The Journal of Engineering Research (TJER), Vol. 17, No. 2, (2020) 135-141

*Corresponding author’s e-mail: smmukherjee3@gmail.com

DOI:10.24200/tjer.vol17iss2pp135-141

DEVELOPMENT OF SPINEL MAGNESIUM ALUMINATE BY SOLUTION
COMBUSTION ROUTE USING THIOUREA AND UREA AS FUEL

Srinath Ranjan Ghosh
1
, Soumya Mukherjee

2, *, and Sathi Banerjee
1

1 Department of Metallurgical & Materials Engineering, Jadavpur University, India
2, * Department of Metallurgical Engineering, Kazi Nazrul University, India

Abstract: In the present article spinel phase magnesium aluminate was synthesized using Magnesium nitrate, Al-
nitrate precursors in 1:2 molar ratio using urea and thiourea as fuel and reducing agent. Nitrate salts were mixed
in a stoichiometric ratio in distilled water with three different molar ratios of two different fuels: urea and
thiourea. The temperature of crystallization was obtained after thermal analysis followed by annealing at a fixed
temperature, fixed soaking period for urea as fuel while variable temperature and soaking period were required
for thiourea as fuel. FTIR analyses were carried out of the samples to verify the M-O co-ordinations for the
phase formation. Prominent octahedral M-O stretching was noted at about 609 cm-1 while that of Al-Mg-O
stretching was noted at about 1100 cm-1 for thiourea based samples. Using Urea as fuel Al-O stretching was
noted at about 539cm-1 while that of Al-Mg-O vibration was noted at about 677cm-1. Morphological features of
the synthesized samples were observed by SEM. Agglomeration was noted for both urea and thiourea as fuel
having irregular polygon shape. Using thiourea as fuel, a bit of porous structure was noted while for urea as fuel
negligible porosity was noted.

Keywords: Magnesium Aluminate; Thermal analysis; Phase analysis; M-O co-ordinations; Morphology

باستخدام عن طریق حرق المحلولالومینات المغنیسیوم تحضیر معدن السبینیل ذو
یا كوقودیا والیوریوالثیور

، وساثي بنرجي*سریناث جوش، سومیا مخرجي

تصنیع ألومینات المغنیسیوم في طور اإلسبنیل باستخدام نترات المغنیسیوم وسالئف النترات خالل ھذه الدراسة تم الملخص:
بنسب متكافئة في الماء اختزال. تم خلط أمالح النترات ریا كوقود وعواملیوكال من الیوریا والثیو باستخدام یةموالر 2: 1بنسبة

اسفرت الدراسة بعد التحلیل الحراري والتلدین للیوریا . لنوعي الوقود المذكورین اعالهالمقطر مع ثالث نسب موالریة مختلفة
ة ریا وجود درجة حرارة وفتریوالثیووقود بینما تطلب استخدام ثابتتین، ریا إلى أن فترة نقع الیوریا ودرجة حرارة تبلوره یووالثیو

ثماني السطوح M-Oلتشكیل الطور. لوحظ تمدد M-Oوتم إجراء التحلیل الطیفي للعینات للتأكد من تنسیقات ،نقع متغیرتین
ریا. وفي حالة یوللعینات القائمة على الثیو 1-سم 1100عند حوالي Al-Mg-Oبینما لوحظ امتداد 1-سم 609البارز عند حوالي

سم 677عند حوالي Al-Mg-Oبینما لوحظ استخدام اھتزاز 1-سم 539عند حوالي Al-O استخدام الیوریا كوقود لوحظ تمدد
من نتائج التجارب أن لوحظ. تمت مالحظة السمات المورفولوجیة للعینات المركبة بواسطة المجھر المسحي األلكتروني. كما 1-

كان للیوریا بینما تؤخذ بعین اإلعتبار ریا بنیة مسامیةیولثیول أنكما ،ریا لھ شكل مضلع غیر منتظمیوتكتل كل من الیوریا والثیو
.بنیة أقل مسامیة

.وقود، ریایوثیو، یوریا، تحلیل حراري، الومینات المغنیسیوم الكلمات المفتاحیة:

Development of Spinel Magnesium Aluminate by Solution Combustion Route Using Thiourea and Urea as Fuel

