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?
Posted 24 October 2013 - 07:21 AM
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.
Posted 24 October 2013 - 11:02 AM
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).ZnO + C → Zn(vap) + CO Wyndham
Posted 24 October 2013 - 11:09 AM
mortar and pestle? i would also try calcining it like suggested.
Posted 24 October 2013 - 12:48 PM
Thank you so much! I am happy if I don't have to add the labor of mortar and pestle though.
Posted 24 October 2013 - 01:11 PM
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.
Posted 24 October 2013 - 04:29 PM
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.
Posted 25 October 2013 - 09:24 AM
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.
Posted 25 October 2013 - 06:45 PM
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
Posted 25 October 2013 - 08:58 PM
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.
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.
Posted 26 October 2013 - 02:07 AM
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!
Posted 26 October 2013 - 07:10 PM
Thanks every one. Did mean manganese carbonate not dioxide.
Posted 25 November 2013 - 06:51 PM
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.
Posted 25 November 2013 - 08:39 PM
Why are using a 800 mesh screen?not much of anything will pass through that
I hope you meant an 80 mesh
Posted 25 November 2013 - 10:59 PM
Yes, Mark, I did mistype "80" mesh.
Thanks Norm for the source of information.
Posted 26 November 2013 - 02:47 PM
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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