Study of the process of thermal dissociation of tantal pentachloride in vacuum
The dependence of the degree of dissociation of TaCl₅α(T, P) vapors on the temperature in the range of 1470...1820 K in a vacuum of 1.33·10⁻² Pa was by using of equilibrium chemical thermodynamics obtained. The experimental data on the dependence of αex(Т, Р) on temperature and vapor mass flow TaCl₅...
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| Zitieren: | Study of the process of thermal dissociation of tantal pentachloride in vacuum / Yu.I. Polyakov, S.G. Rudenkyi, Yu.V. Lukirsky, I.I. Konovalov, V.I. Rak // Problems of atomic science and technology. — 2019. — № 2. — С. 141-144. — Бібліогр.: 6 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-1949422025-02-09T14:43:30Z Study of the process of thermal dissociation of tantal pentachloride in vacuum Дослідження процесу термічної дисоціації пентахлориду танталу у вукуумі Исследование процесса термической диссоциации пентахлорида тантала в вакууме Polyakov, Yu.I. Rudenkyi, S.G. Lukirsky, Yu.V. Konovalov, I.I. Rak, V.I. Physics of radiotechnology and ion-plasma technologies The dependence of the degree of dissociation of TaCl₅α(T, P) vapors on the temperature in the range of 1470...1820 K in a vacuum of 1.33·10⁻² Pa was by using of equilibrium chemical thermodynamics obtained. The experimental data on the dependence of αex(Т, Р) on temperature and vapor mass flow TaCl₅ were analyzed and compared with calculations. У рамках рівноважної хімічної термодинаміки отримана залежність ступеня дисоціації парів TaCl₅α(T, P) від температури в інтервалі 1470…1820 К і вакуумі 1,33·10⁻² Па. Проаналізовано та порівняно з розрахунковими експериментальні дані залежності αексп(Т, Р) від температури і масового потоку парів TaCl₅. В рамках равновесной химической термодинамики получена зависимость степени диссоциации паров TaCl₅α(T, P) от температуры в интервале 1470…1820 К и вакууме 1,33·10⁻² Па. Проанализированы и сравниваются расчетные данные с экспериментальными данными зависимости αэксп(Т, Р) от температуры и массового потока паров TaCl₅. 2019 Article Study of the process of thermal dissociation of tantal pentachloride in vacuum / Yu.I. Polyakov, S.G. Rudenkyi, Yu.V. Lukirsky, I.I. Konovalov, V.I. Rak // Problems of atomic science and technology. — 2019. — № 2. — С. 141-144. — Бібліогр.: 6 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/194942 621.793.16 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Physics of radiotechnology and ion-plasma technologies Physics of radiotechnology and ion-plasma technologies |
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Physics of radiotechnology and ion-plasma technologies Physics of radiotechnology and ion-plasma technologies Polyakov, Yu.I. Rudenkyi, S.G. Lukirsky, Yu.V. Konovalov, I.I. Rak, V.I. Study of the process of thermal dissociation of tantal pentachloride in vacuum Вопросы атомной науки и техники |
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The dependence of the degree of dissociation of TaCl₅α(T, P) vapors on the temperature in the range of 1470...1820 K in a vacuum of 1.33·10⁻² Pa was by using of equilibrium chemical thermodynamics obtained. The experimental data on the dependence of αex(Т, Р) on temperature and vapor mass flow TaCl₅ were analyzed and compared with calculations. |
| format |
Article |
| author |
Polyakov, Yu.I. Rudenkyi, S.G. Lukirsky, Yu.V. Konovalov, I.I. Rak, V.I. |
| author_facet |
Polyakov, Yu.I. Rudenkyi, S.G. Lukirsky, Yu.V. Konovalov, I.I. Rak, V.I. |
| author_sort |
Polyakov, Yu.I. |
| title |
Study of the process of thermal dissociation of tantal pentachloride in vacuum |
| title_short |
Study of the process of thermal dissociation of tantal pentachloride in vacuum |
| title_full |
Study of the process of thermal dissociation of tantal pentachloride in vacuum |
| title_fullStr |
Study of the process of thermal dissociation of tantal pentachloride in vacuum |
| title_full_unstemmed |
Study of the process of thermal dissociation of tantal pentachloride in vacuum |
| title_sort |
study of the process of thermal dissociation of tantal pentachloride in vacuum |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2019 |
| topic_facet |
Physics of radiotechnology and ion-plasma technologies |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/194942 |
| citation_txt |
Study of the process of thermal dissociation of tantal pentachloride in vacuum / Yu.I. Polyakov, S.G. Rudenkyi, Yu.V. Lukirsky, I.I. Konovalov, V.I. Rak // Problems of atomic science and technology. — 2019. — № 2. — С. 141-144. — Бібліогр.: 6 назв. — англ. |
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Вопросы атомной науки и техники |
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2025-11-26T23:57:43Z |
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ISSN 1562-6016. PASТ. 2019. №2(120), p. 141-144.
