On the Variable Value of Recycling

A new and very interesting paper by Gutowski et al [1] (also up at ScienceDaily) discusses the variable value of recycling - more specifically, whether there are energy savings benefits is not always clear; and in some cases, the benefits, if any, are small.  From [1]:

Remanufacturing products that can substitute for new products are generally claimed to save energy.  These claims are made from studies that look mainly at the differences in materials production and manufacturing.  However, when the use phase is included, the situation can change radically. ... For most of these products, the use phase energy dominates that for materials materials production and manufacturing combined.  As a result, small changes in use phase can overwhelm the claimed savings from materials production and manufacturing.

Gutowski et al look at 25 case studies in 8 product groups, including furniture, clothing, computers, electric motors, tires, appliances, engines, and toner cartridges.  In these 25 case studies, it was found that there were only 8 cases of clear energy savings, generally grouped into office furniture (office chair, office desk), textiles (clothing), and select electronic components (laptops and monitors).  The first two categories experience an energy savings with reuse because the usage energy / energy of operation is so low [1].  For the electronics, on the other hand, "energy efficiency improvements within the same kind of devices over the time period (2001-2005) are not large enough to overcome the manufacturing phase savings achieved by reusing."  On the other end of the spectrum, products which are best bought new include high-usage appliances such as dishwashers and refrigerators, and other electronic components (again, including laptops and monitors).  In these cases [1], "the use phase energy has changed significantly due to efficiency mandates and/or the introduction of new efficient technologies." 

So what does this mean to materials science and engineering?  New materials are being developed to improve the efficiency of product use, such as through lighter weight which leads to improved fuel economy, or through improved energy maintenance / control / storage leading to reduced energy loss.  As outlined in Ashby [2], the Use phase of many product life cycles prevails as requiring the largest energy fraction, e.g. in civil aircraft (~95%), family cars (~85%), and appliances (~70%).  As such, high-performance materials often target the above products because of the potential energy savings in their respective Use phase.  These applications can also justify the high cost of the new materials because of the anticipated reductions in usage cost.  But as Ashby outlines [2], there are three additional material phases in product life cycles: 1) Production, which includes the acquisition of the raw materials and by-products of refinement; 2) Manufacture, which includes the conversion of raw materials into product shape; and 3) Disposal, which includes the ability to re-use, disassemble, and recycle the product - and is more difficult to quantify than the other three. 

The energy associated with a Disposal phase is a function of many things.  Borrowing from Ashby [2], this can include energies (or costs) associated with, for example, waste / recycled material transportation, sorting, and storage; the usable energy contained in the waste (e.g. which may be retrieved through incineration); the energy difference between embodied energy of new materials versus the recycling energy of waste materials; the energy required to develop a succeeding material/product; and perhaps most important, energy surrounding the environmental consequences.  

Although energies associated with the Disposal phase were not considered by Gutowski et al, the authors do acknowledge that the re-manufacturing route can reduce landfill burdens as well as the toxic material generation, and thus tilt increased importance to re-manufactured rather than new products.  However, I've already written on the toxicity of some materials and the projects underway to develop alternatives, e.g. replacement coatings to Cadmium and Chromium; in these cases, there is significant Disposal-based energy driving the development of new products which can reduce toxic material generation.  In order to more completely and evenly assess the value of recycling and its role in a product's life cycle - as compared to new material manufacturing - the energy of the Disposal phase needs to be better quantified and calculable.  This need is further driven by the fact that some products identified by Gutowski et al - namely, electronic devices - are experiencing diminishing services lives (estimated as 4 years in [1]) and thus their Disposal phase energies are contributing more to their overall energy fraction.

[1] T.G. Gutowski, et al.  Remanufacturing and energy savings.  Environmental Science & Technology, Vol. 45 (2011), pp. 4540-4547.
[2] M.F. Ashby.  Mechanical Selection and Mechanical Design, 4th Ed.  Butterworth-Heinemann (2010), pp. 440-447.

Theft of Materials

Stolen Copper wire from Australian train lines.  (Source: Herald Sun/Bill Mcauley.)

Certain materials are targets of theft because to steal them the reward (meant strictly in the 'return' sense) is greater than the risk.  The reward - primarily money - depends on many factors, all interwoven, including the price of the material, its scarcity, its supply and demand, its function, its recycle-ability, its manufacture-ability, and its sell-ability.  The discussion below primarily focuses on the more general theft targets with more known and clearly-defined rewards.  In reality, however, anything can be a target for theft.

