(The toroid-type
high-pressure-high-temperature apparatus and assemblies for electrical measuremens at high
pressure in a hydrostatic environment)
The
toroid-type high-pressure-high-temperature apparatus is rather simple in design and
operation and allows to generate pressure in the range of 9-12
GPa with a working volume of 1-0.3
cm3. The advantages of the apparatus are its
convenience for introducing a fluid-filled capsule and numerous electrical leads. It makes
possible measurements of electric, thermal, magnetic and volume properties of matter in a
hydrostatic environment at room and elevated temperatures as well as material synthesis
experiments. (*Recent developing a design gave rise to a new generation of the
high-pressure toroidal devices which extends the pressure limits to 15 GPa in 0.3 cm3 working volume.
History Of The
Toroid Device Creation
Basics Of The Toroid Device Operation
Main Advantages And Useful Features Of
Toroid Devices
Examples Of Experimental Methods
Publications
History
Of The Toroid Device Creation
The high pressure device capable of producing pres-sures greater than 5 GPa at high
temperatures in a large working volume is an important part of high-pressure technology.
Many experiments in physics, geoscience and material science need combination of large
volume and high pressure conditions. Two main types of these devices are widely used: the
belt and the multianvil press. The belt, capable of producing a few runs up to 8 GPa in a
working volume more than 1.0 cm3, is usually not used above 6 GPa to avoid rupture.
The same is true for the multianvil press.
When the problem of synthesis of superhard materials (namely diamond) at high pressure
arose in the Soviet Union, other kinds of high pressure devices were invented. First,
around 1960, the so-called recess type anvil device was developed at the Institute for
High Pressure Physics; it became wide-spread in the Soviet Union. The recess type anvil
apparatus has working parameters similar to those of the belt: the routine pres-sure is 6
GPa with possibility to make a few runs up to 8 GPa, but the electrical leads to the high
pressure zone break often. However, it is cheaper than the belt, and is more simple in
operation. The powerful diamond industry was created in the Soviet Union based on the
recess type anvil apparatus. The usable pressure of 6 GPa is sufficient to produce diamond
powder and then to sinter this powder with the binder.
The next step in the progress of the Soviet diamond industry, high pressure physics, and
geoscience was connected with the so-called toroid device, also invented at the Institute
for High Pressure Physics [Khvostantsev et.al., 1977; Khvostantsev, 1984] and protected by
the patents of leading industrial states such as USA, Japan, Germany, France, Great
Britain. The special features of toroid type apparatus will be described below. In this
section it should be noted that the higher usable pressure of the toroid device made it
possible to produce large polycrystalline diamond samples, analogous to natural carbonado.
As a matter of fact, the toroidal and recess type anvil devices were nearly unknown to
researchers outside the Soviet Union. The first in the West who evaluated the usefulness
of toroid device was Besson (France). For many years his group tried to develop a
miniature toroid device for neutron diffraction experiments above 10 GPa. This attempt was
successful [Besson et al., 1992] and now the toroid device with 100 mm3usable volume operates in the nuclear centers in Grenoble,
Edinburgh, and Los Alamos for structure determination of solids and liquids above 10 GPa.
Presented here is the original design of the toroid device manufactured at the Institute
for High Pressure Physics. “Toroid” passed the test for more than twenty years of
diamond and other materials synthesis and of other physical experiments in the pressure
range of about 10 GPa.
In the simple Bridgman anvils or recess type anvils the compression of the sample takes
place as a result of compression and extrusion of the gasket material. The deformation of
anvils under pressure and excessive extrusion of gasket material hinder obtaining higher
pressures in all high pressure anvil devices. In the toroid device, a new method of
supporting the gasket material surrounding the sample and the central portion of the
anvils is used, with the object of reducing the anvil deformation and gasket extrusion.
The toroid device with recessed central region is shown in Figure 1.
