A Problem about Zinc Coating

[joylinkwu]

Dear Mr. Gordon,

I have prepared a zinc coating on a steel substrate for corrosion resistance with arc wire spray process, and it has been put in the air for 3 months.
I want to know how much the coating was corrupted. So I dipped it in NaOH solution in order to solve something like basic zinc carbonate or zinc oxide. But after a day I found that the coating was bubbly. I consider that the probable reason is a part of zinc oxide, which had been produced during spraying process, was solved.

I wonder if there are some good methods to gain my ends.
Looking forward to your help.

Regards.

Joylinkwu[/u]

[Gordon]

Hi Joylinkwu

to the Surface Engineering Forum.

In the typical environments these coatings are employed, I would expect to see very little degradation of the coating in a 3 month period and measuring the effect I think will be very difficult. Chemical analysis of the coating will always be clouded by the background of oxidation from the spraying process. Measuring mass difference may be a better approach, but this is complicated by the fact that corrosion products retained in or on the coating may show increasing mass initially. Electro-chemical methods are used for shorter term testing /monitoring, but I think for really meaningful results you will need something like this (link dead) to do this yourself may take the rest of your working life

[basakglkn]

Hi,

I was just thinking what would happen if we use a protective gas instead of air?

Well it would not be cost effective for sure, but i assume it would work if you are so keen on decreasing the amount of oxide in the sprayed metal formed during spraying...

Another question is, is not the amount of oxides of TS metal formed during the operation negligable as there is no sufficient time for the kinetics of oxide formation?

All the best...

[ThermalMan]

You could try nitrogen or argon instead of air for arc spraying, this would reduce oxidation, but not eliminate it unless you spray in an inert chamber. I don't really see the point, unless its purely an academic study as it bears no relation to the real world.

3 months testing in air, that possible equates to less than 1% of the potential coating life. I think to be useful the testing period needs to be extended greatly.

A fair amount of oxides are produced during arc spraying, though with zinc most comes of as zinc oxide fume, but I'm sure some is included in the coating.