Humidity-controlled XRD (X-Ray Diffraction) test system and test method for expansive clay minerals

Abstract

The invention relates to a humidity-controlled XRD (X-Ray Diffraction) test system and a humidity-controlled XRD test method for expansive clay minerals. The testing system comprises a sample chamber, a gas circulating pump, a saturated solution bottle and a gas transition bottle. And saturated salt solutions or water corresponding to different relative humidity are filled in the saturated solution bottle. The testing method comprises the following steps: preparing the expansive clay mineral oriented sheet; placing the expansive clay mineral oriented sheet in a sample chamber, and sealing the sample chamber; building a test system, and selecting a saturated salt solution or water under the corresponding relative humidity; and after the relative humidity in the sample chamber is balanced, carrying out XRD test on the expansive clay mineral oriented sheet. Compared with the prior art, the XRD test under different humidity conditions can be carried out on a high-purity and high-orientation expansible clay mineral oriented sheet sample, so that relevant parameters of a crystal layer expansion process are further obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering, and in particular to a humidity-controlled expansive clay mineral XRD testing system and testing method. Background Art

[0002] In the design concepts of high-level radioactive nuclear waste repositories worldwide, multiple barrier systems have been recognized as the safest and most effective system to prevent the migration and leakage of nuclides. Highly compacted bentonite, as an engineering barrier material, performs functions such as water absorption and expansion, sealing construction joints, and preventing nuclide leakage. Montmorillonite, the primary functional material in high-compacted bentonite, expands upon contact with water in two stages: crystal layer expansion and double electrical layer expansion. Under conditions of high dry density and complete confinement, crystal layer expansion plays a dominant role. Therefore, quantitative analysis of the montmorillonite crystal layer expansion process under different moisture content conditions is a key indicator for evaluating the safe operation of deep geological repositories.

[0003] Currently, X-ray diffraction (XRD) is commonly used to analyze the expansion process of montmorillonite crystal layers. The Bragg equation is used to calculate the change in the (001) interplanar spacing to quantify the expansion process. CN116087470A discloses an XRD-based device for measuring soil expansion pressure under varying salinity fields. This device can monitor the changing expansion pressure of expansive soil and the intercrystalline spacing of montmorillonite at different salinities, providing the optimal type of salt solution for the expansive soil and determining the optimal concentration of the salt solution.

[0004] However, the above-mentioned XRD-based testing device and method still have the following problems in sample preparation and test environment control. During the test process, the moisture content of montmorillonite in the expansive clay mineral sample cannot be effectively controlled, and the expansion process of the montmorillonite crystal layer under different humidity conditions cannot be measured. Secondly, the montmorillonite in the bentonite sample often agglomerates with other minerals, resulting in poor surface flatness of its crystal layer and anisotropic mechanical properties; and the interlayer cation exchange process of montmorillonite is slow, which brings challenges to sample purification, making it difficult to accurately characterize conventional micromechanical testing techniques and unable to effectively solve the problems of montmorillonite separation and directional arrangement.

[0005] Therefore, a new testing system and testing method that can perform XRD and testing on expansive clay mineral samples under different humidity conditions still needs to be developed. Summary of the Invention

[0006] The purpose of the present invention is to provide a humidity-controlled expansive clay mineral XRD testing system and testing method in order to overcome the defects of existing crystal layer expansion testing devices and methods, such as difficulty in controlling humidity and difficulty in preparing samples to meet the requirements of micromechanical properties testing.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] The present invention first provides a humidity-controlled expansive clay mineral XRD testing system for performing XRD testing on expansive clay mineral oriented sheets under different humidity conditions, comprising:

[0009] A sample chamber is installed on the XRD sample stage and loaded with the oriented slice of the expansive clay mineral to be tested; the sample chamber is provided with an air inlet and an air outlet;

[0010] a gas circulation pump, the gas inlet of which is connected to the gas outlet of the sample chamber;

[0011] A saturated solution bottle is connected to the gas outlet of the gas circulation pump; the saturated solution bottle contains saturated salt solution or water corresponding to different relative humidity, and the relative humidity control range is 12%-100%;

[0012] The gas transition bottle is connected with the gas inlet of the sample chamber and the saturated solution bottle.

[0013] Furthermore, the sample chamber includes a bottom plate and arched pillars vertically arranged on both sides of the bottom plate.

[0014] Furthermore, the bottom plate is provided with a sample slot for placing the oriented slices of the expansive clay mineral.