UDC 621.793.16
STUDY OF THE PROCESS OF THERMAL DISSOCIATION OF TANTAL
PENTACHLORIDE IN VACUUM
Yu.I. Polyakov, S.G. Rudenkyi, Yu.V. Lukirsky, I.I. Konovalov, V.I. Rak
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
Tel. (057)335-67-82
The dependence of the degree of dissociation of TaCl5(T, P) vapors on the temperature in the range of
1470...1820 K in a vacuum of 1.3310
-2
Pa was by using of equilibrium chemical thermodynamics obtained. The
experimental data on the dependence of ex (Т, Р) on temperature and vapor mass flow TaCl5 were analyzed and
compared with calculations.
INTRODUCTION
The aim of the work is to study the process of ther-
mal dissociation of tantalum pentachloride vapors in the
range of 1470…1820 К in a flow vacuum system, fo-
cused on achieving the possibility of obtaining coatings
Ta thick 250 μm in the form of a sealed corrosion-
resistant shell under irradiation with high-energy-
electrons in the aquatic environment on tungsten plates
of size 66663; 4; 6; 10 mm, which are neutron-
forming elements of the “Source of neutrons” target.
1. EQUILIBRIUM CHEMICAL
THERMODYNAMICS THERMAL
DISSOCIATIONS TaCl5
The general issues of obtaining solid phase conden-
sates by deposition from the gas phase using the CVD
method are described in monographs [1]. A special case
of the kinetics of heterogeneous reversible reactions of
the type A↔vB was considered in [2]. In the specific
case, the deposition of tantalum from the vapors of the
pentachloride is carried out in a flow-through vacuum
system (in contrast to the Van Arkel-De Boer method,
which is implemented in a closed volume).
The use of vacuum conditions during the thermal
dissociation of TaCl5 allows the deposition of tantalum
coatings at an observable rate. Reduced pressure con-
tributes to an increase in the degree of conversion for
reactions that occur with an increase in the number of
particles in the gas phase in accordance with the princi-
ple of Le Chatelier. It is the use of vacuum that allows
the process of thermal dissociation of TaCl5 to produce
solid tantalum.
The technological parameters (substrate temperature,
pressure near the condensate growth surface, specific
mass flow of pentachloride vapors) determine the rate of
precipitation (etching) of tantalum, as well as the struc-
ture and properties of the coating. Thermodynamic cal-
culations of the equilibrium of the chemical reaction
used make it possible to estimate the range of changes
in the technological parameters for an efficient process,
and the comparison with experimental data optimizes
the deposition conditions from the point of view of ob-
taining coatings with desired properties.
The deposition rate of tantalum is:
TaV =
5TaCl
5
5),(
TaCl
Ta
Ta
TaCl
St
m
, (1)
– coefficient depending on the geometry of the reac-
tor (empirically); ),(
5
TPTaCl – equilibrium degree of
transformation TaCl5 at a pressure Р (atm) and a deposi-
tion temperature Т;
5TaClm – the mass of TaCl5, sup-
plied to the surface area of S for the time t ;
Ta –
density Ta;
Ta – atomic weight Ta;
5TaCl – molecu-
lar weight TaCl5.
