JPS5823892B2 - Heat capacity measurement method - Google Patents

Description

[Detailed description of the invention] Heat capacity, thermal diffusivity, and thermal Two constants of conductivity can be measured.

That is, when the energy of the radiation absorbed by the sample, the mass, thickness, density, etc. of the sample are known, the heat capacity is measured by determining the temperature rise on the back surface.

Further, the thermal diffusivity can be determined by the time required for the temperature to rise by half of that temperature, and the thermal conductivity can be calculated from this thermal diffusivity and the heat capacity.

Therefore, the absolute value of temperature rise is not required for measuring thermal diffusivity, but it is necessary to accurately determine the absolute value of temperature rise for measuring heat capacity and conductivity.

Conventionally, thermocouple contacts were attached to the back side of the sample, but there were drawbacks such as large errors due to heat conduction loss, complicated work, and easy detachment when heated to high temperatures.Recently, infrared detection Non-contact observation using instruments is attracting attention.

However, it is necessary to calibrate the relationship between the output of the infrared detector, which receives radiation from the back surface of the sample, and temperature.

Conventionally, for this calibration, the temperature of the reference sample was gradually changed, and the relationship between the temperature T measured with a thermocouple whose contact point was placed near the sample and the output V of the infrared detector was calculated as shown in Figure 1. A calibration curve as shown by the solid line was obtained.

In other words, the output change ΔV of the infrared detector when a laser beam or the like is instantaneously incident on a sample at an arbitrary temperature T1
was measured, and the temperature rise ΔT was determined from the above curve.

However, the above curve includes not only the sample temperature but also the influence of heat rays emitted from the aperture, reflector, etc. in the infrared detection system, and these temperatures change as the sample temperature T changes.

On the other hand, when radiation is instantaneously incident on the sample, the aperture and the like maintain substantially the original temperature.

For this reason, the conventional infrared detection type flash method thermal constant measurement using the above-mentioned calibration curve has the drawback of containing errors.

The present invention provides a heat capacity measurement method that does not have these drawbacks, and will be described below.

FIG. 2 shows an example of an apparatus used in the method of the present invention, in which a flat sample 2 is mounted inside a sample holding cylinder 1 made of alumina or the like.
It is installed in an electric furnace 3, and the surface of the sample is instantaneously irradiated with laser light from a laser light source 6 through a reflecting mirror 4 and a semi-transparent mirror 5 as shown by the arrow.

In addition, the heat rays emitted from the back surface of the sample in the direction of the arrow are passed through an aperture and a toroidal mirror 8 to an infrared detector 9 of indium, antimony, or lead halide.
The temperature of the sample 2 is detected by measuring the output of the thermocouple 10 with a voltmeter 11, and the energy monitor 12 of the laser beam irradiated to the sample and the monitor 13 of the laser beam reflected by the sample detect the temperature of the sample 2. Find the energy absorbed by the sample.

That is, using such an apparatus, a sample 2 whose mass m and, if necessary, thickness t, density ρ, etc. are known, is heated to a desired temperature T.
The sample is held at I, and the sample is momentarily irradiated with laser light to measure the energy ΔQ absorbed by the sample and the change in the output of the infrared detector ΔVx.

Further, as shown in FIG. 3, a suitable standard sample 14 is installed in the apparatus shown in FIG. While holding the standard sample 14, the temperature T of the back surface of the standard sample 14 is observed using the voltmeter 16 by momentarily irradiating the laser beam.

At the same time, the output V of the infrared detector 9 is observed, and changes in the temperature T and output V over time t are recorded.

FIGS. 4(a) and (b) are examples of these recording curves. When the front surface is momentarily irradiated with a laser beam at time to, the temperature T of the back surface and the output V of the infrared detector change at time t.
As time passes, it increases to a very thick value, and then gradually decreases.

By extending this decreasing portion, the temperature rise ΔT and the output ΔV at time to are determined, and ΔT/ΔV is calculated.

