ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR AN INVESTIGATION OF THE COMPOSITION OF AN IRON-RICH NICKEL-ZINC FERRITE Technical Report No. 66 Electronic Defense Group Department of Electrical Engineering By: C. F. Jefferson Approved by: ~ H. W. Welch, Project 2262 TASK ORDER NO. EDG-6 CONTRACT NO. DA-36-039 sc-63203 SIGNAL CORPS, DEPARTMENT OF THE ARMY DEPARTMENT OF ARMY PROJECT NO. 3-99-04-042 SIGNAL CORPS PROJECT 194B May, 1956

TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS iii LIST OF TABLES iv ABSTRACT v I. INTRODUCTION 1 II. PREPARATION AND MEASUREMENT OF SAMPLES 3 III. RESULTS AND DISCUSSION 4 ACKNOWLEDGMENT 15 DISTRIBUTION LIST 16 ii

LIST OF ILLUSTRATIONS Page Fig. 1 Circuit for Measurement of/ + 1 vs Temperature 5 Fig. 2 K pif + )j5 vs Temperature for Ni 474Zn.526Fe204 +.294Fe203 Fired at 10000C 9 Fig. 3 KVjif + 2 vs Temperature for Ni 474Zn 526Fe20 4 +.938Fe203 Fired at 1400~C 5 10 Fig. 4 Curie Temperature vs Initial Composition 11 Fig. 5 The Phase Diagrom for Ni.474Zn.526Fe204 - Fe203 12 Fig. 6 ( y + Y + B 1 of Equation 2 vs Temperature for 3 Com\positions./ 14i iii

LIST OF TABLES Table No. Page 1 Value of I of Equation 1 for Initial x Material Ni.474Zn.526Fe20 4 + BFe203 2 Curie Temperature of Material Having an Initial Composition of Ni.474Zn.526Fe20 4 + BFe203 7 iv

ABSTRACT The composition of the system NiaZnlaFe204 - Fe203 in equilibrium in air at one atmosphere pressure has been investigated. The composition of the spinel phase can be represented as XNiaZnl.aFe204 * YFe Fe204 ~ ZFe203 The value of X/Y, which is the solubility of magnetite in the nickel-zinc ferrite, has been found between the temperatures 700o and 1300~C. The spinel phase also contains some Fe203, which is assumed to be present as yFe203. The value of v at the boundary line between the spinel field and they^inel-hematite field has been found to be independent of the value of X. v

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN AN INVESTIGATION OF THE COMPOSITION OF AN IRON-RICH NICKEL-ZINC FERRITE I. INTRODUCTION In recent years, the preparation of ferrites for use in electrical circuits has received a considerable amount of attention. The ferrite NiaZnl-aFe2O4 is formed when NiO, ZnO and Fe203 are mixed in stoichiometric proportions and then sintered. At temperatures below about 1300~C, no ferrous iron is formed in an air atmosphere. When excess Fe203 is added, however, some of the Fe203 is converted to Fe304, forming a solid solution with NiaZnl aFe204. The conditions necessary for the formation of ferrous iron in Ni-Zn ferrites are discussed in Technical Report No. 581. This report is a continuation of work discussed in Technical Report No. 58. The purpose of this work is to determine the composition of the system NiaZnl-aFe204 - Fe203 as a function of temperature in air at one atmosphere. Technical Report No. 58 contained references to some of the past work on the system RO-Fe203, where R is a divalent cation. For the sake of completeness, these will be reviewed again, with references to additional work included. Kato and Takei2 attribute the magnetic properties of sintered ZnO and Fe203 containing a large amount of FeO23, to either the formation of Fe304 on solid solution with the ZnFeaO4 or the formation of Fe203 as a magnetic second 1. C. F. Jefferson and D. M. Grimes, "A Study of the Preparation of Nickel-Zinc Ferrites," Technical Report No. 58, Electronic Defense Group, Department of Electrical Engineering, University of Michigan, Jan. 1956. 2. Y. Kato and T. Takei, "Studies on Zinc Ferrite: Its Formation, Composition and Chemical and Magnetic Properties," Trans. Amer. Electrochemical Soc., 57, 297-312, (1930).

