Method for characterizing heat accumulation characteristics of metal powder wet mud

Abstract

The application discloses a metal powder wet mud heat accumulation characteristic representation method, and belongs to the technical field of dust explosion safety evaluation.The representation method comprises the following steps: S1: obtaining metal powder wet mud, containing the metal powder wet mud in a column shape in a loading basket, and obtaining the surface area S and the volume V of the metal powder wet mud; S2: placing the loading basket in a closed heating container, obtaining the volume, heating the inside of the heating container by adopting constant power, and obtaining the temperature T of the sample and the environmental pressure p of the heating container in real time; S3: when the temperature no longer rises, if the temperature of the sample appears a temperature peak value, the next step is performed; S4: changing the mass of the sample, and obtaining multiple groups of data; and S5: processing the obtained data to obtain the reaction heat release critical temperature T i and the apparent activation energy E of the sample.The representation method simulates working conditions, is closer to actual conditions, and thus can obtain accurate representation results; and has the advantages of low cost, simple operation, easy popularization, short test period and safety.

Description

Technical Field

[0001] This invention belongs to the field of dust explosion safety assessment technology, specifically relating to a method for characterizing the thermal properties of wet mud in metal powders that is accurate in characterization results, low in characterization cost, easy to operate and promote, has a short testing cycle, and is safe to operate. Background Technology

[0002] In industrial practice, metal dust is typically collected using wet dust removal. The collected dust is soaked in flowing water, where the cooling effect of the water prevents heat buildup. After prolonged immersion in the water, the internal moisture distribution of the metal dust tends to become uniform, resulting in a wet mud state upon removal. This means that water and powder are thoroughly and evenly mixed. During the drying and recycling process, poor ventilation can lead to heat buildup and spontaneous combustion of the metal dust. Therefore, it is necessary to study the heat accumulation characteristics of the wet metal mud to assess its hazards.

[0003] The method for testing the spontaneous ignition behavior of dust accumulations in standard EN 15188, concerning the determination of the spontaneous ignition critical temperature of dust accumulations, is extremely time-consuming. Furthermore, for hydrogen-producing wet metal dust sludge, the ventilation conditions and electrically heated environment pose experimental risks of hydrogen explosion. Apparent activation energy is a key kinetic parameter characterizing the ease of dust thermal decomposition reactions, and is crucial for assessing dust explosion susceptibility, selecting explosion suppressants, and conducting numerical simulations of explosion hazards. Currently, the determination of apparent activation energy mainly relies on thermal analysis instruments such as thermogravimetric analyzers (TGA) or differential scanning calorimeters (DSC). These methods typically use only milligram-level samples, and the samples are in a thin, spread-out state, failing to reflect the true heat and mass transfer conditions under dust accumulation conditions in industrial settings. In addition, thermal analysis instruments are expensive, making them difficult to promote in grassroots safety inspection agencies or rapid on-site assessments, and the data processing complexity is high.

[0004] Therefore, there is an urgent need for a test and analysis method that can reflect the actual working conditions of wet metal dust and sludge, is easy to operate, and has a low cost. Summary of the Invention

[0005] The purpose of this invention is to provide a method for characterizing the heat accumulation properties of wet mud made from metal powder.

[0006] The technical solution of this invention is based on the problems of existing detection results deviating from the actual situation, high detection costs, complex operation, and difficulty in promotion.

[0007] The specific technical solution is explained below:

[0008] A method for characterizing the heat accumulation properties of wet mud made of metal powder includes the following steps:

[0009] S1: Obtain wet metal powder mud, wherein the wet metal powder mud is contained in a columnar shape in a loading basket with pores, and obtain the surface area S and volume V of the accumulated wet metal powder mud;

[0010] S2: Place the loading basket containing the above-mentioned wet mud of metal powder into a sealed heating container, obtain the volume of the heating container, and heat the inside of the heating container with constant power. During heating, the temperature T of the sample and the ambient pressure p and ambient temperature inside the heating container are obtained in real time.

