Method for regulating and controlling adhesive force between molten aluminum and solid interface by changing heat transfer characteristics

Abstract

The invention relates to a method for regulating and controlling interface adhesion between molten aluminum and a solid by changing heat transfer characteristics, which comprises the following steps of: (1) respectively forming an aluminum-aluminum system and an aluminum-silicon system by taking a piece of solid aluminum as a probe and respectively taking a piece of solid silicon and a piece of solid aluminum as substrates; (2) establishing a molecular dynamics liquid-solid adhesion model composed of the probe and the substrate; (3) after the system is balanced, measuring the adhesive force between liquid and solid interfaces; (4) executing a simulation process and processing data: analyzing the energy transfer process of the liquid-solid interface, calculating the thermal conductivity of the interface in the adhesion process, and extracting a phonon spectrum of a liquid contact solid substrate at the interface, and analyzing the relationship between the heat transfer efficiency and the phonon spectrum when the adhesive force between the probe molten aluminum and the solid substrate changes under different contact interface conditions. The invention discloses a heat transfer mechanism of adhesion between liquid aluminum and a solid aluminum / silicon interface when the temperature of a solid substrate rises by combining molecular dynamics and a quantum theory.

Description

Technical Field

[0001] The present invention relates to the field of molecular dynamics technology, and in particular to a method for regulating the adhesion between aluminum liquid and a solid interface by changing heat transfer characteristics. Background Art

[0002] As a basic raw material for industrial development, aluminum is widely used in various fields such as national security, transportation, new energy, and electronic power, so the demand for aluminum has increased significantly. However, raw aluminum cannot be used directly in nature and needs to be smelted and extracted from a mixture of bauxite before it can be used. In the process of electrolytic aluminum production, molten aluminum often adheres to the inner wall of the equipment. As time goes by, the adhesion of liquid aluminum to the solid interface becomes more and more obvious, thereby reducing the productivity of the equipment and causing the quality of the produced aluminum to decline. Therefore, solving the adhesion problem of aluminum liquid-solid interface will greatly improve the output and quality of aluminum, thereby reducing energy loss.

[0003] In order to reduce the adhesion at the liquid-solid interface, some people have changed the solid surface morphology of liquid adhesion based on the hydrophobic surface existing in nature. Research on the hydrophobic properties of plants and animals includes the lotus leaf effect, rice leaves, bird cicada wings, etc. These research fields have simulated good friction reduction and viscosity reduction effects.

[0004] Some scholars have found in the course of their research that molecular dynamics can simulate the adhesion phenomenon of liquid-solid interfaces, and that the adhesion of liquid-solid interfaces is directly related to the wettability of liquids. This method has the characteristics of saving resources and high efficiency. Gao et al. established a polydimethylsiloxane-silicon dioxide model and found that in general, the better the wettability of the solid surface to the liquid, the stronger its adhesion. Liu et al. found that as the temperature of the system increases, the larger the defects on the solid surface, the greater the liquid / solid interface adhesion. Lv et al. found that the grooves on the graphite surface will hinder the diffusion of aluminum, and the adhesion will decrease when aluminum droplets are on the graphite surface. Lai used an atomic force microscope to observe the effect of substrate temperature on the adhesion between two silicon wafer surfaces at different humidity and found that the average adhesion decreases with the increase of substrate temperature. This is because high-temperature dehydroxylation leads to a decrease in the thickness of the interfacial water film, which leads to a decrease in the adhesion of the silicon / silicon interface. He et al. studied the relationship between temperature change and adhesion performance between single-layer and double-layer graphene and silicon dioxide substrates, and found that when the temperature gradually increased from 300K to 500K, due to the thermal relaxation of the interface atoms, the mismatch between graphene and the substrate lattice increased, resulting in a decrease in adhesion energy. Lai measured the trend of the adhesion between two solid surfaces as a function of temperature in a wet environment, and found that the adhesion first increased and then decreased with increasing temperature. Qing calculated the interface energy and adhesion energy of liquid Al / α-A12O3 and found that when the temperature increased from 950K to 1250K, a transition from non-wetting to wetting occurred. This is because the increase in temperature caused the evaporation of aluminum atoms and the diffusion of oxygen atoms in α-A12O3, resulting in a decrease in interface energy, which in turn caused the wettability of the Al liquid to the α-A12O3 surface to change. Cong et al. studied the wettability of aluminum liquid and silicon carbide substrate at temperatures between 973K and 1273K. The results showed that with the increase of temperature, the contact angle (CA) decreased from 125° to 57°, achieving a transition from non-wetting to wetting.

