Pentru a transforma polistirenul în lichid, este nevoie de multă energie termică. În această cercetare, piroliza este utilizată ca metodă de procesare a polistirenului pentru a fi produs alicid. Obiectivul acestei cercetări este de a obține caracteristicile procesului de încălzire și proprietățile produsului lichid. Acest lichid poate fi folosit ca combustibil. Reactorul cu pat fix cu SUS 316L ca material de bază a fost construit pentru a descompune polistirenul cu ajutorul unui încălzitor electric, care a fost controlat folosind controlerul digital PID
CZ USA își păstrează în mod inteligent și cu sârguință armele de armament combatante / tactice și, în general, își învinge jocul și un prim exemplu este noul pistol CZ Scorpion EVO III (sau EVO 3) Micro S2 Reflex 9mm / SBR (pușcă cu șuruburi scurte) în configurație numai semi-automată sau arma de apărare personală (SMG) în configurări select-foc / full-auto, acest ultim produs vizează un canal CZ T2 Reflex (tampon / supresor de sunet) atașat la acesta pentru o funcționare plăcută, silențioasă și distracție tăcută și distractivă. DefenseReview (DR) a acoperit deja modelul CZ Scorpion EVO 3 S1. CZ Scorpion EVO 3 S2 scurtează practic acel pachet de arme folosind pistolul CZ Scorpion EVO III Micro ca pistol de bază. Deci, acum aveți ceva chiar mai mic, mai ușor și mai ușor de manevrat în interiorul structurilor.
Reflex-Suppressed CZ Scorpion EVO III Micro S2 Reflex 9mm SMG/PDW / Pistol/SBR for Military SOF Dynamic CQB/CQC and Civilian Tactical Home Defense! (Video!)
CZ USA keeps intelligently and diligently developing their combat/tactical firearms and generally upping their game, and a prime example is the new reflex-suppressed CZ Scorpion EVO III (or, EVO 3) Micro S2 Reflex 9mm pistol/SBR (Short Barreled Rifle) in semi-auto only configuration, or SMG/personal defense weapon (PDW) in select-fire/full-auto config, This latest product sports a CZ S2 Ti Reflex (over-the-barrel) muzzle can (silencer/sound suppressor)attached to it for pleasant, quiet operation, and silent, deadly fun. DefenseReview’s (DR) already covered the CZ Scorpion EVO 3 S1. The CZ Scorprion EVO 3 S2 basically shortens that weapons package using the CZ Scorpion EVO III Micro as base gun. So, now you’ve got something even smaller, lighter, and more maneuverable inside structures.
Military Special Operations Forces (SOF) missions and a law enforcement (LE) SWAT operations aren’t the only situations were silenced weapons can be advantageous. Many civilian tactical shooters who live in SBR and suppressor-friendly NFA states are now choosing suppressed 5.56mm NATO (5.56x45mm NATO)/.223 Rem. and 9mm carbines and SBRs as their bedside home-defense gun, since their much easier on the ears inside structures, and mitigating the need to don hearing pro before you take care of business. Military SOF and SWAT teams enjoy the enhanced tactical comms (communications) and public-friendly aspect of suppressed weapons. Suppressed weapons are less likely to scare and/or wake up the neighbors, in any scenario.
Anyway, getting back to the Scorpion EVO III Micro S2 Reflex’s design, the CZ S2 Ti Reflex can extends all the way back to the muzzle underneath the handguards, allowing for a roughly 10dB (decibel)-quieter weapon over competing suppressed weapons designs. According to CZ rep Zach Hein, the CZ Scorpion EVO III Micro S2 Reflex’s CZ S2 Ti Reflex can “allows for really good suppression. It’s an all-titanium, fully-welded can. There’s nothing to come loose. It’s direct-thread. So, basically [it’s] just stupid simple, reliable, lightweight and robust.” And, since it’s simple blowback, you don’t get any gas in the face. Pretty nice little weapons package.
Watch Defense Review’s video below to get all the details:
combină nanodiamonds cu straturi bidimensionale de disulfură de molibden și le rupe pentru a crea un lubrifiant uscat cu auto-generare, cu o frecare foarte scăzută, care durează atâta timp încât ar putea fi aproape confundat cu pentru totdeauna. Substanța poate avea sute de aplicații industriale și poate fi utilizată practic ori de câte ori două bucăți de metal se freacă împreună în condiții uscate.
Posted: May 10, 2018
Nanodiamonds are forever
(Nanowerk News) Say goodbye to the slogan “diamonds are forever.” For industries that use dry lubricant, the up-and-coming phrase is more likely to be “broken nanodiamonds are forever.”
Researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory are combining nanodiamonds with two-dimensional molybdenum disulfide layers and breaking them to create a self-generating, very-low-friction dry lubricant that lasts so long it could almost be confused with forever. The substance could have hundreds of industrial applications and can be used virtually wherever two pieces of metal rub together in dry conditions.