Metals

Metal Prices.  As described by Kooi [1], high metals demand on the international market is a key driver leading to scrap metal theft.  The prices of metals can change as fast as by the half-hour, reflecting the instantaneous updates of supply and demand.  A number of companies (e.g. Kitco) monitor price fluctuations in common "base" metals (e.g. Aluminum, Copper, Lead, Nickel, Zinc) as well as the more precious or scarce metals (e.g. Gold, Silver, Platinum, Palladium, and Rhodium).  Prices change quickly over even the course of a day: for example, earlier this month over an 18-hour span, the price of Copper ranged between $3.95 and $4.03 USD per pound, a non-trivial difference of 2%.  Over a 30-day span the price of copper has ranged between $4.38 and $3.91 USD per pound, a difference of more than 10%.  A quick look at the other metals listed above shows Copper is not the only metal with a rapidly fluctuating value.

Common Metal Forms.  Many of the metal items targeted for theft are those in common and recognizable forms.  Kooi [1] has reviewed many of these forms, illustrating a world-wide problem of metals stolen for scrap.  (A Google search will find many more examples).  Copper (and brass) is commonly stolen from a number of sources such as plumbing suppliers, construction sites, vacant luxury homes, cemetery headstones, fire hydrants, and even live electrical transformer stations.  Telephone land lines, street lights, and traffic signals are also frequently cut for their Copper wiring.

Metal theft patterns changes with market prices: as Copper prices dropped mid-way last year, increasing theft of steel and Aluminum metals was reported [2].  Steel is a frequent target for theft because it is common, simple, and easy to steal - as car frames, concrete re-bar, construction materials, beer kegs, manhole covers, assembled bridges, and even playground steel slides - then sold quickly at scrap value [1].  Even railway tracks have been stolen, which are then cut down and sold as scrap.  Aluminum is often stolen as castings from construction sites, car wheels, house siding, bike frames, and plumbing.  But it is not only these easily identifiable, common forms which are targets for theft.  The "scientific community should be on guard, too.  Steel vacuum chambers, electrical cables, chilling units stuffed with copper and aluminum tubing, and other metal-laden laboratory accoutrements all look like money to metal thieves..." [3].

Scarce Metal Forms.  The more scarce (and generally more valuable) metals are also targets for theft.  Catalytic converters on cars, for example, are a key target which contain thin coatings of Platinum, Palladium, and Rhodium - which in 2008 were respectively valued at approximately $65, $15, and $290 per gram [4].  While in a given catalytic converter there is not a considerable amount of these metals (a total mass in the range of ~3-7 grams depending on the converter), with increasing prices there is considerable financial motivation: converter recyclers will buy scrap converters at $70-$100 each [4].  (Recently, Platinum in the form of jewelery has also become a common target for theft.) 

Despite their value, not all metals are easy to sell.  As described by Kooi [1], stolen Gold or Silver jewelery has intrinsic value and can be sold in scrap or melted form or in their original shape.  In contrast, base metals Copper, Aluminum, brass, Zinc, Nickel, Platinum, etc. are generally not worth much (or not easy to sell) outside of scrap form; and so these metals are generally melted and re-shaped by scrap dealers or the thieves themselves.  On the other hand, the valuable metals in catalytic converters reside on a porous ceramic substrate and can not be extracted for sale using simple methods.  To extract the metals, the entire assemblies must be heated with the ceramic up to temperatures in excess of 1500 degrees Celsius, then further refined.  The complexity of this refinement limits the number of buyers for stolen converters, most of whom are designated converter recycling depots.

Valuable metals used in electronics also fit into the category of difficulty in extraction and low theft return.  However, with increasing volume of waste electronics, a correspondingly large volume of valuable metals become locked away.  I previously wrote on this subject with respect to scarce metals: Japan's 'urban mines' contain approximately 6,800 tons of Gold (currently ~$48 per gram), 60,000 tons of Silver (~$1 per gram), and 1,700 tons of Indium (approaching ~$1 per gram).  As the price of metals increase (and as the electronic device lifetime decreases), the value of electronic waste will become greater.  For example, a U.S. Geological Survey 2006 report [5] estimates that an average cell phone (weight 113 grams) contains approximately $1 worth of Copper, Silver, Gold, Palladium, and Platinum combined.  While this may appear to be a rather trivial amount, millions of cell phones are discarded annually.  The overall reward is great enough for 'urban miners' to harvest, so thievery can't be far behind as metal prices increase.

