Quantum Chemical Calculations and Experimental Studies of using Azo Dye as Corrosion Inhibitors for on Carbon Steel in Acidic Medium Hadi Thamer Obaid, Mouayed Yousif Kadhum and Adnan Sultan Abdulnabi Department of Chemistry, College of Education for Pure Sciences, Basrah University, Basrah, Iraq KEY WORDS Corrosion Azo dye Carbon steel Hydrogen evolved Potentiodynamic polarization DFT Abstract: The corrosion of carbon steel in 1 M HCl solution was signi cantly inhibited by azo dye (E)-2-hydroxy-3-((2-hydroxy-4- methylphenyl)diazenyl)-1-naphthaldehyde, (R1H) using both the Potentiodynamic polarization and hydrogen evolution methods, Scanning Electron Microscopy (SEM). The results showed that inhibition efficiency increases with the increasing concentration. The studied R1H showed maximum inhibition efficiency of (83 % by Hydrogen evolution method and 87% by Potentiodynamic method) at 1×10 -3 M concentration and temperature of 298 K. Polarization results showed that the investigated RSH acts as mixed type inhibitor. Adsorption of the R1H on carbon steel surface obeys the Langmuir adsorption isotherms. The Potentiodynamic polarization and hydrogen evolution methods results were well supported by SEM analyses. Quantum chemical parameters are calculated using the Density Functional Theory (DFT) method correlation between theoretical and experimental results is discussed. Corresponding Author: Adnan Sultan Abdulnabi Department of Chemistry, College of Education for Pure Sciences, Basrah University, Basrah, Iraq INTRODUCTION The corrosion of the metal compounds and alloys as well as the deterioration of its characteristics is a major industrial problem. It is considered a worrying source of pollution for the environment, especially, in carbon steel industry, where acids are being used to pickling, descaling and cleaning. Therefore, scientists are encouraged to look for solutions to protect these materials and reduce their environmental impact [1-7] . The most cost- effective method of metallic protection in such media is the use of corrosion inhibitors [3] . He inhibitor is a compound utilized to prevent corrosion by altering the chemistry of an aggressive solution. Utilized inhibitors are the best one of the greatest tests to protect corrosion specifically in a system containing acid [8, 9] . Organic compounds commonly serve as inhibitors and inhibit metal from corrosion by a protective layer formed on the metal surface due to their active centers, especially atoms (N, S and O) and double/triple bonds which concerning their interaction with the metal surface [10-14] . The azo derivatives inhibit the carbon steel corrosion due to the presence of –N = N–group which enhances their adsorption ability on the metal-solution interface [15] . The planarity of π-electrons 1 ACE Journal of Advance Research in Chemical Sciences |ISSN: 2520-3703 |Volume 2 |Number 1 |Page No. 1-9 |2022