How Materials Have Shaped Civilization

How Materials Have Shaped Civilization • The Stone Age – Stone naturally occuring, needs no processing other than making an edge – Axes, weapons, hammering tools – Some kinds more easily make sharp edges: obsidian / flint (start of trade) How Materials Have Shaped Civilization • The Stone Age II – Clay for containers: easy to form in natural state – Firing makes harder. impervious materials (first material processed – change properties rather than shape) – Information storage: writing – Also bone for needles, wood for handles etc. – Ceramics and composites How Materials Have Shaped Civilization • The Bronze Age – Tools need to be shaped to the task at hand. – Stone difficult to shape, unfired clay too unstable in shape, fired clay very brittle – Some tools also need to be flexible: able to bend but spring back – Metals can be shaped, are relatively non brittle and strong – A major advance in civilization – Major challenge: usually not naturally occuring, need processing How Materials Have Shaped Civilization • The Bronze Age – Most readily obtainable metal is copper – Pure metals are actually not that strong – deform through passage of atomic-scale defects called dislocations – Importance of microstructure: impede dislocation flow through grain boundaries, precipitates or other dislocations – With correct processing can bend then harden (then soften again to reshape if needed) – Science is now understood, but took thousands of years of empirical discovery. How Materials Have Shaped Civilization • The Bronze Age – Copper was first metal worked (~ 6000 BC). – Pure deposits (rare), high concentration minerals – Relatively low reduction temperature (1200o C), first smelted ~ 4000 BC – Casting – Took millenia to develop metallurgy of Cu – Required large amounts of charcoal: deforestation How Materials Have Shaped Civilization • The Bronze Age – Early Cu minerals contained high concs. of Arsenic: solid solution strengthening – Problem was that As conc. varied through natural abundance and volatility in processing – Supplies of Cu:As also exhausted – ~ 3000 BC. Add 5-10% tin to Cu: bronze – A new wonder material: reproducible, strong, malleable, castable How Materials Have Shaped Civilization • The Bronze Age – Bronze was the dominant technology for 2000 years – Assyrian king Sennacherib claimed bronze lions three times life size weighing 47 tons – Babylonian king Nebuchadnezzar when capturing Jerusalem reported bronze pillars thirty feet high. – Military dominance: importance of the best metals for weapons. – Agricultural implements and tools key to supporting a growing populations How Materials Have Shaped Civilization • The Iron Age – The Iron-Carbon phase diagram is arguably the blueprint of technology in the modern era – Earliest source was likely pure iron from meteorites – Known, but not widespread until ~ late second millenium BC – Needs high temperatures (melts at 1535 C) to reduce from ores – Importance of processing: need to add C to form rudimentary steels – Lead in this technology gave rise to Hittite empire How Materials Have Shaped Civilization • The Iron Age – Thousands of years were spend struggling with the Fe-C phase diagram empirically! – Introduce C from charcoal, diffuses into hot iron. – Cast iron, 3-4 wt % C melts at 1135 C (attainable in ancient times) but is very brittle – Wrought iron (< 0.1 wt % C) is ductile but melts at 1500 C (not attainable), so couldn’t be cast. – Steel ~ 0.2 – 2.1% C. A “sweet spot” for high strength steel is ~ 0.9 wt % C. Heat, introduce C, rapidly quench to form “martensite” phase, reheat to ‘temper” – Ancients had to control microstructure by trial and error without being able to even see it (or know of it)! – Centuries (millenia) of trial and error. How Materials Have Shaped Civilization • The Iron Age – Again, enormous military importance – those with the best steel win – Toledo steel gave military advantage to Roman’s – could cut through all armor at time without damage to sword (opponents might have to straighten their swords over their knees after each blow) – Damascus steel (microstructure of cementite and pearlite and C nanotubes!) – Also important as mold that can cast molten glass. How Materials Have Shaped Civilization • Glass – Transparent amorphous oxides, most usually silica based. – Discovered earlier than 3000 BC – Made into containers by 1500 BC – Glass blowing developed by ~ 100 BC (required hotter kilns) – Blowing into molds enabled the development of the ubiquitous Roman square based bottle – Containers, windows, art / decoration, eventually scientific instruments How Materials Have Shaped Civilization • Cement and Concrete – Cement had been used by Minoans and Greeks and refined by Romans. – Enabled the extraordinary engineering achievements of the Romans: bridges, aqueducts, major buildings – Major building projects also required a new material to sustain massive loads: concrete – A composite of cement, stone and sand. – Poured locally (cf. shipment of stone) – Consider how many major Roman buildings etc. still standing – Concrete still the material