Ni-Zn FERRITE NANOPARTICLES PREPARED BY COMBUSTION REACTION Ana Cristina F. M. Costaa, Edner Tortellab, Márcio R. Morellib, Ruth H. A . G. Kiminamib a
Federal University of Paraíba, Department of Materials Engineering, 58970-000 Campina Grande PB, Brazil a e-mail:
[email protected] b Federal University of São Carlos, Department of Materials Engineering, 13565-905 São Carlos SP, Brazil b e-mail:
[email protected] Key words: Nanoparticles, combustion reaction; Ni-Zn ferrite Abstract The combustion reaction is an important powder preparation process by which several hundred compounds may be prepared. Ni-Zn ferrite nanoparticles (Ni1-xZnx Fe2O4, x = 0,3; 0,5 and 0,7 mol) have been prepared by a single step solution combustion reaction using nitrates and urea as fuel. XRD, BET, SEM, and helium pycnometer characterized the as-prepared powders. Ni-Zn ferrite nanoparticles prepared by the present method can easily form the well-crystallized particles with a large surface area in the range of 42-64 m2/g. The resulting powders showed extensive XRD line broadening and the crystallite sizes calculated from the XRD line broadening were in the nanometer range (19-25 nm). The results evidenced the influence of different compositional variables on the powders characteristic. Introduction Homogeneous, highly crystalline nanophased powders are needed for the materials with a wide range of technical applications. The conventional methods for the preparation of powder materials involve some soft chemical processes such as sol-gel and precipitation methods, and the solid state reaction of finely ground powders that are heated at temperatures above at least 1000oC for up to several days [1]. The combustion reaction has been introduced in some literature to speed up the synthesis of complex materials. This method has been successfully employed to obtain several materials, such as nanoparticles of TiB2 [2], La2CuO4 e La1.8Sr0.2CuO4 [3], Mg-Zn ferrites [4], Li-Zn ferrites [5], barium hexaferrite [6], ceria-zirconia solid solutions [7], LaMnO3-LaCoO3 solid solutions [8], materials of the NZP structural type [9], alumina titanate [10], ZnO [11] and others. The synthesis of Ni-Zn ferrite powders using combustion reactions, which provides good compositional control, is an alternative worth pursuing. Like the various other methods that have been proposed and used to prepare ceramic powders, the combustion synthesis route enables synthesis at low temperatures and the products obtained are in a finely divided state with large surface areas. Unlike the former, combustion synthesis offers such added advantages as the simplicity of experimental set-up, the surprisingly short time between the preparation of the reactants and the availability of the final product, savings in external energy consumption and the equally important potential of simplifying the processing prior to forming, providing a simple alternative to other elaborate techniques [1218]. This work report the prepared of Ni-Zn ferrite nanoparticles (Ni1-xZnx Fe2O4, x = 0,3; 0,5 and 0,7 mol) by a single step solution combustion reaction using nitrates and urea as fuel.
