Indian scientists have developed an environment-friendly process for improving the anti-corrosive property of high-strength aerospace aluminium alloys.

Aluminium alloys are used in aerospace, automobile, and marine applications due to their low density and high specific strength (strength-to-weight ratio). Among various aluminium alloys, heat treatable wrought alloy compositions possess high mechanical strength and are commonly preferred by the aerospace industry. The aerospace components made of these aluminium alloys, including landing gear, wing spar, fuselage, skins, pressure cabins, and so on, are expected to possess high fatigue life and corrosion resistance.

Scientists at the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, found that the wear and corrosion resistance of aluminium alloys is significantly enhanced by depositing harder alumina coating through anodic-oxidation-based processes — anodising, hard anodising, and micro-arc oxidation (MAO).

While the MAO process employs a dilute concentration of alkaline electrolyte, wherein there is no emission of toxic fumes, the disposal of the spent electrolyte does not attract any environmental regulations. Therefore, MAO is regarded as an eco-friendly process. “The alumina coatings deposited through the MAO technique possess high hardness (1,000-1,900 HV), excellent wear, and corrosion resistance as compared to identically thick hard-anodised (HA) coatings (300-500 HV),” says a press release from ARCI.

The technology involves bombardment of a component surface with spherical balls of a few hundred micrometres size, travelling at a specific kinetic energy. This happens before the MAO coating (SP+MAO) depositions and leads to a ten-fold enhancement in the fatigue life of aluminium alloys without affecting the wear and corrosion resistance of the coating.

The presence of beneficial compressive residual stresses beneath the substrate-coating interface delays the crack propagation and results in superior fatigue life, which can be useful for light-weighting of aerospace structures.

Antimicrobial silver nanomaterial

Researchers from the Indian Institute of Science Education and Research (IISER), Bhopal, have developed a procedure to produce silver nanomaterials that can be used as antimicrobial agents.

Antibiotic resistance is a serious condition in which bacteria and other microbes that invade the human body become resistant to the antibiotics and/or antimicrobials that are meant to kill them. The World Health Organization (WHO) has declared bacterial antibiotic resistance one of the most important crises facing human health today, notwithstanding Covid. This problem is serious for India, the ‘antimicrobial resistance capital of the world’ due to rampant and indiscriminate use of antibiotics in humans, livestock, and agriculture. There is thus a dire need for antibiotic substitutes and the nanotechnological solutions, such as those studied by the IISER Bhopal team, are promising.

The researchers treated silver nitrate, the main component of the ‘election ink’ used to stain nails after voting in India, with tyrosine in the presence of caustic soda. Tyrosine functioned as a reducing agent and capping agent to produce silver nanomaterials. On examining the product under high-resolution microscopes (TEM and SEM), they found two forms of silver nanostructures — nanoclusters and nanoparticles. The nanoparticles were found to kill microbes such as S. cerevisiae (associated with pneumonia, peritonitis, UTI and so on), C. albicans (oral and genital infections), and E. coli and B. cereus (stomach infection) in about four hours.

The researchers found that the nanoparticles generate “singlet oxygen species” that elevate the cellular stress and, consequently, break open and/or disrupt the cell membrane of the microbes and cause leakage of proteins from the cells, thereby killing them.