Smaller is Stronger, Now Scientists Know Why
As structures made of metal get smaller, as their dimensions approach the micrometer scale (millionths of a meter) or less, they get stronger. Scientists discovered this phenomenon 50 years ago while measuring the strength of tin “whiskers” a few micrometers in diameter and a few millimeters in length. Many theories have been proposed to explain why smaller is stronger, but only recently has it become possible to see and record what's actually happening in tiny structures under stress.
Andrew Minor, of the Materials Sciences Division in the Department of Energy's Lawrence Berkeley National Laboratory, with colleagues from Hysitron Incorporated and the General Motors Research and Development Center, used the In Situ Microscope at the National Center for Electron Microscopy (NCEM) to record what happens when pillars of nickel with diameters between 150 and 400 nanometers (billionths of a meter) are compressed under a flat punch made of diamond. The transmission electron microscope is equipped so that samples can be stressed, measured and videotaped while being observed under the electron beam.
“What controls the deformation of a metal object is the way that defects, called dislocations, move along planes in its crystal structure,” Minor says. “The result of dislocation slip is plastic deformation. For example, bending a paper clip causes its trillions of dislocations per square centimeter to tangle up and multiply as they run into one another and slide along numerous slip planes.”
In general, mechanical deformation tends to increase the number of dislocations in a material. But for small-scale structures, with a much greater proportion of surface area to volume, the process can be very different. The videotaped images from the electron microscope helped the researchers understand why nanoscale nickel pillars are so strong by allowing them to observe changes in the microstructure of the pillars during deformation, including a never-before-seen process the researchers dubbed “mechanical annealing.” In bulk materials, annealing, a treatment that reduces the density of defects, is usually accomplished by heating.
Minor said, “The first thing we observed was that, before the test, the nanoscale pillars of nickel were full of dislocations. But as we compressed the pillar, all the dislocations were driven out of the material, literally reducing the dislocation density by 15 orders of magnitude and producing a perfect crystal. We called this effect mechanical annealing.”
The pillars Minor and his colleagues tested were machined from pure nickel using a focused ion beam (FIB), a new technique for small-scale mechanical-compression testing first described in 2004 by Michael Uchic of the US Air Force Research Laboratory and his colleagues. The FIB technique makes it possible to create much smaller structures than the metal “whiskers” first studied in the 1950s, which are made by growing crystals.
Some of the dislocations the researchers observed in the machined pillars were relatively shallow and caused by the ion beams themselves. Others extended through the crystal and were presumably pre-existing defects. Under compression, mechanical annealing caused both kinds of defect to vanish.
“Essentially all the dislocations escape from the crystal at the surface, and you do not get storage of dislocations like you would in larger crystals,” Minor said. “What results is a process called ‘dislocation starvation,’ recently proposed by William D. Nix of Stanford, among others, which has quickly became one of the leading theories of why smaller structures are stronger.”
Minor said, “The idea is that if dislocations escape the material before they can interact and multiply, there are not enough active dislocations to enable the imposed deformation. The structure can only deform after new dislocations are created.”
This is precisely the process he and his colleagues observed with NCEM's In Situ Microscope, strong evidence that “dislocation starvation” is the correct explanation for the increased strength of small structures.
What happens if a defect-free nanoscale nickel pillar continues to be compressed? Something has to give, which happens when new sources of dislocation “nucleate” in the material. As the existing dislocations disappear in the pillar because of mechanical annealing, the nucleation of new dislocation sources happens at progressively higher stresses.
In the pillar structures, plastic deformation may take the form of sudden flattening, bulging, twisting or shearing of the pillar, as bursts of new dislocations propagate through it. Or, the hardened pillars, made stronger by mechanical annealing, may punch right down into the substrate, even though pillar and substrate are the same continuous piece of metal. Both processes were captured in the In Situ Microscope's dramatic videotaped experiments.
The FIB machining used by the NCEM researchers produced nickel pillars that were slightly tapered, and the researchers noted that this geometry affected where and how plastic deformation occurred, generally being greater in the smaller-diameter, free end (top) of the pillar.
In larger pillars, those approaching 300 nanometers in diameter, mechanical annealing was not complete, and some dislocations remained visible even after compression. Yet even these pillars exhibited enhanced strength, and progressively higher stresses were needed to continue deformation, underlining the point that it is the creation of mobile defects that determines strength in these small volumes.
“The beauty of the pillar-testing geometry is that we can straightforwardly define stress. Then we can correlate the measured stresses with discrete plastic events recorded in situ and more clearly interpret the quantitative data from our experiments,” Minor said. “The debate over what determines the strength of a small structure has come down to almost a chicken-and-egg question – is something strong because you need a high stress to move a dislocation that is already there? Or is it strong because you need a high stress to nucleate a new dislocation? In this case, it seems that source nucleation, that is, the 'egg,' is the determining factor."
This work was partially supported by a grant from the US Department of Energy to Hysitron, Inc., and also by a grant from the DOE Office of Science, Office of Basic Energy Sciences.
Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, Calif. It conducts unclassified scientific research and is managed by the University of California.
 Photo Info: Compression of a nickel pillar whose free end has a diameter of about 150 nanometers. Before compression (left) the pillar has a high density of defects, visible as dark mottling. After compression all the defects have been driven out, a previously unobserved process known as "mechanical annealing."
