Dynamic linear expansion coefficient measuring device and measuring method thereof

Abstract

The invention discloses a dynamic linear expansion coefficient measuring device and a measuring method thereof, and belongs to the technical field of material characteristic measurement. The structure comprises a bearing structure, a dimming structure is arranged above the bearing structure, a self-focusing lens structure is installed in the dimming structure, the top of the self-focusing lens structure is connected with a piezoelectric ceramic ring structure, and a coupler installation structure is arranged at the top of the piezoelectric ceramic ring structure. The method comprises the following steps: introducing temperature change delta T to a sample, enabling the sample to generate alternating-current deformation delta L, importing real-time temperature data and corresponding deformation data of the sample into matlab, and calculating the thermal expansion coefficient of the sample by utilizing a phase-locked amplification principle. According to the method, noise caused by environment temperature fluctuation and mechanical vibration can be accurately identified and compensated, and the accuracy and repeatability of data are remarkably improved. The uniformity and stability of the temperature in the measurement process are improved, and the influence of temperature fluctuation on the measurement result is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of material property measurement, and in particular to a dynamic linear expansion coefficient measurement device and a measurement method thereof. Background Art

[0002] In materials science and physics research, accurate measurement of the thermal expansion coefficient (α) of materials is key to understanding the thermodynamic properties of materials. Traditional measurement techniques mainly rely on the static linear expansion coefficient measurement method, which involves measuring the change in sample length at different temperature points and then calculating the thermal expansion coefficient by numerical differentiation. However, this static measurement method has several disadvantages:

[0003] Slow measurement response: Static measurement requires data recording after each temperature point stabilizes, which makes the entire measurement process time-consuming and inefficient. High noise sensitivity: When performing DC measurements at low frequencies, the system is often affected by 1 / f noise. This type of noise increases as the frequency decreases, thus affecting the measurement accuracy. Insensitive to phase change signals: Static measurement methods are difficult to sensitively capture phase change information caused by sudden changes in sample size because these changes occur rapidly in a short period of time.

[0004] In view of these limitations of traditional methods, the present invention proposes a measurement method based on dynamic linear expansion coefficient. This method implements "true differential" measurement of thermal expansion coefficient by applying alternating current (AC) temperature change δT to the sample and simultaneously measuring the corresponding AC deformation δL. This dynamic measurement method has the following advantages:

[0005] Improve measurement efficiency: AC measurement allows continuous and rapid data collection without waiting for each temperature point to stabilize, greatly speeding up data collection. Reduce noise effects: Using AC signals can effectively reduce the impact of 1 / f noise, because the impact of this noise is significantly reduced at high frequencies. This makes the measurement results more stable and accurate. Enhance sensitivity to phase changes: Due to its periodic temperature fluctuations, the AC measurement method can more sensitively capture the rapid jumps in sample size caused by phase changes. Obtain additional physical information: By recording the phase delay of the response relative to the drive, more information about the thermal conductivity and other dynamic thermodynamic properties of the sample can be obtained.

[0006] The AC measurement method of the present invention not only improves the measurement efficiency and accuracy, but also expands the application range of the measurement, enabling researchers to have a deeper understanding of the thermal behavior and phase change mechanism of materials in complex physics, chemistry and materials science research. This new technology will provide important experimental support for the research and development of new materials, especially in applications that require extremely high thermal properties and stability of materials. Summary of the invention

[0007] The purpose of the present invention is to provide a measuring device and a measuring method of a dynamic linear expansion coefficient, which solves the problem of.

[0008] To achieve the above-mentioned purpose, the present invention provides a device for measuring a dynamic linear expansion coefficient, comprising a supporting structure, a dimming structure is arranged above the supporting structure, a self-focusing lens structure is installed inside the dimming structure, the top of the self-focusing lens structure is connected to a piezoelectric ceramic ring structure, and a coupler mounting structure is arranged on the top of the piezoelectric ceramic ring structure.

[0009] Preferably, the supporting structure comprises a supporting plate, a sample holder is arranged at the center of the supporting plate, a sapphire sheet upper pressing plate and a sapphire sheet lower pressing plate are arranged on upper and lower sides of the sample holder respectively, and a sample is placed between the sapphire sheet upper pressing plate and the sample holder.

