Synthesis, characterization and the thermal decomposition of potassium tris(oxalato)lanthanum(III)nonahydrate

Article abstract of DOI:10.1016/S0040-6031(99)00152-5

Potassium tris(oxalato)lanthanum(III)nonahydrate, K₃[La(III)(C₂O₄)₃]·9H ₂O, has been synthesized and characterized by elemental analysis and IR spectral studies. Thermal studies (TG, DTG and DTA) in air showed that the anhydrous compound formed at ca. 192°C. The final end product at 1000°C was shown to be a mixture of La₂O₃, K₂CO₃, K₂O, KLaO₂ and La₂C₃, through the formation of an intermediate mixture of K₂C₂O₄ and K[La(C₂O₄)_x] (where 1.5 < x < 2) at ca. 293°C, and K₂C₂O₄ and La₂O₂CO₃ at ca. 528°C. DSC study in nitrogen upto 650°C showed that the end product was a mixture of K₂C₂O₄ and La₂O₂CO₃. The kinetic parameters, mainly E^* of the dehydration and decomposition steps in TG, were calculated using four non-mechanistic equations. The kinetic parameters, E^*, ΔH, ΔS obtained from DSC study are discussed. Some of the decomposition products were identified by IR and X-ray powder diffraction studies. A tentative mechanism for the decomposition in air is proposed.

Full text of DOI:10.1016/S0040-6031(99)00152-5

Thermochimica Acta 338 (1999) 27±33
Synthesis, characterization and the thermal decomposition of
potassium tris(oxalato)lanthanum(III)nonahydrate
*
N. Deb
Department of Chemistry, North Eastern Regional Institute of Science and Technology, Nirjuli 791109, Arunachal Pradesh, India
Received 26 November 1998; received in revised form 23 April 1999; accepted 15 June 1999
Abstract
Potassium tris(oxalato)lanthanum(III)nonahydrate, K
elemental analysis and IR spectral studies. Thermal studies (TG, DTG and DTA) in air showed that the anhydrous compound
formed at ca. 1928C. The ®nal end product at 10008C was shown to be a mixture of La , K CO , K O, KLaO and La
through the formation of an intermediate mixture of K and K[La(C ] (where 1.5 < x < 2) at ca. 2938C, and K
3
[La(III)(C
2
O
4
)
3
2
]Á9H O, has been synthesized and characterized by
2
O
3
2
3
2
2
2 3
C ,
2
C
2
O
4
2
O
4
)
x
2 2 4
C O
and La O CO at ca. 5288C. DSC study in nitrogen upto 6508C showed that the end product was a mixture of K C O and
2
2
3
2 2 4
*
. The kinetic parameters, mainly E of the dehydration and decomposition steps in TG, were calculated using four
La
2
O
2
CO
3
*
non-mechanistic equations. The kinetic parameters, E , ÁH, ÁS obtained from DSC study are discussed. Some of the
decomposition products were identi®ed by IR and X-ray powder diffraction studies. A tentative mechanism for the
decomposition in air is proposed. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Thermal decomposition; TG±DTA; DSC; Activation energy; X-ray diffraction
1
. Introduction
4608C led [5] to a mixture of K CO and free iron.
2
3
Bancroft et al. [6] have also examined the thermal
decomposition of K [Fe(OX) ] and suggested the
A comprehensive review of oxalato complexes of
3
3
transition and non-transition metals of various types
and their applicability may be found elsewhere [1].
Wendlandt and George [2] studied K [M(OX) ]ÁxH O
presence of K [(C O ) Fe(OX)Fe(C O ) ] (OX ˆ
6
2
4 2
2 4 2
quadridentate oxalato group) as intermediate. The
®nal residue of thermal decomposition of
K [Al(OX) ] has been reported [7] as a mixture of
3
3
2
(
where M ˆ Cr, Fe, Co and Rh) by thermogravimetry.
