TITLE:
The Effect of Anion-Exchange-Treated Water Containing Phosphonic Acid and Benzotriazole on Copper Corrosion Resistance
AUTHORS:
Misato Matsumoto, Rihoko Aoyama, Fuka Takahashi, Yuji Nakamura, Yasuki Matsukawa, Yutaka Yamada, Satoshi Nishida, Osamu Sakurada
KEYWORDS:
Copper, Carbon Film, pitting Corrosion, Anion Exchange-Treated Water, Benzotriazole, Phosphonic Acid
JOURNAL NAME:
Open Journal of Composite Materials,
Vol.16 No.3,
June
17,
2026
ABSTRACT: Copper tubes have high thermal conductivity, excellent workability, and corrosion resistance. For these reasons, they are widely used in air conditioning equipment. However, copper tubes can corrode due to interactions between the material and its environment. The carbon film-dependent pitting corrosion is caused by the relationship between the carbon film on the inner surface of copper tubes and the quality of the water flowing them. Phosphonic acid (HEDP) and benzotriazole (BTA) have been reported to suppress pitting corrosion. Additionally, it has been reported that water quality components such as calcium ions (Ca2+), silicate ions (
SiO
4
4?
) and bicarbonate ions (
HCO
3
?
) are effective. Tap water contains various ions, including chloride ion (Cl?), sulphate ion (
SiO
4
2?
) and bicarbonate ions (
HCO
3
?
). Cl? and
SiO
4
2?
are known as corrosive ions. Conversely,
HCO
3
?
is known as corrosion-inhibiting ions. Anion-exchange treatment is a technology for reducing corrosive ions in tap water. It has been reported that anion-exchange treated water inhibits corrosion in carbon steel pipes used within the same system as copper tubes. However, there are few reports on its corrosion-inhibiting effect on copper tubes. This study focused on the effect of anion-exchange treated water on copper pitting corrosion. The test specimens used different amounts of carbon film. The test solution used untreated water and treated water, with both containing HEDP and BTA. Corrosion potential and anodic polarization measurements were performed on these specimens. In corrosion potential measurement, the corrosion potential continued to rise in untreated water and treated water, regardless of the amount of carbon film. The increase in potential was suppressed with treated water compared to untreated water. After corrosion potential measurements, greenish-blue corrosion products were observed only in untreated water. In anodic polarization measurements, the current density of untreated water tended to show a sharp increase on the noble potential side, regardless of the amount of carbon film. In contrast, this trend was not observed in treated water. Based on these results, it is considered that the treated water containing HEDP and BTA inhibits carbon film-dependent pitting corrosion regardless of the amount of carbon film.