Method for evaluating hygroscopicity of energetic materials with equal mass and different particle sizes under same temperature and humidity conditions

Abstract

The invention discloses a method for evaluating the hygroscopicity of energetic materials with equal mass and different particle sizes under the same temperature and humidity condition, which can strictly control the consistency of the temperature and humidity environment of a simulation system and strictly control the morphology, size and variety of energetic molecular clusters, and is not influenced by external environmental factors and human factors. The invention provides a simpler, safer and more efficient hygroscopicity evaluation method mainly aiming at the problems that long-term storage, efficient utilization, safety and the like of the material are influenced by hygroscopicity change factors possibly existing after refining treatment of the energetic material. According to the method, the development and application of the novel energetic material can be accelerated in the aspect of evaluating the hygroscopicity of the energetic material with different particle sizes, the hygroscopicity results of the energetic material with different particle sizes can be obtained without carrying out experiments, the method has very important significance on optimization of the energetic material, and the time for developing the novel moisture-absorption-preventing energetic material is greatly saved.

Description

Technical Field

[0001] The invention relates to a method for evaluating the hygroscopicity of energetic materials with equal mass and different particle sizes under the same temperature and humidity conditions, belonging to the field of energetic materials. Background Art

[0002] Energetic materials are a type of material that can release a large amount of energy through chemical reactions. They are important components of propellants, explosives, propellants, pyrotechnic agents, etc. In the military field, energetic materials can generate powerful destructive power with the help of their ability to quickly release energy. They are an indispensable key component of weapons and military equipment. In the field of aerospace science and technology, as the basic materials for various types of propellants in rockets, they can provide high energy density and high combustion speed, enabling spacecraft to quickly reach the required speed and orbit, and play a vital role in human exploration of the universe and realization of interstellar travel. At the same time, energetic materials are also widely used in the civilian field, such as as an inflation source for automobile airbags. Therefore, the research on energetic materials is of great significance to national defense construction, scientific and technological progress, and the improvement of human quality of life. However, an important factor affecting the performance of energetic materials is the hygroscopic property. After absorbing moisture, the energy release performance of energetic materials is greatly reduced, and agglomeration and agglomeration will occur, which will affect subsequent processing and even lead to a decrease in the stability and safety of the materials during application. Therefore, it is very important to solve the hygroscopic problem of energetic materials. Since energetic materials are usually used in explosives after being graded, energetic materials of different particle sizes have different performances and their hygroscopicity is also different.

[0003] Therefore, exploring the hygroscopicity of energetic materials with different particle sizes is of great significance for fully understanding the hygroscopic characteristics of energetic materials, evaluating the hygroscopic characteristics of modified energetic materials, and guiding the formulation and development of explosives. At present, the main method for evaluating the hygroscopicity of energetic materials is to test them through experimental methods, such as the commonly used dryer balance method (GJB770B-2005, Explosive Test Method Method 404.1 Hygroscopicity Dryer Balance Method [S].) and dynamic adsorption method (WJ20699-2018, Explosive Performance Test Energetic Material Hygroscopicity Dynamic Adsorption Method [S].). The dryer balance method mainly places the pre-dried and weighed sample in a dryer, adds a saturated solution of a specific salt to the dryer, and places the dryer containing the sample at a certain temperature to create a certain temperature and humidity environment. By weighing the sample before and after moisture absorption and testing the change in sample mass over a certain period of time, the hygroscopicity of the sample is evaluated. Similarly, the dynamic adsorption method also evaluates the hygroscopicity of the sample through experimental methods. Specifically, air of a certain temperature and humidity passes through a certain mass of sample, and the moisture absorption rate of the sample is obtained according to the change in the mass of the sample. Both of these standards for evaluating hygroscopicity are experimental methods. The repeatability of each experiment is greatly affected by environmental and human factors. The consideration of the hygroscopic properties of the sample can only provide a limited reference, and the test requires sample preparation, which takes a lot of time. In addition to the above-mentioned experimental weighing method, foreign studies on hygroscopicity also use in-situ imaging technology and mass spectrometer coupling and other microscopic characterization methods to analyze the hygroscopicity of the sample from a more microscopic perspective. For example, Dominique S. Piens et al. ([Dominique S. Piens, Stephen T. Kelly, Tristan H. Harder, et al. Measuring mass-based hygroscopicity of atmospheric particles through in situ imaging [J]. Environmental Science & Technology, 2016, 50 (10): 5172-5180.]) proposed a new method to measure the mass hygroscopicity of particles. They combined scanning electron microscopy with energy dispersive X-ray analysis (SEM / EDX), scanning transmission X-ray microscopy (STXM) analysis and in situ STXM humidification experiments to quantitatively analyze the hygroscopicity and elemental composition of 15 complex atmospheric particles. This method provides unique quantitative capabilities to characterize the hygroscopicity and chemical properties of individual submicron atmospheric particles.Alla Zelenyuk et al. ([Alla Zelenyuk, Dan Imre, Jeong-Ho Han, et al. Simultaneous Measurements of Individual Ambient Particle Size, Composition, Effective Density, and Hygroscopicity[J]. Analytical Chemistry, 2008, 80, 1401-1407.]) used a humidified tandem differential mobility analyzer (HTDMA) coupled with an ultrasensitive single particle mass spectrometer (SPLAT) to perform real-time simultaneous measurements of the hygroscopic growth factor, density, and composition of individual ambient particles. The authors used particles composed of a mixture of sulfate and oxygen-containing organic matter as an example to expand the multidimensional single particle characterization and obtain relevant quantitative information about individual particles. The authors believe that the system has the required sensitivity and can generate detailed single particle data at a sufficiently high sampling rate to provide statistically significant samples. These methods can be used to evaluate the hygroscopicity of energetic materials of different particle sizes, but there are defects such as unstable control of ambient temperature / humidity, difficulty in preparing and separating samples of different particle sizes, and difficulty in maintaining consistent sample micromorphology.

