Date Uploaded: February 1, 2006, 8:17 pm
Last Edited: January 6, 2013, 12:09 am
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The Science of Galvy
Article © MAIL User: Tesserex
It has the look of authenticity, making it perfect for armor. It's corrosion resistant, and it's very cheap. However, chemically, this is also one of the most complicated materials because of its legendary zinc coating. This article will serve to explain the purpose and chemistry behind this coating, and how it protects the steel from corrosion. The article will also address some myths and concerns that many maillers have when working with this material.
Let's begin with the basics. What exactly is galvanized steel?
Well, first of all, the core is mild steel. Steel, put simply, is an alloy of iron with a small percentage of carbon, along with various other elements that give each type of steel specific properties. Mild steel, for our purposes, just means that it isn't rust proof, or non-stainless. It's fairly soft, and very cheap.
Zinc is a metallic element, abbreviated Zn. It's number 30 on the table. It's bluish-white, quite shiny, and is otherwise ordinary as far as metals go.
Galvanized steel is made by coating mild steel with zinc through one of a few methods. One is hot-dip, where clean, fluxed steel is dipped into a vat of liquid zinc. This coats it with a fairly thick layer, and is common for industrial applications. You can find pieces of hot-dipped galvanized steel on the side of the road as guard rails. Another method, electroplating, is how I think our wire is coated. The layer is thinner because it is added one atom at a time, but it is also much smoother. It involves dipping the steel and a piece of zinc into an electrolyte solution with a current and allowing the Zn ions to float over to the steel.
Now that we know what it is, let's take a look at how galvanized steel works. But before we begin, I'd like to personally dispel a myth that has arisen through the slightest miscommunication among maillers.
It has been mentioned before, but it should be reiterated.
Zinc, the pure metal, is not, I repeat, NOT toxic in any way except for overdose, in which case the zinc overtakes and prevents absorbtion of other important minerals. In fact it is a necessary part of your diet. There is no danger from zinc metal when weaving maille. Still, don't let your guard down yet...
The zinc plating protects the steel underneath from corrosion through a patina which forms in a series of reactions. The first, the one we are all familiar with, actually happens instantly.
2Zn(s) + O2(g) -> 2ZnO(s)
In this reaction, the solid zinc reacts with atmospheric oxygen to form a thin layer of zinc oxide. Zinc oxide is a powdery white substance used in paints and sunscreen. This begins within seconds of the piece being reintroduced to air. The galvy you get already has this layer developed. It is not the dull protective patina. The following is.
ZnO + CO2 -> ZnCO3
Over a long period of time, the zinc oxide layer reacts with carbon dioxide in the air to form zinc carbonate, another white substance that dulls the surface of galvy and protects the steel very well from corrosion. While this may not look very good for maille purposes, it is extremely beneficial for industrial use where maintaining the condition of steel pieces is important far above appearance.
Finally, there is one more substance you may find on your galvy, and this one is the elusive one that may be responsible for some strange properties.
ZnO + H2O -> Zn(OH)2
The oxide layer reacts with moisture in the air or from any other source to produce zinc hydroxide. This substance is also white, but it's much thicker and more visible. It is also easy to remove from the surface with some rubbing.
This along with the regular Zinc Oxide are what cause the bad smell we find on our galvy. Avoiding humidity is the best way to prevent this. Also, the zinc can react with moisture in the skin to produce a green residue.
Finally, the important issue. Safety.
As I stated before, zinc metal is harmless. What is not, however, is the oxide. The oxide layer you will have on all metal pieces is not significant. ZnO, when ingested, is very mildly toxic, so chewing rings shouldn't be a problem (except for your teeth). Zinc Oxide is most dangerous when inhaled. This happens usually when the zinc metal is burned in any way. As it burns, a white wispy cloud of oxide is released.
This is dangerous. Do not weld or burn galvy without ventilation and safety gear. For that matter, if you're going to put the effort into welding your maille, use better materials for it.
Inhalation of Zinc OXIDE is, I repeat, IS HARMFUL. This means do NOT burn galvanized steel. If for any reason you do see white clouds coming from the material, avoid inhaling it.
The other two chemicals, the hydroxide and carbonate, are listed on MSDS as harmful if swallowed, but there shouldn't be enough coating your rings to worry about, even if you accidentally swallow one. If you do, you should be worried about things other than the chemicals making you a little bit sick.
So to recap:
Zinc metal - harmless
Zinc OXIDE - harmful when inhaled
Zinc carbonate - dulling patina substance
Zinc hydroxide - pasty, stinky residue
For reference, here is an email reply I received from Kurt Etter, a corrosion engineer with the American Galvanizers Association:
"The galvanized steel process that you have listed is correct. In order to get a white rust to form on galvanized steel usually it is best to place a piece of steel in a sealed bag with wet paper towels or rags in the bag. Then place these bags in an area that has a high level of sunlight exposure. This creates the humidity which is what creates the oxidation to form and create the white rust. Direct contact with water will not achieve this correctly. The smell that is created from galvanized steel is the zinc hydroxide / zinc oxide that is released from the surface as the steel is oxidized with the air around it. The green color is created from a reaction with the moisture in the skin and creates the oxidation of the steel in an accelerated process."
Thank you for reading. I hope you learned something new about your favorite maille material today.
Original URL: http://www.mailleartisans.org/articles/articledisplay.php?key=372