「120秒の科学」 ＃25 過冷却「120 seconds of…
過冷却とは、水などの液体が凝固点（凍って個体になる温度）よりも低い温度まで液体のまま冷やされることを言います。 たとえば、水は本来0度以下になると凍りますが、ある条件を満たすと0度以下でも凍らず、液体のまま冷やされ続けることがあるのです。 この状態を過冷却、もしくは過冷却水と呼んでいます。刺激を加えると、どのよう変化が見られるのでしょうか？
番組名：120秒の科学 テレビ大阪 毎週土曜日あさ6時54分放送
Supercooling is the process of lowering the water’s temperature below freezing point, without it becoming a solid and then watching it rapidly freeze when force is applied.
You can easily experiment at home, so please try it.
①Place an unopened bottle of distilled or purified water (e.g., created by reverse osmosis) in the freezer. Mineral water or tap water will not supercool very well because they contain impurities that can lower the freezing point of the water or else serve as nucleation sites for crystallization.
②Allow the bottle of water to chill, undisturbed, for about 2-1/2 hours. The exact time needed to supercool the water varies depending on the temperature of your freezer. One way to tell your water is supercooled is to put a bottle of tap water (impure water) into the freezer at the same time as the bottle of pure water. When the tap water freezes, the pure water will be supercooled. If the pure water also freezes, you either waited too long, somehow disturbed the container, or else the water was insufficiently pure.
③Carefully remove the supercooled water from the freezer.
You can initiate crystallization into ice in several different ways. Two of the most entertaining ways to cause the water to freeze are to shake the bottle or to open the bottle and pour the water onto a piece of ice. In the latter case, the water stream will often freeze backward from the ice cube back into the bottle.