[0005] However, the wettability of liquid on the solid surface is usually related to the change of energy. The study of liquid-solid interface energy was first discovered by Kapitza when studying the liquid helium-metal interface under low temperature conditions. Later, Pollack used the acoustic mismatch model to define the liquid-solid interface thermal resistance as a function of phonon density, and Swartz et al. further regarded phonons as plane waves that can propagate or reflect on the interface. Since then, a lot of research has been done on interface thermal resistance. Kim et al. found that the interface thermal resistance is a function of surface wettability, thermal oscillation frequency, wall temperature, thermal gradient and channel; Xue et al.'s simulation study showed that the strength of the bond between liquid and solid atoms determines the interface thermal resistance, and the interface thermal resistance is exponentially dependent on the strength of the weak bond (non-wettability) between liquid and solid atoms, while the strength of the strong bond (wettability) is exponentially dependent; Kim et al. established a one-dimensional lattice vibration model for the liquid-solid interface thermal resistance, and found that the interface thermal resistance is proportional to the fourth power of the ratio of the thermal oscillation frequency of solid and liquid molecules; Ramos-Alvarado et al. found that there is no relationship between the two when studying interfacial heat transfer and wetting. The relationship between quartz and water is ubiquitous, and different phonon modes have different effects on the simulation of heat conduction between crystalline / amorphous silicon and water. Low-frequency phonons play a dominant role in heat transfer at hydrophilic interfaces, while heat transfer at hydrophobic interfaces gradually shifts to high-frequency phonons. Goicochea et al. found that heat transfer between quartz and water interfaces can be regulated by functionalizing the growth of nanopillars on the solid surface to adjust the vibration frequency of atoms on the quartz surface, and the increase in the height and density of these nanopillars will increase the thermal conductivity of the interface. Qian et al. simulated the heat transfer between imidazole liquid and graphene and found that molecular orientation (the parallelism between the imidazole ring and graphene) is a key factor in controlling heat transfer between interfaces. et al. analyzed the contribution of different vibration modes to energy transfer based on the heat flow spectrum of the liquid-solid interface. The interfacial thermal energy transfer was dominated by the surface mode at the boundary of the Brillouin zone and was polarized along the out-of-plane.

[0006] The above literature on the wettability of liquid / solid interfaces mainly focuses on the phenomena observed at high temperatures, and these studies also show that liquid / solid interface adhesion involves energy conversion. However, the heat transfer mechanism when liquid aluminum adheres to a solid substrate below the melting point of aluminum is still unclear. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for regulating the adhesion between aluminum liquid and solid interface by changing the heat transfer characteristics.

[0008] In order to solve the above problems, the present invention provides a method for regulating the adhesion between aluminum liquid and solid interface by changing the heat transfer characteristics, comprising the following steps:

[0009] (1) A piece of solid aluminum is used as a probe, and a piece of solid silicon and a piece of solid aluminum are used as substrates, respectively, to form an aluminum-aluminum system and an aluminum-silicon system; the initial states of the probe and the substrate in different systems are both solid states, and the probe always keeps the same size in different systems;

[0010] ⑵Establish a molecular dynamics liquid-solid adhesion model consisting of a probe and a substrate:

[0011] Setting periodic boundary conditions in the x-axis direction and the y-axis direction of the aluminum-aluminum system or the aluminum-silicon system, and setting a free boundary condition in the z-axis direction;

[0012] The system simulation is relaxed in a microcanonical ensemble, and the melting and adhesion state of aluminum liquid are analyzed in a canonical system. The temperature is controlled by a Berendsen thermostat.

[0013] The interaction between all aluminum atoms adopts the EAM (Embedded atomic method potential) potential; the interaction between all silicon atoms adopts the Stillinger-Weber potential;

[0014] A Lennard-Jones potential is used between the probe and the substrate;

[0015] The potential well constant ε between aluminum and silicon ij and the initial equilibrium distance σ ij It is calculated using the following geometric mean mixing formula:

[0016] and

[0017] Where: ε i is the potential well constant between aluminum atoms, in meV; ε j is the potential well constant between silicon atoms, in meV; σ i is the equilibrium distance between aluminum atoms, in nm; σ j is the equilibrium distance between silicon atoms, in nm;

[0018] ⑶ The system in the initial state is first relaxed for 100ps. When the system reaches equilibrium, the solid aluminum probe is heated to melt it. Then the completely melted molten aluminum is adhered to the solid substrate to measure the adhesion force between the liquid and solid interfaces.

[0019] ⑷Execute the simulation process and process the data:

[0020] The energy transfer process at the liquid-solid interface is analyzed, the interfacial thermal conductivity during the adhesion process is calculated, and the phonon spectrum of the liquid contacting the solid substrate at the interface is extracted. The relationship between the thermal energy transfer efficiency and the phonon spectrum when the adhesion force between the probe aluminum liquid and the solid substrate changes under different contact interface conditions is analyzed.

[0021] In the step (1), the atoms of the aluminum substrate and the silicon substrate are evenly divided into a fixed layer, a temperature adjustment layer and a Newtonian layer from bottom to top.

[0022] The specific process of executing the simulation process and processing data in step (4) is as follows:

[0023] ① Keep the atomic number of the aluminum probe unchanged, melt the probe aluminum and keep it in industrial electrolytic aluminum, use molten aluminum liquid at a temperature of 1143K, and then adhere the aluminum liquid to different solid substrates to analyze the changes in the adhesion force of the liquid-solid interface when the substrate temperature changes from 50K to 400K;

[0024] ② Analyze the relationship between the adhesion force and the liquid-solid interface contact angle under different temperature changes when aluminum liquid adheres to different solid substrates to verify the correctness of the calculation model;

[0025] ③ Analyze the interfacial energy transport during the steady-state adhesion process, obtain the interfacial thermal conductivity from the temperature change between the liquid-solid interface, and the change in the solid substrate phonon spectrum caused by the energy change, and analyze the relationship between the adhesion change of the contact interface under different states and the interfacial thermal conductivity and phonon spectrum.

