Slime in the GPU water block and white crystals in the radiator – about plasticizers, corrosion and the wrong materials | Investigative

1 - Problem definition and root cause analysis 2 - Where the slime comes from 3 - White crystals and mysterious corrosion 4 - It's not cocaine, it's zinc! 5 - Korrosion auf Umwegen und ein nötiges Fazit

Slime? Plasticizers, precipitates and the mysterious “threads”

Let’s start with the supposed slime. After I had dried everything, it almost looked like a poorly cleaned drain at your trusted hairdresser. So all in all, it was quite a hairy affair. Our tangle of threads is even multicolored, which may surprise the layman, but also has something to do with the way it was created. That’s why I’m going to give you a little more theory, but unfortunately I can’t spare you that.

Plasticizer residues in a cooling circuit can manifest themselves in various ways and different chemical elements can be precipitated in the process. These residues can build up on the cooling fins, in radiators and pumps, and over time they can also obstruct the flow and lead to blockages. Plasticizers are often oily or sticky substances that can leave a corresponding layer on surfaces in the cooling circuit. The presence of plasticizers can affect the water quality, which can manifest itself in increased turbidity, altered pH values or increased organic content (e.g. TOC – Total Organic Carbon).

Fun fact: Plasticizer residues can lead to a characteristic odour, especially if they are present in high concentrations or decompose. It then smells and is quickly blamed on rotten water or dead algae. What is usually ignored is the fact that these residues and deposits can lead to chemical interactions with other materials in the system in the long term, which can cause these materials to deteriorate or become brittle.

Plasticizers are chemically very diverse, but the most commonly used plasticizers are phthalates and adipate-based compounds. Phthalates are esters of phthalic acid and are no longer commonly used. Well-known representatives are DEHP (diethylhexyl phthalate) and DINP (diisononyl phthalate). Adipates are esters of adipic acid and a well-known representative is DOA (dioctyl adipate). There are also other plasticizers such as organophosphates and citrates. During the decomposition or hydrolysis of plasticizers, chemical elements and compounds can be precipitated, such as carbon compounds (I found them here, for example, picture below), hydrogen and oxygen (as a component of organic acids and esters)

But how did these strange threads form? The formation of thread-like molecular chains from plasticizer residues during drying is a complex process that is influenced by various physical and chemical mechanisms. When a liquid containing plasticizers begins to evaporate, the concentration of plasticizers in the remaining liquid increases. I deliberately did this very quickly beforehand with the hair dryer. This drying process leads to supersaturation of the plasticizers, which encourages the formation of solid residues.

What I have initiated, however, is a so-called nucleation, because as supersaturation increases, small crystal nuclei begin to form. This is the first step in crystallization. These nuclei then serve as the starting point for the further growth of the crystals, as further plasticizer molecules attach themselves to these crystal nuclei. The specific properties of the plasticizer and the ambient conditions (e.g. temperature, evaporation rate) determine the growth rate and ultimately the shape of the crystals. And very different colorations also occur when, for example, they link carbon molecules:

Under certain conditions, the crystals then grow preferentially in a certain direction, which leads to the formation of filamentous structures. This directional crystallization can be influenced by factors such as the molecular structure of the plasticizer, intermolecular forces and the presence of impurities or other substances in the liquid. This is because plasticizer molecules are often long-chain compounds. During the crystallization process, these molecular chains can align and couple with each other in an ordered manner, resulting in the formation of exactly these thread-like structures. Ergo, the presence of these chains is the best indicator of the presence of released plasticizer.

But it doesn’t just have to be filaments, because in the quieter areas without so much flow, crystalline structures are more likely to be deposited, which can almost look like an egg layer (ice flowers). But even here there is still a lot of carbon, together with sodium (probably from the coolant)

And because it was so beautiful, the whole thing again before I draw my interim conclusion.

Interim conclusion

After complete evaporation of the liquid, the filamentous residues remain as solid structures. These residues consist of ordered, interconnected plasticizer molecules that have joined together to form chains or filamentous crystals. This is exactly how the filamentous structure we are admiring is formed through the combination of supersaturation, nucleation, directed crystallization and intermolecular interactions of the plasticizer molecules during the drying process.