CITRIC ACID PASSIVATION

There are alternatives to nitric acid passivation of stainless steel. There is data available showing that citric acid passivation is equal to or superior to nitric acid passivation.

Citric acid has been used very successfully for years in many industries. There is test data using salt spray, copper sulfate, palladium chloride, boiling water and high humidity on many grades of stainless.

Some of the advances that have been made in the last few years are:

Elimination of rust and corrosion problems on 410 ss that has been a problem for many years with nitric acid passivation (surgical industry).
Chrome oxide : Iron Oxide ratios on the surface of 316 stainless steel that are higher than ever obtained with nitric acid (semiconductor industry). Ratios as high as 12.7 to 1 have been obtained!!!
Complete elimination of passivation problems on orthodontic devices made of 316 stainless steel brazed with gold/palladium (orthodontics industry).
Cleaning and passivation of heat treated 455 stainless steel to pass water immersion tests and eliminate oxide coating to look like electropolished material (surgical industry).
Elimination of the need for Hydrochloric acid to remove heat treat oxides on 440C stainless steel (controls industry).
Improved corrosion resistance compared to nitric acid on 302 and 316 stainless steel. Elimination of rejects that were plaguing the customer (spring industry).

In all cases, it is being done successfully while saving money and providing a safer atmosphere for employees and the environment.

Comparison of CitriSurf and Nitric Acid Passivation

PROPERTY	NITRIC ACID	CITRISURF
Safety	Very hazardous	Very safe to use as directed
Air Breathing	Emits toxic gases	No toxic gases emitted
Ease of use	Bulky safety equipment and extreme care required	Minimum of safety equipment and caution in use
Passivation	Excellent passivation of most grades of stainless	Excellent passivation of nearly all grades of stainless
Environment	Environmentally hazardous	Environmentally friendly
Cost	Low cost raw material; high cost maintenance and waste disposal. High cost of safety and ventilation system	Lower overall cost to use due to lower maintenance and waste disposal costs; longer lasting solutions and lower concentration necessary
Speed	20 minutes to several hours required	4-20 minutes typical, depends on process and grade
Temperature	Elevated temperature required for many grades	Room temperature satisfactory for many grades. Elevated temperature improves speed and performance
Maintenance	Regular solution replacement required with removal of hazardous waste.	Solutions lasts much longer and most operations have no hazardous waste to remove at all
Iron Oxide removal	Removes iron oxide slowly	Readily removes iron oxide
Equipment	Long-term degradation of tanks and area equipment is expected	No deleterious effects on recommended tanks and equipment, or corrosion of equipment in area
Flexibility in use	Must control time/temperature carefully and danger of NO_x emissions is always present	No hazard of leaving product in the tank too long for most products, no hazardous emissions even with poor grades of stainless steel parts
ASTM A-967	Meets requirements	Meets requirements
AMS 2700	Meets requirements	Meets requirements