For reaction
TaCl5 (g) ↔ Ta (s) + 5Cl (g), (2)
running in equilibrium conditions, the value is deter-
mined by the ratio:
= 55 5
4 1/ 41 , (3)
where is the equilibrium constant:
Ta
TaCl
Cl a
5
5
, (4)
Cl ,
5TaCl
– partial pressures Cl and TaCl5, аТа – tanta-
lum activity, аТа = 1.
Equilibrium constant is associated with a
change in the Gibbs free energy as a result of the reac-
tion of the Gibbs-Helmholtz equation (entropy approx-
imation, С = 0):
reactionG = reaction
298 reactionS298 , (5)
where reaction
298 and reactionS298 – changes in enthalpy and
entropy, respectively:
.)(.)( 298298298 inprreaction , (6)
.)(.)( 298298298 inSprSS reaction , (7)
298 – the enthalpy of formation of each of the par-
ticipating substances (pr. – reaction products, in. - initial
materials) at T = 298 K,
298S – entropy, respectively, at
Т = 298 K, and:
KRTGreaction ln , (8)
R – ideal gas constant
molК
J
R
32,8
The validity of writing the process equation in the
form (2) is confirmed by the calculation of the equilib-
rium degree of dissociation 2Cl by the reaction
)(2)(2 gClgCl , (9)
)1/(4 22 , (10)
and
242600 107.181 (J/mol)reactionG , (11)
and reference values for standard enthalpy and entropy
are given below.
TaCl5(g): ∆Hf298 = -182.25 Kcal/mole [3]
∆Hf298 = -182.4 Kcal/mole = -763672 J/mol [4]
S298 = 102.6 cal/mole К = 429.,566 J/(mol К) [4]
Та(s): S298= 9.92 cal/mole·
Кp = 41.533 J/(mol К) [4]
Cl(g): ∆Hf298 = 121302 J/mol [5]
S298 = 165.076 J/(mol К) [5]
Cl2(g): S298 = 222.965 J/(mol К) [5]
The results of calculations according to equation
(10) are given in Fig.1.
Fig. 1. The ratio between the degree of dissociation
diatomic chlorine and temperature
So, in a practically interesting temperature and pres-
sure range, the value
2Cl is close to unity, which allows
reasonably calculating the process equilibrium in ac-
cordance with writing the reaction equation in the form
(2), the change in the free energy of which, taking into
account the above reference data, is:
1470182 437.347 ( / )reactionG J mol , (12)
Taking into account expressions (3), (8) and (12),
we calculate the dependence of temperature on the de-
gree of conversion for pressure P = 2; 0.1; 10
-4
mm Hg,
respectively (Fig. 2)
Fig. 2. Dependence of temperature change T, K on the
degree of transformation α for reaction (2) at pressure
values 266; 13.3; 1.3310
-2
Pа
Fig. 3 shows the dependence of pressure on the de-
gree of transformation .
Fig. 3. The dependence of pressure P on the degree of
transformation according to reaction (2) for
temperatures of 1473, 1573, and 1673 K
The dependence of temperature on pressure for the
values of the degree of transformation = 0.1; 0.4, and
0.7 is presented in Fig. 4.
Fig. 4. The dependence of temperature change on
pressure for the reaction (2), where the curves are given
for the degree of transformation = 0.1; 0.4, and 0.7
The dependence of the vapor pressure of TaCl5 in
the range of 298 – Тmelt in accordance with equation [6]:
6275
log 34.305 7.04log (mm Hg)
(13)
graphically presented in Fig. 5.
Fig. 5. The dependence of vapor pressure tantalum
pentachloride TaCl5 on temperature
The combination of the above data (Figs. 1–5)
makes it possible to evaluate the necessary parameters
of the technological process (intervals of deposition and
evaporation temperatures of tantalum pentachloride,
pressure in a vacuum chamber) before the Ta deposition
experiments.
