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Kinetic Research of Solid-Phase Synthesis of Lithium Pentaferrite
A.P. Surzhikov, A.M. Pritulov, O.V. Galtseva, R.U. Usmanov,
Tomsk Polytechnic University, 30, Lenin ave., Tomsk, 634034, Russia
Tel./Fax: +8(3822) 53-37-87, E-mail: [email protected]
Abstract – In the context of kinetic model of nu-
cleation the analysis of kinetic dependences of ra-diation – thermal synthesis of lithium pentaferrite
The synthesis was carried out from a mechanical mix-
was carried out. It’s shown that the solid-phase
ture of lithium carbonate and iron oxide. It was pressed
synthesis in diffusion – kinetic mode was carried
as tablets by mass thickness 0.6 g/cm2. Radiation-
out. At increasing of roasting temperature the syn-
thermal roasting of specimens was carried out on
thesis changes from diffusion – control into kinetic
pulse electron accelerator ILU-6 (Institute of nuclear
mode of reaction. In conditions of radiation the
Physics, SB RAS, Novosibirsk). Electronic energy was
decrease of energy of activation of process ob-
2.4 MeV, beam current in the pulse – 400 mА, pulse
serves, which connecting with dynamic recharging
duration – 500 µs, pulse repetition rate – 7÷15 Hz.
Average irradiation power of heating ~ 5 kGr/s, in mode of isothermal roasting ~ 3 kGr/s. Local power of absorbed doze is 800 Gr/s within of action of one pulse.
For revealing radiation effects, the thermal synthesis
In material science of multicomponent connections the
was carried out at the same temperatures and durations
problem of activation of solid-phase reactions is ur-
of roasting. Duration of nonisothermal stages (heating
gent. The decision of this problem would allow to
reduce temperature of ceramic synthesis and to reduce
The determination of phase structure and parameters
its duration. This problem in the relation to lithium
of a crystal lattice of researched samples was carried
containing spinels is especially urgent which concern
out by a method of the full-profile analysis of X-ray
to number of the most widespread magnetic materials
pictures with use of a program complex Powder Cell 2.4.
These materials are used in discrete high-speed 3. Results and discussion
phase shifters and are perspective inexpensive cathode
Figure 1 represents the fragments of X-ray pictures,
materials of rechargeable lithium batteries [1].
which were measured after roasting of reactionary
The available data testify, that the influence on sub-
mixtures in thermal and radiation-thermal modes dur-
stance of intensive flows of accelerated electrons is
possible to relate to perspective methods of activation of solid-phase reactions, which capable to warm up
it to high temperatures at the braking in substance (radiation – thermal or (RТ) of influence) [1, 2]. In particular, it was shown in works [1, 2], that at
isochronic roasting of stoichiometric mixture of lith-
ium carbonate and iron oxide in conditions of elec-tronic irradiation the increase of speed of synthesis of
lithium pentaferrite is observed in comparison with
synthesis at thermal roasting. These data practically do
not carry the information about a nature of processes
responsible for observable effect, but proving a pres-ence of radiation stimulation of solid-phase synthesis of lithium pentaferrite.
In this plan the methods of kinetic analysis is sig-
nificant informative, allowing to concretize the mecha-
nism of solid-phase reaction. In the present work, the
results of kinetic researches of RТ synthesis of lithium
Fig. 1. The difractograms of mixture Li Fe5O8 after thermal
pentaferrite are submitted in a range of temperatures
(Т) and radiation-thermal (RТ) roasting at 600 and 700 °С,
during 60 min (О − Li Fe5O8; Х − α-Fe2O3)
There are reflections of a spinel phase and α-Fe2O3
diffusion and kinetic stages of process the model can
at difractogram structure. By us a spinel is identified
be described by the combined equation [4]
as lithium pentaferrite (s.g. Р4332) with a lattice pa-
rameter is 8.329 Å. The presence of superstructural
reflections (110), (210), (211), (310), and (320), char-acteristic for ordered lithium ferrospinel, confirms Kd and Kr are the constants of reaction speed, which an identification of spinel with lithium pentaferrite.
are proceeding on the diffusion and kinetic mechanism
In addition, the full-profile analysis has revealed weak
correspondingly; (1 – с) and с are the partial contribu-
reflections from phase planes of lithium orthoferrite
tions of one-dimensional diffusion increase and one-
2, which were imposed on reflexes of spinel
Corrected experimental kinetic curves were ap-
Comparing difractograms of Т and RТ roasting proximated by equation (2) that has allowed determin-
mixtures, it is visible what the intensity of spinel re-
ing a constant of reaction speeds and partial contribu-
flections essentially increase at increasing of ferritiza-
tions of mechanisms at 700, 800, and 1000 °C. The
tion temperature, and intensity of reflexes of initial
temperature dependences of constants of reaction
RТ roasting is actually equivalent to thermal, but for conducted roasting at higher temperature.
Figure 2 illustrates kinetic curves of accumulation
of lithium pentaferrite at roasting of reaction mixture at 800 °C.
