Nanostructured Metallic Alloys - Materials for the Future

Recent advancements in the field of nano-technology focused attention on developing materials with new and useful characteristics. In particular, there is interest in designing nanocomposite thermites for self-propagating high-temperature synthesis (SHS) applications. The composite material consists of nano-scale particles that are in nearly atomic scale proximity but constrained from reaction until triggered. Once initiated, the reaction will become self-sustaining and a new intermetallic alloy product will be produced1.

These materials consist of a mixture containing nano-scale metals, metal oxides, and/or organic and inorganic polymer binders and are being used for overlapping technologies ranging from materials synthesis1 to local energy generation applications2. For example, when a reactant mixture is ignited to produce a new material, the combustion synthesized product can be useful as a biomaterial3 or the reactants can be tailored to synthesize corrosion resistant high temperature metallic alloys4. When the reaction is significantly exothermic and results in rapid flame propagation, the reactant mixture can be tailored to generate energy for industrial, civil or military applications5.

This short article is focused on examples of future opportunities within nanostructured metallic alloys, but there is a relatively large literature base reporting on observations of unique behaviors of nano versus micron (traditional size) particles1-15.

While some of the fundamentally unique observations specific to nanoparticles are just now being realized, these developments can be exploited to help researchers address current critical issues such as energy generation applications, biomaterials for bone implants and skeletal repair, and the spread and transfer of infectious bacteria and molds.

When individual fuel and oxidizer particles approach nanometer dimensions, nanoparticle thermal and combustion behaviors are unique in that the energy required to initiate a reaction can actually be stored and build-up within the particles. These energy storage formulations consist of fuel metal nanoparticles combined with metals or metallic oxide nanoparticles and are referred to as Nanochargers16.

The Nanocharger stores energy as the particles are held in an inert state, and when triggered, the slow gasless reaction that occurs is controlled by mass transport and energy required to diffuse reactants toward each other. Ignition leads to a slow controlled, self propagating, high temperature conversion of chemical energy to thermal energy. The unique thermal, mechanochemical and combustion properties for nanoparticles are the foundation for this innovative concept: use nanoparticle fuel and oxidizer composites as reactants in a Nanocharger that will store and deliver energy on demand.

Figure 1 shows time stamped still-frame images from the IR camera indicating the nanometric sample stored energy 46 seconds longer than the micron-composite material. Nanochargers could be described as a cross between a battery and molten salts. The reactants achieve similar thermal inertia properties of molten salts (enabling storage), but energy delivery is based on a chemical reaction, more similar to a battery. Storing thermal energy for extended periods may be useful for some forms of renewable energy, such as solar thermal. In this way, heat energy stored within the Nanocharger during the day could be easily delivered during evening hours, when the sun does not shine16.



In the field of combustion synthesis, much work has been done to generate porosity by adding blowing agents to the reactant matrix and Moore et al. provide a review of much of this literature17-18. A foam-type product can be created when a mildly energetic composite includes a modest amount of gasifying agent (GA). During a reaction the gasifying agent generates nucleation sites that promote the formation of bubbles. As the reaction wave passes, the gas pockets within the bubbles escape leaving a porous structure.

In previous combustion synthesis studies, a gasifying agent may be added as a separate reactant and usually in the form of a powder or granular material19. This strategy was shown to be highly successful for synthesizing ceramic materials for biological applications15. However, incorporating blowing agents to synthesis metal alloys has not been widely pursued yet has recently been shown to be feasible using nanoparticles15. Control over properties of the final product, such as porosity, can be achieved by tailoring reactant composition. In 2006, combustion synthesis was used to form porous nickel aluminide and showed that the porosity of the final product is a function of the percentage of gasifying agent present in the reactant matrix15.

Today, this work is extended to understand the mechanics of synthesizing a porous titanium aluminide (AlTi) alloy in order to create an axially graded porosity distribution. Metallic foams are synthesized by means of a self propagating high-temperature reaction producing a highly porous solid metal alloy with customizable material properties. Nano-scale aluminum and nano-scale titanium particles are mixed with either nano-scale aluminum passivated with a gasifying agent such as perfluoroalkyl carboxylic acid (C13F27COOH) or polytetrafluoroethylene (Teflon) (C2F4) particles. When pressed into pellets and ignited with a laser, they produce a reaction product composed of an AlTi alloy that has a highly porous structure.

