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Cobalt hydroxide vs cobalt oxide


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During a search for sodium molybdate I came across some cobalt variants in rural chemical stocks.  I understand that cobalt hydroxide decomposes to cobalt oxide at 168 degrees c (thanks wiki) but I don't know how the decomposition will effect the glaze or how the hydroxide will effect the glaze mix.

I'm about the find out but anyone have any understanding of it and she'd any light before I start?

Cheers,

Liam

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Decomposition products are water vapor and an intermediate cobalt oxide.  This happens at 300c, the decomposition at 168c is only under vacuum.

It will act basically as cobalt carbonate in a glaze formula, just not quite as strong of a colorant.  You can do the stoichiometry and figure out the molar mass to see how much you'd need to use to compensate.  I'd do it for you but I'm at work.  It is soluble and toxic though, so dangerous to work with.

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3 hours ago, Piedmont Pottery said:

Actually, cobalt oxide has more cobalt per unit mass than cobalt carbonate.  You need roughly 1.5 times as much carbonate as you would oxide for the same amount of cobalt.  Neither the carbonate or oxide are soluble in water.

Correct, however the hydroxide, which is different, is different.

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On 10/3/2020 at 8:17 AM, liambesaw said:

Decomposition products are water vapor and an intermediate cobalt oxide.  This happens at 300c, the decomposition at 168c is only under vacuum.

It will act basically as cobalt carbonate in a glaze formula, just not quite as strong of a colorant.  You can do the stoichiometry and figure out the molar mass to see how much you'd need to use to compensate.  I'd do it for you but I'm at work.  It is soluble and toxic though, so dangerous to work with.

Thanks for the quick responses guys, really appreciated.

I'll see if I can add it to Matrix and research "stoichiometry', that's a new one haha.  I hadn't thought that the solubility would increase the toxicity risk but guessing hydroxide makes it soluble? Makes sense and probably why it's been mixed that way so farmers can spread it easily.  Will check with the chemical company.   

I'm not in any rush if you do get a chance to stoichiometrisize it :)  We're currently renovating an old bungalow, so pottery is way down the list of important jobs, when the boss says she needs the bathroom finished, it takes priority, most days haha :) Great time for research though even if I'm only firing test tiles.

Be great if it decomposes to oxide (thanks Piedmont) but might still be too much hassle if it's soluble.   I think I need to understand that better than I do.

Cheers,

Liam

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So cobalt hydroxide is roughy 93 grams per mol, and cobalt oxide is roughly 75 grams per mol.  Using those numbers, you'll need to use roughly 19% more cobalt hydroxide in a recipe versus cobalt oxide.

But like I said, it is soluble and can enter your body through your skin, so you would want to wear gloves when using this compound and any glazes made with it.

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On 10/5/2020 at 10:57 AM, liambesaw said:

So cobalt hydroxide is roughy 93 grams per mol, and cobalt oxide is roughly 75 grams per mol.  Using those numbers, you'll need to use roughly 19% more cobalt hydroxide in a recipe versus cobalt oxide.

But like I said, it is soluble and can enter your body through your skin, so you would want to wear gloves when using this compound and any glazes made with it.

Thanks Liam, you're awesome!

I have a small sample coming and will use it but given the extra risk won't pursue this any further.  

That said, I might half the sample and fire the second half as a dry powder to 300 or 350c to decompose the hydroxide so i'm left with straight cobalt oxide. 

Mark, yes it's a lot cheaper in NZ but not worth the extra risk.  Mostly I'm just wanting to learn more about the chemistry, which is fascinating.   I never did it at school unfortunately so a deep dive now which is cool.

Mostly i'm interested in firing what I find locally in NZ and from the excavations at work (we are constructing an 18 km highway here) so have access to a wide range of clays, rock, volcanic ash and oxide seams.   I've managed to track down a huge amount of local sourced materials country wide but still need to buy a lot of the colorants and more exotic materials.

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