The
device consists of two cemented carbide parts (anvils) with a taper press-fitted into the
steel supporting rings.The gasket, repeating the shape of the anvils, is compressed
between them, the sample assembly being placed in the hole made in the central part of the
gasket. The faces of the anvils are each provided with a circular groove concentric with
their axis; the toroid-like space is filled by the gasket. When the anvils are moving
towards each other under the force applied, the pressure P2 is produced in this toroidal
space, whilst the pressure in the central region near the sample is P1 (P1>P2).
As a result the thickness of gasket in the Toroid-15 device (15 mm diameter of the central
recess, with a working volume of
0.3 cm3) after the 10 GPa pressure run is about 1.5 millimeters
(in the thinnest part). The gasket thickness for Toroid-25 device (25 mm diameter of the
central recess, with a
working volume of 1.0 cm3) after a 9 GPa
run is about 2.3 millimeters.
The pressure P2 in the region of toroidal groove causes the normal and tangential stresses
in the anvil material near the groove. The tangential stresses in the groove region are
smaller and in opposite sign with those acting in the central part of the anvil, which is
subjected to maximum pressure P1. So, the central part of the anvil is supported
effectively, and this support increases with the increase of pressure. It results in a
higher usable pressure and longer lifetime of the anvils. The calibration curves for two
basic cells: Toroid-15 and Toroid-25 are shown in Figure2.
(Pressure-load curves for toroid
devices. The diameter of the central recess is 15 mm for Toroid-15 and 25 mm for Toroid-25. Working volumes are 0.3 cm3and 1.0 cm3 accordingly)
Main
Advantages And Useful Feature
Of Toroid Devices
Simplicity in operation and use. Toroid is an anvil type device consisting of two parts of relatively
small size and weight which can be installed in any hydraulic press. It is very easy
to prepare the cell and sample assembly for experiment.
Reliable operation of electrical leads on loading and unloading (multiple loading-unloading cycles are also possible). The number of electrical leads is limited only by the diameter of the
high pressure region and the thickness of the adjacent leads. Typically there are 12 leads in the experiments where the
physical properties are measured.
The geometry of the toroid cell allows
introduction of a liquid-filled ampoule in the high pressure zone. The combination of compression and flow of the
gasket material permits the ampoule deformation under pressure to be uniform and the final
shape of ampoule is nearly the same as before compression. The hydrostatic sample
environment is favorable for work with single crystals.
The device can be easily adopted for material
synthesis experiments. In this case the solid pressure transmitting medium, heater, and
sample (or metal ampoule, containing liquid and sample) are placed in the central part of
a gasket. The sample can be treated at temperature up to 20000C with the temperature control by a W-W(Re) thermocouple.
Large working volume of the device is its outstanding feature that allows the fabrication of
the large-sized superhard polycrystalline products such as "Corbonado" from
diamonds or boron nitride.
Compared to similar devices designed elsewhere, for instance the "Belt" unit,
the toroidal device is capable of developing higher pressure
in a larger volume, thus enabling the synthesis of
large-sized polycrystalline products.
Examples
Of Experimental Methods
The toroid device is nearly ideal for studies of physical properties that can be realized
on the basis of electrical measurements. The authors have succeeded in measurements of
electrical resistivity, thermopower, thermal conductivity, differential thermal analysis
(DTA), magnetic susceptibility, volume change under pressure via strain gauge technique
and so on. It became possible to use most of the methods mentioned above at elevated
temperatures up to 6000C
(thermal stability limit of liquid) with precise control of
pressure by a manganin gauge. In this way the positions of phase transition points can be
located with high accuracy and P-T diagrams can be constructed. The recent development of
the strain gauge measurements allowed us to study problems of disordered systems
(amorphous solids and porous media compacted from nanocrystall-ine powders).
To
illustrate the experimental possibilities of the toroid device, we consider briefly the
design of liquid-filled ampoule for high temperature measurements of magnetic
susceptibility and the strain gauge technique for studies of the equation of state at room
temperature.