2. EXPERIMENTAL STUDY OF THE TAN-
TAL DEPOSITION RATE DEPENDENCE ON
TEMPERATURE AND MASS FLOW TaCl5
Experiments on the deposition of tantalum were
done in a vacuum unit with a residual pressure of at-
mospheric air of 1.3310
-2
Pа. Samples of tantalum foil
with a thickness 0.3 mm and a size of 5010 mm were
used as substrates. This made it possible to exclude the
influence of a material other than tantalum on the depo-
sition process, since tantalum pentachloride enters into
chemical interaction with practically most materials at a
deposition temperature Ta. For heating the samples used
a water-cooled inductor made of a copper tube
101 mm as a flat Archimedes spiral turns of 6, the
inductor is loaded onto the same axis and that arranged
at a distance of ~ 5 mm composite (two discs) graphite
disk 100 mm with a cut-out in the form of a radial
sector for placement on a large disc diameter of the
sample to be coated tangentially to the circumference of
the discs. The edges of the sample were clamped be-
tween two disks (4 mm thick each) of graphite to create
an electrical contact in order to close the circular cur-
rents induced in the disks, and thereby ensure heating of
the samples (Fig. 6). The inductor was powered from a
high-frequency installation VCHI-63-0.44, operating at
a frequency of 440 kHz.
Fig. 6. Scheme of the device for the study of СVD
deposition process Та of ТаСl5
A graphite tube-steam line with a hole of 4 mm at
its end for the expiration of tantalum pentachloride va-
por entering through the steam line from the removable
evaporator was placed at a distance of 5 mm perpendic-
ular to the central part of the sample plane. The evapo-
rator was maintained at a temperature in the range of
360...390°K with an accuracy of ± 0.5°K, set by a con-
tact thermometer such as MKT with an electronic key.
The change in the mass flow of tantalum pentachloride
vapors to the surface of the substrate and thereby the
regulation of the effective pressure in the deposition
zone of the coating was achieved by changing the tem-
perature of the evaporator. The amount of pentachloride
evaporated during ∆t was determined by weighing the
evaporator with its shutter closed before and after the
experiment on the BTU-2100 scale. In this case, the
evaporator was disconnected from the vacuum chamber
using a detachable vacuum connection. In the course of
the experiment, the temperature of the sample was con-
trolled using an optical pyrometer of the “Promin” type
and operated by changing the high-frequency radiation
power supplied to the inductor from the VChI-63-0.44
generator. The amount of tantalum condensate deposit-
ed during ∆t was determined by weighing the sample
before and after the experiment using a VLR-20 type
balance. The coating thickness was measured using a
micrometer according to the difference of the data be-
fore and after deposition, as well as using microsections.
In Fig. 7 presents data on the dependence of the ex-
perimental utilization factor of tantalum pentachloride
αex on the substrate temperature, which is proportional
to the deposition rate of the coating in equation (1). αex
increases rapidly at temperatures above 1470°K until
reaching saturation at ~ 1820°K.
Fig. 7. Experimental dependence the yield of Ta from
TaCl5 to the coating from the substrate temperature
The value αex does not reach the calculated equilib-
rium value α due to the presence of the coefficient β<1
in equation (1), which depends on the geometry of the
reactor used and indicates the degree of unproductive
scattering of tantalum pentachloride into the vacuum
that is not involved in the coating condensation process
under equilibrium conditions. The data in Fig. 7 refer to
the value of 5 g/h of the mass flow of tantalum pen-
tachloride.
Fig. 8. Experimental dependence of Ta yield from TaCl5
to the coating on the TaCl5 mass flow TaCl5 ( )
and the growth rate of the coating on
mass flow of vapors of TaCl5 ( ).
All data obtained at a temperature of 1720 K
Fig. 8 shows the dependences αex ( ) and the cor-
responding deposition rate of the coating V ( ) in equa-
tion (1) on the mass flow of tantalum pentachloride. The
data in Fig. 8 correspond to the process at a substrate
temperature of 1720 K.
The yield of αex of tantalum to the tantalum pen-
tachloride coating decreases from ≈ 17 to ≈ 10% with an
increase in the mass flow of pentachloride from ≈ 3 to
≈ 11 g/h. This corresponds to the principle of Le Chate-
lier, according to which an increase in the effective
pressure should suppress the yield by reaction with an
increase in the number of particles in the gas phase.
