Mechanistic investigation of the influence of phosphoric and boric acids in the formation of homogeneous Ni–P/ZnO@SiO2 coatings

•Uniform distribution of ZnO@SiO2 NPs was achieved by adding phosphoric and boric acids.•The role of inorganic acids was investigated in the separation of colloid particles.•Probable mechanisms were proposed for the uniform deposition.•The corrosion resistance was improved by deposition of uniform nanoparticles.

High agglomeration of the nanoparticles and low volume fraction of nanosized inert particles within the nanocomposite thin films are found as the practical problems. In our previous work, silica coated ZnO nanoparticles (ZnO@SiO2 NPs) were synthesized to prevent dissolution of the ZnO nanoparticles (ZnO NPs) in the electrolytic Ni bath. The high agglomeration of these core–shell particles led to an unequal particle distribution in the deposit matrix. In this work, we aimed to prepare a highly homogeneous nanocomposite coating by stabilizing the nanoparticles in the medium. Adding the buffering agents, including phosphoric and boric acids to the medium, disclosed their new aspect of these inorganic acids in the prevention of particle agglomeration. The corrosion study of the resulting well-dispersed Ni–P/Zn@SiO2 nanocomposite coating confirmed a significant increase in anticorrosion performance. This increase was about 2.3 times compared to the previously prepared coating. Moreover, the probable mechanisms of phosphoric and boric acids in particle stability through the steric or/and electrostatic repulsion at the interfaces between the colloidal nanoparticles (ZnO@SiO2 NPs) and the electrolyte solution were investigated in detail.

Graphical abstractThe formation of the Ni–P/ZnO@SiO2 nano-composite coatings. (A) The agglomeration of nanoparticles forms the coating with no uniform distribution. (B) In the presence of phosphoric and boric acids, well-dispersed nano-composite coating is formed.Figure optionsDownload full-size imageDownload high-quality image (167 K)Download as PowerPoint slide