Lună: martie 2016

Noul ceramică nanostructurată transformă căldura risipită în electricitate

a proiectat ceramică nanostructurată, care sunt materiale termoelectrice care convertesc căldura produsă în procesele industriale în energie electrică.
Pentru a găsi o sursă alternativă de energie, cercetătorul modelează și proiectează aceste materiale pentru a fi utilizate în diferite industrii, cum ar fi spațiul sau automobilul, pentru a reutiliza căldura eliberată în conducta de eșapament a unei mașini.

Posted: Mar 01, 2016

Novel nanostructured ceramics convert wasted heat into electricity

(Nanowerk News) Talia Alvarez, currently studying her doctorate at the University Of Manchester, UK, designed nanostructured ceramics, which are thermoelectric materials that convert the heat produced un industrial processes into electrical energy.
In order to find an alternative energy source, the researcher shapes and designs these materials for use in different industries, such as space or automobile, in the latter to reuse the heat released in the exhaust pipe of a car.
Nanostructured ceramics
Nanostructured ceramics.
The air temperature exiting said device is at approximately 800 degrees kelvin, and causes the exhaust pipe of an automobile to reach between 700 and 600 degrees Celsius. A temperature difference that can be used to generate electricity, said Alvarez Ruiz, master of science in electrical engineering from the Center of Research and Advances Studies (CINVESTAV) in Mexico.
The aim is to create a ceramic with excellent chemical conditions, which is economical and coats the tube leakage or engine of a vehicle. This assures the recovery of heat and savings on fuel.
More than two thirds of the energy released in burning fossil fuel is wasted as heat and released to the environment. Besides the machines, vehicles, even the human body produces this energy source that goes to waste, said Alvarez Ruiz.
In search for cheap ceramics
The native of Tapachula, Chiapas, in the south of Mexico, shapes and designs nanostructured ceramics which main component is zinc oxide, a semiconductor used in industry, abundant in nature, economical and environmentally friendly.
„What I do is play with the chemical composition of the material and the manufacturing process to improve the properties, because the current ceramics with high efficiency are expensive and toxic”.
Alvarez Ruiz seeks a ceramic that does not have these toxic characteristics. The problem is that the temperature difference needs to be very large and so far in the laboratory only a small voltage is obtained.
„Commercial materials have an efficiency of 4, mine has an efficiency of 0.6. The difference is large but the advantages are many, we aim to reduce production costs that in the future will be beneficial to society.”
Ceramics designed at the University of Manchester could be implemented to take advantage of the heat released in thermoelectric plants and generate enough electricity to power light bulbs.
Source: Investigación y Desarrollo

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Fizicienii primesc un material perfect pentru filtrele de aer

demonstrat că reducerea diametrului fibrelor de la 200 nanometri până la 20 a redus rezistența filtrului la fluxul de aer cu două treimi și acest efect nu mai poate fi explicat prin aerodinamica clasică. Când dimensiunea obstacolului este mai mică decât calea liberă a moleculelor de gaze, metodele standard care estimează rezistența aerodinamică bazată pe teoria continuumului nu mai funcționează. În condiții normale, calea medie liberă a moleculelor de aer produce 65 nanometri.

