Lună: august 2017

Materiale din ceramică ușoară un model pentru armura mai ușoara( Light-weight ceramic materials a model for lighter armor )

Modelul îmbunătățit sa dovedit a prezice mai bine rezistența unei game largi de ținte ceramice atunci când a fost împușcată de un proiectil cu tijă lungă la viteze de până la 3 km / s. Parametrii importanți ai performanței de penetrare a unei ținte ceramice au fost identificați prin acest efort de colaborare, care va ghida modul în care procesele de defecțiuni din ceramică pot fi controlate printr-o proiectare îmbunătățită a materialelor sau printr-o abordare a sistemelor multimateriale

Posted: Aug 18, 2017

Light-weight ceramic materials a model for lighter armor

(Nanowerk News) „While various ceramic materials possess high hardness, they fail easily when pulled apart. That is, when subjected to tensile forces. The amount of tension that these materials can withstand before failure, is a small fraction of the compression they can withstand. As a result, high velocity impact of bullets and fragments causes extensive cracking and fragmentation of the material, reducing its ability to fully utilize its superior hardness to resist complex stress states generated by the impact event,” explained Dr. Sikhanda Satapathy, of ARL’s Soldier Protection Sciences Branch.
side image of a laboratory projectile impacting a ceramic disk backed by polycarbonate
This is a side image of a laboratory projectile impacting a ceramic disk backed by polycarbonate captured using high speed cameras. (Image: US Army Research Laboratory)
Traditionally, the relationship between the granular material’s ability to withstand compression and its ability to resist shearing deformation, which causes material to change shape has been described by the Mohr-Coulomb model. This model approximates the material’s resistance to shearing deformation (shear strength) as a linear function of applied pressure. In reality, the shear strength does not increase linearly with pressure and will saturate at high pressures.
The University of Florida (UF) researchers developed a new model that describes the granular material response more accurately by studying the stress state at which a variety of ceramics fail as reported in the literature by various research teams (International Journal of Solids and Structures, „An improved dynamic expanding cavity model for high-pressure and high-strain rate response of ceramics”).
simulation of a laboratory projectile impacting ceramic backed by polycarbonate showing damage in the ceramic
This is a simulation of a laboratory projectile impacting ceramic backed by polycarbonate showing damage in the ceramic. (Image: US Army Research Laboratory)
The ARL and the UF team collaborated to employ this improved granular response model in conjunction with a dynamic cavity expansion modeling framework to capture the response of ceramics to the complex impact-induced stress state that includes compression, tension and shear. The dynamic cavity expansion modeling framework uses the pressure required to expand a cavity in an intact material to characterize its ability to resist deep penetration. This pressure, of course, is dependent on how the material responds to compression, tension and shear forces.
Due to the applicability of this new model to a broad class of ceramics, the need for expensive experiments to characterize penetration response is significantly reduced. The new penetration model improves the understanding of how brittle ceramic responds to high impact stress by fracturing and comminuting to granular like material, and increases modeling ability of penetration events.
Ceramic Disk
This is the rear surface of the ceramic disk viewed through the polycarbonate backer showing the failure of a ceramic disk as a result of impact by a laboratory projectile. (Image: US Army Research Laboratory)
The improved model has been shown to better predict the resistance of a wide range of ceramic targets when shot at by a long-rod projectiles at velocities up to 3km/s. The important material parameters for penetration performance of a ceramic target have been identified through this collaborative effort, which will guide how the failure processes in ceramic can be controlled through improved material design or through a multi-materials systems approach.
„Understanding the mechanics of material response to projectile impact generated stress conditions is crucial in this research,” Satapathy said.
Source: U.S. Army Research Laboratory

Read more: Light-weight ceramic materials a model for lighter armor

Cercetătorii produc țesături inteligente pentru a neutraliza gazul nervos (Researchers produce smart fabric to neutralize nerve gas )

Țesătura constă dintr-un suport de bumbac modificat cu compozite cu nitruri de carbon cu oxid de carbon-BTC MOF / oxidată. Acestea din urmă au fost dezvoltate anterior în laborator și testate ca medii de detoxifiere a agenților nervoși și detectori colorimetrici.
Combinarea Cu-BTC și gC 3 N 4 -ox a condus la un nanocompozit (MOFgCNo x ) de porozitate și chimie eterogene. După depunerea MOFgCNo x pe textilele de bumbac, a fost obținută o țesătură stabilă cu abilitate supremă de detoxifiere fotocatalitică față de surogatul gazului nervos, dimetil clorofosfat.

