NEW METHOD FOR DETERMINING THE INVARIANT EQUILIBRIUM OF PHASES AT HIGH TEMPERATURES

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80-00809A000600370792-2
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 5
• Document Creation Date: December 22, 2016
• Document Release Date: September 27, 2011
• Sequence Number: 792
• Publication Date: February 9, 1951
• Content Type: REPORT

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1
COUNTRY USSR
SUBJECT Scientific - Chemistry, phase equilibria
at high temperatures
INFORMATION FROM
FOREIGN DOCUMENTS OR RADIO BROADCASTS CD NO.
WHERE
PUBLISHED
DATE
PUBLISHED
LANGUAGE
CENTRAL INTELLIGENCE AGENCY REPORT
uuw1UEN11,.'
CLASSIFICATION CONFIDENTIAL
Thrice-monthly periodical
Moscow/Leningrad
11 Mar 1949
THIS DOCUN[NT CONTAINS INVONNAIION AFFICIINN TH[ IATION0L 09 91131
0/ THE UNITED {TATOS WITHIN THE WANING OF IS FIOMANS ACT NO
U. S. C.. SI AND 11. Al AMENDED. ITS TAANSNISSION ON THE N{VILATION
OF ITS CON MAt'
TO AN
LAW. 1 N[FNOOUCTION OF THIS /O AN ISI PROHINIITED,'S FPO?
MISITID NV TESTS
NEW METHOD FOR DETERMINING THE Ii'VARIANP EQUILIBRIUM
OF PHASES AT HIGH TEMPERATURES
Ya. I. O1'shanskiy
Inst of Geol Sci, Acad Sci USSR
Presented by Aced G. G. Urazov, 4 Jan 1949
Submitted 6 Dec 1948
Digest. Figures referred to are appended]
At present two basic methods for the determination of equilibrium condi-
tions at high temperatures between liquid and solid phases are being applied:
Kurnakov's method of thermal analysis and the statistical method of chilling,
which is used for the investigation of silicate systems.
Kurnakov's method yields excellent results when the liquid phases crystal-
lize without excessive-undercooling. A low viscosity of the liquid on melting.' .
a high'heat conductivity, and high heats of phase transformations are Yavorable
factors contributing to the successful use of the method of thermal analysis.
The statistical method of chilling, which is based on fixation of the liquid in
the form of a glass by rapid chilling,, is used successfully on substances which
do not 'crystallize easily. In some cases neither of these two methods can be
used effectively for a determination of the phase equilibrium. This refers to
systems composed of substances-which are aggressive at high temperatures, so
that the system is contaminated due to the fact that the walls of the crucible
or the protective sheath of the thermocouple dissolve in the liquid. For the
same reason the method of chilling also cannot be used, an additional reason
being that the aggressive melts have a strong tendency to crystallize, so that
they do not form a glass even when chilled very rapidly.
In an investigation of sulfide-silicate systems, we have used a method
based on capillary separation of the liquid phase (1). With the aid of this
method, even the most aggressive melts can be handled. The application of the
Dokladv Akademii Nauk SSSR, Vol LXV, No 2, pp 167-170,
CLASSIFICATION , CONFIDENTIAL
50X1-HUM
50X1-HUM
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DATE OF
INFORMATION 1948
DATE DIST. 9 Feb 1951
NO. OF PAGES 5
CIIPPI FMFNT TO
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method in question to severai. rn_y aggressive melts ha?s been checked in the
course'of the work described at present. The proposed method can be used when-
ever a liquid which is in equilibrium with a solid phase wets the surface of
the latter and has a high fluidity.
To determine the equilibrium between several solid phases and a liquid, a
tablet consisting of a finely powdered, thoroughly homogenized mixture of the
solid phases is prepared first. This tablet is placed on a porous plate made
of one of the solid phases participating in the equilibrium. Upon heating of
the tablet, the liquid formed as a result of the interaction of the solid
phases soaks into the porous plate.
The temperature of formation of the liquid phase can be determined by
keeping the tablet on the plate for a long time and raising the temperature
gradually, then noting the temperature at which a spot formed by the liquid ap-
pears on the plate. The slower the heating is carried out, the higher will be
the precision of the determined temperature.