136

1. INTRODUCTION

Magnesium aluminate has lots of industrial applications due
to its high melting point (2135°C), high-temperature
mechanical strength, chemical inertness, thermal shock
resistance, chemical resistance, and low thermal expansion
coefficient. (C Păcurariu et al. 2007; S.R. Ghosh et al. 2018;
Ali Saberi et al. 2008; P V Marakkar Kutty et al. 2013) The
presence of such properties makes the compound suitable as
high-temperature refractory material for both cement rotary
kiln, and steel ladle. In the initial decades, chromite-based
spinel is extensively used for steel making, glass tank
regenerators, rotary kiln and even for copper industry.
However, environmental concern regarding Cr+6 species
from the chromite spinel is a hindrance to its applications.
(Chandrima Ghosh et al. 2015) The above compound has
spinel structure represented by the formula AB2O4 where A
is the divalent ion, B is the trivalent ion and O represents the
anion. Divalent Mg and trivalent Al ions occupy tetrahedral
(1/8 of available) and octahedral sites (1/2 of available)
respectively. (Shiva Salem 2015) The particular spinel
ceramic also has excellent optical properties and can be used
for transparent ceramics. The optical property enhances its
eligibility as a prominent candidate material for transparent
armour and visible-infrared windows. It is also utilized for
ceramic paints and for making catalyst support, membranes,
dye absorbent and as sensors. For the successful application
of spinel aluminate as dye absorbent, catalyst, sensors, spinel
fabricated needs to possess high purity, controlled particle
size, high surface area and uniform pore size distribution.
(Narges Habibi et al. 2017) Spinel magnesium aluminate also
acts as a potential candidate for humidity sensors. In recent
researches, it is noted that spinel magnesium aluminate as one
potential candidate for photocatalyst to decompose reactive
red methylene used as a dye for industrial operations.
(Mostafa Y Nassar et al. 2014) Purity, particle size, chemical
homogeneity, and reactivity of spinel magnesium aluminate
are influenced by the synthesis route. (Ali Saberi et al. 2008)
The material is found to be synthesized by various methods in
addition to solid-state reaction like sol-gel (Debsikdar J.C
1985; Naskar M.K. et al. 2005) precipitation (Li J-G et al.
2000), aerosol method (Yang N et al. 1992), co-precipitation
(Guo J et al. 2004), combustion synthesis, freeze-drying,
decomposition of an organometallic complex in super critical
fluids, hydrothermal route, plasma spray decomposition of
powders, (Bickmore R Clint et al. 1996; Bratton R.J. 1969;
Barj M. et al. 1992; Pommier C. et al. 1990; Yang Ning et al.
1992; Varnier Olivier et al. 1994) microwave-assisted
combustion route (Torkian Leila et al. 2011), polymerized
complex method (Lee P.Y et al. 2006; Du Xuelian et al.
2014), mechanochemical route (Domanski D. et al. 2004),
self-propagating high-temperature synthesis (Gorshov V. A.
et al. 2017) and others.
In the present article, spinel magnesium aluminate is
synthesized using urea and thiourea as fuel and reducing
agent for three molar ratios along with nitrate precursors. The
annealing temperature is confirmed after carrying thermal
analysis of mixed solutions followed by phase analysis,
bonding analysis and morphological studies.

2. EXPERIMENTAL METHODS

AR grade of magnesium nitrate, aluminium nitrate, urea and
thiourea were used as precursors for synthesizing spinel. The
stoichiometric ratio of magnesium nitrate, aluminium nitrate
were taken in 1:2 molar ratios in distilled water for stirring.
The solution undergoes stirring by magnetic beads for
sufficient time. After proper mixing of nitrates urea, thiourea
was added in 1.25, 1.50 and 1.75 molar ratio with respect to
nitrate salts and again undergoes stirring for about 1 hour to
ensure homogeneity. The resultant solution undergoes drying
in an oven (heater) at about 80°C for about 3-4 hours to
obtain a dry gel-like mass. The gel was put into DTA-TGA
analyzer (Diamond Pyris, Perkin Elmer) in presence of
Nitrogen atmosphere at the heating rate of 10°C/min for
determining the thermal characteristics of the sample.
Crystallization temperature for spinelization was obtained and
after that, the gel was put for annealing at 700°C for 5
hours in the case of urea as fuel. The annealing
temperature was 700°C for 5 hours, 800°C for 4.5
hours and 900°C for 4.5 hours respectively for
thiourea as fuel. Phase analysis was carried by XRD
(Rigaku, Ultima III) having Cu Kα wavelength of
1.54Å, 40KV with a scan range of 10-80° having a scan
rate of 5°/minute. Bonding analysis was carried by FTIR (IR
Prestige-21, Shimadzu) to determine M-O coordination of the
required phase after preparing pellet samples with KBr.
Morphological structures were analyzed by SEM (Jeol, JAX
840A) using carbon conducting tape to stick the powder
sample for better resolution and to avoid electrostatic
charging.

