JPH0718827B2 - Thermophysical property measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to the thermal diffusivity and specific heat of a macroscopic heterogeneous material such as a functionally graded material or a layered material whose composition and physical properties change along the vertical direction of the laminated surface. The present invention relates to measurement of distribution of thermophysical property values such as thermal conductivity.

[Prior Art and Problems] The usual thermophysical property values of a solid material are measured by a laser flash method for thermal diffusivity, an adiabatic method for specific heat, a differential scanning calorimetric method, The steady-state method is generally used for the dropping method and the thermal conductivity, and it can be considered that the measurement technique is established. (For example, Magrich, Cesaryan, Berecky, "Introduction to Thermophysical Properties, Volume 1, Review of Measurement Techniques" (1984) Planham Press, New York; Maglic, Cezairliyan, Pelets.
key `` Compendium of Thermophysical Pproperty Meas
urement Methods, Volume 1, Survey of Measurement Tec
hniques ”(1984), Plenum Press, New York) However, in recent years, development of macroscopic inhomogeneous materials such as functionally graded materials and multi-layer materials that macroscopically introduce controlled compositional inhomogeneity, For such materials, the above-mentioned measuring methods used for ordinary uniform and dense materials cannot be applied as they are. (For example, Nobuyuki Araki, “Advancement of thermal conductivity measurement methods and how to select measurement methods”, Journal of Japan Society of Mechanical Engineers, vol.9.
(0, no.822, pp.79-84, 1987) In addition, such macroscopic heterogeneous materials are often assumed to be used at high temperatures, and thermophysical property values up to high temperatures are required. There is. When measuring an ordinary uniform and dense solid material at a high temperature of 1000 ° C or higher, first measure the thermal diffusivity by the laser flash method, and then determine the thermal conductivity from the specific heat value obtained by the dropping method and the density of the sample. It is common to calculate. However, in a material that is macroscopically inhomogeneous, such as a functionally gradient material, the thermal diffusivity and the specific heat are obtained as average values, so the thermal conductivity cannot be calculated by a simple formula as in the case of a homogeneous material. That is, for macroscopic inhomogeneous materials, it is necessary to measure the distribution of thermal diffusivity and specific heat that changes depending on the position inside the sample, not the average value of the thermal diffusivity of the entire sample or the heat capacity of the entire sample. Becomes

In the ordinary laser flash method, the spatial energy density distribution of the pulsed laser beam is non-uniform, so a one-dimensional heat flow state is not always realized inside the sample, and the transient temperature of only one central part on the back surface of the sample Since the rise is measured, it cannot be applied to the measurement of thermal diffusivity and specific heat distribution. Therefore, at present, there is no method to measure the distribution of thermal properties such as thermal diffusivity, specific heat, and thermal conductivity of macroscopic heterogeneous materials at high temperatures of 1000 ° C or higher, and macroscopic materials such as functionally graded materials and multilayer materials Has become an urgent issue in evaluating thermophysical properties of heterogeneous materials.

[Object of the Invention] The present invention relates to a thermal diffusivity, a specific heat, a thermal conductivity, etc. for a macroscopic heterogeneous material whose composition and physical properties change along a direction perpendicular to a laminated surface such as a functionally graded material and a multilayer material. It is an object of the present invention to provide a thermophysical property measuring method capable of measuring the distribution of a physical property inside a material as a function of position.

[Means for Solving Problems] The present invention takes the following means in order to eliminate the above-mentioned drawbacks.
That is, a flat plate sample showing inhomogeneity in the in-plane direction is cut out from a macroscopic inhomogeneous material whose composition and physical properties change in the direction perpendicular to the laminated surface, and the front and back surfaces thereof are uniformly blackened to make the laser beam uniform. By measuring the in-plane distribution of the transient temperature rise on the back surface of the sample after pulsed radiant heating of the sample surface with a uniform energy density by a pulsed laser beam with a uniform spatial energy density through an optical system, The distribution of thermal properties of macroscopic inhomogeneous materials that change with time was obtained.

