Fabrication of porous hydroxyapatite ceramics by microwave processing
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Porous hydroxyapatite ceramics with porosity up to 73% have been fabricated by microwave processing at 1150 to 1200 °C for 1 to 5 min. Various porosities in these ceramics have been obtained by using starting materials with different morphology, adjusting green density, changing sintering time and temperature, as well as optionally mixing ammonium carbonate in the hydroxyapatite powder during the consolidation process. Porosity, microstructure, and diametral tensile strength of the porous hydroxyapatite ceramics have been studied.
I. INTRODUCTION AND PREVIOUS WORK
II. EXPERIMENTAL
This laboratory pioneered the development of porous hydroxyapatite ceramics by the route of the replamineform (meaning replicated life forms) technique which involves duplicating the microstructure of carbonate skeletal components in ceramic, metal, or polymer materials. Based on the study of the microstructure of sea urchins and corals by Weber et al,l the first and possibly only commercially available biomimetic material even twenty years later was developed by White, Weber, and White2'3 who devised the replamine process, and D. Roy 4 ' 6 who learned to convert the CaCO 3 to hydroxyapatite. These porous hydroxyapatite ceramics are available commercially from Interpore International for dental and bone transplants. Hydroxyapatite [Ca 5 (PO 4 ) 3 OH, HAp] is the obvious material expected to be widely used for biomedical applications in humans. As implants, HAp ceramics, either dense or porous, can be used for different purposes. Quite recently microwave processing has become a new and efficient technique in material processing,7"9 and we have recently applied this technique successfully to develop dense sintered HAp ceramics.10 The results show that, in addition to lowering sintering temperature and enhancing mechanical strength, one can sinter HAp ceramics in a few minutes, consuming less than one-tenth of the energy or time required for the conventional process. Since porous HAp ceramics are relatively more useful in biomedical applications, one is led to ask: "Although they have been prepared by the replamineform technique and others,11 is it possible to prepare porous HAp ceramics by microwave processing?" As will be shown in the present work, the answer is definitely "yes". This paper presents the results of a preliminary study on the fabrication of the porous HAp ceramics using the microwave technique.
A. HAp powders
490 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 2, Feb 1992
Downloaded: 31 Dec 2014
Two kinds of HAp-precursor powders were used: (A) whiskers of pure HAp, with typical size 0.2 x 5 /im, BET surface area 10.8 m 2 /g, synthesized by the hydrolysis of tricalcium phosphate [a;-Ca3(PO 4 ) 2 , cn-TCP, labsynthesized] at 60 °C, pH 7.5-8.5, dried at 165 °C 12 ; (B) pure HAp, agglomerations of very fine crystals, with typical size of 0.05 x 0.3 /im (estimated from micrograph), BET surface area 47.4 m 2 /g, prepared by the hydrolysis of brushite (CaHPO4 • 2H 2 O, J. C. Baker Chemical Co., Phillipsburg, NJ)
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