Production of ferrite nanopowders in radiofrequency thermal plasma

Production of ferrite nanopowders in radiofrequency thermal plasma PhD Theses Loránd Gál Budapest, 2008 HAS Chemical Research Center Institute of Materials and Environmental Chemistry Department of Plasma Chemistry University of Pannonia Doctoral School in Molecular- and Nanotechnology Supervisor: Prof. Dr. János Szépvölgyi

Introduction, aims Large-scale production of ferrites started in the middle of the last century in semiconductor industry. As a result of the extensive research and development work in this area large variety of ferrites of various chemical compositions have been produced. Main goals of the developments of ferrite powders and production methods are to explore new scopes, to improve the production in terms of economy and efficiency and to decrease the environmental impact of ferrite production. The main trends of the development are as follows: - considerable decreasing the time duration of technological processes, - preparation of metastable inverse spinels in single technological step, - production of ultrafine ferrite powders for ceramics with special features, - development of clean technology for reducing environmental impact. Radiofrequency inductively coupled thermal plasma systems are getting more popular in the material science and technology. The high operation temperature prevailing, the robust working process, the attainable material purity can be very useful in technological point of view. The PhD Thesis aims at studying the synthesis of nanosized ferrite powders in a radiofrequency thermal plasma reactor. As reference I also studied the production of ferrites from oxide mixtures by sintering. The reaction products have been characterised in a complex way for morphology, chemical composition, phase and magnetic properties.

Major results 1. Production of zinc ferrite and nickel-zinc ferrites by high temperature annealing Zinc ferrite and nickel-zinc ferrites have prepared from oxide mixtures in air, at 900 C, by annealing for 6 hours. Formation of spinel ferrites was observed in all cases. The products were paramagnetic zinc ferrites with normal spinel structure and ferrimagnetic nickel-zinc ferrites, respectively. In particular conditions the spinel content of the product depended on the grain size of precursors. Results refer to the important role of diffusion processes in spinel formation. 2. Production of zinc ferrite from oxide mixture in radiofrequency thermal plasma reactor Zinc ferrite has prepared from the mixtures of ZnO and Fe 2 O 3 in RF thermal plasma. Composition of zinc ferrites corresponded to the starting Zn:Fe ratio. Their mean particle size varied from 72 to 349 nm, while the zinc ferrite content changed from 59 to 94%. In addition to zinc ferrite spinels magnetite also formed. The total spinel content was in the range of 76-97%. Magnetic properties of zinc ferrite referred to formation of inverse spinel structure. 3. Production of zinc ferrite from metal nitrates in radiofrequency thermal plasma reactor Zinc ferrite has prepared from ethanol solutions of Zn(NO 3 ) 2 6H 2 O and Fe(NO 3 ) 3 9H 2 O in RF thermal plasma. Composition of zinc ferrites corresponded to the starting Zn:Fe ratio. Their mean particle size varied from 119 to 1000 nm, while the zinc ferrite content changed from 50 to 94%. In addition to zinc ferrite, magnetite, ZnO and -Fe 2 O 3 also formed. The total spinel content of ferrite powders varied in the range of 92-99%. In the nitrate case, the products contained more magnetite and less zinc ferrite as compared to the oxide case. It is explained by lower zinc- and iron content in the gas phase for the nitrate case. It favours formation of thermodynamically more stable magnetite on the one hand, and increases the probability of inverse-to-normal transformation of zinc ferrite spinels on the other. Decrease of the concentrations of precursor solutions resulted in smaller particle size and even smaller crystallite size of zinc ferrite, too. The same effect was observed with increased residence in the plasma reactor. In addition, the zinc ferrite content of the product also increased with the residence time. It refers to the incorporation of zinc oxide into spinel structure formed previously. In the oxide case, the reaction products had smaller mean particle sizes, and they exhibited higher saturation magnetisation and thus, they were more ferrimagnetic than products in the nitrate case. However, the conversion of precursors to ferrites was more complete in the nitrate case.

