Soil water potential sensor pottery clay sheet, preparation process and regulation and control method

Abstract

The invention is applicable to the technical field of soil water potential measurement, and provides a soil water potential sensor pottery clay sheet, a preparation process and a regulation and control method.The preparation process comprises the steps that main ingredients and auxiliary ingredients are obtained, the main ingredients at least comprise aluminum oxide, kaolin and synthetic carbon powder, and the auxiliary ingredients at least comprise silica sol; mixing and ball-milling the main materials and the auxiliary materials to obtain a mixture; adding silica sol into the mixture, and stirring for a period of time to obtain uniform fluid slurry; drying the fluid slurry at a preset temperature for a period of time, and carrying out compression molding to obtain a solid wet blank; and carrying out high-temperature sintering on the wet blank to obtain the porous pottery clay sheet. The method has the advantages that the water potential sensor obtained on the basis of the process is high in measurement precision and high in measurement speed, the steps and operation difficulty required for measuring the soil water potential can be remarkably reduced, and a new development direction is provided for high-precision measurement of the soil water potential.

Description

Technical Field

[0001] This invention belongs to the field of soil water potential measurement technology, and particularly relates to a soil water potential sensor ceramic sheet, its preparation process and control method. Background Technology

[0002] Soil water potential refers to the energy state of water in the soil, rather than a direct measurement of soil moisture content. This energy state determines the direction of water flow in the soil and how easily plant roots can absorb water.

[0003] Soil water potential is a key parameter in agricultural and environmental sciences, crucial for understanding the interactions between soil, plants, and the atmosphere, optimizing irrigation strategies, and improving crop productivity. Many measurement methods exist, such as the tensiometer method, which uses a portable soil water potential monitor to measure matrix potential and is commonly used for point-to-point monitoring of farmland and potted soils. However, this method has a narrow measurement range, requires equipment maintenance such as water injection and degassing, and may fail under freezing and drying conditions. Other measurement methods include indirect measurement methods, evaporation / hydraulic property analysis methods, and capacitance estimation methods.

[0004] However, the traditional methods for measuring soil water potential using tensiometers, hygrometers, capacitance estimation, etc., often have limitations in terms of accuracy, durability, and field adaptability. The accuracy of measuring soil water potential based on capacitance estimation using existing mainstream materials is often low. Summary of the Invention

[0005] The purpose of this application is to provide a process for preparing a clay sheet for a soil water potential sensor, aiming to improve the low accuracy of existing measuring capacitors in measuring soil water potential by providing a clay sheet preparation process.

[0006] This application provides a process for preparing a clay sheet for a soil water potential sensor, the process comprising the following steps: Obtain the main ingredients and auxiliary ingredients, wherein the main ingredients include at least alumina, kaolin, and synthetic carbon powder, and the auxiliary ingredients include at least silica sol; The main ingredients are mixed and ball-milled to obtain a mixture; Add silica sol to the mixture and stir for a certain period of time to obtain a uniform fluid slurry; The fluid slurry is dried at a preset temperature for a certain period of time and then molded to obtain a solid wet blank. The wet blank is sintered at high temperature to obtain porous clay sheets.

[0007] Preferably, the mass ratio of alumina, kaolin, and synthetic carbon powder in the added main ingredients is 3:1:1.

[0008] Preferably, the silica sol contains 30% ± 1% SiO2 by mass, no more than 0.2% Na2O by mass, and has a pH range of 6.5 to 8.0.

[0009] Preferably, the method of drying the fluid slurry at a preset temperature for a certain period of time and then molding it is as follows: The fluid slurry was dried at 48-52℃ for 30 minutes to obtain a semi-solid slurry; The semi-solid slurry is placed into a molding machine and molded.

[0010] Preferably, the method of placing the semi-solid slurry into a molding machine for molding is as follows: The semi-solid slurry is filled into the mold, and the sample is flattened using the mold rod; Place the mold into the tablet press, pressurize it to the preset pressure value and hold the pressure, and repeatedly pressurize it to maintain the design pressure for several minutes; After the pressure holding period is over, the mold is removed, and a circular wet blank is obtained.

[0011] Preferably, the method for obtaining porous clay sheets by high-temperature sintering of the wet blank is as follows: Place the wet billet containing moisture into the heating furnace; Starting from room temperature, the temperature is increased to 100°C over 5 minutes, held for 25 minutes, then increased to 800°C at a rate of 17.5°C / min and held for 60 minutes. The temperature was raised from 800℃ to 1200℃ over 60 minutes and then maintained for 60 minutes. The porous clay sheet was obtained by naturally cooling to room temperature.

[0012] Another objective of this application is to provide a clay sheet for a soil water potential sensor, wherein the clay sheet is used to form the dielectric in a soil water potential measuring capacitor, and the soil water potential measuring capacitor is used to form a soil water potential measuring sensor to measure soil water potential values. The clay sheet is prepared based on the soil water potential sensor clay sheet preparation process described above.

[0013] Preferably, the method for measuring soil water potential using the soil water potential measurement sensor is as follows: The sensor is inserted into the soil to be tested, and the dielectric constant value measured by the sensor is obtained. Obtain the capacitance-moisture relationship curve of the clay sheet, and obtain the moisture value of the clay sheet based on the dielectric constant value; Obtain the characteristic curve corresponding to the soil matrix potential-moisture value. After the clay sheet and the soil reach water potential equilibrium, substitute the moisture value of the clay sheet into the characteristic curve to obtain the soil water potential value.