[0026] The simulation process and data processing in step (4) also include: calculating the change in contact angle of the liquid-solid interface under different contact states when the temperature of different solid substrates changes from 50K to 400K, and analyzing the relationship between the change in adhesion and the change in contact angle.

[0027] The simulation process and data processing in step (4) also include: when the temperature of different solid substrates changes, the interfacial heat flow of the aluminum liquid when it is steadily adhered to the solid surface is calculated from the changes in the probe aluminum liquid temperature and the solid substrate temperature, and the rate of heat energy transfer to the substrate when the aluminum liquid adheres to different solid substrates is analyzed.

[0028] Executing the simulation process and processing data in step (4) also includes: after the solid substrate receives energy from the aluminum liquid, calculating the kinetic energy and potential energy changes of the substrate atoms, and analyzing the influence of the energy on the solid substrate.

[0029] The simulation process and data processing in step (4) also include: according to the different performances of atoms after the solid substrate absorbs energy, further analyzing the influence of thermal energy on the solid substrate atoms from the mean square deviation displacement of the solid substrate atoms, and judging whether the solid substrate atoms are in vibration mode or diffusion mode at different temperatures.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1. During the simulation process, the present invention found that when the temperature of the solid substrate rises from 50K to 400K, the adhesion force of the aluminum liquid on the solid aluminum substrate is greater than the adhesion force of the aluminum liquid on the solid silicon substrate, and the adhesion force of the aluminum liquid on the solid aluminum substrate shows a non-monotonic change of first decreasing and then increasing, while the adhesion force on the solid silicon substrate shows a monotonic decreasing trend.

[0032] 2. By measuring the static contact angle of the liquid-solid interface, the present invention finds that the contact angle between the aluminum liquid and the solid aluminum first increases and then decreases, and the contact angle between the aluminum liquid and the solid silicon gradually increases with the change of the substrate temperature, thereby proving that the smaller the contact angle, the stronger the wettability of the liquid-solid interface, and the greater the interfacial adhesion, which also proves the accuracy of the simulation model established by the present invention.

[0033] 3. In order to prove the relationship between the change in adhesion force of molten aluminum on different solid substrates and thermal conductivity, the present invention found through thermal conductivity calculation that: as the substrate temperature increases, the interfacial thermal conductivity gradually decreases, and the thermal conductivity between molten aluminum and solid aluminum is greater than the thermal conductivity between molten aluminum and solid silicon, indicating that the adhesion of molten aluminum on solid aluminum is stronger than that on solid silicon.

[0034] 4. In order to determine the impact of energy changes on substrate atoms, the present invention combines the changes in substrate atomic energy (kinetic energy and potential energy) and the mean square displacement changes of substrate atoms, and obtains that when the solid aluminum substrate adheres to the aluminum liquid at a relatively low temperature, its surface remains intact and causes the vibration of the substrate atoms by absorbing energy from the aluminum liquid; at a higher temperature, the lattice of the solid aluminum substrate atoms is destroyed and some atoms are in a diffused state; within the temperature change range of 50K to 400K, the surface of the solid silicon substrate remains intact and the atoms are always in a state of slight vibration.

[0035] 5. In order to determine the relationship between adhesion change and energy transfer, the present invention calculates the phonon spectra of silicon atoms and aluminum atoms at different substrate temperatures. The calculation results show that as the substrate temperature increases, the low-frequency phonons that dominate the thermal energy transfer decrease, resulting in a decrease in the energy received by the substrate, that is, a decrease in the interfacial adhesion; however, when the aluminum substrate is at a higher temperature, defects are generated due to lattice destruction, and the defects gradually increase with increasing temperature, which in turn leads to an increase in adhesion. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0037] Figure 1 The initial state aluminum-aluminum solid model diagram (a) and the initial state aluminum-silicon solid model diagram (b) established in the present invention are shown.

[0038] Figure 2 Schematic diagram of the solid aluminum melting process and temperature and system pressure change diagram (a), and the interfacial adhesion force of aluminum liquid adhering to solid aluminum and solid silicon substrate (b) in the present invention.

[0039] Figure 3 1 is a front view of the aluminum liquid stably adhering to the solid aluminum substrate and a front view of the aluminum liquid adhering to the solid silicon substrate in the present invention. Figure II (a) The contact angle between the aluminum liquid and the solid aluminum and solid silicon substrates (b).

[0040] Figure 4 It is the temperature of the aluminum liquid and the solid atoms in the contact layer when the aluminum liquid adheres to solid substrates at different temperatures in the present invention (a), the temperature difference between the aluminum liquid and the contact solid atoms when the aluminum liquid adheres to the surface of solid aluminum and silicon substrates (b), the rate at which the solid substrate absorbs heat energy (c), and the interface thermal conductivity between the aluminum liquid and different solid materials aluminum and silicon (d).

[0041] Figure 5 It is the kinetic energy of solid atoms when the aluminum liquid adheres to the solid aluminum substrate (a), the potential energy of solid atoms when the aluminum liquid adheres to the solid aluminum substrate (b), the kinetic energy of solid atoms when the aluminum liquid adheres to the solid silicon substrate (c), and the potential energy of solid atoms when the aluminum liquid adheres to the solid silicon substrate (d).

