A device and method for testing mechanical properties of carbon dioxide hydrate crystals

Abstract

The present invention discloses a device and method for testing the mechanical properties of carbon dioxide hydrate crystals, which belongs to the field of basic physical property measurement in earth science. The device includes a carbon dioxide gas storage cylinder, a nitrogen gas storage cylinder, an environmental control chamber air inlet valve, a gas booster pump, a first pressure sensor, an environmental control device, an environmental control chamber air outlet valve, a vacuum pump, a second pressure sensor, a one-way valve, a gas buffer collection bottle, a data acquisition system, a first temperature sensor, and a third pressure sensor. The present invention can realize the stable generation of carbon dioxide hydrate crystals and ensure that the carbon dioxide hydrate crystals are subjected to nanoindentation experiments under stable conditions, and obtain the mechanical properties of the carbon dioxide hydrate crystals such as indentation modulus, hardness, and crack diffusion, providing technical guarantee and hardware support for studying the mechanical properties of carbon dioxide hydrate crystals at the micro-nano scale.

Description

Technical Field

[0001] The present invention belongs to the field of basic physical property measurement in earth sciences, and in particular relates to a nanoindentation device and method for studying the mechanical properties of hydrate crystals. Background Art

[0002] Nanoindentation is a commonly used method for studying the mechanical properties of materials, characterized by high accuracy, high precision, and non-destructiveness. By applying loads at the nanometer scale, the mechanical properties of materials can be studied, yielding metrics such as elastic modulus, hardness, compression modulus, and fracture toughness. Because nanoindentation allows for highly precise and non-destructive investigation of the mechanical properties and deformation processes of materials, it has a wide range of applications in earth science, such as studying geological materials, rocks, minerals, and their deformation and fracture mechanisms.

[0003] Currently, the study of the structure and properties of carbon dioxide hydrates has become a hot field. Carbon dioxide hydrates have important applications in carbon dioxide fixation and carbon dioxide geological storage, but the study of the mechanical properties of carbon dioxide hydrate crystals still lacks targeted equipment and experimental methods. In exploring the mechanical properties of carbon dioxide hydrates, optimizing nanoindentation technology can provide a powerful experimental means. However, since carbon dioxide hydrate crystals are easily decomposed, they will be affected by the environment during the experiment, such as high temperature, high pressure and humidity, which will lead to errors or uncertainties in the experimental results. Therefore, the present invention proposes a method and device that can stably process carbon dioxide hydrate crystal samples and perform nanoindentation experiments with high precision and accuracy, which can obtain higher quality experimental data and more complete analytical structures. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the prior art and provide a device and method for testing the mechanical properties of carbon dioxide hydrate crystals. This invention enables stable generation of carbon dioxide hydrate crystals and ensures that nanoindentation experiments on carbon dioxide hydrate crystals are conducted under stable conditions, providing technical support for studying the mechanical properties of carbon dioxide hydrate crystals at the micro- and nanoscale.

[0005] The specific technical solutions adopted in the present invention are as follows:

[0006] In a first aspect, the present invention provides a device for testing the mechanical properties of carbon dioxide hydrate crystals, comprising an environmental control device and a data acquisition system;

[0007] The environmental control device has an inner cavity, one end of which is connected to an air inlet pipeline and the other end is connected to an air outlet pipeline; along the direction of fluid flow, the head end of the air inlet pipeline is divided into two branches, the first branch is connected to the carbon dioxide gas storage cylinder and the carbon dioxide pipeline valve in sequence, and the second branch is connected to the nitrogen gas storage cylinder and the nitrogen pipeline valve in sequence, and the two branches are merged through a three-way valve and connected to a first pressure sensor, a gas booster pump and an environmental control cavity air inlet valve in sequence; along the direction of fluid flow, the air outlet pipeline is connected to the environmental control cavity outlet valve, a vacuum pump, a second pressure sensor, a one-way valve and a gas buffer collection bottle in sequence; the inner cavity of the environmental control device includes a nanoindenter, an area scanning optical microscope system, a sample temperature control module and a sample polishing device arranged on a bottom support seat, and is also provided with a first temperature sensor and a third pressure sensor for measuring inner cavity indicators;

[0008] The data acquisition system is respectively connected to the first pressure sensor, the gas booster pump, the vacuum pump, the second pressure sensor, the first temperature sensor, the third pressure sensor, the nanoindenter, the area scanning optical microscope system, the sample temperature control module and the sample polishing equipment.

[0009] Preferably, the environmental control device is a hollow cube structure made of stainless steel, with a downwardly inclined viewing window on the front for observing the inner cavity, and the viewing window is made of three layers of tempered safety glass.

[0010] Preferably, the environment control chamber air inlet valve and the environment control chamber air outlet valve are both one-way valves.

[0011] Preferably, the nanoindenter includes at least one indenter disposed on a mobile device, each indenter being provided with a force sensor; the mobile device is mounted on a support seat and has three degrees of freedom.

[0012] Preferably, the area scanning optical microscope system includes two color CCD cameras arranged on the side and top of the sample, its visible light source is a 3W LED, the microscope magnification range is 22X-2200X, and the maximum resolution is 2560×1920.