[0011] S3: When the ambient temperature inside the heating container no longer rises, determine whether the temperature of the sample reaches a temperature peak. If yes, proceed to the next step; otherwise, end the characterization process.

[0012] S4: Change the mass of the sample while keeping other conditions unchanged, and repeat steps S1 to S3 to obtain multiple sets of data;

[0013] S5: Obtain the temperature rise curves of samples with different masses over time, process the obtained data, and obtain the critical exothermic reaction temperature T of the sample. i And the apparent activation energy E.

[0014] In the above technical solution, constant power heating is used to ensure that the sample obtains a basically constant heating rate, so that the heating process of the sample is always in a quasi-static physical heating process. Here, the quasi-static process of sample temperature and container internal ambient temperature means that in the process of the system changing from one equilibrium state to another, each intermediate state it experiences is infinitely close to the equilibrium state. This indicates that the temperature inside the sample tends to be uniform, which meets the requirements of the Semenov model and lays the foundation for using the Semenov thermal explosion model and subsequent processing.

[0015] When the wet metal sludge begins to undergo exothermic reactions such as oxidation / hydrolysis, the system no longer relies solely on external heating to raise its temperature, but instead incorporates its own exothermic reaction. The curve that should have been heating at a uniform rate will show a sudden increase in the heating rate and the formation of a significant temperature peak.

[0016] In a quasi-static context, such temperature abrupt changes almost exclusively correspond to chemical exothermic reactions and are not masked by complex heating fluctuations. Therefore, temperature abrupt changes in chemical processes that deviate from physical heating processes can be clearly and accurately recorded.

[0017] The heating container dissipates heat to the external environment. As the container temperature rises, the amount of heat dissipated to the external environment increases. When the heating power and the heat dissipation power are equal, the container temperature no longer rises, and a constant temperature environment can be obtained.

[0018] In a further embodiment, S0 is also included: placing an empty loading basket without any samples in the heating container, heating the heating container with the same constant power as in S2, and recording the ambient temperature T in real time during heating. env ;

[0019] The timing sequence of S0 is before S5 and is not restricted by S1~S4.

[0020] The above technical solution can obtain the equivalent ambient temperature when the sample temperature changes abruptly, so as to closely approximate the temperature difference under real conditions and avoid the influence of the reaction heat of wet mud itself.

[0021] In a further embodiment, S5 includes the following data processing method:

[0022] The highest point temperature T of the sample temperature rise curve over time was obtained. max and the corresponding ambient temperature T for the same heating time env ;

[0023] With 1 / T max The x-axis is... Using the vertical axis as the ordinate, experimental data from multiple sets of samples with different masses are represented on the coordinate system. These experimental data are linearly fitted, and the apparent activation energy E is calculated based on the slope of the fitted line.

[0024] In the expression for the ordinate above, p max The temperature T of the sample reaches its highest point, Tmax. max The pressure inside the heating container at that time; p0 refers to the initial ambient pressure inside the heating container before the characterization begins.

[0025] In a further implementation, in S5, the fitting formula for the experimental data is:

[0026] ;

[0027] in, ;

[0028] The fitting formula was derived from the Semenov thermal explosion model through a process of adjustment. The adjustment steps are as follows:

[0029] According to the Semenov thermal explosion model, we can obtain:

[0030] ;

[0031] In the above formula, ρ is the sample density, and c p Here, H is the specific heat capacity at constant pressure of the sample, A is the heat of reaction, E is the pre-exponential factor, R is the apparent activation energy, S is the gas constant, S is the sample surface area, and V is the sample volume. c The heat dissipation coefficient;

[0032] At the point where the sample temperature is highest, the system reaches thermal equilibrium, and the rate of change of the reaction temperature is 0. At this point, ∂T / ∂t = 0, and the above equation satisfies the following energy balance relationship:

[0033] ;

[0034] In the above formula, h c 0 This is the initial heat dissipation coefficient;

[0035] Taking the logarithm of the expression and rearranging it, we obtain the fitted expression.

