb. 2308C, Žc. 2508C and Žd. 2708C for 8 h.
shows the scanning electron micrographs of the synthesized Fe 3 O4 in the temperature range of 210 to 3008C. Glycothermal synthesis of the Fe 3 O4 from nitrates in NH 4 OH led to nearly spherical and ultrafine particles which were on the order of 50 to 150 nm in size. The reaction temperature affected the size and shape of the Fe 3 O4 particles synthesized in 1,4-butanediol solution. The temperature had a great effect on the grain size of the products and the agglomeration among grains. Lowering temperature yielded smaller grains but agglomeration among grains increased. Increasing reaction temperature changed the size of the Fe 3 O4 particles, as expected.
Specific surface areas of the synthesized Fe 3 O4 powder decreased with increasing reaction temperature ŽFig. 3.. After glycothermal treatment at 230, 250, 2708 for 8 h, BET surface areas of the Fe 3 O4 powders were 42.6 m2rg, 39.83 m2rg, 35.35 m2rg, respectively. A typical XRD pattern of Fe 3 O4 particles synthesized in 1,4-butanediol solution is given in Fig. 4. The sharp diffraction peaks are consistent with the well defined and crystallized particles shown, Fig. 2. The transformation of precursor to Fe 3 O4 in 1,4butanediol did occur in the range of 190 to 2708C and 1 to 3.0 MPa.
258
D.-S. Bae et al.r Materials Letters 37 (1998) 255–258
4. Conclusions
Fig. 3. BET surface areas of the Fe 3 O4 powder vs. glycothermal treatment temperatures.
Ultrafine, nearly spherical, and high purity Fe 3 O4 powder could be prepared by neutralizing the nitrate solutions in NH 4 OH and by glycothermal treatment under mild hydrothermal conditions. After glycothermal treatment at 2308 for 8 h, the average particle diameter of the Fe 3 O4 was about 70 nm. The average particle diameter of the Fe 3 O4 increased with increasing reaction temperature and time. The specific surface areas of the synthesized Fe 3 O4 powders decreased with increasing reaction temperature. The results of this study show that it is possible to control the size of the Fe 3 O4 powders by glycothermal synthesis in 1,4-butanediol solution, if the synthesis conditions such as reaction temperatures and time are carefully controlled.
References
Fig. 4. X-ray diffraction patterns of the raw material and Fe 3 O4 particles synthesized by glycothermal treatment at different temperatures.
w1x S. Hirano, Am. Ceram. Soc. Bull. 66 Ž9. Ž1987. 1342. w2x W.J. Dawson, Am. Ceram. Soc. Bull. 67 Ž10. Ž1989. 1673. w3x S. Komarneni, R. Roy, E. Breval, M. Ouinen, Y. Suma, Adv. Ceram. Mat. 1 Ž1. Ž1986. 87. w4x K. Haberko, W. Pyda, Advances in Ceramics, in: N. Claussen, et al. ŽEds.., Vol. 12, Science and Technology of Zirconia II, Am. Ceram. Soc., 1984, 774-83. w5x M. Rozman, M. Drofenik, D. Kolar, Euro-Ceramics 5 Ž1995. 47. w6x S. Komarneni, E. Freagan, E. Bravel, R. Roy, J. Am. Ceram. Sci. 71 Ž1. Ž1988. C26. w7x S.B. Cho et al., in: J.H. Adair, J.A. Casey, C.A. Randall ŽEds.., Sci. Tech. and App. of Colloid. Susp., Sridhar Venigalla, 1995, pp. 139–150.