Supplementary information to the articleDOI 10.1007/s11948-012-9401-8
Material Scarcity – A Reason for Responsibility in Technology Development and Product Design
Andreas R. Köhler
Case study 1: Critical elements used in electronic products and ICT
This case study takes a closer look at the typical applications of critical elements in electronic products. Contemporary high-tech products have become highly dependent on these elements. Information and communication technologies (ICT) in particular contain a variety of speciality and precious metals (Hagelüken et al. 2010). Mobile phones, for example, contain considerable amounts of valuable materials (Meskers et al. 2009). Their printed circuit boards, on which microchips are mounted, contain metals such as copper, silver and gold. The metals serve as electrical interconnections and heat-dispersing contact structures for corrosion prevention, etc. Small capacitors contain the scarce metal tantalum (USGS 2012). Ferrite cores of high frequency coils can contain ceramic compounds of rare earth element (REE) oxides.
Although many of these scarce elements are used in minute amounts in individual products, they play an indispensable role in ensuring that the electronic hardware performs as required. Transistors, the basic building blocks of contemporary silicon-based microelectronics, consist of crystalline silicon that is doped with tiny amounts of doping elements (Kooroshy et al. 2010). The concentration of dopant elements is usually very low and ranges between 0.1 to 100 ppm in the crystal lattice of silicon. Common dopant elements include aluminium, boron and gallium (acceptor atoms for p-type semiconductors) and antimony, arsenic and phosphorus (donor atoms for n-type semiconductors). Optoelectronic components such as light emitting diodes (LEDs), microwave generators and thin film solar cells use doped gallium arsenide (GaAs) as a substrate material. Doping elements are essential in achieving the desired function for such components. Common dopant elements for GaAs are:
- cadmium, magnesium, silicon and zinc (acceptor atoms for p-type semiconductors)
- selenium, silicon, sulphur and tellurium (donor atoms for n-type semiconductors)
Optical glass fibres are doped with rareearth elements such as dysprosium, erbium, neodymium, praseodymium, thulium and ytterbium (Bass 2010). Table 1 provides an overview of the areas of application of rare earth elements (the lanthanide group of the Periodic Table of the Elements [PTE]) in the electronic and electrical sector. Many functional components referred to in Table 1 play an essential role in the Internet infrastructure (e.g. server farms and optical and wireless networks) and in low-carbon energy technologies.
Scandium(Sc) / Gas discharge lamps, high performance aluminium-scandium alloys
Yttrium
(Y) / Phosphors in cathode ray tubes (CRT), oxygen sensors in car exhaust systems, YAG laser rods, component of oxide superconductor materials
Lanthanum
(La) / Optical lenses, high refractive index glass for optical fibres, anodic material of nickel-metal hydride batteries.
Cerium
(Ce) / TV screens and fluorescent lamps.
Praseodymium (Pr) / Permanent magnets, optoelectronics: optical switch, optical amplifier
Neodymium
(Nd) / Permanent magnets used in [electric motors & generators, microphones, loudspeakers, hard disks], ceramic capacitor (dielectric layer), solid-state lasers (Nd-YAG laser rods).
Promethium
(Pm) / Beta radiation source, used in nuclear batteries
Samarium
(Sm) / SmCo permanent magnets, solid-state lasers, infrared light absorbing optical glass
Europium
(Eu) / CRT phosphors, Triphosphors in fluorescent lamps, yellow phosphors for white LED
Gadolinium
(Gd) / Permanent magnets, magneto–optical films, microwave technology, green phosphors for CRT and Radar screens, rewritable media CD-RW
Terbium
(Tb) / Solid-state devices, e.g. crystal stabilizer of fuel cells, sensors, flat panel speaker, green phosphors in CRT, triphosphors in fluorescent lamps
Dysprosium
(Dy) / Permanent magnets, laser materials, hard disks, drive motors for hybrid electric vehicles
Holmium
(Ho) / Fluorescent lamps, high-strength magnets, solid-state lasers, microwave equipment, optical glass fibres
Erbium
(Er) / Optoelectronics: optical glass fibres, erbium-doped fibre amplifiers, fibre lasers
Thulium
(Tm) / YAG laser rods, high temperature superconductors, ceramic magnetic materials
Ytterbium
(Yb) / Fibre lasers, optical fibres, solid state lasers
The examples provide only a very rough overview of the pervasive use of rare earth elements in modern high-tech products. The global demand for these elements is rapidly increasing as a result of mass production in the high-tech sector. For example, the rapid growth of the mobile telecommunications sector and the widespread proliferation of mobile phones in consumer markets have resulted in a growing demand for such elements (Soneji 2009). In the near future, the demand for metals that may be used in high-tech products (technology metals) is expected to increase considerably for the following reasons:
-Innovations in the high-tech sector and green technologies are pushing the demand for technology metals. As a result, competition for these critical elements among different emerging technologies is increasing (Angerer 2009).
