Hardened Zinc

[Karen B]

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?

[Marcia Selsor]

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

[Wyndham]

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

[perkolator]

mortar and pestle?  i would also try calcining it like suggested.

[Karen B]

Thank you so much! I am happy if I don't have to add the labor of mortar and pestle though. 

[Marcia Selsor]

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

[Babs]

 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.

[Wyndham]

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

[Babs]

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

[Mark C.]

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.

[Babs]

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!

[Marcia Selsor]

Try it. It should dissolve better.

Marcia

[Babs]

Thanks every one. Did mean manganese carbonate not dioxide.

[Karen B]

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. 

[Mark C.]

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

I hope you meant an 80 mesh

Mark

[Karen B]

Yes, Mark, I did mistype "80" mesh.

Thanks Norm for the source of information.

[oldlady]

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

[Win G.]

I'm sure you've solved your problem by now.  I had the same problem and am 40 miles from a supplier.  I needed it pronto to finish a glaze batch.  I calcined it to 1000 deg.,  some of it powdered, but not enough. Finally I added CLR - the strongest acid I had around.  It bubbled and stayed lumpy, but by the next morning it had dried and was powdery.  It worked, but now i wonder how the ingredients in CLR will effect the glaze.  Time for another test!