Materials Science - Blog Posts

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Scientists Observe New Exotic Phenomena in Photonic Crystals

Topological effects, such as those found in crystals whose surfaces conduct electricity while their bulk does not, have been an exciting topic of physics research in recent years and were the subject of the 2016 Nobel Prize in physics. Now, a team of researchers at MIT and elsewhere has found novel topological phenomena in a different class of systems — open systems, where energy or material can enter or be emitted, as opposed to closed systems with no such exchange with the outside.

This could open up some new realms of basic physics research, the team says, and might ultimately lead to new kinds of lasers and other technologies.

The results are being reported this week in the journal Science, in a paper by recent MIT graduate Hengyun “Harry” Zhou, MIT visiting scholar Chao Peng (a professor at Peking University), MIT graduate student Yoseob Yoon, recent MIT graduates Bo Zhen and Chia Wei Hsu, MIT Professor Marin Soljačić, the Francis Wright Davis Professor of Physics John Joannopoulos, the Haslam and Dewey Professor of Chemistry Keith Nelson, and the Lawrence C. and Sarah W. Biedenharn Career Development Assistant Professor Liang Fu.

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Biomimicry

Brittle starfish shows how to make tough ceramics

Nature inspires innovation. An international team lead by researchers at Technion – Israel Institute of Technology, together with ESRF -the European Synchrotron, Grenoble, France- scientists, have discovered how a brittle star can create material like tempered glass underwater. The findings are published in Science and may open new bio-inspired routes for toughening brittle ceramics in various applications that span from optical lenses to automotive turbochargers and even biomaterial implants.

A beautiful, brainless brittle star that lives in coral reefs has the clue to super tough glass. Hundreds of focal lenses are located on the arms of this creature, which is an echinoderm called Ophiocoma wendtii. These lenses, made of chalk, are powerful and accurate, and the deciphering of their crystalline and nanoscale structure has occupied Boaz Pokroy and his team, from the Technion-Israel Institute of Technology, for the past three years. Thanks to research done on three ESRF beamlines, ID22, ID13 and ID16B, among other laboratories, they have figured out the unique protective mechanism of highly resistant lenses.

As an example, take tempered glass. It is produced by exerting compressive pressure on the glass which compresses it and leaves it more compact than in its natural state. Glass tempering is performed by rapidly heating and then rapidly cooling the material. In this process, the outside of the material cools more quickly than the inside and thereby compresses the inside. Ophiocoma wendtiilenses are created in the open sea, at room temperature, unlike tempered glass. “We have discovered a strategy for making brittle material much more durable under natural conditions. It is ‘crystal engineering’ and tempering without heating and quenching – a process that could be very useful in materials engineering,” explains Pokroy.

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Dissecting Iron Man Suit - An Engineering Analysis

Structural, energy, and thermal analysis of Iron Man Suits specifically Mark I to Mark XLVI which have the following capabilities in common: external armor, supersonic flight, hovering, weaponry, and decoy flares.

1. STRUCTURAL ANALYSIS 

Wear Resistant and Shock Absorbent Exoskeleton  The physical protective value of exoskeleton is its ability to resist any penetrative loads as well as any shock loads. However, the whole thickness of exoskeleton panels should not be too hard because it will pass on the external impact load into the suit’s internal hardware, or even the human body inside it. All of this can be achieved by combining more than one materials; a hard material on the outside and the soft material on the inside

Hard Outer Layer for Penetrative Loads The materials needed for the exoskeleton’s outer layer should be hard and tactile. Titanium Alloy would be an ideal choice. Fiber glass has good tensile strength but not good shear strength, while titanium has both .Titanium Alloy is not only much stronger, but is also lighter than steel, which will provide more fluidity of movement compared to any heavy material counterparts.

Ductile Inner Layer for Shock Loads There should be a soft inner linings behind titanium panels to serve as shock absorbent. Sorbothane is a material that is extremely soft and has the ability to convert shock loads into heat transfer at a molecular level. It is a proprietary, visco-elastic polymer. Visco-elastic means that a material exhibits properties of both liquids (viscous solutions) and solids (elastic materials).

Sorbothane is a thermoset, polyether-based, polyurethane material. Sorbothane combines shock absorption, good memory, vibration isolation and vibration damping characteristics. In addition, Sorbothane is a very effective acoustic damper and absorber. Even if one drops an egg from the top of a building into a bed of sorbothane, this remarkable material is soft enough to cushion the impact and would not allow the egg to break.

This technique of having a hard material on the outside and the soft material on the inside is not new. It has been used for centuries in Japan for making samurai swords. The hardness of its outer layer give the swords its cutting edge and penetrative power, and its ductility allows it to absorb shock loads when it strikes or struck. 