4. Production of nickel-zinc ferrites from oxide mixture in radiofrequency thermal plasma reactor Nickel-zinc ferrites with different compositions were prepared from mixtures of NiO, ZnO and Fe 2 O 3 in RF thermal plasma. Composition of zinc ferrites corresponded to the starting Zn:Fe ratio. Their mean particle size varied from 76 to 998 nm. The main reaction product was nickel-zinc ferrite with minor amounts of ZnO and -Fe 2 O 3. The nickel-zinc ferrite spinel content varied between 95 and 99%. Measurements of magnetic properties confirmed formation of ferrimagnetic spinels. 5. Production of nickel-zinc ferrite from metal nitrates in radiofrequency thermal plasma reactor Nickel-zinc ferrites with different compositions were prepared from solutions of Ni(NO 3 ) 2 6H 2 O, Zn(NO 3 ) 2 6H 2 O and Fe(NO 3 ) 3 9H 2 O in RF thermal plasma. Composition of zinc ferrites corresponded to the starting Ni:Zn:Fe ratio. Their mean particle size varied from 96 to 281 nm. The main reaction product was nickel-zinc ferrite with minor amount of -Fe 2 O 3. The nickel-zinc ferrite spinel content varied between 99 and 100%, i.e. actually pure spinels have been formed. The saturation magnetisation of the products increased with the nickel content. Increase of the specific energy of ferrite synthesis led to ferrites of smaller particle size and of higher the saturation magnetisation. This finding is explained by the changes in heat- and mass transfer phenomena and to more intensive homogenous nucleation, as well. Correlations were found amongst the feed rate of precursors, the product yield and the morphology: the yield and the particle size increased with the feed rate. The magnetic properties of nickel-zinc ferrites produced in RF thermal plasma changed on annealing. When the reaction products were annealed in air, at 1000 C, for 1 hour, their saturation magnetisation increased by 30% referring to increased ferrimagnetic character. On further annealing, the saturation magnetisation did not change. Particle size of the products formed from oxide mixtures was smaller than that of products prepared from nitrate solutions. However, conversion of precursors to ferrites was more complete in the nitrate case. 6. Correlation between morphology and composition of ferrites Correlations were found between iron content and particle size of ferrites produced in RF thermal plasma. Particles having diameter smaller than 60 nm, contains less than stoichiometric iron, whereas the larger ones contains more than stoichiometric iron. It is explained by thermodynamic and technological reasons (heat transfer, mean residence time), as well.

7. Synthesis of nanosized zinc ferrite in thermal plasma A procedure have been developed to produce nanosized zinc ferrite powders with both normal and inverse spinel content in a single technological step in RF thermal plasma reactor. The mean particle size of reaction product was 26 nm, while its surface area was 40 m 2 g -1. 8. Results of experiments on synthesis of a novel material It has demonstrated that zinc ferrite with purity of 76%, -Fe 2 O 3 with purity of 95% and NiFe 2 O 4 with purity of 99% could be alike produced in RF thermal plasma in a single technological step.

