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Karen B

Hardened Zinc

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Karen B    26

My 50lbs bag of Zinc Oxide which is about 3/4s full has become hardened. I tried using some in a small glaze mixture by putting it in the blender but it did not work. Is there any way to salvage it?

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Marcia Selsor    1,301

put some in a bowl and dry it out in the kiln. fire it up to about 6-700 degrees.

It should breakdown easily after that.If not, take it to 1000 F. You could put some in a bisques bowl and fire it in a bisque and see what happens. That would be a truer calcination.test a small quantity first. I have done this for recipes that call for calcined chemicals. I use them as additions for things like slip going on dry pots. They shrink less.

 

Marcia

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Wyndham    98

I think 1200 f is about as high as you should go. Zinc starts to vaporize at cone 06. Wiki says:

 

ZnO decomposes into zinc vapor and oxygen at around 1975 °C with a standard oxygen pressure. Heating with carbon converts the oxide into zinc vapor at a much lower temperature (around 950°C).[11]

ZnO + C → Zn(vap) + CO     Wyndham

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Marcia Selsor    1,301

Thanks Wyndham. I wasn't sure of the higher temp. for vaporizing zinc. Drying it out in a kiln should dehydrate it. So try it at 6-700 F first and see if it breaks up.Or try 1000 F.

I do this with Calcium and Kaolin to make them calcined when the recipe calls for it or if I am experimenting with underglazes on dry greenware.

 

Marcia

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Babs    386

 i have been known to put it in  a strong back and drive over it a few times in my small truck then sieve it/ mortar it as required.

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Wyndham    98

If possible try to buy calcined zinc, it plays nicer with glazes than reg zinc. I think the 1000-1200 deg temp range drives off chemical water from the zinc, much like drying out a greenware pot where there's physical water and above 1000 deg f driving off chemical water but before sintering and fusing begins.

Wyndham

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Babs    386

Ok As an isolated potter, self taught, reading many boks and articles, and watching carefully what happens!, what is the process of replacing Zinc Oxide with calcined ZincOxide in a glaze formula?

I'm not confident in replacing chemicals in my glazes as I have not had this education. I fire to C03 and also to C5/6

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Mark C.    1,806

Zinc Ox always attracks water and clumps if left exposed in a paper sack or even a plastic bag over time.

You can store it in  mosture proof container

I keep mine up high in warm shop to keep it drier

I always mix the zinc portion of my glaze recipe in my blender with a little water and add it to the mix-warm water will help some.

Mark

 

For Babs (what is the process of replacing Zinc Oxide with calcined ZincOxide in a glaze formula?)

Say you need 50 grams of zinc oxide in recipe and you use calcined zinc Oxide instead-you would still add 50 grams.

Its just the same  about the without the water and its already shrunk.

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Babs    386

so there is no great weight loss associated with the removal of water? 

Does that apply to all calcined chemicals? I use calcined manganese dioxide sometimes and have some non calcined, ok to substitute?? Humidity would affect the water or is it a chemically bound water we are talking about here?

Try it I suppose!

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Karen B    26

As a follow-up to the problem with my hardened zinc:

I put about 6 very lumpy cups of the zinc oxide in a heavy previously fired pot .

 

 I heated it to 700 degrees and held for 20 mins. After cooling enough to open, I found that the lumps broke up, but was not fine enough to mix in a glaze. It would never pass through the 800 mesh sieve.

 

I tried sifting out the finest particles, but realized that I would never get the 2000 or so grams I would need.

 

I commandeered an old coffee grinder from the kitchen and found that it did the job. It quickly made the zinc into a fine powder.

 

I have glazed and fired with that zinc and glazes all look great. 

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Mark C.    1,806

Why are using a 800 mesh screen?not much of anything will pass through that

I hope you meant an 80 mesh

Mark

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oldlady    1,323

norm, i know you want to be exact so maybe you want to re-read your "3 square meters per gram" line.

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