[0036] The above technical solution innovatively applies the Semenov thermal explosion model to the point of highest reaction temperature T. max At this instantaneous quasi-steady state, the rate of heat release from the chemical reaction is exactly equal to the rate of heat dissipation from the system (∂T / ∂t=0). Establishing a heat balance equation at this specific point transforms the complex dynamic process into a solvable static equation, providing a clever entry point for theoretical applications.

[0037] Secondly, traditional kinetic analysis typically obtains multiple sets of data to fit the activation energy by changing the heating rate. The above-mentioned technique obtains fitting data by changing the sample mass (rather than the heating program), keeping the heating power constant, and conducting multiple control experiments. Different S / V ratios result in different heat dissipation capacities, thus causing the sample to reach thermal equilibrium at different temperatures than the ambient temperature under the same heating power. This generates a set of data points that can be used for linear fitting. This method avoids complex temperature program control and simplifies experimental operations.

[0038] Furthermore, based on the understanding that "as environmental pressure increases, gas density increases, and the heat dissipation coefficient increases, which is directly proportional to the square of the pressure increase," the above technical solution includes (p) in the fitting formula. max / p0) 2 This correction incorporates the dynamic effect of the reaction itself causing pressure increases into the heat dissipation model, making the Semenov model-based fit closer to the actual pressure changes inside the sealed container, thus improving the accuracy of the apparent activation energy E calculation.

[0039] In a further embodiment, S5 includes the following data processing method:

[0040] By taking the point with the steepest slope of the temperature-time curve of a sample of a certain mass as a function of time as a tangent, and performing linear fitting on the heating temperature curve of the sample before the reaction begins to obtain an extension line, the sample temperature corresponding to the intersection of the tangent line and the extension line is the exothermic critical temperature T of the reaction for that mass of sample. i .

[0041] In the above technical solution, the point with the steepest slope of the temperature rise curve marks the moment when the heat release rate of the sample's own reaction reaches its maximum; the tangent at this point represents the rapid temperature rise trend under the dominance of the sample's own reaction; the extended line of the heating temperature curve before the reaction represents the theoretical temperature rise path when there is only external heating and no self-reaction.

[0042] This reaction is exothermic, with a critical temperature T. i The acquisition method can accurately separate the heat source, identify the real self-reaction starting point, and has the advantages of being intuitive and highly repeatable.

[0043] In a further embodiment, the constant power setting results in an ambient temperature rise rate of 2~3℃ / min.

[0044] In the above technical solution, in order to reflect the characteristics of the chemical reaction of the wet metal mud itself to the greatest extent, rather than the effect of external heating, the heating power cannot be too low or too high.

[0045] The heating power cannot be too low, otherwise the metal powder wet mud will not be able to produce a self-exothermic phenomenon.

[0046] The heating power should not be too high; it needs to reach the heating power required to establish a quasi-static process. At the same time, it needs to closely resemble the real situation of slow temperature change. Otherwise, the starting point of the reaction of the wet mud itself will be masked by the external heating effect, making it impossible to accurately identify and separate the critical exothermic temperature T at the beginning of the reaction of the sample itself. i In a preferred embodiment, the difference between the sample temperature and the ambient temperature is controlled within 5°C before the sample temperature changes abruptly.

[0047] In a further embodiment, the loading basket is provided with a loading cover, which is made of the same material as the other parts of the loading basket; the loading cover has a thickness and pore shape that are adapted to the other parts of the loading basket.

[0048] In the above technical solution, by setting up loading baskets of the same material and structure, heat dissipation conditions can be unified, laying the foundation for using the Semenov thermal explosion model.

[0049] In a further embodiment, in S2: the temperature T1 at the center of the sample and the temperature T2 at the edge of the sample are obtained respectively, and it is determined whether the difference between T1 and T2 is within 5°C;

[0050] If yes, proceed to the next step; if no, end the representation process.

[0051] In a further embodiment, in S1, the metal powder wet mud is obtained by mixing water from the ice-water mixture with the metal powder and placing it in the loading basket;

[0052] Once the sample temperature reaches room temperature, proceed to step S2 and start timing.