2. ENERGY ANALYSIS : Hovering Capability

Hovering using thrusters (aka repulsors) requires tremendous amount of energy, particularly when the suit is used for a long duration. Energy usage for hovering is dependent upon the hovering methods

Magnetic Levitation requires no energy at all, but is limited to the presence of magnetic field.

Ducted and Open Propellers (helicopter blades). Several human powered helicopters have been made overtime that have achieved flight. It has been experimentally recorded that a 78 kg person in a 58 kg copter requires only 1.1 kW to climb using helicopter blades, and only 60 Watts to maintain altitude.

Jet Thrust is the least energy-efficient method. Because thrust-to-weight ratio needs to be greater than 1 to achieve lift-off, a Jet-pack requires over 1KN of thrust force, depending on the weight of the jet and the person. If wings are attached to the jet-pack, horizontal flight can be achieved with thrust to weight ratio lower than 1, thus improving the duration of the flight and its range.There have been jet-packs made in the past, most iconic display of it was in 1994 Olympics opening ceremony. The fuel used in the jet-pack was mostly hydrogen peroxide. It provides thrust at low temperature compared to other fuels. However, it has low energy density of 810 Wh/kg, giving the jet-packs up to only 30 seconds of flight-time. Jet’s flight time is limited even by using energy-rich fossil fuel. Yves Rossy (aka Jet Man) has successfully used kerosene oil in his flight, but the thruster jets have to be pushed away from the body for safety. His suit allows only several minutes of flight. In addition, if a heavier suit (greater than 25 kg) is used, hydraulics are needed, which would require additional energy and slow down mobility. The Iron Monger suit was an example of hydraulic-driven mobility suit.

3. POWER SOURCE

Tony Stark manages the suit’s energy requirements, including thermal management and artificial intelligence system, through the fictional arc reactor. The reactor is able to provides almost limitless clean energy despite being a very small device. In real life, the only thing that has an energy density comparable to the arc reactor, and would meet all the energy requirements of the suit would be nuclear power. Uranium (fission) energy density is 80.620.000 MJ/kg. However, nuclear power is not suitable to be harnessed in a manned suit, since it generates a tremendous amount of heat.

A more practical solution would be a battery energy-storage. If lithium batteries are used on propeller blades, minutes-long flight time can be achieved. Furthermore, these batteries can readily power suit’s electrical devices / electronics requirements. Lithium ion battery has energy density of 150 Wh/kg (0.5 MJ/kg). Fossil fuel, on the other hand, have a much higher energy density than batteries, but would require a clunky generator to power the suit’s electrical requirements.

Lithium sulfur batteries have 5 times more energy density compared to lithium ion batteries. Lithium sulfur packs had already powered the longest unmanned flight for more than 30 hours. Unless we discover something like an arc-reactor, lithium sulfur batteries could be just the thing to power up the suit. The downside is, it requires hours of charging for just minutes of usage.

There is an alternative option, though not a ‘reactor’ proper. A compact and high-output generator (standard car alternators crank out 50-70 amps at 12 volts for years, and some can go as high as 150 amps) could be spun by a small and strong output electric motor (all alternators have to do is spin). That motor can be powered by a high density battery like used for electric bikes in the 1500w to 2500w range at 20 something volts. This would power a strong and small motor at 3500 to 4000 rpm for hours. That’s more than enough to create power for a number of systems, if they’re built to take advantage of the amperage. And with new constructions of carbon arrays coming out every day, one or more of those could bring a meaningful electric output increase in an otherwise standard generator, even above what we have in cars now.

4. THERMAL MANAGEMENT 

The suit cannot be hermetically sealed. Human body heat evaporates water from the skin. Therefore, air ventilation is a must to remove them. It is also needed to maintain a good supply of oxygen. So, there must be a structure inside the exoskeleton that allows air flow. This would prevent any internal condensation to settle and will also remove buildup of body heat. The layer of sorbothene would act both as a thermal and an electrical insulator. This means that extreme external temperature would not be transferred to the inner layer. The suit would not get too hot or too cold from the outer environment. There should be small fans to draw and pull air from the ambient in controlled amount, and should be able to exchange hot air. With the technology available today, the thermal management of the suit is easily manageable. There are also solid state devices such as thermal pads and thermoelectric generators. Thermoelectric generators can surfaces hot or cold depending on the polarity of the electric current and thus can be an integral component of the suit for controlling the internal temperature.

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What is Liquid Penetrant Testing?

Liquid penetrant testing (LT) is a non-destructive testing technique utilized to detect defects or discontinuities (such as cracks) on the surface of any type of non-porous material such as metal, plastics or ceramics. Liquid penetrant testing (also known as dye penetrant testing or penetrant testing) is primarily utilized in the industrial sector to test metal materials such as oil & gas pipelines and various metal machinery components to prevent failures or accidents. Some of the many defects that can be detected using this process include fatigue cracks, hairline cracks and porosity. A number of industries utilize liquid penetrant testing, including petrochemical, aerospace, engineering, automotive and many more.