Posted: Mar 01, 2016

Physicists get a perfect material for air filters

(Nanowerk News) A research team from the Institute of Theoretical and Experimental Biophysics of the Russian Academy of Sciences have synthesized the material that is perfect for protection of respiratory organs, analytical research and other practical purposes. An almost weightless fabric made of nylon nanofibers with a diameter less than 15 nm beats any other similar materials in terms of filtering and optical properties.
The scientists whose work is published in Macromolecular Nanotechnology Journal („Filtering and optical properties of free standing electrospun nanomats from nylon-4,6”), characterize their material as lightweight (10-20 mg/m2), almost invisible (95% light transmission: more than that of a window glass), showing low resistance to airflow and efficient interception of <1 micrometer fine particulate matter.
An almost weightless fabric made of nylon nanofibers with a diameter less than 15 nm
A sample of the new fabric in reflected light. (Image courtesy of the researchers)
The wording „nanofibers” in the researchers’ article is more than a fashion statement. Previously, the same team demonstrated that reducing fiber diameter from 200 nanometers down to 20 decreased filter resistance to airflow by two thirds, and this effect could no longer be explained by classical aerodynamics. When an obstacle size is smaller than the free path of gas molecules, the standard methods estimating aerodynamic resistance based on the continuum theory no longer work. In normal conditions, the mean free path of air molecules makes 65 nanometers.
The mean free path is the average distance one molecule manages to cover before colliding with another. Only if all obstacles are much bigger than this value, the free stream coming at them can be rightfully considered a continuous medium.
The scientists used the technique called electrospinning: a jet of a dissolved polymer is ejected through a special nozzle aiming at a target under action of an electric field. From the other side, ethanol is electrosprayed. The polymer jet and the alcohol ions take the opposite electric charges. Colliding in the air, they form ultra-thin fibrous films. Electrospinning technology as a way to produce nonwoven fibrous filters has been developed back in the 50s to purify air in atomic industry. However, the researchers introduced an important improvement: instead of obtaining nanomats on a solid conducting substrate like before, now with the new technology, a free filter is formed covering a 55-mm hole in a non-conductive polycarbonate screen.
The published work completed the cycle of the authors’ papers devoted to development of the manufacturing technology and studies of properties of nanofilters manufactured using this new process. It was established that the unique optical and filtering properties originate from a special mechanism of „healing” holes and defects in free standing filters. Such holes literally attract fibers landing onto the filter surface. As a result, a good filter without big holes can be obtained from a minimum amount of nanofibers and, accordingly, with a minimum resistance to airflow. Moreover, active healing of big holes between threads provides the filters with the properties inherent in filters with calibrated pores, so called track-etched membranes (Nuclepores). The scientists have also demonstrated that the „healing” mechanism does not work in the conventional electrospinning technique where nanofibers are deposited onto a conducting substrate completely at random.
The testing of nylon-4,6 electrospun films showed that thess almost weightless and invisible fabrics trap no less than 98% of airborne dust particles. For testing, the scientists used particles from 0.2 to 0.3 micron in diameter. This roughly corresponds to the dust that is not caught by the nasal pharynx, and penetrates the lungs causing a number of dangerous medical conditions. Submicron particles (< 1 micrometer in diameter) are the ones also used to test industrial and medical filters. To assess performance, resistance to airflow is tested as well.
Experiments to measure resistance have been made on singular samples so far. In real filters a multi-layer surface with a complex configuration is normally used. The experiments showed that the nylon-4,6 filtering material had the best properties out of all types of fabric previously described . In terms of interception extent to filter weight ratio and interception-resistance to airflow ratio, the new filtering material beats any existing equivalents by several times.
At first it looks like a ring sitting on a sheet of paper. In reality, it is a sample of the new fabric for filters. The small red spot on top of „l” letter is a spot wherea laser beam penetrates the film. Low intensity of dispersed light demonstrates high transparency of the new material. A transmission index of the new product is higher than that of a good window glass. The picture is courtesy of the researchers.
Speaking about possible applications of this material, the scientists claim it is more than the obvious air and water purification from particulate matter. Since the material surpasses glass in transparency, it can be used in biological research. For example, after pumping air or water through the new filter intercepted microorganisms may be directly observed right on the transparent filter under a microscope. Again, this effect is due to ultra-fine threads. Their thickness is significantly less than even visible light wavelength.
Source: Moscow Institute of Physics and Technology

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Testarea nedistructivă: Privind în interiorul compozitelor

Cercetarea utilizează compozite cu legături de înaltă calitate și altele în mod deliberat făcute cu legături mai slabe. Diferențele în rezultatele de a ajuta echipa îmbunătăți detectarea defectelor sau deteriorare. Un ecran de computer prezinta pete luminoase sau întunecate indică posibilele probleme care, și a realiza un grafic legăturile suprapuși adâncimea probleme potențiale la timpul indicat pe imagine.

