Thermal study of ferritization temperature of Cu-Mg-Zn ferrites: TG/DTG/DTA (STA) studies

Article abstract of DOI:10.1016/S0040-6031(98)00360-8

Oxalates of Cu²⁺, Mg²⁺, Zn²⁺ and Fe²⁺ were coprecipitated from the mixture of respective acetate solutions using 0.6 M oxalic acid solution to form a homogeneous solid solution Mg_xCu_(0.5-x)Zn_0.5Fe₂ (C₂O₄)₃·nH₂O with x=0.00, 0.20, 0.25 and 0.40. To determine ferritization (formation of ferrite) temperature of resulting ferrite system, Mg_xCu_(0.5-x)Zn_0.5Fe₂O₄ with x=0.00, 0.20, 0.25 and 0.40, TG/DTG/DTA studies (STA) were carried out on coprecipitated oxalate complexes. These studies revealed the low ferritization temperature (326°-370°C) of the ferrite system and occurrence of simultaneous decomposition and ferritization processes. The ferrite system was characterized using X-ray diffraction study, which revealed the presence of single spinel phase.

Full text of DOI:10.1016/S0040-6031(98)00360-8

Thermochimica Acta 316 (1998) 159±165
Thermal study of ferritization temperature of Cu±Mg±Zn ferrites:
TG/DTG/DTA (STA) studies
D.N. Bhosalea,*, V.Y. Patilb, K.S. Ranec, R.R. Mahajand, P.P. Bakaree, S.R. Sawanta
a Department of Physics, Shivaji University, Vidyanagar, Kolhapur 416004, India
b Department of Chemistry, New College, Kolhapur 416012, India
c Department of Chemistry, Inorganic Chemistry Section, Goa University, Bambolim, Goa, India
d High Energy Material Research Laboratory, Pashan, Pune, India
e Physical Chemistry Division (S.I.L.), National Chemical Laboratory, Pune 411008, India
Received 20 March 1997; received in revised form 22 December 1997; accepted 5 April 1998
Abstract
Oxalates of Cu2‡, Mg2‡, Zn2‡ and Fe2‡ were coprecipitated from the mixture of respective acetate solutions using 0.6 M
oxalic acid solution to form a homogeneous solid solution MgxCu(0.5 x)Zn0.5Fe2 (C2O4)3ÁnH2O with xˆ0.00, 0.20, 0.25 and
0.40. To determine ferritization (formation of ferrite) temperature of resulting ferrite system, MgxCu(0.5 x)Zn0.5Fe2O4 with
xˆ0.00, 0.20, 0.25 and 0.40, TG/DTG/DTA studies (STA) were carried out on coprecipitated oxalate complexes. These studies
revealed the low ferritization temperature (3268±3708C) of the ferrite system and occurrence of simultaneous decomposition
and ferritization processes. The ferrite system was characterized using X-ray diffraction study, which revealed the presence of
single spinel phase. # 1998 Elsevier Science B.V.
Keywords: Cu±Mg±Zn ferrites; Decomposition (of metal oxalate complexes); Ferritization; TG/DTG/DTA studies; Thermal
study
1. Introduction
investigated and evaluated [2±4]. Schuele [5] has
synthesized copper ferrite having ®ne particle size
by suitably heat treating coprecipitated oxalates of the
Cu±Fe system. Wickham [6] has synthesized spinel
High performance ferrites are commonly produced
by a solid-state reaction using intimately mixed ®ne
powders of component oxides and other salts to
increase reactivity of component oxides [1]. To obtain
an end product having a single phase, it is essential to
maintain scrupulous reaction conditions. Besides
these commonly employed conventional methods,
various nonconventional methods also have been
ferrites MFe2O4 (where MˆMg2‡, Mn2‡, Zn2‡, Ni2‡
,
Co2‡) by decomposing mixed metal oxalate com-
plexes, wherein ignition temperature ranges from
10008 to 13108C, depending on respective M. More-
over, Langbein et al. [7] and St. Fischer et al. [8] have
separately synthesized nickel±zinc ferrites by thermal
decomposition of coprecipitated oxalates. Bremer et
al. [9] have investigated preparation of manganese±
zinc ferrites by thermal decomposition of solid solu-
tion of oxalate complexes.
*Corresponding author. Tel.: +91 231 65 5571; fax: +91 231 65
6133.
0040-6031/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved
P I I S 0 0 4 0 - 6 0 3 1 ( 9 8 ) 0 0 3 6 0 - 8