In this way, combustion synthesis can be used to create a functionally graded porous AlTi alloy and identify correlations between the product microstructure and parameters such as type and amount of gasifying agent present in the reactants. Photographic data allow interpretation of the reaction propagation while characterization of the final product indicated porosity and morphology. These nanostructured metallic alloys may have applications in biomaterial development by tailoring porosity throughout the matrix. Figure 2 show a scanning electron micrograph (SEM) of this AlTi alloy.



Bacterial contamination in hospitals, food industries, and public environments create a major public health issue. Despite considerable research and development efforts, the problem of contaminations related to biomedical devices and food preparation persists. Traditional cleaning methods, such as aerosolized disinfectant sprays or wipes have a limited effectiveness. There is a strong need to mitigate bacterial colonization by engendering materials with properties that include surface chemistry20-22 and surface roughness23-25 which are unfavorable for bacterial attachment and growth. Silver has been used for years in many bactericidal applications because of its strong toxicity to a wide range of micro-organisms20-27.

Research has shown that the bactericidal properties of silver are size dependent, and only nanoparticles present a direct interaction with the bacteria22. Titanium dioxide (TiO2) has also become a popular agent for bacterial neutralization. Several commercial products have been developed that incorporate nanoparticles of TiO2 for antibacterial applications28.

Highly porous, antibacterial solid metallic alloys (or foams) can be created through combustion synthesis. By combining nano-scale Silver Oxide (Ag2O) or TiO2 particles with Aluminum (Al) nano-scale particles, the reaction can produce a self-propagating heat wave that will synthesize metallic foams made of pores only nanometers wide that inherently exhibit antibacterial properties. The extraordinarily high surface areas these foams possess serve as an excellent platform for the neutralization of bacteria. These newly synthesized alloys present a novel approach to bacterial neutralization.

Figure 3 shows nanostructured metallic alloys undergoing bacterial growth tests at 24 and 48 hours. . The bacterial growth is highlighted with a white circle. Figure 3D shows a control sample before and after exposure.



Five important conclusions can be drawn from these results.

1. Combustion synthesis can be used to create nanostructured metallic alloys that have antibacterial properties.
2. Bacteria growth kinetics are a function of reactant particle size.
3. Nanoscale reactants are more effective in neutralizing bacteria.
4. TiO2 particles can delay, but not prevent bacterial growth, and;
5. metallic nanofoams composed of nano-scale Al and Ag2O prevent growth of bacteria.

These nanostructured metallic alloys can be easily created as a structural material or a metallic coating through combustion synthesis and have far-reaching applications in the renewable energy, food service and medical industry. Nanostructured metallic alloys truly are the material of the future.
References

