Galvanizing removal

[lurks]

I am trying to remove the layer of galvanizing from a bolt by means of heat to acquire a sample of the galvanizing to analyze for chemical composition. Does anybody know if this is possible and what temperature is necessary to achieve this. The galvanizing should be Zn (98-99%) alloyed with Lead, Iron, Cadmium, Aluminum, Copper, and Tin.

 

[Compositepro]

Why not scrape some off with a sharp knife? Heat will not remove it without changing its composition (oxidation).

Hydrochloric acid will also work and will probably be used in the chemical analysis, but scraping is so much easier and will make the analysis simpler.

 

[unclesyd]

Years and years ago we stripped zinc with Cu sulphate and years age we used a potentiometric analysis of the zinc for Lead, Cadmium, and others.

There are some standard methods for doing this either NACE or ASTM.

 

[lurks]

The ASTM spec calls for the removal of the zinc by use of Hydrochloric Acid. With this you can analyze the solution of zinc and acid. The reason that I am trying to acquire an ingot of zinc from the bolts is to use our spectrograph internally. From the experimenting that I've done thus far it does not seem possible to separate the galvanizing from the bolt by any other means.

 

[swall]

One problem you are up against is the zinc-iron intermetalic layer between the pure zinc and the iron base. You need a method that will remove the zinc layer only; I'm not sure if the acid trick will work for this.

 

[Ron]

Don't use heat. As others noted, it will change the properties of zinc. Further, if you are taking the sample from a hardened bolt, you might screw up the bolt by heating it.

With the availability of microscopic analysis techniques, you'll only need a small sliver of the galvanizing. If you could remove the bolt, it could be analyzed non-destructively using SEM/EDS.

 

[unclesyd]

If I'm understanding your OP correctly you want zinc from a galvanized component for an internal standard for spectroscopy.
In you case a galvanized bolt taken from a lot of bolts could have the same chemistry as one two or many or none in the lot. There is no traceability on a galvanized fastener. A keg of HDG bolts again could come from one plant or commingled with fasteners from many plants.

To overcome the standardization problem we got 2 plants to make chill bar type samples from each line at several different intervals from initial charge to a dross rake. This was when Pb was still in the mix. By doing it this way we got rid of the Fe problem from sampling by only having to remove a very small sample of Zn from any component.
After Pb was removed from the process we just used a sample of ingot zinc, both virgin and reclaimed.

 

[strider6]

have a look at this site there are a lot of info on galvanizing and u can also ask question.

http://www.galvanizeit.org/aga/specifying-inspecting/inspection-of-hdg/

S



Corrosion Prevention & Corrosion Control

 

[mk3223]

In the past, the worker used to clean the pipe by burning off or grinding off the galvanized material. But, it created the fume which is harmful to human. Also, it might not total clean.

For the test, I suggest to use mechanical method to get a sample.