[0013] Preferably, the sample temperature control module includes a top cover and a base; the base is detachably fixed to the support seat, and an annular protrusion is provided on the top, and a sample stage is provided in the middle depression of the annular protrusion, and an annular second thermoelectric cooling chip is provided between the sample stage and the annular protrusion; the cold end of the second thermoelectric cooling chip faces upward, and the inner periphery is set tightly against the sample stage through thermal conductive silicone grease; an annular groove is provided at the bottom of the top cover for engaging with the annular protrusion, and a hole is provided through the middle, and the hole is used for the working end of the nanoindenter and the sample polishing equipment to extend to contact the sample on the sample stage; an annular first thermoelectric cooling chip is provided between the annular groove and the hole, and the cold end of the first thermoelectric cooling chip faces downward; when the top cover is provided on the base, there is a gap between the top of the sample stage and the top cover, the first thermoelectric cooling chip is just above the second thermoelectric cooling chip and there is a gap between the two, the two gaps are connected and serve as a cooling space; a second temperature sensor is provided in the cooling space.

[0014] Furthermore, heat pipes for passing cooling water are provided inside the top cover above the first thermoelectric cooling chip and inside the base below the second thermoelectric cooling chip; the heat pipes are in contact with the hot ends of the first thermoelectric cooling chip and the second thermoelectric cooling chip to carry away the heat generated by the thermoelectric cooling chips.

[0015] Preferably, the bottom of the grinding head of the sample grinding device is equipped with a semiconductor refrigeration chip for cooling.

[0016] In a second aspect, the present invention provides a test method using any of the carbon dioxide hydrate crystal mechanical property testing devices described in the first aspect, specifically as follows:

[0017] S1: Add 3-5 drops of pure water to the sample stage of the sample temperature control module, then open the nitrogen pipeline valve, close the carbon dioxide pipeline valve, open the gas booster pump, the environmental control chamber inlet valve, the environmental control chamber outlet valve and the vacuum pump, and use nitrogen to clean the pipeline and the inner cavity of the environmental control device to expel impurities; after cleaning, close the nitrogen pipeline valve, open the carbon dioxide pipeline valve, and introduce carbon dioxide gas into the pipeline and the inner cavity of the environmental control device, then close the environmental control chamber outlet valve and the vacuum pump to inject carbon dioxide gas into the inner cavity of the environmental control device; when the third pressure sensor indicates that the pressure value reaches 2MPa, close the carbon dioxide pipeline valve, the gas booster pump and the environmental control chamber inlet valve to complete the carbon dioxide gas injection process; control the temperature of the refrigeration space to 1°C through the sample temperature control module; observe the pressure change curve in the environmental control device and the temperature change curve of the second temperature sensor in the sample temperature control module through the data acquisition system, and when it is observed that the pressure change curve decreases and then gradually returns to stability and the corresponding temperature change curve increases and then gradually stabilizes, it is determined that the carbon dioxide hydrate crystals on the sample stage have been formed;

[0018] S2: Turn on the sample polishing device, set the cooling temperature of the grinding head to -20°C, the grinding speed to 5000 rpm, and the polishing time to 1 hour; adjust the position of the sample polishing device so that the grinding head extends into the top cover hole of the sample temperature control module to polish the carbon dioxide hydrate crystal sample generated on the sample stage; after the sample polishing is completed, use the area scanning optical microscope system to collect images of the upper and side surfaces of the sample surface, and then transmit the collected image data to the data acquisition system, upload the image to the image processing software, complete the image correction, denoising, and sharpening operations, and then import the image into the image processing software to calculate the average surface roughness of the carbon dioxide hydrate crystal sample, and then combine it with the sample surface roughness obtained by the in-situ scanning probe imaging function of the nanoindenter, and compare and analyze the two to obtain the final sample surface roughness value; if the obtained sample surface roughness value is less than 5μm, the sample polishing process is completed; if the obtained sample surface roughness value is greater than 5μm, the sample polishing process is repeated until the sample surface roughness value is less than 5μm;

[0019] S3: Observe the polished surface of the CO2 hydrate crystal sample using an area scanning optical microscope system. After imaging, output the photograph to the data acquisition system. Use image processing software on the computer to analyze the average grain size of the CO2 hydrate crystals. Based on the obtained average grain size of the sample, select the indenter shape and load size of the nanoindenter as follows:

[0020] For samples with an average grain size in the range of [10, 20), a spherical indenter with a load of 1-5 μN was applied; for samples with an average grain size in the range of [20, 50], a spherical indenter with a load of 5-10 μN was applied; otherwise, the sample was re-polished according to S2;

[0021] Set the scanning range and indentation step depth of the nanoindenter according to the experimental requirements, and select the area to be tested; use the calibration tool provided with the nanoindenter to calibrate, ensure that the indenter is orthogonal to the sample surface and complete the calibration; start the instrument detection program of the nanoindenter, and according to the set scanning path, make the indenter enter the selected area and start applying the load; as the load increases, a series of load-depth curves are obtained; during the test, the indentation morphology and image generated on the sample surface, as well as the load-depth curve and load-time curve are collected and recorded in real time; calculate the elastic modulus of the sample based on the data results, and extract the mechanical properties of the sample.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The environmental control device includes the nanoindenter, sample temperature control module and sample polishing device and isolates them from the external environment. It can withstand high pressure, realizing the experimental conditions required to simulate the in-situ formation of CO2 hydrate and maintain constant pressure during the experiment. It realizes the continuity of sample preparation, sample polishing and sample nanoindentation experimental process, and solves the problem that traditional carbon dioxide hydrate crystals need to be transferred to the nanoindentation test bench after preparation, which will cause the hydrate crystals to decompose, resulting in sample loss and failure of mechanical testing.