The view of an ampoule is shown in figure 3a. It consists of teflon parts and metal lids
and is placed in a hole made in the central part of a gasket. Figure 3
((a) liquid-filled ampoule for studies at
hydrostatic pressure and high temperatures; (b) assebmly for magnetic measurements placed
in the top part of an ampoule; (c) sample with the stain gauge bonded;
1-gasket (lithographic stone), 2-teflon ampoule, 3-lid, 4-thermal
insulation (asbestos), 5-heater, 6-sample, 7-thermocouple, 8-coil system for magnetic
measurements, 9-strain gauge, 10-manganin pressure gauge, 11-electrical leads.)
The electrical leads trough the gasket region are made from a wire (0.5 mm
in diameter) enclosed in the tube made of the wire material. Thin wires connected to the
sample or thermocouple are introduced into the same tube from the side of an ampoule. Very
convenient method to prepare the enclosing tube is to wound it with the use of appropriate
wire and rod. This wounded tubes help to prevent lead rupture. Pressure measurements are
done with the use of manganin gauge, its resistance change under pressure being linear up
to 9 GPa in the hydro-static environment [Khvostantsev and Sidorov, 1981]. The liquids
used are methanol-ethanol (4:1) and petroleum ether. The pressure gauge is placed in the
bottom part of an ampoule. The wire heater, sample, and thermocouple are placed in the top
part, which is separated from the pressure gauge by porous thermal insulation material.
This assembly allows us to make measurements of various physical properties or P-T
treatment of the sample in a well characterized pressure and temperature conditions. The
sample assembly for measurement of a magnetic susceptibility is shown in Figure 3b. It was
used to study the Curie point and spin reorientation transitions under pressure in some
invars and Geusler alloys [Sidorov and Khvostantsev, 1994; Gavriliuk et al., 1996]. A
system of two measuring and one exciting coils is placed inside the heater.
Measuring coils, connected in series, have equal number of turns and are wounded in
opposite directions. When excited by an alternating current via exciting coil, the
measuring coil system exhibits nearly zero voltage output signal without the sample or
with the sample in nonmagnetic state. The sample, placed inside one of the coils, causes
the large output signal which depends on its magnetic susceptibility. The example of
pressure dependence of magnetic susceptibility of two invars can be seen in Figure 4.
( Pressure dependence of magnetic susceptibility
for invar materials Er2Fe14B and Fe65Ni35.
Spin reorentation transition and disappearance of ferromagnetism are clearly seen)
Some examples of differential thermal analysis, thermopower and electrical resistance
measurements for solid-solid and solid-liquid phase transitions at high temperature up to 600 0Cand pressure up to 9 GPa can be found elsewhere [Khvostantsev and Sidorov, 1984].
The strain gauge technique was developed for measurements
of volume change at high pressure [Tsiok et al., 1992]. A miniature single-wire
strain gauge is bonded to the sample surface (Figure 3c). The gauge is made from 20
mkm constantan wire. The sample may be single crystal, amorphous solid, or powder
compact. In the latter case the sample is prepared by precompaction of a powder
(confined in a latex envelope) by high-pressure liquid (at 0.2 GPa) and machining to a
desired size. The sample with a strain gauge bonded is then covered by thin elastic
envelope (latex) preventing the penetration of pressure transmitting liquid in the sample.
The relation between length change of the sample and the resistance change of the
gauge was derived and checked experimentally on the basis of NaCl and Al equations of
state. This technique allows the precise quantitative measurement of volume change, the
relative accuracy of measurements and resolution being much better than that
attainable in x-ray diffraction measurements. The resolution of a sample length change is
0.001%, that makes it possible to observe very weak peculiarities on the compression curve
of a sample. The technique developed is very convenient for measurements in disordered
systems (amorphous materials and compacts of ultrafine powder) where the use of
diffraction methods is limited.
