CHAPTER 1 Introduction: material dependence CONTENTS 1.1 Introduction and synopsis 1.2 Materials: a brief history 1.3 Learned dependency: the reliance on nonrenewable materials 1.4 Materials and the environment 1.5 Summary and conclusions 1.6 Further reading 1.7 Exercises 1.1 Introduction and synopsis Thisbookisaboutmaterialsandtheenvironment:theeco-aspectsoftheirproduc- tion,their use, and their disposal atend oflife. It is also about waysto choose and designwiththeminwaysthatminimizetheimpacttheyhaveontheenvironment. Environmental harm caused by industrialization is not new. The manufacturing midlandsof 18th centuryEngland acquiredthe name “Black Country” withgoodrea- son; and to evoke the atmosphere of 19th century London, Sherlock Holmes movies show scenes of fog—known as “pea-soupers”—swirling round the gas lamps of Baker Street. These were localized problems that have, today, largely been corrected. The Renewableandnon-renewableconstruction.Above:Indianvillagereconstruction. (ImagecourtesyofKevinHamptonhttp://www.wm.edu/niahd/journals).Below:Tokyoat night.(Imagecourtesyofhttp://www.photoeverywhere.co.ukindex). 1 MaterialsandtheEnvironment. ©2013ElsevierInc.Allrightsreserved. 2 CHAPTER 1: Introduction: material dependence change now is that some aspects of industrialization have begun to influence the environment on a global scale. Materials are implicated in this. As responsible materialsengineersandscientists,weshouldtrytounderstandthenatureoftheprob- lem—itisnotsimple—andtoexplorewhat,constructively,canbedoneaboutit. This chapter introduces the key role materials have played in advancing tech- nology and the dependence—addiction might be a better word—that this has bred. Addictionsdemandtobefed,andthisdemand,coupledwiththeworld’scontinued population growth, consumes resources at an ever-increasing rate. This has not, in the past, limited growth; the earth’s resources are, after all, very great. But there is increasing awareness that the limits do exist, that we are approaching some of them,andthatadaptingtothemwillnotbeeasy. 1.2 Materials: a brief history Materials have enabled the advance of mankind from its earliest beginnings— indeed the ages of man are named after the dominant material of the day: the Stone Age, the Copper Age, the Bronze Age, the Iron Age (Figure 1.1). The tools and weapons of prehistory, 300,000 or more years ago, were bone and stone. Stones could be shaped into tools, particularly flint and quartz, which could be flaked to produce a cutting edge that was harder, sharper, and more durable than any other naturally occurring materials. Simple but remarkably durable structures could be built from the materials of nature: stone and mud bricks for walls; wood forbeams;bark,rush,andanimalskinsforroofing. Gold, silver, and copper, the only metals that occur in native form, must have beenknownaboutfromtheearliesttime,buttherealizationthattheywereductile, that is, that they could be beaten into a complex shape, and, once beaten, become hard, seems to have occurred around 5500 BC. By 4000 BC, there is evidence that technologytomeltandcastthesemetalshaddeveloped,allowingformoreintricate shapes.Nativecopper,however,isnotabundant.Copperoccursinfargreaterquan- tities as the minerals azurite and malachite. By 3500 BC, kiln furnaces, developed for pottery, could reach the temperature and create the atmosphere needed to reduce these minerals, enabling the tools, weapons, and ornaments that we associ- atewiththeCopperAgetodevelop. But even in the worked state, copper is not all that hard. Poor hardness means poor wear resistance; copper weapons and tools were easily blunted. Sometime around3000BCtheprobablyaccidentalinclusionofatin-basedmineral,cassiterite, in the copper ores provided the next step in technology—the production of the cop- per-tin alloy bronze. Tin gives bronze a hardness that pure copper cannot match, allowing superior tools and weapons to be produced. This discovery of alloying—the hardeningofonemetalbyaddinganother—stimulatedsuchsignificanttechnological advancesthatit,too,becamethenameofanera:theBronzeAge. “Obsolescence”soundslike20thcenturyvocabulary,butthephenomenonisas old as technology itself. The discovery, around 1450 BC, of ways to reduce ferrous Materials: a brief history 3 Date Molecular (1980–present) Age Nano materials 2000 AD Biopol biopolymers (1990) PEEK, PES, PPS (1983) Polymers LLDPE (1980) (1985) “Warm” Polysulfone, PPO (1965) 1980 AD superconductors Age Polyimides (1962) (1962) Carbon fibers, CFRP Acetal, POM, PC (1958) (1961) Shape memory alloys PP (1957) 1960 