-Economy-of-scale principles ruling the high-tech sector stimulate mass consumption of electrical and electronic products. At the same time, market size is increasing due to population growth and economic upturn in newly industrialised countries (e.g. India, China and Brazil).
-Consumers tend to use products for ever shorter times. Many products are replaced by newer ones long before the old products cease to function physically, an obsolescence effect that is known as virtual wear and tear.
Table 2 presents the material composition of mobile phone handsets found in electronic waste samples. Newer generations of smartphones are thought to contain higher relative amounts of certain critical elements because of their design features. For example, the trend towards large touchscreen displays is leading to an increasing demand for indium, which is used in the form of transparent indium-tin oxide (ITO) electrodes.
Table 2 Content of valuable metals in discarded cell phones produced around 2003
Material / g per kg / Material / g per kgSilver (Ag) / 1.4157 / Iron (Fe) / 82.8
Aluminum (Al) / 18.9 / Mercury (Hg) / 0.0000
Arsenic (As) / 0.0068 / Nickel (Ni) / 8.7567
Gold (Au) / 0.3261 / Lead (Pb) / 3.4952
Beryllium (Be) / 0.0219 / Palladium (Pd) / 0.1178
Bismuth (Bi) / 0.0489 / Platinum & Tantalum
(Pt / Ta) / 0.0542
Cadmium (Cd) / 0.0004 / Antimony (Sb) / 0.7703
Chromium (Cr) / 6.2697 / Tin (Sn) / 5.3234
Copper (Cu) / 116 / Zinc (Zn) / 3.4275
Source: (Huisman 2004)
The example above illustrates the complexity of the materialcomposition of contemporary electronic products. Valuable materials and hazardous substances are often combined in the same product and it is difficult to separate them once they are discarded as e-waste. That, among other reasons, makes recycling of post-consumer e-waste impractical in most countries. Even if the copper and gold in end-of-life products are recycled, the technology metals are mostly lost in the residues (shredding dust of metallurgical slag) (Chancerel et al. 2009). As a result, a high proportion of the valuable materials contained in e-waste is disposed of without recovery.
Case study 2: Design of smart textiles
This case study takes a closer look at an emerging technology and how developers and designers can influence the content of critical materials in future products. Electronic textiles represent a productdesign trend that utilises objects of daily life, such as garments, as a platform for smart ICT functions. Textile-integrated electronic devices are currently at an early development stage, and innovation is taking place in the market segments of healthcare, protective clothing for workers and sports clothing. (Schwarz et al. 2010). While garments with integrated electronic gadgets (e.g. mp3 player or solar cells) have already been put on the market, they have failed to breakthrough commercially thus far (Tröster 2011). However, observers of the innovation system expect e-textiles to proliferate in the mass market within the next decade (Byluppala 2011; Allen 2012).
Although a variety of enabling technologies already exists, they need to be adapted to the new application context of wearable technology (Stylios 2007). Examples of electronic components that can be embedded seamlessly into textiles include sensors, actuators, lighting elements, electronic processing units and elements for power generation and storage (Van Langenhove et al. 2012). Table 3 provides an overview of electronic components, which are to be integrated into textile materials.
Table 3 Components and materials that are integrated into e-textiles (examples)
Components and application purpose / Examples of materials usedElectrically conductive fibres:
- electrostatic dissipation, electro-magnetic shielding, electric wiring and contacting, sensor and actuator elements, power distribution / Copper, silver, gold
Intrinsically conductive polymers
(polypyrrole or polyannilline)
Conductive polymer composites containing Nano-particles (e.g. silver-NP; carbon nanotubes)
Contacting and bonding elements / Solder alloys: tin, silver, copper, antimony, bismuth
Conductive adhesives: silver particles
Embedded circuit boards:
- mounting and interconnecting of electronic components, mechanical fixation and protection within the textile / Flexible substrata (e.g. silicon elastomers or polyimide film), metals (copper, silver, gold), fire retardants, lacquer
Electronically active devices:
- providing ICT functionality (smartness) / ICT devices such as mp3-player, micro-controller and embedded periphery, antenna, RFID-tags, flexible displays and LEDs, etc.