So, an increase in the effective pressure P of tanta-
lum pentachloride near the surface of the substrate, due
to an increase in the value
t
mTaCl
5 in equation (1), leads
to a decrease in the equilibrium yield α for the reaction
under consideration.
However, as α decreases, the deposition rate V in-
creases (at a given temperature), since the mass flux of
tantalum pentachloride, which appears in equation (1) as
a linear multiplier, increases.
Practically, when developing a technology for apply-
ing tantalum coatings on specific products, the required
consumption of pentachloride and the deposition rate of
tantalum should be chosen, taking into account the na-
ture of the experimental dependencies shown in Fig. 8a
and 8b. This will allow both economical use of expen-
sive tantalum pentachloride and optimize the tempera-
ture regime of the process and, accordingly, adjust the
finishing properties of coatings, which determine the
operational efficiency and service life of coatings.
CONCLUSIONS
1. The influence of the substrate temperature and
pressure on the process of thermal dissociation of tanta-
lum pentachloride vapors on the heated surface in the
interval of ~ 1470…1820 К was investigated and the
calculated thermodynamic equilibrium data were com-
pared in comparison with experimental ones.
2. The rate of deposition of tantalum increases with
increasing mass flow of vapor of its pentachloride; at
the same time, the utilization rate of tantalum pentachlo-
ride decreases, i.e. its unproductive losses are increasing
due to vapor scattering inside the vacuum chamber.
Saving costly tantalum pentachloride can be
achieved by selecting the optimal process parameters
based on the data of this work.
REFERENCES
1. Осаждение из газовой фазы / Под ред. К. Пау-
элла, Дж. Оксли и Дж. Блочера мл. / Пер. с англ. М.:
«Атомиздат», 1970, 472 с.
2. Ю.И. Поляков, Г.Н. Картмазов, Ю.В. Лукир-
ский и др. Кинетика пиролиза летучих соединений
металлов при нанесении покрытий в вакууме // Во-
просы атомной науки и техники. Серия «Физика
радиационных повреждений и радиационное мате-
риаловедение». 2011, №2(72), с. 163-167.
3. Термические константы веществ / Под ред.
В.П. Глушко. М.: ВИНИТИ АН СССР, 1968, в. 3;
1970, в. 4, ч. 1; 1971, ч. 2; 1974, в.7, ч. 1, 2.
4. О. Кубашевский, С.Б. Олкокк. Металлургиче-
ская термохимия. М., 1982, 392 с.
5. Термодинамические свойства индивидуальных
веществ / Под ред. В.П. Глушко. М.: «Наука», 1978,
т. 1-4.
6. К.Дж. Смитлз. Металлы: Справ. изд. / Пер. с
англ. 1980, 447 с.
Article received 06.03.2019
ИССЛЕДОВАНИЕ ПРОЦЕССА ТЕРМИЧЕСКОЙ ДИССОЦИАЦИИ ПЕНТАХЛОРИДА
ТАНТАЛА В ВАКУУМЕ
Ю.И. Поляков, С.Г. Руденький, Ю.В. Лукирский, И.И. Коновалов, В.И. Рак
В рамках равновесной химической термодинамики получена зависимость степени диссоциации паров
TaCl5(T, P) от температуры в интервале 1470…1820 К и вакууме 1,3310
-2
Па. Проанализированы и сравни-
ваются расчетные данные с экспериментальными данными зависимости эксп(Т, Р) от температуры и массо-
вого потока паров TaCl5.
ДОСЛІДЖЕННЯ ПРОЦЕСУ ТЕРМІЧНОЇ ДИСОЦІАЦІЇ ПЕНТАХЛОРИДУ ТАНТАЛУ
У ВУКУУМІ
Ю.І. Поляков, С.Г. Руденький, Ю.В. Лукирський, І.І. Коновалов, В.І. Рак
У рамках рівноважної хімічної термодинаміки отримана залежність ступеня дисоціації парів TaCl5
(T, P) від температури в інтервалі 1470…1820 К і вакуумі 1,3310
-2
Па. Проаналізовано та порівняно з роз-
рахунковими експериментальні дані залежності експ (Т, Р) від температури і масового потоку парів TaCl5.
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