A design method for efficient activation of kaolin based on molecular dynamics theory

Abstract

The application discloses a design method for efficient activation of kaolin based on a molecular dynamics theory, which comprises a molecular dynamics model construction, a calculation simulation and a design optimization. The application discloses a calcination activation mechanism of kaolin from a molecular scale by means of molecular dynamics calculation, simulates the activation process and activation effect of kaolin under different calcination conditions with temperature, pressure and water content as variables, quantifies the nano-micro structure, energy and kinetic characteristics of the kaolin system under different activation conditions, and thus proposes optimal activation condition parameters, thereby providing theoretical guidance for efficient activation design of kaolin.

Description

Technical Field

[0001] This invention relates to a method for activating kaolin, an auxiliary cementing material, and more particularly to a design method for efficient activation of kaolin based on molecular dynamics theory, belonging to the field of building materials. Background Technology

[0002] Cement is the binder and strength source of modern concrete, and a fundamental material for civil engineering construction. However, the decomposition of calcium carbonate and coal combustion during cement production emit large amounts of CO2, with approximately 860 kg of carbon dioxide per ton of cement clinker. In recent years, the cement industry both domestically and internationally has made good progress in reducing fuel and production energy consumption, but the potential for further energy conservation and emission reduction through simply upgrading processes and equipment is limited. Replacing cement with highly active auxiliary cementitious materials is one of the effective means to reduce the carbon emissions of cement-based materials. Furthermore, with the rapid development of industry, large amounts of aluminosilicate solid waste such as fly ash, slag, and coal gangue occupy significant land resources and severely pollute the environment, urgently requiring development and reuse. Therefore, preparing highly active aluminosilicate auxiliary cementitious materials through calcination and activation treatment of solid waste is an essential path to achieving sustainable development of civil engineering materials.

[0003] Kaolin is a major mineral component of bulk solid wastes such as coal gangue. It has a typical layered structure, with layers bonded by hydrogen bonds and exhibiting asymmetric effects that further strengthen the interlayer bonding, making its structure exceptionally stable. Therefore, its stable crystal structure must be disrupted to an amorphous state to increase its chemical reactivity, thus enabling it to become a raw material for synthesizing new substances. Calcination is the primary method for enhancing the chemical activity of kaolin. Calcination activation at appropriate temperatures produces highly active metakaolin, which has great potential as a novel auxiliary cementing material in practical engineering applications. However, calcination conditions and time significantly influence the activation of kaolin. Too low a calcination temperature fails to disrupt the kaolin's crystal structure, while too high a temperature causes a phase transformation, generating less active mullite, aluminosilicate spinel, etc. Therefore, there are optimal reaction conditions for the calcination activation process of kaolin. Currently, domestic and international scholars have conducted extensive research on the calcination process and application performance of kaolin, but research on the calcination activation mechanism of kaolin remains lacking. Therefore, simulating the calcination and activation process and mechanism of kaolin at the molecular scale and exploring the influence of calcination conditions on its activation characteristics, thereby guiding the design of efficient calcination and activation of kaolin, is of great research significance. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a high-efficiency activation design method for kaolin based on molecular dynamics theory, which solves the problems of unclear activation mechanism of kaolin calcination and lack of high-efficiency activation design methods.

[0005] Technical solution: The present invention provides a method for the efficient activation design of kaolin based on molecular dynamics theory, comprising the following steps:

[0006] (1) Establish a molecular dynamics model of kaolin, given a preset ambient temperature, calculation time step, and set the outer edge of the overall molecular model as a periodic boundary condition, and fully relax the model under the NVT ensemble to form a stable molecular structure.

[0007] (2) Apply a force field to each atom in the molecular dynamics model established in step (1);

[0008] (3) When the molecular dynamics model reaches equilibrium, activation simulation is performed by setting different temperature and pressure conditions under the NPT ensemble.

[0009] (4) After running under the NPT ensemble, the NVT ensemble is used for relaxation, and the Verlet algorithm is used to obtain the coordinate trajectories of each atom in the molecular dynamics model.

[0010] (5) Based on the coordinate trajectories of each atom in the molecular dynamics model obtained in step (4), calculate the Q of each silicon-oxygen tetrahedron according to the definition. n The distribution is used to calculate the degree of decoupling, n. d , where Q n express 29 The chemical environment in which Si exists, and n represents the number of bridging oxygen atoms contained in the silicon-oxygen tetrahedron [SiO4].

