Archive for self-healing
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US firm uses solar power to recover oil reserves
A new technology to increase oil production is being tested on one of US’s oldest oil fields in one of the largest demonstration projects of its kind. The new project was launched by Chevron Technology Ventures at the Coalinga Field in California. More than 7,600 mirrors are being used to focus the sun’s energy onto a solar boiler to produce steam that can then be injected into oil reservoirs to enhance oil recovery.
Professor Roland Winston and his team of student researchers have designed and developed a system that gathers and concentrates sunlight onto specially made collector tubes. The heat generated can then be transformed using existing technology for cooling, heating and a number of other potential uses. The key factor in their design is this: The collectors are entirely stationary. Typically, solar collectors must move and track the sun to achieve optimal energy production, necessitating additional equipment that can be costly to install and complex to maintain.
Global greenhouse gas emissions hit an all-time high in 2010
Global greenhouse gas emissions increased by 5.8% in 2010 to hit an all-time high of 33 billion tonnes, as continued growth in developing countries swamped both greater use of renewable power and gains in energy efficiency, according to an analysis by the European Commission’s Joint Research Centre and the PBL Netherlands Environmental Assessment Agency. Emissions in China and India increased by 10% and 9%, respectively, compared with 3% in the United States.
A team of scientists from the Catalan Institute of Nanotechnology, ICREA, and Universitat Autonoma de Barcelona investigated the properties of a special kind of sudoku, made by assembling tiny molecules into a 3×3 square array The result is not a mind-boggling game, but a detailed picture of how each molecule interacts with its neighbors and conducts electricity when squeezed between two metallic electrodes.
Mirage effect from thermally modulated transparent carbon nanotube sheets (pdf)
The single-beam mirage effect, also known as photothermal deflection, is studied using a free-standing, highly aligned carbon nanotube aerogel sheet as the heat source. The extremely low thermal capacitance and high heat transfer ability of these transparent forest-drawn carbon nanotube sheets enables high frequency modulation of sheet emperature over an enormous temperature range, thereby providing a sharp, rapidly changing gradient of refractive index in the surrounding liquid or gas.
How fuel cells can help cell phones in a hurricane
A cleaner alternative is emerging. Wireless service providers increasingly are investing in fuel cell systems for backup power. Fuel cells use hydrogen and oxygen, the molecules that create water, to produce electricity with no pollution. We see it as a green alternative that is on the rise. Clean and energy efficient fuel cells can help reduce CO2 emissions by 50 percent as well as decrease other toxic emissions and deliver additional environmental and efficiency benefits. They also are very quiet, less costly to maintain and are not targets for theft.
Pump may help materials self repair
Artificial microvascular systems can be integrated into structures and materials to aid in self-repair when there’s damage, such as cracks in a coating applied to a building or bridge. Until now, the systems have relied on capillary force to transport healing agents. The team of researchers at the Beckman Institute of the University of Illinois has developed different methods for self-healing, including microvascular systems for self-repair of polymers. The vascular system works when reactive fluids are released in response to stress, enabling polymerization that restores mechanical integrity.
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A method to defeat damage propagation autonomously in self-healing materials
a) Digital image correlation showing the recovery strain due to the shape memory effect around the crack location.
b) Schematic of complete flow for the combination of active toughening with active healing. Credit Garcia, Lin and Sodano; AIP.
Researchers out of the Multiscale Adaptive Sensors and Structures Lab at Arizona State University have developed an interesting but relatively simple approach to self-healing material, one that somewhat mimics the natural healing mechanism found in bones.
Other approaches to self-healing materials have been demonstrated. The ones I’ve seen with concretes and polymers have depended on a chemical reaction that is triggered by a physical force that then cause the release of a binding agent. Biological systems however, don’t just heal: They also typically act swiftly to stop the spread of damage. Bones, for example, are able to respond to, and minimize, damage through mechanisms familiar to ceramists and other materials scientists and engineers: crack deflection, crack bridging, microcracking ad viscoplastic flow. The body responds to bone damage in a way that simultaneously limits the spread of the injury and re-toughens the damaged region.
The MASS lab group, led by Henry Sodano, use a similar concept in a novel autonomous system, based on shape memory polymers containing a closed-loop fiber optic network, that is the first SHM approach I have seen that successfully pairs healing with a method to prevent damage propagation.
Generally speaking the way their system works is that when the polymer is damaged, one or more fractured fiber optics have reduced transmission. This signals that damage has occurred and immediately initiates a high-power laser diode that provides photothermal energy at the fracture sight. The author, in a paper that appears in the Journal of Applied Physics, describe the process:
“The transmission loss from the fractured fiber optic obtained via a thermal power meter not only signifies a crack in the material, but also initiates a control algorithm to adjust the amount of thermal energy applied, thereby reducing the modulus at the crack location and dissipating the fracture energy. The technique only heats only the polymer locally around the crack tip. This preserves the global properties of the material while adding significant toughness. The shape memory property of the shape memory polymer SMP also allows the crack to be closed such that other healing modalities can be used … The autonomous adaptive material also demonstrated that it could effectively reverse the strain induced by the crack while altering the crack front and effectively healing the induced damage.”
