Techniques for Growing Crystals

Techniques for Growing Crystals

by Ritika

A consistent repeated pattern of connected atoms or molecules would result in formation of a crystal. There are several techniques used for growing crystals.

Nucleation

The process of growing crystals is termed as nucleation. In the process of nucleation, the molecules and atoms used for used for forming crystals are dissolved into their individual units inside a solvent. Because of this dissolving process of solute elements, namely the atoms or molecules inside the solvent, the solvent gets associated with each other and results in forming a bond with each other. Thus, the connection of more and more subunits as above results in production of larger unit. This process gets repeated in such a manner that the size becomes larger that the resultant crystal falls out of the solution. That is, the crystallization process is repeated and resultant crystal is formed. Even after this resultant crystal formation, other solute molecules which are left unattached get attached to the surface of the crystal. This process gets repeated until a state of equilibrium or balance is achieved between the solute molecules in the crystal and those that remain in the solution.

It is also vital to note that the surface which is rough would be always best for growing crystal that is for the process of nucleation than surface which is smooth. One can view this by doing a simple experiment by trying the process of nucleation on a rough piece of string and on a smooth side of a glass. You are sure to observe that crystals get formed more easily on the rough piece of string than on the smooth side of a glass.

Technique for Growing Crystal

There are three normal steps involved in the general technique of growing crystals. The three steps followed are:

  • Process of forming a saturated solution
  • Process of growing seed crystal
  • Repeat the process of growth

Process of Forming a Saturated Solution

The primary step for growing crystals is the formation of saturated solution. The solution enables the probability of solute particles to come together and form a nucleus which would result in formation of a crystal. Maximum care must be taken to prepare the solution as above to achieve the best resultant crystal. In other words, it is best to always use a concentrated solution with as much solute as you can dissolve, namely a saturated solution. It is also possible in some cases, that nucleation is achieved by association between solute particles in the solution without any assistance which is termed as unassisted nucleation. However, to increase the probability of forming crystals, assisted nucleation always must be provided. That is, a place for association for solute particles to aggregate and formation of crystal is done which increases the probability of formation of crystal.

First, one must take a saturated solution for the technique of growing crystal. If you prefer to take dilute solution it would take more time for the air to evaporate some liquid and make it saturated. But if you take directly saturated solution, the crystal formation could begin right from that instance. Add enough water as and when needed to the crystal solution. Also, vital care must be taken while selecting the saturated selection as wrong choice of saturated solution would result in dissolution of the crystals formed. One good guideline for making the saturated solution is to add crystal solutes like alum, sugar, salt and so on to solvents like water. One can also choose other solvents based on the solute taken. For completely dissolving the solute in the solvent, carry out the step of stirring the mixture of solvent and solute added. If you find that even after stirring there is some solute left, without dissolving try to heat the mixture which would enable the solute to dissolve completely. For the process of boiling one can use boiling water or even try heating the mixture of solute and solvent directly on the stove or in a microwave.

Process of Growing Seed Crystal

For growing large amount of crystals, one can pour the saturated solution on substrate like rocks or brick or sponge. This could be then protected from dust by covering the above with paper towels or any other covering material that would protect the setup from dust as well as allow the liquid to slowly evaporate.

For growing a single larger crystal, the technique used is to first get a seed crystal for the same. To get a seed crystal, pour some saturated solution on a plate. This setup is then allowed to evaporate which would result in the formation of crystals at the bottom of plate. The crystal formed at the bottom is called seed crystal which could be got by scarping. Another technique that could be used for growing seed crystals is to pour the saturated solution on a smooth container for instance, a glass jar. Then place a rough element like a piece of string into the saturated solution. This would enable the crystals to get formed on the rough element i.e the string. These crystals are the seed crystals.

Repeat the Process of Growth

We have seen above two techniques for the process of forming seed crystals. Let us now see how to proceed with crystal growth using the seed crystal. Consider the case of seed crystal of being formed on a string as explained before. In that case, first pour the liquid into a clean container. Then suspend the string with seed crystal in this liquid and also cover the container with some material like paper towel. Ensure not to seal it with a lid. Continue this process of growing crystals and take care to pour the liquid into a clean container as soon as you see crystals growing on the container.

If the seed crystal was formed on plate as explained before, then first tie it onto a nylon fishing line. Ensure you have your material smooth which would enable it to attract crystals. This would enable growth of seed crystals faster and more easily. Then suspend the crystal in a clean container with saturated solution and the process to be followed is the same for growing crystal as for growing the seed crystal present on the string.

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