[0011] Furthermore, in step (5), n = 0, 1, 2, 3, 4.

[0012] Furthermore, in step (1), the molecular dynamics model is a model established based on classical molecular dynamics of Newtonian classical mechanics.

[0013] Furthermore, in step (1), the Nose-Hoover isothermal calculation method is used to ensure the stability of the molecular dynamics model during the simulation process.

[0014] Furthermore, in step (1), water molecules are added to the molecular dynamics model to change the water content of the model.

[0015] Furthermore, in step (1), the water content of the molecular dynamics model of kaolin is 0% to 40%.

[0016] Furthermore, in step (2), the force field takes the form shown in equation (1):

[0017] E total = E bond + E angle + E torsion+ E over + E vdWaals + E Coulomb (1)

[0018] In the formula, E total E represents the total potential energy of the molecular dynamics model. bond E represents the bond stretching potential energy. angle E represents the potential energy of bond angle bending. torsion E represents the dihedral torsional potential energy. over E represents the penalty energy for avoiding overcoordination. vdWaals E represents the van der Waals force. Coulomb Represents Coulomb electrostatic potential energy;

[0019] Furthermore, in step (2), the parameters of the force field are extracted from the ReaxFF reaction force field.

[0020] Furthermore, in step (2), after applying a force field to each atom within the molecular dynamics model, simulation calculations are performed on LAMMPS. The Verlet algorithm is used to calculate the position of each atom at the next moment, with the long-range force cutoff radius being... The time step is set to 0.25fs.

[0021] Furthermore, in step (3), the temperature is 900–1300 K and the pressure is 1–100 atm.

[0022] Furthermore, in step (5), the degree of depolymerization n is calculated according to equation (2). d :

[0023]

[0024] In the formula, n d χ(Q) represents the degree of depolymerization. n ) for statistics Q n The relative content of.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0026] This invention includes molecular dynamics model construction, computational simulation, and design optimization. Through molecular dynamics calculations, the calcination activation mechanism of kaolin can be revealed at the molecular scale. The effects of calcination conditions on the activation characteristics of kaolin are investigated using variables such as temperature, pressure, and moisture content. The nano- and micro-structures, energy, and kinetic properties of the kaolin system under different activation conditions are quantified, compensating for the limitations of experimental methods in molecular-scale characterization. The obtained data can provide a basis for kaolin activation design and have guiding significance for the efficient calcination activation and practical engineering applications of kaolin. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the molecular dynamics model of kaolinite;

[0028] Figure 2 The degree of depolymerization is the degree of depolymerization of the kaolin structure system obtained in Examples 2-10. Detailed Implementation

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0030] Example 1

[0031] This invention discloses a highly efficient activation design method for kaolin based on molecular dynamics theory, comprising the following steps:

[0032] (1) A molecular dynamics model of kaolinite was established based on classical molecular dynamics of Newtonian classical mechanics. Given a preset ambient temperature, calculation time step, and the outer edge of the overall molecular model set as periodic boundary conditions, the molecular dynamics model was fully relaxed under the canonical (NVT) ensemble to form a stable molecular structure. The Nose-Hoover isothermal calculation method was used to ensure the stability of the molecular dynamics model during the simulation. The water content of the model was changed by adding water molecules to the molecular dynamics model, so that the water content of the molecular dynamics model of kaolinite was 0% to 40%.

[0033] (2) Apply a force field to each atom in the molecular dynamics model established above. The parameters of the force field are extracted from the ReaxFF reaction force field, and the form of the force field is shown in Equation (1):

[0034] E total = E bond + E angle + E torsion + E over + E vdWaals + E Coulomb (1)

[0035] In the formula, E total E represents the total potential energy of the molecular dynamics model. bond E represents the bond stretching potential energy. angle E represents the potential energy of bond angle bending. torsion E represents the dihedral torsional potential energy. over E represents the penalty energy for avoiding overcoordination. vdWaals E represents the van der Waals force. Coulomb Represents Coulomb electrostatic potential energy;

[0036] After applying force fields to each atom, simulations were performed on LAMMPS. The Verlet algorithm was used to calculate the position of each atom at the next time step within the molecular dynamics model, with the long-range force cutoff radius being [missing information]. The time step is set to 0.25 fs;

[0037] (3) When the molecular dynamics model reaches equilibrium, activation simulation is performed under different temperature and pressure conditions in the isobaric and isothermal (NPT) ensemble; the temperature range is 900-1300K and the pressure range is 1-100atm.