[0042] Figure 6 The mean square error displacement of solid atoms when the aluminum liquid adheres to solid aluminum at a temperature of 100K (a), the mean square error displacement of solid atoms when the aluminum liquid adheres to solid aluminum at a temperature of 200K (b), the mean square error displacement of solid atoms when the aluminum liquid adheres to solid aluminum at a temperature of 250K (c), the mean square error displacement of solid atoms when the aluminum liquid adheres to solid aluminum at a temperature of 350K (d), the mean square error displacement of solid atoms when the aluminum liquid adheres to solid silicon at a temperature of 100K (e), the mean square error displacement of solid atoms when the aluminum liquid adheres to solid silicon at a temperature of 200K (f), the mean square error displacement of solid atoms when the aluminum liquid adheres to solid silicon at a temperature of 250K (g), and the mean square error displacement of solid atoms when the aluminum liquid adheres to solid silicon at a temperature of 350K (h).

[0043] Figure 7The present invention shows the phonon spectrum of the atoms of the solid substrate when the aluminum liquid adheres to the solid aluminum substrate at temperatures of 100K, 150K, 200K, 300K and 400K respectively (a), the phonon spectrum of the atoms of the solid substrate when the aluminum liquid adheres to the solid silicon substrate at temperatures of 100K, 200K, 300K and 400K respectively (b), the phonon spectrum of the atoms of the solid substrate when the temperature of the solid aluminum substrate is 100K, 200K and 300K respectively when there is no aluminum liquid adhesion (c), and the phonon spectrum of the atoms of the solid substrate when the temperature of the solid silicon substrate is 100K, 200K and 300K respectively when there is no aluminum liquid adhesion (d). DETAILED DESCRIPTION

[0044] A method for regulating the adhesion between aluminum liquid and solid interface by changing heat transfer characteristics, comprising the following steps:

[0045] ⑴ A piece of solid aluminum is used as a probe, and a piece of solid silicon and a piece of solid aluminum are used as substrates to form an aluminum-aluminum system and an aluminum-silicon system respectively; the initial states of the probe and the substrate in different systems are both solid states, and the probe always maintains the same size in different systems.

[0046] Among them: the atoms of the aluminum substrate and the silicon substrate are divided into a fixed layer, a temperature adjustment layer and a Newtonian layer from bottom to top.

[0047] The temperature-adjusting layer is used to adjust the temperature of the substrate using a Berendsen thermostat during the simulation process; the Newtonian layer is used to analyze the vibration state of atoms in contact with the aluminum liquid during the whole process.

[0048] ⑵Establish a molecular dynamics liquid-solid adhesion model consisting of a probe and a substrate:

[0049] Setting periodic boundary conditions in the x-axis direction and the y-axis direction of the aluminum-aluminum system or the aluminum-silicon system, and setting a free boundary condition in the z-axis direction;

[0050] The system simulation is relaxed in a microcanonical ensemble, and the melting and adhesion state of aluminum liquid are analyzed in a canonical system. The temperature is controlled by a Berendsen thermostat.

[0051] The interaction between all aluminum atoms is based on the Embedded atomic method potential (EAM); the interaction between all silicon atoms is based on the Stillinger-Weber potential.

[0052] Lennard-Jones potential was used between the probe and the substrate;

[0053] The potential well constant ε between aluminum and silicon ij and the initial equilibrium distance σ ij It is calculated using the following geometric mean mixing formula:

[0054] and

[0055] Where: ε i is the potential well constant between aluminum atoms, in meV; ε j is the potential well constant between silicon atoms, in meV; σ i is the equilibrium distance between aluminum atoms, in nm; σ j is the equilibrium distance between silicon atoms, in nm.

[0056] ⑶ The system in the initial state is first relaxed for 100ps. When the system reaches equilibrium, the solid aluminum probe is heated to melt it; then the completely melted molten aluminum is adhered to the solid substrate to measure the adhesion force between the liquid and solid interfaces.

[0057] ⑷Execute the simulation process and process the data:

[0058] The energy transfer process at the liquid-solid interface is analyzed, the interfacial thermal conductivity during the adhesion process is calculated, and the phonon spectrum of the liquid contacting the solid substrate at the interface is extracted. The relationship between the thermal energy transfer efficiency and the phonon spectrum when the adhesion force between the probe aluminum liquid and the solid substrate changes under different contact interface conditions is analyzed.

[0059] The specific process is as follows:

[0060] ① Keep the atomic number of the aluminum probe unchanged, melt the probe aluminum and keep it in industrial electrolytic aluminum, use molten aluminum liquid at a temperature of 1143K, and then adhere the aluminum liquid to different solid substrates to analyze the changes in the adhesion force of the liquid-solid interface when the substrate temperature changes from 50K to 400K;

[0061] ② Analyze the relationship between the adhesion force and the liquid-solid interface contact angle under different temperature changes when aluminum liquid adheres to different solid substrates to verify the correctness of the calculation model;

[0062] ③ Analyze the interfacial energy transport during the steady-state adhesion process, obtain the interfacial thermal conductivity from the temperature change between the liquid-solid interface, and the change in the solid substrate phonon spectrum caused by the energy change, and analyze the relationship between the adhesion change of the contact interface under different states and the interfacial thermal conductivity and phonon spectrum.

[0063] The present invention also includes one of the following steps:

[0064] When the temperature of different solid substrates changes from 50K to 400K, the contact angle change of the liquid-solid interface under different contact states is calculated, and the relationship between the change in adhesion and the change in contact angle is analyzed.