1. Varma, A., "Form From Fire", Scientific American, pp. 58-61, August (2000).
2. J. Giles, Nature, 427, 580-581 (2004).
3. R.A. Ayers, D. Burkes, G. Gottol, Journal of Biomedical Materials A, 81A (3), 634-643 (2008).
4. Tomasi, R. and Munir, Z. A., "Effect of Particle Size on the Reaction Wave Propagation in the Combustion Synthesis of Al2O3-ZrO2-Nb Composites," J. Am. Ceram Soc. v. 82, n. 8, pp. 1985-1992 (1999).
5. "Combustion Velocities and Propagation Mechanisms of Meta-stable Intermolecular Composites," B. S. Bockmon, M. L. Pantoya, S. F. Son, B. W. Asay, J. T. Mang, Journal of Applied Physics 98(6), 064903 (2005) [DOI: 10.1063/1.2058175].
6. "Combustion Behaviors of Highly Energetic Thermites: Nano versus Micron Composites," M. L. Pantoya and J. J. Granier, Propellants, Explosives, Pyrotechnics 30(1), 53-62 (2005) [DOI: 10.1002/200400085].
7. Dreizin, E.L., Metal-based reactive nanomaterials, Progress in Energy and Combustion Science 35; 141-167 (2009).
8. Wang, L.L., Munir, Z.A., Maximov, Y.M., Review thermite reactions: their utilization in the synthesis and processing of materials, Journal of Materials Science 28 (1993) 3693-3708
9. Rossi, C., Zhang, K., Esteve, D., Alphonse, P., Tailhades, P., Vahlas, C., Nanoenergetic Materials for MEMS: A Review, Journal of Microelectromechanical Systems 16(4), Aug 2007 919-931.
10. Son, SF, Yetter, RA, Yang, V., Introduction: Nanoscale Composite Energetic Materials, Journal of Propulsion and Power 23(4), 643-644 (2007)
11. E. M. Hunt and M. L. Pantoya, Nanostructured Metallic Alloys: Synthesis, Properties and Applications, ISBN: 978-3-8364-3438-6, VDM Verlag Dr. Muller publisher 2007.
12. E. M. Hunt, J. J. Granier, K. B. Plantier and M. L. Pantoya, "Nickel Aluminum Superalloys Created by the Self-propagating High-temperature Synthesis (SHS) of Nano-particle Reactants," Journal of Materials Research 19(10), 3028-3036 (2004).
13. E. Hunt, K. Plantier, M. Pantoya, "Nano-scale Reactants in the Self-Propagating High-Temperature Synthesis of Nickel Aluminide," Acta Materialia 52(11), 3183-3191 (2004).
14. E. M. Hunt and M. L. Pantoya, "Ignition Dynamics and Activation Energies of Metallic Thermites: From Nano- to Micron-scale Particulate Composites," Journal of Applied Physics 98(3), 034909 (2005). [DOI:10.1016/j.combustflame.2004.10.009]
15. E. M. Hunt, M. L. Pantoya and R. J. Jouet, "Combustion Synthesis of Metallic Foams from Nanocomposite Reactants," Intermetallics 14 (6), 620-629 (2006).
16. Hunt E.M. and Pantoya M.L. "Nanochargers: Energetic Materials for Energy Storage," Applied Physics Letters, 95 (25), (2010).
17. Moore JJ, Fend HJ (1995) Combustion synthesis of advanced materials: Part I. reaction parameters. Progress in Materials Science 39, 243-273.
18. Ayers RA, Burkes DE, Gottoli G, Yi HC, Zhim F, Yahia LH, Moore JJ, Combustion synthesis of porous biomaterials. Journal of Biomedical Materials Research Part A 81(3), 634-643.
19. Vasilev K., Cook J., and Griesser H., "Antibacterial surfaces for biomedical devices," Expert Review of Medical Devices: 6, (5), 553-567; (2009).
20. Trapalis C., Kokkoris M., Perdikakis G., and Kordas, G., "Study of Antibacterial Composite Cu/SiO2 Thin Coatings," Journal of Sol-Gel Science and Technology," 26, 1213-1218, (2003).
21. Morones J.R., Elechiguerra J.L., Camacho A., Holt K., Kouri J.B., Ramirez J.T., Yacaman J., The bactericidal effect of silver nanoparticles, Nanotechnology 16: 2346-2353 (1998).
22. Zhao G., Stevens E., Multiple parameters for the comprehensive evaluation of the susceptibility of Escherichia coli to the silver ion, Biometals 11: 27-32 (1998).
23. Faille, C. et al. "Adhesion of Bacillus Spores and Escherichia coli Cells to Inert Surfaces: Role of Surface Hydrophobicity." Canadian Journal of Microbiology 48; 2002.
24. Kenar, L. et al. "Comparative Sporicidal Effects of Disinfectants after Release of a Biological Agent." Military Science 172(6) 2007.
25. Whitney, E. et al. "Inactivation of Bacillus anthracis Spores." Emerging Infectious Diseases 9(6); 2003.
26. Taylor P.L., Ussher A.L., Burrell R.E., Impact of heat on nanocrystalline silver dressings Part I: chemical and biological properties, Biomaterials 26: 7221-7229 (2005).
27. Fujishima A., OhkoY., Saitoh S., Tatsuma T., Niwa C., and Kubota Y., "Antibacterial and Anticorrosion Effects of Titanium Dioxide Photoactive Coatings,"
28. Whitney, E. et al. "Inactivation of Bacillus anthracis Spores." Emerging Infectious Diseases 9(6); 2003.
29. Kistler S.S., Coherent expanded aerogels in jellies, Nature 127: 741 (1931).