Energy harvesting devices / Solar cells, photoadaptive polymers, piezoelectric materials, thermoelectric generators, (containing e.g. silicon, zinc-oxide, nanoparticles, nanowires)
Power storage / Rechargeable batteries (Li-ion)
The amount of electronic material in e-textiles varies widely depending on the intermediate material used, production methods and application. The metal content of metal-coated fibres can be up to 40 percent by weight. Fabrics with interwoven metallic fibres or silver-ink printed structures (e.g. antennas) can have a metal content of up to 54 percent by weight. Precious metals, such as gold and platinum group metals (PGM), are applied in sophisticated e-textile fibres (Schwarz et al. 2008; Han & Meyyappan 2011). The material composition of textile-integrated electronics is thought to be very similar to off-the-shelf electronic components (Table 2). These components are incorporated in flexible and stretchable substrates (laminated on fabric or silicone/polyurethane skin). E-textiles tend to require higher quantities of metals as compared to compact gadgets. Firstly, the textile-integrated electronics are spread over large surface areas. Secondly, in order to make the products fault-tolerant, the electronic structures are usually overdesigned (by using excess material, meander-shaped wiring and redundant structures). Developers strive to make e-textiles that can withstand 25 to 50 washing cycles, which translates into a useful life of less than one year. As such, e-textiles are expected to have rather short service lives and the issue of e-textile recycling has not yet been resolved (Köhler 2011). Critical materials that will be highly dispersed within future e-textiles are unlikely to be recovered from waste. Thus, e-textiles exemplify the prospect of the mass application of high-tech products leading to an increasing wastage of critical elements.
To avoid the depletion of critical materials, developers of e-textiles could adopt existing eco-design principles from the respective sectors of industry (electronics and textile). Textile technology allows for new eco-design approaches for electronics. For example, electronic housing could be made of textile materials instead of metals or plastics. Textile hook-and-loop fasteners allow for easier repair and recycling of old products than screws or clip fasteners. However, many of the existing eco-design principles do not match with the properties of textile-embedded electronics. The design trend towards seamless integration of textile and electronics undermines the ‘Design for Recycling’ (DfR) paradigm, which suggests designing products for easy dismantling. For example, the widespread use of metal-coated fibres clearly conflicts with the DfR principle of limiting the use of surface-coated plastic. There is a need for new eco-design solutions that suit the emerging technology.
Developers of e-textiles may explore the potentials of new technologies and designcritical materials out of e-textiles altogether. Polymer-based electronics, for example, hold promise for the creation of smart functions with lower environmental impacts as compared to silicon-based electronics (Griese et al. 2001; Frazer 2003). Innovations in the field of organic electronics have made rapid progress in recent years (Bettinger & Bao 2010). Although plastic electronicsdo not match the performance of silicon-based electronics, they offer versatile advantages for the creation of e-textiles. π-Conjugated polymers, such as PDOT, PAni and PPy, can substitute for metals in the form of conductive film electrodes for flexible sensors, antennas and large-area lighting elements. The polymers can be modified as semiconductive materials, which allow for the creation of organic and large-area electronics or fibre-shaped electronics (Mattana & Cosseddu 2011). Semiconductive polymers may have the potential to replace scarce metals in mass manufactured products, including OLEDlighting elements, flexible displays and solar cells, film-shaped batteries, roll-to-roll printed logic chips, etc. (Carpi & De Rossi 2005). However, it remains to be demonstrated whether conjugated polymers can fully substitute for critical elements. Prototypes of the technology presented up to now often contain critical elements in the form of transparent ITO electrodes (containing indium) or rear-sideelectrodes (usually made of silver), light-emitting phosphors (based on REE) or photoluminescent complexes (containing PGM) (Salinas et al. 2011). To that end, the expected mass production of organic electronics could entail increasing consumption of critical elements. Technology developers should therefore bear in mind that rebound effects can occur as they pursue the development of cheap, disposableplastic electronic devices.
Case study 3: Application of rare earth elements in energy-efficient lighting
The proliferation of energy-efficient lighting is a key component of European eco-innovation strategies. The EU is aiming for a 20% reduction in carbon dioxide emissions by 2020. CO2 emissionscan be reduced by 15 million tonnes per year through the adoption of energy-saving lighting in the domestic sector (EU 2008). In order to contribute to the achievement of this goal, the EuP Directive enforces the phasingout of inefficient light bulbs (classes F and G) in favour of more energy-efficient lighting technologies (European Commission 2005). As a consequence, incandescent light bulbs with tungsten filaments, non-directional halogen lamps and ‘fat’ linear fluorescent tube lamps (T12/T10) have been banned with effect from 2012. The energy-efficient lamps that currently dominate the domestic lighting market are compact fluorescent lamps (CFL) and fluorescent tubes (FT). These lamps are based on gas discharge technology and require fluorescent phosphors to convert ultraviolet radiation into white light. Traditionally, the standard FT and CFL lamps contain a halophosphate phosphor consisting mainly of antimony/manganese-activated calcium oxide (e.g.Ca5(PO4)3(F,Cl):(Sb,Mn) ) (Chang et al. 2007). In addition, the FT and CFL lamps contain between 5 and 10 mg of mercury to sustain the gas discharge effect. Because of its toxicity, the mercury content is one of the major drawbacks of current state-of-the-art energy-efficient lamps.