[0010] Preferably, the dimming structure comprises a dimming support block, a plurality of dimming tension springs are arranged around the edge of the lower surface of the dimming support block, and a plurality of fine-tuning screws are arranged around the edge of the upper surface of the dimming support block.

[0011] Preferably, the self-focusing lens structure comprises a self-focusing lens, self-focusing lens clamps are arranged on both sides of the self-focusing lens, and a locking nut is arranged at the bottom of the self-focusing lens clamp.

[0012] Preferably, the piezoelectric ceramic ring structure comprises a piezoelectric ceramic ring, and piezoelectric ceramic ring heat sink pads are sleeved on the upper and lower ends and the center of the piezoelectric ceramic ring.

[0013] Preferably, the coupler mounting structure comprises a coupler bracket, a locking nut is mounted on the top of the coupler bracket, and the locking nut is sleeved on the cold finger.

[0014] A method for measuring a dynamic linear expansion coefficient measurement device comprises the following steps:

[0015] S1. Install the sample on the upper surface of the sample holder, and use six identical platinum resistance wires to connect the two platinum resistance wires directly below the sample to the PCB board through dotted lines;

[0016] S2, using a commercial lock-in amplifier to measure the resistance value of the in-situ thermometer versus temperature through the PID temperature control system of the cryostat, and using the system thermometer of the cryostat as a reference to calibrate the in-situ thermometer;

[0017] S3, applying a small AC heating power at a certain equilibrium temperature T0 to introduce a small temperature change δT to the sample, causing the sample to undergo an AC deformation δL;

[0018] S4. After the real-time temperature data and corresponding deformation data of the sample are collected and stored by the acquisition card, they are imported into MATLAB and the principle of phase-locked amplification is used to select a suitable measurement time constant tc for data processing to obtain the amplitudes <δL> and <δT> of δL and δT, and the thermal expansion coefficient of the sample at temperature T0 is obtained.

[0019] Preferably, in step S4, the formula for the thermal expansion coefficient of the sample at temperature T0 is as follows:

[0020]

[0021] Where T0 is the equilibrium temperature, <δT> is the amplitude of the temperature change, and <δL> is the amplitude of the AC deformation of the sample.

[0022] Therefore, the present invention adopts a dynamic linear expansion coefficient measuring device and a measuring method of the above structure, which has the following beneficial effects:

[0023] (1) The present invention utilizes advanced digital phase-locked technology to accurately identify and compensate for noise caused by ambient temperature fluctuations and mechanical vibrations, significantly improving the accuracy and repeatability of data.

[0024] (2) The present invention improves the uniformity and stability of temperature during the measurement process. It not only effectively reduces the impact of temperature fluctuations on the measurement results, but also can maintain high accuracy and high stability during long-term operation.

[0025] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic cross-sectional view of a thermal expansion coefficient measurement sample seat of a dynamic linear expansion coefficient measurement device and a measurement method thereof according to the present invention;

[0027] Figure 2 A schematic diagram of an AC heating wire A based on a platinum resistance wire, an in-situ thermometer B and a DC heating wire C evaporated on the lower surface of a sample holder of a dynamic linear expansion coefficient measuring device and a measuring method thereof of the present invention;

[0028] Figure 3 A schematic top view of a thermal expansion coefficient measurement sample holder of a dynamic linear expansion coefficient measurement device and a measurement method thereof according to the present invention;

[0029] Figure 4 A physical schematic diagram of a sample holder supporting structure of a dynamic linear expansion coefficient measuring device and a measuring method thereof according to the present invention;

[0030] Figure 5The present invention is a schematic diagram of a deformation measuring device for measuring a dynamic linear expansion coefficient and a measuring method thereof.

[0031] Reference numerals

[0032] 1-cold finger, 2-locking nut, 3-coupler support, 4-piezoelectric ceramic ring heat sink pad, 5-piezoelectric ceramic ring, 6-fine-tuning screw, 7-dimming support block, 8-tension spring, 9-sapphire sheet upper pressure plate, 10-support plate, 11-self-focusing lens, 12-self-focusing lens clamp, 13-locking nut, 14-sample, 15-sapphire sheet, 16-sapphire sheet lower pressure plate. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0034] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0035] Example

[0036] The present invention provides a device for measuring a dynamic linear expansion coefficient, comprising a supporting structure, a dimming structure is arranged above the supporting structure, a self-focusing lens structure is installed inside the dimming structure, the top of the self-focusing lens structure is connected to a piezoelectric ceramic ring structure, and a coupler installation structure is arranged on the top of the piezoelectric ceramic ring structure.

