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The thrill of victory and the agony of defeat: Some of each for CNTs
Rice University researchers, Robert Vajtai, Enrique Barrera and Yao Zhao created a conductive cable from iodine-doped nanotubes capable of carrying household current. Credit: Jeff Fitlow/Rice University
Showing how something works is more effective than telling how it works. With the assistance of a fluorescent lightbulb, Rice University researchers demonstrated successful substitution of standard copper wiring with a carbon nanotube cable.
Using double-walled CNTs spun into a cable several centimeters long, a recent Rice PhD, Yao Zhao, constructed a rig that allowed him to run electricity through a CNT cable to a fluorescent lightbulb. The lightbulb was left “on” for several days without interruption and without any sign of degradation in the CNT cable. Zhao is in Enrique Barrera’s research group. CTT recently interviewed Barrara as part of the MSE football series.
The cable was constructed of billions of double-wall CNTs and fabricated by collaborators at Tsinghua University in China. The cables were doped with iodine to increase their conductivity, and Zhao found they could be tied together without losing conductivity.
In a Rice press release, Barrera says the cables have the potential to be just as effective as metal wiring, at about 1/6 the weight. He also said that the chemical processes used to make lab-scale cables will become part of a larger process that starts with raw materials and produces a steady stream of nanocable. The next step for the team is “to make longer, thicker cables that carry higher current while keeping the wire ligtweight.”
The work was published in the Nature journal, Scientific Reports.
Meanwhile, NIST has been studying the reliability of CNTs for electronic devices with the goal of developing measurement and techniques to test fabrication quality and reliability.
Recession and clumping, in gold electrodes after NIST researchers applied 1.7 volts of electricity to the carbon nanotube wiring for an hour. NIST reliability tests may help determine whether nanotubes can replace copper wiring in next-generation electronics.Credit: M. Strus; NIST
Possibly relevant to the Rice work, NIST researchers have been studying failure in CNT networks, where electrons physically jump from one CNT to another, and found that failure seemed to happen between nanotubes, which is the point of greatest resistance. In a press release, NIST postdoctoral researcher, Mark Strus said that by monitoring the initial starting resistance and stages of degradation, it was possible to predict whether the resistance would degrade gradually or sporadically. Gradual degradation is preferred because it allows for operational limits to be set for devices. NIST has developed some electrical stress tests “that link initial resistance to degradation rate, predictability of failure and total device lifetime. The test can be used to screen for proper fabrication and reliability of nanotube networks.”
Also from NIST, a study of CNT interconnects between gold electrodes found that the CNTs carried very high current densities for awhile, but degraded under constant current. By about 40 hours, the edges of the metal electrodes receded and clumped, leading to device failure. Further NIST research is focusing on the intersections between CNT and metals, as well as between different CNTs. In th press release Strus said, “The common link is that we really need to study the interfaces.”
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Materials football game of the week: Purdue vs. Rice
The Game
Purdue at Rice
Sept. 10, 3:30 p.m., ET; Houston, Texas
Rice begins its 100th football season with a golden “NASAversary” celebration commemorating its 50-year collaboration with the NASA Johnson Space Center in Houston. In a September 1962 speech at Rice Stadium, President John F. Kennedy said famously, “We choose to go to the moon in this decade and do other things, not because they are easy, but because they are hard.” The astronaut who embodied the country’s answer to that challenge was Purdue graduate, Neil Armstrong. Together Purdue and Rice have produced 60 astronauts, all of whom trained in Houston.
Purdue enters the fourth meeting of these squads with a 2-1 series lead. The last time these teams met was in 1998 when a relatively unknown Texan, Drew Brees, led the Boilermakers to a 21-19 victory in West Lafayette.
My pick? Purdue by a touchdown.
The home team
Rice University, Mechanical Engineering and Materials Science
Rice University is well known for its research programs in nanomaterials and composite materials, and in a way, the undergraduate materials engineering program mirrors that strength: It is small and mixed into a larger department to which it makes strong contributions.
