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 (ꢁ1.5405 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 concentration0.45 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
x0.00 of the oxalate complex represented by the
formula:
Mg Cuꢀ0:5 Zn0:5Fe2ꢀC2O4 Á nH2O
x
x
3
For the composition with x0.25, 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
Bhosale
