Thermal analysis of lithium peroxide prepared by various methods

Article abstract of DOI:10.1134/S1070363209050041

Behavior of lithium peroxide samples at heating in air was studied by the methods of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). In the temperature range from 32 to 82°C all the studied samples we found to react with water vapor forming lithium peroxide monohydrate as confirmed by the methods of chemical analysis and of qualitative X-ray phase analysis. It was found experimentally that in the temperature range from 340 to 348°C lithium peroxide began to decompose into lithium oxide and oxygen, the starting temperature depended on the method of preparation of lithium peroxide. For all the studied samples polymorphism in the temperature range from 25 to 340°C was not detected.

Full text of DOI:10.1134/S1070363209050041

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 5, pp. 891–894. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © Yu.A. Ferapontov, N.V. Kokoreva, N.P. Kozlova, M.A. Ul’yanova, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79,
No. 5, pp. 719–722.
Thermal Analysis of Lithium Peroxide
Prepared by Various Methods
Yu. A. Ferapontov, N. V. Kokoreva, N. P. Kozlova, and M. A. Ul’yanova
“Roskhimzashchita” Corporation ,
Morshanskoe sh. 19, Tambov, 392680 Russia
e-mail: nihi@tambovnihi.ru
Received October 20, 2008
Abstract―Behavior of lithium peroxide samples at heating in air was studied by the methods of
thermogravimetric analysis (TGA) and differential thermal analysis (DTA). In the temperature range from 32 to
8
2ºС all the studied samples we found to react with water vapor forming lithium peroxide monohydrate as
confirmed by the methods of chemical analysis and of qualitative X-ray phase analysis. It was found
experimentally that in the temperature range from 340 to 348ºС lithium peroxide began to decompose into
lithium oxide and oxygen, the starting temperature depended on the method of preparation of lithium peroxide.
For all the studied samples polymorphism in the temperature range from 25 to 340ºС was not detected.
DOI: 10.1134/S1070363209050041
Lithium peroxide (Li O ) is a compound whose
data are fairly contradictory. In [4, 5] had been re-
ported on irreversible exothermic effect on the DTA
curve at the temperature near 225ºС that had been
2
2
composition includes 34.87% of active oxygen that is
liberated in the reaction with water vapor or carbon
dioxide. By the content of active oxygen, that is, the
oxygen that could be liberated in the course of
chemical processes, Li O is more rich than any other
considered as polymorphic transformation of α-Li O2
2
into β-Li O with increase in reactivity of the sample,
2
2
and this conclusion had been confirmed by the data of
X-ray phase analysis, but in more recent publications
[6, 7] this was not confirmed.
2
2
compound stable under ambient conditions, except
hydrogen peroxide and sodium superperoxide, and its
–
1
stoichiometric capacity on carbon dioxide (488 l kg )
is maximal in the series of all chemosorbents used for
the carbon dioxide conversion. Therefore lithium
peroxide is used widely enough as a component of
chemical compositions of the systems of human
survival (HSS) when people should exist and work
isolated from external environment [1–3]. For a proper
choice of chemical composition of chemosorbents in
designing the HSS systems, increasing the HSS
performance and creation of more comfortable
conditions for the users of the system not only detailed
knowledge is needed of the reaction of these
chemosorbents with water vapor and carbon dioxide,
but also of the basic kinetic parameters of these
processes and factors that can affect these parameters.
A scope of such factors embrace phase transitions,
polymorphic transformations, and other phenomena
proceeding in chemosorbents at heating. However, for
lithium peroxide there are no sufficient data in
literature concerning this problem while the published
Therefore it is significant from scientific and
practical viewpoints to explore behavior of various
samples of lithium peroxide exposed to heating in air,
that is, under conditions that can appear at the
application of human survival systems.
In the course of the experiments we established that
TGA and DTA curves are of the same character for all
samples of lithium peroxide, therefore Fig. 1 shows the re-
sults of thermal study for one sample (no. 3, see the table).
In all samples of lithium peroxide obtained by
different procedures on the DT curves in the range
from 32 to 82ºС an exothermic effect was observed
with simultaneous increase in weight that was assigned
to the reaction of lithium peroxide with water vapor
leading to the formation of lithium peroxide
monohydrate, as had been mentioned in [8, 9] where
the reaction between lithium peroxide and water vapor
had been studied. To verify the validity of our
assumption concerning the nature of the exothermic
891