3
3
Due to photosensitive nature these compounds,
Al O , K CO and K O. The thermal decomposition
2 3 2 3 2
K [M(OX) ] (where M ˆ Mn, Co) have also been
reactions of a number of metal oxalato complexes of
potassium of the type, K [M(OX) ]ÁxH O (where
3
3
studied by Wendlandt and Simmons [3,4], where
the bivalent metal complexes of the type,
K [M(OX) ] were formed as intermediates. The ther-
3
3
2
M ˆ Al, V, Cr, Mn, Fe, Co, Rh) and
K [M(OX) ]ÁxH O (where M ˆ Cu, Zn, Pd, Pt) were
2
2
2
2
2
mal decomposition of K Fe(OX) in nitrogen beyond
3
studied [8] in helium atmosphere. The decomposition
pattern of all the complexes were compared. The
thermolysis of alkali tris(oxalato/malonato)ferrate-
s(III) have been studied [9,10], where the decom-
3
*Fax: +91-360-244307
E-mail address: ndeb@nerist.ernet.in (N. Deb)
position
mode
in
both
the
precursors,
0040-6031/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ( 9 9 ) 0 0 1 5 2 - 5

2
8
N. Deb / Thermochimica Acta 338 (1999) 27±33
M [Fe(C O ) ]ÁxH O and M [Fe(CH C O ) ]ÁxH O
3. Results and discussion
3
2
4 3
2
3
2
2
4 3
2
(
where M ˆ Li, Na, K) are similar. Due to complexing
ability and oxidation state sensitivity, the iron carbox-
ylates of alkali metal are used as inorganic precursors
for the preparation of ferrites. Although, the potas-
sium bis/tris(oxalato)metallates of various types
have been studied, the complexes with lanthanum
are still scarce. Therefore, in continuation of our work
on oxalato complexes [11±16] as well as the recent
work [17] on the type M [La(C O ) ]ÁxH O (where
3.1. Characterization of complex
The complex, K [La(III)(C O ) ]Á9H O, is
3
2
4 3
2
obtained as a white powder. It is insoluble in water
or in common organic solvents, but decomposes in
strong acid or alkali. The water analysis revealed that
the compound contains nine molecules of water. The
microanalytical data and estimated metal contents
show good agreement for the proposed formula of
the complex. The IR peaks are assigned (Table 1) like
earlier studies [11±18,33], which shows the presence
3
2
4 3
2
x ˆ 9 for M ˆ Li and x ˆ 8 for M ˆ Na), the thermal
decomposition of hitherto unknown potassium tris-
(
oxalato)lanthanum(III)nonahydrate has been under-
of a chelated C2O2 group.
�
taken. Keeping in view the possibility of formation
of metal oxide or mixed metal oxide and their possible
catalytic applicability, the study reveals the impor-
tance of the thermal decomposition mode of precursor
to obtain the desired end product. This communica-
tion reports the synthesis, characterization and the
thermal decomposition of potassium tris(oxalato)-
4
3.2. Decomposition of complex
The thermal pro®les (TG, DTG and DTA) of
K [La(III)(C O ) ]Á9H O, are shown in Fig. 1. In
3
2
4 3
2
the TG curve, the ®rst water molecule is removed
at 908C and a plateau at 1678C indicates the elimina-
tion of the remaining seven molecules of water (mass
loss, found, 20.5%; calcd., 21.12%). The compound
become anhydrous at ca. 1928C (found, 24%; calcd.,
23.76%). Nature of DTG change between 358C and
lanthanum(III)nonahydrate,
K [La(C O ) ]Á9H O,
3
2
4 3
2
in air and nitrogen. The kinetic parameters of
each step of the decomposition are calculated and
a tentative scheme of the decomposition is also
proposed.
2
158C shows the stepwise deaquation. An endother-
mic peak in DTA between 908C and 1808C
2
. Experimental
(ÁT ˆ 1378C) corresponds to dehydration. The
min
*
E (activation energy) (Table 2) of the dehydration
The chemicals used were of A.R. grade purity. The
step calculated from TG slope using non-mechanistic
equations, Freeman and Carroll [19], Flynn and Wall
[20], Coats and Redfern [21] and MacCallum±Tanner
preparative method is an extension of the methods
adopted [11±16] for bimetallic oxalato complexes.
