Improving the Corrosion Resistance of Tin-bronze by Surface Modification

Authors

Mahmoud Abbas, Rehab M. El-Maghraby, Esraa Hassan
Faculty of Petroleum and Mining Engineering, Suez University, Suez, Egypt.
Reda F. M. Elshaarawy
2Faculty of Science, Suez University, 43533 Suez, Egypt.

Abstract

Bronze alloys are made of copper-based materials with another metal, usually tin. Many surface modification techniques such as chemical etching, oxidation, electro deposition and sol-gel could be employed to improve surface properties. The organic compound that was used in this study was extracted from chili peppers. FT-IR (Fourier-transform infrared) spectroscopy and UV (Ultraviolet) spectroscopy investigations were applied on the extracted compound and results showed that this compound is mainly capsaicin [N-(4-hydroxy-3-methoxybenzyl)-8-methylnon-trans-6-enamide) (HMMTE)]. Electrochemical deposition was employed under cell voltage equal to 30 volts in a two-electrodes cell where bronze was the anode and stainless steel was the cathode in a solution of 10 ml/L (HMMTE)/distilled-water. Modification of tin-bronze for 1 hr. in 10 ml/L HMMTE/ distilled water solution increased the contact angle from 48° to 132˚. Attension Biolin device (Model: Theta Optical Tensiometers) was used to measure the contact angle at ambient temperature. Electrochemical measurements revealed that a significant improvement in corrosion resistance of tin-bronze in 3.5% NaCl had been achieved. The corrosion rate of tin-bronze decreased from 10.22 mpy to 1.39 mpy. Surface morphology of the samples was investigated with scanning electron microscopy (SEN) and energy-dispersive X-ray (EDX). X-ray diffraction was employed to determined present phases. Surface investigations results confirmed that a layer of red cuprous oxide (Cu2O) was formed on the surface layer after modification which led to the improvement in corrosion resistance. Salt spray test was carried out using Alpha+ Salt Spray Testing Equipment for 13 days on the base and surface modified samples according to ASTM B117. A green layer from [CuCl2 and Cu46Cl24(OH)68-(H2O)4] was observed on the nonmodified specimen (could be patina and bronze disease) while the red layer [Cu2O] is still observed on the modified specimen. Adhesion test (using X-Cut Tape Adhesion test according to ASTM D3359) was also investigated.