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T his paper reports the characteristics and properties used to characterise these coatings. Scanning electron microscopy ( SEM) was used to observe surface and of two diVerent sets of hydroxyapatite ( H A) coatings cross-section morphology of both powder and sprayed obtained by thermal spraying two diVerent H A powders, coatings. T he phase and chemical characteristics of the spray dried H A ( SDH A) and spheroidisided H A samples were evaluated by X -ray diVraction ( X R D) ( SH A) , at various chamber pressures. T he evaluation and Fourier transform infrared spectrometry ( FT IR) . of the coatings following post-spray treatment at 800°C Finally, in order to have a qualitative measure of the is also included. Comparisons to the results from the integrity of the coatings, V ickers hardness testing was as sprayed coatings were made to show the eVects of performed on polished cross-sections of the coatings. post-spray heat treatment. T he median particle sizes SE/S230 for SDH A and SH A were 35 and 47 mm, respectively. T he main diVerence between the powders is their Dr Espanol ( P43690802W@ntu.edu.sg) and Dr K hor density and morphology. T he SH A powder provides are at the Nanyang T echnological University, School higher density and spherical morphology, and a more of Mechanical and Production Engineering, Nanyang porous and rough surface is present in the SDH A Avenue, Singapore 639798, Singapore. Dr Guipont and powders. T hese two powders were sprayed using a Dr Jeandin are at the Ecole Nationale Supérieure des controlled atmosphere plasma spraying ( CAPS) system Mines de Paris/C2P, Center for Plasma Processing, in the inert plasma spray ( IPS) and high pressure BP87, 91003 Evry cedex, France, and Dr Llorca-Isern plasma spray ( HPPS) modes. Four diVerent pressures is at the Universitat De Barcelona, Metallurgical and of 100, 150, 200, and 250 kPa were applied in an argon Chemical Engineering Department, Marti i Franques atmosphere. Post-spray heat treatment was performed 1, 08028 Barcelona, Spain. Manuscript received 12 to increase the crystallinity of the coatings, to homogDecember 2001; accepted 27 A pril 2002. enise their structure, and to convert other calcium phosphate phases to H A . DiVerent techniques were

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