JPH08128977A - Method for measuring thermal expansion coefficient - Google Patents

Abstract

PURPOSE: To measure the thermal expansion coefficient of a conductive material within a wide temperature range extending from room temperature to an ultrahigh temperature within a short time. CONSTITUTION: A pulse current is carried in the longitudinal direction of a conductive sample 1 having a fixed cross section to electrically heat the sample 1 within a short time. During this heating, the thermal expansion coefficient of the sample 1 is determined from the potential difference between a pair of movable voltage probes 3 fixed on the sample 1 side surfaces with a space and moved together with the sample 1 and a pair of fixed voltage probes 4 held with a fixed space and slid on the sample side surfaces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the coefficient of thermal expansion of a conductive material such as metal or graphite material at high temperature.

[0002]

2. Description of the Related Art Up to now, the coefficient of thermal expansion of a solid has been measured by a method represented by the following. One of the methods is optical interferometry.In this optical interferometry, a sample is placed in a high-temperature furnace with a constant temperature, the laser light incident on both end faces of this sample is guided to an interferometer, and both end faces are The coefficient of thermal expansion is determined by measuring the change in the dimension of the sample due to thermal expansion from the change in the phase difference of the reflected light and the wavelength of the light. This method
Since optical interference is used, the coefficient of thermal expansion can be obtained with extremely high accuracy, but the sample surface is a mirror surface, or it is necessary to attach a reflecting mirror to the surface. Further, it requires a precise optical system and is not suitable for measurement at high temperature.

In the push rod type thermal expansion coefficient measuring method, a push rod made of quartz or the like is brought into contact with a sample placed in a high-temperature furnace having a constant temperature, and the push rod and the same material as that are placed near the sample. The coefficient of thermal expansion is determined by measuring the difference in elongation between the reference rods. This method is a standard thermal expansion coefficient measurement method because the structure of the device for measurement is simple, but the measurement accuracy is not very high. Further, at high temperatures, measurement errors due to nonuniform sample temperature are likely to occur. In addition to these, there are many measuring methods such as a microscopic microscope method, an X-ray diffraction method, an electrostatic capacitance method, and an optical / mechanical lever method. To keep the temperature
At high temperatures, measurement errors tend to increase due to nonuniform sample temperature, and it takes a long time to change the measurement temperature and perform some measurements.

[0004]

SUMMARY OF THE INVENTION The technical problem of the present invention is to provide a method capable of accurately measuring the coefficient of thermal expansion of a conductive material in a wide temperature range from room temperature to ultrahigh temperature in a short time. It is in.

[0005]

The method for measuring the coefficient of thermal expansion of the present invention for solving the above-mentioned problems is basically a method for measuring the length of a conductive sample having a constant cross-sectional area and using a pulsed current. The sample is characterized in that the sample is electrically heated in a short time, and the coefficient of thermal expansion of the sample is fixed by a pair of movable voltage probes which are fixed at a side surface of the sample and are moved together with the sample during this heating. , And due to the difference in potential difference between a pair of fixed voltage probes that slide on the side of the sample while being kept at a constant interval, or the amount of movement of a pair of probes that are fixed and spaced along the side of the sample and move with the sample. The coefficient of thermal expansion is determined by measurement, and further, at the time of performing the heating, at least one end of the sample is held by the movable electrode, and the moving amount of the movable electrode during the heating is measured to determine the coefficient of thermal expansion.

More specifically, when measuring the coefficient of thermal expansion of a sample according to the present invention, as shown in FIG. 1, inside the sample container 5 filled with a vacuum or an inert gas, a flat plate shape or a cylindrical shape is used. Both ends of the sample 1 having a constant cross-sectional area are held by a pair of electrodes 2a and 2b. One electrode 2a is a fixed electrode that is fixedly provided, while the other electrode 2b is a movable electrode that has a structure that is movable in the horizontal direction in order to escape thermal expansion. 1
I am trying to give it to.

The sample 1 is connected to the capacitor bank 8 and the current switch 9 via the electrodes 2a and 2b, and by using them to supply a large pulsed current to the sample 1 for a short period of time, It is heated from room temperature to extremely high temperature. The temperature of the sample 1 during heating is measured and recorded from outside the sample container 5 by the radiation thermometer 7 through the optical window 6. Also, the energizing current is simultaneously measured from the potential difference generated in the standard resistor 10 inserted in series in the energizing circuit,
Will be recorded.

