Preliminary Study of Melastoma Malabathricum L. leaf Extract as Green Corrosion Inhibitor in the Car Radiator Coolant

Corrosion has been a major issue in automotive industry. Overheating has been considered the one of the major issues. Overheating is overcome with the cooling system in car radiator. When overheating keeps occurring, formation of corrosion happens. Therefore, car radiator coolant contains synthetic corrosion inhibitor to control the corrosion. Synthetic corrosion inhibitors have negatively impacted the environment through emission of toxic gas.
Researchers are heading towards natural based corrosion inhibitors to solve the environmental issues caused by synthetic corrosion inhibitors. It was found that tannin is a bioactive compound that can be used as natural corrosion inhibitor to replace synthetic corrosion inhibitor. The objectives of this final year project are to extract tannin from Melastoma Malabathricum L. leaf using the solvent extraction method and to evaluate the corrosion efficiency of tannin extract in car radiator coolant using weight loss measurement (WLM) method. The characterisation of powder Melastoma Malabathricum L. leaf was conducted using XRD, and FTIR. XRD results showed the sample is amorphous and FTIR results showed functional groups of alcohols, alkene, alkyne, hydroxyl, methyl, and oxygen ether. WLM was conducted using 4 mediums (HC1, NaOH, deionised water and car radiator coolant) and aluminium substrate from car radiator. The characterisation of aluminium substrate was conducted using XRF. The XRF results revealed the aluminium substrate used is from 2xxx series. WLM consisted of 3 measurements (weight loss, corrosion rate and inhibition efficiency). The results of weight loss and corrosion rate revealed that aluminium substrate in deionised water showed the least weight loss and had the lowest corrosion rate. As for the inhibition efficiency, aluminium substrate immersed in NaOH had the most consistent results.
Optical microscope (OM) was used to observe the microstructure of corroded samples in alkaline mediums. Alkaline mediums were proven to be efficient for corrosion inhibitor study.
Keywords: Corrosion inhibitors, Melastoma Malabathricum L leaf, Tannin