Publications
- Gavriliuk A. G., G. N. Stepanov, V. A. Sidorov, and S. M. Irkaev,
Hyperfine magnetic fields and Curie temperature in the Heusler alloy Ni2MnSn at
high pressure, J. Appl. Phys., 79, 2609-2612, 1996.
- Khvostantsev L. G., L. F. Vereshchagin, and A. P. Novikov, Device
of toroid type for high pressure generation, High Temp.- High Pressures, 9,
637-639, 1977.
- Khvostantsev L. G., and Sidorov V. A., High pressure polymorphism
of antimony. Thermoelectric properties and electrical resistance studies, Phys. St.
Sol.(a), 64, 379-384, 1981.
- Khvostantsev L. G., A verkh-niz (up-down) toroid device for
generation of high pressure, High Temp.- High Pressures, 16, 165-169, 1984.
- Khvostantsev L. G., and Sidorov V. A., Phase transitions in
antimony at hydrostatic pressure up to 9 GPa, Phys. St. Sol.(a), 82, 389-398, 1984.
- Sidorov V. A., and Khvostantsev L. G., Magnetovolume effects and
magnetic transitions in the invar systems Fe65Ni35 and Er2Fe14B
at high hydrostatic pressure, J. Magn. Magn. Mater., 129, 356-360, 1994.
- Sidorov V. A., V. V. Brazhkin, L. G. Khvostantsev, A. G. Lyapin,
A. V. Sapelkin, and O. B. Tsiok, Nature of semiconductor-to-metal transition and volume
properties of bulk tetrahedral amorphous GaSb and GaSb-Ge semiconductors under high
pressure, Phys. Rev. Letters, 73, 3262-3265, 1994.
- Tsiok O. B., V. V. Bredikhin, V. A. Sidorov, and L. G.
Khvostantsev, Measurements of compressibi-lity of solids and powder compacts by a strain
gauge technique at hydrostatic pressure up to 9 GPa, High Pressure Research, 10,
523-533, 1992.
- Tsiok O. B., V. A. Sidorov, V. V. Bredikhin, L. G. Khvostantsev,
V. N. Troitskiy, and L. I. Trusov, Relaxation effects during the densification of
ultrafine powders at high hydrostatic pressure, Phys. Rev.B, 51, 12127-12132, 1995.
-
F.
S. Yel’kin, O. B. Tsiok, and L. G. Khvostantsev, The Strain Gauge
Technique for Measuring the
Compressibility of Solids at High Pressures and Temperatures, Instruments
and Experimental Techniques, Vol. 46, No. 1, 2003, pp. 101–106.
-
L.G.
Khvostantsev, V.N. Slesarev, V.V. Brazhkin, “Toroid-type high pressure
device: history and prospects”, High Pressure Research, 24, No 3, 2004.
-
F.
S. El’kin, O. B. Tsiok, L. G. Khvostantsev, and V. V. Brazhkin, Precise
In Situ Study of the Kinetics of Pressure-Induced Phase Transition in CaF2
Including Initial Transformation Stages, JETP, Vol. 100, No. 5, 2005, pp.
971–976.
-
O.
B. Tsiok, L. G. Khvostantsev, I. A. Smirnov, and A. V. Golubkov,
Electron and Lattice Stages in the Valence Transition
in SmTe
under a High Hydrostatic Pressure, JETP, Vol. 100, No. 4, 2005, pp. 752–759.
-
F.
S. Yel’kin, O. B. Tsiok, V. V. Brazhkin, and L. G. Khvostantsev, «High-precision
in situ investigation of the kinetics of the high-pressure phase
transition in CaF2 including the initial transformation stages»,
Phys.Rev.B., 73, 094113 (2006)
Our
experience enables us to offer our help in various investigation and measurement problems.
Contact person:Dr. Valentin Ryzhov. E-mail:
ryzhov@hppi.troitsk.ru