Posted: Aug 16, 2017

Researchers produce smart fabric to neutralize nerve gas

(Nanowerk News) From the lab of City College of New York chemical engineer and Fulbright Scholar Teresa J. Bandosz comes a groundbreaking development with the potential to thwart chemical warfare agents: smart textiles with the ability to rapidly detect and neutralize nerve gas (Nanoscale Horizons, „Smart textiles of MOF/g-C3N4 nanospheres for the rapid detection/detoxification of chemical warfare agents”).
The fabric consists of a cotton support modified with Cu-BTC MOF/oxidized graphitic carbon nitride composites. The latter were developed in the lab previously and tested as nerve agent detoxification media and colorimetric detectors.
Combining Cu-BTC and g-C3N4-ox resulted in a nanocomposite (MOFgCNox) of heterogeneous porosity and chemistry. Upon the deposition of MOFgCNox onto cotton textiles, a stable fabric with supreme photocatalytic detoxification ability towards the nerve gas surrogate, dimethyl chlorophosphate, was obtained.
The detoxification process was accompanied by a visible and gradual color change, which Bandosz said can be used for the selective detection of chemical warfare agents and for monitoring their penetration inside a protective layer.
„These smart textiles adsorbed almost 7g of CWA surrogate/its detoxification products per gram of Cu. The superior performance was linked to the high dispersion of the MOF crystals on the fibers, and a specific texture promoting the availability of the active copper centers,” said Bandosz, who is seeking funding for additional research.
Source: City College of New York

Read more: Researchers produce smart fabric to neutralize nerve gas

Materialul 2D cu două fețe este primul(2-faced 2D material is a first)

Noul material pe care îl numesc Janus sulfură de molibden seleniu (SMoSe) are o construcție cristalină, cercetătorii spun că pot găzdui un câmp electric intrinsec și care, de asemenea, arată promisiunea producerii catalitice a hidrogenului.Ar putea conduce la numeroase aplicații, cum ar fi un catalizator activ bazat pe plan 2-D, senzori robusti cu piezoelectricitate și actuatori la limita 2-D. ”

Posted: Aug 14, 2017

2-faced 2D material is a first

(Nanowerk News) Like a sandwich with wheat on the bottom and rye on the top, Rice University scientists have cooked up a tasty new twist on two-dimensional materials.
The Rice laboratory of materials scientist Jun Lou has made a semiconducting transition-metal dichalcogenide (TMD) that starts as a monolayer of molybdenum diselenide. They then strip the top layer of the lattice and replace precisely half the selenium atoms with sulfur.
The new material they call Janus sulfur molybdenum selenium (SMoSe) has a crystalline construction the researchers said can host an intrinsic electric field and that also shows promise for catalytic production of hydrogen.
The work is detailed this month in ACS Nano („Janus Monolayer Transition-Metal Dichalcogenides”).
scientists replace all the atoms on top of a three-layer, two-dimensional crystal to make a transition-metal dichalcogenide with sulfur, molybdenum and selenium
Rice University materials scientists replace all the atoms on top of a three-layer, two-dimensional crystal to make a transition-metal dichalcogenide with sulfur, molybdenum and selenium. (Image: Jing Zhang/Rice University)
The two-faced material is technically two-dimensional, but like molybdenum diselenide it consists of three stacked layers of atoms arranged in a grid. From the top, they look like hexagonal rings a la graphene, but from any other angle, the grid is more like a nanoscale jungle gym.
Tight control of the conditions in a typical chemical vapor deposition furnace – 800 degrees Celsius (1,872 degrees Fahrenheit) at atmospheric pressure – allowed the sulfur to interact with only the top layer of selenium atoms and leave the bottom untouched, the researchers said. If the temperature drifts above 850, all the selenium is replaced.
„Like the intercalation of many other molecules demonstrated to have the ability to diffuse into the layered materials, diffusion of gaseous sulfur molecules in between the layers of these Van der Waals crystals, as well as the space between them and the substrates, requires sufficient driving force,” said Rice postdoctoral researcher Jing Zhang, co-lead author of the paper with graduate student Shuai Jia. „And the driving force in our experiments is controlled by the reaction temperature.”
Close examination showed the presence of sulfur gave the material a larger band gap than molybdenum diselenide, the researchers said.
Janus sulfur molybdenum selenium
This image shows top (left) and side views of Janus sulfur molybdenum selenium created at Rice University. Careful control of heating allows sulfur to replace just the top plane of selenium atoms in the new two-dimensional material. (IMage: Jing Zhang/Rice University)
„This type of two-faced structure has long been predicted theoretically but very rarely realized in the 2-D research community,” Lou said. „The break of symmetry in the out-of-plane direction of 2-D TMDs could lead to many applications, such as a basal-plane active 2-D catalyst, robust piezoelectricity-enabled sensors and actuators at the 2-D limit.”
He said preparation of the Janus material should be universal to layered materials with similar structures. „It will be quite interesting to look at the properties of the Janus configuration of other 2-D materials,” Lou said.
Source: Rice University