[0004] Simulation is a method of theoretical analysis based on model building. It has the advantages of low cost, high efficiency, safety, strong controllability, and no interference from environmental factors. Therefore, it is of great significance to innovate a method for evaluating the hygroscopicity of energetic materials with different particle sizes. However, there is no suitable model and method to compare the hygroscopicity of different particle sizes of the same energetic material. If this method and technology can be broken through, it will greatly facilitate the research on the anti-hygroscopicity of energetic materials. It can also provide new theoretical guidance for us to test / evaluate the hygroscopicity of energetic materials with different particle sizes. Summary of the invention

[0005] In view of the problems that the hygroscopicity changes that may exist after the refinement of energetic materials affect the long-term storage, efficient utilization and safety of the materials, the purpose of the present invention is to provide a simple and efficient method for evaluating the hygroscopicity of energetic materials of equal quality and different particle sizes under the same temperature and humidity conditions.

[0006] The technical solution for implementing the present invention is: a method for evaluating the hygroscopicity of energetic materials of equal mass and different particle sizes under the same temperature and humidity conditions provided by the present invention specifically comprises the following steps:

[0007] The first step is to import the standard cif file of the molecular unit cell of energetic material A into Materials Studio molecular simulation software, perform complete structural optimization on the initial unit cell to make the system structure more reasonable, respectively construct two cluster models of the energetic material with equal mass and different particle sizes, and place the two cluster models in a larger cubic grid to make them evenly distributed, multiply the water molecules with known density under certain temperature and relative humidity conditions by n times and fill them into the space between the cluster model and the cubic grid, and respectively construct two initial models of energetic material A at the same temperature and humidity;

[0008] The second step is to perform NVT molecular dynamics calculations on the two initial models constructed respectively, take out the last frame model after the molecular dynamics calculation, and use the Forcite module to perform structural optimization operations without optimizing the unit cell to eliminate the structural instability factors in the structure, and obtain the stable models m and M after moisture absorption;

[0009] The third step is to decompose the stable models m and M after moisture absorption respectively. From each stable model, the models m1 and M1 of single water molecules after moisture absorption, and the models m2 and M2 of single energetic molecular clusters are extracted. The system energy of these six models, i.e., the energy E′ of m1, is calculated using the Forcite module. water and the energy E of M1 water , the energy E′ of m2 cluster and the energy E of M2 cluster , the energy E′ of m total and the energy E of M total Finally, the interaction energy E′ between the energetic molecular clusters with the same mass and different particle sizes and water molecules under the same temperature and humidity conditions is obtained. interaction and E interaction By comparing the interaction energy, the hygroscopicity of energetic material A with equal mass and different particle sizes is evaluated.

[0010] Preferably, in the first step, the energetic material A includes but is not limited to any energetic hygroscopic material such as an oxidant, an explosive, a metal powder, a hydrogen storage material, etc. The oxidant can be ammonium perchlorate (AP), potassium perchlorate (KP), ammonium dinitramide (ADN), ammonium nitrate (AN), etc., and their eutectics, mixed crystals and modified crystals; the explosive can be hexanitrohexaazaisowurtane (CL-20), 1'1-dihydroxy-5,5'-bi-tetrazolyl dihydroxylamine (TKX-50), 3,4-dinitrofuroxan (DNTF) , all-nitrogen / multi-nitrogen energetic materials, and their eutectics, mixed crystals, and modified crystals; the metal powder can be aluminum powder (Al), boron powder (B), magnesium powder (Mg), or its alloy powder, etc.; the hydrogen storage material can be magnesium hydride (MgH2), aluminum hydride (AlH3), lithium aluminum hydride (LiAlH4), magnesium aluminum hydride (Mg(AlH4)2), etc. It is worth noting that this method is also applicable to non-energetic materials; the morphology of cluster models of equal mass and different particle sizes can be spheres, cubes, various cylinders, various cones, and other three-dimensional figures, and their sizes (longest side / diameter) can be Placed in a larger cubic grid means that the side length of the grid is

[0011] Preferably, in the first step, the temperature and relative humidity conditions refer to a temperature of 0 to 100° C. and a relative humidity of 0% to 100%.

