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Pure aluminum in hot DI water




Q. I have some samples of pure aluminum. I've decided to put them in HOT DI water. I do not understand, with all the classic mechanisms, why there is some corrosion and a high level of oxygen not only at the surface. In normal cases, the already formed alumina layer should protect the metal. It is not apparently not the case! Thank you for giving me some explanations!

DO Dang Liem
- China
2002


A. DI water is not exactly neutral, in fact, it is slightly acidic. Therefore a chemical reaction with the metal is not unexpected.

The thin oxide coating that naturally forms on the surface of the aluminum is not enough to protect the metal from extreme environment or physical abuse.

Dado Macapagal
- Toronto
2002


A. It is known that DI rinsing leaves rinsed substrates in a slightly acidic state. The reason is as follows: In the exchange process, the resins take out everything including carbon dioxide, carbonic acid/CO2 and alkalinity. This is what leaves very pure water. Once this water is released to the atmosphere from the exchange process, it will start to absorb carbon dioxide or CO2. It will continue to absorb CO2 and without alkalinity to buffer it, the pH will drop until a maximum saturation level has been reached resulting in a pH level always remaining at 5.5-6.0 pH. The reason for the slightly acidic state is that the pure water does not re-absorb the alkalinity it processed out. The oxygen level at elevated temperature is reduced. You should probably reduce your time in the DI and lower the temperatures to combat oxidation. Remember that aluminum and DI are not very compatible and this is why you see the aggressive water attacking your aluminum.

bob utech
Bob Utech
Benson, Minnesota
2002




Currently I'm faced with components becoming discolored (yellowish) after rinsing with hot DI Water on last rinsing cycle (first 3 cycles using cold DI Water and last cycle using 50 °C DI Water). But discoloration happens randomly on components. Please help to give some explanation. Thanks.

Steve Poh
- Penang, Malaysia
December 26, 2012




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