銅管の蟻の巣状腐食成長メカニズムの研究

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概要

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• It is a great problem for air conditioning units that leakage accidents of refrigerant happen in an extremely short running time after installation.Such a trouble may be caused by ant nest corrosion of copper tube used for a heat exchanger.This type of corrosion is characterized by complicatedly divided microscopic caverns,and can by observed in the cross section of the corroded copper tube by using an optical microscope.The surface of the corroded copper tube usually becomes descolored greyish-brown or blue-violet without showing any corrosion product.This corrosion is produced by organic acid vapor originating from the inside or outside of copper tube.This study reports the investigation of the growth mechanism of ant nest corrosion.The ant nest corrosion could be reproduced in the heating cycle condition of (298K×12 hr 〓 313K×12hr) for 30 days in a humid oxygen atmosphere containing formic acid vapor.Porous accumulation was observed in the corrosion caverns.The chemical analysis of the corrosion caverns by an electron probe mictoanalyzer confitmed that the porous accumulation was copper oxide and no formic acid complex existed in the corrosion caverns.This result means that the formic acid complex dissolves in the solution of inner corrosion caverns.Consequently,the growth mecanism can be explained as follows.A cathodic reaction occurs as O_2+4H^++4e^-→2H_2O on the wet surface of copper tube,and an anodic reaction occurs as Cu→Cu^++e^- in the inner corrosion caverns.Cu^+ in formic acid solution is complexed by CO_2H^-:Cu^++CO_2H^-→Cu^<(l)>(HCO_2).Then Cu^<(l)>(HCO_2) changes to Cu_2O repidly.Cu_2O takes the form of porous oxide.This oxide is dampened with formic acid solution.It is thought that the ant nest corrosion grows as the oxidation reaction of copper at the interface of the porous oxide and metallic copper.Therefore,the more the porous oxide becomes wet,the more corrosion caverns widen.The complicated divided pattern of corrosion caverns is caused by the cracks of porous oxide that are formed by the change in volume of the porous oxide.

• 社団法人日本材料学会の論文
• 1993-08-15

著者

• 宮 一普

  三菱電機(株)先端技術総合研究所

• 宮 一普

  三菱電機(株)材料デバイス研究所

• 瓦井 久勝

  三菱電機(株)材料デバイス研究所

• 松岡 宏昌

  三菱電機(株)材料デバイス研究所

• 松岡 宏昌

  ヨツギ(株)技術開発部

• 宮 一普

  三菱電機(株)

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• 電動パワーステアリングの安全性評価
• 電動パワーステアリングの安全性評価
• 銅管の蟻の巣状腐食成長メカニズムの研究
• 物理現象と腐食(腐食防食)
• 各種分析法による腐食原因解明技術 (特集 冷凍空調設備のメンテナンス) -- (最適計測技術のメンテナンス活用)
• 各種分析法による腐食原因解明技術

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