Synthesis and characterization of ultrafine hydroxyapatite (HAp) powder coating on stainless steel substrate by electrophoretic deposition.

Abstract

In recent years, synthesis and characterization of ultrafine hydroxyapatite (HAp) powder coating on stainless steel substrate by electrophoretic deposition gives an active area of research due to their enhanced applicability in the medical field. This makes them very attractive as prosthetic replacements.
Ultrafine HAp powder was obtained by milling elemental calcium phosphate mineral. The HAp powder was dispersed into isopropyl alcohol by ultrasonication and magnetic stirring. The HAp powder was deposited by electrophoretic deposition (EPD) using lead as anode and stainless steel substrate as cathode. Powder was coated on stainless steel substrate at a voltage of 60 volt and time was varying from 15 minutes to 1.5 hours. It was observed that HAp powder deposited at 60 volt for 45 minute gives the best coating. In another set of experiment, coating time was 45 minutes having periodic time of 10 minutes with gap of 2 minutes. It was also observed that there is lack of adherence of powder particles with the substrate. To improve adherence of particles with substrate a surfactant sodium dodecyl sulfate (SDS or NaDS) (C12H25SO4Na) was added during EPD process and subsequently sintering was performed at 8000C for 2 hours in open atmosphere. X-ray diffraction (XRD) shows the peaks of HAp after deposition.
It was observed from XRD spectra that XRD patterns of HAp powder that was prepared by planetary milling and HAp powder was deposited on stainless steel substrate by EPD at 60 volts for 15 minutes. Here the some peaks of HAp are visible in the coated substrate along with peaks of stainless steel. The intensity of HAp peaks in the coated substrate is lesser than pure HAp powder. This is due to the presence of large peak of stainless steel along with HAp.
It was observed from SEM analysis that HAp deposited on stainless steel substrate at 1 hour shows smooth and good adherence where as for deposition of 1.5 hours shows discontinuous and non-adherence deposition. As the time of deposition is increased there may be formation of thick layer which may generate cracks.