Atomic Layers of Transition Metals Sandwiched to Create Stable Material

By Beth Ellison

Researchers at Drexel University have developed a new material-making method for creating an entirely new stable material for storing energy by ‘sandwiching’ atomic layers of materials such as molybdenum, titanium and carbon.

Babak Anasori, PhD, postdoctoral researcher, led a team of researchers from Drexel’s Department of Materials Science and Engineering to develop the material-making method. This method enabled the production of a stable material with predictable, uniform properties by joining disparate elemental layers. The team demonstrated the effectiveness of this method by creating 2D materials using carbon, titanium and molybdenum.

“By ‘sandwiching’ one or two atomic layers of a transition metal like titanium, between monoatomic layers of another metal, such as molybdenum, with carbon atoms holding them together, we discovered that a stable material can be produced,” Anasori said. “It was impossible to produce a 2-D material having just three or four molybdenum layers in such structures, but because we added the extra layer of titanium as a connector, we were able to synthesize them.”

This finding signifies a new method for combining elemental materials to create superstrong composites and building blocks of energy storage technology. Superstrong composite materials are used in body armor and phone cases. Batteries, supercapacitors, and capacitors are considered to be building blocks for storage of energy. Different combinations of atom-thick layers exhibit new properties, and the team believes that some of these materials could demonstrate durability and energy storage that is not proportional to its size, which could advance new technologies.

“While it’s hard to say, at this point, exactly what will become of these new families of 2D materials we’ve discovered, it is safe to say that this discovery enables the field of materials science and nanotechnology to move into an uncharted territory,” Anasori said.

For over a decade, nanomaterials researchers at Drexel have been attempting to combine 2D sheets of elements in an organized manner to develop new materials. However, it has been very difficult to organize elements at the atomic level.

“Due to their structure and electric charge, certain elements just don’t ‘like’ to be combined,” Anasori said. “It’s like trying to stack magnets with the poles facing the same direction—you’re not going to be very successful and you’re going to be picking up a lot of flying magnets.”

Researchers at Drexel found a method to get around this difficulty. Two decades ago, the head of the MAX/MXene Research Group, Distinguished Professor Michel W. Barsoum, PhD, discovered a MAX phase material. A MAX phase is considered to be something similar to the primordial ooze that generated the first organisms. The various elements of the finished product are in the MAX phase, and some sort of order has to be imposed upon them.

In 2011, Michel W. Barsoum, PhD and Yury Gogotsi, PhD, Distinguished University and Trustee Chair professor in the College of Engineering and head of the Drexel Nanomaterials Group, imposed this order by creating MXene, which is a stable, layered, 2D material.

The researchers used an acid to etch out specific layers of aluminum atoms from a MAX phase block for creating MXenes.

“Think of MXene synthesis like separating layers of wood by dunking a plywood sheet into a chemical that dissolves the glue,” Anasori said. “By putting a MAX phase in acid, we have been able to selectively etch away certain layers and turn the MAX phase into many thin 2D sheets, which we call MXenes.”

The discovery of MXenes for energy storage was a revelation. Graphene was the first 2D material that was considered promising for energy storage, but as it is made up of only one element, and is in the form of a single sheet of carbon atoms, its form cannot be modified easily. Hence, its capabilities to store energy are limited. MXenes, on the other hand, have surfaces that allow them to store more energy.

Researchers then began to conduct studies with “transition metals” in the Periodic Table, and they produced MAX phases that they etched into MXenes with different compositions. The team tested the energy storage properties of the various compositions.

“We had reached a bit of an impasse when trying to produce a molybdenum containing MXenes,” Anasori said. “By adding titanium to the mix we managed to make an ordered molybdenum MAX phase, where the titanium atoms are in center and the molybdenum on the outside.”

Researchers at Oak Ridge National Laboratory’s FIRST Energy Frontier Research Center performed theoretical calculations, which showed that it was possible to utilize this method to create up to 25 new materials, using various combinations of titanium, molybdenum and other such transition metals.

“Having the possibility to layer different elements at the thinnest form of material known to the scientific community leads to exciting new structures and allows unprecedented control over materials properties,” Barsoum said. “This new layering method gives researchers an unimaginable number of possibilities for tuning materials’ properties for a variety of high-tech applications.”

Using other metals such as tantalum, niobium and vanadium instead of titanium could help create more materials with possible new physical properties that support various applications such as energy storage.

“This level of structural complexity, or layering, in 2D materials has the potential to lead to many new structures with unique control over their properties,” Gogotsi said. “We see possible applications in thermoelectrics, batteries, catalysis, solar cells, electronic devices, structural composites and many other fields, enabling a new level of engineering on the atomic scale.”

The team has published their discovery in the ACS Nano journal.