This reactive molecular dynamics simulation shows the formation of ordered onion-like Carbon (OLC) from an amorphous carbon matrix that was formed by tribochemical reaction of sulfur with nanodiamonds. The magnified view of a representative carbon-rich region is indicated (red circle), where graphitic structures nucleate and grow into well-ordered OLC. In this simulation, yellow atoms are sulfur and dark brown atoms are carbon. Scientists ran the simulation on Argonne’s Mira supercomputer under the U.S. Department of Energy’s INCITE program.
The most commonly used solid lubricants on the market today take the form of graphite paste. We use these lubricants to grease doorknobs and bike chains, among other things.
In 2015, Anirudha Sumant of the Nanoscience and Technology division and his colleagues achieved a breakthrough in solid lubrication technology by demonstrating superlubricity (near-zero friction) at engineering scale for the first time by using graphene combined with nanodiamonds. This approach was revolutionary, and since then his group has continued to further develop the technology.
Most recently, Sumant replaced the graphene in the process with molybdenum disulfide, to see how other 2-D materials would behave. He was expecting the process to resemble the one observed with graphene-nanodiamond lubricant. However, the team was surprised when Diana Berman, the lead author and Argonne post-doctoral fellow, couldn’t see nanodiamonds in the material. Instead, she found balls of onion-like carbon.
What was happening? The molybdenum disulfide was breaking up into molybdenum and sulfur and reacting with the nanodiamonds to convert them into onion-like carbon.
“We knew that the culprit must be sulfur damaging the nanodiamonds, but for us it actually helps,” Sumant said.
The Argonne team, which included Sumant, Diana Berman, Subramanian Sankaranarayanan, Badri Narayanan, Mathew Cherukara, Ali Erdemir and Alexander Zinovev, realized that sulfur diffusion was increasing the strain in the nanodiamonds, subsequently breaking them and converting them into onion-like carbon.
This was a blessing in disguise, said Sankaranarayanan, since their efforts also unlocked another secret of how other 2-D materials will interact with nanodiamonds with the same result.
The friction in this new combination is 10 times lower than that of some nonstick coatings including fluoropolymers, which means less heat and less wear and tear on parts and equipment.
“The material the lubricant is used on is going to last longer, and I don’t have to worry about liquid residue and throwing out oily rags as part of the clean-up process,” Harvey said. “We also can use it to make parts that we can’t make today, especially with metal stamping.”
Onion-like carbon, when formed, consists of several layers of spherical graphitic shells that can be used as a dry lubricant. And the process of sprinkling molybdenum disulfide and nanodiamonds together creates this form of carbon automatically, without any additional chemical application.
“It’s interesting to see that these carbon balls can sustain high contact pressure and, due to their unique nanostructure, can glide easily, creating the superlubricity,” said Ali Erdemir, Argonne Distinguished Fellow and collaborator in this study.
“We have now figured out how to generate lubricants during sliding that can last much longer than any other solid lubricants,” Sumant said.
While molybdenum disulfide is a bit more expensive than graphene, less is needed in this process.
“The amount is so small — a few drops for kilometers of sliding — that cost is not an issue,” Sumant said. The dry lubrication method is also much cleaner for use because there are no hazardous chemicals getting thrown away in this process, he added.
Dry lubricants are already common in several industries. However, they are mostly used for thin-film coatings and are prone to catastrophic failure modes. The Argonne-developed superlubricant works very differently from traditional thin-film coatings. The self-generating lubricant readjusts itself continuously, so it lasts longer.
“This really represents the next generation of solid lubricant,” Sumant said.
The potential applications include bearings and mechanical pump seals in dry applications as well as in wind turbines. The technology could also be used in the computer industry; specifically, in magnetic disc drives.
Argonne already has three patents on the superlubricity technology, with a patent pending on this breakthrough, which will soon be available for licensing.
Sumant and Erdemir co-wrote a recent review in ACS Nano („Approaches for Achieving Superlubricity in Two-Dimensional Materials”) on the most current superlubricity technologies and discoveries within the field. This guidepost article may be the first to summarize the current state of global research on superlubricity using two-dimensional materials such as graphene, hexagonal boron nitride and molybdenum disulfide.
Cercetătorii din Suedia au produs un material pe bază de bio care se precizează că depășește puterea tuturor materialelor cunoscute pe bază de bio, fie fabricate, fie naturale, inclusiv mătase din lemn și păianjen.Fibrele de nanoceluloză bio-fabricate, fabricate aici sunt de 8 ori mai rigide și au o rezistență mai mare decât fibrele de mătase naturală din păianjen, considerate, în general, cele mai puternice materiale biologice”
Posted: May 09, 2018
Method assembles cellulose nanofibres into a material stronger than spider silk
(Nanowerk News) Researchers in Sweden have produced a bio-based material that is reported to surpass the strength of all known bio-based materials whether fabricated or natural, including wood and spider silk.
