SU1721489A1 - Dilatometer - Google Patents

Abstract

The invention relates to a measurement technique and can be used to determine the coefficient of thermal expansion of solid materials. The purpose of the invention is to expand the field of application due to the possibility of testing flexible and thin samples. The dilatometer includes a housing inside which the sample attachment points are located. One of the assemblies is fixed at the upper end of the housing, and the other is attached through an elastic membrane to the moving electrode of a capacitive displacement transducer. The attachment points are made in the form of U-shaped clamps, which at their free ends contain a pair of parallel pins, perpendicular to the housing axis. 1 ill., 1 tab.

Description

The invention relates to a measurement technique and can be used to determine the coefficient of thermal expansion (CTE) of solid materials.

A dilatometer is known, comprising a housing with sample attachment points and a capacitive displacement transducer operating in a three-point manner.

The disadvantage of this dilatometer is the limitations of the test specimens, which must be massive and rigid.

Closest to the invention is a dilatometer, comprising a case, specimen attachment points located inside it, one of which is fixed to the upper end of the case and the other through an elastic membrane to the moving electrode of a capacitive sensor.

A disadvantage of the known dilatometer is that it is impossible to measure CTE samples on it in the form of thin and flexible samples, which lose stability due to the force effect on the sample by the attachment points.

The purpose of the invention is to expand the scope of use due to the possibility of using flexible and thin samples.

The drawing shows the design of the dilatometer.

The housing 1 of the dilatometer contains a constant capacitor consisting of

Vj

YU

iЈ SO Yu

elements 2 and 3. The measured capacitance C is determined by the gap d between the stationary 4 and the moving 5 electrodes. The position of the electrode 4 is fixed by a lock nut 6. Sample 7 — a tape (or wire) —is placed between round pins 8 (0 0.1 mm) in U-shaped clamps 9 and 10. The pins 8 are located in holes made at the free ends of the clamps in the direction perpendicular to the axis of the housing 1. The position of the sample 7 in the pins 8 is fixed by a screw 11. The U-shaped space 12 above the pins allows the ends of the sample to remain free, thereby eliminating their influence on the thermal expansion of the cell and reducing the systematic measurement error that leads improve the accuracy of the CTE of thin and flexible designs. The length of the sample is determined by measuring the distance between the pins 8 in the clamps 9 and 10. The clamp 9 is fixed to the housing 1 by a nut 13, and the clamp 10 is connected through the membrane 14c by the electrode 5, while the electrode 5 and the housing 1 are electrically isolated from each other up to 15 and an air space 16. The diaphragm 14 is fastened with a nut. 17 to the housing 1 and provides coaxial placement of the sample without vibration and its translational motion without friction within 2 mm. The membrane is made of thin (0.04 mm) sheet beryllium bronze. The tensile force (1-3 MPa) on the sample is regulated by the nut 13 and is controlled by the value of capacitance C.

All parts of the dilatometer are made of one copper billet and are annealed in vacuum at 600 ° C for 4 hours. Measurements are carried out in the low temperature interval of 80-300 K.

Dilatometer works as follows. zom.

After installing sample 7 between the pins 8 in the clamps 9 and 10, turning the nut 13 creates a tensile force on the sample (1-3 MPa), controlled by the capacitance C (5-7) 1012 F (i.e., the gap d between the electrodes 4 and five). In this case, the membrane 14 bends in the axial direction upwards and in such a spring-loaded state is in the process of the whole measurement. Next, the dilatometer is placed in a chamber (not shown) with a pressure of gaseous gels of 20 Pa. This chamber is placed in a vacuum jacket with a pressure of (1-2) Pa. In the process of heating or cooling the sample, changing its linear dimensions, through the clamp 10 causes the membrane 14 to move in respectively the electrode 5, in connection with which the gap width d changes, which leads to a change in the AC capacitance, which is detected by the VM-484 AC bridge or P5079.

The average coefficient of thermal expansion of the sample arr of the sample in the temperature range (A T T2 - Ti) is calculated by the formula

„To g °

br 1o (T2-T1)

C2-Ci

C2.C1

2L

C2

) + Gbu

- “ex

where I0 and r0 are the sample length and the radius of the electrode 4, respectively, at room temperature;

Ci and C2 are the measured capacitances at temperatures TI to T2;

y-correction taking into account radial

expansion of the electrodes when the temperature varies from Ti to T2;

Axis - coefficient of thermal expansion of pure copper;

“Cx is an amendment to the cell's own stroke determined during the calibration of the device.

To obtain comparative data of the thermal expansion coefficient of pure nickel (99.8 wt.% Ni) of a massive sample (0 4 mm, length 20 mm) and a sample from a tape (thickness 0.04 mm, width 10 mm and length 30 mm), measurements were made in the proposed and well-known dilatometer shown in the table.

As can be seen from the table, the proposed device provides a high accuracy of determining the CTE of the tape.

The dilatometer can be used to study the thermal expansion of amorphous ribbons, polymer films, as well as wire samples. It can be used both for the low temperature range (up to 80 K) and for high 300–1000 K. In the second case

parts of the dilatometer are made of stainless steel. The compactness of the dilatometer makes it possible to place it in a superconducting solenoid and in a high pressure chamber, which provides measurement of such important physical characteristics as magnetostriction and compressibility, data on which for flexible and thin materials are practically absent in the reference literature.

Claims (1)

Dilatometer, comprising a case, specimen attachment points located inside it, one of which is attached to the upper end of the case, and the other through an elastic membrane to a moving electrode of a capacitive displacement sensor, characterized in that to expand the field of application due to the possibility of testing flexible and thin specimens; in it, the attachment points are made in the form of U-shaped clamps containing, on the free ends, a pair of parallel pins located perpendicular to the housing axis. Editor N.Rogulich Compiled by V. Marchenko Tehred M. Morgenthal Corrector S.Cherni