First Principles and Experimental Study on the Atomic Formation of MnS–Al₂SiO₅ Inclusions in Steel

Abstract

The complex inclusions of Al₂O₃–SiO₂ is a common inclusion in the steel, which leads to the stress concentration in the steel products. The formation of MnS on the surface of Al₂O₃–SiO₂ could reduce the stress concentration due to the high plasticity of the MnS. In this study, the formation of MnS–Al₂SiO₅ complex inclusions is investigated at the atomic level by using first principles calculation based on the density functional theory (DFT). The adsorption energy of the atoms of Mn and S on the Al₂SiO₅ (110) surface was calculated with various initial positions and sequence. The interaction among the atoms was calculated to analyze the stable structures after the adsorption of the Mn and S on the Al₂SiO₅ (110) surface. The formation of the MnS on the surface of Al₂SiO₅ was proved by analyze the structure formed by the adsorbed atoms that shows the similar tetracyclic structure of the MnS crystal.

1. Introduction

The oxygen converter is one the most important steelmaking processes in the world at present.¹⁾ The Al–Si composite alloy is one of the most common alloys as the deoxidizing agent in the industrial process, which generates a large amount of complex inclusions of Al₂O₃–SiO₂ in the molten steel. On the other aspect, the manganese is an indispensable element in the steel, which improves the mechanical properties and hardenability of steel. Beside the Mn dissolved in the steel, the Mn combines with residual S element to form MnS inclusion in steel during solidification and cooling.²⁾

Most of the oxide and silicate inclusions in steel are brittle, which break the continuity of steel matrix and lead to the stress concentration and crack under loading.^3,4) It was reported that the oxide inclusions can act as the heteronucleation points during the precipitation of MnS in the solidification and cooling process of the steel, which would form the complex inclusion of MnS–Al₂O₃–SiO₂.⁵⁾ The complex inclusion could reduce the stress concentration between the oxide inclusions and the steel matrix because the sulfide is wrapped on the surface of oxide, which could prevent the crack propagation on the oxide and improve the fracture toughness of the steel.⁶⁾ Wu et al. reported that the microcracks were largely reduced around the complex inclusions of Al₂O₃–MnS than the Al₂O₃.⁷⁾ The MnS around the Al₂O₃ inclusions could largely reduce the stress concentration around the inclusions, due to the high plasticity of the MnS. Therefore, it is necessary to make effort to understand the formation process and control morphological characteristics of complex inclusions in order to improve the properties of steel.⁸⁾

Many researchers have studied the precipitation of complex inclusions. Ohta et al. calculated the mismatch between MnS and oxidized inclusions containing ZrO₂, Al₂O₃, MgO, and MnO–SiO₂ particles through deoxidation experiments to investigate the effect of deoxidation particles on the precipitation of MnS.⁹⁾ The results indicated that the MnS precipitated on ZrO₂ or Al₂O₃ particles in the final solidification region. Li et al. investigated the precipitation mechanism of MnS on Al₂O₃–SiO₂ inclusions with different size and composition during solidification of non-oriented silicon steel and concluded that MnS tends to nucleate on the submicron Al₂O₃–SiO₂ inclusions, in which Al₂SiO₅ is a perfect nucleation site for MnS.¹⁰⁾ Di et al. investigated the effect of Al₂O₃–SiO₂ on the precipitation behavior of MnS by calculating the mismatch of the lattice and the nucleation work between various oxide inclusions with different components and the MnS inclusions found that Al₂O₃–SiO₂ is the core of MnS partially or encapsulated precipitation.¹¹⁾ The early theoretical studies on Al₂SiO₅ reported three types of polymorphs, including kyanite, andalusite, and sillimanite. The crystallographic data of Al₂SiO₅ and MnS shows the Al₂SiO₅ crystal system is orthorhombic,¹²⁾ which is matching to the crystal system of andalusite. The (110) plane is selected as the cleavage planes,¹³⁾ which is the low exponential plane with the lowest surface energy.

