Q&A: Titrating Sulfuric Acid Anodizing Baths

Q: Do you have a recommended analytical method to determine the sulfuric and aluminum concentrations in sulfuric anodizing solutions?

 

Q. Do you have a recommended analytical method to determine the sulfuric and aluminum concentrations in sulfuric anodizing solutions? D.C.

 

A. Here are three good methods that can be used for titrating the sulfuric acid anodizing electrolyte:

 

Sulfuric Acid Anodize Titration Procedure:
 

Principle: One sample is titrated with caustic soda to determine the sum of acid and aluminum. Another is treated with potassium fluoride to precipitate aluminum and titrated to determine acid. The difference is calculated as aluminum.
 

Reagents: Standard sodium hydroxide solution, 1.0 N. Potassium fluoride solution. Dissolve 50 g KF:2H2O in 100 mL of water and neutralize to phenolphthalein. Store in a plastic container. (KF will etch glass.)
 

Procedure: Take two separate 10 mL samples, dilute each to about 150 mL with DI or distilled water and add phenolphthalein. While stirring vigorously, titrate one portion with standard caustic to the indicator end point. Record the titrant volume as “A.”

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