UDC 669.771
PURIFICATION OF MAGNESIUM FROM LOW-FLYING IMPURITIES
AT SUBLIMATION
I.I. Papirov, А.I. Кravchenko, A.V. Shiyan, A.I. Mazin
National Science Center “Kharkov Institute of Physics and Technology”,
Kharkov, Ukraine
E-mail: [email protected]
Sublimation of magnesium with initial concentration of impurities Fe, Ni, Cu, Si, Al ~10-3…10-2% at
temperature 700…800 К with degrees of distillation of 80 % reduces concentration of impurities on 1-2 orders in
the first process and on 1 order still in the repeated process. Sublimation of magnesium with initial concentration of
these impurities ~1% or less is not described by known distillation equations with ideal separation factor.
Metallic magnesium is used in medicine as
constructional material of stents [1]. Corrosion
resistance of magnesium increases when its purity is
rising, thus a special demands are lodged to its purity (in
the first place to content of impurities Fe, Ni, Cu, Si
[2]). Specified impurities are low-flying relative to
magnesium (see [3])
In technology of magnesium a material that is
obtained by electrolysis contains impurities up-to-date
~10-1…1% at content of main component 97…98%
(here and further a concentration is giving in mass
percent). Sublimation is the next stage of treatment of
magnesium (vacuum sublimation at temperature near
900 К with product yield 90 %), that reduces the content
of basic impurities by 2 digits. Condensate with content
of main component 99.98% is a product of that process.
The sublimation of magnesium allows refining the
active material at temperature low melting temperature
(924 К) that is in crystal phase at low interaction of
refined material with material of container [2]. For
example, sublimation of quite pure magnesium with
0.3·10-3% Fе and 0.3·10-3% Cu allowed to reduce the
content of this impurities to 0.1·10-3% and 0.05·10-3%
correspondently [4]. Effective purification of
magnesium is ensured by sublimation with condensation
of vapor in condenser with temperature gradient: when
initial concentration of impurities was 3·10-3% Fe,
85·10-3% Si, 9·10-3% Al and 2·10-3% Ni concentration
of these impurities in midsection of condenser was
≤0.5·10-3%, 1·10-3%, 0.2·10-3% and ≤0.04·10-3%
correspondently [5].
It is interesting to study of further lowering of
content of impurities in magnesium using sublimation.
Herewith there is an aspiration to have mathematical
description of that process and so there is the question
on applicability of known distillation equations for it.
These equations are created under the assumption on
ideal mixing distillated liquid and application of these
equations for declaration of sublimation generally
speaking is problematical [6-8]. Meanwhile, the Martin
distillation equation with ideal separation factor β=рi/р
(where рi and р are pressures of pure elements of
impurity and base correspondently) was used
successfully for preliminary calculation of sublimation
refining of manganese, thulium, erbium, chromium with
purification from line of impurities (at initial level of
ISSN 1562-6016. PASТ. 2014. №1(89), p. 24
impurities ~10-1% and less) [9-12]. So, at study of
sublimation of chromium at temperature 1600 К
sufficiently well coincidence of experimental and
calculation values of impurity concentration of Fe in
condensate was observed (at initial concentration
~10-2…10-1%, with β=0.4) [11, 12]. For calculation of
sublimation of chromium was used one from basic
distillation equation that was simplified for case of
small impurity concentration [13]:
Xc
=
X0
Gc β
)
G0
,
Gc
G0
1 − (1 −
(1)
where Xc and X0 are concentration of impurity in
condensate and initial concentration of impurity
correspondently, Gс and G0 are mass of condensate and
initial mass of material correspondently, β=х2/х1 is a
separation factor where х2 and х1 are concentration of
impurity in a vapor and in liquid correspondently. For
sublimation factor β is considered as relation of
impurity concentrations in a vapor and in solid material.
The task of this research was experimental
determination of efficiency of sublimation refining of
magnesium from low- flying impurities Fe, Ni, Cu, Si,
Al at initial concentration ~10-3…10-2% with elucidation
of applicability of distillation equation for description of
sublimation of magnesium.