However, most of the current studies on complex inclusions in steel focused on the influence of chemical composition on the morphology and composition of complex inclusions, and there was few report on the formation process of complex inclusions at the atomic level. In recent years, the first principles calculation based on the density functional theory (DFT) has been widely used to investigate the adsorption and segregation of atoms on surfaces and interfaces of various materials.^14,15,16) Cheng et al. clarified the effect of titanium, zirconium and aluminum oxides on the ferrite formation in steel matrix by experiments and first principles calculations.¹⁷⁾ Cai et al. calculated the adsorption energy of fluorine on MgAl₂O₄ and N-doped MgAl₂O₄ on basis of the first principles theory.¹⁸⁾ The interface between α-Fe and precipitated MnS inclusions was investigated by calculating the interfacial energy, the work of adhesion and the electronic structure.¹⁹⁾ Therefore, first principles calculation based on DFT has been proved to be a powerful, reliable, and economical method to investigate the adsorption behaviors of the atom on the surface or interface, which was widely applied to investigate the formation of the interface between various materials at the atomic level.

In this study, the complex inclusion of Al₂SiO₅–MnS in steel was observed by the scanning electron microscope and energy dispersive spectrometer (SEM-EDS). The adsorption behavior of MnS on Al₂SiO₅ inclusions was studied by the first principles calculations. The adsorption energy of the atomic formation of MnS–Al₂SiO₅ inclusion with various paths was calculated and analyzed assisted by the discussion of the characteristics of charge of the atoms in the MnS–Al₂SiO₅ inclusion.

2. Experimental

The chemical composition of the experimental steel samples is listed in Table 1. The sample was prepared by the industrial iron mixed with a proper amount of ferromanganese and silicon, which was melt in a corundum crucible with φ30 × 100 mm in the induction furnace with blowing argon. The aluminum pellets were added into the molten steel at 1400°C and the temperature was kept for 3 minutes. The ferrous sulfide was added to adjust the content of the S in the steel. The melt was kept for 10 minutes and cooled to the room temperature. The sample was machined by the electro-spark wire-electrode cutting into a cubic sample with size of 10 × 5 × 10 mm, which was used for observation by the SEM-EDS.

Table 1. Chemical composition of the experimental steel samples (wt%).

C	S	Si	Mn	Cr	Al
0.046	0.011	0.30	0.720	0.210	0.07

3. Computational Methods

The adsorption behavior of MnS on the Al₂SiO₅ (110) surface is discussed from the perspective of atoms in the form of Mn and S, which is divided into two steps. Firstly, the optimum adsorption sites of Mn atom or S atom on the Al₂SiO₅ (110) surface is determined by calculating the adsorption energy of Mn atom or S atom released from different positions to find the structures with the most stable positions for Mn and S respectively. Then, based on the stable structure determined in the first step, the adsorption of the coming S atom or Mn atom is calculated by comparing the adsorption energy of the adsorption. Thus, the most stable formation path of MnS on Al₂SiO₅ (110) is obtained based on the analysis of the adsorption energy of the Mn and S atoms released from various initial positions.

The calculation based on the first principles of DFT and performed by the CASTEP code²⁰⁾ under plane wave basis set.^21,22) The exchange correlation energy and correlation effects²³⁾ were described by generalized gradient approximation (GGA) using the Perdew-Burke-Ernzerhof (PBE) function.²⁴⁾ Spin polarization was considered in all calculation. Ultrasoft pseudopotentials (USPP) was employed to describe the electron-ion interactions.²⁵⁾ The energy cutoff for the plane wave basis was set at 489.8 eV in the current work. For the Brillouin zone sampling, we carried out 3 × 4 × 4 k-points mesh for Al₂SiO₅ bulk using the method of Monkhorst-Pack.²⁶⁾ The crystal structure of Al₂SiO₅ is orthorhombic with shown in Fig. 1, whose space group is pnnm. A vacuum layer of 15.0 Å is added above the top surface of Al₂SiO₅ to eliminate the interaction of the normal periodic repetition of the surfaces. The surface energy calculations is the current work were performed using the p (1 × 1) slab structures. In all the surface calculations, the use of symmetry in bulk crystal was failed and k-point grids is set to 4 × 2 × 1. A stable Al₂SiO₅ (110) surface is obtained by calculate its surface energy with increasing number of layers. The three layers of atoms at the bottom of the structure of Al₂SiO₅ is fixed to act as the bulk base, while the other atoms are relaxed during the adsorption process of the Mn and S atoms.

