Thermal and X-ray diffraction studies of the solid-solid interactions in CuO-MoO3/MgO system

Article abstract of DOI:10.1007/s10973-004-6842-6

The solid-solid interactions in pure and MoO₃-doped CuO/MgO system were investigated using TG, DTA and XRD. The composition of pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations of MoO₃ were 2.5 and 5 mol%. These solids were prepared by wet impregnation of finely powdered basic magnesium carbonate with solutions containing calculated amounts of copper nitrate and ammonium molybdate followed by heating at 400-1000°C. The results revealed that ammonium molybdate doping of the system investigated enhanced the thermal decomposition of copper nitrate and magnesium hydroxide which decomposed at temperatures lower than those observed in case of the undoped mixed solids by 70 and 100°C, respectively. A portion of CuO present dissolved in the lattice of MgO forming CuO-MgO solid solution with subsequent limited increase in its lattice parameter. The other portion interacted readily with a portion of MoO ₃ at temperatures starting from 400°C yielding CuMoO₄ which remained stable up to 1000°C. The other portion of MoO₃ interacted with MgO producing MgMoO₄ at temperatures starting from 400°C and remained also stable at 1000°C. The diffraction peaks of Cu₂MgO₃ phase were detected in the diffractograms of pure and MoO₃-doped 0.3CuO/MgO precalcined at 1000°C. The formation of this phase was accompanied by an endothermic peak at 930°C.

Full text of DOI:10.1007/s10973-004-6842-6

Journal of Thermal Analysis and Calorimetry, Vol. 85 (2006) 2, 321–327
THERMAL AND X-RAY DIFFRACTION STUDIES OF THE
SOLID–SOLID INTERACTIONS IN CuO–MoO3/MgO SYSTEM
H. G. El-Shobaky*
Chemistry Department, Faculty of Science, Cairo University, Egypt
The solid–solid interactions in pure and MoO3-doped CuO/MgO system were investigated using TG, DTA and XRD. The composi-
tion of pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations of MoO3 were 2.5 and
5 mol%. These solids were prepared by wet impregnation of finely powdered basic magnesium carbonate with solutions containing
calculated amounts of copper nitrate and ammonium molybdate followed by heating at 400–1000°C.
The results revealed that ammonium molybdate doping of the system investigated enhanced the thermal decomposition of
copper nitrate and magnesium hydroxide which decomposed at temperatures lower than those observed in case of the undoped
mixed solids by 70 and 100°C, respectively. A portion of CuO present dissolved in the lattice of MgO forming CuO–MgO solid so-
lution with subsequent limited increase in its lattice parameter. The other portion interacted readily with a portion of MoO3 at tem-
peratures starting from 400°C yielding CuMoO4 which remained stable up to 1000°C. The other portion of MoO3 interacted with
MgO producing MgMoO4 at temperatures starting from 400°C and remained also stable at 1000°C. The diffraction peaks of
Cu2MgO3 phase were detected in the diffractograms of pure and MoO3-doped 0.3CuO/MgO precalcined at 1000°C. The formation
of this phase was accompanied by an endothermic peak at 930°C.
Keywords: Cu2MgO3, CuMoO4, CuO, MgMoO4, MgO, MoO3, solid solution
Introduction
to the formation of solid solutions as in the case of (i)
V2O5–MoO3 system a solid solution of a composition
(V2O5)1–x–(MoO3)x with 0≤x≤l is formed at 423 K [24].
(ii) Solid solutions in a formula Cr1–xAlxVMoO7, where
x=0.65 are formed in the system CrVMoO7–AlVMoO7
[25]. (iii) Also a solid solution was formed in the system
V2O5–MoO3–Sb2O4 [26]. The Mo(VI) ions are incorpo-
rated into the crystal lattice of SbVO5 instead of both
Sb(V) and V(V) and the limit of solubility of MoO3 in
SbVO5 does not exceed 20 mol%.
Thermally decomposed metal nitrates and metal car-
bonates have been used as precursors in chemical in-
dustries, as catalysts, in metallurgical processes and
as electrochemical power sources [1–12]. The struc-
tures formed when metals are deposited on the sur-
faces of metal oxides can be quite complex. The ini-
tial monolayers may involve in the formation of
different oxides, leading effectively to oxide/oxide
interfaces. These interfaces are of great importance in
a variety of technological areas, including heteroge-
neous catalysis [13–17].
