Abdullah, Che Wan NoorAkma
(2012)
Hydroxyapatite Coating On Magnesium Based Alloy For
Bioimplant By Cold Spray Deposition Technique.
Masters thesis, Universiti Sains Malaysia.
Abstract
In this study simple cold spray set up has been designed to coat AZ51 with
hydroxyapatite. The details of the set up and design of the spray process has been
presented. It was found that the qualities of hydroxyapatite coating were influenced by
the heating temperature of magnesium substrate, surface roughness of magnesium
substrate and also standoff distance. The coatings formed were compact and had good
adherence to the substrate. The coating thickness varied between 20 to 30 micron
meters. The chemical analysis identified the coatings as hydroxyapatite. Mechanical
properties of the coatings were evaluated by nanoindentation test. The hardness and the
elastic modulus of the coating were 0.1GPa and 9 GPa respectively. Further, the
biocompatibility as well as biodegradation of the hydroxyapatite coated AZ51 along
with uncoated AZ51 samples, were tested by subjecting them to in vitro test with
simulated body fluid solutions. The inductively couple plasma optical emission
spectroscopy and energy dispersive x-ray spectrometry analysis indicated that
hydroxyapatite coating started dissolving after one day but showed signs of regeneration
after 10 days of holding. Accelerated corrosion test in the 3.5% NaCl solution showed
that the HAP coating remarkably protected the AZ51 magnesium substrate till 10 days.
This continued till 21 days when most of the hydroxyapatite was replaced with
magnesium hydroxide and at the end chloride ions were also detected on the surface
indicating formation of magnesium chloride.
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