What is the impact of lead in molten zinc on hot-dip galvanizing? Why is lead used as a lining at the bottom of galvanizing pots?

Lead (Pb) has a cubic crystal lattice, a gray appearance, an atomic weight of 207.21, a melting point of 327°C, and a boiling point of 1540°C. It has limited significance in the galvanized coating during hot-dip galvanizing, and its content is preferably not to exceed 0.3% (equivalent to the lead content in Zn-Grade 4 zinc), as it possesses a higher electrical potential when combined with zinc, thereby reducing the corrosion resistance of the galvanized layer. When the lead content exceeds 0.5%, it not only exacerbates the adverse effects on corrosion but also causes the galvanized layer to appear dull and lifeless. Tests have proven that lead only exists in the pure zinc layer phase and is absent from the iron-zinc alloy layer. Therefore, lead as an alloy component of zinc has no significant effect on the iron-zinc reaction. Some factories place lead in galvanizing pots, with a thickness of up to 10-30 centimeters at the bottom. The purpose is to prevent zinc slag from settling and adhering to the steel bottom due to heat, and also to facilitate the removal of zinc slag during skimming due to lead's low solidification temperature. However, some factories have stopped using lead for several reasons. Firstly, lead cannot be effectively recovered, increasing costs. Secondly, the majority of galvanizing pots now adopt side heating methods. A significant amount of heat is exchanged at the upper part of the sidewalls of the galvanizing pot, making the temperature at the bottom much lower, thus rendering the protection of the pot bottom unnecessary. Thirdly, the emission of lead vapor poses a certain risk to operators and contaminates the environment.