Lanthanum hydroxide, prepared from lanthanum
chloride, was made free from chloride. It was dis-
solved in glacial acetic acid and heated on a steam
bath. Then stoichiometric quantities of a solution of
potassium chloride was added. Awhite compound was
precipitated by dropwise addition of hot saturated
solution of oxalic acid. The compound was ®ltered
off and puri®ed by standard procedures [18]. The
water contents were determined gravimetrically [18]
and thermogravimetrically. The metal contents were
estimated by a literature method [16]. Carbon and
hydrogen contents were estimated on a Carlo±Erba
Table 1
3 2 4 3 2
Selected bands in the IR spectrum of K [La(III)(C O ) ] 9H O
� 1
IR bands (cm
)
Assignments
2
1
1
880±3760b
ꢀ
sy (O±H) ‡ ꢀasy(O±H) or hydrogen bonding
sy(H±O±H)
asy(C=O)
ꢀsy(C±O) and/or ꢀ(C±C)
ꢀsy(C±O) and/or ꢁ(O±C=O)
630S
ꢁ
500±1800b
ꢀ
1365s
1320mS
800mS
ꢀ(La±O) and/or ꢁ(O±C=O) or coordinated
water
6
5
00s
24s
Water of crystallization
ꢀ
sy(C±C) and/or ring deformation
1
108 elemental analyser.
IR spectra, thermal data (DTA, TG, DTG and DSC)
445m, 400s
345s
ꢀ(La±O) and/or ring deformation
ꢁ(O±C=O)
Out-of-plane bending
310vs
and X-ray powder diffraction patterns were recorded
as described earlier [16].
b, broad; S, strong; s, small; vs; very small; m, medium.

N. Deb / Thermochimica Acta 338 (1999) 27±33
29
Fig. 1. TG, DTG and DTA curves of K
3
[La(III)(C
2
O
4
)
3
2
]Á9H O in air.
equation [22] are found to be in good agreement with
each other. Further, a small endothermic peak in DTA
at 1908C is due to removal of the last remaining water
molecule and may be due to rearrangement of an
anhydrous species which separates as K C O and
K[La(C O ) ]. Further, corresponding to a change at
2 4 2
ca. 2838C in DTG and a small endotherm at 2808C in
DTA, in TG a small but distinct step (277±2938C) is
observed. The mass loss of 29% at 2938C apparently
suggests [4] the intermediate is a mixture of
2
2 4
Table 2
Kinetic data evaluated by the methods, (a) Freeman and Carroll, (b) Flynn and Wall, (c) Coats and Redfern and (d) MacCallum±Tanner
equation
*
E (kJ mol
� 1
� 1
A (s )
Compound
[La(C
Step
1
Method
)
Order of reaction
Reaction
K
3
2
O
4
)
3
]
a
b
c
d
34.00
35.40
35.12
34.70
2
9H O
1.0
8
4.60 Â 10
Dehydration
8
3.85 Â 10
2
3
a
b
c
d
40.16
41.00
40.00
39.96
1.0
1.0
6
6
5.17 Â 10
3.73 Â 10
Decomposition
Decomposition
a
b
c
d
152.00
150.50
152.70
153.60
7
7.5 Â 10
8
9.6 Â 10

3
0
N. Deb / Thermochimica Acta 338 (1999) 27±33
Table 3
X-ray powder diffraction pattern of the pyrolysed products of
[La(III)(C ]9H O at 3408C, 5508C and 9708C
Table 3 (Continued )
Pyrolysed product
K
3
2
O
4
)
3
2
Ê
Ê
Ê
d (A) (at 3408C)
d (A) (at 5508C)
d (A) (at 9708C)
Pyrolysed product
0
0
.8840
.8702
0.8656
0.8688
0.8554
0.8513
0.8466
0.8456
0.8415
0.8378
0.8326
0.8296
0.8276
0.8245
0.9766
0.9638
0.9544
0.9509
0.9420
0.9377
0.9295
0.9270
0.9213
0.9161
0.9093
0.9031
0.8948
0.8884
0.8780
0.8742
0.8698
0.8648
0.8568
0.8525
0.8457