On the other hand, MoO3 may interact with the
other mixed oxides with production of molybdate com-
pounds. In case of NiO–MoO3 [18], Co3O4–MoO3/MgO
[20], MoO3/TiO2–ZrO2 [27], Co3O4–MoO3/Al2O3 [28],
Nb2O5–MoO3 [29] and MoO3–A2CO3 or A2MoO4
(A=Na, K, Rb, Cs) [30] systems the corresponding mo-
lybdates were separated CoMoO4, NiMoO4, ZrMo2O8
and CoMoO4, Nb14Mo3O44, Nb12MoO33, A2Mo4O13
·xH2O (x=2–6), respectively.
Pure ammonium molybdate decomposed into
MoO3 at 340°C [18]. Supporting of ammonium
molybdate on different support surfaces changes its
decomposition temperature in the sequence:
MgO<unsupported<ZrO2, Al2O3<SiO2<Nb2O5 [19].
It was found that ammonium molybdate decomposed
at 280°C in Co3O4–MoO3/MgO system [20].
The systems NiO–MgO, MnO–MgO, ZnO–MgO
and Al2O3–MgO forming solid solutions were investi-
gated by different techniques [31–36]. In the
Al2O3–MgO system the range of solid solution was
from 0 to 20 mass% Al2O3. The lattice parameter of
MgO phase decreased with increasing the amount of
alumina due to the increased amount of Al2O3 dis-
solved in the MgO lattice with subsequent formation of
the solid solution. Calcination of (48 mass%)
MoO3-treatment of Al2O3–TiO2 [21], La2O3–TiO2,
In2O3–TiO2 [22] and Co3O4/Al2O3 [23] systems pre-
pared by impregnation had been characterized by XRD,
XPS, FTIR and O2 chemisorption techniques. The char-
acterization studies revealed that the MoO3 concentra-
tion on the surface is greater than in the bulk of the sol-
ids due to the high dispersion of MoO3 on the support
surface. Mixing of MoO3 with another oxides may lead
*
hala_elshobaky@yahoo.com
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2006 Akadémiai Kiadó, Budapest

EL-SHOBAKY
CoO/MgO at 500 and 800°C led to the formation of
An X-ray investigation of the thermal products of
the different mixed solids was performed with a Philips
diffractometer (type PW 1390). The patterns were run
with nickel filtered copper radiation (λ=1.5405 ) at
36 kV and 16 mA with scanning speed 2° in 2θ min–1.
CoO–MgO solid solution. While the calcination of
(4–48 mass%) CoO/MgO at 900°C led to formation of
Co2MgO4 compound [35].
The present investigation reports a study of
solid-solid interactions in the CuO–MoO3/MgO sys-
tem. The techniques employed were DTA, TG and
XRD. These techniques allowed us to clarify the ef-
fects of MoO3 treatment on the thermal behaviour of
mixed solids prepared by the wet impregnation
method and to identify the different phases produced
by heating the mixed solids at various temperatures.
Results and discussion
The thermal behaviour of pure and doped mixed solids
TG of CuMg–I, CuMg–I–5Mo, CuMg–III and
CuMg–III–5Mo performed. Figure 1 depicts the TG
curves of CuMg–I, CuMg–I–5Mo, CuMg–III and
CuMg–III–5Mo. The obtained curves vary between three
and six steps. The different values of mass loss processes
calculated in each process for various solids permitted to
deduce the chemical change corresponding each step.
The results obtained are given in Table 1. Inspec-
tion of Table 1 reveals the following: (i) The TG curves
of CuMg–I mixed solids consist of three steps. The first
step extends between 80 and 130°C, the second between
254.6 and 369.4°C and the last between 376.6 and
406.4°C. These steps correspond to the removal of
physisorbed water, decomposition of copper nitrate and
basic magnesium carbonate, respectively. The last two
steps can be represented by the following equations:
Experimental
Materials
Pure CuO/MgO samples were prepared by treating a
known mass of finely powdered basic magnesium car-
bonate, MgCO3·Mg(OH)2, with different amounts of
copper nitrate dissolved in the least amount of distilled
water making pastes. The proportions of copper nitrate
were calculated so that the molar compositions of the
calcined solids were 0.1CuO/MgO, 0.2CuO/MgO and
0.3CuO/MgO. The pastes thus obtained were dried at
120°C and then calcined for 5 h in air at 400, 600, 800
and 1000°C. The CuO–MoO3/MgO mixed solids were
prepared by treating a known mass of basic magnesium
carbonate with copper nitrate solution containing differ-
ent proportions of it, drying at 120°C and then treating
the dried solids with ammonium molybdate solution.