[0065] When the temperature of different solid substrates changes, the interfacial heat flow of the aluminum liquid when it is steadily adhered to the solid surface is calculated from the changes in the probe aluminum liquid temperature and the solid substrate temperature, and the rate of heat energy transfer to the substrate when the aluminum liquid adheres to different solid substrates is analyzed.

[0066] After the solid substrate receives energy from the aluminum liquid, the kinetic energy and potential energy changes of the substrate atoms are calculated to analyze the effect of energy on the solid substrate.

[0067] According to the different performances of atoms after the solid substrate absorbs energy, the influence of thermal energy on the solid substrate atoms is further analyzed from the mean square deviation displacement of the solid substrate atoms to determine whether the solid substrate atoms are in vibration mode or diffusion mode at different temperatures.

[0068] Example

[0069] The present invention studies the change in adhesion force of aluminum liquid adhering to the aluminum / silicon surface of a low-temperature solid substrate, explores the relationship between heat transfer and adhesion force at the liquid-solid interface, and further reveals the adhesion mechanism of the liquid / solid interface from the interfacial thermal conductivity and lattice vibration state.

[0070] The specific process is as follows:

[0071] 1. Establish molecular dynamics model

[0072] Establish the initial solid-solid model as Figure 1 As shown, the model consists of probe aluminum and a solid substrate. Figure 1 (a) is the probe aluminum and solid aluminum substrate model, Figure 1 (b) is the probe aluminum and solid silicon substrate model. In different models, the probe aluminum atoms are 4224 and the size is 6.48×8.91nm. 2 The size of the aluminum substrate is 14.58×21.47nm. 2 The size of the silicon substrate is 10.86×22.67nm 2 The atoms of the aluminum substrate and the silicon substrate are divided into three parts from bottom to top: the fixed layer, the temperature adjustment layer and the Newton layer. The temperature adjustment layer is used to adjust the temperature of the substrate using the Berendsen thermostat during the simulation process, and the Newton layer is used to analyze the vibration state of the atoms in contact with the aluminum liquid during the whole process.

[0073] In order to accurately simulate the adhesion state of aluminum to different substrates, the whole process is divided into three stages, all of which are implemented in the LAMMPS software package. First, the entire solid-solid system is relaxed for 100ps in the microcanonical ensemble to allow the entire system to reach a stable state. Then, the temperature of the probe aluminum is continuously heated to 1143K in the canonical ensemble, which is the temperature of liquid aluminum in the electrolytic aluminum production process. At this time, the aluminum is completely melted and maintains this state. Finally, the completely melted liquid aluminum is adhered to the surface of the solid silicon substrate and the solid aluminum substrate, and the adhesion behavior and mechanism of the liquid aluminum / solid interface in this state are analyzed.

[0074] The simulation conditions of the whole system include periodic boundary conditions in the x and y directions and free boundary conditions in the z direction. Since the embedded potential EAM potential between metal atoms can accurately simulate the melting process of metals, the EAM potential is used between the probe and the substrate aluminum atoms. The Stillinger-Weber potential is used between silicon substrate atoms. The Lennard-Jones (LJ) potential is used between the probe aluminum atoms and the substrate atoms. The parameters between different atoms are shown in Table 1, where the parameters between aluminum atoms and silicon atoms are calculated based on the geometric mean mixed (mix geometric) formulas (1) and (2).

[0075]

[0076]

[0077] Table 1. LJ potential parameters between aluminum and aluminum, silicon and silicon, and aluminum and silicon

[0078] Atom Type ε(eV) σ(A) Al-Al 0.3928 2.62 Si-Si 0.0174 4.295 Al-Si 0.0827 3.355

[0079] 2. Analysis of solid aluminum melting process and calculation of interfacial adhesion force

[0080] according to Figure 1 To build the initial model, solid aluminum needs to be melted first. Figure 2(a) shows the changes in pressure and temperature during the entire process of melting solid aluminum. The pressure is the total force of all atomic pressures of the probe aluminum during the entire melting process, which can reflect the changes in the structure of the entire system. When the temperature rises to the melting point of aluminum at 933 K, the pressure undergoes a sudden change, that is, at this time, the solid aluminum begins to undergo severe internal deformation, resulting in a change in the pressure of the entire system. Although the temperature continues to rise to 1143 K, the total pressure of the system remains balanced, that is, all solid aluminum has now completely melted into liquid, and the increase in temperature no longer causes a phase change. This state is consistent with the melting point and complete melting state of aluminum. It should be noted that the temperature of the molten aluminum after complete melting is higher than the set value, which is not only the temperature set by the probe but also the result of the increase in the temperature of the atoms of the solid substrate in the contact area, because temperature is an indicator of the average kinetic energy of molecules. The completely molten liquid aluminum will adhere to the solid aluminum / silicon surface, so the adhesion force between the atoms at the liquid / solid interface can be calculated during the stable adhesion process.

