Characterization of Type B Carbonate Apatite Sintered Bodies
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Characterization of Type B Carbonate Apatite Sintered Bodies N.Watanobe1, T.Yoshioka1, T.Ikoma1, T.Kuwayama2, T.Higaki2, J.S.Cross1 and J.Tanaka1 1 Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550 JAPAN 2 Kuraray Medical Inc., 2045-1 Sakazu, Kurashiki, Okayama 710-0801 Japan
ABSTRACT The dissolution kinetics of type B carbonate apatite (CAp) disks sintered at different temperatures were investigated under acidic conditions similar to an osteoclastic desorption process in bone remodeling. The type B CAp disks, which were uniaxially pressed at 98MPa and sintered at temperatures of 600 to 700 ºC, showed single crystalline phase and a high relative density of 60-62 % compared to the stoichiometric density of 3.16g/cm3 of hydroxyapatite (HAp). The dissolution rate of type B CAp disks sintered at 650 ºC was 3.5 times faster than that of HAp disks at 650 ºC. These results indicate that the Type B CAp sintered disks show potential use as a biodegradable material for artificial bone. INTRODUCTION Bone and tooth minerals consist of carbonate apatite (CAp) nanocrystals [1]. The CAp has been classified into three types, depending on carbonate substitution sites in hydroxyapatite (HAp; Ca10(PO4)6(OH)2). Types A, B, and AB refer to the location where carbonate ions substitute for OH-site, PO4-site, and both sites in the HAp lattice, respectively. The chemical and biological properties [2, 3] of type B CAp has been considered suitable for artificial bone materials compared with non-degradable HAp and rapidly degraded tricalcium phosphate (TCP; Ca3(PO4)2). Previously, various sintering methods of type B and type AB CAp have been investigated. The isostatically compacted type B CAp powders at 600 MPa were firstly sintered at 600 ºC to 750 ºC [4, 5] and the carbonate content remained at approximately 6 wt% which was similar to that in bone apatite. Furthermore, the bio-resorbable property and osteoclastic reaction of the type B CAp were investigated [6, 7]. On the other hand, the type AB CAp has been also sintered in dry and wet carbon dioxide atmospheres at 1000 ºC [8] and 1300 ºC [9]. The sintered bodies exhibited the optical transmission at 13% of 2mm in thickness. However, the detailed sintering behavior and dissolution kinetics in osteoclastic environments have not been investigated. In this paper, we investigated the detailed sintering conditions of type B CAp in the temperature range of 500 to 900 ºC. The sintered bodies were characterized by powder X-ray diffractometry (XRD), Fourier transformed infrared spectroscopy (FT-IR), thermogravimetry (TG), and scanning electron microscopy (SEM). The dissolution kinetics of sintered type B CAp under acidic conditions similar to osteoclastic desorption process were investigated. EXPERIMENT Powder Preparation and Sintering Method
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Hydroxyapatite (HAp) and carbonate apatite (CAp) powders were prepared by a wet chemical method. CaCO3 powder was calcined at 1050 oC for 3h. The resultant CaO powder was hydrated wi
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