[0012] Preferably, in the first step, the water molecule with a known density under certain temperature and relative humidity conditions is multiplied by n times so that the density of the water molecule is ≥ 0.0001 g / cm 3 Meet the modeling requirements of Materials studio molecular simulation software.

[0013] Preferably, in the second step, when performing NVT molecular dynamics calculations, the dynamic parameters are set, including: the time is set to 20ps to 1000ps, the temperature control method adopts the Nose method, the calculation accuracy of the structure optimization is greater than or equal to the default Middle accuracy of the Forcite module, and the displacement factor (Displacement) needs to be considered.

[0014] Preferably, in the third step, E′ is determined according to the formula interaction =E′ total -E′ water -E′ cluster , E interaction =E total -E water -E cluster .

[0015] Preferably, in the third step, the calculation accuracy of the energy is greater than or equal to the default Middle accuracy of the Forcite module of the Materials studio software.

[0016] Preferably, in the third step, by comparing the interaction energy E′ interaction and E interaction , the hygroscopicity of energetic material A of equal mass but different particle sizes was evaluated. The larger the absolute value of the interaction energy, the stronger its hygroscopicity.

[0017] The method for evaluating the hygroscopicity of energetic materials with equal mass and different particle sizes under the same temperature and humidity conditions proposed by the present invention has the following advantages compared with the prior art methods:

[0018] (1) The present invention can strictly control the density of environmental water molecules in the simulation system, strictly control the morphology, size, and type of energetic molecular clusters, and strictly control the size of the system model, thereby achieving the purpose of studying the hygroscopicity of various energetic molecules with different particle sizes under the same temperature and humidity conditions (temperature: 0-100°C, relative humidity 0%-100%), and is not affected by external environmental factors and human factors.

[0019] (2) The simulation method proposed in the present invention is simpler, safer and more efficient. The experiment takes a long time from sample preparation to hygroscopic characterization, and the sample particle size is difficult to classify and study separately. The simulation method can simultaneously calculate the hygroscopicity of samples with multiple different particle sizes, which not only helps us better classify and analyze the hygroscopicity of samples of various particle sizes, but also greatly saves our time in evaluating the hygroscopicity of energetic molecules.

[0020] (3) The present invention is helpful to accelerate the development and application of new energetic materials in the evaluation of hygroscopicity of energetic materials with various particle sizes. The hygroscopicity results of energetic materials with different particle sizes can be obtained without conducting experiments. This is of great significance for the optimization of energetic materials and is also applicable to the evaluation of various modified energetic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the unit cell of the ADN crystal in Example 1.

[0022] Figure 2 is the radius in Example 1 Small-size ADN cluster model.

[0023] Figure 3 In Example 1, the density of the filled 3 Initial model of small-size ADN particles after the water molecules. Figure 4 This is the last frame model of the small-particle ADN initial model in Example 1 after 100ps of NVT molecular dynamics.

[0024] Figure 5 This is the stable model m of the small-particle ADN after moisture absorption in Example 1.

[0025] Figure 6 It is the stable model m of the small-particle ADN after moisture absorption in Example 1 and the molecular cluster models of the two systems extracted.

[0026] Figure 7 It is a schematic diagram of the principle of the method for evaluating the hygroscopicity of energetic materials of equal mass and different particle sizes under the same temperature and humidity conditions described in the present invention. DETAILED DESCRIPTION

[0027] In order to further describe the present invention, the following examples are listed, but the present invention is not limited to the examples.

[0028] In addition, for the study of the hygroscopicity of energetic materials with different particle sizes, we hope to conduct a theoretical evaluation of the hygroscopicity of the materials we designed in advance, select the best scheme from a large number of modification schemes, and then conduct experiments to verify it, so as to greatly reduce the cost and time of the experiment and improve the accuracy of the experiment. Therefore, we proposed a theoretical simulation method to study the hygroscopicity of energetic materials with different particle sizes. The advantage of the theoretical method over the actual test is that the same environmental temperature and humidity can be applied strictly as required, and the morphology, particle size, density and other parameters of the required sample model can be constructed as required, and the experimental data will not have large errors due to differences in environmental conditions and the physical properties of the sample itself.

[0029] Taking ADN as an example, the present invention provides a method for evaluating the hygroscopicity of energetic materials with equal mass and different particle sizes under the same temperature and humidity conditions, and its principle schematic diagram is shown in FIG7 .

[0030] Implementation Example 1:

[0031] Step 1: According to the table of saturated vapor pressure of water molecules at different temperatures in books such as chemical engineering manuals or chemical engineering principles, the density of water molecules at standard atmospheric pressure, 30°C, and 100% relative humidity is about 3.036×10 -5 g / cm 3 .

