Investigation Of Nickel And Nickel-phosphorus Coated Tungsten Powders By Pulse Electrodeposition

The performance of composite is improved by the synergistic effect of substrate and coating.Firstly,the powders provide great surface area for metal to deposit,and improve the thermal stability of coating.Secondly,the coating can protect and modify the powders,such as improving the corrosion resistance and thermoelectric property of the powders.The nickel?Ni?and nickel-phosphorus?Ni-P?on tungsten?W?powder were prepared effectively by pulse electrodeposition in the paper,the coating was integrated and uniform.It was studied that the Ni with different phase structure could be prepared?amorphous and cubic?on W powders,by controlling experimental parameters during electrodepostion,and also the W powders could improve the thermal stability of amorphous Ni.The crystallization mechanism was discussed based on Gibbs crystal growth theory and Ostwald's rule.Ni-P coated W powders were prepared successfully in paper,the influence of technological parameters,such as the concentration of reducing agent and current,on the morphology and composition of the coating were studied.It was found that the P content in the coating was closely related to them.The specific research contents are summarized as follows:?1?The voltage and deposition time had a great influence on the phase structure of Ni deposited on W powder.Under the condition of low voltage and short deposition time,the Ni presented amorphous.When prolonged the electrodeposition time or increased voltage,the structure of Ni layer changed from amorphous to crystalline.?2?Combined with DSC data and Kissinger's mathematical model analysis,the thermal stability of amorphous Ni was obviously improved by tungsten powder as heat sink,crystallization temperature increased to 885 K at the rate of 0.333 K?s^-1.At the same time,the crystallization energy of amorphous Ni was calculated to be 149.7kJ?mol^-1,which is obviously lower than that of amorphous alloy.?3?On the basis of Gibbs crystallization theory and Ostwald's theory,the effect of voltage and deposition time on the structure transition of Ni from amorphous state to cubic crystal is analyzed.?4?By analyzing the composition and morphology of Ni-P coating,it was found that the content of P in the sample was greatly affected by the concentration of reducing agent and the current.Ni tended to deposit at high current,while P tended to deposit at low current.The current was lower or the concentration of reducing agent was higher,the higher P content in the coating shown.The morphology of the coating was also determined by the P content,the P content was higher,the spherical structure was more obvious.?5?Based on the XRD data and the Scherrer formula,it was concluded that the crystallinity of the coating was determined by the P content in the coating.The higher content of P was,the broader diffraction peak of the?111?crystal plane became.It was implied that the phase structure of the coating was transformed from crystal to amorphous.Due to the doping of P atoms,the lattice parameter of nickel deviates from the standard value and lattice expansion.