As the distribution of thermal characteristics, the distribution of the thermal diffusivity of the macroscopic heterogeneous material that changes in the vertical direction of the laminated surface from the in-plane distribution of the transient temperature rise rate obtained from the in-plane distribution of the transient temperature rise on the back surface of the sample I asked.

As the distribution of thermal characteristics, the in-plane distribution of the transient temperature rise maximum value obtained from the in-plane distribution of the transient temperature rise on the back surface of the sample is used to determine the per unit volume of the macroscopic heterogeneous material that changes in the vertical direction of the laminated surface. The distribution of the relative value of the heat capacity of was calculated.

As the distribution of the thermal characteristics, the distribution of the absolute value of the heat capacity per unit volume was obtained by proportionally distributing the heat capacity of the whole flat sample measured in advance according to the distribution of the relative value of the heat capacity per unit volume.

As the distribution of the thermal characteristics, the distribution of the absolute value of the heat capacity per unit volume is separately measured by a general method, and the distribution of the density is divided by each position inside the sample. The distribution of the specific heat of the macroscopic inhomogeneous material which changes in the above-mentioned manner was obtained.

As the distribution of the thermal characteristics, as the product at each position of the distribution of the thermal diffusivity and the distribution of the absolute value of the heat capacity per unit volume,
The distribution of thermal conductivity of macroscopic inhomogeneous materials changing in the direction perpendicular to the laminated plane was obtained.

When the thickness of the macroscopic inhomogeneous material was small and the sample cut perpendicular to the stacking plane was not large enough for measurement, a flat plate sample was cut out along a plane having an inclination with respect to the stacking plane.

[Operation] In the above means, the flat surface sample whose composition and physical properties change along the surface is uniformly blackened on its front and back surfaces, so that the absorptance of the sample surface with respect to the laser beam is uniform. As a result, uniform pulsed radiant heating becomes possible. Further, since the emissivity of the back surface of the sample becomes uniform at the radiation temperature measurement wavelength, the relative temperature distribution can be accurately measured.

By irradiating the surface of the sample prepared in this way with a pulsed laser beam having a uniform spatial energy density distribution through a laser beam homogenizing optical system, a one-dimensional heat flow distribution inside the sample is achieved. By measuring the transient changes in the temperature distribution on the back surface of the sample after pulse heating with a high-speed thermal imager, the distribution of the absolute value of the thermal diffusivity and the relative value of the heat capacity per unit volume at each position along the sample surface was measured. Is possible.

The heat capacity of the entire sample can be measured by well-known methods such as the adiabatic method, differential scanning calorimetry method, and dropping method, and the result is proportional to the distribution of the relative value of the heat capacity per unit volume obtained by the above method. By allocating, the distribution of the absolute value of the heat capacity per unit volume can be obtained.

Further, by measuring the density of each part of the sample by a standard method such as a pycnometer method or a density balance method, the distribution of the absolute value of the specific heat can be obtained from the distribution of the absolute value of the heat capacity per unit volume.

The distribution of the thermal conductivity in the sample is obtained as the product of the value of the thermal diffusivity at each position in the sample obtained as described above and the absolute value of the heat capacity per unit volume.

In addition, when the thickness of the material is small and a flat plate sample with a sufficient width cannot be obtained by cutting out perpendicularly to the laminated surface, along a surface inclined by about 5 ° to 20 ° with respect to the plane direction of the plate material. 0.2 mm thickness
Measurement is possible by cutting into a flat plate with a thickness of about 2 mm.

In the present invention, uniform heating of the sample surface is realized by using the laser beam homogenizing optical system, and a local distribution of transient temperature rise on the back surface of the sample is observed. It differs from the ordinary laser flash method in which the sample surface is heated by a multimode oscillation laser beam with non-uniform spatial energy density and the average transient temperature rise of the sample back surface is measured at only one location. .