[0053] The reason for using an ice-water mixture in the above technical solution is:

[0054] ① The low temperature of the ice-water mixture can inhibit the initial reaction between the sample and water, making it safer;

[0055] ② To prevent the wet mud from drying out and clumping after the sample reacts with water, and to obtain a mud-like state that closely resembles reality, where water and powder are fully and evenly mixed.

[0056] ③ By utilizing the properties of ice-water mixtures, wet mud materials with the same initial state (0℃) can be obtained, so that the starting standard of each data point is the same when changing other parameters and can be used for fitting. Therefore, the data is more reliable and has strong repeatability.

[0057] In a further embodiment, the mass of the sample is 5 to 15 grams.

[0058] The above technical solution can construct a stacked sample that matches the actual situation, fill the testing gap between milligram-level thermal analysis and actual working conditions, and make the test results more in line with the actual situation, thus more accurate and practical.

[0059] In summary, the technical solution described in this invention has the following main beneficial effects:

[0060] Compared with existing technologies, the characterization method described in this invention has the advantages of low cost, short testing cycle, and simple process, and is easy to promote.

[0061] Furthermore, the technical solution of the present invention can simulate working conditions and measure the accumulated samples, which is closer to reality and therefore the characterization results are more accurate.

[0062] Further or more detailed beneficial effects will be described in conjunction with specific embodiments in the detailed implementation. Attached Figure Description

[0063] Figure 1 This is a graph showing the changes in sample edge and center temperature, environmental pressure, and blank control environmental temperature over time in Example 1 of the specific implementation method.

[0064] Figure 2 This is a schematic diagram illustrating the acquisition of the critical temperature for the exothermic reaction in Example 1 above;

[0065] Figure 3 This describes the change of sample center temperature over time under different sample masses in a specific implementation method.

[0066] Figure 4This describes the change of the sample center temperature over time under different heating powers in a specific implementation method.

[0067] Figure 5 This is a schematic diagram showing the linear fitting calculation of activation energy for three experimental points obtained from 5g, 10g, and 15g samples, and three experimental points obtained from heating powers of 153w, 178w, and 203w. Detailed Implementation

[0068] The present invention will be further explained in conjunction with the embodiments:

[0069] The core technical problem faced by the technical solutions of this application's embodiments stems from the inventor's accurate understanding of the prior art. Therefore, how to save the testing costs of metal dust fire and explosion safety assessment and obtain relatively accurate characterization results is a technical problem that the inventor urgently needs to solve.

[0070] It should be noted that the embodiments do not constitute a limitation on the scope of protection of the claims of this invention. All technical solutions that can be reasonably expected by those skilled in the art based on the technical concepts provided / proved by the embodiments should be covered within the scope of protection of the claims of this invention.

[0071] The characterization methods involved in the implementation are as follows:

[0072] A method for measuring the heat accumulation characteristics of wet mud containing metal powder, characterized by comprising the following steps:

[0073] Step 1: Sample loading. Under an inert atmosphere, place a porous loading basket containing 5-15g of metal dust in a beaker. The beaker is placed in an ice-water mixture. A certain amount of water is added to the metal dust and stirred until thoroughly mixed to form a wet mud state. After preparation, cover the top of the loading basket with a loading cap of the same material and pore shape as the basket. This ensures the sample is cylindrical or cuboid in shape, with consistent heat dissipation from all sides. Measure its loading surface area S and volume V. The loading basket used in this embodiment is cylindrical with a defined bottom diameter. The loading height is measured using vernier calipers. The basket has a regular shape, allowing for the calculation of surface area and volume using vernier calipers.

