| Abstract: |
The characteristics of HA coatings are of fundamenteal importance for their behaviour in the organism and in particular for their degradation rate. Both in vitro and in vivo resuls have claimed the required preferable presence of crystalline HA rather than other calcium phosphate phases, since they have a lower resorption resistance than stociometric HA. However, the optimal phase composition is a subject of considerable discussion, since the presence of amorphous phases may accelerate the fixation of an implant and thus promote the bone remodeling and attachment. In any case, the abillity to closely control the distribution of all these phases could be the key factor to ensure the mechanical stability of the coating in the long term. Even though the atmospherical plasma spraying is the most widely employed process for the deposition of these materials, a severe HA decomposition is inevitable when using high energy plasma spray devices. In addition, some further drawbacks of the existing technology like the overheating of the titanium substrate and the fatigue penalty of the same, the difficult manipulation of the spray gun, the low process reliability and the numerous safety requirements, justify the development of alternative systems. This work deals with the development of a new low energy plasma deposition device, designed specifically for the deposition of bioactive coatings on small sized bone implants and characterized by a highly reliable and reproducible behaviour, low cost and portability. The process parameters and the gun design have been optimised for the deposition of commertial plasma spray HA powders with different particle size distributions. The microstructure of the coatings was characterised using scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffractometry (XRD). The results are discussed in terms of the coating microstructure and the volume faction of the HA crystal phase with regardt o its decomposition phases. Moreover, the same powder materials have been deposited with a commertial F4 plasma spray gun and the resuting coating properties characterised and presented for comparison.
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