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ANODIZING Organic colorants, or dyes, are by far the most widely used for decorative finishes. The porous anodized aluminum is simply dipped in a dye bath, and over time, dye is absorbed into the surface. The color range is virtually endless as dyes are used at any number of depths of shade and in Coloring Technologies any combination. Anodized aluminum can be colored using a variety of techDyes tend to be large organic molecules that may contain a nologies that can loosely be divided into two classes: organic metal ion. Every dye is unique and and inorganic. has its own fastness characteristics, An oxidative environment—such as a but all fade to some degree as a result of bond cleavage within the Sterrad sterilization cycle—can fade organic molecule. This cleavage can anodized coatings that are colored occur as a result of UV irradiation, with organic dyes. chemical oxidation or a combination of both. The dyes chosen for this study were taken from Clariant's Sanodal range of super high fastness products, dyes that have been developed, tested and proven durable enough for extended outdoor use. Two common inorganic coloring techniques used to provide decorative finishes on anodized aluminum include adsorption and electro-deposition of metal-containing pigments. The most common adsorption method is used to create a gold finish by dipping the anodized aluminum in an ammonium or sodium ferrioxalate salt solution. The heavy metal salt is hydrolyzed and an iron-based pigment is precipitated within the pores of the coating. A lesser known but similar technique uses a sequential dip process where first the part is dipped in a solution of potassium ferrocyanide and then in a ferric nitrate bath. The ensuing double decomposition treatment results in the creation of a nontoxic blue pigment commonly referred to as Prussian blue. Electro-deposition of metallic pigments is achieved by immersing the anodized aluminum in a metal salt solution and applying an AC potential. During the cathodic half cycle, particles of metal are deposited at the bottom of the pores. During the anodic half cycle, the ultra-thin barrier layer oxide separating the porous coating from the aluminum is given time to stabilize. Over time, the metal particles fill the pores and the resulting color deepens. This technique is widely used around hydrogen peroxide gas plasma technology to sterilize instruments and medical devices. Which treatments for anodized aluminum can hold up to multiple rounds of Sterrad? Chart 1 – Organic Dye ID Conc. pH Temp. Immersion Time Color A Sanodal Red B3LW 5 g/L 5.6 140°F 20 min. Red B Sanodye Blue G 3 g/L 5.6 140°F 20 min. Blue C Sanodal Green 3LW 3 g/L 5.6 140°F 20 min. Green D Sanodal Deep Black HBL 10 g/L 5.6 140°F 20 min. Black E Sanodye Yellow 3GL 3 g/L 5.6 140°F 20 min. Yellow F 24 Chemistry Sanodal Turquoise PLW 5 g/L 5.6 140°F 20 min. Turquoise DECEMBER 2013 — pfonline.com