[0074] Step Two: Experimental Measurement. Prepare a sealed heating container equipped with a constant-power heating device that provides adjustable, constant electric heating power to the air inside the container through its walls. The air temperature distribution inside the container should not exceed ±2℃. Place the first thermocouple at the center of the sample to measure the center temperature T1. Place the second thermocouple at the edge of the sample to measure the edge temperature T2. Place the third thermocouple near the wall to measure the ambient temperature T. a Set a pressure gauge to record the ambient pressure;

[0075] Step 3: Condition Judgment. Using constant power heating, the heating container dissipates heat to the environment. As the container temperature rises, the amount of heat dissipated to the environment increases. When the heating power and heat dissipation power are equal, the container temperature no longer rises. Before the ambient temperature stops rising, observe whether a sample temperature peak occurs. exist Before the sample temperature changed abruptly, Sample temperature Is the temperature difference between the ambient temperature and the blank environment controlled within 5℃? If so, proceed to the next step. If no temperature peak appears, increase the constant heating power until a temperature peak appears. If no temperature peak can be observed after the ambient temperature exceeds 100℃, end the experiment and determine that the sample will not experience heat accumulation. When the ambient temperature fluctuates by no more than 2℃ within 1 hour, end the experiment.

[0076] Step 4: Control Experiment. According to Semenov theory, sample volume and heat dissipation area both affect heat dissipation, thus affecting experimental results. When using the same loading basket, sample volume and heat dissipation area are related to sample mass. Therefore, the sample mass can be changed, and steps one and two can be repeated to conduct a control experiment and obtain multiple sets of experimental data.

[0077] Step 5: Blank Control Experiment. During the experiment with the sample, the convection caused by the exothermic reaction of the sample will lead to a brief rise in the ambient temperature inside the container. This ambient temperature does not represent the true ambient temperature at which the sample dissipates heat. Therefore, a blank control experiment is set up without adding the sample. The same constant heating power is maintained, and the blank ambient temperature data is recorded as the equivalent ambient temperature for the experiment.

[0078] The method for analyzing the exothermic critical temperature of the wet mud deposit reaction of this metal powder is as follows:

[0079] The temperature at the center of the sample, corresponding to the intersection of the tangent line drawn from the point with the steepest slope of the sample center temperature rise curve and the extension of the linearly fitted curve of the pure heating temperature curve before the reaction begins, is the critical temperature T for the exothermic reaction. i .

[0080] The method for calculating the apparent activation energy of the wet mud accumulation analysis of the metal powder is as follows:

[0081] According to the Semenov thermal explosion model, when metal dust and wet mud are uniformly mixed, their Biwoe number is relatively small, therefore:

[0082] ;

[0083] Where ρ is the sample density (kg / m³) 3 ), c p H is the specific heat capacity at constant pressure of the sample (J / (kg·K)), and H is the heat of reaction (J / m³). 3A is the pre-exponential factor (1 / s), E is the apparent activation energy (J / mol), R is the gas constant (J / (mol·K)), and V is the sample volume (m³). 3 ), h c The heat dissipation coefficient (W / (m)) 2 As environmental pressure increases, gas density increases, and the heat dissipation coefficient increases, which is directly proportional to the square of the pressure increase. S is the sample surface area (m²). 2 ).

[0084] At the highest point of the reaction temperature, the system reaches thermal equilibrium. The heat dissipation from the metal dust wet sludge via convection and the heat generated by the chemical reaction reach equilibrium, and the rate of change of the reaction temperature is 0. At this point, ∂T / ∂t = 0, satisfying the following energy balance relationship:

[0085] ;

[0086] In the above formula, h c 0 This is the initial heat dissipation coefficient;

[0087] Taking the logarithm of the above equation and simplifying it, we obtain the linear relationship:

[0088] ;

[0089] in:

[0090] ;

[0091] By changing the sample mass, different T values ​​were obtained. max and T env ,by The vertical axis is 1 / T max Using the x-axis as the horizontal axis, a linear fit is performed on each point to obtain the apparent activation energy of the reaction:

[0092] .

[0093] The implementation method is detailed below:

[0094] Example 1:

[0095] The above-described characterization method was used for characterization:

[0096] Heating takes place in a 1.6L cubic constant-volume incendiary bomb, which is heated by heating rods uniformly embedded within it, with a constant heating power of 178W, resulting in a heating rate of approximately 2.4℃ / min. The loading basket is a cylindrical stainless steel mesh basket with a diameter and height of 40mm, and a semi-circular handle at the top, allowing it to be suspended from a hook mounted on the top of the constant-volume incendiary bomb.

