Determination of Sulfuric Acid, Oxalic Acid, and Their Matrix Effects in Aluminum Anodizing Solutions by Ion Chromatography
Abstract
Anodizing and hardcoating (hard anodizing) of aluminum improve corrosion and wear resistance. Acid concentrations (sulfuric, oxalic), pH, and physical plating variables (current, temperature, time) affect oxide coating thickness, porousness, hardness, solubility, and conductivity. Hardcoating solutions typically contain 120-160 g/l sulfuric acid (H2SO4) and 12-21 g/l oxalic acid (H2C2O4), while anodizing solutions typically contain 160-200 g/l H2SO4. Lower acid concentration hardcoating solutions give oxide coatings that are thicker, harder, less porous, less soluble, and more wear resistant compared to higher acid concentration anodizing solutions. Sodium hydroxide (NaOH) and hydrochloric acid (HC1) are commonly used to adjust the pH of these metal finishing solutions. The acids and sodium salts of sulfate and oxalate have been determined in a variety of matrices, although not for anodizing and hardcoating solutions. A reference standard for instrumental analysis of sulfate or oxalate ions is commonly made from either the acids or the sodium salts. Anodizing and hardcoating sample solution acids and sodium salts are present for these analytes and cause matrix effects when compared to the reference standards. These matrix effects may produce considerable variation in the commonly used analytical response of peak height, and result from dissimilar samples and standards affecting the eluent and separator column differently. An improved chromatographic procedure that addresses these matrix effects is given for anodizing and hardcoating solutions.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1988
- Accession Number
- ADA197734
Entities
People
- Samuel Sopok
Organizations
- United States Army Armament Research, Development and Engineering Center