A method for studying early dissolution behavior of tricalcium silicate based on temperature-rising accelerated molecular dynamics simulation

Abstract

The application belongs to the technical field of cement hydration, and discloses a method for researching early dissolution behavior of tricalcium silicate based on temperature acceleration molecular dynamics simulation. The method comprises the following steps: 1) simulation system construction: obtaining the crystal structure of tricalcium silicate C3S, selecting the C3S(010) crystal surface as the reaction surface, and constructing the simulation system in which the C3S(010) crystal surface contacts with water molecules; the simulation system is operated under the periodic boundary condition; the ReaxFF reaction force field and the conjugate gradient algorithm are used for energy minimization; the NVT ensemble is selected during the simulation; 2) dynamic relaxation; 3) temperature acceleration simulation; 4) dissolution rate and hydroxylation analysis; 5) surface structure evolution and chemical bond analysis; and 6) mechanism analysis. The method improves the research efficiency, reveals the dynamic behavior of early dissolution of C3S and the double electric layer formation mechanism from the atomic scale, and provides a theoretical basis for understanding the cement hydration process.

Description

Technical Field

[0001] This invention belongs to the technical field of cement hydration, specifically relating to a method for studying the early dissolution behavior of tricalcium silicate (C3S) using accelerated molecular dynamics simulations with increased temperature. Background Technology

[0002] Tricalcium silicate (C3S) is a major mineral phase in cement clinker, and its hydration reaction plays a decisive role in the early strength development and microstructure formation of cement. The initial dissolution behavior of tricalcium silicate (C3S) during hydration involves complex ion releases (such as Ca2+). 2+ OH - and SiO4 4- The microscopic mechanisms underlying C3S dissolution, including interfacial reactions, are not yet fully elucidated. Traditional experimental methods (such as thermogravimetric analysis and scanning electron microscopy) are insufficient for directly observing dynamic processes at the atomic scale, while conventional molecular dynamics simulations, limited by time scales (typically nanoseconds), struggle to capture key phenomena in actual hydration processes (such as the formation of the induction phase). Therefore, developing a method to accelerate the C3S dissolution process and reveal its microscopic mechanisms is of great significance. Summary of the Invention

[0003] To overcome the shortcomings and deficiencies of existing technologies, the purpose of this invention is to provide a method for studying the early dissolution behavior of C3S based on accelerated molecular dynamics simulations using temperature increase. This invention significantly accelerates the dissolution process of C3S by increasing the simulation temperature to 1300K, and reveals its dissolution mechanism and the reason for the slowed rate during the induction phase. The method of this invention is particularly suitable for atomic-scale studies of the C3S dissolution mechanism during cement hydration.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A method for studying the early dissolution behavior of tricalcium silicate C3S based on accelerated molecular dynamics simulations with heating includes the following steps:

[0006] 1) Simulation System Construction: The crystal structure of tricalcium silicate (C3S) was obtained, and the C3S(010) crystal plane was selected as the reaction plane to construct a simulation system in which the C3S(010) crystal plane of tricalcium silicate comes into contact with water molecules. The simulation system was run under periodic boundary conditions. The ReaxFF reactive force field was used to describe the interaction between C3S and water molecules, and the conjugate gradient algorithm was used for energy minimization. The simulation system in which the C3S(010) crystal plane of tricalcium silicate comes into contact with water molecules was constructed using MaterialsStudio software.

[0007] 2) Dynamic relaxation

[0008] (2-1) Molecular dynamics relaxation was performed at an NVT set at a temperature of 300K to optimize water molecules for 1 ns, where the C3S model was fixed;

[0009] (2-2) At a temperature of 300K, a molecular dynamics simulation of 1ns was performed under the NVT set to relax the C3S model, in which water molecules were fixed.

[0010] (2-3) Subsequently, a 1ns molecular dynamics simulation was performed at an NVT set at a temperature of 300K to relax the entire combined system, in which neither C3S nor water molecules were fixed.

