Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/41619

Title

Structural changes of thermally sprayed hydroxyapatite investigated by Rietveld analysis

Author(s)

Knowles, Jonathan Campbell;  Gross, Karlis A.;  Berndt, Christopher C.;  Bonfield, William

Abstract

Hydroxyapatite (HA) coatings were prepared by three thermal spraying methods: flame spraying, high velocity oxygen fuel spraying and plasma spraying. The HA was then examined by Rietveld analysis using the General Structure Analysis Software package (GSAS) and the results compared with those for the precursor powder. A comparison between HA before and after spraying showed that all three spraying methods caused a distortion in the unit cell in the form of a unit cell a-axis length decrease and a c-axis increase. Overall unit cell volumes showed a difference between the three thermal methods, with flame spraying and high velocity oxygen fuel methods giving a unit cell volume increase and the air plasma spraying method showing a decrease, compared to the starting powders. The two different starting powders used each showed a high oxygen occupancy for the hydroxyl oxygen. When thermally sprayed, both powders gave a reduction in occupancy, which suggested carbonate substitution for the OH group, but this was subsequently removed when thermally processed. The spraying also formed oxyapatite, indicated both by spectral analysis showing a reduction in the hydroxyl peak and by the hydroxyl oxygen occupancy falling to a level below 0.5. Major differences between the three spraying methods could be seen in the distortion index calculations. The thermal spraying techniques gave an increase in the distortion index, but it was significantly higher for the plasma-sprayed coating. Hydroxyapatite (HA) coatings were prepared by three thermal spraying methods: flame spraying, high velocity oxygen fuel spraying and plasma spraying. The HA was then examined by Rietveld analysis using the General Structure Analysis Software package (GSAS) and the results compared with those for the precursor powder. A comparison between HA before and after spraying showed that all three spraying methods caused a distortion in the unit cell in the form of a unit cell a-axis length decrease and a c-axis increase. Overall unit cell volumes showed a difference between the three thermal methods, with flame spraying and high velocity oxygen fuel methods giving a unit cell volume increase and the air plasma spraying method showing a decrease, compared to the starting powders. The two different starting powders used each showed a high oxygen occupancy for the hydroxyl oxygen. When thermally sprayed, both powders gave a reduction in occupancy, which suggested carbonate substitution for the OH group, but this was subsequently removed when thermally processed. The spraying also formed oxyapatite, indicated both by spectral analysis showing a reduction in the hydroxyl peak and by the hydroxyl oxygen occupancy falling to a level below 0.5. Major differences between the three spraying methods could be seen in the distortion index calculations. The thermal spraying techniques gave an increase in the distortion index, but it was significantly higher for the plasma-sprayed coating.

Publication type

Journal article

Source

Biomaterials, Vol. 17, no. 6 (Mar 1996), pp. 639-645

Publication year

1996

Keyword(s)

Biocompatible materials;  Biomechanics;  Carbonates;  Carbonic acid;  Chemical models;  Chemical modification;  Computer aided analysis;  Computer simulation;  Distortion index;  Flame spraying;  Fourier transform infrared spectroscopy;  General structure analysis;  HA;  High velocity oxygen fuel spraying;  Hydroxyapatites;  Hydroxyl group;  Hydroxyl oxygen;  Intermethod comparison;  Oxygen;  Phosphate coatings;  Plasma spraying;  Powders;  Rietveld analysis;  Spectroscopy;  Spectrum analysis;  Sprayed coatings;  Structural changes;  Structure analysis;  Thermal spraying;  Velocity;  X-ray diffraction;  XRD

Publisher

Elsevier

ISSN

0142-9612

Publisher URL

http://dx.doi.org/10.1016/0142-9612(96)88715-1

Copyright

Copyright © 1996 Published by Elsevier Science Ltd.

Peer reviewed