Research press release


Nature Chemistry

High-speed cameras help explain high-school chemistry



今回Pavel Jungwirthたちは、ハイスピードカメラとシミュレーションを用いて、この爆発反応を研究した。その結果、爆発的挙動の引き金となるのは、水に触れるとほぼ即座に起こるアルカリ金属からの電子放出であることが示唆された。また、電子を放出して正の電荷を帯びた金属原子は、互いに強く反発し合うため、針状のスパイクを形成して表面から水中へと急激に飛び出ることも示唆されている。このスパイク突出によって、次の金属-水反応が起こる表面の面積が増大する。このようにして反応が次々と伝わっていく様子が説明できる。

The initial mechanism of the explosion that occurs when alkali metals, such as sodium or potassium, are dissolved in water is described in Nature Chemistry this week.

Dropping alkali metals into water is frequently used to wow high-school chemistry classes. Students are taught that, once triggered, the vigorous explosion is caused by heat release, steam formation and the ignition of the hydrogen gas that is produced. Whilst true, the trigger, and why the initial formation of steam and hydrogen gas does not simply deactivate the surface reaction before an explosion can occur, has not previously been well understood.

Pavel Jungwirth and colleagues used high-speed cameras and simulations to study the explosive reaction. Their data suggests that the explosive behaviour is triggered by an almost immediate release of electrons from the metal, which leaves behind positively charged metal atoms that strongly repel each other. This leads to the rapid protrusion of metal spikes from the surface, which increases the surface area over which the subsequent metal-water reaction can occur, explaining the propagation of the reaction.

doi: 10.1038/nchem.2161


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