Working with cellulose nanofibre (CNF), the essential building block of wood and other plant life, the researchers report that they have overcome the difficulty in translating the incredible mechanical properties of these nanofibres into larger, lightweight materials for use in airplanes, cars, furniture and other products.
“The bio-based nanocellulose fibres fabricated here are 8 times stiffer and have strengths higher than natural dragline spider silk fibres, generally considered to be the strongest bio-based material,” says corresponding author Daniel Söderberg, researcher at KTH Royal Institute of Technology. “The specific strength is exceeding that of metals, alloys, ceramics and E-glass fibres.”
SEM image of the cross-section of the fibre, showing the aligned nanofibrils. (Image: KTH)
The reported progress results from the development of insights into the way physics controls structuring of components, such as CNF, at the nanoscale during fabrication.
This understanding enabled a new process, which involves controlling the flow of nanofibres suspended in water in a 1 mm wide channel milled in stainless steel. Connecting flows of deionized water and low pH water help align the nanofibres in the right direction and enable the supramolecular interactions between CNFs to self-organize into a well-packed state where they are joined together.
“This discovery is made possible by understanding and controlling the key fundamental parameters essential for perfect nanostructuring, such as particle size, interactions, alignment, diffusion, network formation and assembly,” Söderberg says.
Söderberg says the study opens the way for developing nanofibre material that can be used for larger structures while retaining the nanofibres’ tensile strength and ability to withstand mechanical load. The process can also be used to control nanoscale assembly of carbon tubes and other nano-sized fibres.
Measurements of the material were reported for tensile stiffness, 86 gigapascals (GPa), and for tensile strength, 1.57 GPa.
Grafenul material are multe proprietati incredibile, dar pana in prezent a fost dificil de utilizat pe scara larga in industrie, pentru ca isi pierde proprietatile unice si se intoarce la grafitul de origine. Cercetătorul Mamoun Taher a dezvoltat o nouă formă de grafen care poate rezolva problema.
Posted: May 09, 2018
A new generation of graphene incorporates ‘separators’
(Nanowerk News) The material graphene has many incredible properties, but to date it has been difficult to use on a large scale in industry, because it loses its unique properties and goes back to its origin graphite. Researcher Mamoun Taher has developed a new form of graphene that can solve the problem.
“The challenge has been to scale up graphene’s outstanding properties from nanoscale at laboratories to macro-scale at industry without degradation,” says Mamoun Taher. He is a researcher at the Department of Chemistry at Uppsala University and CEO of start-up company Graphmatech.
Mamoun Taher
Graphene is one atom thick two-dimensional carbon material. It is flexible, 200 times stronger than steel, and has many other advantageous properties. The problem is that when it is produced on a large scale, the thin flakes have tendency to re-stick. As a result, the material loses its wonder properties and becomes more like graphite.
The new material, Aros Graphene, has been designed to prevent this by incorporating designed molecules, so called “separators”.
“The separators are designed to separate graphene flakes without degrading their properties, so we have control over the material. The process has been designed to be environmentally accepted, we use water as a solvent and no hazardous chemicals.”
Research in collaboration with companies
Mamoun Taher splits his time between research at the Ångström Laboratory and working with start-up company Graphmatech. By his side is entrepreneur Björn Lind, one of the brains behind the company Disruptive Materials and Upsalite, another material developed from research at Uppsala University.
The development takes place in close partnership with the company ABB and they also have access to ABB’s laboratories in Västerås.
Mamoun Taher made his discovery as a postdoc at Uppsala University. Originally from Syria, after he wrote a doctoral dissertation in the chemistry of interfaces at Luleå University of Technology, he came to Uppsala University. In collaboration with ABB Corporate Research Center in Västerås, he worked with graphene materials, but was struck by how much of the properties were lost when the flakes stuck together.
“I combined my previous research with my studies of graphene, and that’s how Aros Graphene was born.”
Thermal management of electronics
He contacted UU Innovation, the University´s unit for support for commercialisation of research results, and the European organisation InnoEnergy. With their support, the company took off. There are applications in electronics and telecommunication industry, where the material can be used to efficiently dissipate heat from electronics which enables more compacted designs, longer life spam and safer operation.
“We’ve seen that a thermal paste that contains Aros Graphene is 180 percent more thermally conductive than other thermal paste products on the market. In the close future where more and more data centres will be needed to store data, there is huge demand for advanced thermal management solutions.”
GraphMaTech has several other projects, for example on self-lubricating mechanical systems, 3D printing, moving electrical contacts and printed supercapacitors.
“We aren’t just developing a material, but also processes that can be used by graphene producers and other materials-related industries. We’re currently in discussions about licensing our process,” says Mamoun Taher.
