Microscopy and material analysis
Let’s start with microscopy. It is quite interesting to observe how a paste can be spread and when it de facto tears up and down on the glass slide. It can be seen that the paste only adheres moderately well, which may also be due to its composition. The polysiloxane matrix used, i.e. silicone, is very homogeneous, but not particularly flexible and flowing, which is of course also due to its consistency. It is anything but viscous, but also not as fluid as an Arctic MX-6, for example. I think this compromise is a good one, but you also need skills to spread it thinly.
Now let’s see what’s in it and what’s not. I wrote at the beginning about the reasons why I use Alphacool Apex as a reference paste and use it almost exclusively in everyday life. The proportion of highly thermally conductive corundum(Al2O3) is relatively high and we don’t find any cheap zinc oxide (ZnO). I find the use of such different phases in a heat-conducting paste rather unfavorable for my purposes, especially in terms of long-term durability. Yes, you will be able to fill the gaps between the corundum beads better with the even smaller zinc platelets and thus also be more thermally conductive for the moment, but with a pure silicone base I have mixed feelings about this.
Phase-change pads such as the Honeywell PCM 7950 would be ideal, where such errors in the matrix tend to be rare, as the polymer used is much more stable. However, I am always very skeptical about liquid pastes that perform very well and work with such a base of corundum and ZnO. This is precisely why the mysterious “Gaming Paste A” has not become my reference. But this secret will soon be revealed too. I have not found carbon in higher quantities, which suggests less elaborately designed side chains of the silicone in the matrix. With a little skill, you can even achieve consistencies up to that of plasticine.
Test equipment for the material tests, accuracy and test preparation
The material testing and measurement of the pastes and pads is carried out by my Keyence VHX 7000 with EA-300, which enables both exact measurements and fairly precise mass determinations of the chemical elements. But how does it actually work? The laser-induced breakdown spectroscopy (LIBS) I used for this article is a type of atomic emission spectroscopy in which a pulsed laser is directed at a sample in order to vaporize a small part of it and thus generate a plasma.
The emitted radiation from this plasma is then analyzed to determine the elemental composition of the sample. LIBS has many advantages over other analytical techniques. Since only a tiny amount of the sample is needed for analysis, the damage to the sample is minimal. The real damage is caused in today’s article by my rather coarse cutting and separating tools. This still quite new laser technique generally requires no special preparation of the samples for material analysis. Even solids, liquids and gases can be analyzed directly.
LIBS can detect multiple elements simultaneously in a sample and can be used for a variety of samples, including biological, metallic, mineral and other materials. And you get true real-time analysis, which is a huge time saver. As LIBS generally requires no consumables or hazardous reagents, it is also a relatively safe technique that does not require a vacuum as with SEM EDX. As with any analytical technique, there are of course certain limitations and challenges with LIBS, but in many of my applications, especially where speed, versatility and minimally invasive sampling are an advantage, it offers distinct advantages.
I would first like to point out that the results of the percentages in the overviews and tables have been intentionally rounded to full percentages (wt%, i.e. weight percent), as it happens often enough that production variations can occur even within the presumably same material. Analyses in the parts-per-thousand range are nice, but today they are not useful when it comes to reliable evaluation and not trace elements. However, every day in the laboratory starts with the same procedure, because when I start, I work through a checklist that I have drawn up. This takes up to 30 minutes each time, although I have to wait for the laser to warm up and the room to reach the right temperature anyway.
- Mechanical calibration of the X/Y table and the camera alignment (e.g. for stitching)
- White balance of the camera for all lighting fixtures used
- Check alignment of LIBS optics and standard lens, calibrate alignment of laser to own optics (x300)
- Test standard samples of the materials to be measured and correct the curve if necessary (see image above)
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