How big should sugar crystals get?

[eptheta]

Should it grow indefinitely ?(assuming you have a permanently super-saturated solution)
Or does it stop growing when it reaches a certain mass or something ? If so why ?

Also, has anyone had success in growing huge sugar/sucrose crystals (if yes, then would you please post up some pictures)?

Strangely enough, when i searched on Google, not many people posted up their crystal pictures and the few that did, posted relatively small crystals.

Thanks

 

[espen180]

A lecturer/grad student at a university once showed me his crystal growing workshop, where he had pretty big and high quality crystals. I think he had a sizable glucose crystal, a little bigger than a fist i think.

 

[eptheta]

A fist ? Wow ! Did you take any pictures ? I really do want to see some...
I'm growing some sucrose crystals too but they seem pretty small, they're still in solution so I can't measure it properly...

 

[espen180]

No pictures. Just to make it clear, I think this was a glucose crystal, but it might have been sucrose. He and his group used some specialized equipment (temperature control, etc) to make their finer crystals.

 

[SpartanG345]

this tread is making me feel hungry!

 

[Dadface]

Hello eptheta.Try googling "the giant crystal project".I'm sure you will find it interesting.

 

[eptheta]

Oh my god! Its quartz !

The giant crystal project is all about minerals mined from caves etc. I was wondering about laboratory(or in my case kitchen) grown crystals...

 

[ineptuslux]

Here is a pic of a cane sugar crystal cluster I grew in about 9-10 months. I changed the solution and container several times. I donated it to the local High School Science Teacher, the kids probably ate it. :)

 

[eptheta]

Wow, that's big !
Tell me, did you initially plan to grow it uniformly (i.e in its standard crystal configuration) but it went haywire? Or was it your intention to grow a crystal cluster ?

I've tried to grow sucrose crystals too but after a certain point(size/volume) they stopped growing and clusters began to emerge. (I tried only twice and they came out approximately the same size, but then again, two isn't really a very large number to draw conclusions from).
I've attached 2 pictures. You can judge the size based on the standard crystal or the shadow of my finger.

Any particular methods you used ? Or was it just boil, saturate, cool, grow, start over ?
Also kitchen or lab ?

 

[DrDu]

I was wondering whether growing from a solvent other than water (e.g. alcohol) wouldn't be advantageous in the case of sucrose.

 

[eptheta]

I don't even think sucrose is soluble in alcohol.
This reminds me of those salt crystal gardens. Several people suggest using ammonia mixed in water as a solvent...
Maybe a mixture of alcohol and water (and if so, then ammonia and water) could help keep the solution supersaturated if it does dissolve and if I can control the rate of evaporation of the additive..

I'll try it out soon.

 

[ineptuslux]

@ eptheta. Beautiful crystals, I don't know how to grow only one. My formal education stopped at the 9th grade so I'm a self taught scientist. I prepared a supersaturated solution of cane sugar and carbon filtered tap water in a quart mason jar with a piece of cotton Venetian Blinds cord suspended from a pencil and covered it loosely with Saran Wrap so it could evaporate slowly. I kept in the back of a kitchen cabinet in the dark undisturbed. Every couple of months I prepared a new solution in a larger container, let it cool to almost room temperature, pulled the cluster out and swiftly placed it in the new solution/container. It turned into a cluster right off the bat, totally covering the cord. 7 years later I still have a gallon freezer bag with all the smaller crystals that formed on the sides of the containers. It sucks I'm diabetic, I love rock candy. :)

 

[ineptuslux]

Here is another picture with a scale so you can see the size. It was setting on a 4" PVC coupling with cheap shelf paper over it. ;)

 

[eptheta]

While I am back in this thread, I may as well re-ask my original question:
Is there a physical limitation to the size of a crystal grown by suspension in a supersaturated solution ?
I mean theoretically the crystal should grow indefinitely as long as the concentration is maintained throughout, but is there some sort of critical mass or critical volume after which the molecules in solution begin to prefer adding layers to smaller crystals in the vicinity (thus leading to the growth of clusters) as compared to the already large one ? If so, then what is the physical principle behind this ?

Does it require more energy to crystallize on large plane surfaces with fewer contour irregularities (per unit area that is)?
Related to this thought: Is it possible for sucrose (or any crystalline) supersaturate to crystallize in a non-natural structure (it's 10 faced structure) ? i.e. Can the solution be 'induced' somehow to crystallize in plane sheets or as a 5 faced crystal ?
If not, could this explain my original question?

If anyone can answer my questions or point me to some nice resources dealing with this, that would be nice.
Thanks !

 

[DrDu]

I would guess that there are plenty of examples even of natural crystals with 10 (capped tetragonal bipyramid) or 5 (e.g. a caped trigonal pyramid or a trigonal prism (turmaline) ) faces.
And no, in general there are no limitations on the size of a crystal. In general, a larger crystal is more stable than several small crystals.

 

[Borek]

I don't even think sucrose is soluble in alcohol.

My guess is that it is soluble enough. You don't need a high solubility to grow crystals, it is mostly a matter of speed. Large crystals of gypsum found in nature can grow from the water solutions, even if calcium sulfate is considered to be - on the high school level - insoluble.