Read more: 2-faced 2D material is a first

Noul detector bazat pe SQUID deschide noi domenii de studiu cu un nou nivel de sensibilitate (New SQUID-based detector opens up new fields of study with new level of sensitivity )

Anchetatorii speră că o gamă mai largă le va permite să dezvolte, în colaborare cu unitatea SLAC a Departamentului de Energie de la Stanford, un spectrometru unic capabil să colecteze simultan și să măsoare cu precizie multe raze X de înaltă energie din materialele studiate la X Laser cu laser liber. Razele de raze penetrante de la această unealtă puternică sunt utilizate din ce în ce mai mult pentru a înțelege proprietățile materiei în timpuri foarte scurte, dar sunt necesare magistrale mai mari chiar și pentru această sursă strălucitoare de raze X.Versiunile noului instrument pot detecta semnale pe o gamă largă de frecvențe, de la gamma sau raze X la lungimi de undă la lungimi de undă cu lungimi de undă. Detectarea razei gama este crucială pentru contabilitatea materialelor nucleare, în special pentru urmărirea izotopilor de plutoniu în combustibilii nucleari uzați. Deoarece plutonul poate fi folosit pentru a crea arme nucleare, este important să existe metode rapide și exacte pentru a măsura cantitatea de plutoniu din combustibilul nuclear trimis pentru reprocesare.

Posted: Aug 14, 2017

New SQUID-based detector opens up new fields of study with new level of sensitivity

(Nanowerk News) Investigators at the University of Colorado, Boulder and the National Institute of Standards and Technology (NIST) have developed a new sensor array-based instrument that offers ultra-low noise detection of small amounts of energy for a number of applications. The new device allows for the collection of data from many more detectors than was previously possible.
The advance, reported in this week’s issue of Applied Physics Letters („Simultaneous readout of 128 X-ray and gamma-ray transition-edge microcalorimeters using microwave SQUID multiplexing”), is expected to allow applications in fields as diverse as nuclear materials accounting, astrophysics and X-ray spectrometry.
Photograph of a 33-channel SQUID multiplexer chip along with its microwave response
Photograph of a 33-channel SQUID multiplexer chip (20 mm x 4 mm) along with its microwave response showing the associated resonances. Multiple chips are daisy-chained together to achieve larger multiplexing factors. (Image: J.A.B. Mates, University of Colorado Boulder) (click on image to enlarge)
The instrument consists of 128 superconducting sensors and combines their output into a single channel provided by a pair of coaxial cables. In the past, array size was limited by the bandwidth available to combine signals into a reasonable number of output channels. This new research demonstrates a hundred-fold bandwidth improvement, and the investigators plan to do even better soon. They overcame the bandwidth barrier by using very cold superconducting microwave circuitry and superconducting quantum interference device amplifiers, known as SQUIDs, capable of boosting the intensity of small signals.
The new device uses radiofrequency SQUIDs to regulate high-quality microwave resonators. When these resonators are coupled to a common microwave feed line, with each resonator tuned to a different frequency, all sensors can be simultaneously monitored.
“It’s as if one were trying to listen to hundreds of radio stations at one time, through one radio receiver,” said Ben Mates of the University of Colorado and lead author of the work. The SQUID resonators boost the signal in each channel, he explained, allowing simultaneous readout of all the radio stations at once.
Versions of the new instrument can detect signals over a wide range of frequencies, from short-wavelength gamma or X-rays to long-wavelength microwaves. Gamma ray detection is crucial for nuclear materials accounting, particularly for tracking plutonium isotopes in spent nuclear fuels. Since plutonium can be used to create nuclear weapons, it is important to have fast, accurate methods to measure the amount of plutonium in nuclear fuel sent for reprocessing.
Current technology for tracking plutonium uses mass spectrometry, but this method is expensive and time consuming. Faster and less costly technologies based on gamma-ray spectroscopy don’t have the accuracy to rule out small discrepancies in amounts of plutonium from a large facility. Only 8-10 kilograms of missing material is needed to build a nuclear bomb. The new array detectors are candidates to improve the accuracy of gamma-ray spectroscopy so that nuclear material can be tracked more easily.
At the other end of the spectrum, the new instrument is expected to improve astronomical studies of cosmic microwave background radiation, which is mostly uniform, although small and important fluctuations exist in its intensity and polarization. The researchers predict that similar versions of their instrument will be used to search for fluctuations in polarization that are a signature of an inflationary epoch in the earliest moments of the universe.
The investigators hope that a larger array will allow them to develop, in collaboration with the Department of Energy’s SLAC facility at Stanford, a unique spectrometer capable of simultaneously collecting and precisely measuring many high energy X-rays from materials under study at the California facility’s X-ray free electron laser. Penetrating X-rays from this powerful tool are increasingly used to understand the properties of matter on ultrashort timescales, but larger detector arrays are desirable even for this bright X-ray source. Toward this end, future work will focus on increasing the array size to a thousand sensors or more.
Source: American Institute of Physics

