Hopeite and scholzite coatings formation on titanium via wet-chemical conversion with controlled temperature

Abstract A modified wet-chemical conversion technique with controlled mild temperature has been utilized to prepare zinc phosphate (Zn P) and/or calcium-containing Zn P (Ca-Zn-P) coatings on the surface of pure titanium (Ti). Their X-ray diffractometer (XRD) patterns were indexed to typical hopeite (Zn3(PO4)2·4H2O) and scholzite (CaZn2(PO4)2·2H2O), respectively. The influence of solution temperature on coating composition, microstructure and bonding strength between the coating and substrate was investigated by XRD, field emission scanning electron microscope (FE-SEM) and an acoustic emission scratch tester, respectively. A growth behavior of hopeite and scholzite coating was also explored by morphology evolution within the initial reaction stage. The results indicated that the microstructure and crystal size of the coatings were strongly impacted by solution temperature, while a hopeite or scholzite coating with fine and homogeneous microstructure could be obtained at 55 °C. Moreover, the scholzite crystal represented a radially nucleation-growth pattern through tracking observation of morphology evolution.