[0032] Step 2: Import the cif file of ammonium dinitramide (ADN) crystal into Materials Studio 2019 simulation software, and perform complete structural optimization on the initial unit cell of ADN to make the architecture more reasonable ( Figure 1 ), the calculation accuracy of the structure optimization is set to Ultra-fine (Energy: 2×10 -5 kcal / mol,Force:0.001 ), Displacement is set to Then construct eight ADN spherical cluster and place this ADN cluster on a side length In the cubic grid ( Figure 2 ), the fractional coordinates of the body centers of the eight small-size spherical clusters are: (0.25, 0.25, 0.25), (0.25, 0.75, 0.25), (0.25, 0.25, 0.75), (0.25, 0.75, 0.75), (0.75, 0.25, 0.25), (0.75, 0.75, 0.25), (0.75, 0.25, 0.75), (0.75, 0.75, 0.75). The water molecule density calculated in the previous step is 3.036×10 -5 g / cm 3 Multiply by 200 and it is about 0.006g / cm 3 (Because the calculated water molecule density is too small in actual situations, and the minimum density of molecules added by the Amorphous module of Materials Studio 2019 simulation software is 0.0001g / cm 3 Therefore, when adding water molecules, the water molecule density under all temperature and humidity systems is multiplied by n times so that the minimum density of the added water molecules is not less than 0.0001g / cm 3 , so as to achieve the purpose of studying the hygroscopic effect of energetic molecules on water molecules under different temperature and humidity conditions, and to meet the requirements of modeling accuracy of simulation software), fill the water molecules of this density into the gap between this ADN cluster and the cubic lattice, and obtain the radius Initial model of small-size ADN ( Figure 3 ).

[0033] Step 3: Refer to step 2 to construct a radius ADN spherical nanoclusters and place the ADN clusters on a The cubic lattice body center position is filled with 0.006g / cm 3 The water molecules with a density of 2.5 Å are transported into the gap between the ADN cluster and the cubic lattice, and the radius is The initial model of large-size ADN (since the hygroscopicity of clusters with different particle sizes needs to be studied comparatively, in order to control the variables, we divide each group of control experiments into two types: large-size model and small-size model, and control the mass of the two groups of models to be equal. Finally, the hygroscopicity simulation of the two groups under the same temperature and humidity environment is carried out. Therefore, the large-size model is set to radius The spherical clusters of are placed in the grid. In order to control the mass to be equal, 8 radii of spherical clusters placed in the same grid).

[0034] Step 4: Use the Forcite module of Materials studio simulation software to perform NVT molecular dynamics simulation on the constructed ADN initial models of the two particle sizes. The molecular dynamics time is set to 100ps. Finally, the last frame model after the molecular dynamics calculation is taken out ( Figure 4 ), the Forcite module was used to perform structural optimization without optimizing the unit cell to eliminate unstable factors such as stress in the structure, and the stable models m and M ( Figure 5 ), the calculation accuracy of the structure optimization is set to: Energy: 2×10 -5 kcal / mol,Force:0.001 Displacement is set to

[0035] Step 5: Use the atom selection function to decompose the above stable models m and M after moisture absorption, and separate the models m1 and M1 of single water molecules after moisture absorption, and the models m2 and M2 of single energetic molecular clusters ( Figure 6 ), and use the Forcite module to calculate the system energy of the six models with two particle sizes, namely the energy E′ of m1 water and the energy E of M1 water , the energy E′ of m2 cluster and the energy E of M2 cluster , the energy E′ of m total and the energy E of M total . Get the radius The energy of each system of small-size spherical ADN is: E′ water =-2798.799 kcal / mol, E′ cluster =-87305.346 kcal / mol, E′ total1 =-94893.564 kcal / mol, radius The system energies of large-size spherical ADN are: E water =-3644.799 kcal / mol,E cluster =-81768.137 kcal / mol,E total = -89853.566 kcal / mol. Finally, the energy of the stable model after moisture absorption is subtracted from the energy of the individual energetic molecular cluster and then from the energy of the individual water molecule to obtain the radius at 30°C and 100% relative humidity. Small spherical ADN and radius The interaction energies of large-size spherical ADN and water molecules are: E′ interaction =E′total -E′ water -E′ cluster =-4789.419 kcal / mol; E interaction =E total -E water -E cluster =-4440.630 kcal / mol.

[0036] Implementation Example 2:

[0037] Step 1: Calculate the water molecule density under standard atmospheric pressure, 30°C, and 100% relative humidity to be approximately 3.036×10 -5 g / cm 3 .

[0038] Step 2: Import the cif file of the ADN crystal into the Materials Studio 2019 simulation software, perform a complete structural optimization on the ADN initial unit cell to make the system architecture more reasonable, and set the calculation accuracy of the structural optimization to Ultra-fine (Energy: 2×10 -5 kcal / mol,Force:0.001 Displacement is set to Then construct eight ADN spherical cluster and place this ADN cluster on a side length In the cubic grid, the fractional coordinates of the body centers of the eight small-size spherical clusters are: (0.25, 0.25, 0.25), (0.25, 0.75, 0.25), (0.25, 0.25, 0.75), (0.25, 0.75, 0.75), (0.75, 0.25, 0.25), (0.75, 0.75, 0.25), (0.75, 0.25, 0.75), (0.75, 0.75, 0.75). The water molecule density calculated in the previous step is 3.036 × 10 -5 g / cm 3 Multiply by 200 and it is about 0.006g / cm 3 , fill the gap between the ADN cluster and the cubic lattice with water molecules of this density, and obtain the radius Initial model of small-size ADN.

