Passivation Equipment
And Chemistry

It is possible to include both nitric and citric in one line? However, this does make the line’s footprint larger, because there needs to be a dedicated rinse station for nitric and another for citric. They can both share the final rinse station, which is commonly monitored using a conductivity probe that will signal fresh water to be injected into it if the bath conductivity exceeds maximum limits. A vacuum drying station is recommended for faster drying.

Nitric tanks do require ventilation, possibly followed by an air scrubbing process to remove nitric gas. Shops must consult with their local municipalities to determine if an air scrubber is necessary.

Nitric acid bath concentration is determined by measuring its specific gravity, adding more nitric acid if the level is out of range or draining completely. Similarly, citric acid bath concentration is measured using a conductivity meter and, per its reading, more water or more citric acid should be added. Depending on how tight process parameters are, the citric bath might require draining after a week or month of use. These procedures are both akin to monitoring/maintaining a machine tool’s coolant concentrate levels.

For nitric acid, the waste acid must be pumped out of its tank and stored in a drum to be removed by a company certified to handle it. For citric acid, it can be as simple as performing a pH balance and disposing of it as if it is common waste water.