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Tech Front: New Nanoscale Compounds for Better CNG Storage

 

Researchers at Rice University (Houston) have published a new study on nanoscale materials composed of metal organic frameworks (MOF) that could be used to devise more practical storage systems used with compressed natural gas (CNG) vehicles.

Today’s CNG-powered buses and trucks typically use very bulky tanks that store natural gas at very high pressure. But the Department of Energy (DOE) is encouraging researchers to develop newer methods of storage that would allow light vehicles to store the gas at room temperature and at much lower pressures. The Rice research focused on MOFs—nanoscale compounds of metal ions or clusters known as secondary building units and organic ligands, or linkers—that hold the materials together.

A research team led by Rice bioengineer Michael Deem used a custom algorithm to quickly design new MOF configurations able to store compressed natural gas, or methane, with a high “deliverable capacity,” which can be reliably synthesized from commercial precursor molecules.
An example of metal organic frameworks discovered by researchers at Rice University that could be used in creating more practical compressed natural gas storage systems.
Deem and his colleagues at Rice, the Lawrence Berkeley National Laboratory and the University of California-Berkeley reported their results in December in the American Chemical Society’s Journal of Physical Chemistry C. MOFs show potential for applications like drug delivery, sensing, purification and catalysis, but methane storage for transportation is high on the DOE’s wish list, Deem said. “MOFs are being commercialized for methane storage in vehicles now,” he said.

The advantages to using MOFs as a storage medium are many and start with increased capacity over the heavy, high-pressure cylinders in current use. The Rice study found 48 MOFs that beat the best currently available, a compound called MOF-5, by as much as 8%, and the program adhered to standard DOE conditions that an ideal MOF would store methane at 65 bar (atmospheric pressure at sea level is one bar) and release it at 5.8 bar, all at 298 kelvins (about 77° F). That pressure is significantly less than standard CNG tanks, and the temperature is far higher than liquid natural gas tanks that must be cooled to minus 260° F. Lower pressures mean tanks can be lighter and made to fit cars better, Deem said. They may also offer the possibility that customers can tank up from household gas supply lines.

The DOE Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences supported the research, which employed the National Science Foundation-funded DAVinCi supercomputer administered by Rice’s Ken Kennedy Institute for Information Technology. For more information, the abstract is available at http://pubs.acs.org/doi/abs/10.1021/jp5123486.  


Nanoparticle Allows Low-Cost Creation of 3D Nanostructures

A new lithography technique developed by researchers at North Carolina State University (Raleigh, NC) uses nanoscale spheres to create 3D structures with biomedical, electronic and photonic applications. The researchers say the new technique is significantly less expensive than conventional methods and does not rely on stacking 2D patterns to create 3D structures.

“Our approach reduces the cost of nanolithography to the point where it could be done in your garage,” said Chih-Hao Chang, assistant professor of mechanical and aerospace engineering at North Carolina State and senior author of a paper on the research.

Conventional lithography typically uses different techniques to focus light on a photosensitive film to create 2D patterns. The techniques rely on very expensive, specialized lenses, electron beams or lasers. Other techniques use mechanical probes, which are also costly. To create 3D structures, the 2D patterns are essentially printed on top of each other.

A variety of asymmetric hollow-core 3D nanostructures fabricated by illuminating light on nanoparticles.

The NC State researchers’ approach placed nanoscale polystyrene spheres on the surface of the photosensitive film. The nanospheres are transparent, but bend and scatter the light that passes through them in predictable ways according to the angle that the light takes when it hits the nanosphere. The researchers controlled the nanolithography by altering the size of the nanosphere, the duration of light exposures, and the angle, wavelength and polarization of light. The researchers can also use one beam of light, or multiple beams of light, allowing them to create a wide variety of nanostructure designs. The scientists also showed that they can get the nanospheres to self-assemble in a regularly-spaced array, which in turn can be used to create a uniform pattern of 3-D nanostructures.

“This could be used to create an array of nanoneedles for use in drug delivery or other applications,” says Xu Zhang, a PhD student in Chang’s lab and lead author of the paper, “Sculpting Asymmetric Hollow-Core Three-Dimensional Nanostructures Using Colloidal Particles,” was published online Dec. 8 in the journal Small.

To see an abstract of the paper, go to http://onlinelibrary.wiley.com/doi/10.1002/smll.201402750/abstract.  


Putting Some Teeth into Gear Knowledge

“What do you need from gears?” is the question posed by the author of SME Tech Paper TP51PUB29 in explaining that what a purchaser says he wants does not always correspond to what he actually needs. Rather than relying on standardized choices, the author advises tool engineers to keep in mind that “the best gear for any particular application is the cheapest gear that is adequate for the service it is called upon to render,” while meeting conditions of bulk or size, form, position and operation, assembly or functioning. “No two different applications are ever exactly alike. This means for anyone who is closely concerned with the needs of gears, there is never a dull moment.”

Published discussion on the above paper by a General Electric engineer added that a gear designer’s needs may be simple, “but getting what he needs may require him to spend a lot of time investigating gear problems.” Additional commentary from the chief research engineer for the Packard Motor Car Co. discussed that “most engineers have some very definite ideas for surface finish. Our policy has been to ask the gears to tell us the surface finish they desire, as evidenced by the surface condition of the teeth after actual operation at the design loads.” Sometimes that’s what manufacturing engineering is all about.


Gear Finishing

The quality of a finished gear is affected by the quality of the blank on which the gear teeth are cut. TP86PUB383 describes how good inspection and quality control procedures will result in early detection of bad blanks, which can then be removed from the system before subsequent expensive operations are performed on the blank. Stephen P. Radzevich’s paper on finishing precise gears for low-noise car transmissions (TP04PUB261) explains that among various methods for finishing gear teeth, shaving is still the most widely used because of short process times and low costs. The predominant cause of gear noise is transmission error. Modification of the pinion tooth surface with a shaving cutter was found to reduce transmission error up to two times.

Improved surface finishing with honing was a new processing technique mentioned in TP68PUB189 discussing the state of the art in gear production. Another primary emphasis in the paper was on forming the gear teeth rather than cutting them. In aviation, increased helicopter requirements led to heavily loaded, long-life gears—hobbed, hardened and precision ground—in the rotor drive systems from the jet engine.


Research and Improved Techniques

A Texas A&M University research project detailed in TP93PUB146, coauthored by SME past president John E. Mayer, Jr., highlighted precision gear manufacturing at Bell Helicopter Textron. Four high-impact projects in the areas of heat treatment and grinding were identified and yielded significant results. Specific grinding energy causing thermal damage in helicopter gear steel was investigated in TP01PUB168, also by the Texas A&M team and a US Army researcher, and presented at NAMRC 2001.

To satisfy objectives for improved physical properties and grain structure of gears and reduced overall manufacturing costs, roll forming was proposed by Ford Motor Co. engineers in TP70PUB71. True then as now, the team needed “to aggressively meet the continually changing and competitive environment in which we find ourselves today… to challenge traditional concepts and institute new ways of doing an old job.” One of the most critical forms of broaching is the internal or external generation of gear teeth and splines. TP90PUB478 discusses how broach manufacturers have steadily progressed to meet the challenges set before them with new and improved techniques for broaching.

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

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

 

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


Published Date : 2/1/2015

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