Fig. 1.

Crystal structure of Al₂SiO₅. (Al-Pink, O-Red, Si-Yellow). (Online version in color.)

4. Results and Discussions

4.1. SEM Observation Inclusions in Steel

The inclusions in the samples were observed by SEM-EDS. Figure 2 shows the SEM image and EDS analysis of a typical complex inclusion of MnS–Al₂SiO₅ with clear interfaces between the phases of A and B. It seems both the MnS and Al₂SiO₅ are detected in the EDS since the electron beam penetrated the thin MnS layer and reach the Al₂SiO₅ phase. However, in the field of the steel making, the MnS and Al₂SiO₅ are quite common inclusion particles in the steel. Thus, it is reasonable to consider that the MnS is mainly distributed on the outer layer of the oxide inclusions and the core of the complex inclusions is Al₂SiO₅ according to the observation results of the SEM-EDS.

Fig. 2.

SEM image of a typical inclusion and EDS analysis. (Online version in color.)

4.2. Surface Energy of the Slab

The plane (1 1 0) in a single crystal of Al₂SiO₅ was selected as the basal cleavage plane. The surface is established by splitting the bulk phase materials along a crystal plane. The surface energy is the energy required to split bulk phase crystals. For a non-polar surface, the surface energy σ is calculated by using the following Eq. (1),²⁷⁾   

$$\sigma =(E_{slab}-n{E}_{bulk})/2A$$(1)

where, E_slab is the total energy of the modelled slab, n is the number of the bulk unit cell in the slab, E_bulk is the total energy of a bulk unit cell, and A is the surface area of the slab. Figure 3 shows the surface energy of Al₂SiO₅ (1 1 0) surface with a structure containing 1, 3, 5 and 7 layers. As the number of atomic layers increases, the surface energy increases rapidly and then tends to be stable. Therefore, a slab of Al₂SiO₅ with seven layers is sufficient to simulate the stable bulk phase and the surface (1 1 0) for the adsorption of the atoms of Mn and S.

Fig. 3.

Surface energy of slab of Al₂SiO₅ (1 1 0) with increasing layers. (Online version in color.)

4.3. First Step Adsorption of S or Mn

On the Al₂SiO₅ (1 1 0) surface, totally eight positions shown in Fig. 4 are considered as the initial sites for the adsorption process of the Mn and S atoms. An atom of Mn or S is released in a position relatively close to the top layer of the surface as shown in Fig. 4. The stable positions of Mn and S atoms changes to a certain extent comparing with their initial positions after structural optimization to achieve the most stable structures, which are shown in Figs. 5 and 6. The optimal structures with the adsorbed Mn or S atoms were determined by calculating the adsorption energy of the atoms, which is the energy generated in the adsorption process and calculated by the following Equation,   

$$E_{ads}=E_{(Mn/S)/A{l}_{2}Si{O}_5(1\hspace{0.17em}1\hspace{0.17em}0)}-E_{(Mn/S)}-E_{A{l}_{2}Si{O}_5(1\hspace{0.17em}1\hspace{0.17em}0)}$$(2)