[0037] The supporting structure includes a supporting plate 10 , a sample holder 15 is arranged in the center of the supporting plate 10 , a sapphire sheet upper pressing plate 9 and a sapphire sheet lower pressing plate 16 are arranged on the upper and lower sides of the sample holder 15 , and a sample 14 is placed between the sapphire sheet upper pressing plate 9 and the sample holder 15 .

[0038] The dimming structure comprises a dimming support block 7 , a plurality of dimming tension springs 8 are arranged around the edge of the lower surface of the dimming support block 7 , and a plurality of fine-tuning screws 6 are arranged around the edge of the upper surface of the dimming support block 7 .

[0039] The self-focusing lens structure comprises a self-focusing lens 11 , self-focusing lens clamps 12 are arranged on both sides of the self-focusing lens 11 , and a locking nut 13 is arranged at the bottom of the self-focusing lens clamp 12 .

[0040] The piezoelectric ceramic ring structure comprises a piezoelectric ceramic ring 5 , and piezoelectric ceramic ring heat sink pads 4 are sleeved on the upper and lower ends and the center of the piezoelectric ceramic ring 5 .

[0041] The coupler mounting structure comprises a coupler support 3 , a locking nut 2 is mounted on the top of the coupler support 3 , and the locking nut 2 is sleeved on the cold finger 1 .

[0042] A method for measuring a dynamic linear expansion coefficient measurement device comprises the following steps:

[0043] S1. Install the sample on the upper surface of the sample holder, and use six identical platinum resistance wires to connect the two platinum resistance wires directly below the sample to the PCB board through dotted lines;

[0044] S2, using a commercial lock-in amplifier to measure the resistance value of the in-situ thermometer versus temperature through the PID temperature control system of the cryostat, and using the system thermometer of the cryostat as a reference to calibrate the in-situ thermometer;

[0045] S3, applying a small AC heating power at a certain equilibrium temperature T0 to introduce a small temperature change δT to the sample, causing the sample to undergo an AC deformation δL;

[0046] S4. After the real-time temperature data and corresponding deformation data of the sample are collected and stored by the acquisition card, they are imported into MATLAB and processed using the principle of phase-locked amplification. A suitable measurement time constant tc is selected for data processing to obtain the amplitudes <δL> and <δT> of δL and δT. The formula for obtaining the thermal expansion coefficient of the sample at temperature T0 is as follows:

[0047]

[0048] Where T0 is the equilibrium temperature, <δT> is the amplitude of the temperature change, and <δL> is the amplitude of the AC deformation of the sample.

[0049] The sample holder 15 is made of sapphire, which has the advantages of low temperature insulation, excellent thermal conductivity, and great rigidity, which ensure the normal use of in-situ heating and temperature measurement. The sample is mounted on the upper surface of the sapphire sample holder 15, and on its lower surface Figure 1 The six identical platinum resistance wires shown in the figure are formed by electron beam evaporation using a hard mask. The line width is 50μm. During evaporation, titanium is first plated as an adhesive, and then platinum is plated. The thickness ratio of titanium to platinum is 1nm and 25nm. The resistance of a single platinum resistance wire is about 660Ω. The two platinum resistance wires directly below the sample are connected in series through a dotted line, and the dotted line to Figure 2 The PCB board shown is led out and used as an in-situ thermometer. The temperature is changed by the PID temperature control system of the cryostat. The curve of the resistance value of the in-situ thermometer changing with temperature is measured by a commercial phase-locked amplifier, and the system thermometer of the cryostat is used as a reference to realize the calibration of the in-situ thermometer. The temperature value of the in-situ thermometer includes the AC temperature change and the DC temperature scan, that is, the output of the phase-locked amplifier, which is the same as VωM and V2ωM in AC deformation measurement and VF in DC deformation measurement. After being collected by the acquisition card, it is stored and subsequently imported into matlab to realize data processing. The upper and lower two platinum resistance wires are connected in parallel, respectively, as the in-situ AC heating wire and the DC heating wire, and are led out after being dotted to the PCB board; a small AC voltage VACH is applied to the AC heating wire to introduce a small AC temperature change δT; a DC voltage VDCH with a power that increases slowly over time is applied to the DC heating wire to scan the DC temperature T0. The heating wire and the thermometer are directly installed near the sample and the entire structure is very small, which ensures temperature consistency. When measuring the thermal expansion coefficient, a suitable AC heating frequency is selected to ensure that the overall temperature of the sample is consistent during AC heating. The thermal capacitance and thermal resistance design of the AC heat leakage path is optimized so that the AC temperature change is limited to the sample holder 15 and its supporting structure; at the same time, other structures are precisely controlled by the system heating wire of the thermostat and the system thermometer through the PID temperature control system to maintain a constant temperature, thus realizing the in-situ temperature loading and real-time temperature measurement of the sample only. The system heating wire is integrated on the system cold finger, and the system thermometer is installed on the coupler holder 3 closest to the piezoelectric ceramic ring, so as to ensure that the temperature of the piezoelectric ceramic ring remains constant when the DC temperature T0 is scanned at the sample holder.