[0097] The sample used aluminum powder, which was a spherical powder with an average particle size of 1 μm. The mass ratio of aluminum powder to water was 2:1, and the total mass of aluminum powder and water was 10 g. The surface area to volume ratio was 377.8. Experimental measurements showed: exist Before the sample temperature changed abruptly, Sample The temperature difference between the sample temperature and the ambient temperature is less than 5℃; The temperature difference between the sample center and edge was 4.5℃ at the peak center temperature, which is less than 5℃, meeting the conditions for measuring the activation energy of the reaction in this invention. The experimentally measured critical temperature for the exothermic reaction was 51.5℃. The experimentally measured highest temperature at the sample center was 153.2℃, corresponding to an ambient temperature of 44.3℃ for the blank control, with a temperature difference of 108.9℃; the initial pressure was 1.045 bar, the highest pressure was 2.134 bar, and the square of the pressure ratio was 4.17.

[0098] Please refer to the attached document. Figure 1 The results show that the sample edge and center temperatures of Example 1 are in good agreement, indicating that the internal temperature is uniform and the analysis method based on Semenov theory of this patent can be used.

[0099] Please refer to the attached document. Figure 2 This shows the method for obtaining the critical temperature for the exothermic reaction in Example 1.

[0100] Example 2:

[0101] The difference from Example 1 is that the total mass of aluminum powder and water is 5g.

[0102] The measured surface area to volume ratio was 576.2. The temperature difference between the sample center and edge was measured to be 4.7℃ at the peak center temperature, which is less than 5℃, meeting the conditions for measuring the activation energy of the reaction in this invention. The measured critical temperature for the exothermic reaction was 52.1℃. The highest temperature at the sample center was measured to be 133.7℃, corresponding to a blank control ambient temperature of 45.9℃, a temperature difference of 87.8℃; the initial pressure was 1.036 bar, the highest pressure was 1.510 bar, and the square of the pressure ratio was 2.12.

[0103] Example 3:

[0104] The difference from Example 1 is that the total mass of aluminum powder and water is 15g.

[0105] The measured surface area to volume ratio was 278.6. The temperature difference between the sample center and edge was measured to be 0.5℃ at the peak center temperature, less than 5℃, meeting the conditions for measuring the activation energy of the reaction in this invention. The measured critical temperature for the exothermic reaction was 50.2℃. The highest temperature at the sample center was measured to be 174.2℃, corresponding to a blank control ambient temperature of 40.7℃, a temperature difference of 133.5℃; the initial pressure was 1.034 bar, the highest pressure was 2.653 bar, and the square of the pressure ratio was 6.58.

[0106] Based on the data from Examples 1, 2, and 3, the slope was calculated to be -3701.5, and the activation energy was 30.8 kJ / mol. The increase in sample mass led to a slight decrease in the exothermic reaction temperature; therefore, care should be taken to ensure that the ambient temperature during storage does not exceed the corresponding critical exothermic temperature. Due to the relatively low activation energy, it is important to maintain ventilation in the storage area to prevent heat accumulation.

[0107] Comparative Example 1:

[0108] The difference from Example 1 is that the heating power is 153W.

[0109] The surface area to volume ratio was the same as in Example 1, at 377.8. The temperature difference between the sample center and edge was measured to be 2.5°C at the peak center temperature, which is less than 5°C, satisfying the conditions for measuring the activation energy of the reaction according to this invention. The critical exothermic temperature of the reaction was measured to be 51.5°C. The highest temperature at the sample center was measured to be 146.0°C, corresponding to a blank control ambient temperature of 41.9°C, a temperature difference of 104.1°C; the initial pressure was 1.043 bar, the highest pressure was 1.869 bar, and the square of the pressure ratio was 3.21.

[0110] Comparative Example 2:

[0111] The difference from Example 1 is that the heating power is 203W.