Experimental Fine particle oxides of Ni-Zn ferrite with nominal composition Ni1-xZnxFe2O4 with x= 0,3; 0,5 and 0,7% mol were prepared for combustion reaction used urea as fuel. The composition were named C03, C05 e C07, respectively. The materials used were iron nitrate -Fe(NO3)3.9H2O (Merck), zinc nitrate –Zn(NO3)2.6H2O (Merck), nickel nitrate –Ni(NO3)2.6H2O (Merck) and urea – CO(NH2)2 (Synth). Stoichiometric compositions of metal nitrate and urea were calculated using the total oxidizing and reducing valencies of the components which serve as the numerical coefficients for the stoichiometric balance so that the equivalence ratio Φc is unity and the energy released is maximum [19]. Using the concepts in propellant chemistry [19] the elements Ni, Zn, Fe, C, and H are considered as reducing elements with the corresponding valencies +2, +2, +3, +4 and +1, respectively. The element oxygen is considered as oxidizing element with the valency –2. The valency of nitrogen is considered to be zero. Accordingly the oxidizing and reducing valencies of the compounds used in the combustion mixtures can be calculated. The batches were placed in a vitreous silica basin, homogenized and directly heated up in the hot plate to temperature around 480oC until the ignition took place, producing a Ni-Zn ferrite in foam form. The reaction products obtained were ground for 4 hour in attritor mill (Szegvari Attritor System, type: 01STD, Union Process). All powders were characterized by X-ray diffraction (Cukα/Ni Kristaloflex D5000 diffractometer, with a scanning rate of 2o 2θ /min, in a 2θ range of 20-60o); The average crystallite sizes calculated from X ray line broadening (d311) using Scherrer’s formula [20]; Sedimentation (HORIBA –Particle Size Distribution Analyzer, CAPA –700 U.S. version) apparatus, the BET specific surface area and the average particle size were determined in N2/He with a Quantasorb Quantachrome (model Gemini -2370 Micromeritics) apparatus, density using a helium pyknometer (Pyknometer Micromeritics, ACCUPYC 1330) and scanning electron microscopy (Carl Zeiss 940A and Philips XL30 FEG, after Au coating). The lattice parameters were calculated from the X-ray diffraction patterns using the Rietveld method. The ignition temperature was determined by an infrared pyrometer (Raytek, model MA2SC) and ignition flame time was measured with digital chronometer (CONDOR). Results and Discussion The ignition flame time and temperature of the synthesis by combustion reaction exerts an important effect on the final characteristics of powders. These parameters depend, mainly of the intrinsic characteristics of each system. The results of this study indicated that the reduction in the Zn2+ concentration better the characteristics of the powders. Table 1 shows the characteristics of the powders (specific surface area, particle size, crystallite size, powders density and lattice parameters) prepared by combustion reaction for each system C03, C05 and C07. The specific surface area (BET) and the nanoparticle size calculated from BET for powders C03, C05 and C07 were 64, 44 e 42 m2/g and 18, 26 e 27 nm, respectively. The surface area values reduction with the increase of the Zn2+concentration. This results can be attributed, mainly, the ignition flame time and temperature of reaction. The values experimental measure were 623, 703, 749oC and 26, 12, 17 sec for the systems C03, C05 and C07, respectively. This show that the compositional changed of the system by the increase of Zn2+ concentration led the high temperature and smaller ignition time, promoted, this way, the pre-sintering and/or growth of particles. It can also be observed in the Table 1 that the density for the three powders were 94,2; 95,7 e 96,9% of theoretical density. The results of density shows that the powder of system C03 is smaller dense when compared the powders of systems C05 and C07, possibly due to smaller temperature of phase crystallization (ignition temperature).
Table 1 – Powder characteristics of systems Ni1-xZnxFe2O4 with x = 0,3; 0,5 e 0,7% in mol prepared by combustion reaction. Composition
C03 Ni0,7Zn0,3Fe2O4
C05 Ni0,5Zn0,5Fe2O4
C07 Ni0,3Zn0,7Fe2O4
64
44
42
18
26
27
19
24
25
5,03 (95,7)
5,09 (96,9)
Specific superficial area (BET) [m2/g] Particle size* [nm] Crystallite size** [nm] Powder density [g/cm3]
4,95 (94,2)
o
8,359
Lattice parameters (a) [ A ] a=b=c=8,399
8,381
8,400
*Calculated from specific superficial area **Calculated from Scherrer’s formula
The Fig. 1 shows the variation of the ignition flame time and temperature versus Zn2+ concentration in the system Ni1-xZnxFe2O4. The increase in the temperature and reduction in the ignition time observed with the rise of the Zn2+concentration, it can be attributed to the smallest formation heat of the zinc nitrate (∆Hfo = -551,30 kcal/mol) compared with the formation heat of the nickel nitrate (∆Hfo = -528,60 kcal/mol). Besides, the ignition flame time and temperature of the reaction are primarily certain for the phase transition that is an intrinsic characteristic of each system and it varies of material for material [21].
o
Ignition Flame Temperature ( C)
740
Temperature Time
720
25
700 20
680 660
15
640 620 0,3
0,4
0,5
0,6
0,7
Ignition Flame Time (sec)
30
760
10
2+
Zn Concentration (mol)
Figure 1. Ignition flame time and temperature versus Zn2+concentration. Fig. 2 illustrates the morphological appearance of the reaction products (foams) resulting from the combustion reaction for the systems C03, C05 e C07. The micrographs show that the appearance of foams not presented signification morphological changed. The resulting foam of the system C07 showed a denser nature slightly, less porous with a larger state of aggregation of the particles. This is in agreement with the temperature of ignition of the reactions that were larger.
