The Production of Nickel-Zinc Alloys by Powder Injection

Alloys of nickel and zinc are used for the hot dip galvanizing of reactive steels containing around 0.1 pct Si. The production of these alloys is hindered by the low solubility of nickel in molten zinc at normal zinc alloying temperatures (450 °C to 550 °C). The kinetics of the dissolution of nickel in molten zinc were investigated in the temperature range 450 °C to 550 °C to show that the dissolution rate is controlled by mass transfer in the liquid boundary layer. The experiments involved dipping nickel plates into a crucible of zinc, which could be rotated to provide controlled convection around the stationary nickel plates. The dissolution rate of nickel plates immersed vertically in a static zinc melt was measured to determine the diffusion coefficient of nickel in zinc as a function of temperature and the activation energy of diffusion. A mathematical model was formulated to predict the dissolution time of nickel particles suspended in molten zinc. The dissolution times observed during plant-scale alloying tests to produce 0.15 wt pct Ni alloys using powder injection to introduce the nickel into the zinc melt agreed with the predictions of the mathematical model. The plant tests demonstrated that alloying times of less than 10 minutes can be achieved at normal alloying temperatures if the nickel is added as a powder.