where, $E_{(Mn/S)/A{l}_{2}Si{O}_5(1\hspace{0.17em}1\hspace{0.17em}0)}$ is the total energy of the adsorbate/substrate system involving a single Mn or S atom adsorbing on Al₂SiO₅ (1 1 0) slab, and E_(Mn/S) is the energy of an isolated Mn or S atom as the adsorbate before adsorption, and $E_{A{l}_{2}Si{O}_5(1\hspace{0.17em}1\hspace{0.17em}0)}$ is the energy of Al₂SiO₅ (1 1 0) slab as the substrate. The calculated adsorption energy of Mn or S atoms from different initial positions on the Al₂SiO₅ (1 1 0) surface is shown in Table 2. The adsorption energy calculated in Table 2 are compared and discussed below as the relative values. Thus, the influence of the Fe atoms surrounding the Mn and S atoms are not considered for the reference states of E_(Mn/S) in Eq. (2) above.

Fig. 4.

Schematic diagram of the initial positions of the atoms (Top view, Al-Pink, O-Red, Si-Yellow, gray- initial positions). (Online version in color.)

Fig. 5.

Optimized structure with the final position of Mn atom (Top view, Al-Pink, O-Red, Si-Yellow, Mn-Purple). (Online version in color.)

Fig. 6.

Optimized structure with the final position of S atom (Top view, Al-Pink, O-Red, Si-Yellow, S-Blue). (Online version in color.)

Table 2. Adsorption energy of Mn or S released from different initial positions (eV).

Initial positions	T1	T1’	T2	T2’	T3	B1	B2	H
Mn	−6.867	−3.744	−4.257	−3.233	−6.098	−5.958	−4.689	−5.673
S	−4.140	−3.490	−4.245	−3.804	−4.516	−5.643	−5.961	−4.423

It is obviously that the adsorption energy of all the cases are negative, whose absolute values reflect the strength of interaction between the adsorbed atoms and the substance on both sides of the interface. For the Mn atom, the absolute value of the adsorption energy is the maximum when its initial position is at T1 comparing with those at other positions. Similarly, the S atom could achieve the most stable position when it is released from the B2 on the Al₂SiO₅ (1 1 0) surface. Figures 7(a), 7(b), 7(e), and 7(f) compare the positions of Mn atoms on the Al₂SiO₅ (1 1 0) surface released from T1 before and after adsorption. The Mn atom is initially located right above the O atom with a distance of 2.0 Å and angle among the atoms of the Mn–O–Al is 68.487 degrees as shown in Figs. 7(a) and 7(b), from the top and side view respectively. After structural optimization, the stable position of Mn atom is slightly away from the left top of the O atom with a distance of 2.329 Å and the angle among the atoms of the Mn–O–Al is 71.666 degrees, as shown in Figs. 7(e) and 7(f). The S atom is released from the middle of Si–O bridge on the Al₂SiO₅ (1 1 0) surface as its initial position of the adsorption, which is shown in Figs. 7(c) and 7(d), which deviates largely from its initial position and moves to the O–O bridge after adsorption, as shown in Figs. 7(g) and 7(h). It is clear that the charge accumulation between Mn–O and S–O atoms illustrates the intersection and the transformation of the electrons between the atoms, which indicates the Mn atom is more likely to be attracted by the surrounding O atoms comparing the S atom as shown in Fig. 8. Furthermore, the Mn atom is more liable to be adsorbed on the surface of the Al₂SiO₅ comparing with the S atom, which is corresponding to the Mn-depleted zone around the oxide inclusions to induce the acicular ferrite reported in previous studies.²⁸⁾

Fig. 7.

The positions of Mn or S atoms on the surface of Al₂SiO₅ (1 1 0) before and after adsorption. (a) and (c) Top view of the initial positions of Mn or S atoms, (b) and (d) Side view of the initial positions of Mn or S atoms, (e) and (g) Top view of the stable positions of Mn or S atom after adsorption, (f) and (h) Side view of the stable positions of Mn or S atom after adsorption (Al-Pink, O-Red, Si-Yellow, Mn-Purple, S-Blue). (Online version in color.)

Fig. 8.