[0024] 2. The sample temperature control module has a two-layer design with an upper opening. The upper and lower semiconductor layers are placed relative to each other to cool the hydrate crystals. On the one hand, this can ensure the stable formation of carbon dioxide hydrate crystals. On the other hand, the upper opening can ensure that the nanoindenter indenter (i.e., probe) and the sample polishing equipment grinding head are fully cooled before they penetrate into the sample temperature control module. Moreover, since the nanoindenter indenter and the sample polishing equipment grinding head penetrate into the sample temperature control module, combined with the control of the carbon dioxide hydrate crystals by the sample temperature control module, the carbon dioxide hydrate crystals can be stably present without decomposition during the polishing and nanoindentation experiments, thereby ensuring the accuracy of the nanoindentation experiment.

[0025] 3. The grinding head of the sample grinding equipment has a main cooling function. Combined with the passive cooling of the grinding head entering the environmental control chamber, it can avoid the decomposition of carbon dioxide hydrate crystals caused by the increase in temperature during the grinding process.

[0026] 4. An area scanning optical microscope system with a color CCD camera is installed on the nanoindenter and on the side of the sample temperature control module. It can not only achieve high-resolution imaging of the surface of the carbon dioxide hydrate crystal sample, but also obtain the roughness value of the sample surface through top-down and side-view imaging of the sample surface through image calculation and processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The diagram is a structural diagram of a device for testing the mechanical properties of carbon dioxide hydrate crystals.

[0028] Figure 2 This is a diagram of the system structure inside the environmental control device cavity.

[0029] Figure 3 、 Figure 4 This is a simplified structural diagram of the sample temperature control module at different angles.

[0030] In the figure: 1 support base, 2 environmental control device, 3 nanoindenter, 4 regional scanning optical microscope system, 5 sample temperature control module, 6 sample polishing equipment, 7 environmental control chamber air inlet valve, 8 gas booster pump, 9 first pressure sensor, 10 three-way valve, 11 carbon dioxide gas cylinder, 12 nitrogen gas cylinder, 13 environmental control chamber air outlet valve, 14 vacuum pump, 15 second pressure sensor, 16 one-way valve, 17 gas buffer collection bottle, 18 data acquisition system, 19 first temperature sensor, 20 third pressure sensor, 21 second temperature sensor, 22 carbon dioxide pipeline valve, 23 nitrogen pipeline valve, 24 first thermoelectric cooling chip, 25 sample stage, 26 second thermoelectric cooling chip, 27 top cover, 28 base, 29 heat pipe. DETAILED DESCRIPTION

[0031] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0032] like Figure 1 As shown, a carbon dioxide hydrate crystal mechanical property testing device provided by the present invention mainly includes a carbon dioxide gas storage cylinder 11, a nitrogen gas storage cylinder 12, an environmental control chamber air inlet valve 7, a gas booster pump 8, a first pressure sensor 9, an environmental control device 2, an environmental control chamber air outlet valve 13, a vacuum pump 14, a second pressure sensor 15, a one-way valve 16, a gas buffer collection bottle 17, a data acquisition system 18, a first temperature sensor 19, and a third pressure sensor 20.

[0033] The structure and connection method of each component will be described in detail below.

[0034] In the present invention, the environment control device 2 has an inner cavity, one end of which is connected to an air inlet pipe, and the other end of which is connected to an air outlet pipe. Figure 1 As shown, along the direction of fluid flow, the head end of the air inlet pipeline is divided into two parallel branches. The first branch is sequentially connected to the carbon dioxide storage cylinder 11 and the carbon dioxide pipeline valve 22 (i.e., the first branch with the carbon dioxide pipeline valve 22 externally connected to the carbon dioxide storage cylinder 11), and the second branch is sequentially connected to the nitrogen storage cylinder 12 (normal temperature) and the nitrogen pipeline valve 23 (i.e., the second branch with the nitrogen pipeline valve 23 externally connected to the nitrogen storage cylinder 12). The two branches are merged into one pipeline through a three-way valve 10 and then sequentially connected to the first pressure sensor 9, the gas booster pump 8, and the environmental control chamber inlet valve 7. Along the direction of fluid flow, the air outlet pipeline is sequentially connected to the environmental control chamber outlet valve 13, the vacuum pump 14, the second pressure sensor 15, the one-way valve 16, and the gas buffer collection bottle 17.

[0035] In a preferred embodiment of the present invention, the environmental control device 2 is made of stainless steel, which is resistant to carbon dioxide corrosion. It has a hollow cubic structure and can be configured to have dimensions of 1500 mm in length, 750 mm in width, 900 mm in height, and 8 mm in thickness. The front of the environmental control device 2 features a downward-sloping viewing window for viewing the interior. This window is made of triple-layer tempered safety glass.

[0036] As a preferred embodiment of the present invention, the environment control chamber air inlet valve 7 and the environment control chamber air outlet valve 13 are both one-way valves.

