Improved corrosion resistance of carbon steel in soft water with dendritic-polymer corrosion inhibitors

Dendritic polymers with an isothiourea terminal group, carboxyl lateral group, and pentitol core dendrimers with 0 and 1 generations (ITCP-0G and ITCP-1G) were developed as novel phosphorus-free corrosion inhibitors for carbon steel in soft water. The results of weight loss, Tafel polarization, and electrochemical impedance spectroscopy analyses showed that the corrosion inhibition performance of ITCP-0G and ITCP-1G of carbon steel in soft water was much higher than that of the previously reported corrosion inhibitors, whereas the performance of ITCP-1G is superior to that of ITCP-0G. An ITCP-1G concentration of 15 mg⋅L−1 achieved a corrosion inhibition efficiency of 97.62 %, which is higher than the value of 75.19 % achieved by ITCP-0G. The Langmuir adsorption isotherm model indicated spontaneous adsorption of ITCP-1G on the carbon steel surface. Comprehensive surface analysis indicated that S and N in the terminal isothiourea of ITCP molecules bind with iron to form a protective film on the steel surface. Increasing the number of terminal isothiourea groups in the dendrimers results in a stronger binding force with Fe ions, and a stronger protective film is formed on the steel surface. Additionally, larger dendrimer molecules provide better surface coverage of the protective film on the steel surface and better corrosion inhibition performance. Therefore, ITCP-1G had a stronger ability to prevent the anodic corrosion of iron from carbon steel than ITCP-0G. This work will provide new insights into the corrosion inhibition mechanism of corrosion inhibitors in soft water as well as the development of new types of water-softening corrosion inhibitors.