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Nanoporous copper foams (65–80% porosity) are synthesized by dealloying different copper alloys, including Cu20Zn80, Cu35Zn65, and Cu30Al70. Ligament sizes, porosity, and oxide content are examined by scanning electron microscopy, Raman spectroscopy, and X‐ray powder diffraction to determine the nanoporous foam's structure and thermal stability. The pores and ligaments of the copper foams can range in size from 35 to 220 nm. Both parameters can be controlled by either the dealloying process or a subsequent heat treatment. The results show no copper oxide peaks for the as‐prepared samples; however, any heat treatments above 200 °C lead to the formation of Cu oxide (CuO and Cu2O). These foams are shown to retain their structural integrity even after oxidation. A novel method is thus developed for synthesizing nanoporous Cu oxide foams by heat treating nanoporous copper.

Anodization behaviors of AZ91 magnesium alloys in strongly alkaline solutions with and without the addition of fluorine ions have been studied with the emphasis on the effect of the Mg 17 Al 12 ͑␤͒ phase. In the absence of F − ions, the potential of the cell was relatively low and sparks were absent throughout galvanostatic anodizing at a current density of 1 A/dm 2 . After 10 min of anodization, a significant preferential anodization within an ␣ matrix resulted in a nonuniform anodic film in regions of large hemispherical pits. F − ions in strongly alkaline solutions resulted in a marked increase in the cell potential and induced sparks on the alloy. These effects associated with F − ions are likely due to the formation of Mg and Al fluorides, which effectively retards the preferential surface attacks in a strongly alkaline solution. Finally, the anodic film formed without sparking was mainly Mg hydroxide, whereas that resulting from sparking was primarily Mg oxide.In light of their superior specific strength and stiffness, magnesium ͑Mg͒ alloys have been used extensively in the applications where the weight of the structure is a primary concern. To extend their service life, many researches have been performed for better understanding the corrosion behavior of Mg alloys. 1-6 The AZ91 alloy ͑Mg-Al alloy͒, which consists of the ␣ phase ͑Mg solid solution͒ as the matrix and ␣ + ␤͑Al 17 Mg 12 ͒ eutectic phases, has received the most attention because of the potential galvanic corrosion occurring at the ␣/␤ interfaces. The Al content in the ␣ phase and the volume fraction, size, and distribution of the eutectic ␤ particles are of great interest in characterizing the corrosion behavior of Mg-Al alloys in different environments. Increasing the Al concentration of the ␣ phase improves its corrosion resistance due to the formation of a surface layer enriched with Al. 1 The ␤ phase, when present with a large volume fraction, is beneficial to the corrosion resistance of AZ91 by acting as an effective corrosion barrier; conversely, the presence of a small-fraction ␤ phase can be detrimental to the corrosion resistance due to severe galvanic corrosion. 3-5 In phosphoric acid buffered solutions, the ␣ + ␤ eutectic phase in a Mg-Al alloy is an effective anodic barrier at pH 7, but is preferentially attacked at pH 11. 6 Although the understanding of the corrosion behavior of AZ91 has been greatly advanced during the past decade, this alloy still relies on surface treatments for further improving its corrosion resistance properties or for forming a surface layer to enhance the adhesion of a painting layer. 7,8 Among the various surface treatments, the anodization treatment has received ever-increasing attention because anodic films impart Mg alloy with a better corrosion resistance, higher hardness, improved decorative and wear-resistance properties, as well as enhanced paint adhesion. [7][8][9][10][11][12] The factors governing the corrosion properties of Mg-Al alloys can potentially influence the anodization behaviors of the ...

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