Other Materials: Polymers and Ceramics

While metals have value in both product and raw form, polymers have a much smaller market for recycling or use as raw material outside of combustible fuel.  One of the key reasons for this difference is the degradation of polymers with time and use.  For example, the mechanical properties of many polymers (e.g. thermoplastics which can be melted and re-shaped or re-purposed) decrease with increasing number of re-cycles.  This is due to breakdown of the polymer chains over time and limited "mix-ability" of polymers from different sources.  Such breakdown is very different from metals, which can be recycled a far greater number of times - essentially infinite so long as alloy elements can be separated and oxides removed/reduced.  In contrast, many polymers include additives which can not be easily separated from the base polymer, thus complicating recycling.  A second reason, it requires much more energy to produce metals from mined or native sources (e.g. ore) than from recycled sources; in this way, metals more than polymers also have far greater value once in a usable form.   

In a functional device, the value of polymeric parts is at its highest; the value also increases with the functionality of the part.  For example, carbon fiber bicycle frames are high targets for theft, not because of the price of the carbon fiber but because its function as part of a light-weight frame enables a high immediate resale value.  Another example, the polymer Dyneema is used in ballistic armor vests, among other applications.  The polymer is an ultra-high molecular weight polyethylene, which has the same monomer unit as the polyethylene used in plastic shopping bags.  The value in one form is clearly larger than that in the other; but unfortunately between the two recycle-ability is not equally directional.

Ceramic materials (e.g. granite, marble, diamond, etc.) also find themselves in the same category as the polymers and fibers: they are most valuable while providing functionality (and/or possessing immediate resale value in their current form), there are not considerable cost savings by producing from recycled sources, and the two-directional recycle-ability is limited.

Material Solutions to Theft

Solutions are required in order to identify stolen materials, but also to alert users and technicians of critical missing materials, e.g. power cables which can be hazardous if a circuit is incomplete.  There have been a number of policy changes, regulatory agencies, and security measures adopted which have helped reduce the occurrence of thievery, e.g. [1].  In the case of catalytic converters, additional measures have targeted supply chain bottlenecks (converter recycling depots) and thus reduce the success of selling stolen parts.  Complimenting these strategies, below are some of the materials and engineering solutions which have been implemented in an effort to reduce materials theft.

Identification Labels.  This is a truly fascinating field; and with novel Material Re-Design approaches below, I believe this represents the future of materials research and engineering in theft.  A few examples commercially available are:

• One example, SmartWater [6] is a liquid-based solution which uniquely 'tags' targets (e.g. Copper wire), thereby allowing for exact detection of a stolen material under UV light.  This coded liquid remains intact on the conductor jacket even if the wire insulation is burned [1].  Spraying devices can also cover the offender in the liquid, which can't be easily removed or washed off.  
• Another example, MicroDotDNA technology "consists of thousands of polyester substrate microdots, each the size of a grain of sand, onto which unique information is laser etched."
• Proof-positive Copper [7] uses laser-etching methods to add serial codes and reference numbers directly on copper wires; this method can provide information on the material's owner as well as installation location and date.

Material Re-Design.  An approach to prevent theft: make something not worth stealing.  For example, target items such as manhole covers have been replaced with valueless, un-recyclable thermoplastic rejects, reinforced in order to give them the necessary mechanical properties for the application [8].  This is also a great example of re-purposing otherwise waste materials.  Another example, efforts have been made to re-design substation grounding straps in order to reduce exposed copper [1].  Of course, substitution-type material re-design won't be an option for all theft targets, but it can help concentrate focus on the higher-priority ones.

Mechanical Additions.  Finally, a number of commercial products exist to help deter or slow theft of frequently-targeted materials.  These include devices such as the Copper Keeper (to prevent theft of copper wires), as well as the Catlock and CatClamp (to prevent theft of catalytic converters).  As outlined by Kooi [1], these devices enable better security for the materials but at a cost nearly equal to replacing them.  And with increasing market prices for these sought-after metals, more sophisticated prevention approaches will be needed in the future.
 
Materials targeted for theft require a certain ease of identification and understanding of value; financial longevity, stability, and flexibility; omnipotence and malleability in shape and form; and so on.  Metals find themselves with all these characteristics, and are thus the most frequent target for theft.  But as explained above, all materials can be targets for theft if there is immediate resale value and if the thief understands the value of what is being stolen.