0.8411
0.8352
0.8313
0.8277
Ê
Ê
Ê
d (A) (at 3408C)
d (A) (at 5508C)
d (A) (at 9708C)
2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.2055
.1428
.0016
.9541
.8649
.7789
.7083
.6795
.6501
.6175
.5727
.5339
.5123
.4782
.4572
.4231
.3964
.3775
.3621
.3441
.3105
.2824
.2742
.2639
.2400
.2200
.2004
.1886
.1709
.1519
.1359
.1272
.1033
.0778
.0661
.0528
.0204
.0136
.9962
.9805
.9748
.9680
.9612
.9464
.9423
.9350
.9233
.9100
.9042
.8992
.8962
.8870
2.1021
2.0147
1.9581
1.8822
1.8224
1.7765
1.7548
1.7001
1.6465
1.6174
1.5947
1.5731
1.5530
1.5353
1.4993
1.4838
1.4479
1.4140
1.3639
1.3577
1.3488
1.3200
1.3058
1.2632
1.2346
1.1947
1.1752
1.1655
1.1477
1.1185
1.1072
1.1002
1.0553
1.0379
1.0272
1.0014
0.9884
0.9881
0.9745
0.9657
0.9528
0.9311
0.9239
0.9147
0.9072
0.8980
0.8946
0.8894
0.8841
0.8785
0.8719
0.8690
2.1238
2.0763
2.0000
2.0019
1.9468
1.8895
1.8853
1.8638
1.7837
1.7811
1.7494
1.6895
1.6486
1.6125
1.5842
1.5582
1.5131
1.4993
1.4520
1.4305
1.3996
1.3821
1.3675
1.3439
1.3161
1.2922
1.2858
1.2679
1.2538
1.2365
1.2048
1.1905
1.1735
1.1637
1.1548
1.1507
1.1338
1.1222
1.1116
1.0791
1.0727
1.0528
1.0457
1.0395
1.0337
1.0175
1.0108
1.0055
1.0021
0.9930
0.9885
0.9818
0.8624
0.8556
0.8486
0.8458
0.8417
0.8390
0.8337
0.8268
0.8229
1/2K C O and K [La(C O ) ] (calcd. mass loss,
2
2
2
4
2 4 2
3
0.21%). Moreover, K Fe(C O ) is reported
2 2 4 2
[23,24] as intermediate in the decomposition of
K [Fe(C O ) ]. Although, the formation of intermedi-
3
2 4 3
II
ates with reduction of iron species, like K Fe ꢀOX†
6
2
5
II
are reported [10,25±27]; the existence of La is not
found in this study. As the product formed at 2938C is
stable upto 3928C in TG, the pyrolysed product at
3
and IR study. The XRD data (Table 3) con®rmed [28]
408C is subjected to X-ray powder diffraction (XRD)
the presence of K C O . The other mismatched d-
2
2 4
values may be due to K[La(III)(C O ) ]. The IR
spectrum shows the presence of a C O4 group. It
is concluded that the product at 2938C in TG is likely
2
4 x
2�
2
[
17] to be a mixture of K C O and K[La(III)(C O ) ]
2 2 4 2 4 x
(where 1.5 < x < 2). Similar partial fragmentation of
an oxalate group can be found elsewhere [15,29]. The
inclined slope in TG upto 5288C, with a mass loss of
4
dioxycarbonate, La O CO . Prior to the formation of
9.3%, indicates further decomposition to lanthanum
2
2
3
mixture of K C O and 1/2La O CO (calcd. mass
2
2
2
4
2
3
loss, 48.55%), in TG two clear breaks at 4528C and

N. Deb / Thermochimica Acta 338 (1999) 27±33
31
4
mass loss, apparently suggests the intermediate is
808C are displayed. The break at 4808C with 46%
tion. The mixture of K CO and 1/2La O CO at
2 3 2 2 3
7708C (calcd.mass loss, 52.64%) further decomposes
as shown by a slope in TG upto 8368C. The mass loss
of 57% at 8368C indicates the product is a mixture of
K CO3 and 1/2La O3 (calcd. loss 55.87%). DTG
transient which may be a mixture of K C O and
2 4
2
lanthanum oxycarbonate, 1/2La O(CO ) (calcd.
