Mechanism of Faces Growth in Preparing Calcium Sulphate Whiskers Using Sodium Oleate

doi:10.15541/jim20160127

Abstract

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

CLC Number:

TQ174

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.

Figures/Tables 8

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	—

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

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

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

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)

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

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

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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