Why liquid metal thermal paste must not come into contact with aluminum heat sinks

Here in the blog I have already published a few posts about CPU cooling and the purchase of thermal paste (see below). It also concerned aids that contain liquid metal - especially gallium. These pastes usually come with a large, clearly visible warning that they should not come into contact with aluminum, ie not with the heat sink or "heat sink" of the PC. But why liquid metal thermal paste must not come into contact with aluminum heat sinks is usually not stated on the packaging. In the following I have put together a few explanations in text and video form for you.

Why must liquid metal thermal paste not come into contact with aluminum heat sinks? Because gallium and aluminum form an alloy that makes the heat sink brittle. Details and videos below!

Why must liquid metal thermal paste not come into contact with aluminum heat sinks? Because gallium and aluminum form an alloy that makes the heat sink brittle. Details and videos below!

What does gallium do with aluminum?

Basically, the question can be reduced to what is actually going on between the gallium from the thermal paste with liquid metal content and the aluminum of the heat sink. In short, an alloy is going on. Gallium and aluminum combine and form a compound which, due to the so-called lowering of the melting point, becomes liquid at room temperature. 

The reaction spreads from the contact point, so that the heat sink becomes more and more porous. Not only does the thermal conductivity of the component suffer as a result, and thus its use in the PC, it also crumbles very quickly. Since high temperatures are reached when the device is in operation, this happens even faster than at room temperature (see videos).

Liquid metal thermal paste and heat sink

If liquid metal thermal paste and heat sink come into contact, you've screwed up. Because not only do the two elements gallium and aluminum react very quickly; removing one substance from the other is also difficult. The first idea when assembling a PC will be to take the component and clean it with water. 

Bad idea! This is because the resulting alloy reacts even more extremely with water and decomposes the aluminum component even faster. Therefore the only tip that you can basically give: Make sure that under no circumstances does the paste get onto the lamella block! Nothing should drip onto electronic components or the circuit board. Here are a few more videos and useful links.

Gallium-aluminum reaction in the video

There are various videos on YouTube that deal on the one hand with the effect (the decomposition of the heat sink) and on the other hand with its chemical background. Finding a simple, short and soberly explanatory video, however, is an impossibility. Therefore here the smallest evils with partly bad audio, partly unnecessarily lurid presentation.

Useful links on the topic

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