[1] B.R. Kooi.  Theft of Scrap Metal.  Problem-Oriented Guides for Police - Problem-Specific Guides Series, No. 58.  U.S. Department of Justice, April 2010.  ISBN: 978-1-935676-12-6.  (Available On-Line.)  Also see L. Bennett.  Assets under attack: metal theft, the built environment, and the dark side of the global recycling market.  Environmental Law & Management, Vol. 20 (2008), pp. 176-183. (Available On-Line.)
[2] J. Grimaldi.  Thieves ditch copper for other metals.  The Hamilton Spectator (Hamilton, Ontario), July 13, 2010, p. A03.
[3] Stealing metal, metal allergy.  Chemical & Engineering News, Vol. 85, No. 46 (2009), p. 56.
[4] A. Tullo.  The Catalyst Caper.  Chemical & Engineering News, Vol. 82, No. 22 (2008), p. 32.
[5] Recycled Cell Phones - A Treasure Trove of Valuable Metals.  U.S. Geological Survey, Fact Sheet 2006-3097 (July 2006).  (Available On-Line.) 
[6] BT launches nationwide campaign against cable theft; 'SmartWater' invisible paint deployed to 'tag' metal thieves.  ENP Newswire, July 27, 2010.
[7] Proof positive Copper: SouthWire's solution to the Copper theft epidemic.  Transmission & Distribution World, Vol. 62, No. 4 (2010), p. 18.
[8] S. El Haggar and L. El Hatow.  Reinforcement of thermoplastic rejects in the production of manhole covers.  Journal of Cleaner Production, Vol. 17 (2009), pp. 440-446.

In MatSciEng: New Materials in Health and Safety

The MSDS diamond, including flammability, health, reactivity, and protective equipment information.

Despite best efforts and intentions, design and engineering for the lifetime of materials are sometimes incomplete.  In those cases, new materials can be introduced to refine and supplement the old materials or correct them entirely.  When health and safety are at risk, such new materials become the focus of international research and development effort.  In this post I've written about some new work and on-going investigation surrounding new materials in health and safety.

Nuclear Waste Storage in Clay 

A great deal of work is constantly on-going to study and monitor the safe storage of radioactive isotopes.  Care of ScienceDaily, Reich et al from the Gutenberg University Mainz have found that, in addition to other natural materials, natural clay materials can be used as storage for nuclear waste.  More specifically, it has shown that Opalinus Clay (a "Jurassic claystone" or weak mudstone) has the ability to sorb radioactive Plutonium (Pu) and Neptunium (Np) of select oxidation states from aqueous solutions.  For example, Neptunium, "...hardly diffuses through the clay, and even after a month is still almost where it started."  Longer investigations are always required when studying nuclear waste storage; for example, the radioactive half-life for Neptunium is 2.14 million years.

Replacement Coatings of Hexavalent Chromium (Cr)

Chromium metal exists most most commonly in the hexavalent oxidation state.  Hexavalent chromium is also a known human carcinogen via inhalation.  As a result, there is a great deal of motivation to find a replacement metal with similar properties, mechanical and otherwise.  However, the most common forms of hexavalent chrome are coatings - either in the electrolytic hard chrome (EHC) or decorative form - which possess a unique set of properties not easily replaced.  While some solutions do exist as partial replacements, a great deal of work is still on-going in aerospace, defense, and commercial markets to find a complete replacement for hexavalent chrome.   

Nanofiber Materials to Detect Chemical Hazards 

In a recent issue of the journal Advanced Materials [1] (also at ScienceDaily), Kelly et al have used porous Silicon (Si) filters as templates for the fabrication of carbon nanofibers.  These nanofibers have been demonstrated as sensors for hazardous chemical compounds.  More specifically, the nanofibers act as sensors for organic vapours which can cause neurological harm upon inhalation.  In application, such nanofibers can add supplementary information on whether activated charcoal air filters have expired or otherwise ceased to provide protection.

Composite Materials Extract Contaminants from Drinking Water 

Also over at ScienceDaily, a new composite 'multiphase' material has demonstrated the ability to extract radioactive and hazardous impurities - namely, radioactive iodide and arsenic - from drinking water.  Engineered by Drs. Pawlak and Venditti from NCSU, the material is made from natural and biodegradable material components hemicellulose and chitosan.  In addition, the internal structure of the 'multiphase' material is a foam, which possesses an increased surface area which likely helps increase the extraction efficiency.