A pair of voltage probes 3 are brought into contact with the side surface of the sample 1 in order to measure the potential difference in the lengthwise direction of the sample during heating. There are two methods of contacting the sample with the voltage probe 3, one is called a movable voltage probe, and the tip of the movable voltage probe is located on the sample surface at two points separated in the length direction of the sample 1. It is something that is fixed. In this case, the distance between the voltage probes 3 changes with the thermal expansion of the sample.

Another method is called a fixed voltage probe, and the interval between the voltage probes 3 in contact with the sample 1 is always kept constant. In this case, the tip of the voltage probe slides on the sample due to the thermal expansion of the sample 1. When both the movable voltage probe and the fixed voltage probe are used in combination, the voltage probe 3 can be used as the movable voltage probe and the fixed voltage probe 4 can be brought into contact with the other side surface of the sample at the same time. By changing the method of contacting the voltage probe 3 of the sample with the sample to both movable and fixed types,
It is also possible to measure two types of potential difference by heating the sample twice.

When the coefficient of thermal expansion is measured, a pulse-like current is applied to the sample 1 through the electrodes 2a and 2b at both ends of the sample 1 according to the length of the sample, and the sample is left for a short time (for example, 1).
Within a few seconds), the heating is conducted by heating, and the interval at the temperature T of the movable voltage probe and the interval at room temperature at that time are L _m (T) and L _m0 , respectively. When the change is set to ΔL, the thermal expansion of the dimensionless sample is expressed by the equation (1). ΔL (T) / L _m0 = L _m (T) / L _m0 −1 (1) If it is assumed that the cross-sectional area of the sample is constant in the length direction and the distribution of the electrical resistivity of the sample is uniform, If the electric resistances of the sample between the fixed and movable voltage probes are R _f and R _m , respectively, and the distance between the fixed voltage probes is L _f , then L _m can be written as in equation (2). L _m (T) = L _f R _m (T) / R _f (T) (2)

From equations (1) and (2),

[Equation 1] Get.

A cross section of the sample is A, a distance between electrodes is L,
When the electrical resistance of the sample between the electrodes is R, the electrical resistivity of the sample is expressed by (RA / L). Therefore, the apparent sample calculated from R _m and R _f and the size of the sample at room temperature. If the electric resistivity of is set as ρ _m and ρ _f , respectively, the above equation (3) can be expressed by the following equation (4). ΔL (T) / L _m0 = ρ _m (T) / ρ _f (T) −1 (4)

Further, the potential differences measured by the fixed and movable voltage probes are V _f and V _m , respectively, and the energizing currents when the potential differences are measured are I _f and I _m (when the movable and fixed voltage probes are used simultaneously). _Has I _f =
I _m ), the equation (3) can be rewritten as the equation (5).

[Equation 2]

The coefficient of thermal expansion α is given by the equation (6) by differentiating the thermal expansion thus obtained with the temperature.

(Equation 3)

On the other hand, as shown in FIG.
It is also possible to determine the thermal expansion by directly measuring the amount of movement of In this case, it is not necessary to measure the potential difference between the probes, and a non-conductive probe may be used. And
If the moving amounts of the pair of probes 3 in the sample length direction when the room temperature is zero are ΔL ₁ and ΔL ₂ , respectively, the thermal expansion of the sample is expressed by the equation (7). ΔL (T) / L _m0 = ( _{ΔL 1} (T) −ΔL ₂ (T)) / L _m0 (7) The amount of movement of the probe is determined by the strain gauge attached to the probe itself or the column supporting it. It may be measured with a displacement sensor or an optical interferometer.

Further, the moving amount ΔL _e of one movable electrode 2b of the pair of electrodes used for energizing the sample is measured by the same method as the above-mentioned probe, and the thermal expansion is obtained by the equation (8). It is also possible. ΔL (T) / L _mo = ΔL _e (T) / L _e0 −1 (8) Here, L _e0 is the distance between the electrodes at room temperature. in this case,
In a portion of the sample 1 near the electrode, heat conduction to the electrode having a low temperature causes remarkable nonuniformity of the temperature of the sample. But,
Since the sample 1 is rapidly heated by energization in an extremely short time, the region where the temperature is not uniform is sufficiently smaller than the entire sample, and it is considered that the influence on the thermal expansion measurement is small.

[0017]

EXAMPLE FIG. 3 shows a sketch of the periphery of a sample in an apparatus in which the coefficient of thermal expansion was measured according to the present invention. Sample 1
Was a flat plate having a thickness of 0.1 to 1 mm, a width of 10 mm, and a length of about 50 mm, and both ends thereof were held horizontally by electrodes 2a and 2b inside the sample container. Among these electrodes, one electrode 2a is a fixed electrode and the other electrode 2b is a movable electrode for releasing thermal expansion of the sample, and a constant weak tension is applied to the sample 1 by the spring 2c.