[0037] In the present invention, Figure 2 As shown, the inner cavity of the environmental control device 2 is equipped with a support base 1, a nanoindenter 3, an area scanning optical microscope system 4, a sample temperature control module 5, and a sample polishing device 6. The nanoindenter 3, the area scanning optical microscope system 4, the sample temperature control module 5, and the sample polishing device 6 are all arranged on the bottom of the support base 1. The environmental control chamber 2 isolates the nanoindenter 3, the sample temperature control module 5, the sample polishing device 6, and other equipment from the external environment. It is used to control the ambient temperature and CO2 gas concentration to achieve the experimental conditions required for simulating the in-situ formation of CO2 hydrates and maintaining constant pressure during the experiment.

[0038] As a preferred embodiment of the present invention, the nanoindenter 3 includes at least one indenter disposed on a mobile device, and each indenter is provided with a force sensor. The mobile device is mounted on the support base 1 and has three degrees of freedom. The indenter is combined with the mobile device to apply a controllable load to the test material and to move in a direction perpendicular to its plane. The force sensor is deployed on the indenter to measure the force applied to the material in the system and to send these data to the computer control unit (i.e., the data acquisition system 18). The area scanning optical microscope system 4 is connected to the computer control unit (i.e., the data acquisition system 18) and is capable of high-resolution imaging of the material surface, monitoring changes in the sample during the indentation process, and imaging the polished sample. The indenter has a spherical or sharp cutting edge to achieve switching between single-mark and continuous indentation modes.

[0039] Specifically, in this embodiment, the nanoindenter 3 has two indenters, which contain two force sensors and can be switched automatically without stopping to meet the indentation load requirements of different materials. It also includes a user interface unit, through which the experimental data is transmitted to the data acquisition system 18 through the line for human-computer interaction, control of the experimental process and export of experimental data. The nanoindenter 3 has two functions: nanoindentation and nanoscratch. The maximum load during nanoindentation can be 10mN; the load (force) resolution is less than 1nN; the maximum lateral load during nanoscratch is 2mN, and the lateral load resolution is less than 50nN. The nanoindenter 3 has an in-situ scanning probe imaging function. Using the same indenter, mechanical tests such as nanoindentation, nanoscratch, and nanowear testing can be performed, and three-dimensional images of the material surface indentation, scratches, and wear tests before and after the test can be obtained. By finely imaging the material surface, accurate indentation and scratch imaging quality of ±10nm can be achieved. This function can also be used to obtain the specific roughness value of the polished surface of the sample. This can be compared with the image processed data collected by the area scanning optical microscope system 4 to obtain more realistic sample surface roughness data.

[0040] As a preferred embodiment of the present invention, an area-scanning optical microscope system 4 is used to capture high-resolution color photographs of the polished surface of carbon dioxide hydrate crystals. It includes two color CCD cameras positioned on the sides and top of the sample. Its visible light source is a 3W LED. The microscope has a magnification range of 22x-2200x and a maximum resolution of 2560×1920. This area-scanning optical microscope system 4 offers high definition, high magnification, and multiple measurement capabilities. Equipped with color CCD cameras, it can maximize the reproduction of the observed sample's color and offers visual and rapid contrast and brightness adjustments for real-time visualization of sample details. Furthermore, this area-scanning optical microscope system 4 features automatic exposure, automatic focus, and image and video capture and storage, allowing for immediate recording and review of the sample. This area-scanning optical microscope system 4 can capture high-resolution color photographs of the polished surface of carbon dioxide hydrate crystals. Two color CCD cameras are positioned on the top and sides of the carbon dioxide hydrate crystals. Under appropriate conditions, images of the top and sides of the sample are captured, respectively. After obtaining the image, it is uploaded to image processing software. After image correction, denoising, and sharpening, algorithms or tools can be used to determine the average roughness of the polished crystal. The specific calculation rule is to calculate the square root of the sum of the squares of the differences between the intercept values ​​of the surface contour line and the x-axis. In addition, the polished image captured by the color CCD camera on the upper surface of the CO2 hydrate crystal sample can also be transferred to the image processing software to calculate the particle size of the CO2 hydrate crystal, thereby facilitating the selection of appropriate nanoindentation experimental parameters.

