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NaK, or sodium-potassium alloy (commonly pronounced 'knack')〔Houghton, Rick, ''(Emergency Characterization of Unknown Materials )'', CRC Press, 2007, p.89〕 , an alloy of potassium (K) and sodium (Na), is usually liquid at room temperature.〔 Various commercial grades are available. NaK is highly reactive with water and may catch fire when exposed to air, so must be handled with special precautions. == Physical properties == NaK containing 40% to 90% potassium by weight is liquid at room temperature. The eutectic mixture consists of 77% potassium and 23% sodium, is liquid from −12.6 to 785 °C, and has a density of 866 kg/m3 at 21 °C and 855 kg/m3 at 100 °C, making it less dense than water.〔(【引用サイトリンク】BASF "> title=Sodium-Potassium Alloy (NaK) )〕 It is highly reactive with water and is stored usually under hexane or other hydrocarbons, or under an inert gas (usually dry nitrogen or argon〔(【引用サイトリンク】title=MSDS )〕) if high purity and low levels of oxidation are required. When stored in air, it forms a yellow potassium superoxide coating and may ignite. This superoxide reacts explosively with organics. NaK is not dense enough to sink in most hydrocarbons, but will sink in lighter mineral oil. It is unsafe to store in this manner if the superoxide has formed. A large explosion took place at the Oak Ridge Y-12 facility on December 8, 1999, when NaK cleaned up after an accidental spill and inappropriately treated with mineral oil was scratched with a metal tool. The liquid alloy also attacks PTFE ("Teflon"). NaK has a very high surface tension, which makes large amounts of it pull into a bun-like shape. Its specific heat capacity is , which is roughly one-fourth of that for water, but heat transfer is higher over a temperature gradient due to higher thermal conductivity.〔(【引用サイトリンク】url=http://www.nordichardware.com/en/component/content/article/181-danamics-lm10-liquid-metal-put-to-the-test-.html?start=2 ) 2010-01-10 nordichardware.com〕 File:Phase diagram potassium sodium s l.svg|Solid-liquid phase diagram of sodium and potassium〔G.L.C.M. van Rossen, H. van Bleiswijk: ''Über das Zustandsdiagramm der Kalium-Natriumlegierungen'', in: ''Z. Anorg. Chem.'', 1912, ''74'', S. 152–156.〕 File:NaK alloy.jpg|NaK alloy is liquid at room temperature. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「NaK」の詳細全文を読む スポンサード リンク
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