Hydroxyapatite Ceramics from Hydrothermally Prepared Powders
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ABSTRACT Hydroxyapatite (Ca5 (P0 4 ) (OH)) is an effective material for artificial human bone production. Hydroxyapatite powders were hydrothermally produced in this work by reacting Ca(OH) 2 with Na3PO4 "12H2 0 in an autoclave at various temperature and for various times. The particle size of hydroxyapatite was observed to be very fine, uniform, around 50 nm, as well as independent of reaction time. The hydroxyapatite powders were compacted and sintered at various temperatures for 2 hrs. The density, grain size, and hardness of the hydroxyapatite ceramics were measured and compared with those of the hydroxyapatite ceramics produced by the powders from the commercial source. The hydroxyapatite ceramics from the hydrothermal powders were found to have a higher density, smaller grain size, and higher hardness. After the hydroxyapatite ceramics were dipped in a simulated biological body liquid for 10 days, the density and hardness of the hydrooxyapatite ceramics from the hydrothermal powders were less deteriorated than those of the hydroxyapatite ceramics from the commercial powder.
INTRODUCTION Hydroxyapatite powders, i.e., derived from hydroxyapatite (Ca5 (P0 4 )3OH) which is the main composition of human bone, are used to produce artificial bones by the sintering method. Hydroxyapatite powders can be synthesized both at higher temperatures ( >1000°C) by the solid state sintering method under water vapor atmosphere, and at lower temperatures (60-70'C) in an aqueous solution such as by the hydrolysis of CaHP0 4 .21i 2 OE1 3, Ca3 (P0 4) 2 E 2 3 or acid-base ractiOn of Ca4 (P04 ) 20 and CaHPO 4 -2H20[3-5]. High temperture synthesis of hydroxyapatite powders is difficult to conduct and low temperature synthesis is quite slow in the reaction
rate. Conseqently, hydroxyapatite powders are synthesized by a hydrothermal method, e.g.,
by the treatment of C8(NO 3)2 and H3P0 4 reaction precipitate under a temperature higher than 100°C and at a pressure higher than 1 atm. Hydrothermal method is a potential method to produce ceramic powders which are very uniform in chemical composition and particle size. Characteristics of the ceramics produced from the hydrothermal method have received little research attention. In this study, a hydrothermal method was used to produce hydroxyapatite powders and the characteristics of the ceramics produced by these powders were reported. Hydroxyapatite powder produced by Sigma Chemical Company from the hydrolysis of CaHPO4.2H 2 0 was also examined to make a comparasion
of the properties of both powders. EXPERIMENTAL
Hydroxyapatite powders were hydrothermally produced by reacting Ca(OH)2 with Na3PO4 -12H 20 in an autoclave at 120, 140, 160, 180, and 2000C for 24 hrs, and at 2000C for 4, 12, 24, 36, and 48 hrs, respectively. After reaction, the powders were washed and dried. The structure, shape, size, and chemical composition of the powders were analyzed by x-ray diffractormetry, transmission electron microscopy, x-ray fluorescence, and particle size analyzer. The hydroapatite powders were c
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