[0011] 3) Accelerated simulation by heating: In LAMMPS software, the simulation temperature was set to 1300K, and molecular dynamics simulation was performed for 10ns using the NVT ensemble. During the simulation, the temperature was controlled by the Nose-Hoover thermostat. The dynamics of the atoms in the system were described by the classical Newton equation, which was solved using the velocity-Verlet integral algorithm.

[0012] 4) Dissolution rate and hydroxylation analysis: MD simulations were performed at 1300K for 10 ns to calculate the dissolution rate of Ca and Si and the degree of surface hydroxylation.

[0013] 5) Surface structure evolution and chemical bonding analysis: Observe the evolution of C3S surface structure at high temperature, analyze the formation of Ca-Ow and Si-Ow bonds and the water molecule permeation behavior; Ow represents oxygen in water;

[0014] 6) Double layer formation mechanism: The number of Ca and Si atoms adsorbed on the C3S surface was calculated and compared with the number of dissolved Ca and Si atoms. The analysis was carried out in combination with Ca-Ow and H-Os bonds, Si-Os bonds and Si-Ow bonds; Ow represents oxygen in water and Os represents oxygen in C3S.

[0015] Step 1) Specific steps: Obtain the crystal structure of tricalcium silicate C3S, select the C3S(010) crystal plane as the reaction plane, and construct the tricalcium silicate C3S model using Materials Studio software; construct the water molecule model; construct the cubic box of the C3S(010) crystal plane system, and use the PACKMOL package to put water molecules into the vacuum region of the cubic box to obtain the simulation system of tricalcium silicate C3S(010) crystal plane in contact with water molecules. The simulation system has periodic boundary conditions.

[0016] Water molecules introduced into a vacuum region have a density of 1 g / cm³. -3 The size of the simulation system is...

[0017] The ReaxFF reactive force field was used, and the simulation time step was 0.5 fs.

[0018] When using the conjugate gradient algorithm for energy minimization, the cutoff tolerance for energy and force is 1.0 × 10⁻⁶. - 5 kcal / mol.

[0019] Molecular dynamics simulations were all performed using the Large Scale Atom / Molecular Parallel Simulator (LAMMPS) software package. Atomic coordinates, velocities, and energy data of the system were recorded every 0.5 ps.

[0020] Classical Newton's equations:

[0021] v i =v0+a i t;

[0022]

[0023] Among them, a i m i Let v0 and v be the particle's acceleration and mass, respectively. i These are the initial velocity and the velocity of the particle after time t, respectively, r0 and r i These represent the initial position of the particle and its position after time t, respectively.

[0024] Solving using the velocity-Verlet integral algorithm:

[0025]

[0026] In the formula, r(t+δt) is the position of the particle at time δt after time t, r(t) is the position of the particle at time t; v(t) is the velocity of the particle at time t, a(t) is the acceleration of the particle at time t, and δt is the time step.

[0027] The dissolution rate is obtained by calculating the amount of Ca and Si dissolved using LAMMPS, and then converting the result to obtain the average dissolution rate.

[0028] The formula for calculating the degree of hydroxylation is as follows:

[0029] Where, N Ca-Ow To calculate the number of Ca-Ow bonds, N Ca These are the total Ca sites on the C3S surface;

[0030] The beneficial effects of this invention are:

[0031] This invention, based on molecular dynamics simulations, accelerates the simulation by increasing the temperature, converting the 10 ns simulation time into an actual hydration time on the order of milliseconds, significantly improving research efficiency. Furthermore, it reveals the kinetics of early C3S dissolution and the double-layer formation mechanism at the atomic scale, providing a theoretical basis for understanding the cement hydration process. The results of this method can provide theoretical support for optimizing cement paste properties and developing novel cement materials. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a simulated system where a C3S(010) crystal plane is in contact with water molecules; the green spheres represent calcium atoms, the yellow spheres represent silicon atoms, the red spheres / rods represent oxygen atoms, and the white rods represent hydrogen atoms.

