Uni Anodizado Con Cobre

Study on the Black Electrolytic Coloring of Anodized Aluminum in Cupric Sulfate
H.H. Shih* (施幸祥), Y.C. Huang (黃鈺傑), F. Kuo (郭賦)
Department of Chemical Engineering, Tatung University (大同大學化工系) 國科會工程處人才資料庫帳號：0100852

Abstract
In this research, sulfuric acid was used as the electrolytic solution to carry out the anodic oxidation of aluminum for 15 minutes before the anodic oxidized film with athickness of about 20 μm was obtained. Then black electrolytic coloring was done by using a copper sulfate mixed solution as the electrolytic solution. The factors influencing the black electrolytic coloring of aluminum were investigated so as to determine the best operating conditions for black electrolytic coloring. The optimum conditions for the experiment were as follows. Mixing 35 g/L coppersulfate, 10 g/L sulfuric acid, and 2 g/L sodium sulfate yielded the coloring solution. Electrolytic coloring was carried out for 50 minutes in the solution with bath temperature at 40℃ and alternating current voltage at 30 V. A black colored film of about 0.03 of minimum visible light reflectivity and 17.6 of minimum L-value could be obtained. Coloring bath temperature was found to be the mostimportant operating condition for influencing the L-value and visible light reflectivity. Through the corrosion test, it was noticed that the anti-corrosion ability of the structure of anodic film colored at lower bath temperature was better than at high bath temperature. Keywords: anodic oxidation; black electrolytic coloring; copper sulfate; L-value; visible light reflectivity

1. IntroductionMany methods for coloring Al have been described in the patent literatures [1-2]. The most common blackening process is the organic dyeing process. However, the films produced by this method have the disadvantages of weak abrasion resistance and of fading on being illuminated by light. And, mineral pigmentation process produces films with strong fading-resistance but with weak abrasion resistance.Therefore, both above processes are suitable for decoration purpose only. The anodic treatment technique is frequently applied to the surface of Al materials to increase their resistivity to corrosion from the environment [3]. It is well-known that solar energy source plate needs a surface of high absorptivity and low reflectivity to

transform efficiently solar energy into thermal energy [4].To meet the requirement, black electrolytic coloring of Al materials, which are light in weight, low in cost, and good at thermal as well as electrical conductivities, has been gradually developed [5] and applied in the manufacturing process of the solar energy source plate.

2. Experimental 2.1 Specification of the Sample
1100 pure Al sheet was available for anodic treatment and electrolyticcoloring.

2.2 Experimental Process
With 200 g/L sulfuric acid as the electrolytic solution and under the following operating conditions:

temperature at 20℃, pulsed current density of 5 A/dm2, duty cycle of 80%, and frequency of 1000 Hz, the anodic treatment was carried out for 15 minutes; Thereafter, an anodic oxidized film with a thickness of about 20±2 μm was obtained. The Al oxide sheetsafter the anodic treatment were placed in the mixed electrolytic solution of 30-40 g/L copper sulfate, 10 g/L sulfuric acid, and 2 g/L sodium sulfate. At the coloring bath temperature of 10-45℃ and with 10-50 Vac, the electrolytic coloring was performed for 5-70 minutes.

From Fig. 3, when the coloring voltage is less than 25 V, the L-values of the colored films tend to rise in value; the use of25 to 45 Vac yields black coloring films of lower L-values. However, the use of alternating current voltage of 50 V instead slightly increases the L-value. At such a higher voltage, the surface structure of the anodic film shows signs of corrosive destruction. A minimum L-value of about 27.3 can be obtained by carrying out the electrolytic coloring at an alternating current of 30 V. A higher...