Deposition of zinc coatings with fluidized bed technique

Zinc is known to be an ideal coating material for steel protection aiming to improve its anticorrosion performance. Up to now, hot-dip galvanizing is the industrially used coating technique for zinc. Its high environmental impact imposes the development of alternative techniques such as fluidized bed procedure. Under this procedure zinc was deposited by inserting the substrates in the reactor at room temperature. Afterwards the reactor was heated at the process temperature (400 °C) and holding time varied from 0 min to 2 h at the final temperature. The as-coated samples were examined with Scanning Electron Microscopy (SEM) associated with Energy Dispersive Spectroscopy (EDS), Transmission Electron Microscopy (TEM) and X-ray diffraction analysis (XRD). From this process two-layered coatings were formed. The main phases observed were gamma and delta phase of the Fe–Zn phase diagram. Some of the as-received coatings are likely to provide sufficient anticorrosive protection while others are of low quality because of porous areas in their mass. In addition a comparison is made with FBR zinc coatings produced in a preheated reactor, zinc pack coatings and hot-dip galvanized coatings.