Carbon nanotube composite material could replace carbon fiber

The ribbon-like material being wound onto a spool, while being sprayed with polymer and stretched

When people need a material that’s strong yet lightweight, they usually look to carbon fiber. In the near future, however, they may instead choose to go with composite materials made from stretched carbon nanotubes. These materials could theoretically offer the same strength as carbon fiber at one-tenth the weight, or the same weight at ten times the strength. Researchers from North Carolina State University have recently succeeded in creating such a composite.
According to the university, scientists have spent decades trying to achieve the four goals that must be met in order to create CNT (carbon nanotube) composites – the nanotubes must be long in order to effectively carry loads; they must be aligned in rows; there must be a high ratio of CNTs to the polymer or resin used to hold them together; and, in order for the material to bear weight evenly, the nanotubes must be as straight as possible.
NC State’s Dr. Yuntian Zhu, a professor of materials science and engineering, is reportedly the first person to come up with a method of meeting all of these requirements.
The process begins by growing an array of long, skinny carbon nanotubes out of a flat substrate. Because the nanotubes aren’t rigid, they tend to flop over and lean against one another. The CNTs at one end of the array are then pulled sideways, causing all the other nanotubes to topple over in the same direction. As a result, they end up all being aligned.
The aligned array is then wound onto a rotating spool, simultaneously being stretched and being sprayed with a polymer solution that keeps the nanotubes bound together. This respectively results in a straightening of the nanotubes, and a high CNT-to-polymer ratio.
The finished product is a ribbon-like material, several bonded layers of which could supposedly be used to build anything from bicycle frames to aircraft. Because of the CNT-stretching process, that material has 90 percent more tensile strength and is 100 percent stiffer than it would be otherwise. Additionally, its thermal conductivity is almost tripled, while its electrical conductivity is boosted by 50 percent.
A paper on the research conducted by Zhu's team was recently published in the journal Materials Research Letters.
Source: North Carolina State University

GeS “nanoflowers” could blossom in next-gen solar cells

The GeS 'nanoflowers' have petals only 20-30 nanometers thick, and provide a large surface area in a small amount of space

Researchers have already turned to the humble sunflower for inspiration to design more efficient Concentrating Solar Power (CSP) plant layouts, and now a team from North Carolina State University has developed a “nanoflower” structure out of germanium sulfide (GeS) that shows great promise for use in energy-storage devices and more efficient solar cells. The secret is the material's ultrathin petals that provide a large surface area in only a small amount of space.
The researchers created the flower-like structures by first heating GeS powder in a furnace until it began to vaporize. The vapor is then blown into a cooler region of the furnace, where the GeS settles into a layered sheet measuring just 20 to 30 nanometers thick and up to 100 micrometers long. A flower-like structure similar to a carnation or marigold is formed as additional layers are added causing the sheets branch out from one another.
GeS is a semiconductor material that is attractive for use in solar cells because it is inexpensive and non-toxic, while its atomic structure makes it good at absorbing solar energy and converting it into useable power. But solar cells aren’t the only potential applications for the nanoflower technology.
“This could significantly increase the capacity of lithium-ion batteries, for instance, since the thinner structure with larger surface area can hold more lithium ions,” says Dr. Linyou Cao, an assistant professor of materials science and engineering at NC State and co-author of a paper on the research. “By the same token, this GeS flower structure could lead to increased capacity for supercapacitors, which are also used for energy storage.”
The team’s paper is published in the journal ACS Nano.
Source: North Carolina State University

New tech converts regular paper into powerful medical diagnostic tool

 

Researchers at the University of Washington have found a way to turn scraps of common office paper into a powerful diagnostic too

A group of researchers at the University of Washington has found a way to isolate and identify medically interesting molecules using little more than scraps of office paper, a Ziplock bag and a cheap diluted solvent. If properly developed, the system – which requires minimal costs and know-how to build and operate – could be made to administer a wide range of medical tests nearly free of charge.
Healthcare can come at a steep price: according to the American College of Physicians, the costs of unnecessary medical testing in the U.S. alone have soared to upwards of US$200 billion per annum – the grand total being much higher. With such a wide margin for improvement, a lot of research is going into putting a dent in this figure in an effort that could not only reduce expenses at home, but also do a great deal toward raising the standard of medical care in developing (or simply cash-strapped) countries.
One way to tackle the problem is to use cheap but effective materials, such as specially treated paper. Today, most paper-based diagnostics are made from nitrocellulose, a sticky membrane that can detect proteins, DNA or antibodies in the immune system and is used, among many other things, in home pregnancy tests.
Researchers at the University of Washington have worked out a way to replace nitrocellulose with much cheaper scraps of paper – the kind you would find in a typical office setting. When properly treated, the paper can detect a wide range of chemically interesting molecules (even more than nitrocellulose can) and could serve as a virtually zero-cost framework to build devices like home pregnancy tests that work for malaria, diabetes and other diseases.