AD (1957) Amorphous metals HDPE (1953) (1947) Transistor-grade silicon PS (1950) (1947) Super alloys Lycra (1949) 1940 AD (1909–1961) Actinides* Formica (1945) (1942) GFRP PTFE (Teflon) (1943) (1940) Plutonium* PU, PET (1941) (1828–1943) Lanthanides* 1920 AD PMMA, PVC (1933) Neoprene (1931) (1912) Stainless steel Steel Synthetic rubber (1922) (1890) Aluminum production Age Bakelite (1909) 1900 AD (1880) Glass fiber Alumina ceramic (1890) (1856) Bessemer steel Celllose acetate (1872) (1823) Silicon∗ Ebonite (1851) 1850 AD (1808) Magnesium*, Aluminum* Reinforced concrete (1849) (1791) Strontium*, Titanium* Vulcanized rubber (1844) (1789) Uranium* Cellulose nitrate (1835) (1783) Tungsten*, Zirconium* 1800 AD (1765) Crucible steel (1751) Nickel* (1746) Zinc* Rubber (1550) 1500 AD (1737) Cobalt* (1735) Platinum* (1500) Iron smelting 1000 AD Gutta percha (800) Iron Age 500 AD Tortoiseshell (400) Paper (105) Horn (50 BC) 0 BC / AD Amber (80 BC) Lacquer (1000 BC) (1400 BC) Iron Papyrus (3000 BC) 1000 BC (3500 BC) Bronze Bronze Age Glass (5000 BC) (3500 BC) Tin Cement (5000 BC) (4000 BC) Silver Copper Age 10,000 BC (5000 BC) Smelted copper Pottery (6000 BC) (7000 BC) Native copper Wood (prehistory) Stone Age (20,000 BC?) Gold Stone, flint (prehistory) 100,000 BC MFA ‘11 FIGURE 1.1 Thematerialstimeline.Thescaleisnonlinear,withbigstepsatthebot- tom, small ones at the top. A star (*) indicates the date at which an element was first identified. Unstarred labels give the date at which the material became of practical importance. 4 CHAPTER 1: Introduction: material dependence oxidestomakeiron,ametalwithgreaterstiffness,strength,andhardnessthanany other then available, rendered bronze obsolete. Metallic iron was not entirely new: tiny quantities existed as the cores of meteorites that had impacted the earth. The oxides of iron, by contrast, are widely available, particularly hematite, Fe O . 2 3 Hematite is easily reduced by carbon, although it takes temperatures close to 1,100(cid:1)Ctodoit.Thistemperatureisinsufficienttomeltiron,sothematerialpro- duced is a spongy mass of solid iron intermixed with slag; this mixture is then reheated and hammered to expel the slag, then forged to the desired shape. Iron revolutionized warfare and agriculture; indeed, it was so desirable that at one time it was worth more than gold. The casting of iron, however, presented a more diffi- cult challenge, requiring temperatures around 1,600(cid:1)C. There is evidence that Chinese craftsmen were able to do this as early as 500 BC, but two millennia passed before, in 1500 AD, the blast furnace was developed, enabling the wide- spreaduseofcastiron.Castironallowedstructuresofanewtype:thegreatbridges, railway terminals, and civil buildings of the early 19th century are testimony to it. But it was steel, made possible in industrial quantities by the Bessemer process of 1856,thatgaveironthedominantroleinstructuraldesignthatitstillholdstoday. For the next 150 years metals dominated manufacturing. It wasn’t until the demands of the expanding aircraft industry in the 1950s that the emphasis shifted to the light alloys (those based on aluminium, magnesium, and titanium) and to materials that could withstand the extreme temperatures of the gas turbine com- bustion chamber (super alloys—heavily alloyed iron- and nickel-based materials). The range of application of metals expanded into other fields, particularly those of chemical,petroleum,andnuclearengineering. The history of polymers is rather different. Wood, of course, is a polymeric composite, one used in construction from the earliest times. The beauty of amber—petrified resin—and of horn and tortoise shell—made up of the polymer keratin—attracteddesignersasearlyas80BCandcontinuedtodosointothe19th century (in London, there is still a Horners’ Guild, the trade association of those whoworkhornandshell).Rubber,whichwasn’tbroughttoEuropeuntil1550,was already known of and used in Mexico. Its use grew in importance in the 19th cen- tury, partly becauseof thewide spectrum ofproperties made possible by vulcaniza- tion—cross-linking by sulfur—to create materials as elastic as latex and others as rigidasebonite. Therealpolymerrevolution,however,haditsbeginningsintheearly20thcen- tury with the development of Bakelite, a phenolic, in 1909, and of the synthetic butyl rubber in 1922. This was followed mid-century by a period of rapid develop- ment of polymer science, visible as the dense group at the upper left of Figure 1.1. Almost all the polymers we use so widely today were developed in a 20-year span