[0112] The surface area to volume ratio was the same as in Example 1, at 377.8. The temperature difference between the sample center and edge was measured to be 4.5°C at the peak center temperature, which is less than 5°C, satisfying the conditions for measuring the activation energy of the reaction according to this invention. The critical exothermic temperature of the reaction was measured to be 51.5°C. The highest temperature at the sample center was measured to be 163.2°C, corresponding to a blank control ambient temperature of 44.3°C, a temperature difference of 118.9°C; the initial pressure was 1.039 bar, the highest pressure was 2.106 bar, and the square of the pressure ratio was 4.11.

[0113] Based on the data from Example 1 and Comparative Examples 1 and 2, with the sample mass remaining constant, the slope was calculated to be -3389.2 and the activation energy to be 32.3 kJ / mol by fitting the data using the heating power as a variable, with the sample mass remaining constant. The change in heating power had no effect on the exothermic critical temperature.

[0114] Please refer to the attached document. Figure 3 The changes in sample center temperature over time under three sample masses show that the smaller the sample mass, the longer it takes to reach the peak temperature and the lower the peak temperature.

[0115] Please refer to the attached document. Figure 4 The changes in sample center temperature over time under three heating powers show that the lower the heating power, the longer it takes to reach the peak temperature and the lower the peak temperature.

[0116] Please refer to the attached document. Figure 5 The activation energies calculated by changing the sample mass and the heating power were 30.8 kJ / mol and 32.3 kJ / mol, respectively.

[0117] The literature "Study on the Thermal Spontaneous Combustion Mechanism of Polished Aluminum Powder" uses the cross-temperature point method to measure an activation energy of 22.2 kJ / mol. The sample was obtained from an actual accident site, with a median particle size of 19.143 μm. It contains 88% aluminum, 10% silicon, and other elements such as iron, calcium, sulfur, magnesium, potassium, zinc, and copper. This complex elemental composition may explain the lower activation energy. The literature "Study on Hydrogen Production from the Reaction of Pure Aluminum Powder with Water and Related Influencing Factors" uses the hydrogen production rate to measure the activation energy of aluminum powder with a particle size between 0.98 μm and 24.94 μm reacting with water, ranging from 64.2 kJ / mol to 88.7 kJ / mol. However, the sample mass was only 0.5 g, failing to achieve the stacking effect, which may have led to a higher activation energy. The activation energies measured by the method in this patent are 30.8 kJ / mol and 32.3 kJ / mol, which are reliable and valid.

[0118] The similar activation energies obtained from the two methods can be explained by the following: From a purely chemical kinetic perspective, activation energy is an intrinsic property of the reaction itself and does not change with mass or heating power. However, current experimental measurements yield apparent activation energies, which may vary with sample mass and heating power. Based on the examples and comparative cases, sample mass and heating power have relatively little impact on apparent activation energy; both can be used to calculate it.

[0119] However, from a practical point of view, changing the sample mass to calculate the activation energy is more efficient and accurate, because the former only requires finding a suitable heating power and completing one blank control experiment, while the latter requires at least three suitable heating powers and completing at least three blank control experiments.

[0120] In addition, since changing the heating power has a smaller impact on the maximum temperature than changing the sample temperature, the fitting points are more concentrated, and the error caused by small perturbations is relatively large.

[0121] Although the embodiments of this patent only used 1μm aluminum powder as a sample for characterization and analysis, it can still be applied to aluminum, magnesium, and their alloys with different oxidation degrees, particle sizes, and moisture contents, including but not limited to. The reasons are as follows:

[0122] ① Aluminum, magnesium and their alloys have similar thermal conductivity, and their Biot numbers as samples in this patent are similar, which can satisfy the Semenov theoretical assumptions.

[0123] ② The accumulation of heat in wet mud containing aluminum, magnesium, and their alloys all produces hydrogen gas, and their chemical reaction processes are similar.