[0081] Since the van der Waals force between the atoms at the liquid / solid interface determines the wetting effect when the liquid adheres to the solid surface, the magnitude of the adhesion force can be obtained by calculating the intermolecular force between the contacting atoms. The results are as Figure 2 (b) shows. The results show that the adhesion force of liquid aluminum adhering to the solid aluminum substrate is greater than that of liquid aluminum adhering to the solid silicon substrate. In addition, the adhesion force on the aluminum substrate shows a non-monotonic change with the change of the substrate temperature. When the substrate temperature is lower than 200 K, the interfacial adhesion force gradually decreases. When the temperature exceeds 200 K, the interfacial adhesion force increases, while the adhesion force of the silicon substrate gradually decreases with the increase of the substrate temperature.

[0082] 3. Analyze the wetting performance of the interface from the perspective of liquid-solid interface contact

[0083] When a liquid adheres to a solid, the spreading of the liquid on the solid surface is a measure of the wettability of the liquid to the surface. Usually, the liquid-solid interface contact angle (CA) measurement method is used for quantitative analysis.

[0084] According to Young's thermodynamic equation, the relationship between the contact angle of the liquid / solid interface and wettability is as follows: If CA < 90°, it is called mostly wetting, that is, hydrophilic. The definition of a hydrophobic surface is 90° < CA < 150°. If CA > 150°, it is called a superhydrophobic surface. Therefore, the CA on the liquid / solid interface can be used to characterize the wetting characteristics of the liquid on the solid surface. The smaller the CA, the stronger the wettability, the greater the extensibility of the liquid on the solid surface, and thus more intermolecular forces and stronger interfacial adhesion forces are generated.

[0085] According to the model established in the present invention, the number of atoms of the probe aluminum remains unchanged during the entire process from melting to attachment on different substrates, so that the same volume of liquid aluminum will adhere to different solid substrates, making the CA measured on different substrates comparable. Figure 3 (a) depicts the steady-state adhesion of liquid aluminum on the surfaces of solid aluminum and silicon substrates. The specific CA measured is as follows: Figure 3 (b) as shown.

[0086] The results show that the CA of liquid aluminum when it adheres to the aluminum solid surface is much smaller than the CA when it adheres to the silicon surface, that is, θ Al <θ Si Therefore, the adhesion of liquid aluminum to solid aluminum is stronger than that to silicon. Figure 2 As shown in (b), as the temperature increases, the CA of the solid silicon surface gradually increases when the liquid aluminum adheres to it, which corresponds to the decrease in adhesion. The CA on the solid aluminum surface first increases and then decreases, which is also consistent with Figure 2 This corresponds to the adhesion force in (b) which first increases and then decreases. This observation is consistent with the relationship between CA and wettability.

[0087] 4. Thermal conductivity analysis of liquid-solid contact interface

[0088] In the general wetting state, wettability is mainly affected by the change of interfacial energy when the liquid contacts the solid. In order to study the heat transfer mechanism of the adhesion behavior of liquid aluminum / solid aluminum and liquid aluminum / solid silicon interfaces, Figure 4 The heat energy transfer process was analyzed.

[0089] Figure 4 The interface temperature difference shown in (b) is given by Figure 4 The temperature of the liquid aluminum and the solid substrate shown in (a) are calculated to show that the interface temperature difference between the liquid aluminum and the solid aluminum is smaller than the interface temperature difference between the liquid aluminum and the solid silicon, that is, the solid aluminum absorbs more heat energy from the liquid aluminum than the solid silicon. Since heat energy is transferred from the liquid aluminum to the solid substrate within each time step of the adhesion process, and the Berendsen thermostat adjusts the temperature of the solid substrate to the target temperature, a function of the temperature gradient change is realized during the entire adhesion process.

[0090] The present invention further calculates the heat flow of the liquid / solid interface at different solid temperatures according to formula (3), such as Figure 4 (c) The results further prove that solid aluminum has a stronger ability to absorb heat energy than solid silicon.

[0091]

[0092] Where: J represents heat flow, unit is J / s; ΔE(t) represents the heat energy absorbed by the solid during the adhesion process, unit is J; t represents the adhesion time, unit is s.

[0093] The change of thermal energy mainly depends on the interface thermal conductivity between different materials. Therefore, the interface thermal conductivity between liquid aluminum and solid substrate is further calculated according to formula (4): Figure 4 The results show that solid aluminum absorbs more heat energy than silicon due to the greater thermal conductivity of the interface between liquid aluminum and solid aluminum.

[0094]

[0095] Where: G represents the interfacial thermal conductivity, unit MW / m 2 K; A represents the contact area between aluminum liquid and solid, unit is m 2 ; ΔT represents the temperature difference at the liquid / solid interface, unit K.

[0096] 5. Analysis of kinetic energy and potential energy of solid substrate at different temperatures

[0097] Since the temperature change of liquid aluminum and solid substrate will cause energy conversion at the liquid-solid interface, the change of kinetic energy and potential energy of the solid substrate can be obtained, such as Figure 5 The results show that as the temperature increases, the kinetic energy and potential energy of the solid aluminum substrate and the silicon substrate will increase significantly, because the energy of the solid substrate comes from the set temperature of the solid substrate and the large amount of heat energy transferred from the liquid aluminum to the solid state.