Replacement of Cadmium (Cd) Metal Coatings

Similar to the work done to replace hexavalent Chromium, Cadmium (Cd) metal is also a target for replacement.  Cadmium is applied to a wide range of steel parts requiring corrosion protection, ranging from simple nuts and bolts to high-performance aircraft and defense components.  However, Cadmium itself is a toxic metal which can be released from the parts to the environment when in use.  Like Chromium, Cadmium has a unique set of material properties such as lubricity and contact resistance, as well as good corrosion resistance.  However, also like Chromium, complete Cadmium replacement still requires work as suitable material replacements have not been developed to adoptable levels.  Groups such as the Joint Cadmium Alternatives Team (JCAT) continue to drive study in this area.   

Nano-Materials can Detect and Neutralize Explosives 

Returning to ScienceDaily, work done by Prof. Apblett at the Oklahoma State University has focused on chemical-based sensing of explosives.  Apblett et al have sprayed thin coatings of catalytic Molybdenum (Mo) oxide nano-particles on various surfaces; in the presence of hydrogen peroxide-based explosives, the coatings undergo subsequent changes in colour and conductivity, both of which can be measured.  Adding additional spray, which reacts with the peroxide vapour, the coating can also disarm the explosive.  Additional studies performed by Apblett et al on Molybdenum oxides include sorbants for toxic metals, heavy metals, and radionuclides [2,3].

[1] T.L. Kelly et al. Carbon and carbon/silicon composites templated in rugate filters for the adsorption and detection of organic vapors.  Advanced Materials, Vol. 23 (2011), pp. 1776-1781.
[2] M. Chehbouni and A.W. Apblett. Molybdenum-oxide based sorbants for toxic metals.  Ceramic Transactions, Vol. 176 (2006), pp. 15-23.
[3] B.P. Kiran et al. Selective absorption of heavy metals and radionuclides from water in a direct-to-ceramic process.  Ceramic Transactions, Vol. 143 (2003), pp. 385-394.

Processing Limitations in Nano-Materials

Example Nanomaterials from Talapin et al at the University of Chicago (link).

In the recent issue of the journal Nanotechnology (also covered at ScienceDaily), Kelly [1] has written a very interesting article concerning processing limitations of some small-scale engineering designs and constructions.  From ScienceDaily:

The overall goal when entering nanotechnologies into the market is low-cost, high-volume manufacturability, but at the same time, the materials' properties must be highly reproducible within a pre-specified limit, which Kelly states cannot happen below the 3 nm limit when trying to make arrays. 

The top-down approach to manufacturing, which Kelly states is limited, uses external tools to cut and shape large materials to contain many smaller features.  Its alternative, the bottom-up approach, involves piecing together small units, usually molecules, to construct whole materials -- much like a jigsaw puzzle -- however this process is too unpredictable for defect-free mass production of arrays.

As outlined by Kelly, standard manufacture operates under what is called 6-sigma yield - which essentially means there is a manufacturing defect rate of only 0.00034%. Those extremely tight tolerances are simply not met by the respective manufacturing processes of most nanotechnologies.  However, there can be two ways to (re)consider these limitations.

The first is that - given the need for the technology - the scales of production will follow.  Moore's Law is a well-known example.  In short, due to continuous improvement in fabrication equipment and manufacturing technology - much of which was not around when Moore's "Law" was first proposed - the number of transistors possible on a single chip has doubled every two years from the 1970's to the present day.  Based on this, it is reasonable to propose that additional improvements in manufacturing technology will help raise future nanotechnologies out of the "unmanufacturable" category.     

The second way to consider these limitations is with reference to another complex system - the human body - which also possesses a great deal of complex functionality and manufacturing.  For example, our own DNA replication and copying processes would not meet 6-sigma yield if not for clever DNA proof-reading and correcting mechanisms.  In addition, some degree of DNA error is manageable because redundancy exists.  Redundancy might not sound like an ideal situation for large-scale fabrication, but it is a useful tool to help maintain proper system functionality even if a small percentage of components are defective.  And, thermodynamically speaking, if there will be an unavoidable amount of error, then redundancy may be the path of least resistance.  Furthermore, if you accept defects will exist - if not from manufacturing, then due to in-situ operation - the design process changes from a defect-free nanotechnology to one which may perhaps even benefit from a certain concentration of them - much like the way doped semiconductors operate and interact.  But of course, this may not be possible for some nano-materials and their applications, e.g. quantum dots requiring precise confinement energies.