[0124] In the description of this specification, the references to terms such as "embodiment," "basic embodiment," "preferred embodiment," "other embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0125] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0126] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for characterizing the heat accumulation properties of wet metal powder mud, characterized in that: Includes the following steps: S1: Obtain wet metal powder sludge, which is placed in a columnar shape in a loading basket with pores, and obtain the surface area S and volume V of the accumulated wet metal powder sludge. S2: Place the loading basket containing the above-mentioned wet mud of metal powder into a sealed heating container, obtain the volume of the heating container, and heat the inside of the heating container with constant power. During heating, the temperature T of the sample and the ambient pressure p and ambient temperature inside the heating container are obtained in real time. S3: When the ambient temperature inside the heating container no longer rises, determine whether the temperature of the sample reaches a temperature peak. If yes, proceed to the next step; otherwise, end the characterization process. S4: Change the mass of the sample while keeping other conditions unchanged, and repeat steps S1 to S3 to obtain multiple sets of data; S5: Obtain the temperature rise curves of samples with different masses over time, process the obtained data, and obtain the critical exothermic reaction temperature T of the sample. i and apparent activation energy E; The process also includes S0: placing an empty loading basket (without a sample) into the heating container, heating the container with the same constant power as in S2, and recording the ambient temperature T in real time during heating. env ; The timing of S0 is before S5 and is not restricted by S1~S4; In S5, data processing methods include: The highest point temperature T of the sample temperature rise curve over time was obtained. max and the corresponding ambient temperature T for the same heating time env ; With 1 / T max The x-axis is... Using the vertical axis as the ordinate, experimental data from multiple sets of samples with different masses are represented on the coordinate system. These experimental data are linearly fitted, and the apparent activation energy E is calculated based on the slope of the fitted line. In the expression for the ordinate above, p max The temperature T of the sample reaches its highest point, Tmax. max The pressure inside the heating container at that time; p0 refers to the initial ambient pressure inside the heating container before the characterization begins; In S5, the fitting equation for the experimental data is: ； in, ; The fitting formula was derived from the Semenov thermal explosion model through a process of adjustment. The adjustment steps are as follows: According to the Semenov thermal explosion model, we can obtain: ； In the above formula, ρ is the sample density, and c p Here, H is the specific heat capacity at constant pressure of the sample, A is the heat of reaction, E is the pre-exponential factor, R is the apparent activation energy, S is the gas constant, S is the sample surface area, and V is the sample volume. c The heat dissipation coefficient; At the point where the sample temperature is highest, the system reaches thermal equilibrium, and the rate of change of the reaction temperature is 0. At this point, ∂T / ∂t = 0, and the above equation satisfies the following energy balance relationship: ； In the above formula, h c 0 This is the initial heat dissipation coefficient; Taking the logarithm of the expression and rearranging it, we obtain the fitted expression; In S5, the data processing method includes: taking the point with the largest slope of the temperature rise curve of a sample of a certain mass over time as a tangent line, performing linear fitting on the heating temperature curve of the sample before the reaction begins to obtain an extension line, and the sample temperature corresponding to the intersection of the tangent line and the extension line is the exothermic critical temperature T of the reaction for that mass of sample. i ; Before the sample temperature changes abruptly, the difference between the sample temperature and the blank ambient temperature is controlled within 5℃.

2. The characterization method according to claim 1, characterized in that: The constant power setting results in an ambient temperature rise rate of 2~3℃ / min.

3. The characterization method according to claim 1, characterized in that: The loading basket is provided with a loading cover, which is made of the same material as the other parts of the loading basket; the loading cover has a thickness and pore shape adapted to the other parts of the loading basket.

4. The characterization method according to claim 1, characterized in that: In S2: the temperature T1 at the center of the sample and the temperature T2 at the edge of the sample are obtained respectively. When the temperature of the sample reaches a peak, it is determined whether the difference between T1 and T2 is within 5℃. If yes, proceed to the next step; if no, end the representation process.

5. The characterization method according to claim 1, characterized in that: In S1, the metal powder wet mud is obtained by mixing water from the ice-water mixture with metal powder and then placing it in the loading basket. Once the sample temperature reaches room temperature, proceed to step S2 and start timing.

6. The characterization method according to claim 1, characterized in that: The mass of the sample is 5-15 grams.

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