The resulting materials were then dried at 120°C and
calcined for 5 h in air at 400, 600, 800 and 1000°C. The
concentrations of ammonium molybdate solution em-
ployed corresponded to the addition of 2.5 and 5 mol%
MoO3 (with respect to the sum of MgO and CuO).
The nominal molar compositions of the calcined
mixed solids were 0.1CuO/MgO (I), 0.2CuO/MgO (II)
and 0.3CuO/MgO (III). The prepared mixed solid
specimens were designated CuMg–I, CuMg–I–2.5Mo,
0.1Cu(NO3)2+
mass loss (11.4%), 254.6–369.4°C
+0.5MgCO3·Mg(OH)2⎯⎯⎯⎯⎯⎯⎯⎯→
0.1CuO+0.5MgCO3·Mg(OH)2+0.2NO2+0.1O2
CuMg–I–5Mo,
CuMg–II,
CuMg–II–2.5Mo,
CuMg–II–5Mo, CuMg–III, CuMg–III–2.5Mo and
CuMg–III–5Mo. All chemicals employed were of an-
alytical grade and supplied BDH company.
Methods
TG and DTA of various uncalcined materials were car-
ried out using Shimadzu DTA-50H systems. The rate
of heating was kept at 10°C min–1. The analyses were
followed at temperatures between room temperature
and 1000°C with α-Al2O3 as a reference material. A
40 mg sample of each solid specimen was employed in
each case. The measurements were carried out in a cur-
rent of nitrogen flowing at a rate of 50 cm3 min–1.
Fig. 1 TG curves of uncalcined pure and MoO3-doped mixed
solids
322
J. Therm. Anal. Cal., 85, 2006

SOLID–SOLID INTERACTIONS IN CuO–MoO3/MgO SYSTEM
Table 1 TG data of pure and treated uncalcined mixed solids
Mass loss/%
calculated
–
Solid
T/°C
Decomposition steps
found
4.2
80–130
physisorbed water
0.1CuO/MgO
(CuMg–I)
254.6–369.4 11.4
376.6–406.4 34.7
11.6
decomposition of copper nitrate
decomposition of basic magnesium
carbonate
34.7
–
80–140
I) 3.04
physisorbed water
0.1CuO/MgO
+5 mol% MoO3
(CuMg–I–5Mo)
11.5 for copper
steps II+III are corresponding to
decomposition of copper nitrate+amm.
molybdate+2/3 of magnesium
hydroxide
180–220
II) 7.67
nitrate+amm. molybdate
9.2 for total magnesium
hydroxide
261–374
III) 10.06
step IV is corresponding to the
decomposition of the last
1/3 magnesium hydroxide+total
decomposition of magnesium
carbonate
374.5–450
IV) 26.08
22.6 magnesium carbonate
130–170
177–208
208–273
312–381
I) 8.2
–
physisorbed water
0.3CuO/MgO
(CuMg–III)
II) 9.97
III) 2.97
IV) 12.7
25.4 copper nitrate (the sum
of steps II+III+IV=25.64)
decomposition of copper nitrate
decomposition of basic magnesium
carbonate
397–436
V) 24.03
24.3
–
0.3CuO/MgO
90–110
I) 2.9
physisorbed water
+5mol% MoO3
(CuMg–III–5Mo)
110–170
170–210
210–300
II) 11
24.6 copper nitrate+amm.
molybdate (the sum of steps
II+III+IV=24.76)
steps II+III+IV are corresponding to
decomposition of copper nitrate+amm.
