Microstructural Analysis and Photocatalytic Activity of Plasma-Sprayed Titania-Hydroxyapatite Coatings

Abstract

Hydroxyapatite (HAp Ca10(PO4)6(OH)2) is known to be a biomaterial and an adsorbent for chromatography. In this study, HAp was agglomerated with anatase TiO2 to manufacture thermal-spray powders to improve the adsorption activity of TiO2, and then to improve its photocatalytic activity. The microstructures, compositions and photocatalytic activity of plasma-sprayed TiO2, TiO2-10%HAp, TiO2-30%HAp, and HAp coatings were investigated. Due to the low thermal conductivity of HAp compound, not all HAp particles fully melted even under the arc current of 800 A. The addition of HAp inhibited the phase transformation of anatase TiO2 to rutile. Under the arc current of 600 A, the anatase content in the TiO2, TiO2-10%HAp and TiO2-30%HAp coatings was 11, 20 and 42%, respectively. With the increasing of the spraying distance from 70 to 110 mm, the anatase content in the TiO2-30%HAp coatings decreased from 34 to 17% under arc current of 700 A. Furthermore, a slight decomposition of HAp to α-Ca3(PO4)2 was found in the TiO2-30%HAp coatings, it did not decompose to CaO and P2O5 according to the XRD and EDAX analysis. The addition of the secondary gas of helium had no significant influence on the melting state of the TiO2-HAp feedstock powders. Moreover, the HAp in the TiO2-10%HAp and TiO2-30%HAp coatings had adsorption characteristic to acetaldehyde. The photocatalytic activity of TiO2-10%HAp coating was highest among TiO2, TiO2-10%HAp, and TiO2-30%HAp coatings sprayed under the arc current of 600 A for the optimum adsorption property and anatase content.