8
92
FERAPONTOV et al.
Average particle
a
Chemical composition of studied samples
Chemical composition, wt %
Sample no.
Method of preparation
m
diameter d , µm
Li
2
O
2
LiOH
Li
2
СO
3
2
Н О
1
2
Thermal dehydration of Li
2
O
2
·Н
2
О
23.4
23.2
97.7
98.0
0.4
0.3
1.4
1.3
0.5
0.4
Dehydration of Li
2
O
2
2
·Н
2
2
О over dryer
Dehydration of Li
frequency field
2
O
·Н
О in superhigh
3
18.7
97.8
70.3
0.3
0.4
1.5
1.3
0.4
4
Parent Li
2
O
2
·Н
2
О
–
28.0
a
Dispersion characteristics of lithium peroxide monohydrate were not measured.
effect we heated the initial sample of Li O in air to
effect occurs with the maximum at 106ºС that leads to
a decrease in the sample weight approximately by
2.9%. This effect corresponds to the dehydration of the
samples. The following large endothermic effect on the
DTA curves started at the temperatures 348 , 344, and
341ºС and had maxima at 369, 373, and 374ºС for the
samples nos. 1–3 respectively and was accompanied
by the weight decrease by approximately 34%. These
effects correspond to decomposition of lithium
peroxide into lithium oxide and oxygen (stoichiometric
content of active oxygen in the studied samples was
approximately 34.6%). This assumption is confirmed
by chemical analysis and qualitative X-ray phase
analysis showing that the samples of lithium peroxide
after heating at 390ºС (that is, at the temperature
slightly above the considered effect) for 3 h contained
only lithium oxide and carbonate while the parent
Li O was totally absent. The results obtained are in
2
2
4
5ºС at the relative humidity φ = 96% for 1 h and then
the sample was examined by qualitative X-ray phase
analysis. The appearance in the diffractogram of new
reflexes (at sliding angle 2θ = 35.09º, the reflex
corresponding to interplane distance d = 2.543 Å, at
sliding angle 2θ = 30.48º, the reflex corresponding to
interplane distance d = 2.90 Å, and at sliding angle 2θ =
4
0.75º, the reflex corresponding to interplane distance
d = 2.20 Å) proves undoubtedly the appearance in the
studied sample of a new phase with the composition
Li O ·H O [14, 20]. Note that in the time when this
2
2
2
exothermic effect was observed the weights of samples
no. 1 and no. 2 increased by approximately 1.7 %,
while for the sample no. 3 on TGA curve increase in
weight by 2.4 % was seen and a more pronounced
peak on DTA curve. This difference in behavior of the
samples of lithium peroxide prepared by different
methods was attributable to the difference in the
surface area of the samples, that is, to the kinetics of
the process of lithium peroxide interaction with water
vapor. Then for all Li O samples an endothermic
2
2
better agreement with the results of [6, 12] where the
temperature of the start of lithium peroxide decom-
position was reported as 350ºС rather than with the
results published in [4, 5, 7] where the beginning of
decomposition of lithium peroxide was registered at
2
2
315ºС. Finally, on all DTA curves of the studied
Т, °С
DTA, μV
TG, mg
samples was clearly seen an endothermic effect with a
maximum at 424ºС that corresponded to eutectic
melting of Li O–Li СO system observable visually,
5
4
4
3
3
2
2
1
1
00
50
00
50
00
50
00
50
00
20
1
0
–1
TG
2
2
3
DTA
that also was noted in [6, 7].
1
0
5
0
–
2
Thermal analysis of lithium peroxide monohydrate
(sample no. 4) is shown in Fig. 2.
–3
–4
–5
–6
–7
–8
Т
–5
10
15
–
–
The DTA curve shows three endothermic effects,
two of which with decrease in weight. The first effect
beginning at 92ºС with maximum at 105ºС and
accompanied with the sample weight loss by 27.6%
corresponded to the dehydration of this compound
5
0
0
–20
–
50
5
00 1000 1500 2000 2500
Time, s
2 2
Fig. 1. Complex thermal analysis of Li O .
(
theoretical water content in the sample was 28.0%).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 5 2009