[0039] Step 3: Refer to step 2 to construct a radius ADN spherical nanoclusters and place the ADN clusters on a The cubic lattice body center position is filled with 0.006g / cm 3 The water molecules with a density of 2.5 Å are transported into the gap between the ADN cluster and the cubic lattice, and the radius is Initial model of large-size ADN.

[0040] Step 4: The constructed ADN initial models of the two particle sizes were subjected to NVT molecular dynamics simulation using the Forcite module of the Materials studio simulation software. The molecular dynamics time was set to 100ps. Finally, the last frame model after the molecular dynamics calculation was taken out and the Forcite module was used to perform structural optimization operations without optimizing the unit cell to eliminate unstable factors such as stress in the structure. The stable models m and M of the two particle sizes after moisture absorption were obtained. The calculation accuracy of the structural optimization was set to: Energy: 2×10 -5 kcal / mol,Force:0.001 Displacement is set to

[0041] Step 5: Use the atom selection function to decompose the above stable models m and M after moisture absorption, and separate the models m1 and M1 of single water molecules after moisture absorption, and the models m2 and M2 of single energetic molecular clusters. Use the Forcite module to calculate the system energy of the six models of two particle sizes, that is, the energy E′ of m1 water and the energy E of M1 water , the energy E′ of m2 cluster and the energy E of M2 cluster , the energy E′ of m total and the energy E of M total . Get the radius The energy of each system of small-size spherical ADN is: E′ water =-1699.623 kcal / mol, E′ cluster =-228200.205 kcal / mol, E′ total =-238345.224 kcal / mol, radius The system energies of large-size spherical ADN are: E water =-2428.500 kcal / mol,E cluster =-228521.320 kcal / mol,E total = -237472.712 kcal / mol. Finally, the energy of the stable model after moisture absorption is subtracted from the energy of the individual energetic molecular cluster and then from the energy of the individual water molecule to obtain the radius at 30°C and 100% relative humidity. Small spherical ADN and radius The interaction energies of large-size spherical ADN and water molecules are: E′ interaction =E′ total -E′water -E′ cluster =-8445.396 kcal / mol; E interaction =E total -E water -E cluster =-6522.892 kcal / mol. Implementation Example 3:

[0042] Step 1: Calculate the water molecule density under standard atmospheric pressure, 30°C, and 100% relative humidity to be approximately 3.036×10 -5 g / cm 3 .

[0043] Step 2: Import the cif file of ammonium nitrate (AN) crystal into Materials Studio 2019 simulation software, perform complete structural optimization on the initial unit cell of AN to make the system structure more reasonable, and set the calculation accuracy of structural optimization to Ultra-fine (Energy: 2×10 -5 kcal / mol,Force:0.001 ), Displacement is set to Then construct eight AN spherical cluster and place this AN cluster on the edge length In the cubic grid, the fractional coordinates of the body centers of the eight small-size spherical clusters are: (0.25, 0.25, 0.25), (0.25, 0.75, 0.25), (0.25, 0.25, 0.75), (0.25, 0.75, 0.75), (0.75, 0.25, 0.25), (0.75, 0.75, 0.25), (0.75, 0.25, 0.75), (0.75, 0.75, 0.75). The water molecule density calculated in the previous step is 3.036 × 10 -5 g / cm 3 Multiply by 200 and it is about 0.006g / cm 3 , fill the gap between the AN cluster and the cubic lattice with water molecules of this density, and obtain the radius The initial model of small particle size AN.

[0044] Step 3: Refer to step 2 to construct a radius AN spherical nanocluster and place the AN cluster on a The cubic lattice body center position is filled with 0.006g / cm 3 The water molecules with a density of 2.5 Å are transported into the gap between the AN cluster and the cubic lattice, and the radius is The initial model of large particle size AN.

[0045] Step 4: The constructed AN initial models of the two particle sizes were subjected to NVT molecular dynamics simulation using the Forcite module of the Materials studio simulation software. The molecular dynamics time was set to 100ps. Finally, the last frame model after the molecular dynamics calculation was taken out and the Forcite module was used to perform structural optimization operations without optimizing the unit cell to eliminate unstable factors such as stress in the structure. The stable models m and M of the two particle sizes after moisture absorption were obtained. The calculation accuracy of the structural optimization was set to: Energy: 2×10 -5 kcal / mol,Force:0.001 Displacement is set to

[0046] Step 5: Use the atom selection function to decompose the above stable models m and M after moisture absorption, and separate the models m1 and M1 of single water molecules after moisture absorption, and the models m2 and M2 of single energetic molecular clusters. Use the Forcite module to calculate the system energy of the six models of two particle sizes, that is, the energy E′ of m1 water and the energy E of M1 water , the energy E′ of m2 cluster and the energy E of M2 cluster , the energy E′ of m total and the energy E of M total . Get the radius The energy of each system of small-size spherical AN is: E′ water =-2096.039 kcal / mol, E′ cluster =-70092.134 kcal / mol, E′ total =-80074.322 kcal / mol, radius The system energies of the large-size spherical AN are: E water =-3295.462 kcal / mol,E cluster =-74237.809 kcal / mol,E total = -80675.688 kcal / mol. Finally, the energy of the stable model after moisture absorption is subtracted from the energy of the individual energetic molecular cluster and then from the energy of the individual water molecule to obtain the radius at 30°C and 100% relative humidity. Small particle size spherical AN and radius The interaction energies of large-size spherical AN and water molecules are: E′ interaction =E′ total -E′ water -E′ cluster =-7886.149 kcal / mol; Einteraction =E total -E water -E cluster =-3142.417 kcal / mol.