3. RESULTS AND DISCUSSIONS

DTA-TGA curve exhibits initial weight loss in the
temperature range between 100-200°C. From the
curve in Fig. 1 two prominent endothermic peaks at
about 100°C and 200°C are noted. First one suggests
the removal of physically absorbed water and 2nd one
suggests removal of structural water.
A large exothermic peak is observed due to burning or
oxidation of organic compounds which is mainly
mainly a combustion of carbonaceous and sulphur

0 100 200 300 400 500 600 700 800 900

-40

-20

temperature o C

he
at

fl
ow

(m
W

)

weight (m
g)

Figure 1. DTA-TGA curve of Magnesium nitrate: Al-

nitrate precursors in 1:2 molar ratio with
thiourea as fuel and reducing agent having a
heating rate of 15°C/min.

Srinath Ranjan Ghosh , Soumya Mukherjee, and Sathi Banerjee

137

elements due to thiourea corresponding to 2nd
prominent weight loss. A minor endothermic peak is
observed around 350°C due to the initial formation of
γ-alumina. (Macêdo Maria laponeide Fernandes et al.
2007) The second endothermic peak with minor
weight change is noted due to possible dissociation of
nitrate precursor salts at about 450°C (Macêdo Maria
laponeide Fernandes et al. 2007). A broad weak
exothermic peak ranging from 500°C to 700°C is
noted which corresponds to the initiation of the
crystallization process and records the third weight
loss. Crystallization of gel from precursors always
involves weight loss and undergoes exothermic
reaction. Weight loss occurs possibly because of the
presence of the multicomponent compound and their
interactions. The stability of weight loss indicates full
onset of the crystallization process.

Figures 2-7 represent XRD spectra of the
synthesized sample using Urea and thiourea
respectively as fuel. Three different molar ratios of
1.25, 1.50 and 1.75 are considered for each fuel
respectively. It has been noted that for spinel
magnesium aluminate synthesized by urea annealing
temperature and soaking period are kept fixed. For
such conditions, spinel has been noted for all molar
ratios of urea as fuel, reducing agent. Peak intensity is
optimum for all cases. Slight amorphous nature of
spectra is noted for all cases. Lower urea fuel ratio of
1.25 exhibits much better crystalline nature of spectra
than higher fuel ratio. It may be possible due to
higher reduction tendency and calorific value of fuel
with more molar ratio which could also possibly
accelerate the reaction and shorten the transformation
period to induce the required phase. In contrast with
thiourea as fuel, the reducing agent annealing
temperature is increased. Annealing temperature and
soaking period carried are carried as follows 700°C
for 5 hours, 800°C for 4.5 hours and 900°C for 4.5
hours, respectively. The crystallinity of peaks got
increased with temperature for thiourea but in the
present research the focus is on lower temperature
spinelization hence for both fuels 700°C for 5 hours is
taken as reference. For both cases, successful spinel
phase formation is noted. For urea, spinel formation is
verified by comparing the XRD spectra with JCPDS
card file #01-077-1193, #01-075-1800, #01-082-2424
and #01-077-0437 respectively. For thiourea based
fuel spinel is verified by comparing the XRD spectra
with JCPDS card file #01-086-0085, #01-075-1800,
#01-082-2424 and #01-077-0437 respectively. Using
urea as fuel all peaks are indexed as spinel phase. No
intermediates or other phases are noted. Major planes
of growth for Spinel is noted along (311), (220),
(111), (400), (511) and (440) planes. A similar trend
is also noted for thiourea as fuel and reducing agent.
For thiourea based fuel no intermediates or presence
of other phases are noted except for only spinel phase.
Crystallite size is calculated by Scherrers formula
t=0.9λ/βCosθ where t is the crystallite size, λ is the
wavelength, Cu Kα = 1.54Å, β is the full width of

half mean, θ is the angle corresponding to the spectra.
For 1.25, 1.75 molar ratio of urea, crystallite size is
found to be about 36.52nm, while for 1.50 molar ratio
it is noted to be about 48.69nm. In the case of
thiourea, crystallite size is calculated and noted to be
about 42.96nm, 48.69nm and 73.02 nm respectively.
Such variation in crystallite size is noted since
annealing temperature varies. In the present context,
the focus is on lower temperature synthesis
henceforth, further analyses will be carried for
samples synthesized at 700°C for 5 hours for both
urea, thiourea as fuel where full phase development is
noted from XRD analysis.