[0050] In the measurement of thermal expansion coefficient, the side cross-sectional view of the installed overall dimming structure is shown as follows, wherein the actual top view of the sample holder 15, the supporting structure and the dimming structure is shown as follows: Figure 3 As shown, the actual bottom view of the supporting structure is as follows Figure 4 As shown. It can be seen that the sample 14 is installed on the upper surface of the sample holder 15; the sample holder 15 is clamped and fixed by the upper pressing plate 9 of the sapphire sheet and the lower pressing plate 16 of the sapphire sheet through screws; a circular hole is opened on the axis of the supporting plate 10, and its diameter is slightly larger than the diameter of the lower pressing plate 16 of the sapphire sheet. After the sample holder 15 and its supporting structure are installed, they pass through the circular hole from top to bottom and are fixed on the upper surface of the supporting plate 10 by screws. Then, the dimming surface carrying the sample holder structure is coaxially suspended on the dimming support block 7 through the fine-tuning screw 6 and the dimming tension spring 8.

[0051] In order to avoid the deformation of other structural parts other than the sample caused by AC heating from entering the measurement signal of the interferometer as much as possible, a special sample holder support structure and installation method as described above are designed. In this structure, the upper surface of the sample holder 15 and the upper surface of the support plate 10 are coplanar, that is, the lower surface of the sample 14 is coplanar with the vertex of the fine-tuning screw 6, and the background AC deformation during AC heating is limited to the AC change of the distance between the top of the fine-tuning screw 6 and the top of the self-focusing lens 11. As long as the AC heating is not leaked into the fine-tuning screw and other components connected thereto during the measurement of the thermal expansion coefficient, the distance between the top of the fine-tuning screw 6 and the top of the self-focusing lens 11 can be kept constant, and the deformation measured by the interferometer is completely from the thermal deformation of the sample 14 adhered to the upper surface of the sample holder 15. The overall design idea is to increase the thermal capacitance and thermal resistance of the heat conduction path from the AC heating wire to the fine-tuning screw 6 through the selection of structural material, the design of structural size and contact area, and additional thermal insulation and heat conduction design, so that the temperature change of the AC is not leaked. The specific design is as follows:

[0052] The in-plane size of the sample holder 15 is 5mm*5mm, and the diameter of the center hole of the sapphire sheet upper pressure plate 9 and the sapphire sheet lower pressure plate 16 is 6mm, that is, after the sample holder 15 is installed, the contact area with the sapphire sheet upper pressure plate 9 and the sapphire sheet lower pressure plate 16 is about 1mm2, and the extremely small contact area greatly increases the thermal resistance of heat from the sample holder 15 to the sapphire sheet upper pressure plate 9 and the sapphire sheet lower pressure plate 16; the contact area between the sapphire sheet upper pressure plate 9 and the supporting plate 10 is also very small to increase the contact thermal resistance, and the supporting plate 10 has a certain material volume and therefore has a considerable heat capacity; at the same time, Figure 5 As shown, three copper braids of appropriate thickness are used, one end of which is screwed through the screw hole to connect to the pressure plate 9 on the sapphire sheet, and the other end is pressed tightly on the surface of the system cold finger, directly connecting the pressure plate 9 on the sapphire sheet and the system cold finger, increasing the heat conduction channel and further reducing the AC heat and DC heat leaked from the contact point between the pressure plate 9 on the sapphire sheet and the support plate 10. In summary, for in-situ AC heating, the heat conduction modeling between the AC heating wire and the contact point between the fine-tuning screw 6 and the support plate 10 shows that the cutoff frequency fc1 of the low-pass filter of heat conduction in the current design is less than 0.1Hz, so the selection of an AC heating frequency higher than 0.1Hz can ensure that the AC heat does not leak into the fine-tuning screw, thereby making the background deformation at the AC heating frequency 0.

