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Tech Front: New Carbon Nanotubes May Boost Battery Life

 

A team of researchers at the University of Wisconsin (Madison, WI) have discovered high-performing carbon nanotubes that may lead to the development of improved battery life for flexible electronics and also for military and industrial applications.

The research team, led by materials science Associate Professor Michael Arnold and Professor Padma Gopalan, recently released their results in a paper published in the journal ACS Nano. According to the UW-Madison scientists, the carbon nanotube transistors are the highest-performing ever discovered, with an on-off ratio that is 1000 times better and conductance that is 100 times better than any other carbon nanotube transistors.

“Carbon nanotubes are very strong and very flexible, so they could also be used to make flexible displays and electronics that can stretch and bend, allowing you to integrate electronics into new places like clothing,” said Arnold. “The advance enables new types of electronics that aren’t possible with the more brittle materials manufacturers are currently using.”

Schematic (top of image) of a polymer-wrapped carbon nanotube. Scanning microsopy image (bottom) of carbon nanotubes that were aligned via FESA and incorporated as the active channel of a field-effect transistor device.

Consisting of single atomic sheets of carbon rolled into a tube, carbon nanotubes are among the best conductors of electricity. The carbon nanotubes are considered to be among the most promising material to use as a next-generation transistor. The UW-Madison researchers drew on technologies that use polymers to selectively sort the semiconducting nanotubes, achieving a solution of ultra-high-purity semiconducting carbon nanotubes.

Previous techniques to align the nanotubes resulted in less-than-desirable packing density, or how close the nanotubes are to one another when they are assembled in a film. But the researchers developed a new technique, called floating evaporative self-assembly, or FESA, which they described earlier in 2014 in the ACS journal Langmuir. In that technique, researchers exploited a self-assembly phenomenon triggered by rapidly evaporating a carbon nanotube solution.

The team’s most recent development also brings the field closer to realizing carbon nanotube transistors as a feasible replacement for silicon transistors in computer chips and in high-frequency communication devices, which are rapidly approaching their physical scaling and performance limits. The UW-Madison researchers have patented their technology through the Wisconsin Alumni Research Foundation and have begun to work with companies to accelerate the technology transfer to industry.

“This is not an incremental improvement in performance,” Arnold says. “With these results, we’ve really made a leap in carbon nanotube transistors. Our carbon nanotube transistors are an order of magnitude better in conductance than the best thin-film transistor technologies currently being used commercially while still switching on and off like a transistor is supposed to function.”

The work was funded by a grant from the National Science Foundation, as well as grants from the UW-Madison Center of Excellence for Materials Research and Innovation, the US Army Research Office, the National Science Foundation Graduate Research Fellowship Program, and the Wisconsin Alumni Research Foundation. Additional authors on the ACS Nano paper include UW-Madison materials science and engineering graduate students Gerald Brady, Yongho Joo and Matthew Shea, and electrical and computer engineering graduate student Meng-Yin Wu.

An abstract of the paper is available at http://pubs.acs.org/doi/abs/10.1021/nn5048734.  


SME Tech Papers: Learn More & Do More

Information Flows About Metalworking Fluids

“Cutting Fluids: Necessary Nuisance to Productivity Tool” (SME Technical Paper TP02PUB205) sums up the span of knowledge available from SME. “When properly handled, cutting fluids are truly productivity tools. But if they are ignored, they can definitely become a nuisance.” Close to 200 papers are filled with the what, why and how of selecting the best-suited metalworking fluid for each operation and using it under the proper conditions for worker and environmental safety.

Several overview papers provide a tutorial on fluids and coolants, including “A Primer on Metalworking Fluids” (TP91PUB455), “The Why of Metal Working Fluids” (TP65PUB52), “Cutting Fluids–Third Dimension in Metalworking” (TP66PUB218), “Practical Fluid Management” (TP89PUB237) and “Fluid Management” (TP93PUB140).

The 46-page “Primer” highlights the wide range of available fluids “as a tool of production and applied to: (1) provide an adequate cooling action, (2) provide a tolerate tool and die life, (3) produce a satisfactory surface texture for the product and (4) maximize economical production parallel to an established quality standard.”

Additionally covered are metal removing and metalworking dynamics and cutting and grinding mechanics, as well as a discussion of the parameters in formulating metalworking fluids and the classes of metalworking lubricants.

