Hydrothermal Synthesis of Whitlockite

doi:10.15541/jim20160704

Abstract

Abstract:

Whitlockite was firstly synthesized by a hydrothermal method using CaO, Mg(NO₃)₂and H₃PO₄ as starting materials and then characterized by X-ray diffraction, scanning electron morphology, thermal analysis, and X-ray fluorescence. The variation of molar ratio of Mg/(Ca+Mg) in the precursor solution resulted in different crystallization behaviors of whitlockite during hydrothermal treatment. With the increase of the molar ratio of Mg/(Ca+Mg), crystal morphologies of products varied from hexagonal plate (about 30-50 μm) to spheres (about 3-5 μm) and cell parameters of a and c values decreased gradually. Meanwhile, the content of Mg/(Ca+Mg) in the products increased gradually and reached a high value of 13.6%. It was found that the nucleation and growth of whitlockite were almost completed within 2 h. Ca₁₈Mg₂H₂(PO₄)₁₄ was transformed to Ca₁₈Mg₂(PO₄)₁₂P₂O₇ after calcination at temperature ranging from 680℃ to 950℃ due to the dehydration reaction.

Key words: hydrothermal method, synthetic whitlockite, hexagonal plate-like crystal, microsphere

CLC Number:

TB321

LI Guo-Chang, WANG Ping, LIU Chang-Bo. Hydrothermal Synthesis of Whitlockite[J]. Journal of Inorganic Materials, 2017, 32(11): 1128-1132.

Figures/Tables 9

Fig. 1 XRD patterns of different Mg/(Ca+Mg) samples (180℃, 6 h)(a) Mg0.1; (b) Mg0.2; (c) Mg0.3; (d) Mg0.4; (e) Mg0.5

Table 1 Unit cell parameters of samples

Sample	Unit cell parameters
Sample	a/nm	c/nm
Mg_0.1	1.03705	3.71939
Mg_0.2	1.03707	3.71234
Mg_0.3	1.03542	3.71068
Mg_0.4	1.03431	3.70353
Mg_0.5	1.03412	3.70203
PDF# 70-2064	1.03500	3.70850

Table 2 Chemical constituents of different Mg/(Ca+Mg) samples

Mg_L	Chemical constituents/wt%			Molar ratio
Mg_L	CaO	P₂O₅	MgO	Mg_S	Mg_L/Mg_S	(Ca+Mg)/P
Mg_0.1	53.95	43.85	1.85	0.041	0.41	1.62
Mg_0.2	50.95	45.64	3.16	0.076	0.38	1.59
Mg_0.3	49.34	46.04	4.21	0.102	0.34	1.51
Mg_0.4	48.54	46.34	4.89	0.119	0.30	1.51
Mg_0.5	46.74	46.8	6.03	0.136	0.27	1.49

Fig. 2 SEM images of different Mg/(Ca+Mg) samples (180℃, 6 h)(a) Mg0(HA); (b) Mg0.1; (c) Mg0.2; (d) Mg0.3; (e) Mg0.4; (f) Mg0.5

Fig. 3 XRD patterns of samples reacted for different time (Mg0.3, 180℃)(a) 2 h; (b) 3 h; (c) 6 h; (d) 10 h

Table 3 Unit cell parameters of calcined samples

Calcination temperature	Chemical formula	Unit cell parameters
Calcination temperature	Chemical formula	a/nm	c/nm
As-prepared sample	Ca₁₈Mg₂H₂(PO₄)₁₄	1.03707	3.71234
950℃	Ca₁₈Mg₂(PO₄)₁₂P₂O₇	1.03472	3.71176
1200℃	Ca₁₈Mg₂(PO₄)₁₂P₂O₇	1.03412	3.71094

Fig. 4 SEM images of samples reacted for different time (Mg0.3, 180℃)(a) 2 h; (b) 3 h; (c) 6 h; (d) 10 h

Fig. 5 TG and DTA curves of sample Mg0.3

Fig. 6 XRD patterns of the calcined samples (a) As-prepared sample (Ca18Mg2H2(PO4)14); (b) Calcined at 950℃ (Ca18Mg2(PO4)12P2O7), 2 h; (c) Calcined at 1200℃, 2 h (Ca18Mg2(PO4)12P2O7)

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