Figures 8-9 represent FTIR spectra of spinel
synthesized using urea and thiourea as fuel. For both
cases, scanning range is within 450-4500cm-1 while
major M-O coordinations are noted within 1000cm-1.
It has been noted for the urea-based synthesis of
spinel, M-O coordinations are noted mostly within
1000cm-1. Al-O stretching is noted at about 539cm-1
while Mg-O-Al vibration is observed at 677cm-1
approximately. The FTIR analysis is noted to be in
correspondence with research findings by (S.R. Ghosh
et al. 2018; Mukherjee 2020). For thiourea, M-O
coordinations are noted for Al-O stretching, Al-Mg-O
stretching at about 609cm-1 and 1100cm-1
respectively. Spectral peaks at about 1655cm-1,
2356cm-1 and 3311cm-1 are noted for H-O-H
stretching, CH3-CH2 vibration, and O-H bonding
vibration. The presence of H-O-H stretching, O-H
vibration is possibly due to some physically absorbed
moisture on the surface of the sample since FTIR
analysis is carried in a normal atmosphere without any
purging of gas. Figures 10 and 11 represent
morphology obtained by SEM analysis of spinel after
annealing at 700°C for 5 hours using thiourea and
urea of 1.25 molar ratios as fuel. For both fuels,
agglomeration tendency is observed with the irregular
polygonal shape of the agglomerated chunk. Figs. 10
A and B represent morphology for thiourea based
spinel samples with minor porosity on the surface and
negligible interconnected porosity. Figure 10 B
exhibits agglomerated chunk for spinel by thiourea as
fuel having irregular step around the periphery of
agglomerate with some convex fracture at some
portion of the chunk morphology. Figures 10 A-D
execute individual particulates to be spherical or bean
shape to irregular polygonal shape for thiourea based
fuel for spinel formation. Figure 10 D represents a bit
flaky structure for some portion. Figure 11 B
represents an agglomerate chunk with a polygonal
shape having sharp edges while the size of the
agglomerated chunk is noted to be about 4 μm while
individual particulates are about 0.2μm. Figures 11 A-
C execute dense compact formation of spinel using
urea as fuel in compare to a bit porous structure noted
using thiourea as fuel. Individual particulates are
spherical with agglomerate having dimensions close
to 2.5μm to 5μm. Individual particulates are noted to
be about 0.3μm to 0.4μm in range.

Development of Spinel Magnesium Aluminate by Solution Combustion Route Using Thiourea and Urea as Fuel

138

10 20 30 40 50 60 70 80

100

200

300

400

In
ten

sit
y c

Angle 2θ

(urea)1.25700
oC 5hrs

[111] [220]

[311]

[400]

[511]

[440]

Figure 2. XRD spectra of Magnesium nitrate: Al-nitrate

precursors in 1:2 molar ratio with urea as fuel
and reducing agent having 1.25 molar ratio
after annealing at 700°C for 5 hours.

10 20 30 40 50 60 70 80

100

150

200

250

300

350

In
te

ns
ity

c
ps

Angle 2θ

(urea)1.5700
oC 5hrs

[111] [220]

[311]

[400]

[511]

[440]

[533]

Figure 3. XRD spectra of Magnesium nitrate: Al-

nitrate precursors in 1:2 molar ratio with urea
as fuel and reducing agent having 1.50 molar
ratio after annealing at 700°C for 5 hours.

10 20 30 40 50 60 70 80

100

150

200

250

300

350

In
te

ns
ity

c
ps

Angle 2θ

(urea)1.75700
oC 5hrs

[111] [220]

[311]

[400]

[511]

[440]

[533]

Figure 4. XRD spectra of Magnesium nitrate: Al-nitrate

precursors in 1:2 molar ratio with urea as fuel
and reducing agent having 1.50 molar ratio
after annealing at 700°C for 5 hours.