Embodiments of the Invention Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the principle of thermophysical property measurement according to the present invention.
The surface of the macroscopic inhomogeneous material sample 2 cut out in a flat plate shape so as to change the composition and physical properties along the surface direction is instantaneously and uniformly heated by the pulsed radiation heating 1 having a spatially uniform energy density. At this time, in order to keep the absorptance of the sample surface for radiant heating light and the emissivity of the back surface of the sample at the time of radiation temperature measurement constant, the front and back surfaces of the sample are uniformly blackened. If the sample is thin enough for the characteristic length along the plane of change in composition / physical properties, it can be considered that heat will flow in one dimension vertically from the sample front surface to the back surface in each part of the sample. .
In such a state, the change in the one-dimensional temperature distribution of the back surface of the macroscopic inhomogeneous material sample is measured along the direction in which the composition and the physical properties change by using the high-speed thermal imager or the one-dimensional scanning radiation thermometer 3. The results are arranged as the transient temperature rise 4 at each position on the back surface of the sample shown on the right side of the figure, and the composition of macroscopic inhomogeneous material and the one-dimensional rise time distribution 5 along the direction of change of physical properties and the maximum The distribution 6 of temperature rise is obtained.

FIG. 2 shows an actual measurement example of the in-plane distribution of the transient temperature rise based on the above principle. The horizontal axis represents the position on the sample surface, the vertical axis represents the transient temperature rise, and the diagonal axis represents the elapsed time after pulse heating. In Fig. 2, 7 is the time variation of the in-plane distribution of the transient temperature rise for ordinary homogeneous materials, and 8 is the time variation of the in-plane distribution of the transient temperature rise for macroscopic heterogeneous materials whose composition changes in the in-plane direction. Is shown. As shown in FIG. 1, the composition change of the macroscopic inhomogeneous material sample changes only in the one-dimensional direction, and the in-plane increase of the transient temperature rise also changes only in the one-dimensional direction.

In the homogeneous material, the transient temperature rise at the same elapsed time is always constant regardless of the position, as shown in 7. On the other hand, in the macroscopic inhomogeneous material, the temperature rises rapidly at the position where the thermal diffusivity is large and slow at the position where the thermal diffusivity is small, so that the transient temperature rise varies depending on the position, as shown in Section 8.

In FIG. 3, the horizontal axis represents time and the vertical axis represents transient temperature rise, and the data in FIG. 2 are displayed for each position on the sample. In the result 9 for the homogeneous material, the shape of the transient temperature rise curve is the same regardless of the position, whereas in the result 10 for the macroscopic heterogeneous material, the rising speed of the transient temperature rise curve differs depending on the position.

The above measurement corresponds to the simultaneous measurement of the thermal diffusivity and the thermal capacity by the ordinary laser flash method at each position on the sample surface. It is known that the sample back surface temperature after pulsed radiation heating rises according to the curve shown in FIG. The temperature rise reaches the maximum value ΔT after a certain period of time, and then keeps the constant value. The thermal diffusivity is given by the following equation, where t _1/2 is the time required to reach the half-maximum temperature rise ΔT / 2.

Here, 1 is the thickness of the sample.

At the same time, the heat capacity per unit volume is given by the following equation.

Here, q is the energy of pulsed radiation heating absorbed by the unit area of the sample.

However, in this case, it is not easy to evaluate the absolute values of q and ΔT, and the value of C is usually a relative value.

By performing the analysis of FIG. 2 on the measurement curve of the transient temperature rise 4 at each position x on the back surface of the sample shown in FIG. 1, the direction in which the composition and physical properties of the macroscopic heterogeneous material sample change The distribution of the absolute value of the thermal diffusivity along with, and the distribution of the relative value of the heat capacity per unit volume can be obtained. If the heat capacity of the entire sample is separately measured by an established method such as the adiabatic method, differential scanning calorimetry method, or dropping method, the total heat capacity is proportionally distributed by the relative value of the heat capacity distribution per unit volume, The absolute value of the heat capacity distribution per hit is obtained. FIG. 3 shows a measurement example for a multilayer material. Since it is the value at position x, the rise time distribution 5 is t
_1/2 (x), maximum temperature rise distribution 6 is ΔT (x), thermal diffusivity distribution 11 is α (x), heat capacity distribution per unit volume
12 was represented as C (x).