of choice for major buildings (combined with steel) How Materials Have Shaped Civilization • The Dark Ages – For a thousand years after the fall of Rome, technological development in Europe was largely stagnant – Advances from China: Paper + Printing, Gunpowder, Silk – Development of water and wind as sources of energy (windmills, water wheels…); mechanization – Bellows increased the highest attainable temperatures in furnaces: crucial to development of steel – Massive iron works emerged in the middle ages, rapidly increasing production How Materials Have Shaped Civilization • Emergence of The Steel Age – Key limitation was overcoming use of charcoal for smelting – Early use of coal unsuccessful because of sulphur impurities: grain boundary embrittlement – 1709 Abraham Darby employed coke: heated coal to drive off impurities (first used in brewing, developed much earlier in China) – Fortunate coincidence that local coal used by Darby had low S content – Reduced cost of iron massively: pots, pans, nails for general populace – Major engineering works: ships, bridges… – Coal the fuel of the industrial revolution How Materials Have Shaped Civilization • Emergence of The Steel Age – Another critical development was the emergence of steam power: revolutionized mining and transportation and created a major new market: railroads – Until about 1880 cast and wrought iron still dominant; steel manufacturing still too imprecise – Iron railroad tracks had to be replaced every 3-6 months, weapons exploded on first firing; steel urgently needed to continue to fuel industrial revolution – 1856 Bessemer process for large scale steel manufacturing: flow hot air through molten high C iron, access right space in Fe-C phase diagram (“sweet spot at ~ 0.9 wt % C”) How Materials Have Shaped Civilization • The Steel Age – Annual steel production in US: 22,000 tons 1867, one million tons 1880, 9 million tons 1900; now about half a billion tons globally – Emergence of steel navies – Construction: skyscrapers of concrete with steel skeletons (wrought iron also used earlier), mile long bridges – Development of many kinds of steel: stainless (+Cr, Ni), high strength (+W) … – Development of the necessary science (thermodynamics, phase diagrams, kinetics…) How Materials Have Shaped Civilization • Another Crucial Metal: Aluminum – Much lighter than steel and almost as strong: specific strength substantially higher – Melts at 660 C, easy to cast – Has very strong native oxide, so resistant to corrosion and wear. – Could not be obtained historically because oxide ores melt at ~ 2200 C; could not be reduced. – 1886 Hall-Heroult process for large scale manufacture through electrolysis: requires large amounts of electricity. – Now second most widely used metal – Needs strengthening by solid solution and precipitate alloying (Cu, Si..) - increases strength up to a hundred-fold – Broad applications in transportation (especially flight), housewares, packaging – Next generation alloys may be Magnesium based How Materials Have Shaped Civilization • Polymeric Materials: Plastics and Fabrics – A crucial element of the modern age. – Typically very ductile, not very strong, relatively low melt. points. – Long chain repetitive structures (poly x mers), usually (not always) based on carbon and hydrogen. – Natural polymers (in wood, bone, silk, rubber) long used, but synthetic polymers only developed in last century. – Rubber used in waterproof textiles from 1820s, but rather sticky and unstable. In natural form is not elastic. Vulcanization with sulphur changes molecular structure (by cross-linking of chains) so that material is now elastic – returns to original shape after deformation. Also increases stiffness. – Another miracle material, particularly for tires – availability of rubber a key to military strategy in two world wars. – Synthetic rubber is now the dominant global supply How Materials Have Shaped Civilization • Polymeric Materials: Plastics and Fabrics – Cellulose nitrate is derived from wood and is a thermoplastic (material can be shaped and reshaped by heat, a bit like metals). Basis of artificial fibers: rayon, then nylon, then Dacron, then Kevlar – 1930s polyethylene. 1950s high density polyethylene (HDPE), partly crystalline. 1960s polypropylene, a thermoplastic with high strength (for a polymer): auto dashboards, pipes… – Replace H with other atoms: polytetrafluoroethylene (Teflon), polyvinyl chloride, PVC – Add benzene rings to side chains: polystyrene, perspex, plexiglass – Still a very active research field, new products all the time… How Materials Have Shaped Civilization • Modern and Future Materials – Silicon: the foundation of electronics (are we now in the Silicon Age?) – Gallium Arsenide, Indium Phosphide and Gallium Nitride; lasers, light emitting diodes and optics – Silica fibers: telecommunications – Magnetic materials: storage (computation?) – Nuclear materials – Magnetoresistive materials – Biomaterials – Carbon nanotubes, fullerenes, graphene – New multifunctional polymers – Amorphous metals – Nanocomposites .

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