Surface engineering: what's new?

Materials World magazine
,
2 Apr 2014

As one of the most diverse areas of research, there is always something new in surface engineering. Rachel Lawler takes a look at some of the latest developments from across the field.

Smoothing bug splats
Insects hitting car windscreens and motorcycle helmets are disruptive enough, but when they get in the way of aeroplane wings during take off or landing, the smooth flow of air is disrupted, increasing drag and upping fuel consumption. Researchers working at NASA’s Langley Research Centre in the USA have been testing coatings that could help reduce the problem. The team is testing eight different coatings for effectiveness at reducing bug splatter. Not only must the material be able to withstand weather and pressure conditions, but it must also be resistant to the unique chemistry of a bug splat. The researchers are working on their knowledge of insect biology as well as the interaction of the materials with the splats and the conditions on an aeroplane wing. Superhydrophobic materials may work to wick away water and dirt, but insect adhesion varies on different coatings. Team member Mia Siochi admitted that the coatings would have to save enough fuel to justify the cost of application.

Beating smartphone germs
As we become increasingly dependent on our smartphones, the devices are rarely kept beyond the reach of our fingertips. This means that the surfaces of our smartphones can become a thriving source of potentially harmful bacteria. Engineers working at glass and ceramics manufacturers Corning Inc in the USA have found a solution to this problem with the antibacterial Gorilla Glass. The glass is formed with ionic silver, which naturally inhibits the growth of bacteria and works effectively throughout the device’s lifetime. The material is currently undergoing tests with several smartphone manufacturers.

Stealth wins the race
A coating for submarines, designed to help them avoid detection, has been awarded the 2013 Minister’s Award for Achievement in Defence Science in Australia. The rubber coating has been applied to periscopes on the Royal Australian Navy’s Collins-class submarines and reduces their visibility on modern radar systems. Unlike currently used alternatives, it does not rust or deteriorate. Designed by Dr Andrew Amiet at the Defence Science and Technology Organisation of Australia, the material can withstand pressure and salt exposure without peeling and does not require hydrofluoric acid treatment to affix it to the periscope.

Casting moulds
Continuous casting moulds have traditionally been coated with silver-alloyed copper or chromium–zirconium alloyed copper, but today’s models are usually coated using an electroplating process. After use, the plates can become worn and cracks can appear. Milling usually repairs the defects, but can cause the plates to thin. In response firms, including Germany-based company, Evertz, have been working on alternatives. A new electroplating technique compensates for the thinning with extra wall thickness, significantly extending the life of the plates and reducing costs.

Corrosion reduction
An alternative to conventional paints for cargo ships, trains and industrial equipment has been developed by USA-based firm Nanovere Technologies. Nano-Clear is designed to improve the corrosion resistance of surfaces by penetrating the gaps between paint molecules, enhancing its colour, increasing surface hardness and improving the material’s UV resistance. Once dried, this coating will protect the surface and reduce the need for cleaning by 50%. The coating is made using 3D nanostructured polymers that do not break down under UV light, chemical attack or abrasion.

Nanotube coating beats flames
Researchers working at the US National Institute of Standards and Technology have developed a nanotubebased coating that can reduce the flammability of foams commonly used in upholstery. Each year around 6,700 home fires in the USA are thought to be caused by upholstered furniture igniting, according to figures by the National Fire Protection Association. Using a technique that squeezes carbon nanotubes between two polymers and stacks these formations in layers, the researchers created a coating more effective than the brominated flame retardants usually used. The coating reduces flammability by 35% compared to untreated foam and prevents melting and pooling in the foam, which is thought to spread flames.

Smooth sailing
Scientists working at the University of California in the USA may have uncovered evidence that smooth surfaces are not always best for gliding through water. After experimenting with more than 40 coatings for ships, the team found that surfaces covered with tiny ridges offered the optimal shape for smooth sailing. The rough surface reduced drag created by the friction of flowing water and was better able to withstand choppy conditions. The team also experimented with superhydrophobic materials, which repel water by creating a tiny cushion of air around the ship’s hull.