Publications Papers: Gál L., Mohai I., Szépvölgyi J.: Cinkferritek elállítása rádiófrekvenciás termikus plazmában. Építanyag 58 (3) (2006) 66-70. Mohai, L. Gál, J. Szépvölgyi, J. Gubicza, Zs. Farkas: Synthesis of nanosized zinc ferrites from liquid precursors in RF thermal plasma reactor. Journal of the European Ceramic Society 27 (2007) 941-945 J. Szépvölgyi, I. Mohai, Z. Károly, L. Gál: Synthesis of nanosized ceramic powders in a radiofrequency thermal plasma reactor. Journal of the European Ceramic Society 28 (2008) 895-899 T. Feczkó, A. Muskotál, L. Gál, J. Szépvölgyi, A. Sebestyén, F. Vonderviszt: Synthesis of Ni Zn ferrite nanoparticles in radiofrequency thermal plasma reactor and their use for purification of histidine-tagged proteins. Journal of Nanoparticle Research DOI 10.1007/s11051-008-9429-5 Conference proceedings: L. Gál, I. Mohai, Z. Károly, J. Szépvölgyi: Synthesis of Nanosized Zinc Ferrites in RF Thermal Plasma reactor. 17 th International Symposium on Plasma Chemistry, Toronto, Canada, 7-12 August, 2005 ID738 1-6. J. Szépvölgyi, I. Mohai, L. Gál, I. Mészáros, J. Gubicza: Synthesis of Nickel-Zinc Ferrites in RF Thermal Plasma Reactor. 10th International Conference and Exhibition of the European Ceramic Society June 17-21, 2007, Berlin L. Gál, I. Mohai, I. Mészáros, J. Gubicza, J. Szépvölgyi: Synthesis of Zinc Ferrites in RF Thermal Plasma Reactor. 10th International Conference and Exhibition of the European Ceramic Society June 17-21, 2007, Berlin J. Szépvölgyi, L. Gál, I. Mohai, I. Mészáros, J. Gubicza: Synthesis of Spinel Ferrites in Radiofrequency Thermal Plasma Reactor. 18 th International Symposium on Plasma Chemistry, Kyoto, Japan, 26-31 August, 2007.

Presentations: J. Szépvölgyi, L. Gál, I. Mohai, Z. Károly, J. Gubicza: Synthesis of Nanosized Zinc Ferrites in RF Thermal Plasma Reactor. HUNS-2005 (MANS-2005) is a national Mobilization Workshop organized within the framework of EU FP6 NENAMAT project (EU FP6 INCO-CT-2003-510363) 21-22 March, 2005. Budapest, Hungary Gál L., Mohai I., Károly Z., Szépvölgyi J., Gubicza J.: Nanoszemcsés cinkferrit plazmakémiai szintézisének optimalizálása. V. Országos Anyagtudományi, Anyagvizsgálati és Anyaginformatikai Konferencia és Kiállítás, Balatonfüred, 2005. október 9-11. J. Szépvölgyi, I. Mohai, L. Gál, I. Mészáros, J. Gubicza: Synthesis of Nickel-Zinc Ferrites in RF Thermal Plasma Reactor. 10th International Conference and Exhibition of the European Ceramic Society June 17-21, 2007, Berlin L. Gál, I. Mohai, J. Szépvölgyi: Synthesis of Ferrites in Radiofrequency Thermal Plasma Reactor. "The Seventh Students' Meeting", SM-2007 PROCESSING AND APPLICATION OF CERAMICS December 6-8, 2007, Novi Sad, Serbia Poster presentations: L. Gál, I. Mohai, J. Szépvölgyi, J. Gubicza, Zs. Farkas: Synthesis of Nanosized Zinc Ferrites in RF Thermal Plasma reactor. IX Conference & Exhibition of the European Ceramic Society, 19-23 June, 2005, Portorož, Slovenia L. Gál, I. Mohai, Z. Károly, J. Gubicza, J. Szépvölgyi: Synthesis of Nanosized Zinc Ferrites in RF Thermal Plasma reactor. 17 th International Symposium on Plasma Chemistry, Toronto, Canada, 7-12 August, 2005 L. Gál, I. Mohai, I. Mészáros, J. Gubicza, J. Szépvölgyi: Synthesis of Zinc Ferrites in RF Thermal Plasma Reactor. 10th International Conference and Exhibition of the European Ceramic Society June 17-21, 2007, Berlin Muskotál, A., Gál, L., Feczkó, T., Szépvölgyi, J., Vonderviszt, F.: Application of magnetic particles synthesized by thermal plasma for protein purification. Regional Biophysics Conference, Balatonfüred, 21-25 August 2007 J. Szépvölgyi, L. Gál, I. Mohai, I. Mészáros, J. Gubicza: Synthesis of Spinel Ferrites in Radiofrequency Thermal Plasma Reactor. 18 th International Symposium on Plasma Chemistry, Kyoto, Japan, 26-31 August, 2007.