Pentru a optimiza performanța Li + @ C 60 în aplicații precum fotovoltaice și dispozitive de comutare, este important să înțelegeți bine proprietățile sale electronice. O colaborare internationala de cercetare condus de Universitatea din Tsukuba extins recent cunoștințe de Li + @C 60 de gestionare a imaginii unice Li + @C 60 de molecule prin scanarea microscopie tunelare. Scanarea microscopiei de tuneluri poate realiza imagini cu rezoluție la nivel molecular și oferă informații despre structura electronică a moleculelor unice. Fullerenele sunt compuse din 60 de atomi de carbon îmbinate în inele hexagonale pentru a forma o sferă care seamănă puternic cu o minge de fotbal. Fullerenes sunt de mare interes pentru oamenii de stiinta de materiale, deoarece proprietatile lor electronice interesante le fac atractive pentru utilizarea in electronica avansata si nanotehnologie.
Posted: May 09, 2018
Visualization of molecular soccer balls
(Nanowerk News) Fullerenes are composed of 60 carbon atoms joined together in hexagonal rings to form a sphere that strongly resembles a soccer ball. Fullerenes are of great interest to materials scientists because their interesting electronic properties make them attractive for use in advanced electronics and nanotechnology.
The electronic properties of fullerene can be modified by doping with other elements without altering its soccer ball-like shape. In particular, salts of lithium ion-doped fullerene, which is denoted as Li+@C60, have been synthesized in high yield and the structure of Li+@C60 has been determined. Li+@C60 salts have been used in solar cells and molecular switches with promising results.
To optimize the performance of Li+@C60 in applications such as photovoltaics and switching devices, it is important to thoroughly understand its electronic properties. An international research collaboration led by the University of Tsukuba recently expanded knowledge of Li+@C60by managing to image single Li+@C60 molecules by scanning tunneling microscopy. Scanning tunneling microscopy can image materials with molecular-level resolution and provide information about the electronic structure of single molecules.
Calculated geometry and charges of Li+@C60[PF6–]salt. (Image: University of Tsukuba)
„We fabricated a thin-film sample suitable for scanning tunneling microscopy by vacuum evaporation of a Li+@C60 salt on a copper substrate,” study co-author Seiji Sakai explains. „Our subsequent microscopy examination revealed that although some lithium ions escaped during the evaporation process, the sample did contain some Li+@C60 molecules on the copper substrate.”
The microscopy images revealed a mixture of Li+@C60 and undoped fullerene molecules on the copper surface. Both types of molecules were similarly oriented but displayed different heights and electronic structure, allowing them to be differentiated. The team lent further weight to their experimental findings by conducting density functional theory calculations to generate simulated scanning tunneling microscopy images. The experimentally measured and simulated microscopy images agreed well overall.
„Our study provides confirmation of the electronic structure of lithium-doped fullerene,” lead author Yoichi Yamada says. „Such knowledge will aid our ability to modulate the electronic structure of fullerenes to optimize their performance in optoelectronic and switching devices.”
The imaging and electronic structure confirmation of Li+@C60 represent important paving stones on the road to advanced applications of organic materials because they should aid our ability to control the carrier injection and transport properties of fullerenes.
Cercetătorii au înmuiat o pungă de plastic în solvent conținând sulf și au pus-o într-un cuptor cu microunde pentru a oferi ieftin creșterea rapidă a temperaturii necesare pentru transformarea în polietilenă de joasă densitate. Căldura a promovat sulfonarea și carbonizarea plasticului și a indus o densitate mai mare de pori pentru capturarea polisulfurii. Plasticul de polietilenă de joasă densitate ar putea fi transformat într-o schelă de carbon pentru a împărți jumătățile de litiu și sulf ale unei celule de monede pentru baterii.reciclarea plasticului LDPE în schelă de carbon sulfurat prin sulfonare promovată de microunde” ), arată că plasarea unui plastic înmuiat în sulf într-un cuptor cu microunde , inclusiv pungi de plastic transparente, transformă materialul în substanța ideală pentru a crește durata de viață a bateriilor viitoare la mai mult de 200 de cicluri de încărcare-descărcare.reciclarea plasticului LDPE în schelă de carbon sulfurat prin sulfonare promovată de microunde” ), arată că plasarea unui plastic înmuiat în sulf într-un cuptor cu microunde , inclusiv pungi de plastic transparente, transformă materialul în substanța ideală pentru a crește durata de viață a bateriilor viitoare la mai mult de 200 de cicluri de încărcare-descărcare.
Posted: May 09, 2018
Microwaved plastic increases lithium-sulfur battery life span
(Nanowerk News) Purdue engineers have figured out a way to tackle plastic landfills while also improving batteries – by putting ink-free plastic soaked in sulfur-containing solvent into a microwave, and then into batteries as a carbon scaffold.
Lithium-sulfur batteries have been hailed as the next generation of batteries to replace the current lithium ion variety. Lithium-sulfur batteries are cheaper and more energy-dense than lithium ions, which would be important characteristics in everything from electric vehicles to laptops.
But the knock on lithium-sulfur batteries to this point is that they don’t last as long, being usable for about 100 charging cycles.