Global Market for Intelligent Wireless Microsystems Slated for High Growth Through 2012
According to a new technical market research report, Intelligent Wireless Microsystems: Emerging Applications and Markets from BCC Research, the global market for intelligent wireless microsystems (IWM) is expected to be worth $138 million in 2008. This is expected to increase to over $1.3 billion by 2013, a compound average annual growth rate (CAGR) of 56.4 percent.
The market is broken down into applications for beverage merchandizing, chemicals manufacturing, electrical apparatus manufacturing, food manufacturing, special purpose machinery manufacturing, metal production, petroleum refining, plastics manufacturing, pulp and paper processing and transportation. Of these, special purpose machinery has the largest share of the market, valued at nearly $29 million in 2008. This segment is expected to be worth $580 million by 2013, a CAGR of 82.1 percent.
The second largest segment, chemical manufacturing, is worth an estimated $32 million in 2008 and will reach $287 million by 2013, a CAGR of 55.1 percent. The food manufacturing segment, worth $12 million in 2008, will be worth $88 million in 2013, a CAGR of 49 percent.
IWMs represent the first major advance in control systems technology of the 21st century. A disruptive rather than a sustaining technology, IWMs have begun to slowly make inroads in niches within the control systems sector. The 10 industries mentioned above have begun to pioneer the use of IWM.
These same industries will have significant requirements for IWM by 2013. Demand will improve slowly in 2008 and 2009 and then accelerate rapidly. By 2013, IWM devices will have established themselves as superior competitors to multi-parameter control systems in at least these 10 sectors of the economy, including most types of manufacturing.
Huber Announces Price Increases for its Specialty Grade Silica and Silicates
Huber Engineered Materials (HEM), part of J.M. Huber Corp., has announced a price increase for its specialty grade silica and silicates.
The will be effective Feb. 1, or as current contracts allow. Prices will increase an average of 5 to 8 percent, dependent upon the product grade and form. Increases in energy, raw materials costs and rising investments in meeting regulatory requirements cannot be offset by continuing productivity improvements and production efficiencies, Huber officials said.
BASF Raises Prices for Ethyleneamines
Effective immediately, or as existing contracts allow, BASF is raising its prices for ethyleneamines globally as follows:
+ $147.29/to for ethylenediamine (EDA)
+ $73.65/to for aminoethylethanolamine (AEEA)
+ $73.65/to for diethylenetriamine (DETA)
+ $73.65/to for piperazine
+ $73.65/to for AMIX 1000
or by the related level in regional currency. The markups are because of the increased costs for raw materials and energy as well as the ongoing high demand situation.
The products in question are high-class intermediates used amongst others in the manufacture of agro- and paper chemicals, surfactants for detergents and cleaning products, process chemicals for gas treatment, lubricants, cement additives and active pharmaceutical ingredients.
BASF produces ethyleneamines at its Verbund site in Antwerp, Belgium.
Sartomer Company Increases Monomer and Oligomer Prices
Global specialty chemicals manufacturer Sartomer Company will increase the price of its acrylate and methacrylate monomers and oligomers in the Americas region, effective Feb. 1 (or as contract allows). Increases will vary 5 to18 percent based on the product line.
The increases are due to escalating raw material, transport and energy costs.
Sartomer’s acrylate and methacrylate monomers and oligomers are used in coatings, inks, adhesives, sealants, electronics, composites, elastomers and other applications.
Sartomer Company, part of Total's Chemicals branch, is a US-based manufacturer of specialty chemicals. It provides a variety of specialty chemicals designed to enhance processing and performance characteristics in coatings, inks, elastomers, adhesives, sealants, composites and other demanding applications. The company's product offering includes more than 620 monomers and oligomers, photoinitiators, polybutadiene resins, styrene maleic anhydride resins, hydrocarbon resins and other specialty chemicals. |
A single-component metal repair and patching compound that requires no mixing, applies easily, can be sanded and then powder coated and baked or simply painted is available from Alvin Products of Everett, Massachusetts.
Shin-Etsu Silicones of America, Inc. has integrated its KE2004-20 silicone LIMS (Liquid Injection Molding System) product into the production of a next-generation earplug for swimming and hearing protection. The Series’ low durometer (22 Shore A) and low-modulus produced a soft, flexible feel while its advanced physical properties deliver high-tear strength (207 ppi) which significantly reduced scrap and cycle time. 
Recognizing the need to reduce cycle time, Silcotech NA President Michael Maloney contacted Shin-Etsu Silicones of America, Inc. to test its new KE2004-20 silicone LIMS product, which was stated to have the highest tear strength on the market for a 20 durometer product. In addition to their low hardness and high tear strength, KE2004-20’s relatively higher viscosity also translated to improved handling and flash. Its higher strength and outstanding release properties allowed for de-molding parts, particularly those with thin wall thicknesses, without tearing and generating scrap.
Dickson’s Wireless Wizard, a wireless data logger, is now available to engineers monitoring temperature and/or humidity, in a 30-day no obligation trial offer. The wireless data loggers can be monitored in real-time from a desktop PC or other computer workstation and totally eliminate the delays for data downloading and cabling of other temperature and humidity data logger technology.