A determination of the composition of the liquid in equilibrium can be
made when no fewer than three components participate in the equilibrium. Let
us assume that the composition of the liquid which is in equilibrium with the
solid phases A, B, C. and D is to be determined. Then a tablet composed of A
B + C +D and placed on a plate composed of A, to give an example, is heated at
a temperature slightly higher than that corresponding to the equilibrium. A
chemical analysis of the porous plate soaked in liquid will give the ratio of
B:C:D: in the liquid. Repeating the experiment with a porous plate consisting
of, another solid phase, for instance B, we shall obtain the ratio A:C:D in the
same liquid. The two ratios determined in this manner give'the complete compo-
sition A:B:C:D of the equilibrium liquid.
Figure 1 is a schematic drawing of the apparatus in which determinations
according to this method were carried out. The horizontal furnace 1 holds a
long porcelain tube 2, the walls of which are impermeable to gas. The cold
ends of the tube are equipped with rubber sleeves 3 and are stoppered. The
protective sheath of the thermocouple 8 enters.`hrough the stopper at the left.
The thermocouple and its sheath are placed high enough to leave room for sup-
port 4 holding the porous plate 5 and the tablet 6. Support 4 is a refractory
cylinder cut along a plane parallel to the axis. The support can be easily
moved in and out of the tube by means of a hook.;'' .'he choice of the material
for the support does not present any difficultieg;'because the dimensions of
the porous plate and of the tablet can be always held within such limits that
the liquid formed in melting does not soak completely through the porous plate.
Usually the support 4 was made of chamotte. The thermocouple Pt-Pt/Rh
could be moved in the protective sheath and its hot connection 7 was placed
above the tablet. By moving the thermocouple., the hottest spot in tube 2 could
be determined. The tablet was placed in that spot. Glass tube 9 passes through
the stopper at the right end. This tube is closed by a plane-parallel glass
plate affixed to the end of the tube with an adhesive. The correctness of the
tablet's position can be checked by looking through the glass plate. Before
starting to heat the furnace, nitrogen was blown through tube 2. Passage of a
slow current of nitrogen (0.5 liter per hour) was continued. during the experi-
ment. On drying and absorption of C02, the nitrogen was freed from admixtures
of oxygen by passing it through copper /filings7 at 450-5000 C and through a
sodium-potassium alloy at 150-1800.C. On leaving the tube, the nitrogen was
passed through a Tishchenko flask filled with sulfuric acid, which resulted in
a nitrogen pressure in the apparatus higher than the atmospheric. Tube 2 could
be moved out of the apparatus without interrupting the flow of nitrogen, so
that the tablet could be cooled rapidly.
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Notwithstanding the (_t~ij u,'i of the :?trogen, complete absence
of oxygen in the apparatus could not be achieved: small quantities of oxygen
diffused into the apparatus due to the fact that the sealing of the latter was
not completely hermetic, The presence of oxygen could be established by plac-
ing a shiny iron plate into the apparatus: this plate often became tinted as a
result of oxidation,
The accuracy of the thermocouple was checked by determining the melting
points of Cu, K2SO4, and Na2SO4 under the same conditions under which the tab-
let was heated.
For the purpose of checking the new method, the eutectic point of Si02 --
Fe2S104+ Fe was determined. This eutectic point had already been determined
by Bowen (2) by using the chilling method. The tablet was formed of chemically
pure iron reduced with nitrogen, Fe2Si04 prepared in on iron crucible, and
amorphous S102 calcined at 11000 C., These ingredients were thoroughly powdered
and mixed and then formed into a tablet undere adon ofasmall quantity of
on a
alcohol. To determine the eutectic point, resulting tablet
porous plate prepared by sintering Si02 at 1300? C:
Formation of liquid in the tablet is clearly seen, because a greenish spot
appears on the porous plate at the point of contact with the tablet and gradu-
ally spreads on the porous plate. Varying the composition of the tablet, one
determines the lowest temperature at which a spot forms. The upper curve of
Figure 2 shows the dependence of the temperature of appearance of the spot on
the composition of the tablet. The content of metallic iron was kept constant
at 19%.