Experimental was observed that the foams obtained during the combustion reaction are formed soft agglomerates (friable), because they are easily desagglomerated.
(a)
(b)
(c)
Figure 2 – Micrograph obtained by SEM showed the morphological of foams prepared by combustion reaction for system (a) C03, (b) C05 e (c) C07.
Intensity (a.u.)
F
F
F - (Ni,Zn)Fe2O4 H - α Fe2O3 F
F F
H H
20
30
F F
F
F F
F
F H
F H
H
F H
F
40 2θ (degrees)
50
F
C03
C05 C07 60
Figure 3 – X-ray diffractogram patterns of powders as-prepared by combustion reaction for the system Ni1-xZnxFe2O4 with x = 0,3; 0,5 e 0,7%. Fig. 3 shows the diffractograms of the powders for the systems C03, C05 e C07. The X-ray diffraction patterns of powders of the systems C05 e C07 revealed the phase cubic spinel Ni-Zn ferrite as major phase and a small amount of hematite (αFe2O3) as secondary phase. However, the powder of the system C03 showed single-phase cubic spinel Ni-Zn ferrite. These results show to strong influence of the own system on the ignition flame time and temperature of the reaction. The system C03 presented smaller ignition temperature (623oC) when compared with the values to temperature obtained for the systems C05 and C07 that were 703 and 749oC, respectively. However, the largest ignition flame time reached in the system C03 during the reaction it contributed strongly to the complete formation of the crystalline phase Ni-Zn ferrite, without presence of the hematite phase. The values of the lattice parameter, “a”, of the powders for the o
systems C03, C05 e C07 obtained for reaction combustion were 8,359; 8,381 e 8,400 A , respectively. It was observed the lattice parameter increase with the rise in the Zn2+ concentration.
The same behavior was report by Verma et. al. [22] for growing concentrations of Zn2+ (0,2; 0,4; 0,5 and 0,8% mol). The X-ray lines show considerable broadening, indicating the fine particles nature of the system Ni1-xZnxFe2O4. Compared the line broadening of the powder for the system C03 with the line broadening of the systems C05 e C07 is possible observed the finest characteristic of the particles. The average crystallite sizes calculated from X-ray line broadening to (d311) using Scherrer’s formula [20] was 19, 24 e 25 nm for the powders of the systems C03, C05 e C07, respectively. These results are in agreement with the results starting calculated from the specific surface area (BET), as presented in the Table 1.
(a)
(b)
(c) Figure 4 - Micrographs obtained by SEM showing the morphology of the powders prepared by the combustion reaction. (a) C03, (b) C05 e (c) C07. Fig. 4 presented the morphology of the resulting powders C03, C05 and C07 prepared by combustion reaction. The micrograph reveals the tendency the agglomerate of the nanoparticles, increasing the gathering state increasing the agglomeration state with the increase of the Zn2+ concentration. The increase in the Zn2+ concentration resulted in a larger ignition temperature, what favored the rise in the aggregation of the particles, committing, in this way, the characteristics of the powders. For the powders C05 and C07 (Fig. 3b and c) it was also observed presintering of some particles. This happened due to larger ignition temperature reached in these reactions that were 703oC and 749oC to the systems C05 and C07, respectively. For the resulting powder of the system C07 (Fig. 3a), which presented ignition temperature at 623oC was observed a reduction in the state of agglomeration of the nanoparticles.