from1940to1960;amongthemwerethebulkcommoditypolymerspolypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), and polyurethane (PU), the com- bined annual tonnage of which now approaches that of steel. Designers seized on these new materials—they were cheap, brightly colored, and easily molded to com- plex shapes—to produce a spectrum of cheerfully ephemeral products. Design with Materials: a brief history 5 polymers has since matured: they are now as important as metals in household productsandautomobileengineering. The use of polymers in high-performance products requires a further step. “Pure” polymers do not have the stiffness and strength these applications demand; to provide it, they must be reinforced with ceramic or glass fillers and fibers, mak- ing them composites. Composite technology is not new. Straw-reinforced mud brick (adobe) is one of the earliest materials of architecture, one still used today in parts of Africa and Asia. Steel-reinforced concrete—the material of shopping cen- ters, road bridges, and apartment blocks—appeared just before 1850. Reinforcing concretewithsteelgaveittensilestrengthwherepreviouslyithadnone,thusrevo- lutionizing architectural design; it is now used in greater volume than any other man-made material. Reinforcing metals, already strong, took much longer, and eventodaymetalmatrixcompositesarefew. Theperiodinwhichwenowlivemighthave beennamedthePolymerAgehad itnotcoincidedwithyetanothertechnicalrevolution,thatbasedonsilicon.Silicon wasfirstidentifiedasanelementin1823,butfoundfewusesuntiltherealization, in 1947, that, when doped with tiny levels of impurity, it could act as a rectifier. Thisdiscoverycreatedthefieldsofelectronicsandmoderncomputerscience,revo- lutionizing information storage, access and transmission, imaging, sensing and actuation,automation,andreal-timeprocesscontrol. The 20th century saw other striking developments in materials technology. Superconduction, discovered in mercury and lead when cooled to 4.2(cid:1)K (2269(cid:1)C) in 1911, remained a scientific curiosity until, in the mid ’80s, a complex oxide of barium, lanthanum, and copper was found to be superconducting at 30(cid:1)K. This triggeredasearchforsuperconductorswithyethighertransitiontemperatures,lead- ing,in1987,toonethatworkedatthetemperatureofliquidnitrogen(98(cid:1)K),mak- ingapplicationspractical,thoughtheyremainfew. During the early 1990s, scientists realized that material behavior depended on scale, and that the dependence was most evident when the scale was that of nan- ometers (1029m). Although the term nanoscience is new, technologies that use it arenot.Therubyredcolorofmedievalstainedglassesandthediachromicbehavior of the decorative glaze known as “lustre” derive from gold nanoparticles trapped in the glass matrix. The light alloys of aerospace derive their strength from nanodis- persions of intermetallic compounds. Automobile tires have, for years, been rein- forcedwithnanoscalecarbon.Modernnanotechnologygainedprominencewiththe discovery that carbon could form stranger structures: spherical C molecules and 60 rod-like tubes with diameters of a few nanometers. Now, with the advance of ana- lytical tools capable of resolving and manipulating matter at the atomic level, the potential exists to build materials the way that nature does it, atom by atom and moleculebymolecule. If we now step back and view the timeline of Figure 1.1 as a whole, clusters of activityareapparent—thereisoneinRomantimes,onearoundtheendofthe18th century, and one in the mid 20th century. What was it that triggered the clusters? Scientific advance, certainly. The late 18th and early 19th century was the time of 6 CHAPTER 1: Introduction: material dependence the rapid development of inorganic chemistry, particularly electrochemistry, and it wasthisthatallowednewelementstobeisolatedandidentified.Themid20thcen- tury saw the birth of polymer chemistry, spawning the polymers we use today and providing key concepts in unraveling the behavior of the materials of nature. But theremaybemoretoitthanthat.Conflictstimulatesscience.Thefirstofthesetwo periodscoincideswiththeNapoleonicWars(1796(cid:3)1815),oneinwhichtechnology, particularly in France, developed rapidly. The second coincided with the Second WorldWar(1939(cid:3)1945),inwhichtechnologyplayedagreaterpartthaninanypre- viousconflict.Defensebudgetshave,historically,beenprimedriversforthedevelop- ment ofnewmaterials.Onehopesthatscientificprogressand advancesinmaterials arepossiblewithoutconflict,andthatthecompetitivedriveoffreemarketscanbean equally strong driver of technology. It is interesting to reflect that more than three quarters of all the materials scientists and engineers who have ever lived are alive today,andallofthemarepursuingbettermaterialsandbetterwaystousethem.Of onethingwecanbecertain:therearemanymoreadvancestocome. 