While airplane noise may not have any long-term effect on a person’s hearing abilities, many find the experience unpleasant. And the reason some of us have to suffer through this is because planes are built to be light.
The ceilings and floors of airplanes use a honeycomb structure, which provides strength without adding much weight. Sadly, this structure is also very effective in letting sound through. So all the unwelcome sounds of jet engines and rotor blades get plugged right in to your ears.
There may now be a solution. Find out on Quartz, published April 28, 2015.
Materials shape human progress – think stone age or bronze age. The 21st century has been referred to as the molecular age, a time when scientists are beginning to manipulate materials at the atomic level to create new substances with astounding properties.
Taking a step in that direction, Jens Bauer at the Karlsruhe Institute of Technology (KIT) and his colleagues have developed a bone-like material that is less dense than water, but as strong as some forms of steel. “This is the first experimental proof that such materials can exist,” Bauer said.
Material world
Since the Industrial Revolution our demand for new materials has outstripped supply. We want these materials to do many different things, from improving the speed of computers to withstanding the heat when entering Mars’ atmosphere. However, a key feature of most new materials still remains in their strength and stiffness – that is, how much load can they carry without bending or buckling.
All known materials can be represented quite neatly in one chart (where each line means the strength or density of the material goes up ten times):
Jens Bauer/PNAS
The line in the middle at 1000kg/m3 is the density of water – all materials to its left are lighter than water and those on the right are heavier. Few fully dense solid materials are lighter than water. Those that are tend to be porous, like wood or bone, and they exhibit exquisite structures when observed under a microscope, and they served as inspiration for Bauer’s work.
For many years, material scientists have thought that some empty areas on the compressive strength-density chart should be filled by materials that theory predicts. Computer simulations could be used to indicate an optimum microstructure that would give a material the right properties. However, nobody had tools to build materials with defined patterns at the scale of a human hair.
With recent developments in lasers and 3D printing, however, a German company called Nanoscribe started offering lasers that could do just what Bauer wanted. Nanoscribe’s system involves the use of a polymer that reacts when exposed to light and a laser that can be neatly focused on a tiny spot with the help of lenses.
A drop of a honey-like polymer is placed on a glass slide and the laser is turned on. A computer-aided design is fed into the system and the slide carefully moves such that the laser’s stationary focus touches only those points where the material is to be made solid. Once complete, the extra liquid is washed away, leaving behind materials with intricate internal structures.
However, these materials on their own are not as strong as Bauer wanted. So he coats them with a thin layer of alumina (aluminium oxide) before subjecting them to stress tests. Based on the tests, he was able to improve the theoretical models he used to design the internal structure of the materials. Their results were just published in the Proceedings of the National Academy of Sciences.
Even though alumina layers increase the density of these materials, all of them remain lighter than water. Bauer’s strongest material has a specific honeycomb internal structure and is coated with a 50 nanometre-thick (billionth of a metre) layer of alumina. It beats all natural and man-made materials that are lighter than 1000kg/m3, being able to withstand a load of 280MPa (mega pascals is a unit of measuring pressure), which makes it as strong as some forms of steel.
There are limitations. Nanoscribe’s system can only make objects that are tens of micrometres in size. “One of their newer machines can make materials in the milimetre-range, but that’s about it for now”, Bauer added. But that is not enough for any real-life application.
However, there have been rapid improvements in all the areas this work relies on: 3D printing, new polymers and laser technology. That means we may soon have a suite of new, super lightweight materials for everything from skis to aircraft parts. If nothing else, Bauer’s work shows that we are definitely in the molecular age.
Strong materials like ceramic are brittle while ductile materials like metals are weak. Researchers at the California Institute of Technology have developed a material that has ceramic-like strength and metal-like ductility. They have achieved this feat through the use of zirconium based metallic glasses and nano-sized pillared structure.
Metallic glass is by no means a new concept, it was first reported in 1960 and has since attracted a lot of attention owing to their superior mechanical properties like high strength and large elastic strain. Amorphous metal, more commonly known as metallic glass, are non-crystalline metallic materials. They are generally produced by rapid cooling of an alloy that has three or more components in it. These alloys achieve their advantages by using atoms of significantly different sizes which results in low free volume, thus higher viscosity. Although they are have poorer electrical and thermal conductivity than metals, the non-crystalline structure avoids crystal defects like grain boundaries and dislocations thus increasing resistance to erosion and corrosion.
Scanning Electron Microscope image of a typical nanopillar
Jang and Greer fabricated nano-sized pillars (see image) from a bulk metallic glass (Zr35Ti30Co6Be29) using an ion beam to etch the material into its final form. They were able to achieve superior strength of 2.25 GPa (which is equivalent to an elephant standing on 1 sq.cm of that material) and plastic deformability of ~25% by reducing the size to ~500 nm diameter nano pillared structure. At a size reduction to 100 nm, the strength remained same and plasticity was homogeneous. Such high strength has never been reported without sacrificing on the ductility of the material.
With such strength and resistance to erosion, these materials can find application in nanoimprint lithography making nanomolds which are currently silicon-based, expensive and get very easily damaged. Amorphous materials have previously also found use as biomaterials typically as implants in bones. It is possible to control their rate of dissolution by varying the contents of the alloy and thus become implants which eventually get replaced by bone tissue.
Jang, D., & Greer, J. (2010). Transition from a strong-yet-brittle to a stronger-and-ductile state by size reduction of metallic glasses Nature Materials DOI: 10.1038/nmat2622
Akshat Rathi 