Senior Henry Neilson helped build a nano-fatigue tester to use on flexible electronics. Credit: Rice University
The undergraduate curriculum has one eye on fundamental science and the other on advanced applications. As Prof. Enrique Barrera describes, “We are a structure-property relations program with significant teaching in nanotechnology.” That’s what drew senior Robby Palm into the program, “I liked MSCI because it’s sort of the “interdisciplinary” engineering field—the focus on relating macroscale observations/behavior with atomic-scale events/phenomena allows you to work in a wide variety of arenas.”
And, Rice works hard to get its undergrads into a wide variety of arenas. Locally, there are strong connections with the Medical Center, Schlumberger, Hewlett-Packard, Texas Instruments and the Johnson Space Center and its contractors. Students work with these companies during their senior design project. Simulating a real-world job hunt, Barrera says seniors “have to make the connection with a prospective company, explain their role and how much time will be involved.” “Even the shy students,” he says, “learn not to rely on email and how to make face-to-face contact.”
Long before senior year undergrads are offered a cornucopia of hands-on experiences. The Oshman Engineering Design Kitchen is an innovative industry-university incubator where students participate in all aspects of design and get to use CAD/CAM, rapid prototyping, a fully equipped machine shop, etc.
Undergrads are active in professors’ research groups, and not just in materials. Junior Olivia Derr said in an email, “…Materials are in everything, so you could get involved in electrical or mechanical or chemistry or whatever else you wanted.”
Derr and Palm found that working in a research group can take them in unexpected directions. Both spent a summer in China working on alternative energy projects in the labs of their professors’ Chinese collaborators. The next step for most Rice BS materials graduates is graduate school.
The Department of Mechanical Engineering and Materials Science has about 145 undergraduates, and about ten of the juniors and senior have declared themselves as materials science majors. (Rice does not do an official head count until after the must-declare deadline at the end of the sophomore year.) There are 16 faculty and a little over 90 graduate students. The most recent addition to the materials faculty is Edwin (Ned) Thomas, who had been chair of the MIT’s materials science department and became dean of the George R. Brown School of Engineering in July. Faculty engaged in ceramic science research are Enrique Barrera and Andrew Barron.
An unusual feature of the department is that it also offers a BA in materials science. Barrera explained, “The BA degree is designed for students planning on law school, medical school or some other professional school. The BS degree is for those who want to stay in technical careers.” The BA also makes it easier for students to choose materials science as a second major, he said.
According to the 2012 Princeton Review, Rice boasts having the happiest students for the third consecutive year, but they may have some of the most ferocious, too. Derr shared in an email that “Powderpuff football is huge on campus.” She was “knocked out” last year and had to sit out half the season, but the wide receiver/cornerback admitted she is “really excited to get back out there this year and get the Violent Femmes back in the playoffs.” No doubt, gridiron victory will make her even happier.
The visitors
Purdue University, Materials Engineering
SURF’s up! The lack of big water in West Lafayette, Ind., notwithstanding, it’s something returning Purdue engineering undergrads might be heard saying at the end of the summer if they had participated in the Student Undergraduate Research Fellow program on campus.
Senior Lisa Behrens describes her senior project to Purdue alum and astronaut, Michael McCulley. Credit: Purdue University
The 1,900 or so incoming first year engineering Boilermakers might be confused at first, but not for long. The first-year experience of engineering is carefully constructed to guide students through a process of investigation and discovery. In fact, no freshman at Purdue has a specific engineering major; all are required to learn about each department and each branch of engineering before making a choice.
This approach is an advantage for departments, such as Materials Engineering, says Vicki Cline, undergraduate advisor. “Lots of students haven’t heard of materials engineering before. A lot of students interested in chemical engineering come to materials because it is more hands-on. They want to make something.”