1.3 Learned dependency: the reliance on nonrenewable materials Now back to the main point: the environmental aspects of the way we use materi- als.“Use”istooweakaword—itsoundsasifwehaveachoice:use,orperhapsnot use? We don’t just “use” materials, we are totally dependent on them. Over time this dependence has progressively changed from a reliance on renewable materi- als—thewaymankindexistedforthousandsofyears—toonethatreliesonmateri- alsthatconsumeresourcesthatcannotbereplaced. As little as 300 years ago human activity subsisted almost entirely on renew- ables:stone,wood,leather,bone,andnaturalfibers.Thefewnonrenewables—iron, copper,tin,zinc—wereusedinsuchsmallquantitiesthattheresourcesfromwhich they were drawn were, for practical purposes, inexhaustible. Then, progressively, the nature of the dependence changed (Figure 1.2). Bit by bit, nonrenewables dis- placed renewables until, by the end of the 20th century, our dependence on them was,asalreadysaid,almosttotal. Dependence is dangerous; it is a genie in bottle. Take away something on which you depend, meaning that you can’t live without it, and life becomes difficult. Dependence exposes you to exploitation. While a resource is plentiful, market forces ensurethatitspricebearsarelationshiptothecostofitsextraction.Buttheresources fromwhichmanymaterialsareextracted,oilamongthem,arelocalizedinjustafew countries. While these countries compete for buyers, the price remains geared to the cost of production. But if demand exceeds supply or the producing nations reach arrangementstolimitit,thegenieisoutofthebottle.Think,forinstance,oftheprice ofoil,whichtodaybearsnorelationshiptothecostofproducingit. Dependence, then, is a condition to be reckoned with. We will encounter its influenceinsubsequentchapters. Learned dependency: the reliance on nonrenewable materials 7 0% Dependence on nonrenewable materials 100% Date Silicon-based Near-total (96%) communication 2000 AD dependence on controls all commerce nonrenewable and life. materials Oil-based polymers 1980 AD displace natural fibers, pottery, and wood. 1960 AD Metals become the dominant materials of engineering. 1940 AD Aluminum displaces wood in light-weight 1920 AD design. Concrete displaces 1900 AD wood in large structures. 1850 AD Cast iron, steel displace wood and stone in structures. 1800 AD Start of the Industrial Revolution 1500 AD The “Dark Ages” — little material 1000 AD development 500 AD Wrought iron 0 BC / AD displaces bronze. Copper, bronze 1000 BC displace bone and stone tools. 10,000 BC Total dependence on renewable materials 100,000 BC MFA ‘11 0% Dependence on nonrenewable materials 100% FIGURE 1.2 The increasing dependence on nonrenewable materials over time, ris- ing to 96% by weight today. This dependence is not of concern when resources are plentiful but is an emerging problem as they become scarce. (Data in part from USGS [2002].) 8 CHAPTER 1: Introduction: material dependence News-clip: dangerous dependence Oiladdictionputsusatthemercyofourenemies. Western nations rely on Saudi Arabia to pump more oil when prices rise to levels that threaten their prosperity. At the regular OPEC meeting this month theSaudi’sproposal[todoso]wasturneddown.Withrisingdomesticdemand in producing countries, an output freeze would mean tight supplies and price rises. Thereisnosubstitutefuelavailableintheforeseeable futuretoreplaceoil fortransport.Thatmeansdependenceonregimesincountriesthatareunsta- ble,orhostile,orboth.... TheSundayTimes,June19,2011 Much the same situation exists with a number of materials that are critical for modernmanufacturing. 1.4 Materials and the environment All human activity has some impact on the environment in which we live. The environment has some capacity to cope with this so that a certain level of impact can be absorbed without lasting damage, but it is clear that current human activi- ties exceed this threshold with increasing frequency, diminishing the quality of the worldinwhichwenowliveandthreateningthewellbeingoffuturegenerations. At least part of this impact derives from the manufacture, use, and disposal of prod- ucts,andproducts,withoutexception,aremadefrommaterials. ThematerialsconsumptionintheUnitedStatesnowexceeds10metrictonper person per year. The average level of global consumption is barely one eighth of