[0041] As a preferred embodiment of the present invention, Figure 3 and 4As shown, the sample temperature control module 5 creates low-temperature conditions for the formation of carbon dioxide hydrate crystals before the experiment and ensures the temperature of the carbon dioxide hydrate crystals remains stable during the polishing process and nanoindentation experiment. It can achieve precise temperature control with an accuracy of 0.1 degrees Celsius. By coordinating with the pressure control of the environmental control chamber 2, the decomposition of the carbon dioxide hydrate crystals can be minimized. The sample temperature control module 5 mainly comprises a top cover 27 and a base 28. The base 28 is removably fixed to the support base 1. The top of the base 28 is provided with an annular protrusion. The sample stage 25 is located in the recessed area in the middle of the annular protrusion. The sample is placed on the sample stage 25 on the bottom 28. A second annular thermoelectric cooling chip 26 is located between the sample stage 25 and the annular protrusion. This thermoelectric cooling chip is a solid-state cooling device that converts electricity and heat energy into each other through the Peltier effect. Its operating principle is based on the thermoelectric effect. A thermocouple is formed at the junction of two dissimilar materials. When current flows through, the heat generated by the current and the thermoelectric effect combine to cause the object on one side to heat up while the object on the other side to cool down. Since the thermoelectric cooling chip has a hot end and a cold end, the cold end of the second thermoelectric cooling chip 26 is arranged upward, and the inner periphery is set close to the sample stage 25 through thermal grease to achieve cooling of the sample. An annular groove is provided at the bottom of the top cover 27 for engaging with the annular protrusion, and a small hole is provided through the middle. The hole is used for the active ends of the nanoindenter 3 and the sample polishing device 6 to extend into and contact the sample on the sample stage 25 to achieve sample temperature control during the indentation process and the polishing process. A ring-shaped first thermoelectric cooling chip 24 is provided between the annular groove and the hole, and the cold end of the first thermoelectric cooling chip 24 faces downward. Through the relative arrangement of the cold ends of the first thermoelectric cooling chip 24 and the second thermoelectric cooling chip 26, the cooling effect of the carbon dioxide hydrate crystals placed in the middle can be maximized. When the top cover 27 is placed on the base 28 , there is a gap between the top of the sample stage 25 and the top cover 27 . The first thermoelectric cooling chip 24 is located just above the second thermoelectric cooling chip 26 with a gap between them. The two gaps are connected and serve as a cooling space.

[0042] Specifically, to promptly dissipate heat from the hot ends of the first and second thermoelectric cooling chips 24 and 26, heat pipes 29 for supplying cooling water are located inside the top cover 27 above the first thermoelectric cooling chip 24 and inside the base 28 below the second thermoelectric cooling chip 26. The heat pipes 29 contact the hot ends of the first and second thermoelectric cooling chips 24 and 26, and cooling water continuously circulates through the heat pipes. This continuous circulation of cooling water ensures that heat generated by the thermoelectric cooling chips is continuously removed from the environmental control device 2. Furthermore, to maintain temperature stability during the polishing and nanoindentation processes of the carbon dioxide hydrate crystals, a second temperature sensor 21 is located within the refrigeration chamber. This sensor monitors the temperature of the hydrate crystals in real time, reads the temperature signal, and feeds it back to the data acquisition system 18 according to a set ratio for temperature regulation. Once the set temperature is reached, the controller sends a signal to the first and second thermoelectric cooling chips 24 and 26 to maintain the temperature at that set point, and fine-tunes small temperature fluctuations to ensure temperature stability of the hydrate crystals throughout the experiment.

[0043] As a preferred embodiment of the present invention, the main function of the sample polishing device 6 is to polish the surface of the carbon dioxide hydrate crystal so that it can meet the needs of the nanoindentation experiment. The grinding head of the sample polishing device 6 is equipped with an active cooling device, that is, a semiconductor refrigeration chip for cooling is installed at the bottom of the grinding head, which can achieve a maximum cooling of minus 40°C at the grinding head. By continuously cooling the grinding head during the polishing process, the heat generated by the grinding head when polishing the hydrate crystal surface can be reduced, thereby minimizing the decomposition of the hydrate crystal due to the increase in sample temperature. The motor power of the sample polishing device 6 is 0.5 horsepower, the maximum speed is 10,000 rpm, and the surface flatness is less than 0.05 μm. The sample polishing device 6 adopts a high-speed rotating grinding wheel and a liquid-cooled water pump system, equipped with a digital display and timer function, which can control the processing time and rotation speed. During polishing, the sample is fixed to the sample temperature control module 5. By combining sample temperature control by the sample temperature control module 5 with active cooling control of the polishing head, the problem of crystal surface decomposition caused by overheating during polishing can be overcome. The area scanning optical microscope system 4 captures high-resolution color photographs of the polished carbon dioxide hydrate crystal surface. The area scanning optical microscope system 4 captures images of the top and sides of the sample. After image processing, software can calculate the average roughness of the polished crystal, thereby determining whether it meets the requirements of nanoindentation. It can also calculate the particle size of the carbon dioxide hydrate crystals, facilitating the selection of appropriate nanoindentation experimental parameters.

[0044] In the present invention, the environmental control device 2 is also provided with a first temperature sensor 19 and a third pressure sensor 20. The probes of the first temperature sensor 19 and the third pressure sensor 20 are both located in the inner cavity of the environmental control device 2 and are used to measure changes in temperature and pressure indicators in the inner cavity.

[0045] As a preferred embodiment of the present invention, a first temperature sensor 19 and a third pressure sensor 20 can record the temperature and pressure data within the cavity in real time. Both temperature and pressure sensors are connected to a data acquisition system 18, transmitting the data to a computer for real-time recording and aggregation. Software can then be used to analyze temperature and pressure changes over time. The first temperature sensor 19 is a Pt100 platinum resistance with a measurement accuracy of 0.1°C. The third pressure sensor 20 has a range of 25 MPa and an accuracy of ±0.25%.

[0046] In the present invention, Figure 1 As shown, the data acquisition system 18 is respectively connected to the first pressure sensor 9, the gas booster pump 8, the vacuum pump 14, the second pressure sensor 15, the first temperature sensor 19, the third pressure sensor 20, the nanoindenter 3, the area scanning optical microscope system 4, the sample temperature control module 5 and the sample polishing device 6, so as to collect and record the indicators obtained by each device in real time during the experiment.