The distribution 13 of thermal conductivity is expressed by the following equation by definition.

λ (x) = α (x) · C (x) (3) Therefore, if the distribution 11 α (x) of thermal diffusivity and the distribution 12 C (x) of heat capacity per unit volume are known, λ (x) Is easily found.

If the density distribution ρ (x) of each part of the sample is measured by a pycnometer or a density balance, the specific heat distribution c (x) can be obtained from C (x) by the following equation.

FIG. 4 shows an example of the configuration of a measuring device based on this method. Since the laser beam 15 emitted from the high-power pulse laser 14 is usually spatially non-uniform due to multimode oscillation, the spatial energy distribution is made uniform by passing through the laser beam homogenizing optical system 16. The laser beam 1 thus homogenized is reflected by the mirror 17, guided through the upper window into the vacuum chamber 18, and irradiated on the macroscopic inhomogeneous material sample 2 installed in the sample holder 20. The sample 2 is heated by the heater 19 in the temperature range from room temperature to 2000 ° C. or higher, and measurement in a wide temperature range is possible. The change in the one-dimensional temperature distribution on the back surface of the sample 2 is measured by the thermal imager or the one-dimensional scanning radiation thermometer 3 through the lower window. The measurement result is read into the high-speed multi-channel data recording device 21 in synchronization with the laser trigger signal. The measurement result sent to the personal computer 22 is recorded on a floppy disk and analyzed, and a transient temperature rise curve at each position on the back surface of the sample is displayed on the CRT. Further, by inputting the total heat capacity of the sample separately measured and the density distribution of each part of the sample in advance, distributions of thermal characteristics such as thermal diffusivity, specific heat and thermal conductivity of each part of the sample are calculated.

As shown in FIG. 7, since the functionally graded material 23 has a thickness of about 1 to 10 mm, when a flat sample is cut out perpendicularly to the stacking tank surface 24, the width of the sample changes in one-dimensional temperature distribution. It cannot be wide enough for measurement. In such cases, the seventh
As shown in the figure, the measurement can be performed by cutting out a flat plate-shaped sample 26 having a thickness of 0.2 to 2 mm and a width of 10 mm to 20 mm at an inclination of about 5 ° to 20 ° from the laminated surface 24.

[Effects of the Invention] As described above, according to the present thermophysical property measuring method, the thermal diffusivity, specific heat, thermal conductivity, etc. of a macroscopic heterogeneous material whose composition and physical properties change along the vertical direction of the laminated surface can be obtained. It is possible to measure the distribution of thermophysical property values depending on the position in the sample. According to the present invention, thermophysical property measurement of macroscopic heterogeneous materials such as functionally graded materials and multilayer materials, which has been difficult by conventional methods, becomes possible for the first time.
Furthermore, since this thermophysical property measurement method can be easily applied to temperatures as high as 2000 ° C. or higher, there is a demand for the use of new materials in high-temperature environments, especially in advanced energy utilization, peaceful nuclear energy utilization, aerospace, etc. It is expected to promote the development and use of macroscopic heterogeneous materials in the fields where they are used.

[Brief description of drawings]

