JPH0525304B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a laser flash method thermal constant measuring device, and is particularly applicable to the steel industry, the metal industry, the chemical industry, the nuclear industry, the aerospace industry, the ceramic material industry,
This invention relates to improvements in a laser flash method thermal constant measuring device suitable for use in detecting thermal constants such as heat capacity, thermal diffusivity, and thermal conductivity of samples at high temperatures in the magnetic materials industry, cement industry, etc.

[Conventional technology]

In recent years, there has been interest in technology for accurately and precisely measuring the thermal constant of a sample over a wide temperature range. Regarding techniques for measuring this thermal constant, various techniques have been proposed in the fields of electronics and optics, one of which is a thermal constant measuring technique using a laser flash method. For example, there is a thermal constant measuring device that employs this technology, as shown in Figure 7. The thermal constant measuring device shown in the figure is from J.Nucl.Sci.Technol.
This was shown by Takahashi and Murabayashi in Volume 12 (1975). That is, the thermal constant measuring apparatus shown in the figure mainly includes a sample 10 that is held adiabatically, a ruby laser head 14 that generates the laser beam 12 that is irradiated onto the sample 10, and a ruby laser head 14 that is connected to the ruby laser head 14. A laser oscillator 16 for oscillating laser light, a heater 18 for keeping the sample 10 at a constant temperature, a temperature controller 20 for controlling the temperature by adjusting the current to the heater, and the sample 10 and the heater. 18 and a vacuum container 22 whose interior is evacuated; and a photoelectron for detecting the energy of the laser beam 12 incident on the sample 10 and for detecting the amount of light of the laser beam 12 as an electric quantity. A photocell 24 having an element, an integral wattmeter 26 for detecting the electric power of the electric quantity, a thermocouple 28 for converting the temperature of the sample 10 into an electrical signal for detecting the temperature of the sample 10, and the thermocouple. an amplifier 30 for amplifying the output signal of 28; and a transient memory 3 for storing and outputting the output signal of the amplifier 30.
There is one that has 2. As the sample 10, a disk-shaped sample (for example, about 8 to 10 mm in diameter and about 1 to 3 mm in thickness) is used. FIG. 8 shows an enlarged view of the vicinity of the sample 10 when measuring heat capacity. In the figure, a thermocouple 28 is attached to the back side of the sample 10 (by welding in the case of a metal sample, using platinum paste etc. in the case of a non-metal sample), and the temperature of the sample 10 changes due to the electromotive force of the thermocouple 28. Detect. A part of the laser beam 12 irradiated from the laser head 14 passes through the reflecting mirror 34 and is irradiated onto the sample 10 (within 1 millisecond of irradiation time), and the other part reflected by the reflecting mirror 34 is reflected by the laser beam 12. In order to measure the irradiation energy, the photocell 24 receives the light and the integral power meter 2
In step 6, the irradiation energy is measured as a power value.
In the figure, 35 is a slit for focusing the laser beam 12, 36 is a quartz pin for supporting the sample 10, 38 is also a support base, 40 is a lead wire of the thermocouple 28, and 42 is a slit for attaching the laser beam to the sample 10. This is a heat absorbing plate for ensuring that the energy of 12 is absorbed well. With the thermal constant measuring device configured as above, sample 1
In order to obtain a thermal diffusivity α (cm ² S ^-1 ) of 0, remove the heat absorbing plate 42 and measure the time t1/2 (S) at which the temperature rise of the sample 10 is half. That is, if the thickness of the sample is L (cm), the thermal diffusivity α is calculated by the following formula:
It is given by (1). α=1.37・L ² /(π ² t1/2) ...(1) Also, when measuring the heat capacity of the sample 10, all the energy of the irradiated laser beam 12 is absorbed by the sample 10. With the intention of
2. For example, glassy carbon whose laser light absorption rate is close to 1 is adhered to the sample 10. In this way, the energy of the laser beam 12 is not leaked and the sample 1 is
Absorbed by 0. Specific heat capacity C _P (JK ^-1 g
^-1 ) is the energy of the laser light absorbed by the sample 10, E (J), the mass of the sample 10, m (g), the heat capacity of the glassy carbon including adhesive, C (JK ^-1 ),
If ΔT is the temperature rise range detected by the thermocouple 28, it is given by the following equation (2). C _P = (1/m)・{(E/ΔT)−C} ...(2) Furthermore, the thermal conductivity K (Wcm ^-1 K ^-1 ) of sample 10 is:
The following equation (3) is given by setting the density of the sample 10 to ρ (gcm ^-3 ). K=α・_CP・ρ……(3)

[Problems to be solved by the invention]

