Plasma surface treatments of Al2O3/ZrO2 nanocomposites and their influence on the formation and adhesion of calcium phosphates

Abstract In the present work, Al2O3/ZrO2 nanocomposite surfaces were treated with plasma under gaseous atmospheres with different proportions of N2, H2, and O2 to improve the adhesion of biomimetically deposited calcium phosphate layers. Initially, samples of Al2O3/ZrO2 were shaped and sintered at 1500 °C for 2 h. Subsequently, the surfaces were treated and coated with calcium phosphate. The treated and untreated surfaces before and after the deposition of the biomimetic coatings were characterised using scanning electron microscopy, confocal microscopy, infrared spectroscopy, X-ray diffraction, and a scratch test. The results showed that pre-treatment increased the amount of calcium phosphates formed on the surface regardless of the gas composition used owing to the increase in polarity on the treated surfaces and formation of oxygenated groups such as Al-OH and Zr-OH. The phases of calcium phosphates formed were: hydroxyapatite (HA), α-tricalcium phosphate (α-TCP), and β-tricalcium phosphate (β-TCP). Although the HA phase was predominant, the α-TCP phase was responsible for increasing the adhesion of calcium phosphates onto the surface. Among the gaseous compositions used, the combination of 30% N2, 50% H2, and 20% O2 favoured the highest formation of phosphates on the surface of the nanocomposite.