The charge density distribution of Mn and S atoms adsorbed on Al₂SiO₅ (1 1 0) surface. (a) and (c) Adsorption of Mn released from T1 position, (b) and (d) Adsorption of S released from B2 position (O-Red, Mn-Purple, S-Blue). (Online version in color.)

4.4. Second Step Adsorption of S or Mn Atom

The second step is the adsorption of the S or Mn atoms on the stable structure of Mn–Al₂SiO₅ and S–Al₂SiO₅ respectively, which were obtained in the first step. An atom of S or Mn is released from various initial positions listed in Table 3 on the stable structure of Mn–Al₂SiO₅ and S–Al₂SiO₅ respectively. The calculated adsorption energy of the S and Mn atoms with various initial positions is listed in Table 3. It is apparent that the adsorption energy of the coming S atom is the minimum with the initial position at S1 on the surface of the Al₂SiO₅–Mn to achieve a most stable structure, in which the S atoms derives from their initial positions after structural optimization. Figures 9(a), 9(b), 9(e), and 9(f) compare the initial positions of the S and that in the most stable structures after adsorption. The S atom is initially located right above the Al atom with a distance of 2.150 Å, whose distance from Mn atom is 1.377 Å as shown in Figs. 9(a) and 9(b), from the top and side view respectively. After structural optimization, the S atom moves to a stable position above the Al atom with a distance of 4.288 Å and the distance to the Mn atom increased to 2.046 Å that is approximately corresponding the length of the bond between S and Mn in the MnS as shown in Figs. 9(e) and 9(f). The adsorption energy of Mn atoms is the minimum when its initial position is located at S2 on the surface of the S–Al₂SiO₅ structure according to the Table 3. The variation of the positions of Mn atoms on the surface of Al₂SiO₅–S before and after adsorption are compared in Figs. 9(c), 9(d), 9(g), and 9(h). The Mn atom is initially located right above the O atom with a distance of 1.254 Å as shown in Figs. 9(c) and 9(d). After structural optimization, the stable position of Mn atom is away from the right top of the O atom with a distance of 2.022 Å from the atoms to achieve the most stable structure, as shown in Figs. 9(g) and 9(h). The distance between Mn atom and S atom is 3.372 Å after structural optimization, which seems quite large comparing the length of the bond of Mn–S in the normal MnS crystal. Thus, the Mn atom is probably interacts with the S atom in the neighboring cell in the periodical system. Figure 10 illustrates the locations of Mn and S atoms in the periodical repetition with two neighboring cells, in which the distance between the Mn and the S in the neighboring cell is 2.288 Å that is about to match the length of the bond between Mn–S in the normal MnS lattice.

Table 3. Adsorption energy of second step at different sites (eV).

Initial sites of the second step	Top of Al (S1)	Top of O (S2)	Top of Si (S3)	Top of Mn (S4)	Top of S (S5)
Al2SiO5–Mn (A)	−4.699	−3.274	−4.270	−4.545	–
Al2SiO5–S (B)	−3.494	−4.116	−3.418	–	−1.006

Fig. 9.

The positions of Mn and S atoms on the surface of Al₂SiO₅ (1 1 0) before and after adsorption. (a) and (c) Top view of the initially positions S or Mn atom in the cases of A-S1 or B-S2, (b) and (d) Side view of the initially positions S or Mn atom in the cases of A-S1 or B-S2, (e) and (g) Top view of the stable position of Mn and S atom after adsorption, (f) and (h) Side view of the stable position of Mn and S atom after adsorption (Al-Pink, O-Red, Si-Yellow, Mn-Purple, S-Blue). (Online version in color.)

Fig. 10.

The positions of Mn and S atoms on the surface of Al₂SiO₅ (1 1 0) before and after adsorption with p (2 × 1) slab structure. (a) Top view of the Mn atom initially in the case of B-S2, (b) The stable position of Mn atom after structural optimization (Al-Pink, O-Red, Si-Yellow, Mn-Purple, S-Blue). (Online version in color.)