Although liquid penetrant testing is the least technologically advanced method of non-destructive testing (with the others being ultrasonic testing, magnetic particle testing and radiography) – it is still widely used. That’s because liquid penetrant testing has the advantages of being low in cost, versatile and easy to perform. In fact, liquid penetrant testing requires very little training when compared to the other three main forms of non-destructive testing.

So exactly how does liquid penetrant testing work? The material to be tested must first be cleaned – usually using a simple spray cleaner that can be easily wiped off with a cloth or rag. A liquid penetrant solution is then applied to the surface of the material being tested using a simple aerosol spray from a can. The liquid is then left to soak for a predetermined length of time – and will eventually seep into or be drawn into any cracks or defects within the material being tested. After the appropriate amount of “soak time” has passed, the technician wipes the liquid penetrant off of the test object. A developer is then applied to the entire area being tested. The developer is usually a dry white powder such as chalk that is suspended in liquid and sprayed on in aerosol form. The developer then acts to draw out any liquid that may have seeped into a defect – giving a highly visible, colored indication on the surface of the test object.

Liquid penetrant testing relies solely on visual inspection – making the color contrast between the object being tested and the colored indication that reveals defects of utmost importance. For this reason, many technicians utilize fluorescents. This process is the same as conventional liquid penetrant testing, with the exception that a fluorescent penetrant is utilized and then the test object is viewed under ultraviolet light in a darkened environment. The result is that any defects present will glow brightly under the UV light – making visual inspection much easier.

Aside from the obvious advantages of being inexpensive and easy to use, liquid penetrant testing is also popular because of its versatility. In most cases, nothing more than three aerosol cans – cleaner, penetrant and developer – and a few cloths or rags are needed. This allows technicians to easily maneuver into tight spaces such as boilers or high places where ladders are required – easily completing testing in locations where other non-destructive testing techniques are difficult or impossible. For these reasons, liquid penetrant testing continues to be a viable and popular non-destructive testing method.

Tech Service Products is a stocking distributor of industrial supplies and non-destructive testing products such as liquid penetrant testing products.

How platinum powers the world

Platinum bars. Image: Sprott Money@Flickr 

Platinum is one of the most valuable metals in the world. Precious and pretty, it’s probably best known for jewelry – and that is almost certainly its oldest use. But its value has become far greater than its decorative ability; today, platinum powers the world. From agriculture to the oil markets, energy to healthcare, we use platinum far more than we realise.

1. Keep the car running

Platinum is needed to make fuel for transport. Image: Pixabay

Platinum catalysts are crucial in the process that converts naphtha into petrol, diesel, and jet-engine fuel, which are all vital to the global economy. The emissions from those petroleum fuels, however, can be toxic, and platinum is also crucial in the worldwide push to reduce them through automotive catalytic converters. In fact, 2% of global platinum use in 2016 was in converting petroleum and 41% went into reducing emissions – a circle of platinum use that’s more impressive than a ring.

2. Feed the world

Nitric acid is a by-product of platinum which is used in fertilisers. Image: Pixabay

Another vital global sector that makes use of platinum catalysts is agriculture. Without synthetic fertilisers, we would not be able to produce nearly as much food as we need. Nitric acid is essential for producing those fertilisers and platinum is essential for producing nitric acid. Since 90% of the gauzes required for nitric acid are platinum, we may need to use more of it as we try to meet the global food challenge.

3. Good for your health

A pacemaker. Image: Steven Fruitsmaak@Wikimedia Commons 

Platinum is extremely hard wearing, non-corrosive, and highly biocompatible, making it an excellent material to protect medical implants from acid corrosion in the human body. It is commonly used in pacemakers and stents. It is also used in chemotherapy, where platinum-based chemotherapeutic agents are used to treat up to 50% of cancer patients.

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NTU and JTC develop enhanced fire protection for steel

Credit: shutterstock/Anusorn Abthaisong

Scientists from Nanyang Technological University (NTU), Singapore, and national industrial developer JTC have unveiled what they are calling a 3-in-1 coating for better fire and corrosion protection.

‘In a fire, our coating forms a compact charred layer that acts as a protective barrier against the heat,’ explained Aravind Dasari, a Principal Investigator at the NTU–JTC Industrial Infrastructure Innovation Centre.

Called FiroShield, the coating functions like regular paint and is easy to apply, according to the research team. It can be applied on bare steel without the need for sand blasting, and provides protection against fire for two hours. 

Dasari explained, ‘While typical fire coatings will also form a charred layer, those are thick and foam-like, which can fall off easily and leave the steel exposed to the fire. What we aimed at was an innovative coat that works differently from conventional intumescent coatings and can stick to the steel surface for as long as possible under high temperatures, and yet has durability and weather resistance under normal conditions without a need for a top coat of paint.’

To find out more see the January issue of Materials World or visit  bit.ly/2nft8Z3