[0014] Another objective of this application is to provide a method for adjusting the performance of a clay plate in a soil water potential sensor. The method includes: Set a target performance window, wherein the target performance includes one or more of the following performance indicators: saturated moisture content, residual moisture content, clay sheet porosity, sintering density, linear shrinkage, surface roughness, and contact angle. Determine the adjustable control factors and level range, select the particle size A of the skeleton material, the particle size C of the pore-forming agent and the molding pressure M as the main control factors, set up several test combinations within the preset test parameter range, and prepare clay sheet test samples based on the soil water potential sensor clay sheet preparation process of any one of claims 1-6. The performance of the test samples was measured, and the test parameters were corrected according to the following control path: Using molding pressure as the main control factor, when the porosity is low or the saturated water content is lower than the preset target, the molding pressure is reduced to improve pore connectivity and increase the saturated water content; when the linear shrinkage rate is greater than the preset target or the surface roughness is higher than the preset target, the molding pressure is increased to reduce roughness and suppress the linear shrinkage rate; using the particle size of the skeleton material as a synergistic factor, when the saturated water content is low or the absorption time is shorter than the preset index, the particle size of the skeleton material is reduced to improve the specific surface area and the stability of the air inlet channel; using the particle size of the pore-forming agent as a fine factor, when the connectivity is lower than the set target, the particle size of the pore-forming agent is increased. The performance of the test sample was measured again and closed-loop iterative adjustments were made until all indicators fell into the target performance window.

[0015] The embodiment of this application provides a process for preparing a clay sheet for a soil water potential sensor. Its outstanding advantage is that the clay sheet obtained by this process can be used to prepare a water potential sensor. Compared with other dielectric materials or preparation processes, the clay sheet sensor has high measurement accuracy and fast measurement speed, and can significantly reduce the steps and operational difficulty required to measure soil water potential, providing a new direction for the high-precision measurement of soil water potential. Attached Figure Description

[0016] Figure 1 A flowchart illustrating the preparation process of a clay sheet for a soil water potential sensor, provided in an embodiment of this application. Figure 2 This application provides a schematic diagram comparing the porous ceramic material before and after sintering in an embodiment of the present application. Figure 3 This is a schematic diagram illustrating the usage method of a porous ceramic soil water potential sensor provided in an embodiment of this application; Figure 4 This is a graph showing the relationship between the diameter of a microporous clay sheet after firing and its linear shrinkage rate, provided in one embodiment of this application. Figure 5 This is a diagram showing the relationship between the volume and porosity of a microporous ceramic in one embodiment of this application; Figure 6 This is a schematic diagram illustrating the variation of the sintering density of a porous ceramic under the influence of different factors in one embodiment of this application. Figure 7 This is an electron microscope image of the microstructure of a porous ceramic surface under different treatments provided in one embodiment of this application; Figure 8 Grayscale peak images of surface morphology features under different numerical conditions provided in one embodiment of this application; Figure 9 This is a diagram showing the relationship between the contact angle and absorption time of a porous ceramic in one embodiment of this application; Figure 10 This is a schematic diagram of moisture characteristic curves under different treatment conditions provided in one embodiment of this application; Figure 11 This is a schematic diagram illustrating the correlation between different experimental factors, physical properties, and VanGenuchten model parameters, provided in one embodiment of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] It is understood that the terms "first," "second," etc., used in this application may be used herein to describe various elements, but unless otherwise specified, these elements are not limited by these terms. These terms are used only to distinguish the first unit or module from another unit or module. For example, without departing from the scope of this application, the first electrode plate may be referred to as the second electrode plate, and similarly, the second electrode plate may be referred to as the first electrode plate.

[0019] Figure 1 This is a flowchart illustrating the preparation process of a clay sheet for a soil water potential sensor, as provided in an embodiment of this application.

[0020] Those skilled in the art will recognize that soil water potential is a key parameter in agricultural and environmental sciences, crucial for understanding soil-plant-atmosphere interactions, optimizing irrigation strategies, and improving crop productivity. Against the backdrop of increasingly severe global water scarcity and climate change, accurate and real-time monitoring of soil water potential is essential for efficient water resource management. Traditional methods for measuring soil water potential often have limitations in terms of accuracy, durability, and field adaptability.

[0021] In recent years, various sensors based on dielectric principles have become a promising alternative due to their advantages such as continuous monitoring, low maintenance requirements, and compatibility with automated irrigation systems.

[0022] In this embodiment, researchers considered porous ceramics as one of the best materials for use as water potential sensors due to their unique three-dimensional interconnected network structure, tunable pore characteristics, and excellent chemical stability. However, existing research on porous ceramics has largely focused on other products, such as ceramic irrigation devices, while scientific research on porous ceramics specifically for soil water potential sensors is lacking. Therefore, developing high-performance porous ceramic materials specifically suitable for soil water potential sensors has become an important research direction.

[0023] In this application, the researchers conducted extensive experiments to design parameters and optimize processes. The porous ceramic materials produced based on this process can achieve coordination and balance in terms of pore structure, mechanical properties and functional characteristics.

[0024] In one embodiment, a process for preparing a clay sheet for a soil water potential sensor is provided, which may specifically include the following steps: Step S10: Obtain the main ingredients and auxiliary ingredients. The main ingredients include at least alumina, kaolin, and synthetic carbon powder, and the auxiliary ingredients include at least silica sol.

