Anticorrosion properties of three quinoxaline derivatives on mild steel in 1.0 M H_3PO_4 solution

The effect of 3-methylquinoxalin-2(1H)-one (MQO), 3.7-dimethylquinoxalin-2(1H)- one (DMQO) and 3,7-methylquinoxaline-2(1H)-thione (DMQS) on mild steel corrosion in 1.0 M H_3PO_4 has been studied by electrochemical measurements. The results indicated that these compounds act as good inhibitors. The DMQO and DMQS act as a cahodic inhibitors while the MQO acts as a mixed type inhibitors. So, it is found that their inhibition depend on the methyl number in their structure. It is shown also that theDMQO is the best inhibitor where its inhibition efficiency increases with concentration to achieve 92 % at 10^-4 M. A pseudo plate was observed directly from the corrosion potential in the presence of DMQO and DMQS. In addition, the adsorption of DMQO molecules on mild steel surface was also studied and it was found that is adsorbed according to the Langmuir isotherm model. In addition, the temperature influence and immersion time on performance of the best inhibitor (DMQO) was studied. It is establish that its inhibition efficiency increases with immersion time and take its performance at hot temperature.