[0038] (4) After running under the NPT ensemble, the NVT ensemble is used for relaxation, and the Verlet algorithm is used to obtain the atomic motion coordinate trajectory.

[0039] (5) Based on the coordinate trajectories of each atom in the molecular dynamics model, the Q of each silicon-oxygen tetrahedron is calculated according to the definition. n The distribution, and the degree of decoupling n are calculated according to equation (2). d :

[0040]

[0041] In the formula, n d χ(Q) represents the degree of depolymerization. n ) for statistics Q n The relative content, Q n express 29 The chemical environment in which Si exists, where n represents the number of bridging oxygen atoms contained in the silicon-oxygen tetrahedron [SiO4], n = 0, 1, 2, 3, 4.

[0042] Wherein, the degree of decoupling n d The larger the value, the greater the structural activity. In practical kaolin activation, the degree of depolymerization n can be used. d The largest possible progress.

[0043] Example 2 uses the method of Example 1 of the present invention for actual simulation calculation.

[0044] (1) When performing actual simulation calculations using the method of Example 1 of this invention, a molecular dynamics model of kaolinite is first established based on classical molecular dynamics of Newtonian mechanics. The initial kaolinite model is directly downloaded from an open crystallography database. After cell expansion and full relaxation under the NVT ensemble, a stable structure is obtained. The resulting molecular dynamics model of kaolinite is as follows: Figure 1 As shown, the space group is designated P1, and the crystallographic parameters of the model are: α = 91.76°, β = 105.10°, γ = 89.84°. The unit cell contains 32 aluminum-oxygen octahedra, 32 silicon-oxygen tetrahedra, and 64 hydroxyl groups. The water content of the molecular dynamics model was changed to 0% by adding water molecules to the model, as shown in Table 2. The atomic coordinates of the established molecular dynamics model of kaolin are shown in Table 1.

[0045] Table 1. Atomic coordinates of the molecular dynamics model of kaolin.

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053] (2) After establishing the molecular dynamics model, a force field was applied to each atom, and simulation calculations were performed on LAMMPS. The Verlet algorithm was used to calculate the position of the atom at the next time step, with the long-range force cutoff radius being [missing information]. The time step was set to 0.25 fs. The parameters of the force field were extracted from the ReaxFF reaction force field, and the form of the force field is shown in equation (1):

[0054] E total = E bond + E angle + E torsion + E over + E vdWaals + E Coulomb (1)

[0055] In the formula, E total E represents the total potential energy of the molecular dynamics model. bond E represents the bond stretching potential energy. angle E represents the potential energy of bond angle bending. torsion E represents the dihedral torsional potential energy. over E represents the penalty energy for avoiding overcoordination. vdWaals E represents the van der Waals force. Coulomb This represents the Coulomb electrostatic potential energy; the initial velocity of each atom is randomly generated based on the initial temperature.

[0056] (3) The simulation process consists of three steps: First, the initial temperature of the molecular dynamics model is set to 300K and the pressure to one atmosphere. Periodic boundaries are set in the X, Y, and Z directions. The Nose-Hoover isothermal calculation method is used to run the model under a canonical (NVT) ensemble for 100 ps. Then, when the molecular dynamics model reaches equilibrium, it is run under a preset isobaric isothermal (NPT) ensemble for 100 ps. The temperature regulation damping coefficient T-damp is set to 25 fs and the pressure regulation damping coefficient P-damp is set to 250 fs. Finally, the model is run under the NVT ensemble for another 100 ps. The temperature range of the NPT ensemble is 900–1300K and the pressure range is 1–100 atm. In this embodiment, the set temperature is 900K and the pressure is 10 atm.

[0057] (4) During the simulation, the NVT ensemble is used for relaxation, and the Verlet algorithm is used to obtain the coordinate trajectories of each atom in the molecular dynamics model. The thermodynamic parameters such as temperature and pressure, as well as the size of the box, are output once every 1ps, and the coordinates of all atoms in the molecular dynamics model are output once.