Large Scale 3D Printing

CNC router manufacturer Thermwood has launched a programme to develop a 3D additive manufacturing system capable of making large carbon graphite reinforced composite thermoplastic components. The systems utilise a “near net shape” approach where a custom-built vertical, integrated extruder deposits or “prints” carbon graphite filled thermoplastic material to quickly create a structure that is close to the final shape. Once it cools and hardens, it is then five-axis machined to the final shape.

Developed with extrusion specialist American Kuhne, the process minimises three challenges of conventional 3D printing, particularly for large parts: uneven cooling, material waste and extensive post-print processing. The systems will be based on Thermwood’s “Model 77”, semi-enclosed, high wall gantry machine structures, which are currently offered in sizes up to 18 m in length.

The initial development machine, which is nearing completion, can make parts up to around 3 m x 3 m x 2.5 m high. It is equipped with an integrated, vertical 4.5 cm diameter extruder and support equipment capable of processing over 45 kg/h. Despite the relatively heavy weight of the extrusion system and head, which are both mounted on and move with the machine, the machine generates impressive performance with high acceleration rates and high feed rate capability, the companies said.


Graphene Could Shape the Future of Automotive Fuel Efficiency

Evan Milberg

Scientists from The University of Manchester, working with European Thermodynamics Ltd, have found that graphene could lead to greener, more fuel efficient cars in the future by converting heat into electricity. The team, led by Professor Ian Kinloch, Professor Robert Freer and Yue Lin, added a small amount of graphene to strontium titanium oxide to create a composite that can convert heat which would otherwise be lost as waste into an electric current over a broad temperature range, going down to room temperature.

“Current oxide thermoelectric materials are limited by their operating temperatures which can be around 700 degrees Celsius,” explains Freer. “This has been a problem which has hampered efforts to improve efficiency by utilizing heat energy waste for some time. Our findings show that by introducing a small amount of graphene to the base material can reduce the thermal operating window to room temperature which offers a huge range of potential for applications.”

For cars, that means directing the heat to recharge batteries or powering a fuel-intensive air conditioning system. The scientists estimate the average car currently loses around 70 percent of energy generated through fuel consumption to heat. So far, the new graphene composite can convert 3 to 5 percent of that heat into electricity.

“That is not much but … recovering even a small percentage of [wasted energy] with thermoelectric technology would be worthwhile,” says Freer.

In addition to its fuel-saving capabilities, graphene can also be a composite material in the chassis or bodywork to reduce weight compared to traditional materials.


No More Welds: Fasteners for Composites and Other Rigid Materials

Ann R. Thryft, Senior Technical Editor, Materials & Assembly

When I met with the folks from PennEngineering at the Pacific Design & Manufacturing show earlier this year, I asked them what was in the pipeline since I know they’re always looking ahead. Director of global marketing Leon Attarian told me in confidence that the company expected to launch a self-clinching fastener for composites later this year.

That fastener is now available. It’s the PEM VariMount Fastening System, and it works on more than composites: as PennEngineering’s engineers discovered during R&D, it was easy to tweak the design a little so it could work on any rigid material. The VariMount is designed to mount on panels made of composites, as well as metals or plastics, Attarian told Design News.

Some ongoing research by the Fastening and Joining Research Institute, which investigates both adhesive and fastening technologies, is looking at how to design threaded fasteners for use in bolted assemblies made of several different kinds of materials, such as metals, composites, and plastics. A specific area of research is comparing mechanical fastening and adhesive bonding of composite and polymer joints. But many fasteners, if not most commercially available ones, simply don’t work in plastics or composites.

Outside of some very highly specialized fasteners designed for automotive and aerospace applications, components made of composites and other plastics are usually joined together using adhesives. That’s because, assuming it’s even possible to drill holes in composites without breaking them, these materials have a much lower bearing strength than metals. Consequently, fasteners used in aerospace composites, for example, must be designed differently from those used with metals, and require a larger bearing area under the head of the fastener and also under the nut or the collar.

The VariMount assembly can be mounted to a variety of materials using a variety of mounting methods, Attarian said. It consists of a self-clinching PEM fastener permanently mounted on a round steel or stainless steel baseplate, without the need for welds. The entire assembly itself can then be mounted on a composite panel on the front or through the panel’s back.

The baseplate’s wide footprint and multiple radial holes provide for multiple methods of mounting the assembly, including mold-in or laminate with layers, adhesives, standard fasteners, or spot welding. The holes are sized to accept universally standard diameters of rivets, self-clinching fasteners, and loose hardware such as nuts, bolts, and screws. Several different PEM self-clinching fastener types for accepting mating hardware in the application can be specified for VariMount assemblies. You can download a product bulletin here, and find out more about the PEM VariMount Fastening System here, including detailed specifications, fastener drawings, and models.