molybdate
III) 11.2
IV) 2.52
decomposition of magnesium
hydroxide
300–385
403–430
V) 6.55
6.6
decomposition of magnesium
carbonate
VI) 16.2
16.2
mass loss (34.7%), 376.6–406.4°C
0.1CuO+0.5MgCO3·Mg(OH)2⎯⎯⎯⎯⎯⎯⎯→
responds to removal of physisorbed water. The sec-
ond, third and fourth steps correspond to the decom-
position of copper nitrate besides ammonium
molybdate in CuMg–III–5Mo sample in temperature
ranges between 177–381 and 110–300°C in
CuMg–III and CuMg–III–5Mo, respectively. The fi-
nal decomposition step in CuMg–III takes place at a
temperature range between 397–436°C is the decom-
position of basic magnesium carbonate to magnesium
oxide. In case of CuMg–III–5Mo magnesium hydrox-
ide was decomposed firstly in a temperature range
300–395°C then magnesium carbonate decomposed
to magnesium oxide at a temperature range of
403–430°C. From these results it can be concluded
that ammonium molybdate doping of copper nitrate
and basic magnesium carbonate mixed solids en-
hanced the thermal decomposition of both copper ni-
trate and magnesium hydroxide which decomposed at
temperatures lower than those in case of the undoped
mixed solids by 70 and 100°C, respectively.
0.1CuO+MgO+0.5CO2+0.5H2O
(ii) CuMg–I–5–Mo mixed solids decompose via
four steps. The thermal change accompanying each
step is given in the last column in Table 1. These
changes can be represented by the following reactions:
0.1Cu(NO3)2+0.05/7(NH4)6Mo7O24+
mass loss (14.4%), 180–374°C
+0.5MgCO3·Mg(OH)2⎯⎯⎯⎯⎯⎯⎯→
0.1CuO+0.05MoO3+0.17MgCO3·Mg(OH)2+
+0.33MgO+0.333MgCO3+0.2NO2+0.043NH3+
0.355H2O+0.23O2
0.1CuO+0.05MoO3+0.17MgCO3·Mg(OH)2+
mass loss (26.08%),374.5–450°C
0.33MgO+0.33MgCO3⎯⎯⎯⎯⎯⎯⎯→
0.1CuO+0.05MoO3+0.5MgO+0.25O2+
+0.5CO2+0.17H2O
The produced evolved NO2, O2, CO2 and NH3
have not been detected and their formation was spec-
ulatively suggested in the light of TG measurements.
(iii) CuMg–III and CuMg–III–5Mo were decomposed
via five and six steps, respectively. The first step cor-
DTA curves of CuMg–II, CuMg–II–5Mo,
CuMg–III and CuMg–III–5Mo were determined and
J. Therm. Anal. Cal., 85, 2006
323

EL-SHOBAKY
illustrated in Fig. 2. The DTA curves of CuMg–II,
sults are summarized in Table 2 which shows the effect
of calcination temperature, CuO content and dopant
concentration on the peak height of some selected peaks
located at certain d-spacings relative to individual ox-
ides and produced compounds. Table 2 reveals that the
diffractograms of various mixed solid samples and those
treated with MoO3 precalcined in air at 400°C consist of
diffraction peaks of well crystalline MgO phase and
CuO phase with moderate degree of crystallinity. The
mixed solid samples treated with 5 mol% MoO3 consist
of magnesium molybdate MgMoO4 as a minor phase
besides the MgO and CuO phases. The formation of
MgMoO4 is accompanied by a progressive decrease in
the peak height of the diffraction peaks characteristic to
MgO phase. It can also be seen that doping of the inves-
tigated system with 5 mol% MoO3 decreases the peak
height of all diffraction peaks of CuO phase. This ob-
served decrease in the peak height of the CuO peaks
may be attributed to possible solid-solid interaction be-
tween CuO and MoO3 with production of an amorphous
CuMoO4 phase.
