Philosophical Magazine Letters Materials-a brief history

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Materials-a brief historyMike Ashby a

a Department of Engineering, University of Cambridge, Cambridge, CB2 1PZ, UK

To cite this Article Ashby, Mike(2008) 'Materials-a brief history', Philosophical Magazine Letters, 88: 9, 749 — 755To link to this Article: DOI: 10.1080/09500830802047056URL: http://dx.doi.org/10.1080/09500830802047056

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Philosophical Magazine LettersVol. 88, Nos 9–10, September–October 2008, 749–755

Materials – a brief history

Mike Ashby*

Department of Engineering, University of Cambridge,Cambridge, CB2 1PZ, UK

(Received 24 January 2008; final version received 10 March 2008)

Professor Manuel Amaral Fortes has contributed to many aspects of the scienceof materials. Among them, his greatest love was for a material with a historylonger than that of almost any other: cork. Despite its antiquity – Horace(27 BC, [1]), Pliny (AD 77, [2]) and Plutarch (AD100, [3]) document its use over2000 years ago – it was, until the studies by Fortes and his co-workers [4–6],a neglected material, little studied. His work, elegantly compiled in the textCortica [7] has redressed the balance, giving cork its rightful place in the history ofmaterials. This history is the subject of this short article, which the author wouldlike to dedicate to the rich memory of Professor Fortes.

1. A materials time-line

Materials have enabled the advance of mankind from its earliest beginnings – indeed theages of man are named after the dominant material of the day: the stone age, the age ofcopper, the bronze age, the iron age. Figure 1 is a materials time-line. It is interesting tofollow its development, starting from the bottom and working upwards.

The tools and weapons of prehistory, 300,000 or more years ago, were bone and stone.Stones could be shaped for tools, particularly flint and quartz, which could be flaked toproduce a cutting edge that was harder, sharper and more durable than any other materialthat could be found in nature. Gold, silver, and copper, the only metals that occur innative form, must have been known from the earliest time, but the realization that theywere ductile, could be beaten to complex shape, and – once beaten – became hard, seems tohave occurred around 5500 BC. By 4000 BC there is evidence that technology to melt andcast these metals had developed, allowing more intricate shapes. However, native copper isnot abundant. Copper occurs in far greater quantities as the minerals azurite andmalachite. By 3500 BC, kiln furnaces developed for pottery, could reach the temperaturerequired for the reduction of these minerals, making copper sufficiently plentiful to usherin the Age of Copper.

But even in the worked state, copper is not that hard. Poor hardness means poor wearresistance; copper weapons and tools were easily blunted. Sometime around 3000 BC theprobably accidental inclusion of a tin-based mineral, cassiterite, in the copper ores

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ISSN 0950–0839 print/ISSN 1362–3036 online

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Figure 1. The materials time-line. The scale is non-linear, with big steps at the bottom, small onesat the top. A star (*) indicates the date at which an element was first identified. Unstarred labels givethe date at which the material became of practical importance. It was constructed from a largenumber of sources, among them, e.g. [8–11] and the website www.tangram.co.uk.TL-Polymer_Plastics_Timeline.html

750 M. Ashby


provided the next step in technology – the production of the alloy bronze, a mixture of tinand copper. Tin gives bronze a hardness that pure copper cannot match, allowing theproduction of superior tools and weapons. This discovery of alloying – the hardening ofone metal by adding another – was of such importance that it, too, became the name of anera: the Bronze age.