[0098] For the aluminum substrate, the kinetic energy at different temperatures shows an increasing trend, while the potential energy continues to decrease throughout the adhesion process, e.g. Figure 5 (a) and 5(b). This is because in a steady-state system, the atoms leaving the initial equilibrium position will lead to an increase in kinetic energy and a decrease in potential energy. It is worth noting that Figure 5 (b) It can be seen that when the temperature of the aluminum substrate is lower than 200K, the potential energy decreases slowly, and when the temperature is higher than 200K, the potential energy decreases sharply. The reason why the potential energy change rate of the aluminum substrate is different in the two temperature ranges may be that the atomic motion state is different due to the thermal energy of the substrate at different temperatures. When the temperature is lower than 200K, the thermal energy will cause slight vibrations of the atoms, resulting in a slight increase in the kinetic energy of the substrate atoms and a slight decrease in the potential energy. When the temperature is higher than 200K, the thermal energy will cause some atoms to vibrate violently, causing them to completely move away from their original positions, resulting in the rupture of the unit cell and a rapid decrease in the potential energy between atoms.

[0099] like Figure 5As shown in Figures 5(c) and 5(d), the kinetic energy of the silicon substrate remains stable at different temperatures, and its interatomic potential energy remains almost unchanged. This is because the temperature only causes very slight vibrations in the silicon substrate, which does not cause the atoms to move significantly from their equilibrium positions, so the kinetic energy and potential energy remain stable.

[0100] 6. Analyze the state of solid substrate at different temperatures from the mean square deviation displacement

[0101] In order to solve the above-mentioned problem of violent and mild atomic vibration, the motion state of atoms at different temperatures during the adhesion process was further calculated, that is, the mean square displacement (MSD) was used to represent the position change of the substrate atoms. The stable state of MSD represents the vibration state of the atoms, and the rapid and rapid changes indicate that the atoms are in a diffusion state, such as Figure 6 The results show that as the temperature increases, solid aluminum is sensitive to temperature changes, the displacement changes greatly, and the MSD curve changes suddenly when the temperature is higher than 200K, as shown in Figure 6 (a) to (d). This shows that when the temperature is below 200K, the aluminum substrate is in an active vibration state and the substrate unit cell is intact. When the temperature is above 200K, the atoms of the aluminum substrate first experience a period of vibration, and then suddenly increase the atomic diffusion in both the in-plane (X and Y) and out-of-plane (Z) directions, resulting in the destruction of the substrate. Figure 5 As shown in (a) and 5(b), in the vibration state, the kinetic energy increases slowly and the potential energy decreases gradually, while in the diffusion state, the kinetic energy and its amplitude increase rapidly and the potential energy decreases rapidly. Unlike the aluminum substrate, the displacement of the solid silicon substrate changes very little when the substrate temperature increases. Therefore, the solid silicon substrate always maintains a small vibration at different temperatures, and its kinetic energy and potential energy will change slightly during the adhesion process, such as Figure 5 (c) and 5(d). Therefore, it is reasonable that thermal energy can induce different vibrations of the substrate at different substrate temperatures.

[0102] 7. Analyze the thermal energy changes of solid substrates at different temperatures from phonon spectra

[0103] according to Figure 6 It can be seen that the substrate atoms produce lattice vibrations under the influence of thermal energy, and the lattice vibrations between atoms excite the energy carrier - phonons. Because the energy transfer in the heat transfer process of the non-superhydrophobic interface is mainly dominated by low-frequency phonons, the phonon spectra (DOS) of the aluminum substrate and the silicon substrate in the adhesion state are further calculated, as shown in Figure 2. Figure 7 (a) and Figure 7 (b) The results show that as the substrate temperature increases, the phonon spectrum decreases at low frequencies, whether in the vibrational state or the diffusion state, that is, the number of low-frequency phonons excited on the substrate atoms decreases, resulting in a decrease in the heat energy transferred to the solid and a decrease in the interfacial thermal conductivity, as shown in Figure 4 (d) as shown.

[0104] In order to confirm that the change of vibration frequency at different substrate temperatures is caused by the adhesion of aluminum liquid, the phonon spectrum of solid substrate atoms without aluminum liquid adhesion is also calculated, such as Figure 7 (c) and 7(d). Figure 7 (c) and 7(d) show that DOS does not change significantly when the temperature of the substrate changes, which proves that the energy of DOS change is the heat energy transferred from liquid aluminum to the solid substrate. It can be seen that: in the vibration state, the adhesion decreases due to the decrease in interface thermal conductivity; however, in the atomic diffusion state, although the interface thermal conductivity decreases, the lattice rupture is equivalent to the generation of defects on the solid surface, and the increase in defects will lead to an increase in adhesion.

[0105] In summary, the present invention combines molecular dynamics and quantum theory to reveal the heat transfer mechanism of adhesion between liquid aluminum and solid aluminum / silicon interface when the temperature of the solid substrate increases. The results show that as the temperature of the solid substrate increases, the adhesion of the liquid aluminum / aluminum interface decreases first and then increases, while the adhesion strength of the liquid aluminum / silicon interface shows a monotonically decreasing trend. The changes in atomic energy and mean square displacement show that the aluminum substrate remains intact at temperatures below 200K, and lattice destruction occurs when the temperature is higher than 200K; while the silicon substrate remains intact throughout the entire temperature range of the experiment. Phonon spectrum analysis shows that in the state of complete lattice vibration, as the solid temperature increases, the excited low-frequency phonons decrease, resulting in a decrease in interfacial thermal conductivity, thereby reducing adhesion. Although phonon excitation decreases in the diffusion state of lattice destruction, the interfacial adhesion increases due to the generation of surface defects.

