Sublimation, << `suhb` luh MAY shuhn, >> is a process in which a solid changes into a gas or vapor without first becoming a liquid. Sublimation occurs at temperatures and pressures below the triple point. The triple point is the temperature and pressure at which a substance’s solid, liquid, and gas forms exist in equilibrium. A reverse to the process of sublimation—the changing of the vapors into solid form—is called deposition. In the case of water, deposition can be observed as frost.
Sublimation can be used to separate or purify certain materials. For example, applying a vacuum to a mixture of substances can cause some of the substances to sublimate. Applying cold temperature to the vapors can then condense them back to a solid. A process called freeze drying removes water in the form of ice and other materials by sublimation. Freeze drying is used in food preservation. Another common sublimation process involves mothballs changing directly into a gas. Used around clothing, mothballs deter moths from breeding or feeding on clothing.