Purdue researchers have found a way to increase the life span in a process that has the added bonus of being a convenient way to recycle plastic. Their process, which was recently published in ACS Applied Materials and Interfaces („Toward High-Performance Lithium–Sulfur Batteries: Upcycling of LDPE Plastic into Sulfonated Carbon Scaffold via Microwave-Promoted Sulfonation”), shows that putting sulfur-soaked plastic in a microwave, including transparent plastic bags, transforms the material into the ideal substance for increasing the life span of the forthcoming batteries to more than 200 charging-discharging cycles.
Watch a YouTube video explaining this.
“No matter how many times you recycle plastic, that plastic stays on the earth,” said Vilas Pol, associate professor in Purdue’s School of Chemical Engineering. “We’ve been thinking of ways to get rid of it for a long time, and this is a way to at least add value.”
The need to reduce landfills runs parallel to making lithium-sulfur batteries good enough for commercial use.
“Because lithium-sulfur batteries are getting more popular, we want to get a longer life sucked out of them,” Pol said.
Low-density polyethylene plastic, which is used for packaging and comprises a big portion of plastic waste, helps address a long-standing issue with lithium-sulfur batteries – a phenomenon called the polysulfide shuttling effect that limits how long a battery can last between charges.
Lithium-sulfur batteries, as their name suggests, have a lithium and a sulfur. When a current is applied, lithium ions migrate to the sulfur and a chemical reaction takes place to produce lithium sulfide. The byproduct of this reaction, polysulfide, tend to cross back over to the lithium side and prevent the migration of lithium ions to sulfur. This decreases the charge capacity of a battery as well as life span.
“The easiest way to block polysulfide is to place a physical barrier between lithium and sulfur,” said Patrick Kim, a Purdue postdoc research associate in chemical engineering.
Previous studies had attempted making this barrier out of biomass, such as banana peels and pistachio shells, because the pores in biomass-derived carbon had the potential to catch polysulfide.
“Every material has its own benefit, but biomass is good to keep and can be used for other purposes,” Pol said. “Waste plastic is really valueless and burdensome material.”
Instead, researchers thought of how plastic might be incorporated into a carbon scaffold to suppress polysulfide shuttling in a battery. Past research had shown that low-density polyethylene plastic yields carbon when combined with sulfonated groups.
The researchers soaked a plastic bag into sulfur-containing solvent and put it in a microwave to cheaply provide the quick boost in temperature needed for transformation into low-density polyethylene. The heat promoted the sulfonation and carbonization of the plastic and induced a higher density of pores for catching polysulfide. The low-density polyethylene plastic could then be made into a carbon scaffold to divide the lithium and sulfur halves of a battery coin cell.
“The plastic-derived carbon from this process includes a sulfonate group with a negative charge, which is also what polysulfide has,” Kim said. Sulfonated low-density polyethylene made into a carbon scaffold, therefore, suppressed polysulfide by having a similar chemical structure.
“This is the first step for improving the capacity retention of the battery,” Pol said. “The next step is fabricating a bigger-sized battery utilizing this concept.”
a creat un alt material bidimensional, despre care cercetătorii spun că ar putea fi un schimbător de jocuri pentru generarea de combustibil solar.Hematena poate fi un fotocatalizator eficient, în special pentru împărțirea apei în hidrogen și oxigen, și ar putea servi și ca un material magnetic ultrathin pentru dispozitive pe bază de spintronă, au spus cercetătorii.Spre deosebire de carbon și forma sa 2D, grafenul, hematitul este un material non-van der Waals, adică este susținut de rețelele de lipire 3D, mai degrabă decât interacțiunile atomice van der Waals nechemice și relativ mai slabe.
Posted: May 07, 2018
Hematene joins parade of new 2D materials
(Nanowerk News) In the wake of its recent discovery of a flat form of gallium, an international team led by scientists from Rice University has created another two-dimensional material that the researchers said could be a game changer for solar fuel generation.
Hematene created by a Rice University-led team is the first known two-dimensional non-van der Waals material. The transmission electron image shows a single sheet of hematene. Scale bar equals 0.5 microns. (Image: Shyam Sinha and Peter van Aken/Max Planck Institute for Solid State Research, Stuttgart, Germany)
Hematene may be an efficient photocatalyst, especially for splitting water into hydrogen and oxygen, and could also serve as an ultrathin magnetic material for spintronic-based devices, the researchers said.
“2D magnetism is becoming a very exciting field with recent advances in synthesizing such materials, but the synthesis techniques are complex and the materials’ stability is limited,” Ajayan said. “Here, we have a simple, scalable method, and the hematene structure should be environmentally stable.”
Ajayan’s lab worked with researchers at the University of Houston and in India, Brazil, Germany and elsewhere to exfoliate the material from naturally occurring hematite using a combination of sonication, centrifugation and vacuum-assisted filtration.