160
D.N. Bhosale et al. / Thermochimica Acta 316 (1998) 159±165
Synthesis of Cu±Mg±Zn ferrites using a solid solu-
STA 409 differential thermal analyzer. The samples
were heated in air at a heating rate of 108C min 1 TG,
DTG, DTA curves were recorded simultaneously in
the temperature range from room temperature to
7008C.
tion of component oxides have been reported by Koh
et al. [10,11] and Hak et al. [12]. However, synthesis of
Cu±Mg±Zn ferrites by nonconventional methods
(using organic precursors) have not been reported
so far. The present paper reports our nonconventional
method which has an advantage of obtaining homo-
geneous solid solution of respective oxalates. On
further decomposition, it results in the desired ferrite
system. It also includes TG/DTG/DTA study (STA)
for detection of its ferritization temperature and X-ray
diffraction study for characterization of the resultant
ferrite system.
2.2. X-ray diffraction (XRD) study
The solid solution of coprecipitated oxalate
complexes were decomposed at their respective
ferritization temperature obtained from TG's for
three hours and 6008C for one hour in air. X-ray
diffraction (XRD) patterns were recorded using
Philips X-ray diffractometer model PW 1710 using
Ê
CuKꢀ radiation (ꢁˆ1.5405 A) in the 20<2ꢂ<808 range
2. Experimental
and in the intensity range from 250 to 1000 counts
(Fig. 4).
Bremer et al. [9] have prepared manganese-zinc
ferrites by modifying the Wickham method [6] for
preparation of individual oxalates. The method has an
advantage over the conventional metal oxide process
in which acetic acid is obtained as an important by-
product resulting from the synthesis of oxalates using
respective metal acetates [13].
Using standard conversion table, `d' values for the
corresponding `2ꢂ' were derived. The lattice para-
meter were computed using these d values and the
respective (h,k,l) parameters, which identi®ed that the
samples are single spinel ferrites. The reported lattice-
parameter value for Mg0.5Zn0.5Fe2O4 is 0.840 nm [14]
and for Cu0.5Zn0.5Fe2O4 it is 0.841 nm [15]; these
values have been compared with the experimental data
to characterize the samples.
In the present case, iron (II) acetate was prepared by
adding glacial acetic acid (slightly in excess) to the
required quantity of AR grade iron metal powder. To
avoid the oxidation of iron (II) to iron (III), the
reaction was carried out in CO2 atmosphere instead
of N2 atmosphere employed in the above mentioned
method [9]. To maintain the desired stoichiometry, the
required quantities of copper acetate, zinc acetate,
magnesium acetate, iron (II) acetate prepared as
above (having total metal iron concentrationˆ0.45 M)
were added dropwise to the 0.6 M oxalic acid solu-
tion to precipitate the required oxalate complex.
The oxalic acid solution was continuously stirred
for homogeneous mixing. The yellow crystalline
precipitate was digested for 10 min and allowed to
cool to room temperature. The supernatant liquid/
solution was ®ltered off. The precipitate was washed
with doubly distilled water and dried in an oven
at 1008C.
3. Results and discussion
3.1. TG/DTG/DTA study (STA)
On analyzing the TG/DTG/DTA experimental data,
thermal decomposition of a solid solution of an oxa-
late complex is observed to take place in two distinct
steps: Step I includes dehydration of the oxalate
complex and Step II ± decomposition of anhydrous
oxalate complex (Fig. 1) for the composition with
xˆ0.00 of the oxalate complex represented by the
formula:
Mg Cuꢀ0:5 Zn0:5Fe2ꢀC2O4† Á nH2O
x†
x
3
For the composition with xˆ0.25, however, Step I
indicates the presence of two substeps as seen from the
DTG/DTA curves (Fig. 2). All the DTA curves show
that dehydration is an endothermic reaction repre-
sented by a sharp peak, whereas decomposition in
air is an exothermic reaction indicated with a broad
2.1. Thermal analysis: TG/DTG/DTA study (STA)
Simultaneous thermal analysis (STA) of mixed
oxalate complexes was carried out using Netzsch

D.N. Bhosale et al. / Thermochimica Acta 316 (1998) 159±165
161
Fig. 1. STA of oxalate complex: Cu0.5Zn0.5Fe2(C2O4)3, 6.5 H2O.
Fig. 2. STA of oxalate complex: Mg0.25Cu0.25Zn0.50Fe2(C2O4)3ÂÁ6.5H2O.

