GB2226777A

GB2226777A - High pressure cell

Info

Publication number: GB2226777A
Application number: GB8900503A
Authority: GB
Inventors: Lev Grigorievich Khvostantsev; Nikolai Alexandrovich Nikolaev; Vladimir Alexandrovich Sidorov; Antoly Ivanovich Orlov; Alexei Mikhailovich Bukhartsev
Original assignee: INST FIZ VYSOKIKH DAVLENY IM L
Current assignee: INST FIZ VYSOKIKH DAVLENY IM L
Priority date: 1988-12-23
Filing date: 1989-01-10
Publication date: 1990-07-11
Also published as: FR2641614A1; GB8900503D0; DE3843604A1

Description

1 M&C FOLIO: 230P57957 HIGH-PRESSURE CELL The invention relates to

high-pressure equipmrnt for physico-chemical investigations and for the synthesis of new materials, and more specifically, it deals with high-pressure cells.

Such cells may be used for synthesis on superhard materials to be used in the metal machining.

Such cells may also be successfully used for the investigations of physical properties of solids and liquids within a wide temperature range where it is desirable to determine a change in pressure occurring during synthesis of superhard materials or during examinations of a sample and to control pressure or temperature.

A large number of investigations of physical properties of solids under pressure are carried out nowadays at high temperatures. In this connection, an important scientific trend in high-pressure physics has been the study of polymorphous transformation of solids, the climax of which was synthesis of diamond from graphite and cubic boron nitride from a starting hexagonal form.

2 SU-A-1045 642 discloses a highpressure cell comprising a container for a sample to be examined, a heater and heat insulating envelope positioned coaxially with one another. and a means for measuring pressure inside the container coupled to the container and having a pressure pick-up. The means for measuring pressure inside the container in this cell comprises a capillary tube sealingly communicating with the container and with the pressure pick-up, a hydrostatic fluid being within the container.

However, the provision of the capillary tube in the means for measuring pressure inside the container and the pick-up under a high enough pressure of the hydrostatic fluid, when its viscosity increases, thus lowering the accuracy of pressure measurement. In addition, in measuring a pressure above 4 GPa in this cell the capillary tube may break, so the pressure measurement range is narrow.

What is desired is high-pressure a cell which allows pressure measurement accuracy to be improved and which may enlarge the range of pressure measurement.

The present invention provides a high-pressure cell comprising a container for a sample to be examined or treated, a heater and a heat insulating envelope positioned coaxially with one another, and a means for measuring pressure inside the container coupled to the container and having a pressure pick-up, in which 3 the pressure pick-up of the means for measuring pressure inside the container comprises a resistance pick-up and the means for measuring pressure inside the container is positioned coaxially with the container and also comprises a sealed tube or enclosure containing a hydrostatic fluid. the resistance pick-up being positioned inside the tube.

The means for measuring pressure inside the container for the highpressure cell may additionally contain thermocouple positioned on the resistance pick-up.

The high-pressure cell may also comprise a heat insulating spacer positioned between the bottom of the container and the sealed tube of the means for measuring pressure inside the container, and the heater may be positioned between the container and the heat insulating envelope.

The container of the high-pressure cell may be made with an interior space whose dimensions correspond to the dimensions of the sample.

It is possible to ensure the identical pressure of hydrostatic fluid in both the container and the means for measuring pressure, with high enough pressure values. thus enhancing accuracy of pressure measurement.

In addition, pressure above 4GPa may be measured.

The pressure may be continually changed so as to make it possible to control the pressure value at high 1 4 temperatures.

The fact that it is possible to vary temerature and pressure while retaining accuracy of pressure measurement means that more complete information on the condition of the sample can be obtained, e.g. a phase of diagram can be completely plotted during a single test run.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a general view, in longitudinal section, of a high pressure cell; Figure 2 is a general view, in longitudinal section, of a high pressure cell with an additional thermocouple; Figure 3 is a general view, in longitudinal section, of a high-pressure cell with an additional heat insulating spacer; Figure 4 is a general view, in longitudinal section, of a high pressure cell with a container with an interior space whose dimensions correspond to the dimensions of a sample being examined.

The high-pressure cell shown in Figure 1 comprises a heat insulating envelope 1, a container 2, a heater 3, and a sample 4 coaxially positioned one within another. A thermocouple 5 is mounted on the sample 4. Current leads 6 and 7 connected to a power supply (not shown) are coupled to the heater 3. The current lead 6 extends z f through a lid 8 of the container 2. A device 10 for measuring pressure inside the container is positioned under the bottom 9 of the container 2. The device 10 comprises a sealed tube 11, having a lid 12, and a resistance pick-up 13 positioned within the tube in a hydrostatic fluid.