The density of states (DOS), partial density of states (PDOS), and charge density difference (CDD) of the Mn and S atoms adsorbed on the Al₂SiO₅ (1 1 0) surface are analyzed in Fig. 11 to further understand the bonding mechanism among the atoms with the basal slab. The DOS reflects the distribution of electrons in each orbit of the atoms that reflecting the interaction between the atoms, which reveals the information of the chemical bond among the atoms. The spin polarization of the system is not apparent, thus only the diagram with spin upward density is shown in Figs. 11(a) and 11(b), in which the fermi level is set to zero. It is apparent that, by comparing the DOS and the PDOS, the p orbital of O, Al and Si atoms are the component sources of valence bands, which describes the structure of Al₂SiO₅. The d orbital of Mn atom and the p orbital of O and S atoms are hybridized in the range of −5 to 0 eV, indicating the formation of covalent bond between Mn–O and Mn–S in the case of A–S1 shown in Fig. 11(a). While the interaction between Mn–S are more apparent than that between Mn–O in the case B-S2 shown Fig. 11(b) due to the different adsorption order of the atoms comparing with the case of A-S1.

Fig. 11.

Density of states (DOS) and the partial density of state (PDOS) of the system. (a) Case A-S1 (b) Case B-S2. (Online version in color.)

Figure 12 shows the CDD of the Mn and S atoms adsorbed on Al₂SiO₅ (110) surface obtained by different adsorption sequences, which illustrates the difference between the bonded charge density and the atomic charge density at the corresponding point. The red region around the atom represents gaining electrons, while the blue region represents losing electrons. The charge accumulation between the atoms of Mn, O, and S are quite obviously, which indicates that the Mn, O, and S atoms form chemical bonds with the atoms on the Al₂SiO₅ (110) surface. The accumulated charge between Mn and O atoms collects in the middle of the bond, which is a covalent bond, forming a shielding strengthening of the two nuclei, which will reduce the repulsion between the nuclei and help reduce the total energy of the system. In addition, the interaction between Mn and O atoms is stronger than that between Mn and S atoms.

Fig. 12.

The charge density distribution of Mn and S atoms adsorbed on Al₂SiO₅ (1 1 0). (a), (c) Charge density under A-S1 condition, (b), (d) Charge density under B-S2 condition, (O-Red, Mn-Purple, S-Blue). (Online version in color.)

4.5. Formation of MnS on Al₂SiO₅ Surface

As discussed above, it is obvious that the case A-S1 presents the minimum adsorption energy for the adsorption of the Mn and S atoms, which indicates the path and order of the adsorption of the atoms. Thus, it is reasonable to conclude that the adsorption process of MnS on Al₂SiO₅ (110) surface is Mn followed by the S atom located above the Al atom in Figs. 9(e) and 9(f). During the adsorption process to form the structure shown in the case of A-S1, the distance between the S and Al atoms increases from 2.150 Å to 4.288 Å to achieve the most stable structure. Additionally, the position of the S atom is lower than that of the Mn atom in the Fig. 9(b), which shifts to a stable position above the Mn atom in the Fig. 9(f). Thus, it is reasonable to speculate that the MnS is growing up normal to the surface of the Al₂SiO₅. In order to further demonstrate the growing model and path of the MnS, a second S atom is released from the positions above the Mn atom in the structure shown in Figs. 9(e) and 9(f). The initial position of the second S atom is shown in the Figs. 13(a) and 13(b). The calculated adsorption energy of the second released S atom is −3.754 eV. The most stable structure achieved after the adsorption of the second S atoms is shown in Figs. 13(c) and 13(d). Figure 14 show the CDD of Mn and S atoms adsorbed on the Al₂SiO₅ (110) surface, in which blue areas represent the region losing 0.03 eV of electrons to form positive charge, and the yellow areas represent the region gaining 0.03 eV of electron to form negative charge. The charge accumulation among the Mn, S, and O atoms illustrates the intersection and the transformation of the electrons among them, which indicates the Mn atom is attracted by the surrounding O atoms while the interaction between the Mn and S is relatively weaker, as shown in Figs. 14(a) and 14(b).