[0053] Therefore, the present invention adopts the above-mentioned dynamic linear expansion coefficient measuring device and its measuring method, and utilizes advanced digital phase-locked technology to accurately identify and compensate for the noise caused by ambient temperature fluctuations and mechanical vibrations, significantly improving the accuracy and repeatability of the data. It improves the uniformity and stability of temperature during the measurement process. It not only effectively reduces the impact of temperature fluctuations on the measurement results, but also can maintain high accuracy and high stability during long-term operation.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A device for measuring a dynamic linear expansion coefficient, characterized in that: It comprises a supporting structure, a dimming structure is arranged above the supporting structure, a self-focusing lens structure is installed inside the dimming structure, the top of the self-focusing lens structure is connected to the piezoelectric ceramic ring structure, and a coupler installation structure is arranged on the top of the piezoelectric ceramic ring structure.

2. A dynamic linear expansion coefficient measuring device according to claim 1, characterized in that: The supporting structure comprises a supporting plate, a sample holder is arranged at the center of the supporting plate, a sapphire sheet upper pressing plate and a sapphire sheet lower pressing plate are arranged on the upper and lower sides of the sample holder respectively, and a sample is placed between the sapphire sheet upper pressing plate and the sample holder.

3. The dynamic linear expansion coefficient measuring device according to claim 1, characterized in that: The dimming structure comprises a dimming support block, a plurality of dimming tension springs are arranged around the edge of the lower surface of the dimming support block, and a plurality of fine-tuning screws are arranged around the edge of the upper surface of the dimming support block.

4. The dynamic linear expansion coefficient measuring device according to claim 1, characterized in that: The self-focusing lens structure comprises a self-focusing lens, self-focusing lens clamps are arranged on both sides of the self-focusing lens, and a locking nut is arranged at the bottom of the self-focusing lens clamp.

5. The dynamic linear expansion coefficient measuring device according to claim 1, characterized in that: The piezoelectric ceramic ring structure comprises a piezoelectric ceramic ring, and piezoelectric ceramic ring heat sink pads are sleeved on the upper and lower ends and the center of the piezoelectric ceramic ring.

6. The dynamic linear expansion coefficient measuring device according to claim 1, characterized in that: The coupler mounting structure comprises a coupler bracket, a locking nut is mounted on the top of the coupler bracket, and the locking nut is sleeved on the cold finger.

7. A method for measuring a dynamic linear expansion coefficient measuring device according to claims 1 to 6, characterized in that: The following steps are involved: S1. Install the sample on the upper surface of the sample holder, and use six identical platinum resistance wires to connect the two platinum resistance wires directly below the sample to the PCB board through dotted lines; S2, using a commercial lock-in amplifier to measure the resistance value of the in-situ thermometer versus temperature through the PID temperature control system of the cryostat, and using the system thermometer of the cryostat as a reference to calibrate the in-situ thermometer; S3, applying a small AC heating power at a certain equilibrium temperature T0 to introduce a small temperature change δT to the sample, causing the sample to undergo an AC deformation δL; S4. After the real-time temperature data and corresponding deformation data of the sample are collected and stored by the acquisition card, they are imported into MATLAB and the principle of phase-locked amplification is used to select a suitable measurement time constant tc for data processing to obtain the amplitudes <δL> and <δT> of δL and δT, and the thermal expansion coefficient of the sample at temperature T0 is obtained.

8. The device and method for measuring the dynamic linear expansion coefficient according to claim 7, characterized in that: In step S4, the formula for the thermal expansion coefficient of the sample at temperature T0 is as follows: Where T0 is the equilibrium temperature, <δT> is the amplitude of the temperature change, and <δL> is the amplitude of the AC deformation of the sample.

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