Experimental procedure for growing piezoelectric crystals

[JessicaHelena]

At school I and a handful of other kids are devising an experiment to send up to ISS to test it over a period of 30 days next year. (Yep, we're quite fortunate to have this opportunity!) We've chosen to grow piezoelectric crystals using (super)saturated solution of the piezoelectric crystal salts and using a seed crystal attached to a string so that hopefully the crystals will grow along the string. However, so far we've had little success (or frankly, no success) and the deadline's coming soon, so we are quite worried. It seems that sometimes we oversaturate the solution that at some point they turn mushy and solidify, or other times the seed crystals just dissolve before any other crystals have had a chance to form.

Here's the procedure we followed (for using supersaturated solutions):
- We have 20 ml distilled water in a beaker at room temperature.
- Using a measuring spoon, we put in little amounts of piezoelectric crystals and dissolve it thoroughly until the distilled water + crystals solution becomes clear again.
- We repeat the step above, until we have stirred long enough but we still see bits of crystals undissolved.

In earlier experiments, after this step, we've tried heating up the beaker since heating up makes the solution absorb more salts. When we cool it down in a pan full of ice, that's when the solution turns all mushy and solidify, and we had to heat the beaker up again (lightly) to get it back to liquid state. I think some of those experiments succeeded in creating crystals (and others failed) but none of them would grow crystals along a string we put inside.

In later experiments, since we didn't think heating up the solution was so good of an idea, we just dissolved the salt in room temperature. That too, worked irregularly.

Does anyone have any suggestions as to what we should do? Are there parts in our experimental procedure that we should change? We've been googling guidelines online and following those (we don't really have a mentor), but things don't seem to go as well as the guidelines seem to say.

Most importantly, since we are given 30 days in a microgravity environment, we don't want to be done in just a couple of days and have nothing else to do. However, all our experiments so far, if successful, produced crystals in about a day, which worries us. How can we lengthen the duration of the experiment?

Any help would tremendously be appreciated!

 

[DrDu]

What salt do you use? Potassium hydrogen tartrate?
I would try the following:
Best dissolve it in heat and filter the solution into a dry (!) recipient. Then let slowly cool down.
And better try to weigh the salt. Maybe you can try different concentrations and crystallization temperatures?

 

[JessicaHelena]

We use rochelle salt — potassium sodium tartrate.

Could you explain what you mean by a recipient? Would that be where I put the solution into after heating?
Also, would we use a filter paper then?

 

[JessicaHelena]

Or do you think it might be easier if we changed the salt?

 

[DrDu]

Sorry, yes, I meant Rochelle salt.
First I want to say that this is a super interesting opportunity and that I want to gratulate you for having the opportunity to participate.
On the other hand, I think this is not a simple task. Maybe you can tell us how old you are? Don't you have a teacher who is advising you?
Heating the solution until everything is dissolved is a good idea. Then filter the still hot solution into a new recipient, where crystallization shall take place.
A recipient is simply a jar which, for your purposes, should not have any scatches on the inner side, as these may be sites where crystallization starts unwantedly.
A new Erlenmeyer flask may be ideal. Please take care that it is really dry, as already some drops of water are sufficient to turn a saturated Rochelle salt solution into an undersaturated one.
Instead of putting simply a string inside the solution, I would consider putting a small seed crystal inside which you may attach to a thin nylon string (don't touch the crystal with your fingers while trying to knot it to the string! The fat from your fingers will prevent even growth of the crystal.).
To lengthen the experiment I would recommend you to consider repetitions with different conditions, like temperature and concentration of the salt.
Please feel free to ask any further questions, although my knowledge about crystallization is also rather limited. Maybe @Borek can help?

 

[JessicaHelena]

Thank you for all the information.
We are high schoolers (mostly juniors and seniors), and we do have a physics teacher as our 'mentor', but he's afraid this is more chemistry and not really his expertise, so we've been asking around the chemistry teachers at our school. Most of them couldn't really help us so far.
How can we tie a nylon string without touching it directly? Should we wear latex(or latex-free?) gloves?
Also, does the string have to be a nylon string?

 

[DrDu]

I think this is quite a shame for your high school that you don't get better support!
Regarding your question, it is best to grow some seed crystals of several mm in size from a very concentrated solution (i.e. putting it in the fridge for some hours)
and use these. Instead of Nylon you can also use a hair. If you have problems to make a node, you can also try to glue the crystal to the hair with a tiny drop of instant glue. Much space for your own experiments!