[0025] Step S20: Mix and ball mill the main ingredients to obtain a mixture.

[0026] Step S30: Add silica sol to the mixture and stir for a certain period of time to obtain a uniform fluid slurry; Step S40: Dry the fluid slurry at a preset temperature for a certain period of time, and then press it to obtain a solid wet blank. Step S50: The wet blank is sintered at high temperature to obtain porous clay sheets.

[0027] In this embodiment, the porous ceramic composition mainly includes key components such as a framework material, a binder, and a pore-forming agent. The framework material constitutes the basic structural morphology of the ceramic; the addition of the binder makes the contact between the framework materials tighter, thus significantly improving the mechanical strength of the ceramic; the pore-forming agent, after volatilization or decomposition during sintering, leaves voids that endow the ceramic with a specific pore structure and water absorption properties. It is pressed into shape using a mold under molding pressure and fired with the aid of a sintering aid. Through extensive experimental exploration, preferably, in this embodiment, alumina, silica sol, carbon powder, and kaolin are used as the porous ceramic framework material, binder, pore-forming agent, and sintering aid, respectively. Figure 2 The diagram shows a comparison of a porous ceramic material before and after sintering. Figure a represents the material before sintering, and figure b represents the material after sintering. Purple represents the framework material; blue represents the binder; and yellow represents the pore-forming agent. After sintering, a stable porous ceramic material is finally formed.

[0028] The advantage of the preparation process provided in this application is that the clay sheet obtained by this process can be used to prepare a water potential sensor. Compared with other dielectric materials or preparation processes, the clay sheet sensor has high measurement accuracy and fast measurement speed, and can significantly reduce the steps and operational difficulty required to measure soil water potential, providing a new direction for the high-precision measurement of soil water potential.

[0029] In a preferred embodiment, the mass ratio of alumina, kaolin, and synthetic carbon powder in the added main ingredients is 3:1:1.

[0030] In the embodiments of this application, preferably, alumina (Al2O3, purity: 99.9%), kaolin (Na2O·Al2O3·H2O, particle size: 10μm) and synthetic carbon powder (C) can be accurately weighed and mixed in a mass ratio of 3:1:1.

[0031] In a preferred embodiment, the silica sol contains 30% ± 1% SiO2 by mass, no more than 0.2% Na2O by mass, and has a pH range of 6.5 to 8.0.

[0032] In this embodiment of the application, after ball milling, an appropriate amount of silica sol is added to the mixed powder. The composition of the silica sol can preferably adopt the above-mentioned ratio.

[0033] In a preferred embodiment, the method of drying the fluid slurry at a preset temperature for a certain period of time and then molding it is as follows: The fluid slurry was dried at 48-52℃ for 30 minutes to obtain a semi-solid slurry; The semi-solid slurry is placed into a molding machine and molded.

[0034] In a preferred embodiment, the method for placing the semi-solid slurry into a molding machine and molding it is as follows: The semi-solid slurry is filled into the mold, and the sample is flattened using the mold rod; Place the mold into the tablet press, pressurize it to the preset pressure value and hold the pressure, and repeatedly pressurize it to maintain the design pressure for several minutes; After the pressure holding period is over, the mold is removed, and a circular wet blank is obtained.

[0035] In a preferred embodiment, the method for obtaining porous clay sheets by high-temperature sintering of the wet blank is as follows: Place the wet billet containing moisture into the heating furnace; Starting from room temperature, the temperature is increased to 100°C over 5 minutes, held for 25 minutes, then increased to 800°C at a rate of 17.5°C / min and held for 60 minutes. The temperature was raised from 800℃ to 1200℃ over 60 minutes and then maintained for 60 minutes. The porous clay sheet was obtained by naturally cooling to room temperature.

[0036] In this embodiment, the following compression molding method is used as a specific preparation example: The mold assembly used in this embodiment includes a hollow cylindrical mold sleeve with an inner diameter of 30 mm and a mold base. During assembly, the mold sleeve and mold base are fixed, and a mold piece with a diameter of 30 mm and a 3 mm center pin is placed. The sample is filled into the mold, and a mold rod with an inner diameter of 3 mm and an outer diameter of 30 mm (hollow cylinder) is used to flatten the sample. Subsequently, the mold is placed in a tablet press, the drain valve is tightened, and the pressure handle is cranked to apply pressure to the preset pressure value. During the pressure holding period, pressure is repeatedly applied to maintain the design pressure for 10 minutes. After the pressure holding period, the drain valve is loosened, the mold is removed, and the mold base is removed, with a demolding tool placed underneath. The drain valve is tightened again, and the pressure handle is cranked to remove the sample from the mold. After demolding, a ring-shaped wet blank with a diameter of 30 mm and a 3 mm center hole is obtained.

[0037] In the high-temperature sintering step, the moist green body containing water is placed in a high-temperature muffle furnace, and a two-step sintering method can be used for firing. First, the temperature is raised from room temperature to 100°C over 5 minutes, held for 25 minutes, then raised to 800°C at a rate of 17.5°C / min and held for 60 minutes to complete the first stage of sintering. Subsequently, the temperature is raised to 1200°C over 60 minutes and held for 60 minutes to complete the second stage of sintering. After sintering, the microporous ceramic is allowed to cool naturally to room temperature to obtain the desired sample.

[0038] In one embodiment, a clay sheet for a soil water potential sensor is provided. The clay sheet is used to form the dielectric in a soil water potential measuring capacitor, which is used to form a soil water potential measuring sensor to measure soil water potential values. The clay sheet is prepared based on the preparation process of a soil water potential sensor clay sheet as described above.