0 10 20 30 40 50 60 70 80 90

100

200

300

400

500

In
te

ns
ity

cp
s

Angle 2θ

(thio)1.25700
oC 5hrs

[111]
[220]

[311]

[400]

[511]

[440]

[533]

Figure 5. XRD spectra of Magnesium nitrate: Al-nitrate

precursors in 1:2 molar ratio with thiourea as
fuel and reducing agent having 1.25 molar
ratio after annealing at 700°C for 5 hours.

10 20 30 40 50 60 70 80

100

200

300

400

In
te

ns
ity

cp
s

Angle 2θ

(thio)1.5800
oC 4.5 hrs

[111] [220]

[311]

[400]

[511]

[440]

[622]

Figure 6. XRD spectra of Magnesium nitrate: Al-nitrate

precursors in 1:2 molar ratio with thiourea as
fuel and reducing agent having 1.25 molar
ratio after annealing at 800°C for 4.5 hours.

10 20 30 40 50 60 70 80

200

400

600

800

In
te

ns
ity

c
ps

Angle 2θ

(thio)1.75900
oC 4.5 hrs

[111] [220]

[311]

[400]

[422]

[511]

[440]

[533]

Figure 7. XRD spectra of Magnesium nitrate: Al-nitrate

precursors in 1:2 molar ratio with thiourea as
fuel and reducing agent having 1.25 molar
ratio after annealing at 900°C for 4.5 hours.

Srinath Ranjan Ghosh , Soumya Mukherjee, and Sathi Banerjee

139

1000 2000 3000 4000

0.0

0.1

0.2

0.3

0.4

0.5
ab

so
rb

an
ce

(a
.u

)

wave number (cm-1)

(urea)1,25 700
oC 5hrs539 677

1403
3435

Figure 8. FTIR spectra of Magnesium nitrate: Al-nitrate

precursors in 1:2 molar ratio with urea as fuel
and reducing agent having 1.25 molar ratio after
annealing at 700°C for 5 hours.

1000 2000 3000 4000

0.0

0.1

0.2

0.3

0.4

Ab
so

rb
an

ce
(a

.u
)

wave number (cm-1)

(thio)1.25 700
oC 5hrs

1100609

1655

2356

3311

Figure 9. FTIR spectra of Magnesium nitrate: Al nitrate

precursors in 1:2 molar ratio with thio urea as
fuel and reducing agent having 1.25 molar ratio
after annealing at 700°C for 5 hours.

Figure 10. SEM morphology of Spinel Magnesium Aluminate using thiourea as fuel and reducing agent having 1.25
molar ratio after annealing at 700°C for 5 hours.

D
C

Development of Spinel Magnesium Aluminate by Solution Combustion Route Using Thiourea and Urea as Fuel

140

Figure 11. SEM morphology of Spinel Magnesium
Aluminate using urea as fuel and reducing
agent having 1.25 molar ratio after annealing
at 700°C for 5 hours.

CONCLUSION

Spinel magnesium aluminate was prepared using
thiourea and urea as a fuel and reducing agent.
Thermal analysis of precursors along with fuel
indicate the onset of crystallization in the range of
500-700°C. The goal of low-temperature spinelization
was achieved for both cases as the temperature was
about 700°C with 5 hours soaking period and
confirmed from XRD phase analysis. FTIR analysis
confirmed the M-O coordinations and it was noted
that Al-O coordination was about 539cm-1 while Mg-

O-Al vibration was observed at about 677cm-1.
Agglomerated mass with irregular polygon shape was
noted as morphological features after using both urea
and thiourea as fuel, reducing agent for synthesizing
spinel magnesium aluminate. Using thiourea as fuel,
the dimension of the agglomerated chunk was about
4μm and for individual particulate, it was about
0.2μm. Similarly, using urea as fuel agglomerate was
in the range of 2.5 to 5μm and for individual
particulate was about 0.3 to 0.4μm. Thiourea induces a
slight porosity in structure while negligible dense
mass was noted using urea as fuel.

CONFLICT OF INTEREST

The authors declare that there are no conflicts of
interest as regards this article.

FUNDING

There is no funding from any external agency to carry
out the experiment

ACKNOWLEDGMENT

The authors would like to thank the Department of
Metallurgical & Material Engineering for providing
technical support to carry out DSC-TGA analysis,
XRD, FTIR and morphology studies by SEM.

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