The temperature curve exhibits a minimum at a composition of the tablet
corresponding to the eutectic liquid. The . minimueute temperature agrees this
very curve
corresponds to the eutectic point (1183) C), a
with the eutectic point of 1178? C found by Bowen according to the method of
chilling. When a tablet the composition of which differs considerably from the
eutectic is heated, forma.t'on of the spot occurs at temperatures considerably
exceeding the equilibrium temperature, as can be seen from the curve. This is
explained by the fact that in such tablets the quantity of liquid formed is
insufficient to moisten the silicon dioxide plate. The curve near the minimum
has a low enough slope, however, so that in the case of tablets the composition
of which differs by 10-15% from the eutectic, the temperature difference does
not exceed the range of experimental errors..
As has been mentioned already, complete freedom from oxygen could act be
achieved notwithstanding thorough purification of the nitrogen. For that rea-
son, the experiments were repeated in an iron crucible (cf. Figure 3), at that
the penetration of noticeable quantities of oxygen to the tablet was prevented.
Crucible 1 was closed by means of cover 2, and iron filings were placed on top
of the cover. The crucible was pleced in an apparatus similar to the one de-
scribed above, except that it was in a vertical position, The thermocouple in
its protective sheath was introduced into the crucible through opening 3 bored
in the bottom of the crucible. Heating was carried out in a current of nitro-
gen, as before. The inner surface of the crucible always remained perfectly
clean, because the oxygen was absorbed by the iron filings.
Analysis of the S102 plate gave the relationship FeO:Fe203 = 5000 or Fe: O=
3.46. To determine the relationship Si02:0 (where 0 is the oxygen combined
with iron) in the liquid, a tablet having a composition near to the eutectic
dro en at-
h
a
i
y
g
n
was heated on a porous iron plate prepared by sintering iron
mosphere at 900? C. Analysis yielded the relationship S102:0 = 2,48. Thus,
the icomposition of the eutectic liquid is Si02:Fe:O - 2..48,3.46:1, which also-,
agreis well with Bowen's result (2..50:3..45.1)0
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NFiP+ IN,,IIA .
From the point of view of t.c pr_opcsed procedure, the equilibrium Fe2SiO -
Si04 - 5102 - Fe - melt is not particularly favorable; because the melt satu-
rated with S102 has a rather high viscosity. Much more favorable are condi-
tions with regard to the equilibrium FeS - FeO - Fe - melt, which was investi-
gated by the same method. Porous plates were prepared from FeO or Fe, but it
was use doesanot resu tlinta noticS10eab2lepldisplacemenates, ofththee the The2loveres
curve of Figure 2 gives the dependence of the temperature at which a spot be-
gins to form on the composition of the tablet, (The quantity of Fe in the tab-
lets is constant and amounts to 21%.) It can be seen from the curve that in
this case the temperature of beginning spot formation is practically indepen-
dent of the composition of the tablet within an extensive range,
For the investigation of equilibria, the following experimental technique
is recommended. First, by using tablets consisting of equal quantities of all,
participating solid phases, the temperature and the composition of the equilib-
should orientation.
rium liquid are determined approximately for the purpose se of
com-
a tablet for an exact determination of the eutectic, point,
position which is close to that of the equilibrium liquid. It should not be
too lt co ihowevplateer, solideptely hase and soak
1e Yaa Io O1'shanskiy, DAN SSSR, Vol LIX, 513, 1948-
2. N~ L. Bowen and J. F. Schairer, Classical Investigations in the Field of
Physical Chemistry of Silicates /translated into Russian7, Leningrad, 1937,
p 87.
Furnace
Porcelain tube
Rubber sleeves
Support
Porous plate
Tablet
Hot connection of the thermocouple
Protective sheath of the thermocouple
Glass tube
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s0 t0
w.:gb~~'SiOz
fey ` iY'aighf7 r~0
Eu1?fi<
Figure 20 Temperature Dependence of Melting as indicated by
appearance of spot on the porous plate) on the Com-
position of the Tablet
1~ Crucible
2. Crucible cover
3. Hole for the insertion of
thermocouple
4 o Tablet
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Figure 3> Iron Crucible