RU1781564C - Method of determination of phase transitions of first kind - Google Patents

Abstract

Using experimental experimental physics of high pressures SUMMARY OF THE INVENTION A sample is placed between a piston and a fixed force sensor, the displacement of the piston is measured under the influence of a load applied to the sample, measured first by a moving force sensor, then 4 by a fixed force sensor. The phase transition pressure is determined by the jump on the dependence of the load measured by the stationary force sensor on the load measured by the movable force sensor, and the jump of the phase transition volume is determined by the dependence of the piston displacement on the load measured by the fixed force sensor 3 s

Description

The invention relates to the field of experimental high pressure physics.

Known methods for determining the pressure and volume jump during phase transitions of the first kind, in which the test substance is placed in a cylindrical channel of a high pressure chamber and compressed using a piston equipped with seals to prevent leakage of the sample, the Phase transition is determined by measuring the nature of the dependence of the displacement of the piston on applied to force or pressure in the chamber measured by an internal sensor located in a hydrostatic medium In the latter case, the creation of a hydrostatic capsule and a shutter for introducing wires into the chamber, which greatly complicates the design of the high-pressure chamber

The purpose of the invention is to increase the accuracy and sensibility of determining and calculating the magnitude of pressure and volume jump during a phase transition.

This goal is achieved by the fact that another, fixed force sensor is introduced into the high-pressure chamber, on which the sample rests. The pressure in the sample is measured using two force sensors - movable and stationary. In addition to the traditional method of determining the phase transition from the dependence of the displacement on the force on the moving piston, this method allows you to build the dependence of the force measured by one sensor on the force measured by another sensor, which shows features in the region of the first-order phase transition T Thus, we can locate and determine the phase transition pressure without measuring the displacement of the piston

The method allows to determine the pressure and volume jump during the phase transition by measuring the piston displacement in the dependent SP

WITH

x4

The stress of the stationary piston. The hysteresis loop of the dependence of the displacement on the force applied to the moving piston has a large pressure width and in order to determine the transition pressure, it is necessary to introduce an assumption on the friction behavior during the forward piston stroke, which leads to systematic errors, the magnitude and sign of which are difficult to estimate. In this method, when measuring the force by a stationary sensor, which does not include the training of a moving piston, the hysteresis of the loop significantly narrows to the hysteresis of the phase transformation in the test substance, which increases not only the accuracy of determining the pressure, but also the accuracy of determining the volume jump at phase transition.

In FIG. 1 is a diagram of an apparatus for implementing the method for determining phase transitions; in Fig.2 - the dependence of the strength of the stationary sensor from the efforts of the moving sensor; Fig. 3 shows the dependence of the displacement of the piston on the forces of the movable and stationary sensors.

In the proposed device, the sample 1, which is located in the cylinder 2 of the high-pressure chamber, is supported through the piston 3 on a fixed force sensor 4. The force applied to the sample through the rod b and the upper piston 5 is measured by a movable force sensor 7. Displacement sensors 8. associated with the rod 6 and the fixed force sensor 4, measure the displacement of the piston, which is then converted into a change in the length of the sample under pressure

The high pressure chamber through the sleeve 9 is supported on the bottom plate of the press.

In FIG. Figure 2 shows in arbitrary units the dependence of the force of the stationary sensor PI on the force of the movable sensor R for the model substance КЗУз at a temperature of 20 ° С. The phase transition with increasing pressure is determined by

jump 1, and with a decrease in pressure - jump 2.

In FIG. 3 in arbitrary units shows the dependence of the displacement of the piston L on

the force F of the movable (solid curve) and fixed (dashed curve) sensors for the same sample. The volume jump is determined by the dependence of the displacement of the piston L on the readings of the stationary sensor (dashed curve).

This method of determining phase transitions of the first kind compared with existing methods has the following advantages: an increase in the sensitivity and accuracy of determining the pressure of the phase transition almost by an order of magnitude due to a significantly smaller influence of friction on the force measured by a stationary sensor, and an increase in the accuracy of determining the volume jump during a phase transition due to narrowing of the hysteresis loop and No need to make an assumption about the symmetry of friction relative to the direction of movement of the piston .

Claims (1)

SUMMARY OF THE INVENTION A method for determining phase transitions of the first kind by the displacement of a piston under the action of a load applied to a sample, measured by a movable force sensor, characterized in that, in order to increase sensitivity, the sample is placed between the piston and a stationary force sensor, additionally measured the piston displacement under the action of the applied load measured by the fixed force sensor, while the phase transition pressure is determined by the jump on the dependence of the load measured by the non-stationary force sensor on the load measured by the movable force sensor, and the jump in the phase transition volume is determined by the dependence of the piston on load measured by a fixed force sensor 700 Kno 500 30Ж i ii i ..i i t, i i.i i- .i-i .. i-jii-i-i-i-i-i-i-i-i-i-i-i 500 700 fig i , 9kbar i-i-i-i-i-i-i-i-i-i-i 700 900  FIG. 2. 400,900 Fig.Z