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Topic: What Will Dissolve Kaolin + Alumina Hydrate?  (Read 5426 times)

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Offline socalfusions

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What Will Dissolve Kaolin + Alumina Hydrate?
« on: July 15, 2010, 10:44:26 PM »
I'm curious if there are any chemicals which will dissolve a flame treated 50/50 mix of Alumina Hydrate and Kaolin from Soda Lime, Lead and Borosilicate glass surfaces.

The 50/50 mix is used as a coating on metal mandrels to prevent melted glass (often formed into beads) from sticking to it and allows removal of the glass later on. The mix itself is quite difficult to clean from the bead after it has cooled which led me to wonder if there are chemicals that would dissolve the mixture of kaolin and alumina hydrate while not damaging the glass.

Some things mentioned in another thread were dispersants, namely poly(acrylic acid) + derivatives, although I haven't been able to test this out. I was led to believe that sodium hydroxide would be capable of dissolving kaolin (not sure about alumina hydrate) but it would also severely damage the glass making it an unsuitable solution, I'm also unfamiliar if it could even dissolve the kaolin since it has been treated at such a high temperature on a torch.

The person that mentioned the dispersants also said that there was quite a bit of literature on the topic since kaolin is so heavily utilized in the industry, but I have had a hard time discovering any of it. I'd appreciate any feedback.

Offline discodermolide

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Re: What Will Dissolve Kaolin + Alumina Hydrate?
« Reply #1 on: July 18, 2010, 12:41:43 PM »
Try an aqueous HF solution in a plastic ( Teflon) vessel. Careful with HF solutions they are very toxic. Look up the properties of Hf before use
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Offline DrCMS

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Re: What Will Dissolve Kaolin + Alumina Hydrate?
« Reply #2 on: July 18, 2010, 05:48:30 PM »
@discodermolide
Did you read the actual question before you wrote your answer?

Try reading it again paying particular attention to this part.

The mix itself is quite difficult to clean from the bead after it has cooled which led me to wonder if there are chemicals that would dissolve the mixture of kaolin and alumina hydrate while not damaging the glass.

HF will dissolve the glass so is not suitable.


@ socalfusions
To be honest I do not think there is a chemical solution to this problem. 
Dispersants poyacrylate or otherwise are designed to allow high solid slurries to be pumped etc.  Kaolin mixed with water makes a paste but if you add a small amount of polyacrylate dispersant say 0.1% you can prepare a mobile slurry.  The kaolin does not dissolve; the polyelectrolyte absorbs on the the surface of the particles and as opposite charges repel it prevents the particles sticking together allowing the high solid slurry to flow.  If the kaolin is baked onto a glass surface dispersants will not help much.
Anything that will actually dissolve the alumina or kaolin is also likely to dissolve the glass such as NaOH or HF solutions.

Offline socalfusions

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Re: What Will Dissolve Kaolin + Alumina Hydrate?
« Reply #3 on: July 18, 2010, 11:20:34 PM »
Try an aqueous HF solution in a plastic ( Teflon) vessel. Careful with HF solutions they are very toxic. Look up the properties of Hf before use

Yes, as DrCMS said I intend to use this on borosilicate glass, which would also be damaged, thanks for your respone nonetheless.

@discodermolide
Did you read the actual question before you wrote your answer?

Try reading it again paying particular attention to this part.

The mix itself is quite difficult to clean from the bead after it has cooled which led me to wonder if there are chemicals that would dissolve the mixture of kaolin and alumina hydrate while not damaging the glass.

HF will dissolve the glass so is not suitable.


@ socalfusions
To be honest I do not think there is a chemical solution to this problem.  
Dispersants poyacrylate or otherwise are designed to allow high solid slurries to be pumped etc.  Kaolin mixed with water makes a paste but if you add a small amount of polyacrylate dispersant say 0.1% you can prepare a mobile slurry.  The kaolin does not dissolve; the polyelectrolyte absorbs on the the surface of the particles and as opposite charges repel it prevents the particles sticking together allowing the high solid slurry to flow.  If the kaolin is baked onto a glass surface dispersants will not help much.
Anything that will actually dissolve the alumina or kaolin is also likely to dissolve the glass such as NaOH or HF solutions.

I understand what you're saying, I figured that an acid or base that was strong enough to dissolve or turn the kaolin mix into a past would likely damage the glass.

Do you know if their is anything that can be added to the kaolin / alumina mix that would allow it to dissolve or break down under water / other substance, while still being able to withstand the heat from the torch? Perhaps something  such as NaCl could be added to the mix before you put it under the torch, which might break the kaolin / alumina mix down when placed in water, although I'm sure the high heat from the torch will limit the possible choices.

Thank you for your insightful reply!
« Last Edit: July 18, 2010, 11:30:49 PM by socalfusions »

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