Copyright AZoM.com, Professor Emily M. Hunt (West Texas A&M University)

Some eco materials for a green sustainable home

Using green building supplies is a way to make a green home even more environmentally-friendly. From recycled products to energy efficient equipment, there are endless avenues of sustainability and efficiency with the full range of eco-friendly building materials.
The Benefits of Using Eco-Friendly Building Materials

Why do people make the effort to seek out green building supplies, when conventional materials are much easier to find? For the well-being of themselves, the builders, and the world at large. Eco-friendly building materials generally come with less chemicals which may harm the internal environment of the home, the people who are working with the materials, and the environment in which they are either taken from or manufactured in. Many chemicals, such as plasticizers and fluoropolymers, go unnoticed, and for the most part their long-term health effects are unknown.

Building materials are also considered eco-friendly if they are energy efficient and require little maintenance, even after several years. A product that is more sustainable is going to either save energy or money, or both, proving its worth within the first few years of having a new green home.

Also, those materials that did not have a huge negative impact on the environment are considered green building supplies. Even if they are not completely eco-friendly, as most products require some form of energy use, if only for transportation, factors such as efficiency or sustainability lead to a higher overall environmental benefit.
Instantly Eco-Friendly Green Building Supplies

* Recycled Materials: When post-consumer products are used as raw materials, at least partially, building supplies take up less new materials from the environment, and serve to eliminate waste by utilizing it.

* Rapidly Renewable Materials: Materials that have a short harvest rotation, so they are quickly and naturally replenished, are definitely eco-friendly. They also are biodegradable, which is an added benefit for the distant future, as the destruction of the home will not have as much of a negative impact on the environment. Cork and natural paints are examples of rapidly renewable materials.

* Agricultural Waste Products: Straw, rice hulls, orange peels, can all be used to make materials.

* Certified Wood: Wood which has been approved by a third party, based on standards put in place by the Forest Stewardship Council, is guaranteed to come from a well-managed forest, therefore ensuring that the necessary building materials have a minimal impact on the environment.

Indirectly Eco-Friendly Green Building Supplies

* Low-Maintenance Materials: Eco-friendly building supplies, such as fiberglass windows and slate shingles will last for years, minimizing the overall amount of materials which will need to be used for the lifetime of the home.

* Minimally Processed Supplies: Products that are in or close to their natural state have a smaller impact on the environment as they never have to be manufactured, for example, natural stone.

* Supplies with Low Toxicity: There are many occasions when there is the opportunity to make a home more eco-friendly by choosing a substitute product that has minimal toxic potential, such as using fluorescent lights, which have less mercury than conventional lights.

* Energy Efficient Equipment: Energy efficient versions of products such as dishwashers, refrigerators, and water heaters, can potentially save an enormous amount of energy. Look for Energy Star designated machines.

* Quality Building Components: The extra cost and effort of high quality building materials, such as high-performance windows or structural insulated panels will go a long way in energy efficiency.

* Renewable Energy Systems: Any product that reduces the use of fossil fuels, such as solar water heaters or photovoltaic systems, is extremely eco-friendly.



Read more: http://www.brighthub.com/environment/green-living/articles/53717.aspx#ixzz16TWWEgzr

Paying attention to the materials that make up a green home is very important, but keep in mind that green building supplies are not everything. Without energy efficient design, a minimalist approach, and the right location, all the eco-friendly materials in the world will not make a home green.

Sources:

Wilson, Alex. "Your Green Home: A Guide to Planning a Healthy, Environmentally Friendly New Home." (New Society Publishers, 2006).