thisbutisgrowingtwiceasfast.Thematerials(andtheenergyneededtomakeand shape them) are drawn from natural resources: ore bodies, mineral deposits, fossil hydrocarbons. The earth’s resources are not infinite, but until recently, they have seemed so: the demands made on them by manufacturing throughout the 18th, 19th, and early 20th century seemed infinitesimal, the rate of new discoveries alwaysoutpacingtherateofconsumption. This perception has now changed. The realization that we may be approaching certain fundamental limits seemsto have surfaced with surprising suddenness, but warnings that things can’t go on forever are not new. Thomas Malthus, writing in 1798, foresaw the link between population growth and resource depletion, predict- ing gloomily that “the power of population is so superior to the power of the earth to produce subsistence for man that premature death must in some shape or other visitthehumanrace.”Almost200yearslater,in1972,agroupofscientistsknown as the Club of Rome reported their modeling of the interaction of population growth, resource depletion, and pollution, concluding that “if (current trends) con- tinue unchanged ... humanity is destined to reach the natural limits of develop- ment within the next 100 years.” The report generated both consternation and Materials and the environment 9 criticism,largely onthegrounds thatthemodeling was over-simplified anddidnot allow for scientific and technological advance. But in the last decade, thinking about this broad issue has reawakened. There is a growing acceptance that, in the wordsofanotherdistinguishedreport: ... many aspects of developed societies are approaching ... saturation, in the sensethatthingscannotgoongrowingmuchlongerwithoutreachingfunda- mental limits. This does not mean that growth will stop in the next decade, butthatadecliningrateofgrowthisforeseeableinthelifetimeofmanypeo- ple now alive. In a society accustomed ... to 300 years of growth, this is somethingquitenew,anditwillrequireconsiderableadjustment.*** The causes of these concerns are complex, but one stands out: population growth.Examine,foramoment,Figure1.3.Itisaplotofglobalpopulationoverthe last 2,000 years. It looks like a simple exponential growth (something we examine in more depth in Chapter 2) but it is not. Exponential growth is bad enough—it is easytobecaughtoutbythewayitsurgesupward.Butthisisfarworse.Exponential growth has a constant doubling time—if it’s exponential, a population doubles in size at fixed, equal time intervals. The doubling times for global population are marked on the figure. For the first 1,500 years, it is constant at about 750 years, but after that, starting with the Industrial Revolution, the doubling time halves, then halves again, then again. This behavior has been called “explosive growth”; it is harder to predict and results in a more sudden change. Malthus and the Club of Romemayhavehadthedetailswrong,butitseemstheyhadtheprincipleright. 9,000 8,000 45 7,000 s n o milli 6,000 Population n, 5,000 doubling time, atio years pul 4,000 90 o p al 3,000 b o 330 Gl 2,000 750 1,000 750 MFA ‘11 0 0 500 1000 1500 2000 Year FIGURE 1.3 Global population growth over the last 2,000 years, with the doubling timesmarked. 10 CHAPTER 1: Introduction: material dependence 1500 Population of the 25 most populous countries MFA ‘11 s) n o milli 1000 0 ( 1 0 2 n n i o ati 500 ul p o P 0 China India USA Indonesia Brazil Bangladesh Nigeria Russia Japan Mexico Vietnam Philippines Germany Ethiopia Egypt Iran Turkey Thailand France Congo UK Italy Korea, Rep. South Africa Ukrane FIGURE 1.4 The populations of the 25 most populous developed and developing countriesin2010. Global resource depletion scales with the population and with per-capita con- sumption. Per-capita consumption in developed countries is stabilizing, but in the emerging economies, as already said, it is growing more quickly. Figure 1.4 shows thedistributionofpopulationinthe25mostpopulousnationscontaining,between them, three quarters of the global total. The first two—China and India—account for 37% of the total, and it is in these two that material consumption is growing mostrapidly. Givenallthis,itmakesensetoexplorethewaysinwhichmaterialsareusedin design and how this might change as environmental prerogatives become increas- inglypressing.Thechaptersthatfollowexplorethis. News-clip:population, affluence, and consumption BeabullasChinashops. Theworld’slargestpopulationisenjoyingrisingwagesandagrowingdisposable income.Inshort:1.3billionarerapidlybecomingactiveconsumers.... TheTimes,May21,2011 Nofurthercommentneeded.