A schematic shows the atomic arrangement of iron (blue) and oxygen (white) atoms in hematene, a two-dimensional material that was exfoliated from hematite for the first time by Rice University scientists and their international partners. (Image: Cristiano Woellner and Douglas Galvao/State University of Campinas, Brazil)
Hematite was already known to have photocatalytic properties, but they are not good enough to be useful, the researchers said.
“For a material to be an efficient photocatalyst, it should absorb the visible part of sunlight, generate electrical charges and transport them to the surface of the material to carry out the desired reaction,” said Oomman Varghese, a co-author and associate professor of physics at the University of Houston.
“Hematite absorbs sunlight from ultraviolet to the yellow-orange region, but the charges produced are very short-lived. As a result, they become extinct before they reach the surface,” he said.
Hematene photocatalysis is more efficient because photons generate negative and positive charges within a few atoms of the surface, the researchers said. By pairing the new material with titanium dioxide nanotube arrays, which provide an easy pathway for electrons to leave the hematene, the scientists found they could allow more visible light to be absorbed.
The researchers also discovered that hematene’s magnetic properties differ from those of hematite. While native hematite is antiferromagnetic, tests showed that hematene is ferromagnetic, like a common magnet. In ferromagnets, atoms’ magnetic moments point in the same direction. In antiferromagnets, the moments in adjacent atoms alternate.
A transmission electron microscope image shows bi-layer and monolayer hematene, exfoliated from hematite, a common iron ore, by scientists at Rice University and their international partners. The material shows promise as a catalyst for advanced solar fuel generation and spintronics applications. The scale bar equals 50 nanometers. (Image: Ajayan Research Group/Rice University)
Unlike carbon and its 2D form, graphene, hematite is a non-van der Waals material, meaning it’s held together by 3D bonding networks rather than non-chemical and comparatively weaker atomic van der Waals interactions.
“Most 2D materials to date have been derived from bulk counterparts that are layered in nature and generally known as van der Waals solids,” said co-author Professor Anantharaman Malie Madom Ramaswamy Iyer of the Cochin University of Science and Technology, India. “2D materials from bulk precursors having (non-van der Waals) 3D bonding networks are rare, and in this context hematene assumes great significance.”
According to co-author Chandra Sekhar Tiwary, a former postdoctoral researcher at Rice and now an assistant professor at the Indian Institute of Technology, Gandhinagar, the collaborators are exploring other non-van der Waals materials for their 2D potential.
Cercetătorii de la Universitatea din Geneva (UNIGE) și CEA, CNRS și UGA au studiat BACOVO – un material cuantic unidimensional necunoscut publicului larg – în colaborare cu cercetătorii din centrele neutronice ILL și PSI. Ei au descoperit în acest material o nouă tranziție fazică topologică, guvernată nu de un singur tip de excitație topologică, ci de două tipuri diferite. În plus, au putut alege care dintre cele două seturi ar domina celălalt.
Posted: May 07, 2018
The apparent inner calm of quantum materials
(Nanowerk News) Transitions between different phases of matter are part of our day-to-day lives: when water freezes, for example, it passes from liquid to solid state. Some of these transitions may be of a different kind, resulting from so-called topological excitations that force all the particles to act in unison.
Researchers from the University of Geneva (UNIGE) and the CEA,CNRS and UGA have been studying BACOVO – a one-dimensional quantum material unknown to the general public – in collaboration with scientists from the neutronic centers ILL and PSI. They have discovered in this material a novel topological phase transition, governed not by a single type of topological excitation, but by two different ones. In addition, they were able to choose which of the two sets would dominate the other.
The helix structure of BACOVO: the oxygen atoms, represented in red, are organized in octahedra around the cobalt atoms, located at their center. The blue arrows represent the small moments carried by the cobalt atoms, ordered antiferromagnetically along the helical chain. (Image: CEA/CNRS/UGA)
The researchers drew on the work of the 2016 Nobel Prize for physics awarded to David Thouless, Duncan Haldane, and Michael Kosterlitz. The three physicists predicted that a set of topological excitations in a quantum material is likely to induce a phase transition. Numerous theories have been developed about these topological excitations, including the feasibility of combining two of them in a single material.
But is that a real possibility? And if so, what would happen? The teams from UNIGE and CEA, CNRS and UGA were able to provide the first experimental confirmation of the theory predicting the existence of two simultaneous sets of topological excitations and the competition between them. All in all, it is a small revolution in the mysterious world of quantum properties.
Theory and experimentation intimately linked
The researchers from CEA, CNRS, and Université Grenoble Alpes were working on a one-dimensional antiferromagnetic material with particular properties: BACOVO (BaCo2V2O8).