[0047] The present invention further provides a test method using the above-mentioned carbon dioxide hydrate crystal mechanical property test device, which is specifically as follows:

[0048] S1: Preparation of carbon dioxide hydrate crystal sample, as follows:

[0049] 3-5 drops of pure water are added to the sample stage 25 of the sample temperature control module 5 to facilitate the subsequent formation of carbon dioxide hydrate crystals.

[0050] a. Open the nitrogen pipeline valve 23, close the carbon dioxide pipeline valve 22, open the gas booster pump 8, the environment control chamber inlet valve 7, the environment control chamber outlet valve 13, and the vacuum pump 14, and use nitrogen to purge the pipeline and the inner cavity of the environment control device 2 to expel impurities. After the purge is completed (about 5 minutes), close the environment control chamber outlet valve 13 and the vacuum pump 14, close the gas booster pump 8 and the environment control chamber inlet valve 7, close the nitrogen pipeline valve 23, open the carbon dioxide pipeline valve 22, then open the environment control chamber outlet valve 13 and the vacuum pump 14, then open the gas booster pump 8 and the environment control chamber inlet valve 7, and introduce carbon dioxide gas into the pipeline and the inner cavity of the environment control device 2. After five minutes of continuous operation, close the environment control chamber outlet valve 13 and the vacuum pump 14 to inject carbon dioxide gas into the inner cavity of the environment control device 2.

[0051] b. When the pressure value displayed by the third pressure sensor 20 reaches 2 MPa, the carbon dioxide pipeline valve 22, the gas booster pump 8 and the environment control chamber air inlet valve 7 are closed to complete the carbon dioxide gas injection process.

[0052] c. The temperature of the refrigeration space is controlled to 1°C through the sample temperature control module 5.

[0053] d. Determine whether carbon dioxide hydrate crystals have formed: 1) Visually observe whether carbon dioxide hydrate crystals have formed. If crystal structures are observed, it is determined that carbon dioxide hydrate crystals have formed. 2) The data acquisition system displays changes in the chamber pressure. After the carbon dioxide is injected and the chamber pressure stabilizes, carbon dioxide molecules gradually transfer from the gas phase to the water phase during the formation of carbon dioxide hydrate crystals and combine with water molecules to form hydrates. Therefore, when the data acquisition system observes a decrease in pressure and then gradually returns to stability, it can be considered that carbon dioxide hydrate crystals have formed. 3) The data acquisition system displays changes in the temperature of the sample temperature control console. Since the formation of carbon dioxide hydrate crystals is an exothermic process, when the data acquisition system records a sudden increase in the temperature curve and then gradually stabilizes, it can be considered that carbon dioxide hydrate crystals have formed.

[0054] In actual use, in order to ensure the accuracy of the judgment, the pressure change curve in the environmental control device 2 and the temperature change curve of the second temperature sensor 21 in the sample temperature control module 5 can also be observed through the data acquisition system 18. When it is observed that the pressure change curve decreases and then gradually returns to stability and the corresponding temperature change curve increases and then gradually stabilizes, it is judged that the formation of carbon dioxide hydrate crystals on the sample table 25 is complete.

[0055] S2: Sample polishing and roughness calculation, as follows:

[0056] a. Turn on the sample polishing device 6 and set the grinding head cooling temperature to -20°C, the grinding speed to 5000 rpm, and the polishing time to 1 hour. Adjust the position of the sample polishing device 6 so that the grinding head extends into the hole in the top cover 27 of the sample temperature control module 5 to polish the carbon dioxide hydrate crystal sample generated on the sample stage 25.

[0057] b. After the sample is polished, the sample surface is observed using an area scanning optical microscope system 4, and it is determined whether the surface is smooth and uniform, free of impurities and wear marks, etc., to ensure that the flatness of the sample surface reaches the micron level to complete a preliminary estimate. Subsequently, the area scanning optical microscope system 4 is used to collect images of the upper and side portions of the sample surface, and the side and top views of the polished carbon dioxide hydrate crystal sample are collected. The collected image data is then transmitted to the data acquisition system 18, and the image is uploaded to the image processing software to complete the image correction, denoising, and sharpening operations. The image is then imported into the image processing software to calculate the average surface roughness of the carbon dioxide hydrate crystal sample, and then combined with the in-situ scanning probe imaging (i.e., SPM+) function of the nanoindenter 3 to obtain the sample surface roughness, the two are compared and analyzed to obtain the final sample surface roughness value. If the obtained sample surface roughness value is less than 5 μm, the sample polishing process is completed. If the obtained sample surface roughness value is greater than 5 μm, the sample polishing process is repeated until the sample surface roughness value is less than 5 μm.

[0058] S3: Perform nanoindentation on a CO2 hydrate crystal sample as follows:

[0059] The pressure in the environment control device 2 and the temperature in the sample temperature control module 5 are controlled to remain constant.

[0060] a. Estimation of grain size: The surface of the polished carbon dioxide hydrate crystal sample is observed using an area scanning optical microscope system 4 . After imaging, the photograph is output to a data acquisition system 18 . The average grain size of the carbon dioxide hydrate crystals is analyzed on a computer using image processing software.