[0039] In this embodiment, as Figure 3 As shown, a schematic diagram of the use of a porous ceramic soil water potential sensor is provided. In use, the capacitive sensor is buried in the soil, and the ceramic sheet serves as the dielectric between the two measuring substrates in the capacitive sensor.

[0040] In this embodiment, the soil water potential sensor uses a porous ceramic sheet as the measuring medium, which forms a capacitor with two electrode plates. After the circuit board measures the dielectric constant of the capacitor, the moisture value of the porous ceramic sheet is output after conversion using the capacitance-moisture curve of the ceramic. Since the pore structure of the porous ceramic is similar to that of soil, it is tightly buried in the soil, and water potential equilibrium is achieved with the soil through water vapor exchange. Finally, the moisture value of the ceramic is converted into the soil water potential value using the matrix potential-moisture characteristic curve.

[0041] In a preferred embodiment of this application, the method for measuring soil water potential using the soil water potential measurement sensor is as follows: The sensor is inserted into the soil to be tested, and the dielectric constant value measured by the sensor is obtained. Obtain the capacitance-moisture relationship curve of the clay sheet, and obtain the moisture value of the clay sheet based on the dielectric constant value; Obtain the characteristic curve corresponding to the soil matrix potential-moisture value. After the clay sheet and the soil reach water potential equilibrium, substitute the moisture value of the clay sheet into the characteristic curve to obtain the soil water potential value.

[0042] In this embodiment, the measurement steps in the above measurement method can be executed automatically or semi-automatically by the measurement control system in the sensor, and each step can be automatically executed by multiple program modules.

[0043] In a preferred embodiment of this application, the applicant has also developed a method for evaluating the performance of porous ceramic sheets, the performance of which is comprehensively considered based on the following dimensions: Surface morphology and roughness dimensions. Porous ceramic materials were polished, soaked, dried, and sputter-coated with gold. The microstructure of the porous ceramics was observed using a scanning electron microscope (SEM). Based on the SEM image data, a digital image processing workflow was constructed using the Python platform. Gray-level normalization and noise filtering were performed using the OpenCV library. According to the following formula, the arithmetic mean roughness Sa characterizes the average surface undulation, the root mean square roughness Sq reflects the intensity of surface fluctuations, and the fractal dimension D quantifies the surface complexity. ; ; ; Where Sa is the arithmetic mean roughness, μm; h(x,y) is the surface height function; A is the surface area, μm2; Sq is the root mean square roughness, μm; D is the fractal dimension; ϵ is the reciprocal of the side length; N(ϵ) is the side length required to cover the image, μm.

[0044] Porosity and bulk density dimensions. The porosity and bulk density of porous ceramics were determined using a modified Archimedes method. The specific test procedure is as follows: After ultrasonic cleaning (ethanol medium, 40 kHz, 15 min) to remove surface impurities, the ceramics were placed in a drying oven for vacuum drying (105℃, 10⁻⁻⁶). 1 After drying to constant weight (mass change < 0.1%), weigh the sample. Immerse the sample in deionized water for 48 hours, and weigh the porous ceramic in water after it becomes saturated. Wipe the surface of free water with a moistened non-woven cloth and then measure the mass in air. The porosity and bulk density of the ceramic can be calculated using the following formula: ; ; Where: P is the porosity of the sample, %; ρ is the density of the sample, g / cm3; ms is the mass of the sample in the dry state, g; mf is the buoyant weight of the sample in water after saturation water absorption, g; mw is the mass of the sample in air after saturation water absorption, g.

[0045] The relationship between the diameter and linear shrinkage rate of porous ceramic discs. The diameter of the porous ceramic disc was measured four times using vernier calipers, and the average diameter was taken to obtain the diameter of the sintered porous ceramic disc. This average, combined with the initial wet blank diameter, yielded the radial linear shrinkage rate of the porous ceramic. The formula is shown below.

[0046] ; In the formula: l2 is the diameter of the sintered sample, mm; l1 is the diameter of the sample before sintering, mm; η is the linear shrinkage rate, % Sintering density dimension. Sintering density refers to the actual density of the sintered body divided by the theoretical density of the material. The actual density of the sintered body refers to the density of the material after sintering, which can be determined by measuring the mass and volume of the sintered body. The theoretical density of the material refers to the density of the material in a perfect crystal structure without any pores or defects. The theoretical mass is obtained by adding the mass of completely ablated carbon powder to the actual weight of the sintered ceramic sample. The theoretical volume is obtained by multiplying the height of the wet blank before sintering by the surface area of ​​the mold.

[0047] ; In the formula: ρF is the sintered density of the ceramic, %; ρ1 is the actual density of the ceramic, g / cm3; ρ2 is the theoretical density of the ceramic, g / cm3.

[0048] Surface contact angle and water absorption time dimension. The water absorption rate of porous ceramics in a dry state can be measured using a contact angle meter. In the experiment, 5 μL of deionized water was used as the medium. The water absorption process of the porous ceramics was recorded using a camera, and the video images were processed. The contact angle of the first frame image of deionized water contacting the ceramic surface was analyzed using ImageJ software, and the number of frames from the contact of deionized water with the porous ceramic surface to complete absorption was calculated. Finally, by dividing the number of frames by the frame rate, the time required for the ceramic to absorb 5 μL of deionized water in a dry state was obtained as the water absorption time.

