The process of ternary Ni–Co–P alloy films deposited on fly ash cenospheres (FACs) through a modified electroless plating way is documented. A pretreatment of FACs by γ-aminopropyltriethoxy silane (APTES) was introduced prior to electroless plating, which improved the continuity and uniformity of the alloy films remarkably. During the plating process, three factors were taken into consideration to investigate the composition and the plating rate of the deposits: mole ratios of NiSO4/CoSO4, the sodium hypophosphite concentration and pH of the plating bath. The obtained Ni–Co–P alloy deposits were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results suggest that the as-plated deposits were Ni–Co–P alloy microparticles, which transformed from amorphous state to crystal phases with the increase of calcining temperature. In addition, the electroless Ni–Co–P deposits exhibit soft magnetic properties at room temperature. The magnetic performances of the deposits would be ameliorated with the increase of the cobalt content of the coating and calcining temperature.

Preparation and characterization of electroless Ni–Co–P ternary alloy on fly ash cenospheres

Electroless Ni-Co-P coating and Ni-Co-P-SiO2 nanocomposites were successfully applied on AZ91D magnesium alloy via environmentally friendly cerium-lanthanum-permanganate treatment and their properties were compared with traditionally binary Ni-P coating. The prepared coatings were analyzed using scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy. Moreover, the corrosion behavior of the coatings in 3.5 wt.% NaCl was evaluated by two electrochemical methods. It is found that the Ni-Co-P coating possesses more uniform and compact structure and better corrosion protection characteristics in comparison with the Ni-P coating. The plating rate of Ni-Co-P bath is relatively lower than the Ni-P bath, but it significantly increases after addition of SiO2 nanoparticles more probably due to adsorption of silica nanoparticles on alloy surface. The corrosion resistance of Ni-Co-P-SiO2 composite coatings was superior with respect to Ni-P and Ni-Co-P coatings due to formation of thick and compact coating with tortuous grain boundaries.

Corrosion Resistance Enhancement of AZ91D Magnesium Alloy by Electroless Ni-Co-P Coating and Ni-Co-P-SiO2 Nanocomposite

Electroless Ni-Co-P-coating of fly-ash cenosphere particles is demonstrated in the present investigation. The Electroless Ni-Co-P-coating process is modified by replacing the conventional sensitization and activation steps with only using activation step with Ag(NH3)2+ activator. The cenospheres are characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDX), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS) during and after the coating process. Relatively uniform coating is obtained under the given coating conditions. The possible mechanism of electroless Ni-Co-P-coating of cenospheres utilizing Ag(NH3)2+ activator is suggested. The low density Ni-Co-P coated cenospheres may be utilized for manufacturing conducting polymers for EMI-shielding application and microwave absorbing materials.

Y.C. Hsu

Papers

Growth behavior of electroless Ni–Co–P deposits on Fe