Through a series of seminars, open houses, faculty presentations and labs, freshmen learn about the department. Cline says “Our undergraduates are the best recruiting tools we’ve got. They are very engaging, very excited and satisfied with their major. When freshmen encounter them, it’s like ‘wow’!”
Cline says the advantage of Purdue’s first year approach is that the retention rate of materials majors is very high, “If students leave the major it is almost always because they have a whole different interest. Most transfer to management.”
The current sophomore–junior–senior enrollment in materials engineering is 130. The department has 23 tenure-track faculty and just over 80 graduate students.
The materials engineering program is one of the most lab-oriented programs on campus and is not limited to coursework. Undergraduates are encouraged to get involved in research programs like SURF. Cline says the department considers it a priority because it helps students evaluate graduate school as a post-graduate option, and it helps guide their technical elective choices.
Prof. Carol Handwerker (ACerS Fellow and former member of the Society’s board of directors) notes that faculty benefit, too, from having undergrads in the lab. For one, they provide real-time feedback about teaching and seeing connections between the lecture hall and the physical world. She also says, “Undergrads are more adept at using programs like MATLAB and Mathematica. They are good at working with GUI interfaces and creating tools for the whole group.”
A team approach is used for the senior research project. Groups of 4-5 students spend the fall term working with their industry sponsor to study a problem via site visits and plant tours. They study the problem and generate a proposal. Then, in the spring, they collect samples, analyze data, etc. and present the project to the industry sponsors and peers. As would be expected in the Midwest, the program sponsors are largely from the heavy manufacturing sector: Cummins Engine, Rolls-Royce, Arcelor-Mittal, Corning, Alcoa and others.
The materials department ascribes to the concept of the “global engineer,” and has study abroad programs established with Imperial College in London, Tohoko University in Sendai, Japan and an internship program with KTH in Stockholm.
It should also be noted that Purdue is a partner institution, through its Civil Engineering Department, in the Center for Advanced Cement-Based Materials, and has a number of faculty and programs with a cements focus.
In general, the most popular course, by far, is a wine appreciation class taught by the food science department. Competition to get one of the 450 spots each semester is reportedly fierce even though the course is very rigorous, covering geography, history, economics, marketing and, of course, sampling.
Purdue does not offer a music major, so the 350-piece Boilermaker Marching Band is comprised of undergrads from all over campus, and quite a few materials engineering students are involved. In 2010 it was the first Big Ten band to be invited to march in the Macy’s Thanksgiving Day Parade.
Faculty involved in ceramic materials research include Handwerker, John Blendell, Rod Trice, Kevin Trumble, Elliott Slamovich, Edwin García, Carlos Martinez and Lia Stanciu.
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Video of the week: Rice University demos technique to ‘write’ supercapacitors on sheets of graphite oxide
A team led by Rice University professor Pulickel Ajayan has been experimenting with the property of graphite oxide to act as an ionic conductor when hydrated. One of the “tricks” they discovered is that they could use this property to make a sheet of GO into a working supercapacitor by writing patterns into it with a laser.
The laser changes GO into reduced graphite oxide. They say the resulting supercapacitors withstand thousands of store–release cycles.
According to a news release from Rice, the investigators didn’t expect to find that hydrated GO can hold ions and serve as a solid electrolyte and an electrically insulating separator. ”[W]e’re able to convert a sheet of GO into a supercapacitor without adding anything,” says Ajayan. “All you need are a pattern and the electrodes, and you have a device. Of course, the devices also perform in the presence of external electrolytes, which is even better. I think you’re going to see a lot of tiny devices that need smaller power sources. Intermediate-sized devices might also be powered by this material; it’s very scalable.”
Wei Gao, graduate student and lead author of a paper recent paper published in Nature Nanotechnology (doi:10.1038/nnano.2011.110) (and one of the stars in the above video), says in the release, “This is quite easy, as GO soaks up water like a sponge and can hold up to 16 percent of its weight.”
