Hydroxyapatite coating on AZ91 magnesium alloy via sol-jel method for biomaterial applications


Thesis Type: Postgraduate

Institution Of The Thesis: Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey

Approval Date: 2017

Student: SEVDA ALBAYRAK

Supervisor: HANİFİ ÇİNİCİ

Abstract:

AZ91 magnesium alloy block specimens were produced by powder metallurgy method for use in biomedical applications and after hydroxyapatite (HA) coating was performed by sol-gel method using dip coating method, in this study. The effect of the number of dips (1, 3, and 5 dipping) and calcination temperature (300, 400, and 500 ° C, 1 °C/min heating rate, 1 hour) were investigated. In order to obtain HA with a Ca/P stoichiometric ratio of 5/3, calcium nitrate tetra hydrate (Ca(NO3)2.4H2O) and di phosphorus penta oxide (P2O5) were used as Ca and P precursors, respectively. The substrate AZ91 Mg alloy specimens were immersed in the obtained solution by dip coating method at a fixed rate (200 mm/min). Coated samples were exposured to drying and calcination processes. Surface roughness values of uncoated and HA coated samples were measured by surface profilometry. Coating thicknesses and surface morphologies were analyzed with SEM and AFM. Structural analysis was investigated by XRD. Finally, corrosion behaviors of those specimens were tested by potentiodynamic electrochemical corrosion tests using SBF at 37 °C and 7,4 pH value. As a result of the study, a homogeneous HA coating layer was obtained on the surfaces. As the number of dips and calcination temperature increased, the coating thickness and surface roughness increased. It was also found that the increase in the number of dips and calcination temperature, increased the corrosion resistance. It was observed that the calcination temperature is close to the melting point of AZ91 Mg alloy adversely affected the quality of the coating and the corrosion resistance of the specimens.