The team filled a Ziplock bag with a 10 percent solution of divinyl sulfone – a cheap industrial solvent that is commonly used as an adhesive – and added a stack of paper. They then shook the mix for a couple of hours, extracted the paper from the bag, and let it out to dry.
When treated this way, the paper acquires a very interesting property: it normally feels smooth to the touch, but becomes sticky in the presence of chemicals that are of medical interest – proteins, antibodies and DNA, just like nitrocellulose, but also sugars and the small-molecule drugs used to treat most medical conditions.
To test their concept, the researchers printed an invisible pattern of galactose onto a treated scrap of paper. They then exposed the paper to fluorescent ricin, a poison that sticks to galactose, and detected that the poison was present in the exact same pattern in which the galactose had just been printed. This showed that the paper had indeed become sticky in the presence of a galactose, retaining it in place.
"We wanted to make the system as independent of the end applications as possible, something to not just ask a single question but many personal health questions,” assistant professor Daniel Ratner, the main author of the study, commented. “‘Is there protein in the urine? Is this person diabetic? Do they have malaria or influenza?'"
After producing this simple but effective framework, the researchers are hoping that other groups will build on their work to develop actual diagnostic tests in the near future.
A paper detailing the study was published in the journal Langmuir.
Source: University of Washington

Heat-conducting composite pipes could make desalination less costly

Fraunhofer's polymer-copper desalination pipes

In a typical desalination plant, pipes made from titanium or other expensive types of metal are an integral part of the process. Now, however, scientists have created a new type of piping material that is much cheaper to produce – potentially making desalination possible in countries that previously couldn’t afford it.
Ordinarily, hot water or gas is pumped through pipes composed of titanium or a high-alloy steel. That piping conducts heat from the water or gas, which is transferred to its outer surface, causing it to become hot. When seawater is then sprayed onto the outside of that hot pipe, its pure water content evaporates and is collected, while its salt content forms into a sludge on the pipe.
In an effort to come up with a less costly heat-conductive piping material, researchers from Germany’s Fraunhofer Institute for Manufacturing Technology and Advanced Materials combined a polymer with copper microfibers – the mix is as much as 50 percent copper, by volume. The resulting composite can reportedly still be processed like regular plastic, yet it conducts heat like metal.
Pipes made from the material are now being tested in a desalination plant, where gas heated to 70ºC (158ºF) is continuously being pumped through them. The scientists plan on assessing the material’s thermal conductivity along with its corrosion resistance, then tweaking the mixture as needed.
Source: Fraunhofer

 

A graphene coating can make copper nearly 100 times more resistant to corrosion

Following on from news out of the University at Buffalo earlier this year that a graphene varnish could significantly slow the corrosion of steel, researchers from Monash and Rice Universities have used a graphene coating to improve copper’s resistance to corrosion by nearly 100 times. The researchers say such a dramatic extension of the metal’s useful life could result in significant cost savings for a wide range of industries.
Metals are often treated with polymer coatings to help prevent corrosion, but their protective capabilities can be easily compromised by scratches. Although graphene is only one-atom thick and is invisible, not changing the appearance or feel of the metal, it is exceptionally strong and much harder to damage. This gives the material enormous potential for protecting metals even in harsh environments.

Using chemical vapor disposition, the researchers applied the graphene coating to copper at temperatures between 800 and 900 degrees Celsius (1,472 and 1,652° F). They then tested it in saline water and witnessed resistance to corrosion almost 100 times that of untreated copper.
“We have obtained one of the best improvements that have been reported so far,” said study co-author Dr Mainak Majumder. “Other people are maybe five or six times better, so it’s a pretty big jump.”
The researchers are now expanding their research to see if the technique produces similar results with other metals. They are also looking for ways to apply the coating at lower temperatures in an effort to simplify production and enhance the technique’s market potential.
The team's paper appears in the journal Carbon.
Source: Monash University

Black silicon could boost efficiency of traditional solar cells

 

Dark silicon could improve efficiency in traditional solar cells by harvesting energy in the infrared spectrum

Researchers at the Fraunhofer Institute for Telecommunications have developed a system that allows solar cells to effectively harvest energy from the infrared spectrum, tapping into a source of energy that in the past has mostly been out of reach. The new technology, which promises to work well with commercially available solar cells, has the potential of becoming a standard in the solar panels of tomorrow.
When photons hit the surface of a solar cell, the energy they carry can be absorbed by a semiconductor. If the energy absorbed is higher than a set threshold – which is known as the energy gap, and depends on the semiconductor used – electrons are freed from the semiconductor and can be used to generate an electric current.

The energy carried by a photon is proportional to its frequency. In silicon solar cells, photons in the infrared often don't carry enough energy to produce electricity, and IR light simply passes through the cell, unused. Red photons are carrying just enough energy to knock an electron loose and photons in the blue spectrum or beyond (UV light) are carrying too much energy – so part of it is used to free a single electron, but the rest is wasted as heat. The inability to fully extract the energy carried by a photon is the main reason why solar cells are so inefficient.
Over the past few years, researchers have produced solar cells that can absorb infrared and ultraviolet light more effectively. Now, researchers at Fraunhofer Institute have come up with a straightforward way to capture more energy from the infrared spectrum, developing something that could very well become standard technology in the solar cell of the near future.
The research is based on absorbing infrared light using what's known as black silicon. This material is made by using precision lasers to "zap" sulfur atoms into the silicon lattice in well-defined patterns.
The sulfur lowers the energy gap, and therefore allows much lower-energy photons to free electrons from the semiconductor. In theory, this should boost the solar cell's efficiency; unfortunately, though, the smaller energy gap also makes it easier for electrons to "travel" in the opposite direction, causing electricity to be lost once again.
The researchers at Fraunhofer set out to address this issue and came up with a conceptually simple yet ingenious solution. They chose to change the patterns of laser pulses that drive sulfur atoms into the silicon lattice, altering their conformation to maximize the number of electrons that can climb "up" the energy gap and become conductive, while minimizing the number of electrons that can go back "down" it.
Prototypes of the cells have shown that the mechanism can double the efficiency of black silicon, but the researchers are still looking to identify the configuration of sulfur atoms that can result in the best performance.
The next step will be to embed the cells with already existing commercial technology, and the good news is that the two are very much compatible, and seem to complement each other. By simply removing the back cover of a traditional solar cell and incorporating a layer of black silicon, the team has found that they can increase efficiency of such panels by about one percent.
The researchers are now planning to market a laser system that manufacturers can use to produce the black silicon themselves and include it in their products as standard.
Source: Fraunhofer HHI