By the way, in the above conventional thermal constant device,
When the surface of the sample 10 is irradiated with the laser beam 12, the temperature of the sample 10 becomes higher than the ambient temperature (usually the temperature of the inner wall of an electric furnace), and heat transfer from the sample 10 to the surroundings occurs due to heat conduction, convection, and radiation phenomena. Heat leaks out. Especially at high temperatures, sample 1
If the temperature difference between 0 and the surroundings is constant, heat leakage due to radiation increases as compared to the cube of temperature T, resulting in a large amount of heat leakage, and this heat leakage is the largest cause of measurement error. Become. For this reason, heat capacity measurement using the laser flash method has a measurement limit determined by the heat leakage on the high temperature side. As a method of correcting errors due to heat leakage such as the above-mentioned radiant heat loss, after the sample is irradiated with laser light and the temperature rises rapidly, the temperature is prevented from gradually decreasing due to heat leakage from the sample to the surroundings. Therefore, there is a method of extrapolating the sample 10 to the time immediately after laser beam irradiation. (J.Chem, published November 1979.
(described by Yoichi Takahashi et al. in Thermodynamics). However, even in the above method, measurement errors due to heat leakage become large, and the measurement limit is about 1100K. In addition, thermal diffusivity measurements are nominally capable of measuring up to about 3000K, but at high temperatures heat leakage causes the reliability of the measured values to become significantly inferior.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned conventional problems, and it reduces heat leakage from the sample to improve the reliability of the measured thermal constant value, and also increases the measurable upper limit temperature. An object of the present invention is to provide a laser flash method thermal constant measurement device that can measure a wide range of thermal constant measurement values.

[Means to solve the problem]

The present invention mainly consists of a sample that is adiabatically held;
A laser beam oscillation system for generating a laser beam to irradiate the sample, a temperature control system for keeping the sample at a constant temperature, and a vacuum inside containing the sample and a part of the temperature control system. A laser flash method thermal constant measurement comprising: a vacuum vessel, a laser energy detection system for detecting the energy of the laser beam incident on the sample, and a sample temperature detection system for detecting the temperature of the sample. In the device,
a condensing system for condensing the laser beam irradiated onto the sample to approximately one point midway through its optical path; and a small hole that covers the periphery of the sample and serves as an optical path for the laser beam condensed to approximately one point. A metal shield member is formed on the incident side of the laser hole to reduce heat leakage in the lateral and vertical directions of the sample, and a metal shield member attached to the shield member is used to detect the temperature of the shield member. A shield temperature detection means and an energization heating means for heating the shield member by applying current to the shield member are provided, and based on the detected temperatures of the sample and the shield member, the temperature of the sample and the shield member are equalized. The above object is achieved by controlling the optical oscillation means and the energization heating means.

[Effect]

