To: Rochelle Bo yd , U.S. Environmental Protection Agency , OAQPS

From: Mark Bahner , RTI International Date: August 20 , 201 2 Subject: Anodized Aluminum as a Potential Source of Hazardous Air Pollutants (HAPs)

**1.0 EXECUTIVE SUMMARY**  Certain ty pes of anodized aluminum are potential sources of HAPs when used in the feed/charge material in secondary aluminum production furnaces. If d yes are used, the dyes can contain organic materials and HAP metals
. If sealers are used, they also can contain organic materials and HAP metals. Therefore, organic HAPs and metallic HAPs can be generated when the d ye s or sealers are on feed/charge to secondary aluminum processing units. **2.0 ANODIZING PROC**  **ESS DESCRIPTION**  Anodizing aluminum is an electrol yt ic process used to increase the natural oxide lay er on aluminum parts. Anodizing increases resistance to corrosion and wear, and provides better adhesion for coatings. Anodic films can also be used for a n umber of aesthetic effects, such as to allow dy eing (coloring). Ty pical processes and conditions for anodizing aluminum are shown in Figures 1 and 2 (Newman, 2011).

**Figure 1. P rocesses in Anodizing Aluminum (Newman, 2011).**  Submerse part in 140 degree cleaner for 5 min, rinse

 Etch part in room temp caustic solution (lye) 10
- 30 seconds or longer if matte finish is desired, rinse
 Desmut part at room temp for 1
- 3 min if previously etched, stripped or alloy

calls for it (such as 2024 alloy), rinse
 Anodize part at 12 ASF for 1 hour duration at room temp (65
- 70 degrees), rinse, rinse again
 Dy e part in 140 degree dy e for 15 seconds to 15 min (depending on shade desired), rinse
 Seal part in 170
- 180 degree Nickel Acetate Sealer for 20 min, rinse and hang part to dry **Figure 2. Processes and Conditions for Anodizing Aluminum (Newman, 2011).**
**3 .0**  **POTENTIAL SOURCES OF HAPs IN THE ANODIZING PROCESS**  The potential sources of HAPs in the annodizing process come from organic materials used in dy es and sealers (if d ye s and sealers are used) and potentially also HAP metals in the dy es and sealer (e.g., nickel and chromium). For example , the Material Safety Data Sheet (MSDS) in Attachment 1 is for a black d ye manufactured b y Caswell, Incorporated. The dy e contains formic acid ( CH 2 O 2 , <3%) and hex yl ene gl ycol ( C 6 H 14 O 2 , <3%) . Both of these constituents could be converted into organic HAPs when the aluminum feed/charge is heated to the melting point, in the same manner that organic HAPs can be produced when paints or oils can produce organic HAPs when the feed/charge his heated to the aluminum melting point. The black dye also contains chr omic acid ( H 2 CrO 4 , <3%) which contains the HAP metal chromium. The MSDS in Attachment 2 is for a sealer manufactured b y Caswell, Incorporated. The sealer contains nickel acetate tetrahydrate ( C 4 H 14NiO 8 , <100%). The organic material can be converted into HAPs, and nickel is a HAP. **4 .0**  **REFERENCES** Newman, 2011. “Anodizing Aluminum.” Ron Newman. Available at: http://www.focuser.com/atm/anodize/anodize.html . Accessed August 20, 2012.**ATTACHMENT 1** MSDS for Caswell, Incorporated Black Dy e (MSDS No: DYEBLK)**ATTACHMENT 2** MSDS for Caswell, Incorporated Anodizing Sealer (MSDS No: ANSEAL )