Ultimately, as Kelly writes, some nanotechnologies are unfortunately bound to remain on a lab bench:

Many results in nanoscience can be shown to be intrinsically unmanufacturable in terms of ideas for applications in electronic or optoelectronic components, and so will remain as scientific curiosities.

Time will tell which are the most manufacturable and which are so in a sustainable manner.  

[1] MJ Kelly. Intrinsic top-down manufacturability. Nanotechnology, Vol. 22 (2011), 245303.

In MatSciEng: Metal Glass, Tiny Diamonds, and Fruit Fibers

Limited time to write about all new things Materials Science and Engineering has left me with a number of items I've been meaning to write about - or at least bring to light.  This post will be an update of sorts, as well as a trial run for a new format - one which I aim to use in the future in order to focus on newly-published developments for a more current and broad scope.  (Because hey, this is the internet after all.)

It's a Metal; It's a Glass

The atoms in metals are typically arranged in an ordered lattice structure, for example residing on the corners of cubes placed side-by-side.  In contrast, the molecules in glass have a much more random structure ("amorphous"), not keeping to any particular ordered or repeated lattice arrangement.  Bulk metallic glass (BMG) is a material which consists of metal atoms but without the lattice.  In most cases, BMGs possess material properties much different than the lattice metal counterpart.  For example, while strength is typically increased, ductility is decreased - which limits the ability for the BMG to be formed into shapes.   

However, as recently reviewed by Schroers et al [1] (also see ScienceDaily), BMGs can be formed using a specific method (thermoplastic blow molding) which utilizes specifically the BMG's limited ductility mechanisms.  The end result is an apparent ductility (or formability) which is significantly greater.  And because this process is inexpensive, complex shapes (particularly, shells or hollow containers) can be fabricated for a wide range of commercial products where previously only low-strength, cheap, and/or poor quality metals have been allowed.

Diamonds: Not Just for Expensive Jewelery Anymore

Keeping on with metals and glass, diamond has a number of properties advantageous to materials engineers.  For example, it has a thermal conductivity more than twice that of silver and about three times that of copper. Diamond also offers high hardness, low coefficient of thermal expansion, high melting point, and high wear resistance.  And in particulate form, diamond is relatively inexpensive: you can purchase 5 grams of sub-micron-sized synthetic diamond particulate from Alfa Aesar for about $200 (5 g is roughly 1.5 cubic centimetres).  This makes diamond particulate a good candidate for composite materials.

Which are exactly what Nadler's group from Georgia Tech Research Institute have made (from ScienceDaily).  By processing films of silver containing diamond particulate, and tailoring the amount of diamond included in the composite, the thermal properties (e.g. conductivity 25% greater than in copper, and the coefficient of thermal expansion) could be engineered for critical defense-oriented electronics.

"Ductile" Concrete

Continuing with the composites focus, I've been recently directed to the Journal of Advanced and High-Performance Materials (site here), a periodical dedicated to the advancement of materials in building sciences.  In the current issue Li [2] outlines the development and state-of-the-art of Engineered Cementitious Composite (ECC) - a composite consisting of concrete reinforced with internal fibers.  The fibers act to interrupt and distribute large cracks into smaller ones as well as keep micro-cracked concrete together (Figure 1).  The end result is a concrete material - which can also be sprayed on existing concrete as a protective layer - possessing greater damage tolerance, toughness, resilience, and energy absorption capacity (particularly in dynamic or blast loading).

Figure 1.  "Ductile" ECC in bending.  Image taken from Li [2].

I Love to Drive, Drive, Drive ...

We now interact with a variety of plastic/polymer products made from corn, potato, bamboo, as well as other "grown" materials.  Also care of ScienceDaily, fibers from pineapples and bananas are now being used to produce plastic parts and components for automotive, defense, and other high-performance applications.  The Brazilian researchers report their "nano"-cellulose polymer fibers have a stiffness almost as great as Kevlar - known for its use in bullet-proof vests - with the added benefit that the parts can be bio-degradable. 