[0049] In a preferred embodiment, the moisture characteristic curve is obtained as follows: During the water absorption process of porous ceramics, the water potential value decreases with increasing humidity; conversely, during dehydration, the water potential value gradually increases with decreasing humidity. A moisture characteristic curve is used to describe this phenomenon, with volumetric water content on the x-axis and water potential on the y-axis. First, microporous ceramic sheet samples were selected and immersed in a water tank for 48 hours to ensure complete saturation. Then, the volumetric water content of the samples was calculated using the gravimetric method, and the samples were placed in a dew point water potential meter at an ambient temperature of 25°C to measure the corresponding water potential value. Ten samples were then placed sequentially on an electronic scale and dried in a 25°C drying oven. Every 30 minutes, a sample was removed, and its corresponding water potential value was measured. By comparing the difference in the values ​​displayed on the electronic scale before and after placing the sample in the drying oven, the volumetric water content of the sample was calculated. After all tests were completed, the obtained data was fitted using VanFit software according to the following model formula to establish the moisture characteristic curve: ; In the formula: θ(φ) is the volumetric water content of the microporous ceramic; φ is the water potential value of the microporous ceramic; It is the residual moisture content of the soil; α represents the saturated water content of the soil; α and n are the fitting parameters.

[0050] The above methods can accurately depict the moisture characteristic curve of porous ceramics during the dehumidification process, providing strong support for in-depth research on its moisture transport characteristics.

[0051] In a preferred embodiment, in order to demonstrate the effectiveness of the manufacturing process provided in this application and its improvement over the prior art, the following method is provided to verify the performance of the material.

[0052] In one embodiment, this application provides a method for obtaining the relationship between material particle size and molding pressure on the physical structure of porous ceramics. Specifically, this includes the relationship between diameter and linear shrinkage, the relationship between porosity and bulk density, and factors affecting sintering density. Relationship between diameter and linear shrinkage rate: Linear shrinkage rate is an indicator characterizing the rate of linear dimensional change of materials during sintering, and it directly affects the quality of porous ceramic products. For example... Figure 4 As shown, the diameter differences of the porous ceramic sheets in all treatments were not significant, all falling within the range of 29-29.6 mm. However, some differences still existed, which were generally due to variations in the linear shrinkage rate of each treatment. Specifically, the linear shrinkage rate was as follows: Group M1 (molding pressure: 10 MPa) exhibited the highest average linear shrinkage rate (2.797%); the average linear shrinkage rate of Group M2 (molding pressure: 15 MPa) decreased to 1.661%, indicating that the linear shrinkage rate of porous ceramics decreased significantly as the molding pressure increased (from 10 MPa to 15 MPa). With further increases in molding pressure (from 15 MPa to 20 MPa), the average linear shrinkage rate of Group M3 (molding pressure: 20 MPa) was 2.217%, showing an increase. Therefore, within the molding range of 10-20 MPa, the average linear shrinkage rate may exhibit a U-shaped trend with increasing molding pressure. This phenomenon indicates that the compaction effect caused by molding pressure dominates the shrinkage behavior. Higher molding pressure leads to an increase in the initial packing density of the green body, limiting particle migration space during sintering. Under greater pressure, particles such as alumina break down, resulting in an increase in linear shrinkage. Furthermore, analysis of variance was performed on the three experimental factors. The results showed that alumina particle size and carbon powder particle size did not show significant differences (p>0.05), indicating that the skeleton particle size and pore-forming particle size do not significantly affect the linear shrinkage. Molding pressure showed a significant difference (p=0.021<0.05), indicating the presence of a main effect; molding pressure significantly affects the linear shrinkage. Although molding pressure has some impact on the linear shrinkage, the diameter of the porous ceramic molding (29-29.6 mm) relative to the design diameter (30 mm) is within 3%, which meets industrial production standards.

[0053] The relationship between porosity and bulk density: The porosity of porous ceramics directly affects their saturated water content and flexural strength. Excessively high porosity may reduce the flexural strength of the ceramic material, making it prone to fracture. Conversely, excessively low porosity may reduce the connectivity between pores, affecting the material's hydraulic properties. Figure 5 The variation patterns of porosity and bulk density of porous ceramics under different treatments are shown. When alumina particle size (A) is used as the grouping variable, the following characteristics were observed: Group A1: average porosity 37.10%, corresponding to a bulk density of 1.86 g / cm³. 3Group A2: Average porosity 40.75% (highest value), bulk density 1.90 g / cm³ 3 Group A3: Average porosity 36.09%, bulk density 1.95 g / cm³ 3 Within each group, the porosity was ranked according to the molding pressure. The highest porosity was observed at 15 MPa (M2), and the lowest at 20 MPa (M3). Among the nine different treatments, the highest porosity was observed at an alumina particle size of 75 μm and a molding pressure of 15 MPa. Furthermore, analysis of variance was performed on the three experimental factors. The results showed that both alumina particle size and molding pressure were significant (p < 0.05), indicating the presence of a main effect; both the framework particle size and molding pressure significantly affected the porosity. The carbon powder particle size did not show a significant effect (p > 0.05), indicating that the pore-forming particle size did not significantly affect the porosity. This is because the framework particles and pore-forming agent particles formed a multi-level particle size distribution, with the diameter of the pore-forming agent particles being smaller than the pore diameter formed by the accumulation of framework particles. The pore-forming agent particles were insufficient to expand the pores formed by the accumulation of framework particles. The lower the molding pressure, the looser the contact and bonding between particles, resulting in higher porosity and lower bulk density.

