TiO2- geopolymer based novel corrosion protective micro-coatings to emaciate mild steel oxidation in severe environments

Abstract

Now-a-days, cementitious geopolymer coatings are one of the most studied and adaptable coating systems to combat corrosion on low-carbon steel/structural steel. Due to its green and sustainable nature, it has enormous potential to partially replace traditional organic coatings in terms of corrosion resistant properties and economic aspects. Herein, corrosion protection and antibacterial efficiency of titanium oxide (micro-sized, 5/10/15%) containing sodium aluminosilicate (N-A-S-H) geopolymer coating for mild steel is reported to enhance the lifetime of structural steel. Developed coatings were characterized using XRD, FTIR and FESEM. Characterization results indicated the presence of titanium containing new inorganic phase (Sodium titanium oxide hydrate) along with sodium aluminium hydrate phases in XRD, supported by Ti-O stretching vibrations in FTIR along with Si-O-Al stretching vibrations. Microstructural studies using FESEM indicated the uniform distribution of TiO2 in NA-S-H gel matrix. Results revealed that developed coatings depicted corrosion protective characteristics and exhibited adhesion strength between 16.14 and 17.3 MPa. The scratch resistance test revealed that the coating could bear a point load of greater than 5 kg. Minimum percentage weight change and adhesion loss were observed for coating after immersion in NaCl/H2O for 119 days. An accelerated corrosion test (ASTM B117) was performed in the salt environment for 500 h and the best corrosion protective performance was observed for coating formulation containing 10 % TiO2 with maximum rust grading 5. Electrochemical studies showed better corrosion resistance performance for coating formulation containing 10 % TiO2 as compared to the other two formulations containing 5 and 15% TiO2. The antibacterial efficiency of coatings was evaluated by colony count assay (viability method) against the most commonly found gram-positive bacteria Staphylococcus aureus and one gram-negative bacteria Escherichia coli. All three TiO2-incorporated geopolymer coating formulations revealed a good bacterial reduction in percentage with the best performance observed for coating formulation containing 15% TiO2. The accelerated weathering test (ASTM G154-500 h) was performed to ensure the durability and stability of the developed formation. This study developed a novel, environment-friendly, and lucrative cementitious coating material which is potentially suitable for preventing early oxidation and bacterial fouling of mild steel structures.