The temperature rise ΔTx on the back surface of the sample can be obtained by multiplying that value by ΔVx determined for sample 2 as described above.

Figure 5 depicts the relationship between the time t and the temperature T on the back surface when sample 2 is irradiated with laser light, and the curve after the temperature T reaches its maximum value is extended. , temperature rise ΔT1 at time to when the laser beam was irradiated
By determining this, the heat capacity Cp can be calculated as ΔQ Cp=-mΔT1.

Note that if the time at which the temperature rise reaches ΔV2 is tl, then the thermal diffusivity α is given by 2α−0,139−1, and the thermal conductivity λ is λ−ρCpα.

In addition, using a standard sample, we sequentially hold it at each temperature and irradiate it with a laser beam, etc., as shown in Figure 6.
By preparing in advance a calibration curve or a calibration table that determines the relationship between temperature T and ΔT/ΔV, it is possible to immediately determine the required temperature increase ΔT1 at any temperature for any sample.

As explained above, in the present invention, radiation is instantaneously incident on the surface of a standard sample to which a thermocouple is attached, and the sample is detected based on the relationship between the temperature rise determined by the thermocouple and the output of an infrared detector. This is to obtain the temperature rise ΔT1 on the back surface.

Therefore, it is possible to accurately measure heat capacity without including errors due to temperature changes in the aperture or reflecting mirror in the optical system between the sample and the infrared detector.

That is, the conventional calibration curve as shown by the solid line in FIG. 1 is based on the output Vs due to the heat rays radiated from the sample and the output Va due to the heat rays from the aperture of the optical system, the reflecting mirror, etc.

In addition, when the sample temperature T is gradually changed, a part of the heat rays emitted from the sample enters the aperture, etc., and the temperature also changes.
changes, and the temperature T and the output Vs from the hot wire from the sample
The relationship with is shown as a broken line.

When a sample is instantaneously irradiated with radiation, the output Va of the infrared detector based on the heat rays of the aperture etc. is kept constant, so the output change ΔV of the detector is due only to the thermal change of the sample. It is something.

Therefore, the actual temperature change ΔT' on the back surface of the sample is given by the point (Vs+ΔV) on the above-mentioned broken line, but since the broken line is an unknown curve, this temperature change ΔT'
cannot be known, and the temperature change ΔT determined by the solid curve clearly contains an error.

The method of the present invention does not include such errors and can accurately measure the temperature change on the back surface of the sample and accurately determine the heat capacity of the sample.

[Brief explanation of the drawing]

Fig. 1 shows a calibration curve according to the conventional method, Fig. 2 shows an example of the configuration of an apparatus for carrying out the method of the present invention, and Fig. 3 shows a part of the calibration apparatus according to the method of the present invention. FIG. 4 is an example of a measurement curve for obtaining a calibration value using the method of the present invention, FIG. 5 is an example of a curve obtained using the method of the present invention, and FIG. This is an example of a calibration curve. In the figure, 2 is a sample, 14 is a standard sample, 9 is an infrared detector, 6 is a laser beam, 3 is an electric furnace, and 10 and 15 are thermocouples.

Claims (1)

[Claims] 1 Instantly irradiate the surface of a plate-shaped sample held at a desired temperature with radiation, detect changes in the heat rays emitted from the back surface with an infrared detector, and attach a thermocouple contact to the back surface to maintain the temperature. The surface of the plate-shaped reference sample held is momentarily irradiated with radiation, the heat rays emitted from the back surface are detected by the same detection system as the heat ray detection system of the sample, and the output of the infrared detector and the thermocouple are detected. The method is characterized in that the temperature rise on the rear surface of the sample is determined based on the relationship with the temperature rise detected in the sample, and the heat capacity of the sample is obtained from this temperature rise, the radiant energy absorbed by the sample, and the mass of the sample. Heat capacity measurement method.