A B
C
Figure 2 - Calcium phosphate stabilisation with incorporation of hydrophobic monomers A , B & C & without hydrophobic monomers
three main changes occurred in the industry :
• Cooling water circulating water pH ranges increased to mitigate mild steel corrosion
• Alternative corrosion inhibitors for mild steel were required
• New polymer functionalities were needed to stabilise the corrosion inhibitors and control additional mineral scale
Phosphates & zinc
The list of effective alternatives to Cr 6 + is quite short . Here we will focus on phosphorus ( e . g . orthophosphate , polyphosphates and phosphonates ) and zinc chemistry .
The former has become the dominant approach in most industrial cooling systems . Where allowed , phosphorus chemistry has been paired with zinc to deliver highly successful results . Inorganic phosphates , polyphosphates and zinc are extremely low-cost , have defined and proven mechanisms of action , and are highly efficacious as mild-steel inhibitors under neutral to alkaline conditions .
However , cooling water systems that had been operating at pH ranges
58 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981