TP66PUB218’s author, R.L. Quanstrom of Cincinnati Milling & Grinding Machines, points out that not just any fluid can bring expensive machine setups to peak efficiency. “The fluid must be engineered to do the job, taking into account all of the conditions surrounding the metal removal process it is to facilitate.” Additionally, proper installation of the system and maintenance of the coolant are essential. And “do not surprise the system with special additives” unless compatibility with the coolant is checked, to avoid aggravating a problem.


Aerosol Issues

Cutting fluid aerosol generation poses air quality problems during machining operations. Authors at several North American Manufacturing Research Conferences (NAMRC) have presented research work on this issue. In TP00PUB98, SME Fellows Steven Y. Liang and David A. Stephenson and colleagues develop a set of quantitative models to predict the generation rate of shop-floor aerosol resulting from cutting fluid in the turning process. Study of the relative importance of spinoff vs. splash mechanisms through the model calculation indicated that spinoff is the dominating mechanism at high rotational speeds and high flow rates.

Another paper (TP02PUB67) by Liang (Georgia Institute of Technology; Atlanta), with Hitomi Yamaguchi (University of Florida; Gainesville) and Zhong Chen, examines analytical models that describe the aerosol concentration and particle size distribution as functions of grinding condition and fluid application parameters. The predictive models can estimate the resulting air quality based on given grinding process parameters.

Atomized cutting fluids can be effective for increasing tool life in micromilling, as opposed to flood, high-pressure and liquid-nitrogen-based systems used in macromachining. Three generations of a cutting fluid application system based on ultrasonic atomization are described in TP10PUB25 by M. Rukosuyev, C.S. Goo and M.B.G. Jun of the University of Victoria (British Columbia, Canada) and S.S. Park of the University of Calgary (Alberta, Canada). The effects of various system input parameters, such as mist and spray velocities on spray focusing, were evaluated in each iteration of the atomization system. The final version is capable of focusing the spray less than 1.0 mm in focus height in a compact system that can be integrated in microscale machine tools.

Metalcutting


Microbial Matters

Increasing the life of metalworking fluids requires knowledge of the mechanisms and organisms of spoilage and monitoring of microbial contamination. Microbial matter has mattered as a topic over the decades, with papers from the 1970s and ’80s to now.

“If one considers the cost of the concentrates, changing the coolants, cleaning the machines, loss of tool life, reduced production and increased disposal problems, it becomes obvious that coolant rancidity is a very expensive problem for the metalworking industry,” states the author of TP73PUB233, a biology professor. The author’s findings in regard to biological stability are that preservatives are most effectively added to the diluted coolant rather than to the concentrate. The same author writes in 1985 on public attitudes, chemical identities and animal studies involving the safety of water-based cutting fluids for human workers (TP85PUB195).

Another microbiologist author, Frederick Passman in TP84PUB238 and TP89PUB236, describes methods for estimating and monitoring microbial loads, including direct counts, viability counts, metabolic activity determinations and cell constituent concentration testing. “Regardless of the method selected to control microbial loads in metalworking fluids, a means of measuring its effectiveness must be identified and used…generally with at least one microbial parameter and one or more physical-chemical parameters measured routinely.”

In the very bio-technical TP84PUB238, Passman describes a rapid catalase (enzyme) test to assist shop-floor personnel in estimating catalase-positive microorganisms so that a change in levels can be addressed with increased microbial control measures. System monitoring plans, covered in TP89PUB236, aid the timely assessment of coolant condition and determine the effectiveness of corrective measures. A monitoring plan (“a realistic action plan,” not “a wasteful paperwork exercise”) should be developed based on system size, number of coolant systems in the plant, availability of personnel, nature of metalworking operation and coolant performance requirements.

Another NAMRC paper, by Steven Skerlos and colleagues from the University of Michigan (Ann Arbor), investigated how to identify and quantify specific hazardous mycobacteria in metalworking fluids using epi-fluorescence microscopy or flow cytometry. Previous testing methods had a long lag time, limiting the ability to control infection of workers or correct fluid contamination.

SME Technical Papers (coded as TP…PUB…) and search options for the collection are available at http://tinyurl.com/SearchTPs.

 

TechFront is edited by Senior Editors Patrick Waurzyniak, pwaurzyniak@sme.org, and Ellen Kehoe, ekehoe@sme.org.

 

This article was first published in the March 2015 edition of Manufacturing Engineering magazine. Click here for PDF.


Published Date : 3/1/2015

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