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

Corrosion in a roundabout way

Stainless steel, especially chromium-nickel steels (such as 304 or 316 stainless steel), are highly resistant to corrosion. The chromium oxide layer on the surface protects the material from oxidation and corrosion. In a water cooling system, the passivation layer (chromium oxide) ensures high resistance to rust and general corrosion as long as the pH value of the water remains in the neutral range and no aggressive chemicals are present. With increasing age and decreasing anti-corrosives, however, stainless steel becomes a problem.

However, under certain conditions, e.g. low pH value, spot corrosion (pitting) can occur. 316 stainless steel is more resistant to pitting corrosion than 304 stainless steel. In high temperature and stress environments, stainless steel can also be susceptible to stress corrosion cracking (SCC). However, this is less common in water cooling systems as temperatures are usually moderate, or should be.

Copper has excellent thermal conductivity, which makes it an ideal material for heat exchangers and heat sinks. It enables efficient heat transfer and dissipation. Copper is also generally resistant to corrosion, but it can corrode under certain conditions. In the presence of oxygen and water, copper oxides can form. But this is exactly what I have not found. And now?
At high chloride concentrations, copper can be more susceptible to corrosion. However, it usually forms a protective patina layer that slows down further corrosion.

However, if brass and stainless steel are in contact with each other because they are surrounded by an electrolyte (e.g. water), galvanic corrosion can occur. Brass and stainless steel have different electrochemical potentials, which causes the less noble metal (in this case the brass) to corrode while the more noble metal (stainless steel) remains protected. In a water circuit, brass usually corrodes faster than pure copper when it is in contact with stainless steel. In a so-called galvanic pair, the less noble metal corrodes faster. Zinc, an essential component of brass, is less noble than copper. Therefore, brass tends to corrode faster than pure copper when it comes into contact with stainless steel.

Dezincification

A specific form of corrosion in brass is dezincification, in which the zinc from the alloy selectively corrodes and leaves behind porous copper. This weakens the material and accelerates corrosion. This type of corrosion occurs particularly in warm, slightly acidic or slightly alkaline water conditions. Nothing else can be observed on the exposed areas of the brass threaded insert. This is because brass has a more complex microstructure compared to pure copper, which can lead to different rates of corrosion in different areas. This can lead to localized weak points and accelerated corrosion.

Summary and conclusion

In a water cooling system, both chrome-nickel steel and copper and brass are very suitable due to their respective properties, but their interaction must be carefully monitored and also thought through. Stainless steel offers high corrosion resistance, while copper and brass offer excellent thermal conductivity. Particular attention should be paid to avoiding galvanic corrosion when both materials are used in the same system. If Bykski had nickel-plated these two components, i.e. jetplate and cover, the corrosion of the brass and the subsequent, highly visible dezincification would not have happened.

As a general rule, in water cooling circuits, flocculated material tends to accumulate in certain places, such as bottlenecks and bends and in radiators, because the flow speed of the water slows down there, which favors sedimentation. Particles have more time to settle when the flow is slower. Radiators often have complex and narrow structures that slow down the flow and can even cause turbulence. This turbulence causes particles to be washed out and deposited. The pressure is lowest in the last radiator, so that it is conducive to the dezincification and, above all, deposition of the dissolved zinc. This also explains the cause and location of the white coating.

The plasticizers, on the other hand, are a completely different matter. There, the very relatively fine and narrow structure of the microchannels under the jetplate has caused an accumulation of the plasticizers released from the tubes. The evidence of the threads produced by drying out is actually clear. In this case, inferior and unsuitable tubing with far too many plasticizers was simply used. Even the best anti-corrosive agents will not help, because it is not corrosion, but chemical contamination of the coolant.

So the reader has observed two completely different problems and I had another exciting day today with a lengthy analysis and some nice findings. If anyone also notices inexplicable things in the water circuit or if products corrode unexpectedly or give up the ghost: Feel free to contact me, because in the end everyone benefits from such an analysis, even me. Win-win on all sides, that’s how it should be! 🙂