[0061] b. Select the appropriate probe (i.e., indenter) shape and load size: Based on the obtained average grain size of the sample, select the indenter shape and load size of the nanoindenter 3, as follows:

[0062] For samples with an average grain size in the range of [10, 20), nanoindentation testing was performed using a spherical indenter with a load of 1-5 μN. For samples with an average grain size in the range of [20, 50], nanoindentation testing was performed using a spherical indenter with a load of 5-10 μN. If the average grain size is not within these ranges, re-polish the sample according to S2 until it meets the requirements of the above ranges.

[0063] c. Software settings: Set the scanning range and indentation step depth of the nanoindenter 3 according to the experimental requirements, and select the area to be tested.

[0064] d. Calibrate the indenter: Use the calibration tool provided with the Nanoindenter 3 device to ensure that the indenter is perpendicular to the sample surface and complete the calibration. This process can be repeated multiple times to confirm the measurement accuracy.

[0065] e. Start Scanning: Before starting the experiment, set up the test environment and inspect the sample details. Then, start the instrument detection program of the nanoindenter 3. According to the set scanning path, the indenter enters the selected area and begins to apply the load. As the load increases, a series of load-depth curves are obtained.

[0066] f. Data acquisition: During the test, the indentation morphology and image generated on the sample surface as well as the load depth curve and load time curve are collected and recorded in real time.

[0067] g. Data processing and analysis: Calculate the elastic modulus of the sample based on the data results, and extract the mechanical properties of the sample such as compression modulus, hardness and crack diffusion.

[0068] The present invention can achieve stable generation of carbon dioxide hydrate crystals and ensure that carbon dioxide hydrate crystals are subjected to nanoindentation experiments under stable conditions, thereby obtaining mechanical properties such as indentation modulus, hardness and fracture toughness of carbon dioxide hydrate crystals, providing technical guarantee and hardware support for studying the mechanical properties of carbon dioxide hydrate crystals at the micro-nano scale.

[0069] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A device for testing mechanical properties of carbon dioxide hydrate crystals, characterized in that: It includes an environmental control device (2) and a data acquisition system (18); The environmental control device (2) has an inner cavity, one end of which is connected to an air inlet pipeline, and the other end of which is connected to an air outlet pipeline; along the flow direction of the fluid, the head end of the air inlet pipeline is divided into two branches, the first branch is connected to a carbon dioxide gas storage bottle (11) and a carbon dioxide pipeline valve (22) in sequence, and the second branch is connected to a nitrogen gas storage bottle (12) and a nitrogen pipeline valve (23) in sequence, and the two branches are connected to a first pressure sensor (9), a gas booster pump (8) and an environmental control chamber air inlet valve (7) in sequence after being combined through a three-way valve (10); along the flow direction of the fluid, direction, the gas outlet pipeline is connected in sequence to the gas outlet valve (13) of the environment control chamber, the vacuum pump (14), the second pressure sensor (15), the one-way valve (16) and the gas buffer collection bottle (17); the inner cavity of the environment control device (2) includes a nanoindenter (3) arranged on the bottom support seat (1), a regional scanning optical microscope system (4), a sample temperature control module (5) and a sample polishing device (6), and is also provided with a first temperature sensor (19) and a third pressure sensor (20) for measuring the inner cavity index; The data acquisition system (18) is respectively connected to the first pressure sensor (9), the gas booster pump (8), the vacuum pump (14), the second pressure sensor (15), the first temperature sensor (19), the third pressure sensor (20), the nanoindenter (3), the area scanning optical microscope system (4), the sample temperature control module (5) and the sample polishing device (6); The sample temperature control module (5) comprises a top cover (27) and a base (28); the base (28) is detachably fixed to the support seat (1), and is provided with an annular protrusion on the top, and a sample stage (25) is provided at a recessed portion in the middle of the annular protrusion, and an annular second thermoelectric cooling chip (26) is provided between the sample stage (25) and the annular protrusion; the cold end of the second thermoelectric cooling chip (26) faces upward, and the inner periphery is arranged close to the sample stage (25) through thermal conductive silicone grease; the bottom of the top cover (27) is provided with an annular groove for engaging with the annular protrusion, and a hole is provided through the middle, and the hole is used for nanopressure. The active ends of the trace meter (3) and the sample polishing device (6) extend into contact with the sample on the sample stage (25); a first annular thermoelectric cooling chip (24) is provided between the annular groove and the hole, and the cold end of the first thermoelectric cooling chip (24) faces downward; when the top cover (27) is covered on the base (28), there is a gap between the top of the sample stage (25) and the top cover (27), the first thermoelectric cooling chip (24) is located just above the second thermoelectric cooling chip (26) and there is a gap between the two, and the two gaps are connected and serve as a cooling space; a second temperature sensor (21) is provided in the cooling space.

2. A carbon dioxide hydrate crystal mechanical property testing device according to claim 1, characterized in that: The environment control device (2) is a hollow cubic structure, made of stainless steel, and has a visual window on the front side that is tilted downward to facilitate observation of the inner cavity, and the visual window is made of three layers of tempered safety glass.

3. A carbon dioxide hydrate crystal mechanical property testing device according to claim 1, characterized in that: The environment control chamber air inlet valve (7) and the environment control chamber air outlet valve (13) are both one-way valves.

