Science Focus (issue 25)

What happens when several drops of the liquid metal gallium are added to an aluminum can? Our high school chemistry class taught us that nothing would happen. But if you wait for a while, you will be surprised to see the can shatters into pieces with just a single touch. Are our chemistry teachers wrong? No. The shattering of aluminum cans upon exposure to gallium is not caused by a chemical reaction. Instead, it is the result of a physical phenomenon known as liquid metal embrittlement (LME). Although a metal object (say an aluminum can) may appear as a single piece, it actually consists of many small crystals called grains. As shown in Figure 1, when the can comes into contact with specific liquid metals like gallium, the latter can penetrate the boundaries, or spaces, between the grains [1]. This significantly weakens the cohesion of the grains and hence the strength of the aluminum can, making it susceptible to fracture. Thinking Out of the Box: Removing Medical Devices with a Liquid Metal 有何不可:利用液態金屬移除醫療裝置 By Helen Wong 王思齊 Figure 1 The process of liquid metal embrittlement (LME) [2]. While LME has been a common source of metal structure failure in industries such as aerospace and construction, a group of researchers at the Massachusetts Institute of Technology recently “harnessed this failure mechanism in a productive way [2, 3].” Metals have properties ideal for making