Morphology and composition of nickel–boron nanolayer coating on boron carbide particles

This work is focused on electroless coating of Ni–B nanolayer on B4C particle surfaces. The B4C particles used are approximately 2 lm in average size. Effects of activation agent PdCl2, complexing agent C2H8N2, and reducing agent NaBH4 addition rate are studied. The solids loading of B4C is 0.625 g/L and the concentration of Ni2+ ions is 0.004 mol/L in the electroless coating solution. Scanning electron microscopy (SEM) shows that when B4C:Pd2+ molar ratio is 1:0.005, a Ni–B nanolayer with the smallest Ni–B nodule size covers the B4C particle surfaces. Complexing agent C2H8N2 decreases Ni2+ ion release rate. Ni:C2H8N2 ratio of 1:6 is the preferred complexing agent amount for achieving a continuous Ni–B nanolayer. The Ni–B nanolayer formation is also strongly dependent on the rate that Ni2+ ions are reduced. Slow Ni2+ reduction leads to increased Ni content in the Ni–B nanolayer. When the above three factors are combined at the optimal values for the electroless coating process, well-defined Ni–B nanolayer is obtained. SEM cross section analysis shows the Ni–B nanolayer completely covers the B4C particles with less than 55 nm thickness