[0054] Sintering density, as a key parameter for measuring sintering quality, reflects the number of pores in the sintered body. Generally, the higher the sintering density, the fewer pores in the sintered body, and the better the material's strength, hardness, and other properties. Figure 6 This section compares the sintering density and bulk density of porous ceramics under different treatment conditions. The results are grouped based on the alumina particle size (A), a key experimental factor. Figure 6It can be seen that the average sintering densities of porous ceramics with alumina particle sizes of 50μm, 100μm, and 75μm are 87.35%, 87.07%, and 84.59%, respectively, showing a non-linear relationship between sintering density and alumina particle size. Within each group, the sintering density also exhibits a regular non-linear relationship with the molding pressure (M), with the lowest sintering density at 15MPa (M2) and the highest at 10MPa (M1). In addition, variance analysis was performed on the three experimental factors. The results showed that alumina particle size, carbon powder particle size, and molding pressure all had a significant impact on the sintering density (p<0.05). Among them, alumina particle size and molding pressure had a more significant impact (p<0.01). The average sintering density of porous ceramics showed a "U-shaped" trend (i.e., first decreasing and then increasing) with increasing alumina particle size and molding pressure. This may be because small-sized alumina particles (50μm) have a large specific surface area, high surface energy, and strong sintering driving force, and can form a dense initial packing even under low pressure (10MPa). High pressure (20MPa) forces large particles (100μm) to form a higher green body density, but large particles have lower sintering activity and insufficient densification efficiency. Medium-sized particles (75μm) under medium pressure (15MPa) cannot form a high contact point density like small particles, nor can they be fully densified by high pressure like large particles, resulting in uneven packing and the lowest sintering density.

[0055] In one embodiment, such as Figure 7 As shown, scanning electron microscope (SEM) images of porous ceramic surfaces under different treatment conditions are presented. The red box indicates the surface microstructure of the porous ceramic when the molding pressure is at its maximum. Figure 7 It can be seen that as the molding pressure gradually increases, larger alumina particles and carbon powder particles are more prone to breakage. Under scanning electron microscopy, the roughness of the porous ceramic surface is significantly reduced, the granular texture is weakened, and the surface becomes increasingly flat.

[0056] In one embodiment, such as Figure 8 As shown, a grayscale peak image of surface morphology characteristics obtained by scanning electron microscopy is presented. The arithmetic mean roughness, root mean square roughness, and fractal dimension are calculated from the grayscale image, which can quantify the roughness of the surface morphology. Figure 8 It can be seen that when the molding pressure, alumina particle size, or carbon powder particle size are at their maximum (A3C1M3, A1C3M3), the porous ceramic surface exhibits the lowest arithmetic mean roughness and root mean square roughness, and the highest fractal dimension, resulting in the smoothest surface. Conversely, when the molding pressure, alumina particle size, and carbon powder particle size are relatively small (A1C2M2), the porous ceramic surface shows higher arithmetic mean roughness and root mean square roughness, exhibiting a pitted morphology with obvious porosity. In conclusion, under high molding pressure (20MPa), the surface roughness of ceramics is significantly reduced.

[0057] In a preferred embodiment, this application investigated the relationship between the contact angle of the ceramic sheet and the absorption time. The contact angle is the angle formed when a liquid comes into contact with a solid surface, and it has a significant impact on the water absorption rate of microporous ceramics. A larger contact angle indicates poorer wettability between the liquid and the solid surface, which reduces the rate at which the liquid enters the micropores, thus leading to a lower water absorption rate. Figure 9 The contact angle and absorption time of porous ceramics were determined. Grouping was based on alumina particle size, a key experimental factor. Figure 9 It was found that when the alumina particle size was 100 μm, the porous ceramic had the shortest average water absorption time and the smallest contact angle. Furthermore, an analysis of variance was performed on the three experimental factors. The results showed that both alumina particle size and carbon powder particle size were significant (p < 0.05), indicating the existence of a main effect; both alumina particle size and carbon powder particle size significantly affected the absorption time. The molding pressure did not show a significant effect (p > 0.05), indicating that molding pressure did not significantly affect the absorption time. At an alumina particle size of 100 μm, a carbon powder particle size of 25 μm, and a molding pressure of 15 MPa, the microporous ceramic had the smallest contact angle and the shortest water absorption time. The pore structure of porous ceramics has a significant impact on its water absorption rate; the richer the pore structure and the better the connectivity, the faster the water absorption rate of the porous ceramic. Simultaneously, the uniformity of pore distribution also affects the stability of the water absorption performance. The pore size also significantly affects the water absorption rate of porous ceramics. Generally, the larger the pore size, the easier it is for water molecules to enter the pores, thus accelerating the water absorption rate. However, excessively large pore sizes may shorten the residence time of water molecules in the pores, affecting the increase in water absorption. The surface energy of the material also has a significant impact on the contact angle; a higher contact angle means higher surface energy, which affects the adsorption and spreading of liquids on the surface of microporous ceramics. In summary, the water absorption rate of porous ceramics in water potential sensors is influenced by a combination of factors, including contact angle, surface energy, pore size, and porosity.