Fig. 13.

The positions of Mn and S atoms on the surface of Al₂SiO₅ (1 1 0). (a) and (b) Top view and side view of the initial position of the second S atom, (c) and (d) The final structure of the adsorption of the second S atom (Al-Pink, O-Red, Si-Yellow, Mn-Purple, S-Blue). (Online version in color.)

Fig. 14.

The charge density difference among the Mn and S atoms adsorbed on Al₂SiO₅ (1 1 0) surface. (O-Red, Mn-Purple, S-Blue). (Online version in color.)

Figure 15 compares the structure of the MnS and the structure of the Al₂SiO₅ with Mn and S atoms adsorbed on the surface. The bond length between Mn and S atoms in the structure of the MnS is 2.396 Å and angle among the atoms of the S–Mn–S is 109.471 degrees as shown in Fig. 15(a). The bond lengths between the Mn and S atoms adsorbed on the surface of Al₂SiO₅ are 2.006 Å and 2.004 Å, the bonds length between Mn and O atoms are 1.852 Å or 1.857 Å. Both the bond lengths between Mn–S and Mn–O on the surface of the Al₂SiO₅ are shorter than those in the MnS crystal which is indicative of the higher bond energies between the atoms and the more stable structure after adsorption. The angle among the atoms of the S–Mn–S is 108.841 degrees, while the angles among the atoms of the S–Mn–O are 113.303 degree and 111.782 degrees. All the angles are quite close to the angle of S–Mn–S in the structure of the MnS as shown in Fig. 15(b). The Mn and S atoms form a tetracyclic structure in the MnS crystal, while the adsorbed Mn atom forms a tetracyclic structure with S and O atoms during the adsorption above the surface of Al₂SiO₅ as well. Thus, it provides reliable proof that the growing model of MnS on the basal slab of Al₂SiO₅ is normal to the surface (110). Therefore, the path of the formation of MnS on the surface of Al₂SiO₅ is shown in Fig. 16.

Fig. 15.

Comparison of the structure of the MnS and adsorption structure on the surface of Al₂SiO₅. (Online version in color.)

Fig. 16.

The optimal path of the atomic adsorption. (Online version in color.)

5. Conclusions

In this paper, the formation of MnS–Al₂SiO₅ complex inclusion are analyzed in the atomic level by using the first principles calculation based on the DFT. The adsorption energy of the Mn and S atoms on the Al₂SiO₅ (110) surface is compared with various initial positions and adsorbing sequence. The DOS, PDOS, and CDD are discussed to prove the interaction between the atoms.

(1) The plane (110) in the structure of Al₂SiO₅ with 7-layer was selected as the surface for the adsorption, in which the four layers of atoms from the top are relaxed in the simulation.

(2) In the first step, the most stable structure is obtained with the position of Mn atom slightly away from the left top of the O atom with a distance of 2.329 Å, in which the angle among the atoms of the Mn–O–Al is 71.666 degrees.

(3) The case A-S1 in the second step adsorption presents the minimum adsorption energy for the adsorption of the Mn and S atoms. The adsorption process is the Mn atom followed by the S atom located above the Al atom and Mn atom, indicating the growing model of the MnS on the suface of Al₂SiO₅.

(4) The adsorbed Mn and S atoms forms a tetracyclic structure with the O atoms on the surface of Al₂SiO₅, which is quite similar to the tetracyclic structure of MnS crystal. It indicates the growing mode of the MnS around the Al₂SiO₅ is normal to the surface.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (No. 51874061), Natural Science Foundation of Chongqing (No. cstc2020jcyj-msxmX0449), Excellent Youth Foundation of Hebei Province, China (No. E2021209039), Hebei Financial Support Project for the Introduced Overseas Student (No. C20210309) and Venture & Innovation Support Program for Chongqing Overseas Returnees (No. cx2019026).

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