[0106] The technical solution provided by the present invention is described in detail above. Specific examples are used herein to illustrate the principle and implementation of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be pointed out that for ordinary technicians in this field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for regulating the adhesion between aluminum liquid and solid interface by changing the heat transfer characteristics, comprising the following steps: (1) A piece of solid aluminum is used as a probe, and a piece of solid silicon and a piece of solid aluminum are used as substrates to form an aluminum-aluminum system and an aluminum-silicon system respectively; The initial states of the probe and the substrate in different systems are both solid, and the probe always maintains a constant size in different systems; ⑵Establish a molecular dynamics liquid-solid adhesion model consisting of a probe and a substrate: Setting periodic boundary conditions in the x-axis direction and the y-axis direction of the aluminum-aluminum system or the aluminum-silicon system, and setting a free boundary condition in the z-axis direction; The system simulation is relaxed in a microcanonical ensemble, and the melting and adhesion state of aluminum liquid are analyzed in a canonical system. The temperature is controlled by a Berendsen thermostat. The EAM potential is used for the interaction between all aluminum atoms; the Stillinger-Weber potential is used for the interaction between all silicon atoms; A Lennard-Jones potential is used between the probe and the substrate; The potential well constant ε between aluminum and silicon ij and the initial equilibrium distance σ ij It is calculated using the following geometric mean mixing formula: and Where: ε i is the potential well constant between aluminum atoms, in meV; ε j is the potential well constant between silicon atoms, in meV; σ i is the equilibrium distance between aluminum atoms, in nm; σ j is the equilibrium distance between silicon atoms, in nm; ⑶ The system in the initial state is first relaxed for 100ps. When the system reaches equilibrium, the solid aluminum probe is heated to melt it. Then the completely melted molten aluminum is adhered to the solid substrate to measure the adhesion force between the liquid and solid interfaces. ⑷Execute the simulation process and process the data: The energy transfer process at the liquid-solid interface is analyzed, the interfacial thermal conductivity during the adhesion process is calculated, and the phonon spectrum of the liquid contacting the solid substrate at the interface is extracted. The relationship between the thermal energy transfer efficiency and the phonon spectrum when the adhesion force between the probe aluminum liquid and the solid substrate changes under different contact interface conditions is analyzed.

2. A method for regulating the adhesion between aluminum liquid and solid interface by changing heat transfer characteristics as claimed in claim 1, characterized in that: In the step (1), the atoms of the aluminum substrate and the silicon substrate are evenly divided into a fixed layer, a temperature adjustment layer and a Newtonian layer from bottom to top.

3. The method for regulating the adhesion between aluminum liquid and solid interface by changing the heat transfer characteristics as claimed in claim 1, characterized in that: The specific process of executing the simulation process and processing data in step (4) is as follows: ① Keep the atomic number of the aluminum probe unchanged, melt the probe aluminum and keep it in industrial electrolytic aluminum, use molten aluminum liquid at a temperature of 1143K, and then adhere the aluminum liquid to different solid substrates to analyze the changes in the adhesion force of the liquid-solid interface when the substrate temperature changes from 50K to 400K; ② Analyze the relationship between the adhesion force and the liquid-solid interface contact angle under different temperature changes when aluminum liquid adheres to different solid substrates to verify the correctness of the calculation model; ③ Analyze the interfacial energy transport during the steady-state adhesion process, obtain the interfacial thermal conductivity from the temperature change between the liquid-solid interface, and the change in the solid substrate phonon spectrum caused by the energy change, and analyze the relationship between the adhesion change of the contact interface under different states and the interfacial thermal conductivity and phonon spectrum.

4. The method for regulating the adhesion between aluminum liquid and solid interface by changing the heat transfer characteristics as claimed in claim 1, characterized in that: The simulation process and data processing in step (4) also include: calculating the change in contact angle of the liquid-solid interface under different contact states when the temperature of different solid substrates changes from 50K to 400K, and analyzing the relationship between the change in adhesion and the change in contact angle.

5. The method for regulating the adhesion between aluminum liquid and solid interface by changing the heat transfer characteristics as claimed in claim 1, characterized in that: The simulation process and data processing in step (4) also include: when the temperature of different solid substrates changes, the interfacial heat flow of the aluminum liquid when it is steadily adhered to the solid surface is calculated from the changes in the probe aluminum liquid temperature and the solid substrate temperature, and the rate of heat energy transfer to the substrate when the aluminum liquid adheres to different solid substrates is analyzed.

6. The method for regulating the adhesion between aluminum liquid and solid interface by changing the heat transfer characteristics as claimed in claim 1, characterized in that: Executing the simulation process and processing data in step (4) also includes: after the solid substrate receives energy from the aluminum liquid, calculating the kinetic energy and potential energy changes of the substrate atoms, and analyzing the influence of the energy on the solid substrate.

7. The method for regulating the adhesion between aluminum liquid and solid interface by changing the heat transfer characteristics as claimed in claim 1, characterized in that: The simulation process and data processing in step (4) also include: according to the different performances of atoms after the solid substrate absorbs energy, further analyzing the influence of thermal energy on the solid substrate atoms from the mean square deviation displacement of the solid substrate atoms, and judging whether the solid substrate atoms are in vibration mode or diffusion mode at different temperatures.

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