[0058] (6) Based on the coordinate trajectories of the atoms within the molecular dynamics model, the Q of each silicon-oxygen tetrahedron is calculated according to the definition. n The distribution, the degree of decohesion n is calculated according to formula (2). d :

[0059]

[0060] In the formula, n d χ(Q) represents the degree of depolymerization. n ) for statistics Q n The relative content of.

[0061] To further investigate the effects of different activation conditions on the calcination activation characteristics of kaolin, Examples 3-10 were set up. The experimental procedures were the same as in Example 2, with the molecular dynamics model set to a water content of 0%, 20%, or 40%, a temperature of 900K, 1100K, or 1300K, and a pressure of 10 atm, 50 atm, or 100 atm (see Table 2 for details). Orthogonal experiments were designed and simulations were performed to obtain the depolymerization degree n in each example. d The relationship between temperature, pressure, and moisture content is shown in Table 2 and... Figure 2 As shown.

[0062] Table 2 Degree of depolymerization of kaolin structural system

[0063]

[0064]

[0065] From Table 2 and Figure 2 It can be seen that the degree of depolymerization of the model varies under different calcination simulation conditions. The greater the degree of depolymerization, the higher the activity of the kaolin structure system. Among them, Example 5 has the highest degree of depolymerization, reaching 3.61, when the water content is 20%, the temperature is 1100K, and the pressure is 100atm.

Claims

1. A highly efficient activation design method for kaolin based on molecular dynamics theory, characterized in that, Includes the following steps: (1) Establish a molecular dynamics model of kaolin, given a preset ambient temperature, calculation time step, and set the outer edge of the overall molecular model as a periodic boundary condition. Under the NVT ensemble, fully relax the model to form a stable molecular structure. Change the water content of the model by adding water molecules to the molecular dynamics model. (2) Apply a force field to each atom in the molecular dynamics model established in step (1); the form of the force field is shown in equation (1): E total = E bond + E angle + E torsion + E over + E vdWaals + E Coulomb （1） In the formula, E total This represents the total potential energy of the molecular dynamics model. E bond This represents the bond stretching potential energy. E angle This represents the potential energy of the bond angle bending. E torsion This represents the dihedral torsional potential energy. E over This indicates the penalty energy for avoiding overcoordination. E vdWaals This represents the van der Waals force. E Coulomb Represents Coulomb electrostatic potential energy; (3) When the molecular dynamics model reaches equilibrium, activation simulation is performed by setting different temperature and pressure conditions under the NPT ensemble; (4) After running under the NPT ensemble, the NVT ensemble is used for relaxation, and the Verlet algorithm is used to obtain the coordinate trajectories of each atom in the molecular dynamics model; (5) Based on the coordinate trajectories of each atom in the molecular dynamics model obtained in step (4), calculate the Q of each silicon-oxygen tetrahedron according to the definition. n The distribution, the degree of decohesion n is calculated according to equation (2). d : n d = （2） Among them, Q n express 29 The chemical environment in which Si exists, n d For the degree of depolymerization, c(Q) n ) for statistics Q n The relative content of n, where n represents the number of bridging oxygens contained in the silicon-oxygen tetrahedron [SiO4].

2. The efficient activation design method for kaolin based on molecular dynamics theory according to claim 1, characterized in that, In step (1), the molecular dynamics model is a model established based on classical molecular dynamics of Newtonian classical mechanics.

3. The efficient activation design method for kaolin based on molecular dynamics theory according to claim 1, characterized in that, In step (1), the Nose-Hoover isothermal calculation method is used to ensure the stability of the molecular dynamics model during the simulation.

4. The efficient activation design method for kaolin based on molecular dynamics theory according to claim 1, characterized in that, In step (1), the water content of the molecular dynamics model of kaolin is 0%~40%.

5. The efficient activation design method for kaolin based on molecular dynamics theory according to claim 1, characterized in that, In step (2), the parameters of the force field are extracted from the ReaxFF reaction force field.

6. The efficient activation design method for kaolin based on molecular dynamics theory according to claim 1, characterized in that, In step (2), after applying a force field to each atom in the molecular dynamics model, simulation calculations are performed on LAMMPS. The Verlet algorithm is used to calculate the position of each atom at the next moment. The long-range force cutoff radius is 10 Å, and the time step is set to 0.25fs.

7. The efficient activation design method for kaolin based on molecular dynamics theory according to claim 1, characterized in that, In step (3), the temperature is 900 ~ 1300 K and the pressure is 1 ~ 100 atm.

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