[0058] In one embodiment, such as Figure 10 As shown, a schematic diagram of a moisture characteristic curve under different treatment conditions is presented. The green curve represents the dehumidification process, and the red curve represents the moisture absorption process. Based on the Van Genuchten model parameterization theory, the mechanism by which each parameter regulates the curve shape can be described as: residual moisture content (θ) r The lower boundary of the control curve shows that during the dehumidification process, the group with a toner particle size of 6 μm had the highest average residual moisture content, while the lowest residual moisture content was found in group A3C2M1, followed by group A2C3M1. During the moisture absorption process, group A1C3M3 had the lowest residual moisture content, followed by group A2C3M1. The saturated moisture content (θ) sThe upper limit of the control curve was determined. During the dehumidification process, the saturated moisture content of group A2C1M2 was the highest, followed by A1C2M2. During the moisture absorption process, the saturated moisture content of group A1C1M1 was the highest, followed by A1C2M2. The air intake value (α) affects the inflection point characteristics of the curve. A smaller air intake value will cause the curve to form a gentle transition zone from high negative pressure to low negative pressure. Combining the fitted function curve and parameter table, group A3C1M3 is more consistent with the air intake value of the porous ceramic used in the sensor. The n value controls the slope of the medium suction range. When n is relatively large, the curve is gentler, and when n is relatively small, the curve is steeper. To ensure the measurement range and accuracy of the soil water potential sensor, this study determined that the suitable treatment for the soil water potential sensor was A1C2M2, based on the evaluation principles of "high saturated moisture content, small curve n value, and low residual moisture content".

[0059] The table below shows the Van Genuchten model parameters for porous ceramics under different treatments, combined with... Figure 10 The moisture characteristic curves and model parameters in the table below show that the curve for group A2C3M1 has the steepest slope, and its n value is significantly lower than that of other groups. In a preferred embodiment, such as Figure 11 As shown, a schematic diagram illustrating the correlation between different experimental factors, physical properties, and VanGenuchten model parameters is presented.

[0060] Figure 11 Correlation analysis in (a) shows that sintering density is significantly positively correlated with linear shrinkage (p<0.001), because both sintering density and linear shrinkage are related to the diameter of porous ceramics before and after sintering; sintering density is significantly negatively correlated with porosity (p<0.05), and studies have found that increased porosity reduces ceramic density, thereby reducing sintering density; Saturated moisture content was significantly negatively correlated with alumina particle size (p<0.05) and significantly positively correlated with porosity (p<0.05). Increased porosity would cause porous ceramics to absorb more moisture in a saturated state, thus increasing the saturated moisture content. Residual moisture content and n were significantly negatively correlated with carbon powder particle size (p<0.05). Smaller carbon powder particles leave smaller pores after ablation, which can improve the ability of porous ceramics to retain moisture during drying and increase the residual moisture content of porous ceramics. The air intake value (α) was significantly positively correlated with residual moisture content (p<0.05), and n was significantly positively correlated with θr (p<0.001).

[0061] Furthermore, we established a path model for the regulation of Van Genuchten model parameters by skeleton particle size, pore-forming particle size, and molding pressure. Figure 11(b) Since the apparent variables linear shrinkage (LS) and sintering density (SD) are closely related to the diameter of porous ceramics before and after sintering, the latent variable SL is introduced as a comprehensive correspondence and abstract representation of the two. It was found that porosity is significantly negatively controlled by molding pressure and SL, which in turn directly positively controls θr. When controlling residual moisture content, the direct effect of porosity on saturated moisture content is 0.8463, with no indirect effect. The residual moisture content can be controlled by changing molding pressure (Pressure→Porosity, Total=-0.2618) and SL (SL→Porosity, Total=-0.8978). The direct effect of carbon powder particle size on n is 0.3209, and increasing the carbon powder particle size will lead to an increase in n. The structural equation model shows that there are mutual influences among the parameters of the Van Genuchten model. Saturated moisture content has a significant positive effect on n (saturated moisture content→n, Total=1.1924), and residual moisture content has a significant positive effect on n (θr→n, Total=-0.3619). Controlling the residual moisture content to increase will lead to a decrease in n.

[0062] In a preferred embodiment, based on the above research, this application also provides a method for adjusting the performance of a clay plate for a soil water potential sensor. The method includes: Set a target performance window, wherein the target performance includes one or more of the following performance indicators: saturated moisture content, residual moisture content, clay sheet porosity, sintering density, linear shrinkage, surface roughness, and contact angle. Determine the adjustable control factors and level range, select the particle size A of the skeleton material, the particle size C of the pore-forming agent and the molding pressure M as the main control factors, set up several test combinations within the preset test parameter range, and prepare clay sheet test samples based on the soil water potential sensor clay sheet preparation process of any one of claims 1-6. The performance of the test samples was measured, and the test parameters were corrected according to the following control path: Using molding pressure as the main control factor, when the porosity is low or the saturated water content is lower than the preset target, the molding pressure is reduced to improve pore connectivity and increase the saturated water content; when the linear shrinkage rate is greater than the preset target or the surface roughness is higher than the preset target, the molding pressure is increased to reduce roughness and suppress the linear shrinkage rate; using the particle size of the skeleton material as a synergistic factor, when the saturated water content is low or the absorption time is shorter than the preset index, the particle size of the skeleton material is reduced to improve the specific surface area and the stability of the air inlet channel; using the particle size of the pore-forming agent as a fine factor, when the connectivity is lower than the set target, the particle size of the pore-forming agent is increased. The performance of the test sample was measured again and closed-loop iterative adjustments were made until all indicators fell into the target performance window.

