1.What are the electrical properties of the oxide layer itself?
The Nature of Zinc Oxide: Pure zinc oxide is actually a semiconductor. This means its conductivity lies somewhere between that of conductors (such as metals) and insulators (such as rubber).
Conductivity Mechanism: Zinc oxide's conductivity is closely related to its purity, structural defects, and ambient temperature. Under certain conditions, its conductivity is acceptable, but it is by no means a good conductor.
Comparison with Pure Zinc: Metallic zinc is an excellent conductor. When zinc oxide forms on the surface, this semiconducting film acts like a "shell" with greater resistance surrounding the conductor.
2.What about scenarios that require low-resistance, high-reliability electrical connections?
Increased contact resistance: When two galvanized components are connected (for example, by bolting), current must flow through the contact surface. The surface oxide layer significantly increases contact resistance.
Consequences:
Energy loss: According to Joule's law, increased resistance generates more heat at the joint, wasting energy.
Overheating of the joint: When high current flows, excessive contact resistance can cause severe heating at the joint, posing a fire risk.
Voltage drop: This causes a drop in voltage at the end of the line, affecting the proper functioning of equipment.
Poor welding quality: During spot welding or roll welding, the oxide layer can hinder the smooth flow of current, resulting in a weak or inoperable weld.
3.What role does it play as a functional coating or for general purposes?
Electrostatic Shielding: Even with an oxide layer on the surface, galvanized steel coils still provide excellent electrostatic shielding because they are conductive.
Ordinary Structural Parts: For ordinary structural parts that do not carry high currents, the presence of an oxide layer does not affect their structural function.
4.What factors affect the conductivity of the oxide layer?
Thickness: The naturally formed oxide film is very thin (typically only micrometers), so its overall resistance is not extremely high. However, if oxidation is severe and the film becomes thicker, conductivity will further decrease.
Composition and Structure:
Pure zinc oxide layer: Relatively dense, with poor conductivity.
Mixed layer: The "dust" on the surface of galvanized steel sheet is a mixture of zinc oxide, zinc hydroxide, basic zinc carbonate, etc., with a looser structure, and its conductivity may be worse than that of dense zinc oxide.
Environment: In humid environments, the oxide layer may absorb moisture, forming an electrolyte film, which in turn promotes conductivity through electrochemical means (but this often accelerates corrosion).
5.What are the effects on electrical connections?
This is extremely detrimental. It will significantly increase contact resistance, leading to overheating, increased energy consumption, and unreliable connections. It must be eliminated.