[0047] Implementation Example 4:

[0048] Step 1: Calculate the water molecule density under standard atmospheric pressure, 30°C, and 100% relative humidity to be approximately 3.036×10 -5 g / cm 3 .

[0049] Step 2: Import the cif file of the AN crystal into the Materials Studio 2019 simulation software, perform a complete structural optimization on the ADN initial unit cell to make the system architecture more reasonable, and set the calculation accuracy of the structural optimization to Ultra-fine (Energy: 2×10 -5 kcal / mol,Force:0.001 ), Displacement is set to Then construct eight AN spherical cluster and place this AN cluster on the edge length In the cubic grid, the fractional coordinates of the body centers of the eight small-size spherical clusters are: (0.25, 0.25, 0.25), (0.25, 0.75, 0.25), (0.25, 0.25, 0.75), (0.25, 0.75, 0.75), (0.75, 0.25, 0.25), (0.75, 0.75, 0.25), (0.75, 0.25, 0.75), (0.75, 0.75, 0.75). The water molecule density calculated in the previous step is 3.036 × 10 -5 g / cm 3 Multiply by 200 and it is about 0.006g / cm 3 , fill the gap between the AN cluster and the cubic lattice with water molecules of this density, and obtain the radius The initial model of small particle size AN.

[0050] Step 3: Refer to step 2 to construct a radius AN spherical nanocluster and place the AN cluster on a The cubic lattice body center position is filled with 0.006g / cm 3 The water molecules with a density of 2.5 Å are transported into the gap between the AN cluster and the cubic lattice, and the radius is The initial model of large particle size AN.

[0051] Step 4: The constructed AN initial models of the two particle sizes were subjected to NVT molecular dynamics simulation using the Forcite module of the Materials studio simulation software. The molecular dynamics time was set to 100ps. Finally, the last frame model after the molecular dynamics calculation was taken out and the Forcite module was used to perform structural optimization operations without optimizing the unit cell to eliminate unstable factors such as stress in the structure. The stable models m and M of the two particle sizes after moisture absorption were obtained. The calculation accuracy of the structural optimization was set to: Energy: 2×10 -5 kcal / mol,Force:0.001 Displacement is set to

[0052] Step 5: Use the atom selection function to decompose the above stable models m and M after moisture absorption, and separate the models m1 and M1 of single water molecules after moisture absorption, and the models m2 and M2 of single energetic molecular clusters. Use the Forcite module to calculate the system energy of the six models of two particle sizes, that is, the energy E′ of m1 water and the energy E of M1 water , the energy E′ of m2 cluster and the energy E of M2 cluster , the energy E′ of m total and the energy E of M total . Get the radius The energy of each system of small-size spherical AN is: E′ water =-1068.413 kcal / mol, E′ cluster =-201698.293 kcal / mol, E′ total =-213792.708 kcal / mol, radius The system energies of the large-size spherical AN are: E water =-2315.779 kcal / mol,E cluster =-208045.746 kcal / mol,E total = -215545.871 kcal / mol. Finally, the energy of the stable model after moisture absorption is subtracted from the energy of the individual energetic molecular cluster and then from the energy of the individual water molecule to obtain the radius at 30°C and 100% relative humidity. Small particle size spherical AN and radius The interaction energies of large-size spherical AN and water molecules are: E′ interaction =E′ total -E′ water -E′ cluster =-11026.002 kcal / mol; Einteraction =E total -E water -E cluster =-5184.346 kcal / mol.

[0053] Implementation Example 5:

[0054] Step 1: Calculate the water molecule density under standard atmospheric pressure, 30°C, and 100% relative humidity to be approximately 3.036×10 -5 g / cm 3 .

[0055] Step 2: Import the cif file of ammonium perchlorate (AP) crystal into Materials Studio 2019 simulation software, perform complete structural optimization on the AP initial unit cell to make the system architecture more reasonable, and set the calculation accuracy of the structural optimization to Ultra-fine (Energy: 2×10 -5 kcal / mol,Force:0.001 ), Displacement is set to Then construct eight The AP spherical cluster is placed on the edge length In the cubic grid, the fractional coordinates of the body centers of the eight small-size spherical clusters are: (0.25, 0.25, 0.25), (0.25, 0.75, 0.25), (0.25, 0.25, 0.75), (0.25, 0.75, 0.75), (0.75, 0.25, 0.25), (0.75, 0.75, 0.25), (0.75, 0.25, 0.75), (0.75, 0.75, 0.75). The water molecule density calculated in the previous step is 3.036 × 10 -5 g / cm 3 Multiply by 200 and it is about 0.006g / cm 3 , fill the gap between the AP cluster and the cubic lattice with water molecules of this density, and obtain the radius Initial model of small particle size AP.