„We performed various experiments on BACOVO, an oxide characterised by its helical structure,” underline Béatrice Grenier, Sylvain Petit and Virginie Simonet, researchers at the CEA, CNRS and UGA. „But our experimental results evidenced a puzzling phase transition” – which is why their team called on Thierry Giamarchi, a professor in the Department of Quantum Matter Physics in UNIGE’s Faculty of Science. The Geneva physicist explains: „Based on their results, we established theoretical frameworks capable of interpreting them. These theoretical models were then tested again using new experiments so they could be validated.”
Creating the „standard model”
The aim was to understand how BACOVO’s quantum properties act, especially their topological excitations. „For this purpose, we used neutron scattering, meaning we sent a neutron beam onto the material. The neutrons behave like small magnets that interact with those of BACOVO, according to a strategy „disturb in order to reveal”, helping us to understand their properties,” says Quentin Faure, Ph-D student at the Institute for Nanoscience and Cryogenics (CEA/UGA) and Néel Institute. When the model developed at UNIGE matches the experiment, it becomes the material’s „standard model”. Professor Giamarchi enthusiastically points out: „And, in fact, the model we established with Shintaro Takayoshi predicted exactly the outcome seen in the experiment!”
A material with unexpected properties
But this experiment also led to a discovery that the scientists had not anticipated. „After settling on the „standard model” for BACOVO, we observed unexpected properties,» says Shintaro Takayoshi, researcher in the Department of Quantum Matter Physics in UNIGE’s Faculty of Science. When placed in a magnetic field, BACOVO develops a second set of topological excitations that are in competition with the first one, confirming theories from the 1970s and 1980s organised around the field opened up by the work of the Nobel scientists.
„As well as proving the existence of this confrontation between two sets of topological excitations within the same material – an unprecedented event – we were able to experimentally control which set would dominate the other”, adds the Genevan researcher. And that is a first!
What was originally a theoretical hypothesis became a verified experiment. The in-depth analysis of BACOVO undertaken by the physicists proved that two sets of topological excitations come into direct confrontation in the same material and control the state of matter, which differs according to the dominant set, yielding a quantum phase transition. Furthermore, the scientists succeeded in controlling which set prevails, meaning they could adjust BACOVO’s state of matter at will.
„These results open up a whole range of possibilities in terms of quantum physics research,” concludes Professor Giamarchi. „It’s true that we are still at the fundamental level, but it’s through this kind of discovery that we are getting closer every day to applications for the quantum properties of materials… and why not quantum computers!?”
Ei au depus straturi de oxid de zinc pe un amestec de sticlă și nanosfere polimerice. Odata ce structura a fost completa, cercetatorii ar putea dizolva polimerul, lăsând o rețea de sfere de sticlă acoperite cu oxid de zinc și pori goi. Această structură conține toate elementele necesare pentru a acționa ca un fotoanod, partea unei frunze artificiale care utilizează lumina pentru a transforma apa în oxigen și energie.Cercetătorii au testat materialul în curs de brevetare, folosind un dispozitiv numit potențiostat pentru a măsura cantitatea de energie generată sub formă de curent.
Posted: May 07, 2018
Chemists develop improved method to create artificial photosynthesis
Researchers covered glass and polymer nanospheres with a thin layer of zinc oxide (left). After the polymer spheres were dissolved (right), they had a material that could act as a photoanode. (Image: Robert Coridan)
Plants use photosynthesis to convert sunlight into chemical energy, which they store in the form of sugars or fatty acids. A device known as an artificial leaf mimics this natural process, providing a reliable, economical and sustainable source of storable chemical fuels, such as hydrogen.
Artificial photosynthesis has an advantage over traditional photovoltaics, which produce electricity only when the sun is shining. An artificial leaf stores the energy from sunlight as chemical bonds which can be used to generate power at any time, matching the advantage of that coal and natural gas have over photovoltaics.
Currently, materials for artificial photosynthesis devices are expensive to produce because they must integrate all of the components that carry out the necessary light absorption, chemical catalysis, and other processes, and each of these components must be assembled on the nanoscale.
“Typical nanostructured materials for these applications use the same expensive and energy-consuming fabrication methods that are used to build microprocessors,” explained Robert Coridan, assistant professor of chemistry and biochemistry. Coridan worked with Mya Norman, an instructor in chemistry and biochemistry; Walker Perez, who recently earned a bachelor’s degree in chemical engineering; and Chandler Kline, an undergraduate chemical engineering student.
This research team used a method called atomic layer deposition to build nanostructures one atomic layer at a time. They deposited layers of zinc oxide onto a mixture of glass and polymer nanospheres. Once the structure was complete, the researchers could dissolve the polymer, leaving a network of zinc oxide-coated glass spheres and hollow pores. This structure contains all the elements necessary to act as a photoanode, the part of an artificial leaf that uses light to turn water into oxygen and energy.
Coridan explained that a similar process could be used to create a photocathode, the part of an artificial leaf that takes the protons and electrons created by the photoanode and recombines them to form hydrogen, which can be stored and used as fuel.
