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Crystal growing


paulsutton
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I tried to grow some Salt crystals a while back, it worked using table salt, however this also contains Sodium Ferrocyanide.   Would I be better using pure Sodium Chloride (from a chemical supplier) ?

I think the crystals should be more cuboid shaped,  which I think is how the molecular structure is for Sodium Chloride.  I have attached a photo of my previous attempt results. 

I am not what the Sodium Ferrocyanide does,  it is an anti caking agent or something. so that may explain the results.

 

Thanks

 

Paul

salt1-20-9-2021.JPG

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41 minutes ago, paulsutton said:

I tried to grow some Salt crystals a while back, it worked using table salt, however this also contains Sodium Ferrocyanide.   Would I be better using pure Sodium Chloride (from a chemical supplier) ?

I think the crystals should be more cuboid shaped,  which I think is how the molecular structure is for Sodium Chloride.  I have attached a photo of my previous attempt results. 

I am not what the Sodium Ferrocyanide does,  it is an anti caking agent or something. so that may explain the results.

 

Thanks

 

Paul

salt1-20-9-2021.JPG

I'm not sure that the sodium ferricyanide will interfere to that extent. @John Cuthbermay know better.  But as I recall, to grow a nice cuboid crystal you need to suspend a "seed" crystal, tied with a cotton thread or something, in a supersaturated solution and let it grow slowly and undisturbed for several days. What you want is for just one crystal to grow slowly, rather than a mass, suddenly. Maybe if you have some coarse salt you can select one grain and use that. Important that there are no other crystals or particles in the supersaturated solution or these will also be nuclei for crystallisation.

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I think that part of the reason they use ferrocyanide is that it alters the crystal growth leading to a change in caking behaviour and also perhaps crystal form.
 

Adding a little copper sulphate solution to the salt solution will form an insoluble copper ferrocyanide precipitate which you can filter off.
People are still doing work on this sort of thing
https://pubs.acs.org/doi/full/10.1021/cg201661y?mobileUi=0

It's a good idea to filter solutions before letting them crystallise, even if the best you can do it so filter through a paper tissue.

However, I think the problem you have there is capillary creep. A couple of drops of cooking oil on the string above the level of the liquid may help keep the solution where it is meant to be.

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