The sublimation of magnesium was performed in a
device in which a crucible and a condenser are united by
tubular vapor line. In the vapor line the not compact
layer of zirconium chips and two not continuous barriers
was above the crucible (the layer of chips and barriers
prevented the direct flight of vapor parts from crucible
to condenser without re-evaporation). Titanium was
exploited as container material. The device was placed
in vacuum chamber with work pressure ~10-5 mm Hg.
The evaporation of magnesium was executed at
temperature 700…800 К with degrees of distillation
80 %. The condenser had temperature on 50…70 К
smaller than the temperature of evaporation. Starting
magnesium as ingot or lamellar material with
continuation of the basic component 99,98% (in the first
process) or as crushed condensate (in the repeated
process) is placed in crucible. Elemental composition of
materials was defined by laser mass spectrometry.
The results of experiments and calculations are
given in Table 1 and 2. Calculations were performed
using eq. (1) with ideal separation factor β=рi/р (values
of рi and р was took from reference literature [3] – some
values of рi was turned out by extrapolation).
At initial level of impurities ~10-3…10-2% the
content of Al reduces on 2 orders and the content of Ni,
Cu, Si and Fe reduces on 1 order (Tabl. 1) that is as
sublimation of electrolytic magnesium [2] with initial
content of impurities on 2 orders higher. At repeated
sublimation of condensate the efficiency of purification
decreases: content of impurities in product decreases not
more then on 1 order (see Tabl. 1). Meanwhile it is
extremely big divergence (on 7…14 orders – for
different impurities) between experimental and
calculated values of purification efficiency Xс/X0
impossible to interpret by interaction of impurity and
base (known values of activity ratio are in interval
10-3…103 [4, appendix 2]) and another possible causes
must be considered for explanation of this divergence
(such as capture of impurities by current of vapor of
base, formation flying compounds, enrichment of
surface layer of evaporable material by impurity as
result of small diffusion speed of impurity in crystal
magnesium). Note that sublimation of magnesium
executed at temperature twice smaller (on absolute
scale) in comparison with sublimation of manganese,
thulium, erbium, chromium (that is at noticeably smaller
diffusion coefficient).
Table 1
Content of impurities Xс in magnesium condensate and
X0 in initial magnesium (10-3 mas. %) and Xс/X0 at
evaporation temperature 800 К and degrees of
distillation 80% (first process)
Xс/X0
Impurity
X0
Xс
Experiment Calculation
Al
10
0.4
~10-2
~10-9
-1
Ni
0.3
0.05
~10
~10-9
-1
Cu
0.7
0.08
~10
~10-11
-2
Si
15
2
~10
~10-14
-1
Fe
3
0.6
~10
~10-15
Table 2
Content of impurities Xс in magnesium condensate and
X0 in initial magnesium (10-3 mas. %) and Xс/X0 at
evaporation temperature 700 К and degrees of
distillation 80% (repeated process)
Xс/X0
Impurity
X0
Xс
Experiment Calculation
Al
0.4
0.04
~10-1
~10-10
Ni
0.05 <0.05
<1
~10-11
Cu
0.08 <0.08
<1
~10-12
-1
Si
2
0.25
~10
~10-14
-1
Fe
0.6
0.18
~10
~10-15
Note too, that concentration of sulfur S in
condensate is near to concentration of this impurity in
initial material (~10-3 %) then monatomic sulfur (with
β~10-6) is impossible to consider as low-flying impurity
in magnesium. But another allotropic forms of sulfur
(S2, S4 and other) with vapor pressure higher then
pressure of magnesium are known too [3]. Content of
sulfur S and light-flying impurities Zn and K decreased
at further heat treatment at temperature 600…700 К
(with loss of part of material).
Follow summary are made.
1. Sublimation of magnesium at temperature
700…800 К with degrees of distillation 80 % reduces
concentration of impurity Al from initial concentration
~10-2% on 2 orders and of impurities Fe, Ni, Cu, Si
from ~10-3% on 1 order. In repeated process the
concentration of all specified impurities degrees still on
1 order (concentration of Fe degrees in limit of 1 order).
2. Sublimation of magnesium with initial content of
impurities Fe, Ni, Cu, Si, Al ~1% or less (for each
impurity) is not described by known distillation
equations with ideal separation factor - in contrast to
sublimation of manganese, thulium, erbium or
chromium at temperatures 1600…1700 К with
purification from a number of impurities at initial
concentration of impurity ~10-1% or less.