[0033] Figure 2 This is a schematic diagram showing the change in the amount of Ca and Si dissolved at 1300K over time.

[0034] Figure 3 This is a schematic diagram showing the change in the degree of hydroxylation on the C3S surface over time at 1300K.

[0035] Figure 4 This is a schematic diagram of the formation of the electric double layer on the C3S surface; water: water, C3S particle: C3S crystal. Detailed Implementation

[0036] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the implementation of the present invention is not limited thereto.

[0037] Example 1

[0038] (1) Simulation System Construction: A simulation system of C3S(010) crystal plane in contact with water molecules was constructed using Materials Studio. The C3S crystal structure was obtained from a crystallography database, and the C3S(010) crystal plane was selected as the reaction plane. The unit cell parameters of C3S were... α = 90°, β = 116.31°, γ = 90°. The triaxial coordinate system was converted to orthogonal coordinates, and the unit cell C3S was expanded. The dimensions of the expanded C3S model are as follows: α = 90°, β = 90°, γ = 90°. Water molecules are randomly placed in this vacuum region (referring to the vacuum region of a cubic box containing C3S crystals) using PACKMOL packages, and the density is 1 g / cm³. -3 .like Figure 1 As shown, the size of the simulated box is set to... The system was run under periodic boundary conditions (periodic boundary conditions applied along three orthogonal directions). The ReaxFF reactive force field was used to describe the interaction between C3S and water molecules. The simulation time step was set to 0.5 fs to ensure simulation accuracy. Energy minimization was performed using the conjugate gradient algorithm to eliminate unreasonable contacts and stresses in the initial configuration; the cutoff tolerances for energy and force were 1.0 × 10⁻⁶. - 5 kcal / mol. The NVT ensemble was used throughout the simulation to ensure that the number of atoms, volume, and temperature of the simulated system remained constant.

[0039] In the Large Scale Atomic / Molecular Massive Parallel Simulator (LAMMPS) software, molecular dynamics relaxation was performed under an NVT ensemble at 300 K to optimize the water molecule for 1 ns, with the C3S model fixed. Then, at 300 K, another 1 ns molecular dynamics simulation was performed under the NVT ensemble to relax the C3S model, with the water molecule fixed. Subsequently, a further 1 ns molecular dynamics simulation was performed under the NVT ensemble to relax the entire combined system, with neither C3S nor the water molecule fixed.

[0040] (2) Accelerated Simulation with Heating: The simulation temperature was set to 1300 K in the Large-Scale Atom / Molecular Parallel Simulator (LAMMPS) software. Molecular dynamics simulations were performed using the NVT ensemble for 10 ns. The temperature was controlled by a Nose-Hoover thermostat during the simulation. The atomic dynamics in the system were described by classical Newton's equations, which were solved using the velocity-Verlet integral algorithm. All molecular dynamics simulations were implemented using the LAMMPS software package. Atomic coordinates, velocities, and energy data of the system were recorded every 0.5 ps.

[0041] Classical Newton's equations:

[0042] v i =v0+a i t;

[0043]

[0044] Among them, a i m i Let v0 and v be the particle's acceleration and mass, respectively. i These are the initial velocity and the velocity of the particle after time t, respectively, r0 and r i These represent the initial position of the particle and its position after time t, respectively.

[0045] Solving using the velocity-Verlet integral algorithm:

[0046]

[0047] In the formula, r(t+δt) is the position of the particle at time δt after time t, r(t) is the position of the particle at time t; v(t) is the velocity of the particle at time t, a(t) is the acceleration of the particle at time t, and δt is the time step.

[0048] (3) Dissolution rate and hydroxylation analysis: The dissolution rates of Ca and Si and the degree of surface hydroxylation were recorded and compared with the dissolution rate of C3S(010) crystal surface at room temperature (~28 μmol·m⁻¹). 2 ·s) -1 Comparison. In this embodiment, the amount of Ca and Si dissolved was calculated using LAMMPS, and the dissolution rate is shown in Table 1.

