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Zinc (Zn) and its alloys are considered as promising biodegradable metals due to its suitable degradability and important physiological functions. However, in the process of degradation, excessive release of Zn ions (Zn2+) will significantly affect the cytocompatibility and antibacterial properties. Surface modification technology can not only control the corrosion behavior of biodegradable metals but also improve its biocompatibility and antibacterial properties according to clinical requirements. In this study, an in-situ hopeite (HP, Zn3(PO4)2·4H2O) coating was prepared on Zn alloy by phosphate chemical conversion (PCC) method using Zn2+ provided by self-corrosion of the substrates. And the effect of phosphating time on the microstructure, phase composition, corrosion resistance, and wettability of HP coatings was investigated. The results showed that a complete HP coating was formed on the Zn alloy after reaction for 1 min, even if Zn2+ were supplied by self-corrosion without an additional Zn source. It also revealed that the reaction time had a marked impact on the morphologies and microstructures of the HP coating. The electrochemical test results proved that the prepared HP coatings had obvious protection on the Zn alloy and could regulate the corrosion rate of the substrate. Meanwhile, the Zn alloy modified by the PCC method also possessed excellent hydrophilicity. These primary findings might support new opportunities in the exploration of controllable coatings on biomedical Zn alloys.

The effect of nano-scaled Si3N4 particles on the microstructure, mechanical and electrochemical behavior of hopeite (Zn3(PO4)2·4H2O) conversion coating on pure titanium was investigated. Different concentrations of nanoparticles were dispersed into the phosphating bath to incorporate the process of coating deposition. The XRD results demonstrated that nano-Si3N4 were doped into the coatings without any decomposition or reaction with the hopeite phase. A finer and denser microstructure of the composite coating could be obtained at the addition of 0.5 g/L Si3N4 in comparison with the pure hopeite coating. Moreover, the composite coating presented a higher bonding strength and corrosion resistance related to the refinement of microstructure and filling of the embedded nanoparticles. It is suggested that the incorporation of nano-Si3N4 particles in conversion coating is a promising approach for performance optimization.

Magnesium phosphate (MgP) has garnered growing interest in hard tissue replacement processes due to having similar biological characteristics to calcium phosphate (CaP). In this study, an MgP coating with the newberyite (MgHPO4·3H2O) was prepared on the surface of pure titanium (Ti) using the phosphate chemical conversion (PCC) method. The influence of reaction temperature on the phase composition, microstructure, and properties of coatings was systematically researched with the use of an X-ray diffractometer (XRD), a scanning electron microscope (SEM), a laser scanning confocal microscope (LSCM), a contact angle goniometer, and a tensile testing machine. The formation mechanism of MgP coating on Ti was also explored. In addition, the corrosion resistance of the coatings on Ti was researched by assessing the electrochemical behavior in 0.9% NaCl solution using an electrochemical workstation. The results showed that temperature did not obviously affect the phase composition of the MgP coatings, but affected the growth and nucleation of newberyite crystals. In addition, an increase in reaction temperature had a great impact on properties including surface roughness, thickness, bonding strength, and corrosion resistance. Higher reaction temperatures resulted in more continuous MgP, larger grain size, higher density, and better corrosion resistance.