Obsolescence sounds like twentieth century vocabulary, but the phenomenon is asold as technology itself. The discovery around 1450 BC of ways to reduce ferrous oxides tomake iron, a material with greater stiffness, strength and hardness than any other thenavailable, rendered bronze obsolete. Iron was not entirely new: tiny quantities existed asthe cores of meteors that had impacted the earth. The oxides of iron, by contrast, arewidely available, particularly hematite, Fe2O3. Hematite is easily reduced by carbon,although it takes high temperatures, close to 1100�C, to do it. This temperature isinsufficient to melt iron, so the material produced was a spongy mass of solid ironintermixed with slag; this was reheated and hammered to expel the slag and then forgedinto the desired shape. Iron revolutionized warfare and agriculture; indeed, it was sodesirable that at one time it was worth more than gold. However, the casting of iron was amore difficult challenge, requiring temperatures around 1600�C. Two millennia passedbefore, in 1500 AD, the blast furnace was developed, enabling the widespread use of castiron. Cast iron allowed structures of a new type: the great bridges, railway terminals, andcivil building of the early nineteenth century are testimony to it. But it was steel, madepossible in industrial quantities by the Bessemer process of 1856, that gave iron itsdominant role in structural design that it still holds today. The demands of the expandingaircraft industry in the 1950s with the development of the jet engine, shifted emphasis tothe light alloys (those of aluminum, magnesium and titanium) and to materials that couldwithstand the extreme temperatures of the turbine combustion chamber. The developmentof super alloys – heavily alloyed iron and nickel-based materials – became the focus ofresearch, delivering an extraordinary range of alloys able to carry load at temperaturesabove 1200�C. The range of their applications expanded into other fields, particularlythose of chemical and petroleum engineering.

The history of polymers is rather different. Wood, of course, is a polymeric composite,which was used for construction from the earliest times. The beauty of amber – petrifiedresin – and of horn and tortoise shell – the polymer keratin – already attracted designersas early as 80 BC, and remained so into the nineteenth century (there is still, in London,a Horners’ Guild, the trade association of those who worked with horn and shell).Rubber, brought to Europe in 1550, was already used in the Mexico for a Mayan ballgame Pok-a-Tok. The importance of rubber grew in the nineteenth century, partly becauseof the wide spectrum of properties made possible by vulcanization – cross-linking bysulfur – giving materials as elastic as latex or as rigid as ebonite.

The real polymer revolution, however, has its beginnings in the early twentiethcentury with the development of Bakelite, a phenolic, in 1909 and synthetic butylrubber in 1922. This was followed in mid-century, by a period of rapid developmentof polymer science. Almost all the polymers we use so widely today were developed in a20-year span from 1940 to 1960, among them the bulk commodity polymers polypropylene(PP), polyethylene (PE), polyvinyl chloride (PVC), and polyurethane (PU), the combinedannual tonnage of which now approaches that of steel. Designers seized on these – theywere cheap and easily molded to complex shapes – to produce a spectrum of brightlycolored, cheerfully ephemeral, products. Design with polymers has since matured: they are

Philosophical Magazine Letters 751


now as important as metals in household products, automobiles, and most recently, inaerospace.

The polymers of transport and aerospace are more that just that: ‘‘pure’’ polymersdo not have the stiffness and strength these applications demand. They arecomposites, reinforced with fillers and fibers. Composite technology is not new.Straw-reinforced mud brick is one of the earliest of the materials of architecture andremains one of the traditional materials for building in parts of Africa and Asia eventoday. Steel-reinforced concrete – the material of shopping centres, road bridges, andapartment blocks – appeared just before 1850. Reinforcing concrete with steel to give ittensile strength where previously it had none, was easy. Reinforcing metals, already strong,took much longer and even today metal-matrix composites are few. But polymers, withmany attractive properties but lamentable stiffness, made scientists think. The technologyfor making glass fibres had existed since 1880, used to make ‘‘glass wool’’ insulation. Glasswool, or better, woven or layered glass fibres, could be incorporated in thermosettingpolyesters or epoxies, giving them the stiffness and strength of aluminum alloys. By themid 1940s, glass fibre reinforced polymer (GFRP) components were in use in the aircraftindustry. The real transformation of polymers into high-performance structural materialscame with the development of aramid and carbon fibres in the 1960s. Incorporated asreinforcements, they give materials with performance (meaning stiffness and strength perunit weight) that exceeded those of all other bulk materials, giving them their now-dominant position in sports equipment and aerospace.