2
3 2
mass loss, 45.32%). The type of DTG changes
between 3908C and 5358C corresponds to the above
changes. Moreover, the respective exothermic (i.e.
oxidative decomposition of K[La(C O ) ]) and
2
2
change in the range 768±8428C is for the above
changes. The mass loss in TG continues due to melting
of K CO to K O. The K CO melts [32] at 9108C.
2
4 x
2
3
2
2
3
endothermic peaks (i.e. due to changes of La O(CO )
2
The solid±solid reaction of K CO and K O (molten
state) with La O at high temperature yields potassium
2 3
3 2
2 3 2
to La O CO ) at 4208C and 4508C followed by
2
2
3
exothermal nature upto 5088C in the DTA pro®le
supports the TG changes. The E values (Table 2)
calculated from TG curve (392±5288C portion) using
four non-mechanistic equations [19±22] are found to
be in excellent agreement. The product formed at
lanthanite, KLaO . The mass loss of 59.5% at 10008C
2
*
in TG supports the presence of 1/2K O, 1/2K CO and
1/2La O (calcd. 59.10%) in the ®nal residue. The IR
2 3
2
2
3
�
1
bands at 710, 670, 640 and 415 cm of the gray white
calcined product at 9708C for 30 min suggests [31] the
presence of K CO3 and La O . The XRD data
5
288C in TG is stable over a long temperature range;
2
2 3
the pyrolysed product at 5508C shows the IR bands at
ca. 1650 and 1615 cm , which indicates the presence
(Table 3) con®rmed [28] the presence of La O ,
3
2
�
1
K CO (trace), K O and KLaO . A trace of La C
2 3 2 2 2 3
[
®
1] of K C O . The XRD data (Table 3) further con-
2 4
is also detected from XRD data as carbon formed due
to disproportionation of CO(g) to CO (g) reacts with a
2
rmed the presence of K C O along with a trace of
2
2
4
2
*
portion of La O at high temperature. The E values
K CO . The remaining mismatched d-values may be
�
due to La O CO . Further IR bands due to CO
3
2
3
2 3
2
calculated for the ®nal TG step (770±8368C portion)
are shown in Table 3. The values are found to be
similar for all the methods [19±22]. The DSC pro®le
(Fig. 2) in nitrogen shows several endothermic peaks.
The peaks are integrated and the kinetic parameters
are included in Table 4. A large endotherm between
31.38±179.618C (Fig. 2a) including a shoulder peak in
the range 91.52±109.718C (Fig. 2b) are for the step-
wise release of water. Immediately after the dehydra-
tion step, a small endothermic peak between 185.02±
2
2
3
group at 1360±1550, 1030, 670 (also due to
�
1
K CO ) and ca. 845 cm gives credence [29,30] to
2
3
the presence of a dioxycarbonate of lanthanum. In TG,
2
% mass loss up to 7708C (obs. 51.3%) from 5288C,
may be due to decomposition of potassium oxalate to
K CO . However, K C O decomposes [10] to K CO
3
2
3
2
2
4
2
at 7008C. The trace of K CO identi®ed from XRD
data indicates that the decomposition of K C O starts
before 5508C where La O CO acts as a catalyst. The
IR band at ca. 670 cm and another at ca. 710 cm
are due [31] to K CO . Moreover, the presence of a
trace of KCO and LaCO cannot be ruled out as