THERMAL ANALYSIS OF LITHIUM PEROXIDE
893
DTA, μV TG, mg
The second endothermic effect beginning at 340ºС
with a maximum at 374ºС corresponded to the
decomposition of Li O formed after dehydration of
Т, °С
00
5
450
50
0
–50
–100
150
–200
5
0
DTA
2
2
4
3
3
00
50
00
–5
Li O ·H O. At the decomposition the sample weight
2
2
2
–10
–15
–20
Т
loss was 24.1% due to the evolution of oxygen from
the peroxide (theoretical content of active oxygen in
the studied sample was 24.5%). The data obtained on
the temperatures of lithium peroxide monohydrate
dehydratation and dehydrated lithium peroxide
decomposition are consistent with the results in [11].
However, like the case of the samples of lithium
peroxide, on the DTA curve are absent effects in the
range 200–240ºС that should suggest the occurrence of
polymorphous transformations. This fact contradicts to
the data of [11] where on the DTA curve a weak
exothermic effect has been registered at 225ºС that was
interpreted as revealing polymorphism, that is, trans-
formation of α-Li O into β-Li O . The last endo-
–
250
TG
–
25
2
1
1
00
50
00
50
0
–30
–35
–40
–
–
250
300
–
–
45
50
–
50
500 1000 1500 2000 2500
Time, s
Fig. 2. Complex thermal analysis of Li
2
O
2
·Н
2
О.
monohydrate at the thermal exposure (sample no. 4).
Compositions of the examined samples determined by
the chemical analysis [15–21] and confirmed by the
data of qualitative X-ray phase analysis are shown in
the table. The X-ray phase analysis was carried out on
2
2
2
2
thermic effects that begins at 424ºС and shows a
maximum at 436ºС corresponds to the melting of
Li O–Li СO eutectic.
a DRON-5 diffractometer with filtered CuK -radiation
α
2
2
3
(
λ = 1.54051 Å). Scan increment 0.05º, scan range 20º ≤
While performing the thermal analysis in air in the
2θ ≤ 120º, exposition 3 sec in each point. The table
also contains dispersion characteristics of the examined
samples estimated by means of specially developed
method of measuring particle size of the peroxide
substances based on their inertial separation [17].
temperature range from 25 to 340ºС on the lithium
peroxide samples prepared by different methods, with
different chemical and dispersion compositions, and on
lithium peroxide monohydrate we did not find any data
indicating polymorphism in the studied samples either
due to the change in the crystal lattice or due to the
transition from non-equilibrium state to the equilib-
rium one. The experimental results obtained by us do
not confirm reports [4, 5, 11] about existence of
lithium peroxide in two polymorphic states.
Thermogravimetry and differential thermal analysis
of the samples were carried out under nonisothermal
conditions on an instrumental complex TAG-24 of
“
Setaram” company (France). For the investigation
were taken samples with the weight ~30 mg.
Temperature was registered with an accuracy 0.01ºС ,
change in the sample weight was measured with an
accuracy 0.01 mg. The examined samples were placed
in a corundum crucible. The measurements were
carried out in air at ordinary pressure, heating rate
EXPERIMENTAL
For examination were taken various samples of
lithium peroxide formed in the reaction at 33ºС of solid
lithium hydroxide and 50% aqueous hydrogen per-
oxide at the molar ratio LiOН/Н О = 1.85. The
5
degrees per minute. Temperature was measured by
2
2
platinum–platinum-rhodium thermocouple that has
been graduated on the commonly used reference
points.
intermediate adduct, lithium peroxide monohydrate
Li O ·Н О) was isolated by filtration and then it was
(
2
2
2
dehydrated either by heating in a muffle furnace at
0ºС for 4 h (sample no. 1), or by prolonged exposure
ca. 3 days) at room temperature over zeolite layer
sample no. 2) or by exposure to a superhigh frequency
8
(
(
ACKNOWLEDGMENTS
This work is financially supported by Russian
Foundation for Basic Research, grant no. 09–0800263.
field for 7 to 12 s depending on the sample weight
sample no. 3) [8–14]. To avoid formation of lithium
carbide at the dehydration of Li O ·Н О in superhigh
(
2
2
2
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