Corrosion inhibition and scale inhibition mechanisms of zinc gluconate and nitrilotri(methylphosphonic acid)

With increasing the circulation time of cooling water, the concentrations of ions (such as Cl − , Ca 2+ , Mg 2+ , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">SO</mml:mi> </mml:mrow> <mml:mn>4</mml:mn> <mml:mrow> <mml:mn>2</mml:mn> <mml:mstyle displaystyle="false" scriptlevel="0"> <mml:mtext>-</mml:mtext> </mml:mstyle> </mml:mrow> </mml:msubsup> </mml:math> ) gradually rise, causing the formation of scales and the corrosion of pipelines. They seriously affect the safety and treatment quality of industrial water circulation systems. Therefore, developing protective measures for carbon steel corrosion and scaling in circulating cooling water systems is of great practical significance. In this paper, a high-efficiency corrosion and scale inhibitor composed of zinc gluconate (ZG) and nitrilotri(methylphosphonic acid) (ATMP) was developed in simulated circulating cooling water. Eight groups of experiments were designed through orthogonal array design to screen the optimal compound ratio. The corrosion inhibition mechanism was studied using electrochemical methods and surface characterizations, and the scale inhibition performance was evaluated by static methods, surface analysis and molecular dynamics simulations. The results indicated that ZG200-ATMP10 exhibited the optimal corrosion inhibition efficiency (98.92%), and ZG200-ATMP8 exhibited the best scale inhibition efficiency (97.62%). ZG-ATMP primarily prevented metal corrosion by forming a Zn-ATMP chelate, which co-deposited with Zn(OH) 2 on the metal surface to create a protective film, achieving the corrosion inhibition effect, and mainly inhibited the formation of calcite (110) surface by chelating Ca 2+ , achieving the scale inhibition effect.