FIG. 1 is a diagram showing the principle of thermophysical property measurement according to the present invention. FIG. 2 is an example of actual measurement of the temporal change in the in-plane distribution of the transient temperature rise when the present invention is applied to a homogeneous material and a macroscopic inhomogeneous material. FIG. 3 is a measurement example of a transient temperature rise curve at each position when the present invention is applied to a homogeneous material and a macroscopic inhomogeneous material. FIG. 4 is a graph showing calculation of the thermal diffusivity and the heat capacity per unit volume from the measurement curve of the excessive temperature rise at each position on the back surface of the sample. FIG. 5 is a graph showing a measurement example of a multilayer material and a distribution of thermal diffusivity, heat capacity per unit volume, and thermal conductivity obtained by analyzing the measurement. FIG. 6 is a block diagram of a measuring apparatus showing an embodiment of the present invention. FIG. 7 is a perspective view showing that a sample to which the present thermophysical property measuring method can be applied can be prepared by obliquely cutting out a thin macroscopic inhomogeneous material. 1 ... Uniform pulsed radiation heating 2 ... Macroscopic inhomogeneous material sample 3 ... Thermal imager or one-dimensional scanning radiation thermometer 4 ... Excessive temperature rise at each position on the backside of sample 5 ... Rise time distribution 6 …… Distribution of maximum temperature rise 7 …… Time change of in-plane distribution of transient temperature rise in homogeneous material 8 …… Time change of in-plane distribution of transient temperature rise in macroscopic heterogeneous material 9 …… Each homogeneous material Transient temperature rise curve at position 10 …… Transient temperature curve at each position of macroscopic heterogeneous material 11 …… Distribution of thermal diffusivity 12 …… Distribution of heat capacity per unit volume 13 …… Distribution of thermal conductivity 14 …… High-power pulsed laser 15 …… Direct laser beam 16 …… Laser beam homogenization optical system 17 …… Mirror 18 …… Vacuum chamber 19 …… Heater 20 …… Sample holder 21 …… High-speed multi-channel data recorder 22 …… Personal Computer 2 3 ... Macroscopic inhomogeneous materials such as functionally graded materials and multi-layer materials 24 ... Direction along the lamination plane 25 ... Direction in which composition and physical properties change 26 ... A plane that is inclined with respect to the lamination plane , Cut flat sample

Claims (7)

[Claims] 1. A flat plate sample showing inhomogeneity in the in-plane direction is cut out from a macroscopic inhomogeneous material whose composition and physical properties change in the direction perpendicular to the laminated surface, and the front and back surfaces thereof are uniformly blackened to obtain a sample. By measuring the in-plane distribution of the transient temperature rise on the back surface of the sample after pulsed radiant heating of the surface at a uniform energy density, the distribution of the thermal properties of the macroscopic inhomogeneous material that changes in the vertical direction of the laminated surface can be determined. A method for measuring thermophysical properties, characterized by obtaining. 2. A distribution of thermal characteristics of a macroscopic inhomogeneous material that changes in the vertical direction of the laminated surface from the in-plane distribution of the transient temperature rise rate obtained from the in-plane distribution of the transient temperature rise on the back surface of the sample. The thermophysical property measuring method according to claim 1, wherein a distribution of thermal diffusivity is obtained. 3. As a distribution of thermal characteristics, a macroscopic inhomogeneity that changes in the vertical direction of the laminated surface from the in-plane distribution of the maximum value of the transient temperature rise obtained by the in-plane distribution of the transient temperature rise on the back surface of the sample. The method for measuring thermophysical properties according to claim 1, wherein the distribution of the relative value of the heat capacity per unit volume of the material is obtained. 4. As a distribution of thermal characteristics, the heat capacity of the whole flat sample measured in advance is proportionally distributed according to the distribution of the relative value of the heat capacity per unit volume obtained in claim (3), and The method for measuring thermophysical properties according to claim 1, wherein the distribution of the absolute value of the heat capacity is obtained. 5. As the distribution of thermal characteristics, the distribution of the absolute value of the heat capacity per unit volume obtained in claim (4) is divided by the density distribution measured in advance at each position inside the sample. The thermophysical property measuring method according to claim 1, wherein a distribution of the specific heat of the macroscopic inhomogeneous material that changes in the direction perpendicular to the laminated surface is obtained as the obtained quotient. 6. The product at each position of the distribution of the thermal diffusion surface obtained in claim (2) and the distribution of the absolute value of the heat capacity per unit volume obtained in claim (4) as the distribution of thermal characteristics. The method for measuring thermophysical properties according to claim 1, wherein a distribution of the thermal conductivity of the macroscopic inhomogeneous material that changes in the direction perpendicular to the laminated surface is obtained as the above. 7. When the thickness of the macroscopic inhomogeneous material is small and a sample cut out perpendicularly to the laminated surface cannot obtain a sufficient size for measurement, a flat plate shape is formed along a plane inclined with respect to the laminated surface. The thermophysical property measuring method according to claim 1, wherein a sample is cut out.