Langmuir 2000, 16, 8213-8216
Preparation of Spherical Bioceramic Fine Particles Reinforced by Alumina Using an Emulsion Liquid Membrane System Takayuki Hirai,* Masayuki Hodono, and Isao Komasawa Department of Chemical Science and Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan Received April 12, 2000. In Final Form: July 11, 2000
Introduction The use of an emulsion liquid membrane (ELM, waterin-oil-in-water (W/O/W) emulsion) system for the selective separation of metals is presently the subject of extensive study. In this technique, the metal ions are extracted from the external water phase into the organic membrane phase and then stripped and concentrated into the internal water phase. It has been found recently, however, that the internal water phase may also be used for the preparation of both size-controlled and morphology-controlled fine particles, owing to the restricted reaction area of the micrometer-sized internal water droplets. Since the ELM system also has a high selectivity, a further purification and preconcentration of the target metals are no longer required. Calcium phosphates constitute the major constituent of bone and hold great promise as a potential biomaterial for bone implantation, owing to their ability to bond to bone. Hydroxyapatite is the main mineral constituent of natural bone, and thus synthetic calcium phosphate ceramics such as hydroxyapatite and β-TCP (β-Ca3(PO4)2, whitlokite) may create excellent bonding with natural tissue and may even stimulate new bone growth. Both hydroxyapatite and β-TCP ceramics are widely applied nowadays to coat artificial joint and tooth roots.1 A plasmaspraying process, as presently widely employed to deposit the calcium phosphate coating, requires both a spherical morphology and a narrow particle size range for the feed powder. In the previous study,2 the preparation of spherical and size-controlled calcium phosphate particles, using the ELM system, was therefore investigated. The use of hydroxyapatite and β-TCP as a loaded implant is, however, considerably limited by their low mechanical reliabilities. A mixture of calcium phosphate with another material, however, appears to provide a key in improving fracture toughness; thus, the fracture toughness of calcium phosphate, when reinforced with zirconia or alumina, has been shown to be increased.3-7 The present work was thus carried out, in an attempt to prepare composite particles of calcium phosphate and alumina, as an extension of the previous study,2 using the ELM system. Experimental Section VA-10 (2-methyl-2-ethylheptanoic acid), supplied by Shell Chemical Co., and sorbitan sesquioleate (Span 83), supplied by Tokyo Kasei Kogyo Co., Ltd., Tokyo, Japan, were used in all (1) de Groot, K. J. Ceram. Soc. Jpn. 1991, 99, 943-953. (2) Hirai, T.; Hodono, M.; Komasawa, I. Langmuir 2000, 16, 955960. (3) Champion, E.; Gautier, S.; Bernache-assollant, D. J. Mater. Sci., Mater. Med. 1996, 125-130. (4) Choi, J.; Kong, Y.; Kim, H.; Lee, I. J. Am. Ceram. Soc. 1998, 81, 1743-1748. (5) Jiang, G.; Shi, D. J. Biomed. Mater. Res. 1998, 43, 77-81. (6) Juang, H.; Hon, M. Mater. Sci. Eng. C2 1994, 77-81. (7) Ji, H.; Marquis, P. M. J. Mater. Sci. 1993, 28, 1941-1945.
8213
experiments as the extractant and surfactant, respectively. Calcium nitrate (Ca(NO3)2), aluminum chloride (AlCl3), orthophosphoric acid (H3PO4), and all other chemicals were supplied by Wako Pure Chemical Industries, Ltd. The internal water phase for the emulsion (50 mmol/L H3PO4 and 1-30 mmol/L AlCl3) and the organic membrane phase (kerosene containing 0.5 mol/L VA10 and 8 wt % Span 83) were mixed at a volume ratio of 6:4 and were emulsified mechanically by use of a homogenizer (12 000 rpm). The resulting W/O emulsion (10 mL) was added to an external water phase solution (50 mL, 10 mmol/L Ca(NO3)2 and 0.1 mol/L NH3) and stirred vigorously by magnetic stirrer (stirring speed ) 500 rpm) to form a W/O/W emulsion. The resulting size of the W/O emulsion droplets, dispersed in the external water phase, was 1173 K. This decomposition of calcium phosphate was confirmed by the XRD analyses of the calcined particles. The calcium phosphate particles prepared in the ELM system containing hydroxyapatite demonstrate an exothermic peak at around 1000 K (decomposition to β-TCP), as shown in previous work.2 The composite particles prepared in the present work may, therefore, also contain a hydroxyapatite phase in their composite structure. The SEM images for the composite particles, prepared by the ELM system and calcined at 1273 K for 2 h, are shown in Figure 4a. No significant change in the size or morphology of the composite particles was apparent at calcination temperatures below 1273 K. The precipitates obtained in homogeneous solution, however, as shown in Figure 4b, became larger in size (