[0015] Furthermore, the air inlet and the air outlet are arranged on the same arched support or respectively on two arched support.

[0016] Furthermore, the arched pillars are connected and sealed by sealing tape, so that a closed testing space is formed in the sample chamber.

[0017] Furthermore, the sealing tape is a polyimide tape with high X-ray transmittance, which will not affect the position of the diffraction peak.

[0018] Furthermore, the saturated salt solution is selected from: LiCl, corresponding to a relative humidity of 12%; MgCl2, corresponding to a relative humidity of 33.1%; K2CO3, corresponding to a relative humidity of 43.2%; NaBr, corresponding to a relative humidity of 58%; NaNO2, corresponding to a relative humidity of 66.1%; NaCl, corresponding to a relative humidity of 75.5%; (NH4)2SO4, corresponding to a relative humidity of 81.3%; ZnSO4, corresponding to a relative humidity of 90%; and K2SO4, corresponding to a relative humidity of 97.6%.

[0019] The present invention also provides a testing method using the above-mentioned expansive clay mineral XRD testing system, comprising the following steps:

[0020] S1. Preparation of expansive clay mineral oriented sheets:

[0021] The bentonite powder after preliminary screening is dissolved in a saturated salt solution to prepare a bentonite suspension of a certain concentration; a dispersant is added to the bentonite suspension, the pH is adjusted, and the suspension is fully dispersed under ultrasonic conditions to promote uniform distribution of particles and prevent agglomeration;

[0022] Under the above dispersion conditions, interlayer cation exchange purification is performed through a flow system, followed by multiple washings to obtain a stable bentonite suspension; the suspension is allowed to stand to allow coarse particles to settle, and the high-purity montmorillonite in the supernatant is collected;

[0023] Use a rubber-tipped dropper to sample the montmorillonite supernatant and add it dropwise to deionized water for repeated washing until the chloride ions are completely removed (this can be verified with silver nitrate solution).

[0024] The washed montmorillonite supernatant is evenly dripped onto a smooth inert silicon wafer and allowed to air dry naturally to form oriented sheets of expansive clay minerals with an oriented structure.

[0025] S2: Place the oriented expansive clay mineral sheet obtained in S1 in a sample chamber and seal the chamber; build a test system and select a saturated salt solution or water at a corresponding relative humidity;

[0026] S3: Start the gas circulation pump and perform XRD test on the oriented slices of expansive clay minerals after the relative humidity in the sample chamber is balanced.

[0027] Furthermore, in step S1, the particle size of the bentonite powder after screening is no greater than 75 μm.

[0028] Furthermore, in step S1, the saturated salt solution is a saturated NaCl solution.

[0029] Furthermore, in step S1, the mass fraction of bentonite in the bentonite suspension is 1.5-3 wt%.

[0030] Furthermore, in step S1, the dispersant is sodium hexametaphosphate.

[0031] Furthermore, the amount of the dispersant used is 0.08-0.12% of the bentonite suspension.

[0032] Furthermore, in step S1, the pH is adjusted to 8-10. The purpose of adjusting the pH is to ensure maximum dispersion of the montmorillonite particles.

[0033] Furthermore, in step S1, the standing time is not less than 12 hours.

[0034] Furthermore, in step S1, the surface flatness of the nanoscale silicon wafer is less than 3 μm, and the roughness is less than 0.5 nm.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The humidity control unit of the present invention, which is composed of a gas circulation pump, a saturated solution bottle and a gas transition bottle, can adjust the humidity in the sample chamber, so that XRD tests can be performed on the oriented sheet samples of expansive clay minerals under different humidity conditions, and the relevant parameters of the crystal layer expansion process can be further obtained.

[0037] (2) The testing method of the present invention is based on the existing XRD test. It not only optimizes the sample preparation method of the oriented sheets of high-purity and high-oriented expansive clay minerals, but also introduces humidity control performance into the XRD test to meet the needs of testing the crystal layer expansion characteristics of expansive clay minerals under different humidity conditions. It can be used as a general microstructural feature testing method in the field of civil engineering.

[0038] (3) The test system of the present invention can achieve gradient control of relative humidity between 12% and 100% by replacing different types of saturated salt solutions or water, so as to facilitate the quantitative analysis of the expansion process of montmorillonite crystal layers under different moisture content conditions, which is of great significance for the optimization design of buffer materials in nuclear waste disposal repositories and their long-term performance evaluation.