162
D.N. Bhosale et al. / Thermochimica Acta 316 (1998) 159±165
Fig. 3. DTA of oxalate complex: (a) Mg0.20Cu0.30Zn0.50Fe2(C2 O4)3Á7.5H2O; and (b) Mg0.25Cu0.25Zn0.50Fe2(C2O4)3Á6.5H2O.
Table 1
Stepwise and total mass loss in % and its variation with x for the oxalate complex system: MgxCu(0.5 x)Zn0.5Fe2(C2O4)3ÁnH2O
x
Proposed formulae for oxalate complexes Stepwise and total mass loss in %
TG (experimental)
TG (theoretical)
dehydration decomposition
total
dehydration decomposition total
0.00
0.20
0.25
0.40
Cu0.5Mg0.5Zn0.5Fe2(C2O4)3Á6.5H2O
Mg0.20Cu0.30Zn0.50Fe2(C2O4)3Á7.5H2O
Mg0.25Cu0.25Zn0.50Fe2(C2O4)3Á6.5H2O
Mg0.40Cu0.10Zn0.50Fe2(C2O4)3Á7.5H2O
20.40
19.80
20.65
21.96
37.23
39.22
35.87
37.37
57.63
59.02
56.52
59.33
21.00
23.80
20.70
24.14
35.90
34.82
35.79
35.53
56.90
58.62
56.49
59.67
Table 2
Onset and termination temperatures observed during dehydration and decomposition steps for MgxCu(0.5 x)Zn0.5Fe2(C2O4)3ÁnH2O system
with various x
x
TG
dehydration (Step I)/(8C)
decomposition (Step II)/(8C)
substep I
substep II
onset
onset
termination
onset
termination
termination
0.00
0.20
0.25
0.40
116
116
148
142
204
209
185
191
Ð
Ð
204
209
209
209
326
337
337
370
Ð
Ð
185
191
209
209

D.N. Bhosale et al. / Thermochimica Acta 316 (1998) 159±165
163
hump (Figs. 1 and 2). The exothermic reaction of
decomposition is con®rmed by separately recording
DTA's (Fig. 3) for the samples with compositions
xˆ0.20 and 0.25.
Table 1 includes experimentally observed total
mass loss in %, in comparison with total mass loss
in % based on theoretical calculations. Table 1 also
presents the proposed formulae for respective oxalate
complexes. The total mass loss in % experimentally
observed is used to calculate the total number of water
molecules present in the respective oxalate complex
system and agrees well with the corresponding
theoretically calculated one. Table 1 also gives
stepwise mass loss in % observed experimentally
from TG curves during the dehydration and decom-
position steps as compared with theoretical ones.
The corresponding onset and termination tempera-
ture for these steps observed from TG/DTG/DTA
curves are given in Table 2. These temperatures
observed for separately recorded DTA curves
remain the same. DTA curves also indicate the type
of reaction occurring in these temperature ranges
(Figs. 1±3).
The dehydration and decomposition steps/reactions
can be represented as follows,

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D.N. Bhosale et al. / Thermochimica Acta 316 (1998) 159±165
Fig. 4. XRD patterns of oxalate complex with xˆ0.25: (a)
decomposed at 3378C for 3 h; and (b) decomposed at 6008C for
1 h.
The ferritization (formation of the ferrite) and
Typical representative XRD patterns for Xˆ0.25 are
shown in Fig. 4 in which the oxalate complexes are
decomposed at 3378C (ferritization temperature) for
3 h and at 6008C for 1 h. They exhibit a single spinel
phase. No other impurity phases existed. The observed
lattice parameters are given in Table 3. These values
are comparable with those reported [14,15].
The temperature ranges, for the different steps
observed during dehydration and decomposition pro-
cess for each separate oxalate system represented by
decomposition processes are occurring simulta-
neously in the temperature range of 2098 to 3708C
(max) as the nascent MO's are highly reactive and,
therefore, helps ferritization at a low temperature
range, such as 326±3708C. This phenomena has
been con®rmed by the separate preparation of these
compositions at respective ferritization temperatures
by following the same procedure, and the ferrites
thus formed are characterized by XRD. That any
further change is absent is evident from the TG,
DTG, DTA curves recorded beyond this temperature
range.
Table 3
Variation of lattice parameter, a with x in MgxCu(0.5 x)Zn0.5Fe2O4
3.2. X-ray diffraction (XRD) study
Mg2‡ content x
Lattice parameter, aÆ0.002 A
Ê
The single spinel phase of all the samples has been
characterized by using XRD data from which lattice-
parameter constants could be calculated by the stan-
dard method.
0.00
0.20
0.25
0.40
8.398
8.397
8.386
8.375

D.N. Bhosale et al. / Thermochimica Acta 316 (1998) 159±165
165
MC2O4ÁnH2O (where MˆMg2‡, Zn2‡, Cu2‡, Fe2‡
)
Acknowledgements
have been reported by Duval [16].The maximum
temperature required is 5908C in case of decomposi-
tion of zinc oxalate to zinc oxide, among the required
metal oxalates. Therefore, to make sure that dehydra-
tion and decomposition reactions are complete, we
have synthesized ferrite system at 6008C and recorded
their XRD pattern. For characterization of the
samples, a similar procedure has been adopted. On
comparing all the XRD patterns, it revealed
that ferritization is completed at such a low tempera-
ture, ranging from 3268 to 3708C, for compositions
The authors thank Mr. Sunil P. Velapure of the High
Energy Material Research Laboratory, Pashan, Pune
(India).
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