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN phase, depending upon the method of preparation. Kushima and Amanumal investigated the same system and concluded that while some Fe203 is converted to Fe304, the magnetic properties of the Fe203-rich material was due to Fe203 in solid solution with ZnFe204. Roberts and Merwin2 investigated the system MgO-FeO-Fe203 in air at one atmosphere. In the system FeO-Fe203, above 1386 + 5~C, the stable phase was found to be a magnetite solid solution containing excess oxygen, while below this temperature the stable phase is a hematite solid solution containing less oxygen than Fe203. The solubility of MgO in MgFe204 was found to be about 1% from 17500C to 1000~C. Berger3 investigated the same system and determined the solubility of Fe203 in zinc ferrite by measurement of the lattice constant. He found the composition of the stable phase to be 76 mole % Fe203 at 1400~C, 64 mole % at 1200~C, and about 61 mole % Fe203 at 1000~C. From density considerations he concluded that the solid solution contained lattice holes, which could be accounted for by assuming the presence of yFe203. Smolenski4 investigated the, solid solutions of (Ni 3Zn.7) Fe204-Fe203 and attempted to explain the magnetic properties on the basis of Neel's theory. He found that with increasing Fe203 content, the saturation magnetization 1. Kushima and Amanuma "On the Constitution of Zinc Ferrite," Memoirs of the Faculty of Engineering, Kyoto University, 16, 191-203, (1954). 2. H. S. Roberts and H. E. Merwin, "The System MgO-FeO-Fe O in Air at One atmosphere," American Journal of Science, 21, 145-157, (1917. 3. S. V. Berger, "Rontgenunderokningar Av Spinellfasen I System ZnO-Fe2O3," Festskrift Tellagnad J. Arvid Hedvall, 31-42, (1948). 4. A. Smolenski, "Non-Metallic Ferromagnetics-Ferrites," Izvestigy Akademii Nauk SSSR Seriya Fizicheskaya, 26, 728-738, (1952). 2

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN increased for a time and then decreased. The Curie temperature increased and the magnetic permeability decreased. The Fe203 in solid solution with Ni.3Zn.7Fe204 is given to be yFe203. The basis for this conclusion is not given. Toropov, Rabkin, Freingenfeld, and Epsteinl investigated the system NiO-ZnO-Fe203 and attempted to correlate the phase composition with the magnetic properties. They plotted a triaxial diagram of the system NiO-ZnO-Fe203 showing the area of solid solutions. The firing temperature is given as 1350-14000C. The statement is made that the effect of changing the temperature is to change the amount of Fe304 and to change the area of solid solutions. The temperature effect on the compositions is not adequately investigated. Geisler2 found that CoFe204. would dissolve Fe203 above 10000C and that it could be precipitated again by ageing at temperatures below 8000C. The compositions investigated are not given. He speculates that the first-formed Fe203 is yFe203, but, due to the similarity of structure between CoFe204 and 7Fe203, it cannot be detected by x-ray analysis. II. PREPARATION AND MEASUREMENT OF SAMPLES The procedure followed in the preparation of the samples is given in Technical Report No. 58 and will not be repeated here. Methods used to identify the composition of the sintered oxides were (1) chemical analysis, (2) microscopic examination, (3) Curie temperature measurements, and (4) X-ray analysis. 1. N. A. Toropov, L. I. Rabkin, E.ZH. Freigenfeld and B. Sh. Epstein, "The Influence of Several Technological Factors on Phase Composition and Magnetic Properties of Nickel-Zinc Ferrites," Journal of Technical Physics, Vol. 23, Issue 9, (1941). 2. A. H. Geisler, "Structure of Permanent Magnetic Alloys," Transactions of Amer. Soc. for Metals, 43, 70-99, (1951). __ —--------------------- 3

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN The procedure used to determine the amount of ferrous iron is also given in Technical Report No. 58. Microscopic examination of the material was accomplished by mounting the samples in a bakelite mount and polishing according to standard metallographic techniques. The Curie temperatures were obtained by measuring the fall-off of Al2 + (2 with temperature, where pl is the real part and (p the imaginary part of the initial permeability. This is nearly equal to 1l except in the tail of the curve. The Curie temperature is defined here as the temperature at which |/1l2 + ~22 starts to drop. The circuit diagram for the measurements is given in Fig. 1. X-ray powder photographs were taken using a Debye-Scherrer camera. The pictures were taken with CoKI radiation. III. RESULTS AND DISCUSSION Table 1 contains data for the moles of Fe304 per mole Ni-Zn ferrite sintered at various temperatures and water quenched. The method of calculating these data from the results of ferrous iron analyses is given in Technical Report No. 58. The value of Y/X (see composition I) increases with temperature for any given composition and approaches the value indicated as the theoretical limit, which is the value the material would have if the excess Fe203 were completely converted to Fe304. The Curie temperature of the material investigated is given in Table 2. The material used in the measurement of the Curie temperature was fired for lengths of time varying from three hours for the material fired at 14000C. to five days for the material fired at 1000~C. The material fired at 900~C was prefired at 11500C for four hours, and then refired at 9000C for 24 hours. The 4

