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Chemical Depth Profiling of Anodized Extrusion Surfaces Using rf-GD-OES

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Chemical Depth Profiling of Anodized Extrusion Surfaces Using rf-GD-OES

Thomas Björk, Corrosion and Metals Research Institute (KIMAB), Stockholm, Sweden
Jan-Olov Nilsson, SAPA Technology, Finspång, Sweden


ABSTRACT --- The present paper addresses chemical characterization of
anodized extrusions using glow discharge optical emission spectroscopy (GDOES).
The study is motivated by the importance of rapid, accurate analysis
techniques for quality and process verification of these, analytically complex
surfaces. A set of anodized surfaces were produced with different thickness, both
un-sealed and sealed with hot water. The test materials were characterized using
GD-OES in the radio frequency (rf) mode. The thickness was assessed with an
eddy current probe. Most attention was given to the elemental depth profiles of
Al, O, Si, H, S, and Fe, and how these elements vary with anodizing parameters.
The actual thickness of the materials varied between 12 and 30 μm. The rf-GDOES
depth profiles show how sulfur is depleted in the sealing process, and how
the oxide is enriched in oxygen and hydrogen. The oxide is composed of
aluminum to about 20 wt% and oxygen to about 80 wt%. This is surprising, but
reflects the massive adsorption of oxygen and water inside the porous oxide
structure. The different appearance of the depth profiles recorded show that the
analysis technique is very well suited for control of the different steps of the
anodizing process. Probably, it can be used for evaluation of technical properties,
e.g., strength, hardness and corrosion resistance.

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