detected [28] from XRD data (Table 3), which is
due to reaction of CO(g) evolved during decomposi-
2
3
2
2 4
2
�
2
3
1
� 1
*
1958C (Fig. 2c) with large E value suggests some
rearrangement of anhydrous form which may take
place very slowly and is quite stable. Further endother-
mic decomposition of the species takes place and
corresponds to another medium endotherm in the
2
3
Table 4
DSC data of K
3
[La(III)(C
2
O
4
)
3
2
]Á9H O in nitrogen
*
Step
Temperature
Peak Temperature ln k
(8C)
0
E
ÁH
(kJ mol
ÁS
(JK mol )
Order of
reaction
�
1
)
� 1
� 1
� 1
range (8C)
(kJ mol
)
a
81.38±179.61
91.51±109.71
138.25
101.59
26.87 Æ 0.58
214.97 Æ 4.64
106.32 Æ 2.29
676.86 Æ 14.62
287.55
4.50
699.20
12.02
1.14 Æ 0.02
1.97 Æ 0.04
b
(shoulder peak)
c
d
e
f
185.02±195.00
270.77±295.28
299.68±302.93
312.57±320.69
423.75±500.53
190.00
284.60
301.16
316.73
453.66
290.93 Æ 6.28
195.01 Æ 4.21
1539.39 Æ 33.25
303.47 Æ 6.55
58.80 Æ 1.27
1129.38 Æ 24.39
918.06 Æ 19.83
7355.00 Æ 158.89
1501.83 Æ 32.45
387.02 Æ 8.36
2.59
16.11
0.14
5.60
28.89
0.25
1.33 Æ 0.02
1.39 Æ 0.03
2.02 Æ 0.04
0.81 Æ 0.01
1.29 Æ 0.02
0.42
0.72
g
50.20
69.08

3
2
N. Deb / Thermochimica Acta 338 (1999) 27±33
Fig. 2. DSC curves of K
3
[La(III)(C
2
O
4
)
3
2
]Á9H O in nitrogen.
range 270.77±295.288C (Fig. 2d). The product at this
stage may be similar to the product assumed at 2938C
from TG study in air. The E value (Table 4) of this
loss of 48.22% of the annealed sample upto 6508C
indicates the formation of K C O and 1/2La O CO
(calcd. loss 48.55%).
2
2
4
2
2
3
*
step is also very high. Immediately after this step, two
very small endotherms are observed (Fig. 2e and f).
Further, the ¯at endothermic nature of the DSC curve
between 423.75±500.538C (Fig. 2g) is for ®nal
decomposition in this study in nitrogen. The mass
The water vapour, carbon monoxide and carbon
dioxide evolved during decomposition were identi®ed
by IR spectroscopy [33].
Above study suggests the following tentative
mechanism for the thermal decomposition in air.
908C
1678C
K ‰LaꢀC O † Š Á 9H O
K ‰LaꢀC O † Š Á 8H Oꢀs† ‡ H Oꢀv†
K ‰LaꢀC O † Š Á H Oꢀs† ‡ 7H Oꢀv†
3
2
4 3
2
3
2
4 3
2
2
3
2
4 3
2
2
ca: 1908C
ca: 2938C
K2C2O4ꢀs† ‡ K‰LaꢀC2O4† Šꢀs† ‡ H2Oꢀv†
K2C2O4ꢀs† ‡ K‰LaꢀC2O4† Šꢀs†
2
x
4808C
5288 C
ꢀ
where1:5 < x < 2† ‡ lCOꢀg†
K2C2O4ꢀs† ‡ 1=2La2OꢀCO3† ꢀs†‡mCOꢀg†‡nCO2ꢀg†
2
5
28� 7708C
K C O ꢀs† ‡ 1=2La O CO ꢀs† ‡ pCO ꢀg†
K C O ꢀs†ꢀtrace† ‡ K CO ꢀs†
2
2
4
2
2
3
2
2
2
4
2
3
pyrolysed product at 5508C
770� 8368C
‡
1=2La2O2CO3ꢀs† ‡ xCOꢀg†
K2CO3ꢀs† ‡ 1=2La2O3ꢀs†‡yCOꢀg†‡zCO2ꢀg† ‡ Cꢀs†
1
0008C
1
=2La O ꢀs† ‡ 1=2K CO ꢀs† ‡ 1=2K Oꢀs† ‡ KLaO ꢀs† ‡ La C ꢀs†
2
3
2
3
2
2
2
3
pyrolysed product at 9708C

N. Deb / Thermochimica Acta 338 (1999) 27±33
33
[
[
[
6] G.M. Bancroft, K.G. Dharmawardena, A.G. Maddock, Inorg.
Nucl. Chem. Lett. 6 (1970) 403.
7] D. Broadbent, D. Dollimore, J. Dollimore, Analyst 94 (1969)
4
. Conclusions
The thermal studies (TG, DTG and DTA) in air
shows that the potassium oxalate separates from
543.