Read more: New SQUID-based detector opens up new fields of study with new level of sensitivity

Fabricarea spumei de nitrura bor de hexagon pentru absorbtia de CO2( Fabricating hexagonal boron nitride foam for CO2 absorption)

Cu structura sa stratificată naturală, nitrura de bor hexagonală (h-BN) a apărut ca un material important 2D, având proprietăți excelente, cum ar fi stabilitatea la temperaturi ridicate, conductivitatea termică ridicată, precum și rezistența mecanică.Spuma are, de asemenea, o absorbție excelentă de CO 2 de 340% și depozitare la valori de presiune variabile, în principal datorită grupărilor funcționale cu azot și o suprafață crescută.
Mai mult, când este acoperit cu polidimetilsiloxan (PDMS), spuma prezintă proprietăți superioare de ecranare prin laser, rezistând unei cantități variate de energie laser, cu o degradare structurală minimă.

Posted: Aug 13, 2017

Fabricating hexagonal boron nitride foam for CO2 absorption

(Nanowerk News) In ACS Nano („Lightweight Hexagonal Boron Nitride Foam for CO2 Absorption”), scientists report a technique to fabricate lightweight 3D macroscopic porous structures formed from hexagonal boron nitride (h-BN) nanosheets.
With its naturally occurring layered structure, hexagonal boron nitride (h-BN) has emerged as an important 2D material, possessing excellent properties such as high temperature stability, high thermal conductivity, as well as mechanical strength.
The fabrication of three-dimensional porous nanostructures from interconnected two-dimensional (2D) materials such as graphene, clays, metal dichalcogenides, etc. has proven to be a promising technique to exploit their properties for several applications including catalysis, energy storage, biological and environmental applications, mechanical damping, and gas sequestration.
Characterization and morphology of h-BN/PVA foams
Characterization and morphology of h-BN/PVA foams. (a) Schematic representation depicting the h-BN nanosheets connected by poly(vinyl alcohol) (PVA) molecules. Typical chains contain 30 monomers (∼6.2 nm chain length). The PVA molecules act like a glue to link the nanosheets through van der Waals interactions between the hydroxyl groups in the PVA and boron/nitrogen atoms in the nanosheets. (b) Structural stability of the h-BN/PVA foam. (c) Mechanical stability of the lightweight foam carrying a vial without any visible degradation. (d) Stable structure of the foam when subjected to liquids. (e) Pristine foam disintegrates in the presence of water, whereas h-BN/PVA maintains its stable interconnected morphology (Rice University owns the copyright for the logo displayed and is used with permission). (f,g) Lowmagnification and high-magnification image of the foam. (© ACS) (click on image to enlarge)
In this new work, the researchers first liquid-phase-exfoliated h-BN in water to separate the layers, and then poly(vinyl alcohol) (PVA) was added (1-1.5 wt %), followed by in situ freeze-drying.
The hybrid structure exhibits enhanced mechanical properties, large surface area, and increased porosity.
According to the team, their fabrication method allows for the creation of intermolecular bonding between h-BN layers, where PVA acts like a bridge to link the individual layers, thus forming a network structure at the nanoscale.
Unlike pristine h-BN foams, which normally disintegrate immediately once removed from a freeze-drier, h-BN/PVA foams show a robust freestanding structure with favorable mechanical stability.
A detailed molecular dynamics study further verified and provided insights on the origins of such interconnections in improving the mechanical integrity.
The foam also exhibits excellent CO2 absorption of 340% and storage under varying pressure values, mainly due to nitrogen functional groups and an increased surface area.
Furthermore, when coated with polydimethylsiloxane (PDMS), the foam shows superior laser shielding properties by withstanding a varied amount of laser energy with minimal structural degradation.
By Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny.

Read more: Fabricating hexagonal boron nitride foam for CO2 absorption