[0049] Table 1. Dissolution Amount and Dissolution Rate of Ca and Si

[0050]

[0051] Depend on Figure 2 It can be seen that the dissolution rate of Ca atoms on the C3S(010) crystal plane reaches 2.65 × 10⁻⁶. 8 μmol·(m 2 ·s) -1 It is 9.46 × 10 at room temperature. 6 This represents a 6-order-of-magnitude improvement; the dissolution rate of Si atoms reached 4.60 × 10⁻⁶. 7 μmol·(m 2 ·s) -1 It is 1.64 × 10⁻⁶ at room temperature. 6 The dissolution rates of Ca and Si atoms increased by six orders of magnitude, respectively. When the reaction temperature in the molecular dynamics simulation was 1300 K, a 10 ns C3S crystal dissolution reaction was simulated using molecular dynamics. Compared with the dissolution rate of the C3S(010) crystal face at room temperature, the dissolution rates of Ca and Si atoms increased by six orders of magnitude, equivalent to an actual hydration time of approximately milliseconds at room temperature. The degree of hydroxylation is defined as the ratio of the number of Ca-Ow bonds to the total number of Ca sites on the C3S surface (Ow represents oxygen in water, and Os represents oxygen in C3S). A higher degree of hydroxylation indicates a higher degree of C3S hydration.

[0052] The formula for calculating the degree of hydroxylation is:

[0053] Where, N Ca-Ow To calculate the number of Ca-Ow bonds, N Ca The total Ca sites on the C3S surface (referring to the (010) crystal plane).

[0054] Depend on Figure 3 It can be seen that the degree of hydroxylation reaches 2130%.

[0055] (4) Surface structure evolution and chemical bonding analysis: The evolution of the C3S surface structure was output using LAMMPS. H and Ow atoms in water molecules can penetrate approximately [missing information - likely referring to a specific molecular structure or component]. The changes in the number of Ca-Os, Ca-Ow, Si-Os, Si-Ow, H-Os, and H-Ow bonds were statistically analyzed. After a 10 ns molecular dynamics simulation, approximately 1100 Ca-Os bonds and 150 Si-Os bonds were reduced. Ca-Ow and Si-Ow bonds increased with a similar trend, with approximately 1070 Ca-Ow bonds and 150 Si-Ow bonds. Si gradually detached from the C3S surface to form silanol groups (such as H3SiO4). - H2SiO4 2- or HSiO4 3- ).

[0056] (5) Double layer formation mechanism: A surface region (referring to the (010) crystal plane) was defined on the C3S surface. The number of Ca and Si atoms in this region was calculated and defined as adsorbed Ca and Si atoms. In the range of 8–10 ns, the number of adsorbed Ca atoms and dissolved Ca atoms showed similar trends and their changes were consistent (approximately 30). The number of adsorbed Si atoms and dissolved Si atoms showed similar trends and their changes were consistent (approximately 10). When Ca… 2+ When the ratio of silanol groups to silicon groups is approximately 3, the silanol groups dissolved from the C3S crystal adsorb onto the C3S crystal surface, forming a silicon-rich layer. At this point, the C3S solid surface exhibits a negative potential, attracting positively charged Ca atoms. 2+ Ca 2+ Adsorbed on the surface of the silicon-rich layer, it forms an electrical double layer, thereby reducing the C3S dissolution rate, such as... Figure 4 As shown.

[0057] Figure 1 This is a schematic diagram of a simulated system where a C3S(010) crystal plane is in contact with water molecules; the green spheres represent calcium atoms, the yellow spheres represent silicon atoms, the red spheres / rods represent oxygen atoms, and the white rods represent hydrogen atoms.

[0058] Figure 2 This is a schematic diagram showing the change in the amount of Ca and Si dissolved at 1300K over time.

[0059] Figure 3 This is a schematic diagram showing the change in the degree of hydroxylation on the C3S surface over time at 1300K.

[0060] Figure 4 This is a schematic diagram of the formation of the electric double layer on the C3S surface.

