Simple Principle Of Electrolytic Coloring
|Electrolytic coloring is caused by the reduction of metal ions on the barrier layer at the bottom of the membrane hole.|
But the barrier layer of aluminum is not chemically active. The key to electrodepositing metal on the barrier layer is to activate the barrier layer. Electrolytic coloring uses sine wave alternating current, that is, the polarity change of the alternating current is used to activate the barrier layer, the barrier layer is damaged in the negative half cycle, and the positive half cycle is oxidized and repaired, so that the barrier layer is activated. So electrolytic coloring uses alternating current. So how can alternating current reduce metals? This is because the barrier layer has semiconductor characteristics and can perform rectification. When the potential of the counter electrode is higher (positive) than the potential of the aluminum part, the negative component of the current on the aluminum part side will dominate. Under the effect of the cathodic reduction, metal ions that diffuse into the pores of the membrane are reduced and precipitated.
Studies have shown that noble metals, copper and iron group metal ions are reduced to metal colloidal particles, and some oxo acid radicals such as selenate, molybdate, and permanganate are reduced to precipitate as metal oxides or metal compounds, and are deposited on the film wall.
The tint of electroless plating coloring varies with the type of metal salt and the amount of metal deposited. In addition to the characteristic color of the metal, it is also related to the size, shape and particle size distribution of the metal colloidal particles. If the size of the colloidal particles is in the visible light wavelength range, Light waves are selectively absorbed and diffused so that different shades can be seen.
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