Fig. 2. Kinetic dependences of degree of transformation α
of reaction mixture: RT – radiation-thermal synthesis; T –
thermal synthesis; solid lines – approximation by equation (1);
a similar kind (therefore we do not give them here). All established kinetic dependences are adequately
αi is the degree of transformation; τі is the duration of
process; a, b, and α0 are the adjusting parameters.
Using adjusting results and the approach, which
was stated in work [3], the amendment to duration of
isothermal roasting and the levels of apparent satura-
Arrenius's dependences of constants of reaction
tion of kinetic curves were determined. It has allowed
speeds, leaking at kinetic Kr and diffusion Kd mechanisms
describing results by more simple equation, in which
the initial non-stationary site is absent.
In the context of kinetic model of nucleation, the
The effective energy of activation of process of
mathematical processing of experimental kinetic de-
synthesis was determined on an inclination of straight
pendences was carried out. For transitive diffusion–
lines. This values and partial contributions of mecha-
kinetic area and in the assumption of independence of
Table. Partial contributions of mechanisms and energies electron beam there is an essential decrease of activa-of activation of speed constants of reactions of diffusion –
tion energies Er and Ed. The decrease of effective en-
kinetic mode of synthesis of lithium pentaferrite
ergy of activation at radiation-thermal synthesis is
possible to explain by short-term decrease of a cation
Diffusion Kinetic charges from Fe3+ into Fe2+ owing to creation of the
large concentration of free electrons by accelerated
electron beam in material. As the ions Fe3+ have higher
charge in comparison with ions Fe2+, the movement of
cation Fe3+ on a lattice of spinel is more complicated,
than movement of ions Fe2+. The decrease of activation
energy for the specified ions is possible to explain by
0.69 0.31 reduction of energy of electrostatic interaction with
environmental anions, i.e., the decrease of Madelung
0.38 0.62 component of connection energy. The dynamic over-
charge of cations Fe3+ at radiation – thermal condi-
tions is equivalent to decrease of their effective
0.14 0.86 charge, also causes an increase of mobility of iron ions
0.70 0.65 and an acceleration of reaction as a whole. Cations Li+
concern to ions with constant valency, it is difficult to
0.55 0.48 expect of decrease of their charge even at presence of
superequilibrium concentration of free electrons.
The data of Table show, that despite of compara-
Therefore offered mechanism of radiation intensifyca-
bility of the partial contributions as a whole, the most
tion of synthesis is most probable, if a limiting stage
powerful contribution brought a mechanism of diffu-
of synthesis is a migration of ions Fe3+.
sion–kinetic reaction. At 800 °С, the contributions of mechanisms are approximately equal. At 1000 °С the
kinetic mechanism dominates. The increase of kinetic
Radiation-thermal synthesis of lithium pentaferrite
component is evidence about significant decrease of
realized with the same succession of sold-phase trans-
diffusion impediment with increase of temperature formations, as at thermal ferritization. Reaction carries
of process and at bridge into RT mode of synthesis. in diffusion–kinetic mode with decreased energy of
At the same time, the close values of activation energy
activation of process. The explanations of observed
of process in a formation zone of lithium pentaferrite
Er and activation energy of transport of mobile reagent Ed testify about practical concurrence of values of po-
The overcoming of potential barriers is necessary
to reagent for moving into a reactionary zone and for
Hui Yang, Solid State Ionics 178, 1590 (2007).
subsequent formation of chemical connection. It is [2] A.P. Surzhikov and A.M. Pritulov, Radiation- possible to assume, that Er and Ed have an identical
thermal sintering of ferrite ceramic, Moscow, En-
nature, and the observable distinctions are caused by
various distortion of a crystal lattice in a reaction zone
[3] P.N. Oleinikov, G.P. Muraviova, and N.N. Oleini-
kov, Izv. AN SSSR. Inogr. Mater. 31, 1572 (1995).
Concerning the mechanism radiation stimulation [4] A.A. Buruchin, N.N. Oleynikov, B.R. Churagulov,
of synthesis the following is possible to note. From the
table it is visible, that in conditions of influence of an
INTRODUCTION . 274 I. THE EXISTENCE OF INEQUALS . 276 II. INTRODUCING A PATENT REGIME IN INDIA. 278 A. The Background . 278 B. Towards an Indian Patent Policy . 281 1. Patents and Underdeveloped Nations . 282 2. Inventions Relating to Chemicals, Food, and Pharmaceuticals. 283 3. Industrialization. 286 III. ESTABLISHING AN INDIAN PATENT REGIME . 289 A. Indian Patent Legislation . 289 1.
Are Endoscopic Antireflux Therapies Cost-EffectiveCompared with Laparoscopic Fundoplication?Background and Study Aims: A number of endoscopic antire-Results: Assuming that EAT has no impact on potential LF laterflux therapies (EATs) have emerged as potential nonmedicalon, the outcome of both strategies (LF, or EAT first with LF intreatment options for patients with gastroesophageal reflux di