4. A carbon dioxide hydrate crystal mechanical property testing device according to claim 1, characterized in that: The nanoindenter (3) comprises at least one indenter arranged on a mobile device, each indenter being provided with a force sensor; the mobile device is mounted on a support seat (1) and has three degrees of freedom.

5. A carbon dioxide hydrate crystal mechanical property testing device according to claim 1, characterized in that: The area scanning optical microscope system (4) comprises two color CCD cameras arranged on the side and top of the sample, its visible light source is a 3W LED, the microscope magnification range is 22X-2200X, and the maximum resolution is 2560×1920.

6. A carbon dioxide hydrate crystal mechanical property testing device according to claim 1, characterized in that: Heat pipes (29) for passing cooling water are provided inside the top cover (27) located above the first thermoelectric cooling chip (24) and inside the base (28) located below the second thermoelectric cooling chip (26); the heat pipes (29) are in contact with the hot ends of the first thermoelectric cooling chip (24) and the second thermoelectric cooling chip (26) and are used to carry away the heat generated by the thermoelectric cooling chips.

7. A carbon dioxide hydrate crystal mechanical property testing device according to claim 1, characterized in that: The bottom of the grinding head of the sample grinding device (6) is equipped with a semiconductor refrigeration chip for cooling.

8. A test method using the carbon dioxide hydrate crystal mechanical property test device according to any one of claims 1 to 7, characterized in that: The details are as follows: S1: Add 3-5 drops of pure water to the sample platform (25) of the sample temperature control module (5), then open the nitrogen pipeline valve (23), close the carbon dioxide pipeline valve (22), open the gas booster pump (8), the environment control chamber air inlet valve (7), the environment control chamber air outlet valve (13) and the vacuum pump (14), and use nitrogen to clean the pipeline and the inner cavity of the environment control device (2) to discharge impurity gases; after the cleaning is completed, close the nitrogen pipeline valve (23), open the carbon dioxide pipeline valve (22), and introduce carbon dioxide gas into the pipeline and the inner cavity of the environment control device (2), then close the environment control chamber air outlet valve (13) and the vacuum pump (14) to inject carbon dioxide into the inner cavity of the environment control device (2). carbon dioxide gas; when the third pressure sensor (20) displays a pressure value reaching 2MPa, the carbon dioxide pipeline valve (22), the gas booster pump (8) and the environment control chamber air inlet valve (7) are closed to complete the carbon dioxide gas injection process; the temperature of the refrigeration space is controlled to be 1°C through the sample temperature control module (5); the pressure change curve in the environment control device (2) and the temperature change curve of the second temperature sensor (21) in the sample temperature control module (5) are observed through the data acquisition system (18); when it is observed that the pressure change curve decreases and then gradually returns to stability and the corresponding temperature change curve increases and then gradually tends to be stable, it is determined that the formation of carbon dioxide hydrate crystals on the sample stage (25) is complete; S2: Turn on the sample grinding device (6), set the cooling temperature of the grinding head to -20°C, the grinding speed to 5000 rpm, and the grinding time to 1 hour; adjust the position of the sample grinding device (6) so that the grinding head extends into the hole of the top cover (27) of the sample temperature control module (5) to grind the carbon dioxide hydrate crystal sample generated on the sample table (25); after the sample is polished, use the area scanning optical microscope system (4) to collect images of the upper and side surfaces of the sample surface, and then transmit the collected image data to the data acquisition system (18), and upload the image into the image processing software to complete the image correction, denoising and sharpening operations, then import the image into the image processing software to calculate the average value of the surface roughness of the carbon dioxide hydrate crystal sample, and then combine it with the sample surface roughness obtained by the in-situ scanning probe imaging function of the nanoindenter (3), and compare and analyze the two to obtain the final sample surface roughness value; if the obtained sample surface roughness value is less than 5 μm, the sample grinding process is completed; if the obtained sample surface roughness value is greater than 5 μm, the sample grinding process is repeated until the sample surface roughness value is less than 5 μm; S3: The surface of the polished carbon dioxide hydrate crystal sample is observed by an area scanning optical microscope system (4), and the photograph is output to a data acquisition system (18) after imaging, and the average grain size of the carbon dioxide hydrate crystal is analyzed by applying image processing software on a computer; according to the obtained average grain size of the sample, the indenter shape and load size of the nanoindenter (3) are selected, as follows: For samples with an average grain size in the range of [10,20], a spherical indenter with a load of 1-5 μN is applied; for samples with an average grain size in the range of [20,50], a spherical indenter with a load of 5-10 μN is applied; otherwise, the sample is re-grinded according to S2; The scanning range and indentation step depth of the nanoindenter (3) are set according to the experimental requirements, and the area to be tested is selected; the calibration tool provided with the nanoindenter (3) is used for calibration to ensure that the indenter is orthogonal to the sample surface and complete the calibration; Starting the instrument detection program of the nanoindenter (3), according to the set scanning path, the indenter enters the selected area and starts to apply the load; as the load increases, a series of load-depth curves are obtained; During the test, the indentation morphology and image generated on the sample surface as well as the load depth curve and load time curve are collected and recorded in real time; the elastic modulus of the sample is calculated based on the data results, and the mechanical properties of the sample are extracted.

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