Posted: Feb 01, 2016

Nondestructive testing: Looking inside composites

(Nanowerk News) Researcher David Moore holds a rectangle of hard carbon composite material, smooth with a faint woven pattern on its surface. The sample shows normal wear and tear until he turns it over to reveal a circular impact mark with cracks radiating from it.
The question for Moore, his Sandia National Laboratories colleague Timothy Briggs in California and their teams is whether the impact caused significant, hidden damage inside the composite. They’re developing nondestructive ways to detect damage in composites, using traditional medical inspection techniques such as X-rays and sonograms and advanced methods including infrared imaging, ultrasonic spectroscopy and computed tomography.
Sandia National Laboratories technologist Andrew Lentfer passes a roller probe over a composite as researcher David Moore checks data on a screen
Sandia National Laboratories technologist Andrew Lentfer passes a roller probe over a composite as researcher David Moore checks data on a screen. The nondestructive testing technique sends sound waves into the composite material, returning data with each swipe of the roller probe.
Sandia began studying composites several years ago to see whether the lightweight materials could be used in national security applications. While a composite in a cell phone needs to last only a couple of years, “typically materials for national security applications must survive for decades. This makes you think differently about where and why you would use a material,” said Moore, who works in the Structural Dynamics and X-ray/Nondestructive Evaluation department. “We need to study the lifecycle of a component. We tend to think deeply about the consequences of fracture or deformation and how we can verify what happened.”
The work supports many aspects of Sandia’s national security mission, including energy efficiency and performance improvements in lightweight vehicles or wind turbine blades, said Briggs of Sandia California’s Lightweight Structures organization.
Composites join together separate materials with different characteristics. They often consist of a soft polymer matrix with reinforcing fibers like carbon, Kevlar or glass. Composites can use bundles of thinner-than-a-hair carbon strands that yield a high strength-to-weight ratio. The final shape and strength is obtained after heating the part in an industrial oven that sets the polymer resin and yields the qualities necessary for a structural component.
Composites are increasingly important in aerospace and other industries because they’re strong and weigh less than metals. Most can be bonded to metal for such uses as aircraft wings, making planes lighter and less expensive to fly.
Outside surface of a composite doesn’t hint at what’s inside
“We have a rich history of understanding metals and their failure mechanisms,” Moore said. “Composite materials are very different.”
If a service truck backs into a composite aircraft fuselage, an examination of the impact site might not detect damage under the surface. That highlights the reason for nondestructive techniques that can fully evaluate how composites react in various circumstances.
The research team is assessing the accuracy of nondestructive methods and how they could be used on a production floor. “You have to know what could go wrong in the processing steps and how to circumvent those, and then you want to make sure if you’re going to make one or a hundred or a thousand that you’re making them the same way all the time,” Moore said.
“Once we establish the limits of detectability, the threshold of good, bad and questionable, we’ll be able to say, ‘We want this composite bonded to this material with a defined quality and it shall be inspected with this technique,’” he said.
Sandia’s Lightweight Structures Lab defines and consolidates materials to study, using particular stack sequences of composite material layers to tailor strength and stiffness. It works in concert with the National Security Campus in Kansas City, Missouri, in everything from developing process methods to building prototypes to qualifying designs for particular applications.
After making composites, the fabrication lab cuts out specimens for instrumented experiments — abusing the carefully made sample to study deformation, fracture and damage growth. Briggs “pulls, stretches, torques and crushes them. He performs these mechanical experiments so we can understand the fracture mechanisms around failure,” Moore said. “Then we try to detect some of those failure modes.”
Characterizing material properties helps computer modeling, simulation
“The fundamental characterization of composites measures material properties and structural characteristics, which in turn provides information to validate computer modeling and simulation,” Briggs said.
