Microscopy and surface analysis
Smearing under pressure helps to identify the “tear-off edges” and therefore also the adhesion of the paste. Pastes that are too fluid also allow the silicone, including the smallest particles, to be simply wiped out. Pastes that are too viscous tend to show abrupt tear-off edges. Please click on the images for a full screen:
The risk of outgassing or bleeding from a simple silicone base is definitely an issue. The larger the particles and the more liquid the silicone oil used, the greater the risk of bleeding and outgassing of the silicone base. Pump-out effects are then a very unsightly consequence. We can now see all three pastes at 1000x magnification and with an additional particle measurement. Again, please click for full screen:
Material analysis
Let’s take a closer look at what’s actually inside and what’s not. The NT-H2 from Noctua contains various fillers, mainly very fine, cheap zinc oxide. The aluminum oxide content is significantly lower, but the high silicon content (silicone) in particular shows that it is better not to endlessly dilute and stretch a paste. The ZnO is normally used as a gap filler between the somewhat larger (and harder) Al2O3 grains. Here, however, these somewhat more expensive particles are almost a rare sight (see microscopy above).
![](https://www.igorslab.de/wp-content/uploads/2024/08/10-LIBS-980x735.jpg)
Now let’s take a look at the Gelid GC-Extreme, which performs and looks very similar. Apart from a few color nuances, the content of the metal oxides is almost the same. Lots of cheap ZnO and hardly any sections of more expensive, well-ground Al2O3 particles. Apart from the slightly different coloring, you could almost think it comes from the same vat. Ok, even the performance is almost identical.
![](https://www.igorslab.de/wp-content/uploads/2024/08/09-LIBS-980x735.jpg)
But if you look at the Thermalright TF7, you quickly realize why it performs best, because this is what a modern paste should actually look like. The proportion of zinc oxide is significantly lower and the proportion of silicone is also lower. This is logical, as the paste is therefore somewhat more viscous and, above all, more durable.
![](https://www.igorslab.de/wp-content/uploads/2024/08/09-LIBS-1-980x735.jpg)
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