[0063] In this embodiment, the above adjustment process can be derived based on the above research method, and the specific process will not be described in detail here.

[0064] Those skilled in the art will understand that Figure 1 The flowchart shown is only a partial diagram of the structure related to the present application and does not constitute a limitation on the present application.

[0065] In one embodiment, the method for preparing porous clay sheets for soil water potential measurement provided in this application can be implemented as an automated preparation method or process.

[0066] It should be understood that although the steps in the flowcharts of the various embodiments of this application are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in each embodiment may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least a portion of the sub-steps or stages of other steps.

[0067] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Furthermore, any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory.

[0068] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A process for preparing a clay sheet for a soil water potential sensor, characterized in that, The preparation process includes the following steps: Obtain the main ingredients and auxiliary ingredients, wherein the main ingredients include at least alumina, kaolin, and synthetic carbon powder, and the auxiliary ingredients include at least silica sol; The main ingredients are mixed and ball-milled to obtain a mixture; Add silica sol to the mixture and stir for a certain period of time to obtain a uniform fluid slurry; The fluid slurry is dried at a preset temperature for a certain period of time and then molded to obtain a solid wet blank. The wet blank is sintered at high temperature to obtain porous clay sheets.

2. The preparation process of the clay sheet for a soil water potential sensor according to claim 1, characterized in that, The mass ratio of alumina, kaolin, and synthetic carbon powder in the added main ingredients is 3:1:

1.

3. The preparation process of the clay sheet for a soil water potential sensor according to claim 1, characterized in that, The silica sol contains 30% ± 1% SiO2 by mass, no more than 0.2% Na2O by mass, and has a pH range of 6.5 to 8.

0.

4. The preparation process of the clay sheet for a soil water potential sensor according to claim 1, characterized in that, The method of drying the fluid slurry at a preset temperature for a certain period of time and then molding it is as follows: The fluid slurry was dried at 48-52℃ for 30 minutes to obtain a semi-solid slurry; The semi-solid slurry is placed into a molding machine and molded.

5. The preparation process of the clay sheet for a soil water potential sensor according to claim 4, characterized in that, The method for molding semi-solid slurry by placing it into a molding machine is as follows: The semi-solid slurry is filled into the mold, and the sample is flattened using the mold rod; Place the mold into the tablet press, pressurize it to the preset pressure value and hold the pressure, and repeatedly pressurize it to maintain the design pressure for several minutes; After the pressure holding period is over, the mold is removed, and a circular wet blank is obtained.

6. The preparation process of the clay sheet for a soil water potential sensor according to claim 1, characterized in that, The method for obtaining porous clay sheets by high-temperature sintering of the wet blank is as follows: Place the wet billet containing moisture into the heating furnace; Starting from room temperature, the temperature is increased to 100°C over 5 minutes, held for 25 minutes, then increased to 800°C at a rate of 17.5°C / min and held for 60 minutes. The temperature was raised from 800℃ to 1200℃ over 60 minutes and then maintained for 60 minutes. The porous clay sheet was obtained by naturally cooling to room temperature.

7. A clay sheet for a soil water potential sensor, characterized in that, The clay sheet is used to form the dielectric in the soil water potential measuring capacitor, and the soil water potential measuring capacitor is used to form a soil water potential measuring sensor to measure the soil water potential value. The clay sheet is prepared based on the preparation process of a clay sheet for a soil water potential sensor as described in any one of claims 1-6.

8. A clay sheet for a soil water potential sensor according to claim 7, characterized in that, The method for measuring soil water potential using a soil water potential measurement sensor is as follows: The sensor is inserted into the soil to be tested, and the dielectric constant value measured by the sensor is obtained. Obtain the capacitance-moisture relationship curve of the clay sheet, and obtain the moisture value of the clay sheet based on the dielectric constant value; Obtain the characteristic curve corresponding to the soil matrix potential-moisture value. After the clay sheet and the soil reach water potential equilibrium, substitute the moisture value of the clay sheet into the characteristic curve to obtain the soil water potential value.

9. A method for controlling a clay plate of a soil water potential sensor, characterized in that, The control method is used to adjust the properties of the clay sheet, and the control method includes: Set a target performance window, wherein the target performance includes one or more of the following performance indicators: saturated moisture content, residual moisture content, clay sheet porosity, sintering density, linear shrinkage, surface roughness, and contact angle. Determine the adjustable control factors and level range, select the particle size A of the skeleton material, the particle size C of the pore-forming agent and the molding pressure M as the main control factors, set up several test combinations within the preset test parameter range, and prepare clay sheet test samples based on the soil water potential sensor clay sheet preparation process of any one of claims 1-6. The performance of the test samples was measured, and the test parameters were corrected according to the following control path: Using molding pressure as the main control factor, when the porosity is low or the saturated water content is lower than the preset target, the molding pressure is reduced to improve pore connectivity and increase the saturated water content; when the linear shrinkage rate is greater than the preset target or the surface roughness is higher than the preset target, the molding pressure is increased to reduce roughness and suppress the linear shrinkage rate; using the particle size of the skeleton material as a synergistic factor, when the saturated water content is low or the absorption time is shorter than the preset index, the particle size of the skeleton material is reduced to improve the specific surface area and the stability of the air inlet channel; using the particle size of the pore-forming agent as a fine factor, when the connectivity is lower than the set target, the particle size of the pore-forming agent is increased. The performance of the test sample was measured again and closed-loop iterative adjustments were made until all indicators fell into the target performance window.

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