Read more: http://www.brighthub.com/environment/green-living/articles/53717.aspx#ixzz16TWpuCdd

Belgium to push 'sustainable materials' initiative

The Belgian EU Presidency wants to clean up industrial processes in Europe by promoting a "cradle-to-cradle" approach to resource management in the manufacturing sector, EurActiv has learned.
Background

Growing resource scarcity and rising raw material costs are dampening prospects for economic growth in Europe, inciting policymakers to look for ways of decreasing the environmental impact of industrial activity.

Assessing the environmental impact of products throughout their whole lifecycle – from raw material extraction to transport, consumption and final disposal – is being touted as the new mantra in environmental policymaking and sustainable business decision-making.

The European Commission first embraced life-cycle thinking in its Green Paper on Integrated Product Policy (IPP) in 2001, followed by a Communication on IPP in 2003.

Other examples of existing life-cycle related EU policies and instruments include the 2005 Thematic Strategies on the Prevention and Recycling of Waste and on the Sustainable Use of Natural Resources, as well as the 2008 Sustainable Consumption and Production Action Plan.


Meeting in Ghent on 12-13 July, EU environment ministers will debate a study by the Belgian EU Presidency on "sustainable materials management" (SMM).

The study, obtained by EurActiv, advocates "a fully integrated way of addressing materials use" in manufacturing in order to limit resource depletion and air, soil and water pollution.

"If we carry on using materials the way we are now, this will ultimately result in the depletion of raw materials and harm the environment," the Belgian EU Presidency said.

The objective is to move from waste policies to "materials policies," which cover the full life-cycle of products and manufactured goods, from the extraction of raw materials to product design, manufacture, consumption and disposal.

"A policy that is limited to waste prevention and recycling is insufficient to significantly reduce Europe's [ecological] footprint and avoid a further depletion of natural capital," the study argues.

As an alternative, the Belgian EU Presidency wants to promote the concept of "sustainable materials management," a broader notion which covers the whole life-cycle of products in a so-called "cradle-to-cradle" approach.

"SMM, as the Belgian Presidency wants to promote it, aims at the efficient and environmentally responsible use of materials, independent of whether they are raw materials, products or waste," reads an introduction to the study.

European 'platform' to explore way forward

At the Ghent ministerial meeting, Belgium will propose to establish a "European platform on sustainable materials management" that would be tasked with developing a "joint future vision on SMM".

"That's new on the European agenda. It is the first time we have discussed about that," said a high-level source in Belgium. "We want Council conclusions which can be useful for 2011," when the European Commission is expected to adopt a roadmap on resource efficiency, the official added.

When established, the platform will "launch experiments which go beyond established practices" in areas such as waste collection and recycling, re-use and repair or recovery of industrial residues.

In total, the study has identified twelve areas where the SMM approach could be applied, including closed loop industry systems for residues (of construction waste for example), biomaterials, cradle-to-cradle or IT systems that track the logistics supply chain. "IT can give enterprises tools to effectively manage supply chains and to monitor the product and material flow up- and downstream, in turn allowing for material savings," the study says.

'Scattered' EU policy framework

To remedy the current "scattered" EU policy landscape, the study advocates a realignment of all EU initiatives on waste, natural resources, raw materials, integrated product policy, eco-design and sustainable consumption and production.

It also argues for better integration of sustainable materials management with broader policy areas such as agriculture, competitiveness and innovation.

"Policymakers in different policy fields – such as environment, energy, climate, innovation and economics – have to work together more intensively to make our material use more sustainable," the Belgian Presidency argues.

"At EU level, structures should be set up to allow for systematic and institutionalised cooperation on SMM challenges, both within the European Commission and in the Council."

A fine collection of billingsgates in a glass fronted display box

Resource Efficient and Sustainable

Earth Friendly and Resource Efficient

Once seen as extreme or eccentric, environmentally friendly living spaces are going mainstream. You don't have to strain your budget or your sense of style to choose a healthy home -- these days, it's easy being green. Here's what's new in environmentally friendly products and materials for the home.

This category encompasses materials that are recycled, sustainably harvested, or organically grown. One retro option now available again (from Forbo and Armstrong) is real linoleum -- made from biodegradable linseed oil, pine rosins, and wood flour on a jute backing.