In the present invention, when measuring the thermal constant of a sample by the laser flash method, a condensing system, a metal shield member, a shield temperature detection means, and an energization heating means are provided, and the condensing system emits a laser beam. A laser hole condenses the light to approximately one point in the middle of the optical path, covers the sample with the shield member, and condenses the light to approximately the one point from a small hole as an optical path formed on the laser beam incident side of the shield member. to heat the sample, reduce heat leakage in the lateral and vertical directions of the sample with the shield member, detect the temperature of the shield member, and based on the detected temperature of the sample and the shield member, The laser beam oscillation means and the energization heating means are controlled so that the temperatures of the sample and the shield member are equalized. Therefore, when measuring the thermal constant of a sample using the laser flash method, it is possible to improve the reliability of the measured thermal constant by reducing the heat path from the sample, and to raise the upper limit of measurable heat leakage. Enrichment of measured values of thermal constants can be measured. For this reason, in all industrial fields that handle high temperatures, such as the steel industry, metal industry, chemical industry, nuclear industry, ship aerospace industry, ceramic materials industry, magnetic materials industry, and cement industry, thermal constants at high temperatures, such as heat capacity, Significant difficulties in material and process design due to inaccurate measurements of thermal diffusivity, thermal conductivity, etc., or lack of high-temperature measurements due to limitations of measurement equipment with upper temperature limits. However, with the present invention, it is possible to collect highly accurate thermal constant measurement values even at high temperatures, which eliminates the above-mentioned problems and has a large impact on the above-mentioned industrial fields. , extremely useful.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. In this example, in the thermal constant measuring apparatus shown in FIG. 7 above, a sample 10
A condensing lens 46 for condensing the laser beam 12 to be irradiated onto approximately one point in the middle of its optical path, and a condensing lens 46 that covers the periphery of the sample 10 and serves as an optical path for the laser beam 12A that is condensed at approximately one point. A metal shield member 50 having a small hole 48 formed on the incident side of the laser beam 12 for reducing heat leakage in the lateral and vertical directions of the sample 10, and the shield member attached to the shield member 50. Each thermocouple 52A to 52C, which will be described later, is used to detect the temperature of 50, a power source 60 for heating the shield member 50 by directly applying current to the shield member 50, and a lead wire 54 connecting the power source 60 and the shield member 50. , a timing circuit 62 for controlling a laser oscillator 16 and a power supply in order to control the temperature rise range of the sample 10 and the shield member 50 based on the detected temperatures of the sample 10 and the shield member 50. The condensing lens 46 makes the diameter of the small hole 48 as small as possible, so that the condensing lens 46 itself does not approach a high temperature part, and the laser beam 12 focused on approximately one point passes through the small hole 48. As you pass,
The structure and installation are such that the laser beam 12 passing through the small hole 48 spreads almost uniformly and irradiates the surface of the sample 10. The shield member 50 is a cylinder 56 made of thin metal (for example, molybdenum Mo, tungsten W, etc.).
The sample 10 is surrounded by upper and lower disks 58. There is a small hole 48 on the disk 58 in the upper part.
is formed with an opening having a suitable diameter (preferably 3 mm or less) to ensure an optical path for the laser beam 12. Note that the cylinder 56 and each disc 58 are bonded to each other with an insulating inorganic adhesive 61. Regarding the thermocouples 52A to 52C, the thermocouple 52A is attached to the cylinder 56 of the shield member 50, and the thermocouples 52B and 52C are attached to the upper and lower disks 58. These thermocouples 52A to 52C are connected to an amplifier 30 via lead wires 59A to 59C to amplify their electromotive force.
Further, each of the thermocouples 28, 52A to 52C has a diameter of about 50 to 100 (μm), and a thermocouple containing a chromeru-constantan component is used up to a temperature of about 1100K, and a platinum-containing thermocouple is used up to a temperature of about 1700K. A material containing a platinum-rhodium component, and a material containing a tungsten-tungsten rhenium component at temperatures of 1700K or higher can be used. Further, in a temperature range of 1500K or more, an infrared temperature sensor can be used to measure the temperature change of the sample 10 instead of using a thermocouple as described above. A 2 (V) battery is connected in parallel to the power supply 60 of the circuit that directly energizes the cylinders 56 and 58.
In addition, as shown in Figure 1, a resistor for output voltage adjustment is required.
R ₁ and R ₂ can be provided. Control of the temperature rise range due to this energization differs depending on the temperature rise range of the sample 10, but is performed by appropriately selecting the number of batteries to be connected and adjusting the energization time in the range of 1 to 500 milliseconds. be able to. Furthermore, above,
The lower disks 58 are connected by a lead wire 63. The timing circuit 62 simultaneously irradiates the sample 10 with the laser beam 12 and directly energizes the shield member 50, and in order to make the temperature rise width of the sample 10 and the temperature rise width of the shield member 50 the same, first,
The electromotive force of each thermocouple 28, 52A to 52C attached to the sample 10 and the shield member 50 is transferred to the amplifier 3.
After being amplified by 0, the transient memory 32 is input as a temperature signal. The timing circuit 62 then processes each thermocouple 2 from the input temperature signal.
The energy of the laser beam 12 is adjusted by controlling the laser oscillator 16 so that the electromotive forces of 8, 52A to 52C are equal. As the heat absorbing plate 42 shown in the figure, another heat absorbing plate can be installed instead of the glassy carbon. When measuring the heat capacity, the energy of the laser beam 12 was absorbed by the heat absorbing plate 42, but when measuring thermal diffusion, the sample 10 was directly irradiated with the laser beam 12 without placing the heat absorbing plate 42. can be measured. Next, the results of measuring the heat capacity C _P and the thermal diffusivity α using the thermal constant measuring device to which the present invention is applied will be explained. In this case, molybdenum Mo is used for the cylinder 56 and disk 58 of the shield member 50, and the lead wires 54 and 6 connected to the cylinder 56 and disk 58 are
3 uses molybdenum Mo wire, and each thermocouple 28,
Lead wires 40, 59A to 59 to 52A to 52C
For C, a platinum-13% platinum rhodium wire was used. As sample 10, strontium ferrite (SrFe ₁₂ O ₁₉ ) and platinum (Pt) were each made with a diameter of 10 mm.
The specific heat capacity (JK ^-1 g ^-1 ) of the sample was measured at a temperature of 1550K. The results of measuring the strontium ferrite in the sample as described above are shown in FIG. in this case,
The measurement temperature is 1550K, the sample weight is 0.8011g, the glassy carbon of the heat absorption plate is 0.0098g, and the adhesive is 0.0052g.
It was hot at g. The sum of the heat capacities of the glassy carbon and the adhesive was 0.0226JK ^-1 , and the measured average value of the specific heat capacity was 0.7540JK ^-1 g ^-1 . From the figure, it can be seen that the accuracy (reproducibility) is high because the deviation during measurement at 1550K is small, within ±0.7%. Further, although it has not been possible to perform highly accurate measurements in the temperature range of 1100K or higher in the past, it is understood that the present invention allows effective measurement of heat capacity even in this temperature range. Similarly, FIG. 3 shows the results of measuring platinum as a sample. The figure shows the measured value of the specific heat capacity (JK ^-1 g ^-1 ) of platinum when the sample weight is 3.3568 g.
The figure shows that the specific heat capacity can be measured with fairly high accuracy up to 1700K. On the other hand, as the prior art, J.
Chem.Thermodynamics shows data on the molar heat capacity of platinum measured using only a drop calorimeter in the temperature range of 1700K, as shown in Figure 4. Since the measured value in this case is obtained as the enthalpy value H (Jmol ^-1 ) with respect to temperature T (K), the molar heat capacity can be obtained by smoothing this enthalpy temperature curve and differentiating it with respect to temperature. Therefore, although the data dispersion does not appear on the surface in the figure,
The variation in the primary data (at least 1% in the temperature range above 1100K) should be largely reflected in the variation in the heat capacity of the secondary data.
There were problems with reliability. Next, FIG. 5 shows the measurement results of the thermal diffusivity α (cm ² S ^-1 ) of platinum in the sample. In this case, the sample was directly irradiated with laser light and heated without using a heat absorbing plate.
Further, for comparison, data obtained by measuring the thermal diffusivity α of platinum using a conventional method is shown in FIG. This data is
Shown in Volume 10 of The TPRC Date Series
Due to thermophysical properties of Matter. As can be seen from FIG. 6, it can be seen that the data on the thermal diffusivity α of platinum obtained by the conventional method fluctuates greatly with temperature, and tends to vary. On the other hand, in the measurement using the apparatus of the present invention shown in FIG. , it can be seen that the reliability of the measurement is high. In the above embodiment, the sample 10 was surrounded by a shield member 50 formed of a cylinder 56 and a disc 58 as shown in FIG. 1, but the structure of the shield member 50 is limited to that shown in the figure. First, other shield members can be used as long as they are formed to surround the sample 10 so as to reduce heat leakage in the lateral and vertical directions of the sample 10. Further, the material of the shield member 50 or the lead wire is not limited to molybdenum, and shield members or lead wires made of other materials may be used.

