When I was cleaning a heatsink from an older laptop, the aluminum, and I think also a bit of copper, started to disintegrate very quickly and sometimes violently. I used a cleaning solution that was made for removing thermal paste and cleaning CPUs and PCBs. After some time, the only thing left of the heatsink was some grey powder or ash. I have cleaned many heatsinks and CPUs with it before, and this never happened, and I can’t reproduce it.
Copper metal “dissolves” in nitric acid (HNO3). Actually, the nitrate ion oxidizes the copper metal to copper (II) ion while itself being transformed to NO2 gas in the process; the copper (II) ion then binds to six water molecules.
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