CuMg–II–5Mo, CuMg–III exhibit six endothermic
peaks while DTA curves of CuMg–III–5Mo consist
of seven endothermic peaks. The minima of these
peaks are found at 90–100, 191–205, 295, 338,
378–392, 410–434 and 930°C. Most of these peaks
are strong and sharp. The first set of peaks indicates
the departure of physisorbed water. The set of peaks
located at 191–205 and 295°C correspond to the ther-
mal decomposition of copper nitrate and ammonium
molybdate in case of the doped samples. The peak lo-
cated at 338°C is found only in CuMg–III–5Mo sam-
ple which is indicative for the decomposition of mag-
nesium hydroxide. The peaks located at 378–392°C
and 410–434°C characterize the thermal decomposi-
tion of basic magnesium carbonate in case of
CuMg–II, CuMg–II–5Mo, CuMg–III and indicative
for the decomposition of magnesium carbonate in
case of CuMg–III–5Mo. The final endothermic peaks
located at 930°C correspond to the formation of a new
CuO–MgO compound. The identification of the
newly formed compound will be examined by XRD
investigation of the solids preheated at 1000°C.
Preliminary experiments showed that the ther-
mal decomposition of ammonium molybdate in air at
400°C resulted in the formation of well crystalline
orthorhombic MoO3. The fact that the amounts of
MoO3 added (4 and 8 mass% MoO3) is below the de-
tection limit of X-ray diffractometer might suggest
that most of molybdenum species added was concen-
trated in the uppermost surface layers of the mixed
solids. In other words, the concentration of MoO3 on
the top surface layers should be much greater than the
nominal amount added. This behaviour is expected
because doped solids were prepared by the wet im-
pregnation method and not by coprecipitation [37].
The absence of all diffraction peaks of MoO3 in the
patterns of the mixed oxides indicates its complete
conversion into MgMoO4 and CuMoO4 phases.
The X-ray diffractograms of different pure
mixed solids investigated precalcined at 400°C re-
vealed also that the increase in the concentration of
CuO from 0.1 to 0.3 mol/mol MgO is accompanied by
an increase in the degree of crystallinity CuO phase
and a decrease in the peak height of MgO phase. So,
the increased concentration of CuO inhibits the crys-
tallization of MgO.
XRD investigation of various solids
X-ray diffractograms of various mixed solids preheated
at 400, 600, 800 and 1000°C were measured. These re-
Table 2 shows that for pure and doped mixed ox-
ide solids, raising the calcination temperature to
600°C is accompanied by an increase in the peak
heights of MgO, CuO and MgMoO4 phases besides
the appearance of the diffraction peaks of CuMoO4
phase upon doping with 5 mol% MoO3. For the pure
and MoO3 treated CuMg–II solids the intensities of
the diffraction peaks relative to MgMoO4 increase as
a function of MoO3 added. The increase in the abun-
dance of MgMoO4 and the formation of CuMoO4
Fig. 2 DTA curves of uncalcined pure and MoO3-doped
mixed solids
324
J. Therm. Anal. Cal., 85, 2006

SOLID–SOLID INTERACTIONS IN CuO–MoO3/MgO SYSTEM
Table 2 The effect of precalcination temperature and composition on the height of some diffraction lines h (a. u.*)
d=3.35 
Tcalcination
/
d=3.29  d=1.93 
68% CuMoO4 21% MgMoO4
d=2.28 
100% Cu2MgO3
d=1.216  d=1.87 
26% MgO 32% CuO
67% CuMoO4+
100% MgMoO4
Solid
°C
0.1CuO/MgO
70
65
47
65
59
32
48
37
28
5
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
+2.5 mol% MoO3
+5 mol% MoO3
0.2CuO/MgO
–
–
–
1.5
–
18
11
8
+2.5 mol% MoO3
+5 mol% MoO3
0.3CuO/MgO
400
–
2.5
6
40
30
18
–
–
+2.5 mol% MoO3
+5 mol% MoO3
–
–
4
15
0.1CuO/MgO
100
90
80
85
78
62
65
59
40
15
12
9
–
–
–
–
–
–
–
–
–
–
–
–
–
+2.5 mol% MoO3
+5 mol% MoO3
0.2CuO/MgO
5
22
32
–
7
6
28
23
17
42
36
29
–
–
–
+2.5 mol% MoO3
+5 mol% MoO3
0.3CuO/MgO
600
9
11
–
35
62
–
12
–
+2.5 mol% MoO3
+5 mol% MoO3
–
11
14
43
84
18
0.1CuO/MgO
148
132
118
135
120
110
102
87
32
21
–
–
–
–
–
–
–
–
–
–
–
–
+2.5 mol% MoO3
+5 mol% MoO3
0.2CuO/MgO
11
29
–
15
31
–
108
210
–
18
75
+2.5 mol% MoO3
+5 mol% MoO3
0.3CuO/MgO
800
69
25
52
–
14
32
–
104
233
–
58
102
90
+2.5 mol% MoO3
+5 mol% MoO3
16
31
11
17
87
66
75
138
0.1CuO/MgO
194
176
169
163
144
139
145
120
115
–
–
–
–
–
–
–
–
–
–
14
35
–
–
13
29
–
–
89
185
–
–
–
+2.5 mol% MoO3
+5 mol% MoO3
0.2CuO/MgO
–
–
+2.5 mol% MoO3 1000
+5 mol% MoO3
23
35
–
10
20
–
88
147
–
–
–
0.3CuO/MgO
63
50
35
+2.5 mol% MoO3
+5 mol% MoO3
8
8
53
100
17
17
*a. u. arbitrary unit; d is the d spacing
phases are evidenced by the progressive decrease in
the peak height of the diffraction peaks of MgO and
CuO phases.