The MASS lab is also doing work in other interesting areas including Active Structural Fibers (SiC fibers with piezoceramic shell for structural health monitoring, power harvesting, vibrational control, etc.), active piezoelectric nanocomposites (to increase the electroelastic properties of the nanocomposites) and multifunctional piezoelectric carbon fibers (piezoceramic shell on carbon fiber for sensors and actuators).
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Materials stories that may also be of interest
At the end of each week, I end up with a list of a bunch of stories I started to write about, or started to investigate or didn’t even get that far even though the topic looked intriguing, but, I had a meeting to go to …
Anyway, it’s Friday, and rather than have these stories evaporate into the ether, I’ve close out each week by providing some raw links to some of these orphan tales. Check ‘em out:
New solar thermal tower power plant being built that requires only sun and air
Making materials mend: Self-healing in action
The money man behind America’s rare earth minerals
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Rhode Island grad student makes progress in new self-healing concrete approach
Credit: University of Rhode Island
While working on her master’s degree, University of Rhode Island grad student Michelle Pelletier says she has come up with an effective and inexpensive method of creating self-healing concrete using embedded microencapsules of sodium silicate.
I’ve written about self-healing concrete in the past, particularly the ground-breaking work of Victor Li at the University of Michigan. Just to review the problem, although concrete is quite durable, it tends develop cracks when it is overstressed, compressed or flexed. Currently, not much can be done about major cracks caused by, for example, collisions or earthquakes, but many researchers have been focused on micro-sized cracks that are found much more frequently. These micro cracks can be the starting point for larger cracks and material failure. Thus, if these tiny cracks can be “healed” soon after formation, the effective life of concrete structures can be greatly extended.
Pelletier’s method involves mixing a small amount (about 2 %) of the microencapsulated sodium silicate into the concrete mix. Then, as small stress cracks begin to form, the capsules burst and release the healing agent into the adjacent areas. Pelletier says the sodium silicate reacts with the calcium hydroxide naturally present in the concrete to form a calcium-silica-hydrate product to heal the cracks and block the pores in the concrete. She says the resultant gel-like material forms a “scar” that that hardens in about one week.
In comparison tests with normal concrete, Pelletier told me that healing mix recovered 26 percent of its original strength – after being stressed to near breaking – versus just 10 percent recovery by the standard mix.
Pelletier says that’s good – but no good enough. “The 2% addition to the mix as a good start, but I’d really like to see a system that restores 75% of the concrete strength. We started with a very small addition, so I think that goal is possible.” She cautions that it may be several years before this approach is ready for commercialization.
Regarding the potential costs of her new concrete mix, Pelletier believes doesn’t think the microencapsulated sodium silicate will add much to the price. “Lots of additives are already being put into concrete,” say Pelletier. “The process of encapsulating the sodium silicate isn’t complicated and the raw materials are very cheap.
Pelletier says the schools research on self-healing concrete started several years before she arrived and was initially funded by the Rhode Island Department of Transportation. She says URI faculty recruited her to work on the project because of her chemistry background.
Although she plans on gaining work experience instead of continuing with grad school after she is finished with her MS program, she says URI will continue the research, and also investigate whether sodium silicate can serve to inhibit the corrosion of the steel rebar and mesh often placed in concrete.
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Video of the week II - Self-healing concrete
Following on the heels of our first Video of the week, this is look at Victor Li’s latest innovation: self-healing concrete.
Cement and Concrete Research is soon to publish a paper by Li, who is a professor in material science and engineering at the University of Michigan, that describes a type of concrete that forms many tiny cracks when overloaded instead of a few large ones, leading to a process in which the concrete effectively “heals” itself.
Even after a 3 percent tensile strain, Li’s samples recovered nearly all of its original strength. “We found, to our happy surprise, that when we load it again after it heals, it behaves just like new, with practically the same stiffness and strength,” Li said. “Self-healing of crack damage recovers any stiffness lost when the material was damaged and returns it to its pristine state. The material can be damaged and still remain safe to load.”
Li and his research group have spent more than a decade developing what he calls engineered cement composites. An early version of this ECC is what made the bendable concrete possible. The current version of ECC keeps cracks under 60 micrometers. The cracks, though small, expose small amounts of unhydrated cement in the concrete. When the concrete is subjected to water and carbon dioxide, it forms a tiny calcium carbonate “scar.” Li found in his lab that between one and five wet-dry cycles are needed to reach final level of healing.
This kind of thing is always great stuff, but cost-benefit analyses often deflate some great innovation. Here, the question is whether a signficant extension in the lifespan of something like a concrete highway can offset the premium paid for ECC-enhanced materials that at one point were looking like they would cost three-times as much as traditional concrete. Nevertheless, U-M says it is is pursuing patent protection for the intellectual property, and is seeking commercialization partners to help bring the technology to market.
Li is supposed to be delivering a keynote address on self-healing concrete at the International Conference on Self-Healing Materials in Chicago in June 2009.
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