Two-year test proves liquid metal thermal paste solidifies instead of drying out

There's always concerns about liquid metal thermal paste drying out or degrading over time, but we have an electron microscope test after 2 years and… no. No degradation, the paste is chemically reacting to the cooler's surface in order to solidify into a compound. This is interesting for anyone making high-end PCs and wondering whether liquid metal paste is here to stay. The user can now be confident that interface is stable and won't require frequent reapplication.

Nickel plating limits the solidified layer to 10 times the thickness of bare copper

Specifically, what we have here is Thermal Grizzly's liquid metal paste as a thermal interface material. This was tested on copper and nickel-plated coolers. The liquid metal in the paste, which is gallium, will melt around 30°C and react with the metal surface.

Spec comparison

• Reaction Product (Copper): CuGa2 (Copper Gallium)
• Reaction Product (Nickel): NiGa5 (Nickel Gallium)
• Layer Thickness (Copper): 50 to 100 micrometers
• Layer Thickness (Nickel): 1 to 5 micrometers
• Melting Point (Gallium): 30 degrees Celsius

On naked copper, the gallium reacts into CuGa2 (copper-gallium), where 1 copper atom bonds with 2 gallium atoms. This creates a clear layer that grows in thickness until it reaches a stable value.

It grows around 1µm a day until reaching a stable 50 to 100µm thickness. CuGa2 compound has heat conductivity around 100W/mK, lower than the 400W/mK copper. With nickel-plated surfaces, it's NiGa5, forming only 1 to 5µm thick layer. Nickel-plating prevents it from growing any further (10x thinner than bare copper) and this is what you want with these paste types.

Solid compound stable until around 254°C, so you can't re-melt it to reapply. der8auer states that it's not changing any further after 2 years of testing. So the material won't dry out, it's solid-ifying into a permanent structure. Direct quote from tester, which is very good because it confirms the chemical reaction is complete and stable in the long run.

Kit's $22.11 direct for 30g paste, polishing pen, microfiber cloth. Gallium price has gone through the roof (from 300€/kg to 2500-3000€/kg because of export bans). Thermal Grizzly plans to change the nickel with other coatings, hopefully next year, as far as long term compatibility is concerned. So perhaps future iterations will even better protect the copper underneath.