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ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN TABLE (1) Value of Y of Equation (1) for Initial X Material Ni474Zn.526Fe 204+ BFe203 Temp. B =.135 B =.294 B =.938 B = 2.00 B = 3.00 700.004.004 800.015.012 900.035.028 1000.06.050.054.051 1050.083.079.090 1100.085.143.142.149 1150.159.237.247 1200.175.412.431 1250.180.509.688 1300.187.542 1.07 1.27 1350.190.570 1.15 1400.194.585 1.20 Theoretical Limit.09.196.625 1.33 ________________________, 6 ______I________________

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN TABLE (2) Curie Temperature of Material Having an Initial Composition of Ni 474Zn.526Fe204 + BFe203 B 900~C. 1000~C. 11000C. 1200~C. 13000C. 14000C. 0 230 259 256 261 268.135 276 280 293 280 280 298.294 272 280 322 327 328 325.570 267 286 328 380 368 374.938 260 284 330 418 424 416 2.000 421 477 465 3.000 418 486 498 4.000 474 5.667 474 Pure Fe0357 * * Fired at 1425~C. _______________________________~ 7

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN Curie temperature of Fe304 was obtained from material prepared by firing Fe203 at 1425~C. All material was water quenched. A comparison of Curie temperatures measured in a nitrogen atmosphere, an oxygen atmosphere, and an air atmosphere showed that the measurements were not sensitive to the atmosphere used. All measurements were subsequently made in an air atmosphere. A plot of + l 2L versus temperature for a typical material is given in Fig. 2. Some of the material exhibited a behavior as shown in Fig. 3. While the explanation for this behavior is not known, it did not interfere with the determination of the Curie temperatures. The Curie temperature is plotted against the initial composition in Fig. 4. From this plot the composition of the material on the boundary line between the one phase and two phase area at 10000, 11000, 12000, and 1300 can be obtained. With these data and the additional information obtained by microscopic examination of the material, the phase diagram in Fig. 5 was obtained. X-ray diffraction pictures identified the second phase as a Fe203. (Hematite). The data in Table 1 indicate that the composition of the spinel phase in the one phase area consists of a solid solution of NiaZnl.aFe204, Fe304 and yFe203. This is in agreement with the findings of H. S. Roberts and H. E. MerwinI in the system MgO-FeO-Fe203. The composition of the spinel phase might best be represented as: XNiaZnl-aFe204 YFeFe204 * ZFe2O3 (1) 1. op. cit., page 2, footnote 2. 2. The Fe203 in the spinel phase might also be written so as to show the relationship between 7Fe203 and Fe304 as follows: Fe2/3 01/3Fe204' 8

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ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN In this notation the data in Table are Y/X. This ratio can be interpreted as the solubility of magnetite in the Ni-Zn ferrite when the spinel phase is in equilibrium with the Fe203 phase, as is the case in the two phase area. It can be seen that in this region the ratio Y/X is a constant at a given temperature. The Y value of Yz can be thought of as a measure of the amount of excess oxygen in the spinel phase. The calculation of this ratio at the boundary line between the spinel field and the spinel-Fe203 field can be done as follows. In the two phase area the compositions can be given as: XNiaZnl_aFe2O4 * YFeFe2O4 * ZFe203 + BFe203 (2) y The ratio yZ can be calculated from a knowledge of the initial composition Y+Z+B and the ferrous iron content. In the one phase area B=0 and the ratio becomes y ~rZ -- As the temperature is increased further, Z approaches zero and the ratio approaches 1. The value of Y has been plotted in Fig. 6 for three composiY+Z+B tions. The composition at which the second phase disappears has been marked. It can be seen that the value of yr. at this temperature is.7 for all compositions. Darken and Gurry found that magnetite prepared in air contained excess oxygen. At the boundary between the magnetite-hematite and the magnetite field which occurs at 13900, the composition of the magnetite in terms of the components Fe304 and Fe203 was found to be.7 mole % Fe304. Written in terms of composition (1) this is: YFeFe204 - ZFe203 (3) |where they found that NFe3O4 Y = =.-7. Since composition (3) is identical where they found that NFe304 = Y+Z to composition (1) where x = O, it appears that this ratio is independent of the value of x of composition (1). 1. L. S. Darken and R. W. Gurry, "The System Iron-Oxygen II.Equilibrium and Thermodynamics of Liauid Oxide and Other Phases," J. Amer. Chem. Soc., 68, 798-816, (1946). 1 _ —------------- ~13 ~

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ACKN.OWLEDGMENTS The author wishes to thank Professor Edgar F. Westrum of the Chemistry Department for his helpful discussions during the course of this work and Hsien Wu Chang for his part in measuring Curie temperatures. 15

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