In another embodiment of the high-pressure cell, shown in Figure 2, the device 10 for measuring pressure inside the container also comprises a thermocouple 14 positioned on the resistance pick-up 13.

In still another embodiment. shown in Figure 3, the high pressure-cell also comprises a heat insulating spacer 15 positioned between the bottom 9 of the container 2 and the sealed tube 11 of the device 10 for measuring pressure inside the container. The heater 3 is positioned between the container 2 and the heat insulating envelope 1.

And finally, in a further embodiment of the high-pressure cell, shown in Figure 4. a container 16 having a lid 17 is made with an interior space 18 whose dimensions correspond to the dimensions of the sample 4 being examined, e.g. a flowable sample as shown.

The high-pressure cell functions in the following manner.

A pressure increase inside a high-pressure apparatus (not shown) results in a pressure inside the container 2 (Figure 1) of the high-pressure cell, which is filled 1 6 with a liquid or gas, and inside the sealed tube 11 of the device 10 for measuring pressure inside the container, which is filled with liquid. Build up of pressure in the high-pressure cell is recorded by its resistance pickup 13. After the pressure build-up, electric current is caused to flow in a circuit formed by the current lead 6, heater 3, and current lead 7. The heater 3 heats the sample 4 being examined. The temperature of the sample 4 is measured by means of the thermocouple 5. An increase in temperature of the sample 4 results in an increase in pressure in the container 2, which causes an increase in pressure in the sealed tube 11. This pressure increase is recorded by the resistance pickup 13.

The temperature of the resistance pick-up 13 is much lower than temperature of the heated sample 4 as the liquid surrounding the sample 4 has a low heat conductance. In addition, the tube 11 had good thermal contact with massive metal parts of the high-pressure apparatus (not shown). Consequently, the resistance pick-up 13. which is positioned inside the-tube 11, cannot be substantially heated. This facility allows temperature influence on readings of the pick-up to be eliminated. However, the temperature of the pick-up 13 may be monitored by means of the thermocouple 14 (Figure 2).

With a strong enough heating of the sample 4, the Z11 7 heat insulating spacer 15 is used to limit heating of the pick-up 13 (Figure 3). Arranging the heater 3 between the container 2 and heat insulating envelope 1 simplifies assembly and facilitates conduct of a test run.

In a case when non-hydrostatic pressure can act upon the sample 4, use is made of the container 16 (Figure 4) having the lid 17 and the interior space 18 whose dimensions correspond to the dimensions of the sample 4 being examined. The medium transmitting pressure to the sample 4 in this case is the material of the container 16.

When predetermined temperature and pressure are achieved in the sample 4 (Figures 1 to 4), its properties are changed, e.g. a phase transition occurs with a decrease in volume. Pressure in the sample 4 thus drops, and this pressure change is transmitted to the liquid in the sealed tube 11. This pressure drop is recorded by the pick-up 13. If it is necessary to restore previous conditions of temeperature and pressure in the sample 4, pressure acting upon the high-pressure cell is changed by varying the force of a press (not shown). Temperature of the sample 4 is also changed by changing power of electric current flowing in the-heater 3.

Therefore, the high-pressure cell allows continual measurement of pressure acting upon the sample 4 to be 1 8 carried out, for maintaining a preset constant pressure at a pre-set temperature.

The cell also enhances safety in working with highpressure equipment.

Finally, the high-pressure cell can be used in various types of highpressure apparatuses.

1 (1 1 1

Claims

CLAIMS:

9 1 A high-pressure cell comprising a container for accommodating a sample to be examined or treated, a heater and a heat insulating envelope positioned one inside another, and means for measuring pressure inside the container, aligned with the container and comprising a sealed enclosure containing a hydrostatic fluid and a resistance pick-up inside the tube.
2 A cell as claimed in claim 1, wherein the pressure measuring means includes a thermocouple on the resistance pick-up.
A cell as claimed in claim I or 2, including a heat insulating spacer positioned between the container and the sealed enclosure.
4 A cell as claimed in any preceding claim, wherein the heater is positioned between the container and the heat insulating envelope.
A cell as claimed in claim 4, wherein, in use, the dimensions of the interior space of the container correspond to the dimensions of the sample.
6 A high-pressure cell substantially as described with reference to, and as shown in any of Figures 1 to 4 of the accompanying drawings.

Published 1990 at The Patent Office, State House. 6671 High Holborn, London WC1R4TP. Further copies maybe obtained from The PatentOffice