concentration of CuO from 16.67 to 23.08 mol%
(0.2CuO/MgO, 0.3CuO/MgO). In the case of
CuMg–II–5Mo, the peak height at 1.216  (MgO
phase 26%), 3.289  (CuMoO4 phase 68%) and at 1.93
 (MgMoO4 phase 21%) were found to decrease from
110 to 66 (a. u.), 52 to 31 (a. u.) and 32 to 17 (a. u.), re-
spectively (Table 2). This finding may be discussed in
terms of a possible dissolution of CuO in MgO matrix
forming a solid solution. This speculation is confirmed
by the observed limited increase in the lattice parame-
ter (Table 3) of MgO (ionic radius of Mg2+=0.66 )
upon increasing the concentration of CuO (ionic radius
of Cu2+=0.72 ). The lattice parameter of MgO in pure
mixed oxide solids precalcined at 800°C increased
from 4.2058 to 4.2145 . Also the lattice parameter of
MgO in heavily doped mixed oxide solids calcined at
800°C increased from 4.2020 to 4.2116  (Table 3).
The observed limited increase in the lattice parameter
The diffractograms of pure mixed solid oxides
CuMg–I, CuMg–II and CuMg–III solids and those
treated with 2.5 and 5 mol% MoO3 and then
precalcined at 800°C (Table 2) consisted of MgO and
CuO phases, are similar to all investigated mixed sol-
ids preheated at 600°C. Moreover, the diffraction
peaks of MgMoO4 and CuMoO4 appeared in case of
other solid samples treated with 2.5 and 5 mol% MoO3
and preheated at 800°C. It is clear that the increase in
both the calcination temperature and the amount of
MoO3 added enhanced much the solid–solid interac-
tions between MoO3 and both MgO and CuO produc-
ing MgMoO4 and CuMoO4. On the other hand, the
peak heights of MgO, MgMoO4 and CuMoO4 suffer a
measurable decrease (Table 2) due to increasing the
J. Therm. Anal. Cal., 85, 2006
325

EL-SHOBAKY
Table 3 Lattice parameter of pure and heavily MoO3-doped
CuO/MgO mixed solids
of MgO phase may be attributed to the small differ-
ence in the ionic size of Mg2+ and Cu2+. The decrease
in the peak heights of MgO, MgMoO4 and CuMoO4
due to increasing the concentration of CuO from 0.2 to
0.3 mol/mol MgO may indicate that CuO much prefer-
ably dissolves in MgO lattice rather than interacting
with MoO3 producing a solid solution.
Lattice
Tcalcination/°C
Solid
parameter/
0.1CuO/MgO
0.2CuO/MgO
0.3CuO/MgO
4.1980
4.2029
4.2092
400
Table 2 shows that the diffractograms of the pure
and doped CuMg–I, CuMg–II and CuMg–III solids
precalcined at 1000°C consist, only, of the diffraction
peaks of MgO phase and new diffraction peaks char-
acteristic to Cu2MgO3 phase in case of pure and
doped CuMg–III (rich in CuO only) besides the
MgMoO4 and CuMoO4 phases. In fact, the observed
endothermic peak located at 930°C in the case of the
system rich in copper stands as evidence for the for-
mation of Cu2MgO3 phase. The absence of any dif-
fraction peaks of this compound in the case of pure
and MoO3–doped CuMg–II precalcined at 1000°C al-
though the appearance of endothermic peak at 930°C
suggests that its amount is below the detection limit of
the X-ray diffractometer.
