硝酸ナトリウム添加浴からの亜鉛-シリカ分散めっきの析出挙動とその皮膜特性(電気めっき)(<特集>表面処理)

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The deposition behavior and the coating characteristics of an electrodeposited Zn-SiO_2 composite coating have been studied. SiO_2 particles were maintained in good suspension in the plating bath without any special agitation. The SiO_2 deposition rate was increased when sodium nitrate was added to the plating bath. The amount of sodium nitrate required for SiO_2 deposition was mainly determined by the pH of the plating bath. When the pH was low, sodium nitrate was required in relatively large amounts for SiO_2 deposition. SiO_2 particles were distributed uniformly in the coating except for the extreme surface. The extreme surface layer consists of SiO_2-rich phase. The grain size is fine and the orientation of the deposit is random for the Zn-SiO_2 composite coating. The coating contains small amounts of an oxidized zinc, probably zinc hydroxide. The Zn-SiO_2 deposition mechanism has been proposed as follows : (1) Nitrate is electrochemically reduced at the cathode and raises the pH of the electrolyte at the cathode-solution interface. (2) The increase in pH makes the SiO_2 particles coagulate and, at the same time, zinc hydroxide precipitates on the surface of the SiO_2 particles. (3) The cathode is covered with those co-precipitates and the deposition occurs through them. We have speculated that, according to "the Adsorption mechanism" proposed by GUGLIELMI, the SiO_2 deposition rate is high for the nitrate-added bath because the cathode is adsorbed by the SiO_2-rich precipitate.
社団法人日本鉄鋼協会の論文
1991-07-01

硝酸ナトリウム添加浴からの亜鉛-シリカ分散めっきの析出挙動とその皮膜特性(電気めっき)(<特集>表面処理)

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