[0056] Step 3: Refer to step 2 to construct a radius AP spherical nanoclusters and place the AP clusters on a The cubic lattice body center position is filled with 0.006g / cm 3 The water molecules with a density of 1.37 × 10.3 ... The initial model of large-particle AP.

[0057] Step 4: The constructed AP initial models of the two particle sizes were subjected to NVT molecular dynamics simulation using the Forcite module of the Materials studio simulation software. The molecular dynamics time was set to 100ps. Finally, the last frame model after the molecular dynamics calculation was taken out and the Forcite module was used to perform structural optimization operations without optimizing the unit cell to eliminate unstable factors such as stress in the structure. The stable models m and M of the two particle sizes after moisture absorption were obtained. The calculation accuracy of the structural optimization was set to: Energy: 2×10 -5 kcal / mol,Force:0.001 Displacement is set to

[0058] Step 5: Use the atom selection function to decompose the above stable models m and M after moisture absorption, and separate the models m1 and M1 of single water molecules after moisture absorption, and the models m2 and M2 of single energetic molecular clusters. Use the Forcite module to calculate the system energy of the six models of two particle sizes, that is, the energy E′ of m1 water and the energy E of M1 water , the energy E′ of m2 cluster and the energy E of M2 cluster , the energy E′ of m total and the energy E of M total . Get the radius The energy of each system of small-size spherical AP is: E′ water =-1365.066 kcal / mol, E′ cluster =-48745.316 kcal / mol, E′ total =-59692.305 kcal / mol, radius The system energies of large-size spherical AP are: E water =-2707.560 kcal / mol,E cluster =-53260.125 kcal / mol,E total = -60652.955 kcal / mol. Finally, the energy of the stable model after moisture absorption is subtracted from the energy of the individual energetic molecular cluster and then from the energy of the individual water molecule to obtain the radius at 30°C and 100% relative humidity. Small particle size spherical AP and radius The interaction energies of large-size spherical AP and water molecules are: E′ interaction =E′ total -E′ water -E′ cluster =-9581.923 kcal / mol; Einteraction =E total -E water -E cluster =-4685.270 kcal / mol.

[0059] Implementation Example 6:

[0060] Step 1: Calculate the water molecule density under standard atmospheric pressure, 30°C, and 100% relative humidity to be approximately 3.036×10 -5 g / cm 3 .

[0061] Step 2: Import the cif file of the AP crystal into the Materials Studio 2019 simulation software, perform a complete structural optimization on the AP initial unit cell to make the system architecture more reasonable, and set the calculation accuracy of the structural optimization to Ultra-fine (Energy: 2×10 -5 kcal / mol,Force:0.001 ), Displacement is set to Then construct eight The AP spherical cluster is placed on the edge length In the cubic grid, the fractional coordinates of the body centers of the eight small-size spherical clusters are: (0.25, 0.25, 0.25), (0.25, 0.75, 0.25), (0.25, 0.25, 0.75), (0.25, 0.75, 0.75), (0.75, 0.25, 0.25), (0.75, 0.75, 0.25), (0.75, 0.25, 0.75), (0.75, 0.75, 0.75). The water molecule density calculated in the previous step is 3.036 × 10 -5 g / cm 3 Multiply by 200 and it is about 0.006g / cm 3 , fill the gap between the AP cluster and the cubic lattice with water molecules of this density, and obtain the radius Initial model of small particle size AP.

[0062] Step 3: Refer to step 2 to construct a radius AP spherical nanoclusters and place the AP clusters on a The cubic lattice body center position is filled with 0.006g / cm 3 The water molecules with a density of 1.37 × 10.3 ... The initial model of large-particle AP.

[0063] Step 4: The constructed AP initial models of the two particle sizes were subjected to NVT molecular dynamics simulation using the Forcite module of the Materials studio simulation software. The molecular dynamics time was set to 100ps. Finally, the last frame model after the molecular dynamics calculation was taken out and the Forcite module was used to perform structural optimization operations without optimizing the unit cell to eliminate unstable factors such as stress in the structure. The stable models m and M of the two particle sizes after moisture absorption were obtained. The calculation accuracy of the structural optimization was set to: Energy: 2×10 -5 kcal / mol,Force:0.001 Displacement is set to