[0039] (4) The oriented flake samples of the expansive clay minerals of the present invention are processed through multiple steps such as physical screening, saturated salt solution washing, dispersant regulation, and dispersion. Not only can high-purity montmorillonite flakes be effectively extracted, but also the oriented arrangement of montmorillonite crystal layers can be achieved through natural sedimentation to meet the requirements of the montmorillonite crystal layer expansion property test, and have broad engineering application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the overall structure of the test system of the present invention.

[0041] Figure 2 Schematic diagram of the structure of the sample chamber of the present invention.

[0042] Figure 3 Schematic diagram of the explosion of the sample chamber of the present invention.

[0043] Figure 4 This is a SEM characterization image of the oriented sheet of expansive clay mineral prepared in Example 2 of the present invention.

[0044] Figure 5 This is the XRD pattern in Example 2 of the present invention.

[0045] Description of the marks in the figure:

[0046] 1-Oriented flakes of expansive clay minerals;

[0047] 2-sample chamber, 21-air inlet, 22-air outlet, 23-bottom plate, 231-sample slot, 24-arch support, 25-sealing tape;

[0048] 3-Gas circulation pump;

[0049] 4-Saturated solution bottle;

[0050] 5-Gas transition bottle. DETAILED DESCRIPTION

[0051] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0052] In the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes and should not be understood as indicating or implying relative importance; in addition, unless otherwise expressly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediate medium, or it can be internal communication between two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0053] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not require further definition or explanation in subsequent drawings.

[0054] The present invention first provides a humidity-controlled expansive clay mineral XRD testing system for performing XRD testing on an expansive clay mineral oriented sheet 1 under different humidity conditions. Figure 1-3The test system of the present invention specifically includes a sample chamber 2, a gas circulation pump 3, a saturated solution bottle 4, and a gas transition bottle 5. The sample chamber 2 is installed on the XRD sample stage and loaded with the oriented sheet 1 of the expansive clay mineral to be tested. The sample chamber 2 is provided with an air inlet 21 and an air outlet 22. The air inlet of the gas circulation pump 3 is connected to the air outlet 22 of the sample chamber 2. The saturated solution bottle 4 is connected to the air outlet of the gas circulation pump 3. The saturated solution bottle 4 is filled with saturated salt solutions or water corresponding to different relative humidity levels, and the relative humidity control range is 12%-100%. The gas transition bottle 5 is connected to the air inlet 21 of the sample chamber 2 and is connected to the saturated solution bottle 4.

[0055] In some specific embodiments, the sample chamber 2 includes a bottom plate 23 and arched pillars 24 vertically arranged on both sides of the bottom plate 23 .

[0056] In some specific embodiments, the bottom plate 23 is provided with a sample slot 231 for placing the oriented expansive clay mineral sheet 1 .

[0057] In some specific embodiments, the air inlet 21 and the air outlet 22 are provided on the same arched support 24 or are respectively provided on two arched support pillars 24 .

[0058] In some specific embodiments, the arched pillars 24 are connected and sealed by a sealing tape 25 , so that a closed testing space is formed in the sample chamber 2 .

[0059] In some specific embodiments, the sealing tape 25 is a polyimide tape with high X-ray transmittance.

[0060] In some specific embodiments, the saturated salt solution is selected from: LiCl, corresponding to a relative humidity of 12%; MgCl2, corresponding to a relative humidity of 33.1%; K2CO3, corresponding to a relative humidity of 43.2%; NaBr, corresponding to a relative humidity of 58%; NaNO2, corresponding to a relative humidity of 66.1%; NaCl, corresponding to a relative humidity of 75.5%; (NH4)2SO4, corresponding to a relative humidity of 81.3%; ZnSO4, corresponding to a relative humidity of 90%; and K2SO4, corresponding to a relative humidity of 97.6%.

[0061] The present invention also provides a testing method using the above-mentioned expansive clay mineral XRD testing system, which specifically comprises the following steps:

[0062] S1. Preparation of expansive clay mineral oriented sheets:

[0063] The bentonite powder after preliminary screening is dissolved in a saturated salt solution to prepare a suspension of a certain concentration; a dispersant is added to the bentonite suspension, the pH is adjusted, and the suspension is fully dispersed, and the suspension is fully dispersed under ultrasonic conditions to promote uniform distribution of particles and prevent agglomeration; under the above dispersion conditions, interlayer cation exchange purification is performed through a flow system, followed by multiple washings to obtain a stable bentonite suspension; the suspension is allowed to stand to allow coarse particles to settle, and high-purity montmorillonite in the supernatant is collected; the montmorillonite supernatant is sampled using a rubber-tipped dropper, and the sample is added dropwise to deionized water for repeated washing until the chloride ions are completely removed (which can be verified with a silver nitrate solution); the washed montmorillonite supernatant is evenly added dropwise to a smooth inert silicon wafer and naturally air-dried to form an oriented film sample of an expansive clay mineral with an oriented structure;

