


To:		Rochelle Boyd, U.S. Environmental Protection Agency, OAQPS

From:		Mark Bahner, RTI International 

Date:		August 20, 2012

Subject:	Anodized Aluminum as a Potential Source of Hazardous Air Pollutants (HAPs)
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Executive Summary

Certain types of anodized aluminum are potential sources of HAPs when used in the feed/charge material in secondary aluminum production furnaces. If dyes 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 dyes or sealers are on feed/charge to secondary aluminum processing units. 
 2.0	ANODIZING PROCESS DESCRIPTION
Anodizing aluminum is an electrolytic process used to increase the natural oxide layer on aluminum parts. Anodizing increases resistance to corrosion and wear, and provides better adhesion for coatings. Anodic films can also be used for a number of aesthetic effects, such as to allow dyeing (coloring). Typical processes and conditions for anodizing aluminum are shown in Figures 1 and 2 (Newman, 2011).



Figure 1. Processes 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 
* Dye part in 140 degree dye 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 dyes and sealers (if dyes and sealers are used) and potentially also HAP metals in the dyes and sealer (e.g., nickel and chromium).  

For example, the Material Safety Data Sheet (MSDS) in Attachment 1 is for a black dye manufactured by Caswell, Incorporated. The dye contains formic acid (CH2O2, <3%) and hexylene glycol (C6H14O2, <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 chromic acid (H2CrO4, <3%) which contains the HAP metal chromium. 

The MSDS in Attachment 2 is for a sealer manufactured by Caswell, Incorporated. The sealer contains nickel acetate tetrahydrate (C4H14NiO8, <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 Dye (MSDS No: DYEBLK)


                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                       
                                 ATTACHMENT 2
                                       
                        MSDS for Caswell, Incorporated
                      Anodizing Sealer (MSDS No: ANSEAL)
                                       
                                       
                                       
                                       