【Effect of the invention】

As explained above, according to the present invention, it is possible to reduce the leakage of heat from the surroundings of the sample, thereby improving the reliability of the measured values of thermal constant measurement, and
By raising the measurement upper limit temperature, excellent effects such as enrichment of measurement data such as thermal conductivity measurement data can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the main parts, including a partial block diagram, showing the structure near the sample and shield member of an embodiment of the thermal constant measuring device according to the present invention, and FIG. 2 explains the operation of the embodiment. Similarly, Figure 3 is a diagram showing an example of the measurement data of the specific heat capacity of the sample.
Similarly, FIG. 4 is a diagram showing an example of measurement data of the specific heat capacity of other samples. Similarly, FIG. FIG. 6 is a diagram showing an example of thermal diffusivity data measured using a conventional method. FIG. 7 is a diagram showing an example of thermal diffusivity data measured using a conventional method. , a block diagram including a partial sectional view, and FIG. 8 is a sectional view of a main part showing the structure around a sample of a conventional thermal constant measuring device. 10...sample, 12...laser light, 14...
Ruby laser head, 16...Laser oscillator, 2
0... Temperature controller, 22... Vacuum container, 24...
Photocell, 28,52A-52C...thermocouple,
42... Heat absorption plate, 40, 59A to 59C... Thermocouple lead wire, 46... Condensing lens, 48... Small hole, 50... Metallic shielding member, 54, 63
... Lead wire, 56 ... Cylinder, 58 ... Disc, 6
0...Power supply, 62...Timing circuit.

Claims (1)

[Claims] 1. Mainly includes a sample held adiabatically, a laser beam oscillation system for generating laser light to irradiate the sample, and a temperature control system for maintaining the sample at a constant temperature. , a vacuum container containing the sample and a part of the temperature control system and having a vacuum inside; a laser energy detection system for detecting the energy of the laser beam incident on the sample; and a temperature of the sample. A laser flash method thermal constant measuring device having a sample temperature detection system for detecting the temperature of the sample, comprising: a condensing system for concentrating the laser beam irradiated onto the sample to approximately one point in the middle of its optical path; A metal plate that covers the periphery of the sample and has a small hole formed on the laser light incident side as an optical path for the laser light focused on approximately one point, to reduce heat leakage in the lateral and vertical directions of the sample. A shield member, a shield temperature detection means attached to the shield member for detecting the temperature of the shield member, and an energization heating means for heating the shield member by supplying current to the shield member are provided, and the temperature is detected. A laser flash method thermal constant measuring device characterized in that the laser beam oscillation means and the energization heating means are controlled based on the temperatures of the sample and the shield member so that the temperatures of the sample and the shield member are equalized.