8] K. Nagase, Bull. Chem. Soc. Jpn. 46 (1973) 144.
K[La(C O ) ] (where 1.5 < x < 2) at a much lower
2
[9] B.S. Randhawa, P.S. Bassi, S. Kaur, Indian J. Chem. A 28
1989) 463.
10] A.S. Brar, B.S. Randhawa, J. Solid state Chem. 58 (1985)
53.
4 x
(
temperature than the lithium and sodium analogues
17]. Subsequently slow decomposition of potassium
oxalate to K CO takes place as with lithium and
[
[
[
1
2
3
11] N. Deb, P.K. Gogoi, N.N. Dass, Bull. Chem. Soc. Jpn. 61
(1988) 4485.
sodium oxalate [17], but La O was produced at
3
2
8
368C through the formation of both oxycarbonate
[12] N. Deb, P.K. Gogoi, N.N. Dass, J. Therm. Anal. 35 (1989) 27.
[
13] N. Deb, P.K. Gogoi, N.N. Dass, Thermochim. Acta 145
1989) 77.
14] N. Deb, S.D. Baruah, N.N. Dass, Thermochim. Acta 45
1995) 457.
and dioxycarbonate at 4808C and 5288C respectively.
Whereas in case of lithium analogue the formation of
oxycarbonate was not observed, sodium analogue
(
[
(
produced only La O(CO )
2
at 5388C. Like
3 2
[15] N. Deb, S.D. Baruah, N.N. Dass, Thermochim. Acta 285
(1996) 301.
M [La(C O ) ]ÁxH O (where M ˆ Li and Na) [17],
3
2
4 3
2
[
[
[
[
16] N. Deb, S.D. Baruah, N. Sen Sarma, N.N. Dass, Thermochim.
Acta 320 (1998) 53.
the compound K [La(C O ) ]Á9H O, also produced
3
2
4 3
2
KLaO along with K O and La C through the solid±
2
2
2 3
17] N. Deb, S.D. Baruah, N.N. Dass, Thermochim. Acta 326
(
solid reaction of K CO and La O at high tempera-
2
3
2 3
1999) 43.
ture (ca 10008C). A mixture of potassium oxalate and
lanthanum dioxycarbonate was assumed to be the end
product at 6508C in nitrogen from the DSC study. The
18] T.K. Sanyal, N.N. Dass, J. Inorg. Nucl. Chem. 42 (1980)
811.
19] E.S. Freeman, B. Carroll, J. Phys. Chem. 62 (1958) 394.
*
[20] J.H. Flynn, L.A. Wall, J. Res. Nat. Bur. Stand. A 70 (1966) 6.
E values calculated by four non-mechanistic equa-
tions were in excellent agreement for dehydration and
two decomposition steps.
[
[
[
[
[
21] A.W. Coats, J.P. Redfern, Nature 201 (1964) 68.
22] J.R. MacCallum, J. Tanner, Eur. Polym. J. 6 (1970) 1033.
23] N. Tanaka, M. Manjo, Bull. Chem. Soc. Jpn. 40 (1967) 230.
24] N. Tanaka, K. Sato, Bull. Chem. Soc. Jpn. 43 (1970) 789.
25] G.M. Bancroft, K.G. Dharmawardena, A.G. Maddock, Inorg.
Chem. 9 (1970) 223.
Acknowledgements
[
26] A.A. Medvinskii, V.I. Poskevnev, Zh. Strukt. Khim. 15 (1974)
623.
The author thankful to Dr.S.D. Baruah, Regional
Research Laboratory, Jorhat for the DSC pro®les.
[
27] H. Sato, T. Tominaga, Bull. Chem. Soc. Jpn. 52 (1979) 1402.
[28] Joint Committee on Powder Diffraction Standards, Inorganic
Index to the Powder diffraction File, 1971, 1601, Parklane,
Pennsylvania.
[
29] M.G. Usha, M. Subba Rao, T.R. Narayanan Kutty, Thermo-
chim. Acta 43 (1981) 35.
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[
[
[
(
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(
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(