[0064] S2: Place the oriented expansive clay mineral sheet obtained in S1 in a sample chamber and seal the chamber; build a test system and select a saturated salt solution or water at a corresponding relative humidity;

[0065] S3: Start the gas circulation pump and perform XRD test on the oriented slices of expansive clay minerals after the relative humidity in the sample chamber is balanced.

[0066] In some specific embodiments, in step S1, the saturated salt solution is a saturated NaCl solution.

[0067] In some specific embodiments, in step S1, the dispersant is sodium hexametaphosphate.

[0068] In some specific embodiments, in step S1, the pH is adjusted to 8-10.

[0069] In some specific embodiments, in step S1, the standing time is not less than 12 hours.

[0070] In some specific embodiments, in step S1, the substrate is a nanoscale silicon wafer; the surface flatness of the nanoscale silicon wafer is less than 3 μm, and the roughness is less than 0.5 nm.

[0071] The above embodiments can be implemented individually or in any combination of two or more. The above embodiments will be described in more detail below with reference to specific examples.

[0072] Example 1:

[0073] This embodiment constructs a humidity-controlled XRD testing system for swelling clay minerals, which is used to perform XRD tests under different humidity conditions on swelling clay mineral oriented sheets 1. The testing system of this embodiment includes a sample chamber 2, a gas circulation pump 3, a saturated solution bottle 4, and a gas transition bottle 5.

[0074] The sample chamber 2 of this embodiment is mounted on an XRD sample stage and loaded with an oriented sheet of expanded clay mineral to be tested. The sample chamber 2 is provided with an air inlet 21 and an air outlet 22. The sample chamber 2 includes a base plate 23 and arched supports 24 vertically disposed on either side of the base plate 23. The base plate 23 is provided with a sample slot 231 for placing the oriented sheet of expanded clay mineral 1. The air inlet 21 and the air outlet 22 are located on the same arched support 24. The arched supports 24 are connected and sealed with sealing tape 25, forming a sealed test space within the sample chamber 2. The sealing tape 25 is a polyimide tape with high X-ray transmittance.

[0075] The air inlet of the gas circulation pump 3 of this embodiment is connected to the air outlet 22 of the sample chamber 2. The saturated solution bottle 4 is connected to the air outlet of the gas circulation pump 3. The saturated solution bottle 4 is filled with saturated salt solutions or water corresponding to different relative humidity levels, and the relative humidity control range is 12%-100%. The gas transition bottle 5 is connected to the air inlet 21 of the sample chamber 2 and is also connected to the saturated solution bottle 4. The saturated solution bottle 4 and the gas transition bottle 5 are both composed of a bottle body, a sealing plug (a conventional wooden plug or rubber plug is selected), and a pipeline. The sealing plug is provided with two through holes, one for introducing gas and the other for outputting gas.

[0076] The saturated salt solution of this embodiment can be selected according to different humidity requirements: LiCl, corresponding to a relative humidity of 12%; MgCl2, corresponding to a relative humidity of 33.1%; K2CO3, corresponding to a relative humidity of 43.2%; NaBr, corresponding to a relative humidity of 58%; NaNO2, corresponding to a relative humidity of 66.1%; NaCl, corresponding to a relative humidity of 75.5%; (NH4)2SO4, corresponding to a relative humidity of 81.3%; ZnSO4, corresponding to a relative humidity of 90%; K2SO4, corresponding to a relative humidity of 97.6%; water, corresponding to a relative humidity of 100%.

[0077] Specifically, the equilibrium process of the gas humidity in the sample chamber 2 in this embodiment is:

[0078] The gas within sample chamber 2 is fed via a pipeline into the air inlet (exhaust port) of a gas circulation pump 3. The gas output from the exhaust port of the gas circulation pump 3 is then piped directly into the saturated solution in a saturated solution bottle 4. The gas, treated with the saturated solution, is fed via a conduit into a gas transition bottle 5 and further into sample chamber 2. This gas circulation achieves relative humidity equilibrium within sample chamber 2, enabling XRD testing of expansive clay minerals under varying humidity conditions.

