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[deleted] t1_isg380z wrote

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ekjustice t1_isge6q2 wrote

It has a current going through the liquid and into the metal object, that's why they call it "galvanized". The electricity bonds the zinc to the steel better than just dipping it.

Some items are just dipped in liquid zinc "hot dipped". This leaves more zinc on the item and tends to be more expensive.

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the_snook t1_isghskh wrote

It can also depend on the type of coating. Some "galvanized" steel is actually Zincalume, which is coated with a zinc-aluminium-silicon alloy. From memory, I think Zincalume has more prominent crystal structure (though maybe it was just because of the particular manufacturer of the stuff I saw).

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JenJudy t1_ishjwho wrote

The term galvanized originally meant electroplated, and didn't specify what metal was used, but it gradually came to mean primarily electroplating with zinc. In modern usage, it simply means coated with zinc, regardless of whether it's electroplated or hot dipped, at least according to Merriam-Webster who give this definition:

>: to coat (iron or steel) with zinc

>especially : to immerse in molten zinc to produce a coating of zinc-iron alloy

This is consistent with the way the term is used indescribing finishes on bolts, etc, by both professional sources such as McMaster or consumer sources such as home depot. The most common options are called zinc plated, which is electroplated, and hot dip galvanized, which does not involve an electric chemical process, in contrast to the origin of the term.

It's surely irritating to electrochemists that the meaning has shifted to go beyond electrochemical processes, but language change is inevitable.

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BigBobby2016 t1_isg69jf wrote

Is there any galvanized steel that doesn’t have patterns? OP says “some”

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shouldco t1_isgah1l wrote

Yes and no.

The prominence of the patten varies to the point of not being discernible. In theory you could have a single crystal but let's just say that is practically impossible for anything commercially produced.

Basically each section of the pattern is a single crystal of zinc. Which means there was basically one nucleation point every 1/2 a square inch or so. In order to get that few you need a pretty smooth piece of steel so it is more prominent on things like cold rolled steel and sheet metal. Stuff like cast steel has a very rough texture and can have thousands of nucleation points per sqin and as such you will basically just see a flat gray color with the naked eye.

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Br4veSirRobin t1_isghn1y wrote

It's called galvanneal and it is used in painted car panels. After dipping in zinc the steel goes through a furnace to slow nucleation-crystallization. It is a matte gray finish and paint sticks to it very well.

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LameTrouT OP t1_isgicpz wrote

I believe they must do this for hand rails ls that get a color after getting gavinized?

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Br4veSirRobin t1_isgj7kg wrote

The patterns on the surface of galvanized steel are called 'spangle'. People who use galv steel order spangle size. Antimony is used in the molten zinc bath for spangle size control among other process controls. Metallurgist here.

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cr0n1c t1_ish88jy wrote

So far down to find someone finally saying Spangle. Thank you.

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Br4veSirRobin t1_isgirrk wrote

True. Any painted galvanize is is usually galvanneal. I was a metallurgical engineer in both carbon steel and titanium.

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shouldco t1_isgmwn7 wrote

Thank you, I was unfamiliar with that industrial application.

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[deleted] t1_isg4jmu wrote

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TuckerMouse t1_isgcjj5 wrote

The other responses talk about the zinc crystallization, but I wonder if you mean something else. Do you mean how sheets of galvanized steel often have a pattern of indents, maybe in two perpendicular or close to perpendicular angles, and some galvanized steel is smooth, like hand rails or guard rails on a highway?
If so, the indents, or embossing, help with traction when walking on it, help keep it rigid, helps water flow off it, and other benefits, while a hand rail or guard rail doesn’t benefit from any of that, so why bother spending the money embossing something that is at best aesthetic and at worst actively detracts from the function.

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littleherb t1_iskq4v5 wrote

You may be referring to "white rust", which is zinc hydroxide. The way galvanizing works is by depositing a sacrificial layer of zinc over the steel, usually by dipping the steel parts in molten zinc. As the zinc cools, it forms a protective layer of zinc oxide on its exterior surface. If it is allowed to get wet (directly or from high humidity/condensation), the zinc bonds with the hydrogen and oxygen from the water to form zinc hydroxide or "white rust". Stacked sheet metal is especially prone to this due to stacking, where moisture can be trapped between layers. You will also see this on larger structural members if they are not stored properly immediately after galvanizing.

Reference: I am a structural engineer with a lot of history in steel. Also: https://www.metalsupermarkets.com/what-is-white-rust/

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TeaTimeSoon t1_isnoxx7 wrote

I used to be the person responsible for the sale of over 30% of the entire UK demand for the artificial sweetener know here in the UK as saccharin. My largest customer in the UK was a large electroplating company called William Canning of Birmingham. They called saccharin a "brightener" but actually it is simply a zinc crystal disruptor and acts at the boundaries of the deposited zinc crystals as the zinc ions attach to the surface during electroplating. The optical effect of large zinc crystals is avoided using saccharin. The saccharin molecules act as a kind of traffic control officer at the boundary edges and new crystals are formed which are so small the surface will appear to be polished.

I believe a similar effect is seen with zinc/nickel and pure nickel electroplating as well. The effect is seen immediately after electroplating and is not a corrosion induced artifact.

It is always amazing to look at a zinc plated surface where a "brightener" has not been used. The crystal boundaries are so large - in fact I think they look attractive in their own right. No good if you want a shiny finish though!

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