* Recycled products are filling the market faster than aluminum cans at a sporting event. Look for rubber and polymer roofing that imitates slate to reduce weight and maintenance. In countertops, IceStone blends 75 percent recycled glass with concrete for durable countertops, backsplashes, shower surrounds, walls, and floors. See 20 standard colors at their Web site, www.icestone.biz.



* Lumber choices may seem confusing. Avoid products produced from old growth timber or endangered tropical hardwoods. Seek out certified and managed forests, recycled or reclaimed wood (salvaged from riverbeds or old buildings), or composites such as hardwood-veneered MDF (medium-density fiberboard) for doors and cabinets. An early green favorite with architects, fast-growing bamboo makes beautiful, durable flooring. Teragren sells bamboo in random lengths, wide planks, and a new "floating" (non-glued) product. Look for inspiring photographs at the Teragren Web site, www.teragren.com.



* Outdoor products have evolved, too. Treated lumber eliminated arsenic for less toxic preservatives. Formed from ground wood fibers and resin, composite decking and railing won't rot or need painting. CorrectDeck (www.correctdeck.com) is splinter-free and cool underfoot, and its woodgrain planks can be joined with

* High-performance windows, especially with low-emissivity (low-E) glazings, are among the best-known ways to save energy for heating and cooling.


* Water-saving appliances include Energy Star-rated dishwashers and front-loading washing machines. In the bathroom, all new toilets must use only 1.6 gallons of water per flush, but Sterling's Rockton model also has a .8-gallon-flush option, which can save a household of four up to 6,000 gallons of water per year over 1.6-gallon models. Get details at their Web site, www.sterlingplumbing.com.


* Structural Insulated Panels (www.sips.org) are gaining acceptance for use in walls, floors, and roofs. Panels sandwich a rigid foam core (usually expanded polystyrene) between OSB, or oriented strand board. OSB mixes wood strands made from fast-growing trees with wax and a binder to form mats. These mats are layered across each other for strength, then heat-pressed into panels that makers say save time and energy over stick-built construction.


* Tankless water heaters don't keep water hot in a standing tank all day long. Instead, these compact, on-demand units attach to your plumbing system and heat water as it runs through a heat exchanger. You only pay to heat water when you need it. Rinnai claims its Continuum model is 50 to 70 percent more efficient than a traditional standby heater. A digital control pad maintains and limits water temperature indefinitely. One version lets you preset showers, automatically fill tubs, and even enjoy TV and radio on a 7-inch screen. For more information, see the Web site www.foreverhotwater.com.


* Photovoltaic panels let you generate your own power from the sun. Tax credits and utility company rebates can help yield a five-year payback. BP Solar sells complete installed solar home power systems through more than 40 home centers in Southern California and plans to expand to Northern California, New Jersey, New York, and Hawaii. Use the solar savings estimator at www.bpsolar.com to calculate potential costs and savings based on your zip code, electric bill, and system size.

Healthful Materials

Air-tight construction addressed the energy crisis of the 1970s, but few foresaw that this approach could be harmful to your health. When building materials emit fumes and trapped air creates mold, sick building syndrome and environmentally triggered illness and allergies can result. One solution is to shop for low-emitting interior products and materials.

Started in Germany, the Bau-biologie movement aims to create living spaces that are both harmonious with nature and human health. Proponents recommend nontoxic building materials, natural air movement to control humidity, filtering of air pollutants, and radiant or passive solar heat.

An offshoot of Washington state and EPA programs, the GREENGUARD Environmental Institute (www.greenguard.org) certifies low-emitting interior products and materials through quarterly air-quality performance tests. When you build with these products, you can breathe easier.

* Low- or no-VOC products. Air-polluting volatile organic compounds (VOCs) include toxic solvents and formaldehyde. Some new fiberglass insulation is VOC-free; other lung-friendly insulation includes recycled cotton batts (containing cloth trimmings usually scrapped) and soy-based sprayed-in foam.
* Low- or no-odor coatings. Sherwin-Williams' zero-VOC Harmony line has virtually no odor during application and drying. Its water-base Duration Home formulas are even more stain-resistant and washable yet contain fewer VOCs than typical paints. Pick healthy paint for your project at www.sherwin-williams.com.