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Experiment shows liquid metal TIM doesn’t dry out; it turns solid
Liquid metal’s hardened layer conducts heat about a quarter as well as the copper it replaces.
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YouTuber hardware enthusiast and Thermal Grizzly boss der8auer tested a two-year-old liquid metal thermal interface material (TIM) application with an electron microscope in his new video, discovering that it doesn’t dry out. Instead, the gallium bonds with the copper in a reaction to form a solid compound. On copper, that layer’s heat conduction performance is about one-quarter of the bare metal’s, and nickel plating keeps it about 10 times thinner.
His test showed the TIM as liquid after one hour, no liquid visible with crystals everywhere at the two-month mark, and then unchanged after two years. “After a total of two years, this honestly did not change further,” he said. The test relied on storing the setup in a vacuum or a nitrogen-filled box between sessions to avoid oxidation.
The TIM in question is an alloy of gallium and indium, often including tin, which is liquid at room temperature (Thermal Grizzly sells its own as Conductonaut); gallium melts at about 30 degrees Celsius, with the gallium-indium-tin mix melting at only 11 degrees. Improving cooling at the interface bottleneck is becoming a real issue as heat per surface area continues to rise. His examples are the RTX 5090 and RTX 5080, which he says have “twice” and “three times” the power density of the 8800 GTX.
How the liquid metal reacts depends on the cooler material. With aluminum, the gallium travels along the grain boundaries once the oxide layer is broken, and this weakens the metal. His demo on a scrap 2 mm aluminum sheet showed surface swelling after about five minutes, and it became brittle within half an hour. This reaction has been “common knowledge for a very long time.”
With copper, the liquid metal on the cold plate of Thermal Grizzly’s new stainless steel water block can’t be wiped off with isopropyl alcohol or acetone after less than five minutes. The gallium bonds with copper to form CuGa2, one copper atom to two gallium atoms, with the leftover indium and tin forming other solid areas. This makes the film look like it is solidifying. CuGa2’s heat conductivity is rated at about 100 W/mK versus copper’s roughly 400. Since CuGa2 stays solid up to about 254 degrees Celsius, “you will not be able to melt it again.”
The layer grows about 1 micrometer a day until it reaches about 50 to 100 micrometers, depending on temperature and how much gallium is available; his example of pure gallium between copper plates at 70 degrees Celsius shows about 4 micrometers over 96 hours. The liquid metal “doesn’t really dry out”; it “reacted chemically and it formed a solid compound,” so the metal is still there in another form.
On nickel-plated coolers, the gallium forms NiGa5 instead, one nickel atom to five gallium atoms, which is also solid at room temperature. The nickel plating stops the layer at about 10 times thinner, at 1 to 5 micrometers, or 5 to 10 micrometers on his slide, but NiGa5 conducts heat worse than the copper-gallium compound. However, nickel is “most of the time superior” in his estimation because much less gallium gets absorbed into the surface, and it protects the copper underneath.
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