Preparation of Millimeter-scale Alumina Hollow Spheres by Oil1-in-water-in-oil2 Emulsions

doi:10.15541/jim20150462

Abstract

Abstract:

To prepare millimeter-scale alumina hollow spheres by oil₁-in-water-in-oil₂ emulsions, the influence factors of formation of precursor and curing process were studied. Composite droplets with paraffin liquid as inner core and alumina sol as outer shell were used as precursor. Results showed that the com-droplets had homogeneous and complete core-shell structure when emulsion generator was designed that inner oil could be injected into water phase with the size of millimeters scale. Thickness and diameter of droplets were adjusted by both controlling the injection speed of oil and water phase in the range of 30-80 μm and 800-2200 μm. In the curing process, the semisolid spheres kept hollow structure and spherical when the speed of rotation between 20 r/min to 60 r/min and the flask being put in horizontal. Finally, the prepared hollow ceramic spheres with wall thickness in micrometer-scale and diameter in millimeter-scale formed complete hollow structure and high sphericity after calcining at 1200 ℃ for 4 h. The surface of sphere was relatively smooth with roughness of about 22 nm. The main crystal of the prepared ceramic hollow spheres was alpha alumina.

Key words: alumina hollow spheres, oil₁-in-water-in-oil₂ emulsion, composite droplets, flow focusing micro-channel

CLC Number:

TQ174

LI Hao-Ting, LIAO Qi-Long, WANG Fu. Preparation of Millimeter-scale Alumina Hollow Spheres by Oil₁-in-water-in-oil₂ Emulsions[J]. Journal of Inorganic Materials, 2016, 31(3): 329-336.

Figures/Tables 9

Fig. 1 Schematic diagram of co-flow micro-emulsion generator

Table 1 Parameters of materials (T=25℃)

Parameters	Alumina sol aged for differeut time/d					Paraffin	Silicone oil
Parameters	1	5	10	15	20	Paraffin	Silicone oil
Density, ρ / (g﹒mL^-1)	1.012	1.024	1.027	1.052	1.073	0.835	0.963
Viscosity, η  (mPa﹒s)	26.56	37.90	48.23	58.44	98.36	35.98	400.00

Fig. 2 Three kinds of composite droplets (model A, model B, model C)

Fig. 3 Diameter and wall thickness of com-droplets at different velocities of water phase (Voil=1 mL·h-1)

Fig. 4 Diameter and wall thickness of com-droplets at different velocities of oil phase (Vwater=6 mL·h-1)

Fig. 5 Schematic of three different rotate types

Fig. 6 Number of intact droplets at different speed after curing (n=10)

Fig. 7 Photographs of com-droplets, semisolid spheres and SEM images of ceramic spheres by model A, B and C

Fig. 8 Characterization of the ceramic sphere(A, B, C): SEM of spheres; (D, E, F): optical images of spheres; (G, H): surface roughness analysis; (I): XRD patterns

References 29

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Preparation of Millimeter-scale Alumina Hollow Spheres by Oil₁-in-water-in-oil₂ Emulsions

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