油酸钠控制硫酸钙晶须晶面生长的机理研究

doi:10.15541/jim20160127

摘要/Abstract

摘要：

结合油酸钠溶液化学计算、硫酸钙晶须晶面衍射和分子动力学模拟, 研究了硫酸钙晶须不同晶面的结构、油酸钠在不同晶面的吸附和硫酸钙晶须的晶面生长。结果表明: 硫酸钙晶须晶面中, 钙原子与氧原子、氢原子规律分布在(200)晶面和(400)晶面表面; 与其它晶面相比, 油酸钠与(200)晶面和(400)晶面的作用能较小, 吸附构型稳定; (200)晶面和(400)晶面上油酸根与钙离子之间的距离分别为0.239 nm和0.237 nm, 小于作用后的油酸根与钠离子之间的距离, 得出钙原子是油酸根在晶须晶面作用的活性位点。油酸钠的选择性吸附阻止了(200)晶面和(400)晶面的生长, 晶面生长速率的差异使得晶须沿c轴择优生长。

关键词: 硫酸钙晶须, 晶面, 分子动力学, 径向分布函数

Abstract:

The crystal structure of calcium sulphate whiskers and adsorption of sodium oleate on crystal faces were investigated through methods of solution chemistry calculation, X-ray diffraction analysis and molecular dynamics simulation. Furthermore, the growth of crystal faces was explored in presence of sodium oleate. Results showed that calcium, oxygen and hydrogen atoms were primarily distributed on crystal faces of (200) and (400). Interaction energies between sodium oleate and faces of (200) and (400) were much smaller than those of other faces. Distances between oleic acid and calcium on crystal faces of (200) and (400) were 0.269 nm and 0.237 nm, respectively, which were smaller than those between oleic acid and sodium. It could reasonably deduce that calcium was the active site of crystal faces. The selective adsorption of sodium oleate prevented growths of (200) face and (400) face. Differences in growth rate of crystal faces made whiskers grow along c-axis.

Key words: calcium sulphate whiskers, crystal face, molecular dynamics simulation, radial distribution function

中图分类号:

TQ174

郝海青, 袁致涛, 李丽匣, 张晨. 油酸钠控制硫酸钙晶须晶面生长的机理研究[J]. 无机材料学报, 2016, 31(11): 1184-1190.

HAO Hai-Qing, YUAN Zhi-Tao, LI Li-Xia, ZHANG Chen. Mechanism of Faces Growth in Preparing Calcium Sulphate Whiskers Using Sodium Oleate[J]. Journal of Inorganic Materials, 2016, 31(11): 1184-1190.

图/表 8

表1 试样粒度分布统计表

Table1 Statistical data of sample size distribution

Size fraction/mm	Productivity /%			Cumulative productivity /%
Size fraction/mm	Sample A	Sample B	Sample C	Cumulative productivity /%
>0.074	20.35	19.17	19.76	19.76
0.038~0.074	39.39	38.54	38.97	58.73
0.027~0.038	14.27	14.29	14.28	73.01
0.019~0.027	7.92	8.25	8.09	81.10
0.014~0.019	3.67	4.12	3.90	85.00
0.010~0.014	3.58	3.63	3.60	88.60
0~0.10	10.82	12	11.40	100.00
Total	100.00	100.00	100.00	—

图1 0.15%油酸钠作用下硫酸钙晶须SEM形貌

Fig. 1 SEM image of calcium sulfate whisker with 0.15% sodium oleate

图2 油酸钠溶液各组分的logC-pH图(CT=1.64×10-4 mol/L)

Fig. 2 The logC-pH relationship of sodium oleate solution system (CT=1.64×10-4 mol/L)

图3 0.15%油酸钠作用下硫酸钙晶须晶面衍射强度

Fig. 3 Diffraction strength of crystal faces with 0.15% sodium oleate

图4 晶面结构图

Fig. 4 Structure of some crystal faces(a) (200) face; (b) (400) face; (c) (002) face; (d) (310) face; (e) (530) face; (f) (510) face (Note: Crystal faces are defined by two black lines which are parallel to each other)

表2 油酸钠在不同晶面的作用能

Table 2 Interaction energy of sodium oleate on different faces

additive	Interaction energy, ∆E/(kJ·mol^-1)
additive	(200)	(400)	(002)	(310)	(530)	(510)
Sodium oleate	-3259.43	-2827.17	-3003.67	-1051.77	-913.50	-453.43

表3 不同晶面上油酸根与钠离子的距离

Table 3 Distance between oleic acid and sodium on different faces

Distance, r /nm	Before adsorption	(200)	(400)	(310)	(530)	(510)	(002)
r_COO--Na⁺	0.268	0.467	0.495	0.253	0.325	0.267	0.433

图5 不同晶面上粒子的径向分布函数

Fig. 5 Radial distribution functions of atoms on different faces(a) (200) face; (b) (400) face; (c) (002) face; (d) (310) face; (e) (530) face; (f) (510) face

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