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 of 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 us now take a closer look at what is actually in it and what is not. The DOWSIL TC-5550 contains well-balanced fillers and since the Al2O3 is also used in finer grinding grades, not so much finer ZnO is needed as a gap filler. The aluminum oxide content is therefore significantly higher, while the matching silicon content (silicone) shows that the aim was to keep the paste easy to spread without making it too liquid. This compromise has worked well.
![](https://www.igorslab.de/wp-content/uploads/2024/08/12-LIBS-980x735.jpg)
Now let’s take a look at the Gelid GC-4, which performs significantly worse and also looks crumblier. ZnO has been completely omitted from this paste, which is now taking its toll, as the Al2O3 is unfortunately not as finely ground for cost reasons.
The Snowman TGM5 / TGM10 at least has some ZnO in it again, although not much. The performance is similar to GC-4, but the paste is a little easier to apply and should also show fewer pump-out effects, as the consistency is more stable.
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