[0061] This invention uses Materials Studio software to set initial conditions (C3S model, water molecule model, etc.), set force field parameters and minimize energy, establish a simulation system of C3S(010) crystal plane in contact with water molecules, write an in file, import it into LAMMPS software for simulation (kinetic relaxation and temperature acceleration simulation). If an error occurs, adjustments are made according to the error message. If no error occurs, the results are output, the output file is obtained and analyzed, the model is verified, certain fixed / unchanging data are examined, if reasonable, it is summarized and analyzed (e.g., dissolution rate and hydroxylation analysis, surface structure evolution and chemical bonding analysis, double layer formation mechanism), if unreasonable, the simulation system is adjusted.

[0062] The embodiments of this invention aim to provide a method for studying the early dissolution behavior of C3S based on accelerated molecular dynamics simulations using temperature rise. The feasibility and advantages of this method are demonstrated through specific simulation parameters, data analysis, and results. However, the scope of protection of this invention is not limited to the specific implementation methods described in the above embodiments. Any technical solution based on the core idea of ​​this invention, including but not limited to the following situations, should be considered within the scope of protection of this invention: those skilled in the art can adjust the simulation temperature, time step, force field parameters, etc., according to actual needs to adapt to different research objectives or material systems. The method of this invention is not only applicable to the study of the early dissolution behavior of C3S, but can also be extended to the study of the hydration processes of other cement minerals (such as C2S, C3A) or similar materials.

Claims

1. A method for studying the early dissolution behavior of tricalcium silicate based on accelerated molecular dynamics simulation with heating, characterized in that: Includes the following steps: 1) Simulation system construction: The crystal structure of tricalcium silicate (C3S) was obtained, and the C3S(010) crystal plane was selected as the reaction plane to construct a simulation system in contact with water molecules. The simulation system was run under periodic boundary conditions. The ReaxFF reactive force field was used to describe the interaction between C3S and water molecules, and the conjugate gradient algorithm was used for energy minimization. The NVT ensemble was used throughout the simulation. 2) Dynamic relaxation (2-1) Molecular dynamics relaxation was performed at an NVT set at a temperature of 300K to optimize water molecules for 1 ns, where the C3S model was fixed; (2-2) At a temperature of 300K, a molecular dynamics simulation of 1ns was performed under the NVT set to relax the C3S model, in which water molecules were fixed. (2-3) Subsequently, a 1ns molecular dynamics simulation was performed at an NVT set at a temperature of 300K to relax the entire combined system, in which neither C3S nor water molecules were fixed. 3) Accelerated simulation by heating: In LAMMPS software, the simulation temperature was set to 1300K, and molecular dynamics simulation was performed for 10ns using the NVT ensemble. During the simulation, the temperature was controlled by the Nose-Hoover thermostat. The dynamics of the atoms in the system were described by the classical Newton equation, which was solved using the velocity-Verlet integral algorithm. 4) Dissolution rate and hydroxylation analysis: MD simulations were performed at 1300K for 10 ns to calculate the dissolution rate of Ca and Si and the degree of surface hydroxylation. 5) Surface structure evolution and chemical bonding analysis: Observe the evolution of C3S surface structure at high temperature, analyze the formation of Ca-Ow and Si-Ow bonds and the water molecule permeation behavior; Ow represents oxygen in water; 6) Mechanism analysis: The number of Ca and Si atoms adsorbed on the C3S surface was calculated and compared with the number of dissolved Ca and Si atoms. The double layer mechanism was obtained by combining the analysis of Ca-Ow and H-Os bonds, Si-Os bonds and Si-Ow bonds. Ow represents oxygen in water and Os represents oxygen in C3S.

