How Does Temperature Affect Growing Crystals?

Crystals

• Crystals are solid materials that form when atoms or molecules form into repeating patterns of molecules. For instance, the atoms in a crystal of table salt will form repeating cube shapes on a molecular level. However, the shape of the molecules may or may not be the same as the shape of the crystal. Many ordinary substances form crystals, such as salt or sugar, which is why growing crystals is a common science project for students.

Solutions

• Regardless of the material that a crystal is made from, all crystals are created in basically the same way, by making a crystal solution. A substance, the solute, is dissolved into a liquid, typically water. This liquid is known as the solvent, and combining the two creates a solution. A specific kind of solution is needed for crystals: a supersaturated solution. When the solvent is heated, it is typically easier for the solute to dissolve into it. A hot solution is able to contain more solute than one that is cool. As the heated solution cools, the solvent is unable to contain the solutes, and they precipitate out of the solution as crystals. Changing the ambient temperature changes how quickly the solutes precipitate out of the solution.

High Temperatures

• The evaporation rate of a solvent increases as the ambient temperature increases. A solvent can only contain a certain amount of solute, so when the solvent evaporates, some of the solute comes out of the solution because there is no longer enough solution to dissolve it. This forms crystals. A higher ambient temperature causes crystals to form more quickly than a low temperature because it removes solvent from the solution, forcing the crystals to form quickly. Crystals formed in this way are typically very small.

Low Temperatures

• Low temperatures inhibit the evaporation of a solvent. The crystals precipitate out of the solution slowly, a small amount at a time. However, this method encourages the growth of very large, pure crystals, as large crystals require more time to form. Crystals grown in this way are considered higher quality than those grown quickly, so people have found many ways to slow the growth of crystals in order to obtain large, high-quality crystals for science and industry.