The period in which we now live might have been named the polymers andcomposites-era had it not coincided with a second revolution, one based on silicon. Siliconwas first identified as an element in 1823 but found few uses until the discovery in 1947that, when doped with tiny levels of impurity, it could act as a rectifier. The discoverycreated the fields of electronics, mechatronics and modern computer science, revolutioniz-ing information storage, access and transmission, imaging, sensing and actuation,numerical modelling, and much more. This is rightly called the information age, enabledby the development of transistor-grade silicon.

The twentieth century saw other striking developments in materials technology.Superconduction, discovered in mercury and lead when cooled to 4.2K (�269�C) in 1911,found no applications outside scientific research. But in the mid-eighties, two physicists atthe IBM research centre in Zurich discovered a complex oxide containing barium,lanthanum, and copper that was superconducting at 30K. In 1987, this triggered a searchfor superconductors with yet higher transition temperatures, leading, to one witha transition temperature above 98K, the temperature of readily available liquid nitrogen,making applications practical.

In the last two decades, the area of biomaterials has developed rapidly. Implantingmaterials in or on the human body was not practical until aseptic surgical techniques weredeveloped in the late 1800s. Non-toxic metal alloys were introduced, but tended to fracturein service. It was not until the development of polymer-based systems, and subsequently,with a new wave of discoveries in cell biology, chemistry, and materials science, thatsynthetic biomaterials became a reality.

During the early 90s it was realized that material behaviour depended on scale, andthat the dependence was most evident when the scale was that of nanometers. Althoughthe term nano-science is new, the use of nano-technology is not. The proteins and mineralsof soft and mineralized tissue in plants and animals are dispersed on a nano-scale.

752 M. Ashby


The ruby red colour of stained glass and the lustre of certain glazes, both centuries old,derive from gold nanoparticles trapped in a glass matrix. Nanoparticles of carbonhave been used for the reinforcement of tires. Modern nano-technology gainedprominence with the discovery of various forms of carbon such as the C60 moleculeand carbon nano-tubes, even though these are not really new but have always existed asparticles in smoke. With the advance of tools capable of resolving and manipulatingmatter at the atomic level, it becomes possible (though at present expensive) to build thingsthe way nature does it, atom by atom and molecule by molecule.

2. Expanding the boundaries of material-property space

The material development documented in the time-line were driven by the desire for evergreater performance. One way of examining the progress of this is by following the wayin which properties have evolved on material-property charts. Material property charts[13,14] display materials on axes based on two of their properties. Materials have manyproperties of course – mechanical, thermal, electrical, optical, and many more – so, thenumber of such pair-wise combinations is large. Each chart can be thought of as a slicethrough ‘‘material property space’’ – a multidimensional space with material properties asits axes. The references cited above contain many of these.

Figure 2 is an example of just one of them. It is a Strength-Density chart. There aremany obvious incentives for seeking materials with greater strength: more durable andeffective tools and weapons; faster, more economical transport; larger, more daringstructures. In more recent times, it has been high strength at low weight that is frequentlysought with transport and aerospace as the direct drivers.

The chart is plotted for six successive points in historical time, ending with thepresent day. The materials of pre-history, shown at (a), cover only a tiny fraction of thisstrength–density space. By the time of the peak of Roman empire, around 50 BC (b), thearea occupied by metals has expanded considerably, giving Rome critical advantages inweaponry and defence. The progress thereafter was slow: 1500 years later (c) although, notmuch has changed significantly, cast iron now appears. Even 500 years after that,(d) expansion of the occupied area of the chart is small; aluminium only just creeps in.Then, things accelerate. By 1945, the metal’s envelope has expanded considerably and anew envelope – that of synthetic polymers – now occupies a significant position. Betweenthen and the present day the expansion has been dramatic. Much of the space is now filled,and the filled area starts to approach fundamental limits (not shown here) beyond which itis not possible to go.