[0079] Example 2:

[0080] This example uses the test system in Example 1 and takes natural bentonite ore from the Gaomiaozi bentonite area in Inner Mongolia as an example to conduct XRD-based crystal layer expansion characteristic tests under different humidity conditions. The specific test process is as follows:

[0081] (1) Preparation of high-purity and high-orientation montmorillonite film samples to be tested

[0082] 1.1 Physical screening and purification of bentonite powder:

[0083] First, a vibrating screener was used to physically sieving the bentonite to remove large impurities, reducing the bentonite powder particle size to less than 0.075 mm. Two grams of the sieved bentonite powder was dissolved in 98 grams of saturated sodium chloride solution. A small amount of dispersant (0.1% sodium hexametaphosphate by weight of the suspension) was added, and the pH of the suspension was adjusted to 8-10 using 0.1 mol / L NaOH solution. The mixture was then thoroughly stirred and ultrasonicated to promote uniform particle distribution and prevent agglomeration.

[0084] 1.2. Montmorillonite purification treatment:

[0085] Under the above-mentioned dispersion conditions, interlayer cation exchange purification was carried out through a flow system, followed by multiple washings to obtain a stable bentonite suspension; the above suspension was allowed to stand for 24 hours to allow impurities such as quartz and feldspar to precipitate, and high-purity montmorillonite in the supernatant was collected; the montmorillonite supernatant was sampled using a rubber-tipped dropper, added dropwise to deionized water, and repeatedly washed until the chloride ions were completely removed, and verified using a 0.1 mol / L silver nitrate solution.

[0086] 1.3. Preparation of highly oriented montmorillonite films:

[0087] Use a pipette to take 370 μL of high-purity montmorillonite supernatant and drop it onto a single-crystal silicon substrate (nanoscale silicon wafer) with atomic-level roughness. The surface flatness of the silicon wafer is less than 3 μm and the roughness is less than 0.5 nm to ensure the quality of the film. To avoid dust contamination, a culture dish is placed on top of the silicon wafer, and one side of the culture dish is raised to ensure smooth drainage of water. After the droplets are naturally air-dried, a highly oriented purified montmorillonite film is finally obtained, that is, an oriented sheet of expansive clay minerals. Figure 4 As shown, the film has an excellent directional arrangement structure and can meet the requirements of microstructure testing.

[0088] (2) Place the prepared expanded clay mineral oriented sheet in the sample groove of the sample chamber and seal the sample chamber with polyimide tape with high X-ray transparency, making sure no gaps are left. The sample chamber is then connected to the gas circulation pump, saturated solution bottle, and gas transition bottle in the test system through corresponding pipes. The saturated solution bottle is filled with a saturated salt solution of the corresponding relative humidity, thus constructing a complete test system.

[0089] (3) The sample chamber is placed on the XRD test sample table and clamped, the gas circulation pump is turned on, and after the relative humidity in the closed sample chamber reaches equilibrium, the crystal layer expansion characteristic test based on the X-ray diffraction test is started.

[0090] The XRD scan was performed using a Smartlab diffractometer equipped with a parallel beam optical system to minimize errors caused by sample misalignment. A nickel (Ni) filter was used for the XRD scan, and an incident angle of 1° was used. Copper target Kα radiation (wavelength ), generated at a voltage of 45 kV and a current of 100 mA. The scanning range was set at 2–12° (2θ) at a rate of 1° (2θ) / minute, focusing on the 001 reflection peak of the montmorillonite crystal plane. Based on the 2θ angular position of the d001 diffraction peak under different humidity conditions, the interlayer spacing was calculated using Bragg's law (Equation 1), thus revealing the crystal layer expansion characteristics of the expansive clay mineral.

[0091]

[0092] Where λ is the wavelength of the incident wave; θ is the angle of incidence; and d001 is the interlayer spacing of montmorillonite.

[0093] In the test of this embodiment, by changing the type of saturated salt solution in the saturated solution bottle, a gradient change from 12% to 100% of relative humidity was achieved. Figure 5 As shown, as the relative humidity (RH) increases from 12% to 100%, the 001 diffraction peak of the montmorillonite film shifts significantly from 2θ = 7.02° to 2θ = 4.7°. This shift reflects the change in interlayer spacing and the intercalation of water molecules between the layers. At an RH of 12%, the montmorillonite film forms a monolayer of water molecules; when the RH is between 66.1% and 90%, a bilayer of water molecules is observed between the layers. Notably, a "transition zone" exists between RH of 33.1% and 66.1%, transitioning from a monolayer to a bilayer of water molecules. This may be attributed to the inherently heterogeneous hydration state of the montmorillonite film sample. When the RH increases to 97.6% and above, a trilayer of water molecules forms, representing the final crystal expansion state of montmorillonite.

