EXTRACTOS LÍQUIDOS NATURALES DE MORINDA CITRIFOLIA Y ALOE-VERA COMO POSIBLES INHIBIDORES DE LA CORROSIÓN EN ACEROS INDUSTRIALES

Abstract

It is well known that metallic materials could be corroded during their service due to their exposed environment, which is considered as one of the main problems in the manufacture industry that has been occurred in the last century. Corrosion can cause from loss of human lives until spill of economic, in addition to failure in electrical power plants, serious disasters on bridges, collapsing concrete buildings, immediate deterioration of ships, leaking pipelines, mechanical damage failure, surface alteration properties, another sever damages in infrastructure, in addition to this damage, corrosion also causes irreversible impact on the environment as air or soil pollution and global warming. In order to reduce the damage caused by corrosion mechanism, different kind of methods, procedures and/or treatments have been developed, among which the use of corrosion inhibitors (IC), where a classification as organic inhibitor has been existed, this creates a stack of molecules to form multi-layer between the metal material and the corrosive media. Therefore, in this research the efficiency of inhibition (EI) of two biodegradable natural liquid-extracts is evaluated in an aqueous solution of hydrochloric acid (HCl) 1 Molar, also IC molecules are considered as a new alternative capable of inhibiting the chemical deterioration of any metallic material and consequently minimize the corrosion problems above describe. The liquid inhibitors studied here were; extracts from Morinda Citrifolia leaves (ethanol extracted) and GEL (aqueous extracted) leaves of Aloe-Vera, commonly known as Sabila. These liquid-extracts were added at different volume ratios to acid (HCl-1M) media. Their performance as corrosion inhibitor is then monitored and evaluated by electrochemical techniques as polarization TAFEL (Ecorr vs. I) and spectroscopy Impedance electrochemical (EIS, Zreal vs. Zimag). From EIS parameters, the EIS data were analyzed by a correlation with an appropriate equivalent electric circuit (EEC) and the TAFEL data were used to determined EI%, whereas the thermodynamic analysis by using the adsorption isotherms the type of inhibitor was classified as mixed. Additionally, Optical Microscopy images were obtained before and after undergoing industrial steels in contact with the corrosive solution without extracts from the leaves of Morinda Citrifolia and Aloe-Vera that serve as inhibitors. On the other hand, properties such as contact angle, viscosity and surface tension of the natural organic molecules were obtained in order to determine the wettability and the mechanism of adsorption of organic molecules (natural liquid extracts) with the surface of the steels exposed to corrosive environment. According to the EIS results of industrial steels (AISI 1045, 4140 and 8620) studied here, they had pitting corrosion after hours exposure in HCl-1M. Meanwhile, the use of GEL extracted from Aloe-Vera (Aloe) demonstrated to be corrosion inhibitor efficiencies, EI~ 75% at 10 ml to 1045 steel, 4140 steel EI~ 70% at 16 ml and 8620 for steel EI~ 30% from 2ml. Meanwhile the ethanol extract of Morinda Citrifolia proved to be an excellent inhibitor capable to minimize the pitting corrosion process from 4 or 6 mL of its volume concentration (steel 1045, EI> 93.1%, steel 4140 and 8620 EI> 92.9%). This difference in inhibition efficiency relates to the contact angle and the surface tension of the drop of Morinda Citrifolia or Aloe-Vera, in which the contact angle results greater and better adsorption to extracted of Morinda Citrifolia.