Overclocking enthusiast and Thermal Grizzly CEO der8auer examined a two-year-old liquid metal TIM application using an electron microscope. He found that the material doesn't evaporate or dry out; instead, the gallium in the alloy reacts with the copper cooler surface to form a solid intermetallic compound. The reaction begins within minutes and continues over months, eventually leaving no liquid metal visible.
On bare copper, the gallium forms CuGa2 (one copper atom to two gallium atoms), which has a thermal conductivity of about 100 W/mK compared to copper's roughly 400 W/mK. The layer grows about one micrometer per day until reaching 50–100 micrometers, depending on temperature and gallium supply. Because CuGa2 remains solid up to about 254°C, the TIM cannot be melted back into a liquid once this reaction occurs.
Nickel plating changes the reaction: gallium forms NiGa5 instead, which conducts heat worse than CuGa2 but keeps the reaction layer about 10 times thinner (1–5 micrometers). The source notes that nickel is "most of the time superior" because it protects the copper underneath and absorbs less gallium. However, removal of the residue is difficult, and Thermal Grizzly sells a polish specifically for this purpose.
The test also highlighted that liquid metal reacts destructively with aluminum, causing embrittlement within half an hour. The source recommends liquid metal only for enthusiasts with high-power-density components, and notes that gallium prices have risen sharply due to export controls, with China supplying 99% of the world's gallium.