[0094] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A humidity-controlled XRD testing system for swelling clay minerals, used for performing XRD testing on swelling clay mineral oriented sheets (1) under different humidity conditions, characterized in that: include: A sample chamber (2) is mounted on an XRD sample stage and loaded with an oriented sheet of expansive clay mineral to be tested (1); an air inlet (21) and an air outlet (22) are provided on the sample chamber (2); a gas circulation pump (3), the gas inlet of which is connected to the gas outlet (22) of the sample chamber (2); A saturated solution bottle (4) is connected to the gas outlet of the gas circulation pump (3); the saturated solution bottle (4) is filled with saturated salt solutions or water corresponding to different relative humidity, and the control range of relative humidity is 12%-100%; The gas transition bottle (5) is communicated with the gas inlet (21) of the sample chamber (2) and is also communicated with the saturated solution bottle (4).

2. A humidity-controlled expansive clay mineral XRD testing system according to claim 1, characterized in that: The sample chamber (2) includes a bottom plate (23) and arched pillars (24) vertically arranged on both sides of the bottom plate (23); The arched pillars (24) are connected and sealed by a sealing tape (25), so that a closed testing space is formed in the sample chamber (2).

3. A humidity-controlled expansive clay mineral XRD testing system according to claim 2, characterized in that: The bottom plate (23) is provided with a sample groove (231) for placing the expanded clay mineral oriented sheet (1).

4. A humidity-controlled expansive clay mineral XRD testing system according to claim 2, characterized in that: The air inlet (21) and the air outlet (22) are arranged on the same arched support (24) or respectively on two arched support pillars (24).

5. The humidity-controlled expansive clay mineral XRD testing system according to claim 2, characterized in that: The sealing tape (25) is a polyimide tape with high X-ray transmittance.

6. The humidity-controlled expansive clay mineral XRD testing system according to claim 1, characterized in that: The saturated salt solution is selected from: LiCl, corresponding to a relative humidity of 12%; MgCl2, corresponding to a relative humidity of 33.1%; K2CO3, corresponding to a relative humidity of 43.2%; NaBr, corresponding to a relative humidity of 58%; NaNO2, corresponding to a relative humidity of 66.1%; NaCl, corresponding to a relative humidity of 75.5%; (NH4)2SO4, corresponding to a relative humidity of 81.3%; ZnSO4, corresponding to a relative humidity of 90%; K2SO4, corresponding to a relative humidity of 97.6%.

7. A testing method using the humidity-controlled expansive clay mineral XRD testing system according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Preparation of expansive clay mineral oriented sheets: The bentonite powder after preliminary screening is dissolved in a saturated salt solution to prepare a bentonite suspension; a dispersant is added to the bentonite suspension, the pH is adjusted, and ultrasonic dispersion is performed; Under ultrasonic dispersion conditions, interlayer cation exchange purification was carried out through a flow system, followed by multiple washings to obtain a stable bentonite suspension. After the suspension is allowed to stand to allow the coarse particles to settle, the high-purity montmorillonite in the supernatant is collected; The montmorillonite supernatant is added dropwise to water and repeatedly washed until the chloride ions are completely removed; the washed montmorillonite supernatant is added dropwise to a smooth inert silicon wafer and allowed to air dry naturally to form an oriented sheet of expandable clay minerals with an oriented structure; S2: Place the oriented expansive clay mineral sheet obtained in S1 in a sample chamber and seal the chamber; build a test system and select a saturated salt solution or water at a corresponding relative humidity; S3: Start the gas circulation pump and perform XRD test on the oriented slices of expansive clay minerals after the relative humidity in the sample chamber is balanced.

8. The testing method according to claim 7, characterized in that: In step S1, the particle size of the bentonite powder after screening is no more than 75 μm; The saturated salt solution is a saturated NaCl solution.

9. The testing method according to claim 7, characterized in that: In step S1, the dispersant is sodium hexametaphosphate; The pH is adjusted to 8-10; The standing time is not less than 12 hours.

10. The testing method according to claim 7, wherein: In step S1, the surface flatness of the silicon wafer is less than 3 μm, and the roughness is less than 0.5 nm.

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