Gao and her coauthors say the performance of their supercapacitor compares favorably with existing thin-film microsupercapacitors.
Ajayan discourages comparisons to bulk supercapacitors, but says it would be fairly easy to put these thin devices in an array and predicts in the video that with such an assembly, “Ultimately we could get pretty good power.”
Rice says the research opens the way to interesting possibilities, including devices for use in fuel cells and lithium batteries.
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Materials stories that may also be of interest
Check ‘em out:
Low-cost system spots failing bridges; new sensor technology helps make bridges safer
Rice University researchers ‘armchair’ nanotubes could improve power grid’s efficiency
Russia offers Germany help on rare earths supply
Centre for Sustainable Energy Technologies invents heat-regulating building material
GE Lighting acquires Lightech, a technology leader in LED drivers and $10 million and GE collaboration light way for growth of Nuventix, maker of LED cooling technology
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Rice group: Silica + titania = cheap, green, improved water purification
Tanzania water source. Credit: Bob Metcalf
I don’t have enough historical perspective to know if this is truly a eureka moment or not, but a group from Rice University reports that adding a small amount of silica (or another inexpensive silicon source) can amp up the anti-viral, anti-bacterial power of titanium dioxide for producing disinfected drinking water.
The researchers Huma R. Jafry, Michael V. Liga, Qilin Li and Andrew R. Barron report in Environmental Science & Technology that, at least in non in situ testing with model bacteriophage MS2, adding a dose of silica to a commercial TiO2 product, P25, triples the material’s ability to kill viruses and increases the adsorption of viruses onto P25 nanoparticles.
Liga’s website mentions that researchers are looking at several TiO2 dopants, and have also been testing the improved photocatalyst against a model organic pollutant, congo red dye, and discusses the possibility of even stronger effects:
“Our composite catalysts have been found to inactivate viruses over five times faster than the base titanium dioxide material. Future research will be focused on inactivating pathogenic adenovirus, which is of concern to the drinking water treatment industry. We will also attempt the construction of a lab scale treatment reactor employing the photocatalyst.”"If you’re using titanium dioxide, just take it, treat it for a few minutes with silicone grease or silica or silicic acid, and you will increase its efficiency as a catalyst,” he said.
In a news release from Rice, Barron says they have supercharged the performance of the titania with little increase in cost. “Basically, we’re taking white paint pigment and functionalizing it with sand,” he says.
Barron and the others say they are setting the performance bar fairly high by looking at how the silica-titania mix would perform against Yangtze river contamination. “We chose the Yangtze River as our baseline for testing, because it’s considered the most polluted river in the world, with the highest viral content. Even at that level of viral contamination, we’re getting complete destruction of the viruses in water that matches the level of pollution in the Yangtze,” he says.
A couple of the researchers admit they accidentally stumbled into this revelation. Liga says he noticed a jump in the TiO2 performance when then-grad student Huma Jafry was heating a titania solution in a sealed flask. Jafry reported that she had done nothing knowingly different, but eventually she and Liga realized it might be the silicone grease used to lubricate the sealing stopper, a hypothesis they later confirmed.
Barron attributes the improved power of TiO2 to band bending that creates a path for electrons freed by the UV to react with water to create a surge of hydroxyl radicals. “Because the silicon-oxygen bond is very strong, you can think of it as a dielectric. If you put a dielectric next to a semiconductor, you bend the conduction and valence bands. And therefore, you shift the absorption of the ultraviolet (used to activate the catalyst) . . . If your conduction band bends to the degree that electrons find it easier to pop out and do something else, your process becomes more efficient,” he says.
“In places where they don’t have treatment plants or even electricity, the SODIS [solar disinfection - ed.] method is great, but it takes a very long time to make water safe to drink,” says coauthor Quilin Li. “Our goal is to incorporate this photocatalyst so that instead of taking six hours, it only takes 15 minutes.”
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