On the other end of the spectrum, a "smart material" is a catch-all phrase that describes a material that possesses added "active" functionality as opposed to being passive only.  For example, when electric currents are passed through piezo materials, they can oscillate or vibrate.  In this fashion, automotive noise (or noise of any kind) can be dampened and eliminated altogether, thereby reducing energy losses.  On the other hand, these same materials can be used to capture the oscillation or vibration energy in a car and turn it into useful electrical energy.  Work with these kinds of materials is on-going at the Fraunhofer Institute Adaptronics Alliance in Germany (also see ScienceDaily).  Also there, safety devices are being designed consisting of magneto-rheological fluids - in other words, fluids which can change their state (from solid to water and everywhere in-between) by the strength of a magnetic field passed through them.  A large number of applications are currently in the conceptual stage, such as safety mechanisms for machinery or gears.

Take-Away Materials, Today

Finally, I'll end with a take-away message which you can literally take with you.  Materials Today has a great collection of podcasts reviewing current work being done in materials science and engineering.  In particular is a March 16 2011 podcast by Prof. James Tour at Rice University who discusses "Developments in Graphene".  Graphene - an atomically-thick version of graphite - has powerful potential in strength, conductivity, electronics, and computing.  It's a thesis topic on its own, so I'll leave that for a later post.  You can also find a number of recent articles over at Nature Materials and Science concerning recent developments with graphene.  In May of this year will be a conference in Boston regarding the "road to applications" for this powerful material in the next 5-10 years.

[1] J. Schroers et al. Thermoplastic blow molding of metals.  Materials Today, Vol. 14(1-2) (2011), pp. 14-19.
[2] V.C. Li.  High-ductility concrete for resilient infrastructures.  Journal of Advanced and High-Performance Materials, Winter 2011, pp. 16-21. (Available On-Line.)

Lightweight Cellular Materials and Lessons from Nature

New hybrid or composite materials can be considered a combination of two or more constituent parts.  The end result is a material that possesses a set of properties not offered by either individual part alone.  A basic example, concrete reinforced with rebar is a composite material possessing both strength (provided by the concrete) and toughness (provided by the steel).

The concept of a "constituent part" can be extended further to include liquids and gases.  This is the approach taken by Ashby [1], who has considered cellular materials as hybrids of 1) solid material and 2) air.  Like composite materials consisting of two interwoven solid materials, the arrangement of the "air" component in cellular materials can also be designed through the wide range of manufacturing techniques [2]:

Variety of metal foams and their fabrication methods (from Wadley [2] - click to enlarge).

As the architecture of these materials is designed, so are the resultant characteristics (e.g. density, strength, energy absorption, resonant frequency, and the list goes on).  There is a great deal of very interesting on-going work which focuses on processing, properties, and applications of these cellular materials - most of which focuses on the light-weight structural benefits.  For more information, see bi-annual conferences Cellular Materials (CellMat) and Porous Metals / Metalic Foams (MetFoam).    

Natural Structures and Sustainable Design

Some of you may have already noticed now closely the above cellular materials mimic those of natural structures, of which a well-known example is spongy (trabecular) bone:

The internal cellular structure of spongy (trabecular) bone.  (Source: National Cancer Institute.)

The employment of this cellular structure illustrates mechanical benefits such as light weight and high load-bearing structural efficiency.  However, as recently studied by Doube et al [3] (also from ScienceDaily), this cellular design is not restricted to select organisms; in fact, the adoption of a cellular bone structure is wide-spread and is allometric (i.e. scalable with organism size) across a large number of mammals and birds from elephant to shrew.

Such a prevalent example of natural materials design is therefore not as much a niche evolutionary development as it is a generally-adopted (and powerful) design tool.  And because tools such as these came about through evolutionary means, they therefore also offer insight into new dimensions for human-powered sustainable materials design and development.