0.1CuO/MgO
0.2CuO/MgO
0.3CuO/MgO
4.2019
4.2070
4.2119
600
800
0.1CuO/MgO
0.2CuO/MgO
0.3CuO/MgO
4.2058
4.2130
4.2145
0.1CuO/MgO
0.2CuO/MgO
0.3CuO/MgO
4.2074
4.2150
4.2190
1000
400
0.1CuO–5MoO3/MgO
0.2CuO–5MoO3/MgO
0.3CuO–5MoO3/MgO
4.1975
4.2002
4.2025
0.1CuO–5MoO3/MgO
0.2CuO–5MoO3/MgO
0.3CuO–5MoO3/MgO
4.1985
4.2035
4.2085
600
0.1CuO–5MoO3/MgO
0.2CuO–5MoO3/MgO
0.3CuO–5MoO3/MgO
4.2020
4.2057
4.2116
The complete disappearance of all diffraction
peaks of CuO as a separate phase in all solids
precalcined at 1000°C clearly indicates its complete
dissolution in MgO lattice forming CuO–MgO solid
solution as detected from Table 3 which shows that
the lattice parameter of MgO decreased progressively
by increasing the amount of CuO. The diffraction
lines of this new compound are separated only at the
highest concentration of CuO. Table 2 reveals that
raising the calcination temperature to 1000°C is ac-
companied by: (i) An increase in peak height of MgO
indicating an effective improvement in its degree of
crystallinity. (ii) A decrease in the intensities of the
diffraction peaks of CuMoO4 phase as a result of an
enhanced formation of Cu2MgO3. (iii) The peak
heights of MgMoO4 were not changed on raising the
calcination temperature from 800 to 1000°C. This
finding suggests that the solid–solid interactions be-
tween MoO3 and MgO reach their maximum limit at
800°C i.e raising the calcination temperature to
1000°C did not affect the enhancement of the
MgMoO4 formation. (iv) The intensity of the
Cu2MgO3 peaks decreased on doping with MoO3 due
to the CuO–MoO3 interactions. In other words,
MoO3-doping of the system investigated opposes the
formation of Cu2MgO3 compound.
800
0.1CuO–5MoO3/MgO
0.2CuO–5MoO3/MgO
0.3CuO–5MoO3/MgO
4.2064
4.2100
4.2155
1000
in calcination temperature above this limit led to an
enhanced formation of CuO–MgO compound. In fact
at 1000°C the sample rich in CuO gave some diffrac-
tion peaks of Cu2MgO3 phase, indicating that most of
CuO underwent solid–solid interaction with MgO at
such high temperature.
Conclusions
• Ammonium molybdate doping of the investigated
mixed solids much stimulates the thermal decomposi-
tion of copper nitrate and dehydroxylation of basic
magnesium carbonate by 70 and 100°C, respectively.
• MoO3 interacted readily with magnesium oxide and
copper oxide at temperatures starting from 400°C to
produce MgMoO4 and CuMoO4,which remained
thermally stable up to 1000°C.
• A portion of copper oxide reacts with MoO3 to
yield CuMoO4 while the other portion dissolved
completely in the matrix of MgO producing
CuO–MgO solid solution.
Inspection of Table 3 shows clearly that the pro-
gressive increase of MgO lattice due to dissolution of
some of copper ions is maximum at 400°C and mini-
mum at 1000°C in case of the pure solid samples. This
finding might indicate that heat treatment of MgO
treated with CuO species at 400°C led mainly to the
formation of CuO–MgO solid solution. The increase
• Copper oxide interacted readily with MgO at 930°C
yielding a new compound of formula Cu2MgO3
compound.
326
J. Therm. Anal. Cal., 85, 2006

SOLID–SOLID INTERACTIONS IN CuO–MoO3/MgO SYSTEM
21 B. M. Reddy, B. Chowdhurya, E. P. Reddy and
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327