The researchers tested their patent-pending material by using a device called a potentiostat to measure the amount of energy it generated in the form of current.
a dezvoltat foi de carbon de înaltă rezistență, super-dură, care pot fi fabricate inexpensiv la temperaturi scăzute.
Echipa a realizat foile prin îmbinarea chimică a trombocitelor de carbon grafitic, care este similar cu grafitul găsit în plumbul moale al unui creion obișnuit. Procesul de fabricație a dus la obținerea unui material ale cărui proprietăți mecanice depășesc acelea ale compozitelor din fibră de carbon utilizate în mod curent în diferite produse comerciale.Deoarece foile noastre sunt fabricate la temperaturi scăzute, acestea sunt costuri reduse, în plus față de rezistența înaltă a foilor duritatea și rezistența la oboseală, au o conductivitate electrică ridicată și sunt capabile să protejeze împotriva radiațiilor electromagnetice
Posted: May 07, 2018
Scientists make strong, super-tough carbon sheets at low temperature
(Nanowerk News) An international research team led by scientists at Beihang University in China and The University of Texas at Dallas has developed high-strength, super-tough sheets of carbon that can be inexpensively fabricated at low temperatures.
The team made the sheets by chemically stitching together platelets of graphitic carbon, which is similar to the graphite found in the soft lead of an ordinary pencil. The fabrication process resulted in a material whose mechanical properties exceed those of carbon fiber composites that are currently used in diverse commercial products.
„These sheets might eventually replace the expensive carbon fiber composites that are used for everything from aircraft and automobile bodies to windmill blades and sports equipment,” said Dr. Ray Baughman, the Robert A. Welch Distinguished Chair in Chemistry at UT Dallas and director of the Alan G. MacDiarmid NanoTech Institute. Baughman is a corresponding author of an article describing the material published online this week in the Proceedings of the National Academy of Sciences („Sequentially bridged graphene sheets with high strength, toughness, and electrical conductivity”).
This false-color, scanning electron microscope image shows the fractured surface of a sequentially bonded graphene sheet. An international research team led by scientists at Beihang University in China and The University of Texas at Dallas developed the high-strength, super-tough sheets, which can be inexpensively fabricated at low temperatures. (Image: Beihang University)
Today’s carbon fiber composites are expensive in part because the carbon fibers are produced at extremely high temperatures, which can exceed 2,500 degrees Celsius (about 4,500 degrees Fahrenheit).
„In contrast, our process can use graphite that is cheaply dug from the ground and processed at temperatures below 45 degrees Celsius (113 degrees Fahrenheit),” said Dr. Qunfeng Cheng, professor of chemistry at Beihang University and a corresponding author. „The strengths of these sheets in all in-plane directions match that of plied carbon fiber composites, and they can absorb much higher mechanical energy before failing than carbon fiber composites.”
Graphite consists of platelets made up of stacked layers of graphene. Graphene is simply a single layer of carbon atoms, arranged in a pattern that looks like a chicken wire mesh fence, where each hexagon in the mesh is formed by six carbon atoms.
„While scientists can continuously make large sheets of graphene by high-temperature processing, and have shown these sheets to have remarkable strength, it is impractical to make thick plates of graphite by merely stacking large-area graphene sheets,” Cheng said. „One would need to stack about 150,000 graphene sheets to make a graphite sheet having about the thickness of a human hair.”
The researchers found inspiration in natural nacre, also known as mother-of-pearl, which gives some seashells their strength and toughness. Nacre is composed of parallel platelets that are bound together by thin layers of organic material, similar to the way bricks in a wall are held together by mortar.
„Instead of mechanically stacking large-area graphene sheets, we oxidize micron-size graphite platelets so that they can be dispersed in water, and then filter this dispersion to inexpensively make sheets of oriented graphene oxide,” Baughman said. „This process is akin to hand-making sheets of paper by filtering a slurry of fibers.
„At this stage, the sheets are neither strong nor tough, meaning they cannot absorb much energy before rupturing,” he said. „The trick we use is to stitch together the platelets in these sheets using sequentially infiltrated bridging agents that interconnect overlapping neighboring platelets, and convert the oxidized graphene oxide to graphene. The key to this advance is that our bridging agents separately act via formation of covalent chemical bonds and van der Waals bonds.”
Sheets that incorporated the bridging agents were 4.5 times stronger and 7.9 times tougher than agent-free sheets, said Beihang University PhD student Sijie Wan, who is a lead author of the journal article. „Unlike carbon fiber composites, no polymer matrix is needed,” he said.
„While sheets of expensive carbon fiber composites can provide a similar strength in all sheet-plane directions, the energy that they can absorb before fracture is about one-third that of our sequentially bridged graphene sheets,” Wan said. „Because our sheets are fabricated at low temperatures, they are low cost. In addition to exhibiting high sheet strength, toughness and fatigue resistance, they have high electrical conductivity and are able to shield against electromagnetic radiation. These properties make these sequentially bridged graphene sheets quite attractive for possible future applications.”
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