[1] M.F. Ashby.  Hybrids to fill holes in material property space.  Philosophical Magazine, Vol. 85 (2005), pp. 3235-3257.
[2] H.N.G. Wadley.  Cellular metals manufacturing.  Advanced Engineering Materials, Vol. 4 (2002), pp. 726-733.  (Available On-Line.)
[3] M. Doube, et al.  Trabecular bone scales allometrically in mammals and birds.  Proceedings of the Royal Society B, Vol. 278 (2011), DOI: 10.1098/rspb.2011.0069

On Materials Science and Engineering in Energy

Solar tower concentrates light reflected from surrounding panels.  (Source: Paul Langrock/Zenit/Laif/Redux)

A thoroughly interesting report [1] has recently been published regarding the future of materials science and engineering in energy and related fields.  The report is available on-line here; and it is also summarized in the latest issue of the Journal of Minerals, Metals, and Materials (JOM) [2].  The report is written well and with the general public in mind; for the hobby scientist, it also helps convey a thought-provoking state-of-the-art in materials science and engineering.  To summarize the already-summarized article in JOM, the topics in the report - and subjects which will be in the forefront of future materials study - are:

Functional Surface Technology (or: making the surfaces of materials perform in new/different/improved ways).  This includes:

• Catalysts with high selectivity and conversion efficiency.  When catalysts aren't efficient, energy is wasted.
• Smart coating / lubricant systems for lightweight alloys.  Lighter alloys such as aluminum and magnesium tend to wear down relatively quickly. 
• Coatings to inhibit galvanic corrosion.  Corroded materials' performance rapidly degrades.
• Solar photovoltaic materials utilizing a broader spectrum of light.  Current solar panels only collect a fraction of the light energy available.
• Treatment processes to rebuild or enhance surfaces.  Materials' recycle-ability, re-use, and service life can all extended.
• High flux membranes for selective separation of atmospheric gases.  Capture of carbon dioxide emissions, for example, can be made more efficient and scalable to industrial levels.    

Higher-Performance Materials for Extreme Environments.  This includes:

• High-temperature, phase-stable alloys.  Long-term properties degrade in industrial systems which operate using high-temperature and chemically-aggressive conditions.
• Thermoelectric materials with high conversion efficiency.  Thermoelectric materials convert waste heat into electricity, and can help recapture lost energy.
• Lightweight, high-strength ductile materials.  Trade-offs typically exist: strength at the expense of ductility; light weight at the expense of strength; and so on.
• Irradiation-resistant structural alloys for nuclear applications.  Nuclear irradiation degrades the mechanical properties of many materials. 
• High-pressure hydrogen-resistant materials.  Storage and handling of hydrogen is not an easy task.
• Collaborative, comprehensive materials database.  Materials development can be sped and cost reduced.
• Predictive materials performance code.  Computer modeling of materials' mechanical properties will enable rapid, inexpensive, and iterative development.

Multi-Materials Integration in Energy Systems (or: composites to provide what the individual components can't).  This includes:

• Low-cost carbon fibers and composites manufacturing processes.  Carbon fiber products are too expensive to manufacture for widespread use.
• Joining process for assembling multi-material structures. Some material pairs are incompatible (i.e. structurally or chemically) and can not form suitable joints or be brought into contact.
• High energy density, low-cost battery cathodes.  Improved battery longevity, storage, and discharge will enable new alternative energy technologies.
• Low-cost fuel cell catalyst.  A current benchmark catalyst, Platinum, rare and expensive, is not ideal.
• Integrated computational materials engineering modeling package.  Initial composite design and proof-of-concept can be performed first through computation, saving development time and costs.

Sustainable Manufacturing of Materials.  This includes:

• Net-shape processing of structural metals.  Scrap and waste (e.g. from machining a block of steel into its final shape) can be reduced.
• Additive manufacturing of components and systems.  Energy-intensive production methods and industrial systems as a whole can be made more efficient.
• Low-cost processing and energy reduction technology for metals.  Lightweight metals such as aluminum, titanium, and magnesium can benefit greatly from improved processing methods.
• Separation of materials for recycling.  Major efficiency barriers surround the screening and sorting of mixed materials.  Carbon fiber recycling is also expensive.
• Real-time sensor technology for gases and molten metals.  Enhanced detection methods are needed for identifying damage during processing of high-performance and energy-intensive products. 

This report covers a lot of ground regarding sustainability of materials science and engineering in energy and related fields.  But it also presents a good overview of the diversity and breadth of the meaning or interpretation of sustainability - an important point that should be considered alongside the sustainability design itself.  

[1] Linking Transformational Materials and Processing for an Energy-Efficient and Low-Carbon Economy: Creating the Vision and Accelerating Realization - Opportunity Analysis for Materials Science and Engineering.  The Mining, Metals, and Materials Society (2011).  (Available On-Line.)
[2] L. Robinson.  Opportunity analysis for MSE - Report defines pathway to a more sustainable energy future.  JOM, Vol. 63 (Issue 2) (2011), pp. 30-33.