First-principle calculation of water adsorption on CaO(100) face under external electric field

doi:10.3969/j.issn.1001-1935.2021.01.010

Abstract

Abstract:

Magnesia-calcia refractory is an ideal refractory for smelting clean steel,but the free calcia in it is easy to hydrate,which limits its wide application.In this paper,the adsorption behavior of H₂O molecules on CaO(100) face was studied by first-principle calculation.On this basis,the effect of applied electric field on the adsorption behavior of H₂O on CaO(100) face was studied.The results show that H₂O molecules are the most easily adsorbed on the bridge sites of CaO(100) face with perpendicular-up and perpendicular-down.The distance and adsorption energy between H₂O and CaO(100) face increase with the increase of the applied electric field intensity.At the same time,the bond angle of H₂O keeps decreasing,and it tends to be single H₂O.The results of charge transfer show that with the increase of the negative electric field intensity,the electrons transferred from Ca atom to O atom are less and less,which indicates that the interaction between H₂O and CaO(100) face is weakening.Under the action of positive electric field,the distance between the H₂O and the CaO(100) has little change with the increase of electric field intensity,but the adsorption energy gradually changes from negative to positive.The applied electric field can inhibit the adsorption of H₂O on CaO(100) face,providing a new method for the waterproofing of magnesia-calcia refractory materials.

Key words: magnesia-calcia refractories, hydration resistance, external electric field, first-principle calculation, adsorption

摘要：

镁钙系耐火材料是冶炼洁净钢的理想耐火材料,然而其中的游离氧化钙易水化,限制了其广泛的应用。在本工作中,采用第一性原理计算的方法研究了H₂O分子在CaO(100)表面的吸附行为。在此基础上又研究了外加电场对H₂O分子在CaO(100)表面吸附行为的影响。结果表明:H₂O分子最容易以垂直向上取向和垂直向下取向吸附于CaO(100)表面的桥位。在外加负电场的作用下,H₂O分子与CaO(100)表面之间的距离和吸附能均随电场强度的增强而增大。同时H₂O分子的键角不断减小,逐渐趋向于单独水分子。电荷转移结果表明,随着负电场强度的增加,Ca原子向O原子转移的电子越来越少,这再次表明H₂O分子与CaO(100)面的相互作用不断减弱。在外加正电场的作用下,随着电场强度的逐渐增强,H₂O分子和CaO(100)面间的距离变化不大,但吸附能逐渐由负值变为正值。外加电场可以抑制H₂O分子在CaO表面的吸附,为镁钙系耐火材料防水化提供了一种新方法。

关键词: 镁钙系耐火材料, 防水化, 外电场, 第一性原理计算, 吸附

CLC Number:

TQ175.1

Shan Jingyi, Wang Junkai, Huang Zhenxia, Dai Xinyu, Hu Qianku, Zhou Aiguo. First-principle calculation of water adsorption on CaO(100) face under external electric field[J]. Refractories, 2021, 55(1): 44-50.

闪静祎, 王军凯, 黄珍霞, 戴新宇, 胡前库, 周爱国. 外电场对水在CaO(100)表面吸附的第一性原理计算[J]. 耐火材料, 2021, 55(1): 44-50.

Figures/Tables 12

Fig.1 Sketch of CaO(100) face

Fig.2 Initial and optimized configurations of hollow(H),bridge(B) and top(T) sites adsorbed by H2O on CaO(100) face

Table 1 Value of adsorption energy and charge at different sites

吸附位点	E_ad/eV	电荷/e
H	-1.205	-0.166
B	-1.206	-0.166
T	-0.420	-0.146

Fig.3 Different adsorption orientations of H2O

Fig.4 Initial and optimized configurations of H2O adsorbed on B point of CaO(100) face

Table 2 Values of electron charge,bond length,adsoption energy before and after adsorption of H2O with different orientations (the “-” denotes gaining electrons)

构型	E_ad/eV	电荷/e	$L H 1 — O$ /nm	$L O — H 2$ /nm
B-a	-0.349	-0.015	0.097 5	0.097 5
B-b	-0.152	0.008	0.097 0	0.097 0
B-c	-0.156	0.091	0.097 1	0.097 1
B-d	-1.206	-0.166	0.096 8	0.144 4
B-e	-1.206	-0.166	0.096 8	0.144 5

Table 2 Values of electron charge,bond length,adsoption energy before and after adsorption of H2O with different orientations (the “-” denotes gaining electrons)

构型	E_ad/eV	电荷/e	$L H 1 — O$ /nm	$L O — H 2$ /nm
B-a	-0.349	-0.015	0.097 5	0.097 5
B-b	-0.152	0.008	0.097 0	0.097 0
B-c	-0.156	0.091	0.097 1	0.097 1
B-d	-1.206	-0.166	0.096 8	0.144 4
B-e	-1.206	-0.166	0.096 8	0.144 5

Fig.5 Optimized B-d configurations with positive or negative electric field

Fig.6 Variation of adsorption energy,bond angle and distance under different negative electric fields

Table 3 Value of adsorption energy and distance under di-fferent electric fields

E/(V·nm^-1)	E_ad/eV	d/nm
0.000 0	-1.205	0.191 3
-2.056 9	-0.979	0.196 1
-3.599 6	-0.157	0.200 8
-4.113 8	0.253	0.202 3
-5.142 3	1.285	0.207 2

Fig.7 Optimized structures of H2O adsorbed on CaO under different electric fields

Fig.8 Charge changes of O and Ca atoms at different electric fields

Fig.9 Variation of adsorption energy and distance under different positive electric fields

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