[0064] Step 5: Use the atom selection function to decompose the above stable models m and M after moisture absorption, and separate the models m1 and M1 of single water molecules after moisture absorption, and the models m2 and M2 of single energetic molecular clusters. Use the Forcite module to calculate the system energy of the six models of two particle sizes, that is, the energy E′ of m1 water and the energy E of M1 water , the energy E′ of m2 cluster and the energy E of M2 cluster , the energy E′ of m total and the energy E of M total . Get the radius The energy of each system of small-size spherical AP is: E′ water =-761.534 kcal / mol, E′ cluster =-144921.348 kcal / mol, E′ total =-155644.278 kcal / mol, radius The system energies of large-size spherical AP are: E water =-1674.513 kcal / mol,E cluster =-151650.442 kcal / mol,E total = -159185.773 kcal / mol. Finally, the energy of the stable model after moisture absorption is subtracted from the energy of the individual energetic molecular cluster and then from the energy of the individual water molecule to obtain the radius at 30°C and 100% relative humidity. Small particle size spherical AP and radius The interaction energies of large-size spherical AP and water molecules are: E′ interaction =E′ total -E′ water -E′ cluster =-9961.396 kcal / mol; Einteraction =E total -E water -E cluster =-5860.818 kcal / mol.

[0065] Data Analysis:

[0066] It can be seen from Examples 1 and 2 that when the same mass of ADN is at 30° C. and 100% relative humidity, the hygroscopicity gradually increases as the particle size decreases (Table 1), and the simulation results are consistent with the actual results.

[0067] Table 1 Interaction energy between medium mass spherical ADN with different particle sizes and water molecules in Examples 1 and 2

[0068]

[0069]

[0070] It can be seen from Examples 3 and 4 that when the AN of equal mass is at 30° C. and 100% relative humidity, the hygroscopicity gradually increases as the particle size decreases (Table 2), and the simulation results are consistent with the actual results.

[0071] Table 2 Interaction energy between medium mass spherical AN with different particle sizes and water molecules in Examples 3 and 4

[0072]

[0073] It can be seen from Examples 5 and 6 that when the same mass of AP is at 30° C. and 100% relative humidity, the hygroscopicity gradually increases as the particle size decreases (Table 3), and the simulation results are consistent with the actual results.

[0074] Table 3 Interaction energy between medium mass spherical AP with different particle sizes and water molecules in Examples 5 and 6

[0075]

Claims

1. A method for evaluating the hygroscopicity of energetic materials of equal mass and different particle sizes under the same temperature and humidity conditions, characterized in that: The specific steps include: The first step is to import the standard cif file of the molecular unit cell of energetic material A into Materials Studio molecular simulation software, perform complete structural optimization on the initial unit cell, respectively construct two cluster models of energetic material A with equal mass but different particle sizes, and place the two cluster models in a larger cubic grid to make them evenly distributed, multiply water molecules with known density under certain temperature and relative humidity conditions by n times to fill the space between the cluster model and the cubic grid, and respectively construct two initial models under the same temperature and humidity conditions; The second step is to perform NVT molecular dynamics calculations on the two initial models, take out the last frame model after the molecular dynamics calculation, and use the Forcite module to perform structural optimization operations without optimizing the unit cell to eliminate the structural instability factors in the structure, and obtain the stable models m and M after moisture absorption respectively; The third step is to decompose the stable models m and M after moisture absorption respectively. From each stable model, the models m1 and M1 of single water molecules after moisture absorption, and the models m2 and M2 of single energetic molecular clusters are extracted. The system energy of these six models, i.e., the energy E′ of m1, is calculated using the Forcite module. water and the energy E of M1 water , the energy E′ of m2 cluster and the energy E of M2 cluster , the energy E′ of m total and the energy E of M total Finally, the interaction energy E′ between the energetic molecular clusters with the same mass and different particle sizes and water molecules under the same temperature and humidity conditions is obtained. interaction and E interaction By comparing the interaction energy, the hygroscopicity of energetic material A with equal mass and different particle sizes is evaluated.

2. The method according to claim 1, characterized in that In the first step, the size of the cluster model is The side length of the cube grid is 3. The method according to claim 1, characterized in that In the first step, the temperature and relative humidity conditions refer to a temperature of 0 to 100° C. and a relative humidity of 0% to 100%.

4. The method according to claim 1, characterized in that In the first step, the water molecule with known density under certain temperature and relative humidity conditions is multiplied by n times to make the density of the water molecule ≥ 0.0001 g / cm 3 Meet the modeling requirements of Materials studio molecular simulation software.

5. The method according to claim 1, characterized in that In the second step, when performing NVT molecular dynamics calculations, the dynamic parameters are set, including: the time is set to 20ps~1000ps, the Nose method is used for temperature control, the calculation accuracy of the structure optimization is greater than or equal to the default Middle accuracy of the Forcite module, and the displacement factor needs to be considered.

6. The method according to claim 1, characterized in that In the third step, E′ is determined according to the formula interaction =E′ total -E′ water -E′ cluster , E interaction =E total -E water -E cluster .

7. The method according to claim 1, characterized in that In the third step, the energy calculation accuracy is greater than or equal to the default Middle accuracy of the Forcite module of Materials studio software.

8. The method according to claim 1, characterized in that In the third step, by comparing the interaction energy E′ interaction and E interaction , the hygroscopicity of energetic material A of equal mass but different particle sizes was evaluated. The larger the absolute value of the interaction energy, the stronger its hygroscopicity.

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