Data from these destructive tests is correlated with nondestructive evaluations from Moore’s team to understand what caused the material to respond the way it did, Briggs said. The effort hinges on close collaboration with Sandia’s materials characterization groups and modeling and simulation colleagues to help validate their computer-based simulations.
Composites must support a particular weight and size. “Anyone can build a structure to carry the load, but we have to design our structures to fit within a geometric envelope and be lightweight,” Briggs said. “We cannot simply over-engineer to unrealistic levels. We have to be very smart and efficient with our designs, yet provide enough margin for long-term reliability.”
Materials bonded in an oven or autoclave often have different thermal expansion rates — aluminum expands more than fiber-reinforced plastics, for example. Once a composite cools after curing, residual stresses can build up inside, particularly at interfaces. If the composite can’t handle those stresses, the bonds can fail.
Sandia is developing advanced techniques to complete sample inspections in less than 5 minutes in some cases. “This is a way to gain a lot of information very quickly about the quality of the bonds,” Moore said.
Team studies specific nondestructive techniques
His team uses the deliberately mistreated composites to assess such inspection techniques as advanced ultrasonics, flashed or active thermography and computed tomography.
Ultrasonic testing has been around for 60 years, but computers and other improvements now allow study of more complex applications. Technologist Andrew Lentfer demonstrates, scanning a piece of composite with a handheld ultrasonic roller that resembles a small paint roller with a hollow, water-filled barrel. As he scans the composite’s layers, a computer screen maps them in color: Yellow-green is OK; blue indicates weakness. Rollers can scan curved surfaces, even large ones like airplanes.
Fibers and interfaces in a composite scatter ultrasonic waves moving through the material. Moore compares it to ocean waves: “If a wave hits a rock face in the ocean it moves around it; if a wave washes up on the sand it gets absorbed; and if it hits a seawall the wave energy is redirected quickly. Those are the same fundamentals we investigate: ultrasonic energy moving through a composite matrix.”
Knowledge gained from characterizing materials helps develop new nondestructive techniques “so when we establish an inspection criteria, we have a better feel for what we can detect and what we cannot,” he said.
Flashed thermography, commercially available for more than 20 years, flashes very high-energy light onto a surface for 15 microseconds, then an infrared camera watches how the surface cools. The process takes only minutes.
“It’s very fast, but you have to understand the fundamentals of heat flow and how the material surface either gives off heat to its surroundings or transfers heat within itself,” Moore said.
Studies use good, not-so-good composites to test differences
The research uses composites with high-quality bonds and others deliberately made with weaker bonds. Differences in results help the team improve detection of defects or damage. A computer screen shows light or dark spots indicating possible problems, and an overlaid graph ties the depth of the potential problem to the time indicated on the image.
“The question becomes, is that a concern? Is that a crack or not?” Moore said. “We’ll be able to answer those questions. If the defect propagates deep into the material, we may not detect it. It’s wise to understand the capabilities of the technique and then perform the math and science behind it.”
Computed tomography systems are efficient for finding small defects. The technique rotates a sample 360 degrees while taking 1,000 images, similar to a medical CT scan, and generates an image from each thin slice of the object. Since each image taken is two dimensional, computer algorithms reconstruct, calculate, locate and display everything to represent the object in three dimensions.
“Once the 3-D image is reconstructed, you look at the front surface and then start moving through the thickness to view what is below the surface,” Moore said. “This technology gives us a knowledge baseline and validates how the other techniques are performing.”
Sandia must ensure designs meet requirements by specifying and qualifying an inspection technique, and now is writing inspection procedures for the National Security Campus, Moore said. “Once we establish criteria and limits of acceptability, the product definition can be established,” he said.
Source: Sandia National Laboratories

Read more: Nondestructive testing: Looking inside composites