REFERENCES
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Pikalov A.I. Materials of medical stents. Kharkov: NSC
KPTI, 2010, 40 p. (in Russian).
2. Eydenzon M.A. Magnesium. M.: “Metallurgiya”,
1969, 352 p. (in Russian).
3. Nesmeyanov A.N. Pressure of vapour of chemical
elements. M.: AS USSR, 1961, 396 p. (in Russian).
4. Ivanov V.Ye., Papirov I.I., Tikhinskiy G.F.,
Amonenko V.V. Pure and superpure metals. M.:
“Metallurgiya”, 1965, 263 p. (in Russian).
5. Azhazha V.M., V’yugov P.N., Bobrov Yu.P.,
Virich V.D., V’yugov N.P., Shiyan A.V., Dolya I.B. To
question on refining of magnesium by sublimation
method // Vse materialy (All materials): Encyclopedic
handbook, 2010, N 4, p. 2-7 (in Russian).
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the theory of deep purification of substances. – M.:
“Nauka”, 1981, 320 p. (in Russian).
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refining of metals in vacuum. M.: “Metallurgiya”, 1969,
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“Metallurgiya”, 1973, 320 p. (in Russian).
9. Nikiforova T.V., Volkov V.T., Nisel’son L.A.
Research of purification of manganese by vacuum
distillation // Vysokochistye veshchestva, 1987, N 6,
p. 107-111 (in Russian).
10. Boyarskiy L.A., Blinov A.G., Chistyakov O.D.,
Kol’chugina I.B., Berezovskiy G.A. Obtainment high
pure thulium and erbium and research theirs magnetic
properties // Vysokochistye veshchestva. 1988, N 4,
p. 16-25. (in Russian).
11. Kravchenko A.I. Refining of gallium and
chromium by distillation and sublimation in vacuum.
Author's abstract of dissertation. Kharkov: KPTI, 1990,
20 p. (in Russian).
12. Kovtun G.P., Kravchenko A.I., Shcherban’
A.P. Refining of chromium by distillation in vacuum //
Neorganicheskiye materialy (Inorganic materials).
1998, v. 34, N 7, p. 819-823 (in Russian).
13. Kravchenko A.I. About distillation equations at
small concentration of impurity // Voprosy atomnoy
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Article received 03.07.2013
ОЧИСТКА МАГНИЯ ОТ МАЛОЛЕТУЧИХ ПРИМЕСЕЙ ПРИ СУБЛИМАЦИИ
И.И. Папиров, А.И. Кравченко, А.В. Шиян, А.И. Мазин
Сублимация магния с исходным содержанием примесей Fe, Ni, Cu, Si, Al ~10-3…10-2% при температуре
700…800 К со степенью перегонки 80% снижает содержание примесей на 1…2 порядка в первом процессе и
ещё на 1 порядок – в повторном процессе. Сублимация магния с исходным содержанием указанных
примесей ~1% и менее (для каждой примеси) не описывается известными уравнениями дистилляции с
идеальным коэффициентом разделения – в отличие от сублимации марганца, тулия, эрбия или хрома при
температурах 1600…1700 K с очисткой от ряда примесей при исходном уровне отдельных примесей ~10-1%
и менее.
ОЧИСТКА МАГНIЮ ВIД МАЛОЛЕТУЧИХ ДОМIШОК ПРИ СУБЛIМАЦIЇ
I.I. Папiров, O.I. Кравченко, O.B. Шиян, O.I. Мазiн
Сублiмацiя магнiю з вихiдним вмiстом домiшок Fe, Ni, Cu, Si, Al ~10-3…10-2 % при температурi
700…800 К з ступенем перегонки 80% знижує вмiст домiшок на 1…2 порядки у першому процесi та ще на 1
порядок – у повторному процесi. Cублiмацiя магнiю з вихiдним вмiстом домiшок ~1% та менше не
описується вiдомими рiвняннями дистиляції з ідеальним коефіціиєнтом розподiлу – у відмінності від
сублімації марганцю, тулiю, ербiю чи хрому при температурах 1600…1700 K з очисткою вiд ряду домiшок з
вихiдним вмiстом ~10-1% та менше.