Other papers: B. Todorovic-Markovic, Z. Markovic, I. Mohai, Z. Karoly, L. Gál, K. Fglein, P.T. Szabó and J. Szépvölgyi: Efficient synthesis of fullerenes in RF thermal plasma reactor. Chem. Phys. Letters 378 (2003) 434-439 imp.f. (2003) 2,438 Z. Markovic, B. Todorovic-Markovic, M. Kuzmanovic, I. Mohai, Z. Károly, L. Gál, A.K. Fglein, P.T. Szabó, J. Szépvölgyi: Efikasna sinteza fulerena u RF termalnom plazma reakturu. Novi Materijali 12 (3) (2003) 7-10. M. Bystrzejewski, A. Huczko, H. Lange, Z. Karoly, L. Gal: RF plasma synthesis of carbon encapsulates. Polish Journal of Applied Chemistry XLIX, no. 1 2, 23 31 (2005) Other conference proceedings: Z. Károly, J. Szépvölgyi, L. Gál, I. Mohai: Processing of silica nanopowders in RF thermal plasma reactor. 16 th International Symposium on Plasma Chemistry, Taormina, Italy, 22-27 June, 2003 229.1-229.4. I. Mohai, J. Szépvölgyi, Z. Károly, L. Gál, M. Tóth, I. Sáray: Thermal plasma vitrification of metallurgical wastes. 16 th International Symposium on Plasma Chemistry, Taormina, Italy, 22-27 June, 2003 290.1-290.6. Todorovic-Markovic B., Markovic Z., Mohai I., Károly Z., Gál L., Szépvölgyi J.: Optical Emission Spectroscopy of Induction RF Plasma in Fullerene. Processing 22-nd Summer School and International Symposium on the Physics of Ionized Gases (SPIG), ed. Hadzievski, L., Vinca Institute of Nuclear Sciences, Belgrade (2004) pp. 337-340. Z. Károly, L. Gál, J. Szépvölgyi: Effect of Synthesis Conditions on the Morphology of ZnO Powder Produced in RF Thermal Plasma. 17 th International Symposium on Plasma Chemistry, Toronto, Canada, 7-12 August, 2005 ID213. 1-6. Other presentation: Szépvölgyi J., Mohai I., Károly Z., Gál L.: RF Thermal Plasma Synthesis of Nanocrystalline Zirconia. Nanotech Northern Europe 2007. Helsinki, Finland, 2007.

Other poster presentations: Z. Károly, J. Szépvölgyi, L. Gál, I. Mohai: Processing of silica nanopowders in RF thermal plasma reactor. 16 th International Symposium on Plasma Chemistry, Taormina, Italy, 22-27 June, 2003 I. Mohai, J. Szépvölgyi, Z. Károly, L. Gál, M. Tóth, I. Sáray: Thermal plasma vitrification of metallurgical wastes. 16 th International Symposium on Plasma Chemistry, Taormina, Italy, 22-27 June, 2003 Z. Károly, L. Gál, J. Szépvölgyi: Effect of Synthesis Conditions on the Morphology of ZnO Powder Produced in RF Thermal Plasma. HUNS-2005 (MANS-2005) is a national Mobilization Workshop organized within the framework of EU FP6 NENAMAT project (EU FP6 INCO-CT-2003-510363) 21-22 March, 2005., Budapest, Hungary Z. Károly, L. Gál, J. Szépvölgyi: Effect of Synthesis Conditions on the Morphology of ZnO Powder Produced in RF Thermal Plasma. IX Conference & Exhibition of the European Ceramic Society, 19-23 June, 2005, Portorož, Slovenia Z. Károly, L. Gál, J. Szépvölgyi: Effect of Synthesis Conditions on the Morphology of ZnO Powder Produced in RF Thermal Plasma. V. Országos Anyagtudományi, Anyagvizsgálati és Anyaginformatikai Konferencia és Kiállítás, Balatonfüred, 2005. október 9-11.