The innovation trend towards more energy-efficient fluorescent lamps entails an increasing use of tricolour phosphors, which contain heavy rare earth elements (including La, Gd, Tb and Eu) as well as the transition metal yttrium. The triphosphors consist of red, green and blue-emitting compounds (e.g. Eu3+-activated Y2O3 (red); Tb3+-activated CeMgAl11O19 (green) and Eu2+-activated BaMgAl10O17 (blue)). The concentrations of REE within the phosphors are relatively low (e.g. 1 to 15 mole percent europium in red YEO phosphor; 33 mole percent terbium in green Tb3+ quenched phosphors) (Srivastava & Ronda 2003). One fluorescent luminaire system (strip lighting) with two T5 fluorescent tubes, for example, contains a triphosphor with 8.4 g bastnasite (a concentrate consisting of 70% rare earths oxides) (Navigant Consulting 2009). In spite of the relatively low concentrations of REE in modern phosphors, they contribute 7 percent by volume or 32 percent by value to the global consumption of REE (British Geological Survey 2011). The growing use of energy-efficient CFL is believed to entail an increasing demand for heavy REE (Gd, Tb and Eu), which are scarcer than the light REE. This will lead to increasing raw material prices for these elements with prices expected to double by 2015 (Gowing 2011).
The advent of novel lighting technologies will influence the demand for REE-containing phosphors. Solid-state lighting (LED) and organic semiconductors (OLED) expand the range of choices for energy-efficient lighting. Designers and architects can accelerate the transition towards more energy and resource-efficient lighting as they opt for white light-emitting diode (LED) luminaries instead CFL. Phosphor-converted white LEDs (pc-WLEDs) exhibit up to 40 percent higher energy efficiency as compared to CFL. Commercially available pc-WLEDs are set to exceed the luminous efficacy of CFL and may reach 200 lm/W by 2020 (Ye et al. 2010). PC-WLEDs require lower amounts of phosphors because they are smaller than CFL or FT. Nevertheless, this technology will contribute to the consumption of REE and other technology metals, depending on the amount of lighting installed. The solid-state technology is based on the semiconductors gallium nitride or indium gallium nitride. The most common technology to create white light makes use of yellow YAG (yttrium aluminium garnet) phosphor that is excited by blue light. Commonly, these phosphors are doped with REEs, (e.g. Ce, Gd, Eu and Tb).
OLEDs are often regarded as the next generation of energy-efficient lighting technology (Kalyania & Dhobleb 2012). The technology is based on polymer electroluminescence and can be produced by printing very thin layers of a conjugated polymer (e.g. poly(p-phenylene vinylene) on glass sheets or plastic film. Various semiconductive polymers have been investigated for use in OLEDs. Highly efficient OLEDs deploy phosphorescent complex molecules to achieve internal quantum efficiencies close to 100%. These complexes are often composed of an organic host material that contains critical metals, such as iridium, platinum or terbium (Adachi et al. 2001, Chen, Z., et al. 2009). Moreover, the OLEDs contain indium in form of ITO transparent anode material. The active layers and the electrodes are made of thin films (100nm thickness). The quantity of critical metals used per OLED module is very low.
The innovation trend towards white LED or OLED lighting is not a-priori a viable strategy for designingout critical elements. The consumption of these materials will depend on factors that are influenced by product design and user behaviour. Total material consumption is determined by the useful lives of products and their replacement rates in particular. There is a tendency towards the use of new lighting technologies for disposableproducts because LED (and in the future OLED) are cheap thanks to massproduction. Moreover, there is a trend in product design of applying light sources to products that were not previously illuminated, such as clothing. Prototypes of photonic textiles with textile-integrated LED (e.g. the Galaxy Dress) provide an impression of possible future mainstream products with short lifecycles (Seymour 2010). Future technological progress will allow for the direct application of OLED at the fibre level (Mattana 2011). According to the prevailing views in the product design community, these technologies are destined for future proliferation in the fashion market. In this case, one can expect rebound effects that may lead to an increase in the consumption of technology metals in spite of their minute concentrationsin individual products.