Any slice through material property space shows development like this. What are thefundamental limits and how closely are they now approached? A fascinating question, butone beyond the scope of this short article.

3. A final word

If we now step back and view the time-line of Figure 1 as a whole, clusters of activityare apparent – there is one in Roman times, one around the end of the eighteenth century,one around 1940. What was it that triggered the clusters? Scientific advance, certainly.The late eighteenth and early nineteenth century were the time of rapid development



Mike Ashby, Cambridge, 2007

(a) (b)

(c) (d)

(e) (f)

Figure 2. The progressive filling of material-property space over time (the charts list the date at thetop left) – here, the way in which the materials have been developed over time to meet demands onstrength and density are shown. Similar time-plots show the progressive filling of similar plots for allmaterial properties.

754 M. Ashby


of inorganic chemistry, particularly electro-chemistry, and it was this that allowed new

elements to be isolated and identified. The mid-twentieth century saw the birth of

polymer chemistry, and it was this understanding which enabled the development of the

polymers we use today. But there may be more to it than this. Conflict stimulates science.

The first of these periods of expansion accompanied the campaigns that extended the

Roman Empire (510 BC–476 AD). The second coincides with that of the Napoleonic Wars

(1796–1815), one in which technology, particularly in France, developed rapidly. And the

third encompasses that of the Second World War (1939–1945), in which technology played

a greater part than in any previous conflict. One hopes that scientific progress and

advances in materials are possible without conflict. The competitive drive of free markets

appears to be an equally strong driver. It is interesting to reflect that more than half of all

the material scientists and engineers who have ever lived are alive today, and all of them

are pursuing better materials and better ways to use them. We can be certain of one thing:

there are many more advances to come.

References

[1] Horace, Q. (27 BC) ‘‘Odes’’, Book III, ode 8, line 10, Edward C. Wickham and H.W. Garrod,

eds., in the Oxford Classical Texts series, 1912.[2] Pliny, C. (AD 77) ‘‘Natural History’’, Vol 16, Section 34, translated by Bostock, J. and Riley,

H.T., Taylor and Francis, Red Lion Court, Fleet Street, London, 1855.[3] Plutarch, (AD 100) ‘‘Life of Camillus. The Parallel Lives’’, Vol 2, Ch. XXV, Loeb Classical

Library edition of 1914, Harvard University Press, Cambridge Mass, USA. p.154.[4] M.E. Rosa and M.A. Fortes, J. Mater. Sci. 23 (1988), p.35.

[5] M.E. Rosa and M.A. Fortes, J. Mater. Sci. 23 (1988), p.879.[6] M.E. Rosa and M.A. Fortes, J. Mater. Sci. 26 (1991), p.341.[7] M.A. Fortes, M.E. Rosa, and H. Pereira, Cortica (in Portuguese) IST Press, Lisbon, Spain,

2004, ISBN 972-8469-33-0.[8] Encyclopædia Britannica, 11th ed., The Encyclopædia Britannica Company, New York, USA,

1910.[9] J. Delmonte, Origins of Materials and Processes, Technomic Publishing Company,

Pennsylvania, USA, 1985, ISBN 87762-420-8.[10] C. Singer et al. (eds.), A History of Technology (21 volumes), Oxford University Press, Oxford,

UK, 1954–2001, ISSN 0307-5451.[11] R.F. Tylecoate, A History of Metallurgy, 2nd ed., The Institute of Materials, London, UK,

1992, ISBN 0-904357-066.[12] M.F. Ashby, Materials Selection in Mechanical Design, 3rd ed., Butterworth Heinemann,

Oxford, UK, 2005, ISBN 0-7506-6168-2.[13] M.F. Ashby, H.R. Shercliff and D. Cebon, Materials: Engineering, Science, Processing and

Design, Butterworth Heinemann, Oxford, UK, 2007, ISBN 978-0-7506-8391-3.



Philosophical Magazine Letters Materials-a brief history

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