Conclusions The synthesis for combustion reaction is a favorable process for obtains of crystalline powders with nanoparticles (19-25 nm) Ni-Zn ferrite. The reduction in the Zn2+ concentration led a smaller temperature and a larger time of ignition, increasing the specific surface area. The increase of the ignition time strongly contributed to formation of the crystalline Ni-Zn ferrite phase, without presence of the hematite phase in the system C03. The X-ray lines broadening confirmed the nature of the nanoparticles of the powders obtained by combustion reaction, which were at 19, 24 and 25 nm for the powders of the system Ni1-xZnxFe2O4 with x = 0,3; 0,5 and 0,7 mol, respectively. Acknowledgements The authors would like to thank the Brazilian institutions, CAPES and CNPq for financial support. References 1. C. H. Yan, Z. G. Xu, F. X. Cheng, Z. M. Wang, L. D. Sun, C. S. Liao, J. T. Jia, Solid State Comm. 111 (1999), p. 287-291. 2. R. L. Axelbaum, S. E. Bates, W. E. Buhro, C. Frey, K. F. Kelton, S. A. Lawton, L. J. Rosen and S. M. Sastry, NanoStruct. Mater. 2 (1993), p. 139-147. 3. S. Sundar Manoharan, V. Prasad, S. V. Subramanyam and K. C. Patil, Physica C 190 (1992), p. 225-228. 4. K. Suresh, K. C. Patil, J. Mater. Sci. Lett. 13 (1994), p. 1712-1714. 5. K. Suresh, K. C. Patil, J. Mater. Sci. Lett. 14 (1995), p. 1074-1077. 6. S. Castro, M. Gayoso, J. Rivas, J. M; Greneche, J. Mira, C. Rodríguez, J. Mag. Mag. Mater. 152 (1996), p. 61-69. 7. S. T. Aruna and K. C. Patil, NanoStruct. Mater. 10 [6] (1998), p. 955-964. 8. S. T. Aruna, M. Muthuraman, K. C. Patil, Mater. Res. Bull. 35 (2000), p. 289-296. 9. E. Breval and D. K. Agraval, J. Am. Ceram. Soc. 81 (1998), p. 1729. 10. A. M. Segadães, M. R. Morelli and R. H. G. A. Kiminami, Sixt Inter. Conf. Sci. Hard Mat., 1 (1998), p. 59. 11. V. C. Sousa, A. M. Segadães, M. R. Morelli, R. H. G. A. Kiminami, Inter. J. Inorg. Mater. 1 (1999), p. 235-241. 12. M. M. A. Sekar, K. C. Patil, J. Mater Chem. 2 [7] (1992), p. 739-743. 13. D. A. Fumo, M. R. Morelli, A. M. Segadães, Mater. Res. Bull. 31 [10] (1996), p. 12431255. 14. D. A. Fumo, J. R. Jurado, A. M. Segadães, J. R. Frade, Mater. Res. Bull. 32 [10] (1997), p. 1459-1470. 15. A. M. Segadães, M. R. Morelli, R. G. A. Kiminami, J. Eur. Ceram. Soc. 18 [7] (1998), p. 771-781. 16. C. S. Hong, P. Ravindranathan, D. K. Agrawal, R. Roy, J. Mater. Sci. Lett. 12 (1994), p. 1072-1075. 17. P. Ravindranathan, S. Komarneni, R. Roy, J. Mater. Sci. Lett. 12 (1993), p. 369-371. 18. A. Dhas, K. C. Patil, Ceramic. Int. 20 (1994), p. 57-66. 19. S. R. Jain, K. C. Adiga, V. Pai Verneker, Combust. Flame 40 (1981), p. 71 – 79. 20. H. Klung, and L. Alexander, in “X ray diffraction procedures”, Wiley, New York, EUA, (1962), p. 491ff. 21. Y. Zhang and G. C. Stangle, J. Mater. Res. 9 [8] (1994), p. 1997-2004. 22. A. Verma, T. C. Goel, R. G. Mendiratta, P. Kishan, J. Mag. Mag. Mater. 208 (2000), p. 1319.