2. The method for studying the early dissolution behavior of tricalcium silicate based on accelerated molecular dynamics simulation with heating according to claim 1, characterized in that: Step 1) Specific steps: Obtain the crystal structure of tricalcium silicate C3S, select the C3S(010) crystal plane as the reaction plane, and construct the tricalcium silicate C3S model using Materials Studio software; construct the water molecule model; construct the cubic box of the C3S(010) crystal plane system, and use the PACKMOL package to put water molecules into the vacuum region of the cubic box to obtain the simulation system of tricalcium silicate C3S(010) crystal plane in contact with water molecules. The simulation system has periodic boundary conditions applied along three orthogonal directions.

3. The method for studying the early dissolution behavior of tricalcium silicate based on accelerated molecular dynamics simulation with heating, as described in claim 2, is characterized in that: Water molecules introduced into a vacuum region have a density of 1 g / cm³. -3 ; The unit cell parameters of C3S are α = 90°, β = 116.31°, γ = 90°; the triaxial coordinates were converted to orthogonal coordinates, and the unit cell C3S was expanded. The dimensions of the expanded C3S model are as follows: α=90°, β=90°, γ=90°; The size of the simulation system is 4. The method for studying the early dissolution behavior of tricalcium silicate based on accelerated molecular dynamics simulation by heating according to claim 1, characterized in that: The ReaxFF reactive force field was used, and the simulation time step was 0.5 fs; When using the conjugate gradient algorithm for energy minimization, the cutoff tolerance for energy and force is 1.0 × 10⁻⁶. -5 kcal / mol.

5. The method for studying the early dissolution behavior of tricalcium silicate based on accelerated molecular dynamics simulation with heating according to claim 1, characterized in that: The dynamic relaxation in step 2) was performed using the LAMMPS software, a large-scale atomic / molecular parallel simulator.

6. The method for studying the early dissolution behavior of tricalcium silicate based on accelerated molecular dynamics simulation by heating according to claim 1, characterized in that: The classical Newton equations: v i =v0+a i t; Among them, a i m i Let v0 and v be the particle's acceleration and mass, respectively. i These are the initial velocity and the velocity of the particle after time t, respectively, r0 and r i These represent the initial position of the particle and its position after time t, respectively. Solving using the velocity-Verlet integral algorithm: In the formula, i(t+δt) is the position of the particle at time δt after time t, r(t) is the position of the particle at time t; v(t) is the velocity of the particle at time t, a(t) is the acceleration of the particle at time t, and δt is the time step.

7. The method for studying the early dissolution behavior of tricalcium silicate based on accelerated molecular dynamics simulation with heating according to claim 1, characterized in that: Formula for calculating the degree of hydroxylation: Where, N Ca-Ow To calculate the number of Ca-Ow bonds, N Ca These are the total Ca sites on the C3S surface; The higher the degree of hydroxylation, the higher the degree of C3S hydration; In step 6), after C3S dissolves, when Ca... 2+ When the ratio of silanol groups is 2.6–3.4, silanol groups dissolved from the C3S crystal adsorb onto the C3S crystal surface to form a silicon-rich layer. At this time, the C3S solid surface has a negative potential, attracting positively charged Ca... 2+ Ca 2+ Adsorbed on the surface of the silicon-rich layer, it forms an electric double layer mechanism, which leads to a decrease in the C3S dissolution rate.

8. The method for studying the early dissolution behavior of tricalcium silicate based on accelerated molecular dynamics simulation with heating according to claim 1, characterized in that: Adjust the temperature, simulation temperature, time step, and force field parameters of the dynamic relaxation in steps 2) to 4) to adapt to different research objectives or material systems; The tricalcium silicate C3S is replaced with C2S and C3A cement minerals.

9. The method for studying the early dissolution behavior of tricalcium silicate based on accelerated molecular dynamics simulation with heating, as described in any one of claims 1 to 8, is characterized in that: The method described above is used to study cement hydration.

10. The method for studying the early dissolution behavior of tricalcium silicate based on accelerated molecular dynamics simulation with heating according to claim 9, characterized in that: The study of cement hydration refers to the study of the early dissolution behavior of C3S and the reasons for the slowdown in the induction period during the cement hydration process; or the study of the hydration process of C2S and C3A cement minerals.

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