Sunday, May 29, 2011

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.

Sunday, May 22, 2011

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.


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.

Saturday, May 7, 2011

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.