A pair of pointed voltage probes 3 were brought into contact with the surface of the sample 1 with a constant force using a spring. When this voltage probe is used as a movable voltage probe, the tip of the voltage probe is put into a recess having a depth of about 0.3 mm machined on the sample surface, and the screw fixing the voltage probe 3 is loosened to It was set so that it could move with the thermal expansion of the sample 1. On the other hand, the voltage probe 3
In the case of using as a fixed voltage probe, the fixing screw of the voltage probe 3 was tightly tightened, and the tip of the voltage probe 3 was brought into contact with the portion of the sample surface where there was no dent at regular intervals.

The sample 1 is a semiconductor switch using a capacitor bank and a FET, and a large pulse-like current is passed for a short time within 1 second, so that the temperature from room temperature to 2800.
It was electrically heated to a temperature up to ° C. The energization current in the energization heating state, the potential difference between the voltage probes, and the temperature of the sample surface center measured by the radiation thermometer 7 through the optical window 6 are temporarily recorded in the transient memory.
Transferred to a personal computer, the coefficient of thermal expansion of Sample 1 was calculated from these data.

FIG. 4 shows the apparent electrical resistivity of the graphite material (POCOAXM-5Q1 graphite) measured using a moving and fixed voltage probe. The difference between these two electrical resistivities indicates the change in length due to the thermal expansion of the sample. FIG. 5 shows the equations (4) and (6) from these data.
The thermal expansion of a sample calculated using a formula and a thermal expansion coefficient are shown. This measurement revealed that the thermal expansion of the sample can be measured with a relatively small variation in the temperature range of 800 ° C to 2800 ° C. The coefficient of thermal expansion of the sample calculated from this data varies a little, but averages about 9 × 1
It was 0 ^-6 K ^-1 .

[0021]

According to the thermal expansion coefficient measuring method of the present invention described in detail above, the thermal expansion coefficient of the conductive material in a wide temperature range from room temperature to ultrahigh temperature is much shorter than that of the conventional method. It can be measured in time (1 minute or less). Further, since only the sample is uniformly energized and heated in a short time, a large-scale high-temperature furnace or the like is not required, and the measurement error due to the nonuniform temperature of the sample can be minimized. Furthermore, the method of measuring the coefficient of thermal expansion using the electrical resistivity of the sample has the advantage of simplifying the structure of the measuring device because it is not necessary to measure the dimensional change of the sample due to thermal expansion.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining the principle of a thermal expansion coefficient measuring method according to the present invention.

FIG. 2 is an explanatory diagram of a moving amount of a voltage probe and a movable electrode according to the present invention.

FIG. 3 is a sketch drawing around a sample in an example of the present invention.

FIG. 4 is a graph showing the apparent electrical resistivity of a graphite sample measured according to the present invention.

FIG. 5 is a graph showing the thermal expansion and the coefficient of thermal expansion of the graphite material measured according to the present invention.

[Explanation of symbols]

 1 sample 2a fixed electrode 2b movable electrode 3 voltage probe 4 fixed voltage probe 5 sample container 6 optical window 7 radiation thermometer

Claims (3)

[Claims] 1. A method of lengthening a conductive sample having a constant cross-sectional area, in which a pulsed electric current is applied to electrically heat the sample in a short time, and during heating, the sample is fixed at an interval on the side surface of the sample. It is characterized in that the coefficient of thermal expansion of the sample is obtained from the difference in the potential difference generated between the pair of movable voltage probes that are moved together with the sample and the pair of fixed voltage probes that are held at a constant interval and slide on the side surface of the sample. Method of measuring coefficient of thermal expansion. 2. A method of lengthening a conductive sample having a constant cross-sectional area by applying a pulsed electric current to heat the sample in a short time and fixing it at a side surface of the sample with a space during heating. A thermal expansion coefficient measuring method, characterized in that the thermal expansion coefficient of a sample is obtained by measuring the amount of movement of a pair of probes that move together with the sample. 3. A method of lengthening a conductive sample having a constant cross-sectional area, in which a pulsed current is passed to electrically heat the sample in a short time, and at least one end of the sample is held by a movable electrode when this heating is performed. Then, the thermal expansion coefficient measuring method is characterized in that the thermal expansion coefficient is obtained by measuring the moving amount of the movable electrode during the heating.