When Al is anodized in dilute (1M) malic acid, the surface of Al is covered with barrier layer, where as it is covered with porous film when Al is anodized in a high concentrated (5M) and high temperature malic acid. The discrimination between the growth of barrier layer and porous film is not so difficult, because their Lissajous' figures obtained in oscilloscope by using 1-P all wave rectifier on anodizing of Al is appearently different. The voltage, at which the current wave form showed zero, coincided with the voltage (
Eb) referred to barrier layer.
Eb on anodizing of Al in a concentrated malic acid at 20°C indicated a high value. When anodizing of Al is done under the condition of such a low temperature, the porous film on Al did not grow. However, under the condition of high temperature, ionic current (
Ip) for the formation of oxide film was increased and the porous film grew on the surface of Al. The reason of the growth was due to that the voltage of barrier layer showed a low value at high temperature, because the barrier layer became thinner by chemical dissolution. When Al-Si alloy was anodized in 1M H
2SO
4 with a constant voltage, 20V and 40V of peak voltage (
Ep) for anodizing, the Lissajous' figures showed a form of barrier layer formation. And, when a constant voltage of 80V was applied, the Lissajous' figures showed the form which was for growing into porous film. As result, black porous film grew on the surface of the Al-Si alloy. Barrier layer was formed in 1.1>
Ep/
Eb, while porous film grew in 1.1<
Ep/
Eb.
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