ELECTROCHEMICAL EVALUATION OF BIOGLASS/Al2O3 COATINGS SUPPORTED ON AISI 316L STAINLESS STEEL AND ITS RELATIONSHIP WITH THE FILMS BIOACTIVITY

Abstract

Bioglass/ Al2O3 powders and coatings at different ratios were synthesized by sol-gel process in order to evaluate the effect of alumina in the bioactive and electrochemical properties of the bioglass coatings. The ceramic powders were structurally characterized using the x- ray diffraction and Infrared spectroscopy techniques, which evidenced that aluminum ions replace calcium ions in the bioglass and that Si-O-Al bond is formed in the composites. From in vitro bioactivity tests in simulated body fluid could be inferred that the new bonds decrease  the  bioglass  bioactivity  because  aluminum  acts  as  a  barrier  to  the  generation  of  Si-OH  bonds,  which  are  necessary  for nucleation  of  apatites  from  the  simulated  body  fluid.  The  electrochemical  characterization  performed  through  linear  polarization resistance, potentiodynamic polarization and electrochemical impedance spectroscopy testing showed that the increasing of the alumina content  of  the  bioglass/Al2O3  composite  promotes  the  AISI  316L  steel  substrate  polarization  resistance.  Although  bioglass  coating provides a lower protection to the substrate against corrosion, because of its high reactivity in the simulated body fluid, such behavior is reversed once the apatite layer has been formed, since it acts as a diffusional barrier to medium electroactive species.