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AN INTRODUCTORY COURSE – THE ROLE OF MATERIALS THROUGH THE HISTORY OF HUMAN CIVILIZATION Roberto Fieschi and Marco Bianucci Physics Department, University of Parma, Via G. Usberti 7, A43100 Parma, Italy; [email protected] Institute for Marine Science (ISMAR-CNR), Forte Santa Teresa, Pozzuolo di Lerici, 19032 Lerici, Italy; [email protected] ABSTRACT The raison d’être for inserting a simple, complementary course on the history of materials and its role in the history and development of human civilization at the beginning of the material science curriculum is presented and explained. An outline of how this could be done is shown, with examples from Prehistory, the Age of metals, and later historical Ages. Suggestions are made in each section as to how the narration can offer the teacher hints on the connections with contemporary developments and interpretations. For some types of materials a schematic list of the main stages of development in the subsequent times is also given. INTRODUCTION We assume that a typical curriculum includes Physics (classical, quantum, statistical physics), Chemistry (inorganic, organic, electro-chemistry), Mathematics, Computational tools, etc. The young undergraduate is thus submitted to the need of acquiring an amount of basic knowledge before tackling the actual problems of Material Sciences (MS). As a consequence, he/she does not have the possibility of appreciating the real nature of MS and its role in the development of the past and future of our society. This “hard”, or technological, approach of the traditional curriculum could divert the less determined student from the original purpose of taking a

good course in MS. In order to both avoid this risk and capture the interest of our students from the very beginning, it is advisable to develop a complementary line into a good and suitable traditional curriculum. This can be achieved by introducing a simple and appealing course on the history of materials and their role in the development of human civilization. Materials have played a key role in the evolution of mankind. In fact, prehistoric and early historic Ages were identified by Thomsen in 1836 according to the materials used in workmanship: Stone, Bronze and Iron Ages. In the following, we shall outline how this soft approach could be introduced. Along with the description of the uses of

materials, an overview of their main physical properties and of the role they still play in our society is proposed. Suggestions to teachers on how to connect the historical context with the actual scientific explanations or the recent developments is written in italics and included in a separate note on the relevant page. The outcomes of this approach should be a stimulus to students to appreciate the importance of materials and of MS and technology, and should foster the interest to acquire a more deep and sound knowledge of the subject. The topics covered in this article are by no means exhaustive. Different choices can be made, according to the main interests of the entire curriculum: more emphasis on metals and alloys, or semiconductors, or polymers and plastics, or composites, and so on. As the credit hours, the choice depends on the equilibrium with the traditional disciplinary courses. It is evident that there is no space for an exhaustive course on the history of materials during the old and the present ages. Thus, the reference to recent developments has been condensed into a list of dates and events. As to the delivery methods, the lesson could be enriched by showing many images, schemes, diagrams, and possibly, also animations and simulations. No labs are necessary; it is advisable to incorporate a guided tour to local Museums of Archaeology and of Science and Technology. To help students and teachers to follow this approach, in the ‘90th years we made two exhaustive courses on MS on a CD ROM support with hundreds of multimedia contents and tools. We included an important section devoted to the history of the Science and Technology of MS, stressing the connection with different disciplines, like Art, customs and traditions.

BACKGROUND The history of the discovery and the invention of materials are widely treated in the current literature. However, it is not generally included in specific curricula of advanced studies on chemistry, physics or MS. We think that this absence should be rectified, so that young students shall be exposed to appealing approach to the subsequent traditional technological studies. An obstacle to this unconventional approach could be that typical teachers of “hard” sciences do not master the historical background of their subject. A guideline should then be prepared or, even better; one should turn the historians of science and technology for help. Prehistory: From about 3,000,000 to 6,000 years ago During prehistory and for a considerable part of the history of mankind, well before the development of science as we know today, solid materials were used mainly for their mechanical properties, whose practical interest is evident; few other properties have been considered: thermal properties for the warmth of fur and, often, only by chance, magnetism, electricity, optical properties. Only four natural materials had been mastered, i.e., developed into tools, during the dawn of civilization: stone, wood, bone and leather-fur. Of the first and the third of these materials we have many archaeological finds, due to their chemical stability, while this is not true for the other two, and the evidence is indirect or inductive. For the mastering of stone, the obstacle to overcome was how to control the shape. This was a difficult and gradual process; it took several hundred thousand years to go from about ten different tools made of splintered stones during the Lower Paleolithic (Chellean) to a hundred during the Higher Paleolithic (Tixier, 1984), see some examples in Figure 1.

Figure 1. Paleolithic stone tools (By José Manuel Benito Álvarez). Left: First simple chopped stone tools, Lower Paleolithic. Center: A lower Paleolithic bifacial, which represented a significant technological progress. Right: Scraper for skins, Middle Paleolithic

The most ancient tools known to date have been found in Africa and date back around 3 million years. The craftsmen were not the direct ancestors of Homo sapiens but Australopithecus hominid. Much later stone was exploited for monuments, housing, statues, urns, and mosaics. Wood is still nowadays one of the most widely used materials: industrial consumption is about 1.6 billion m3. In buildings the drawbacks of the limited resistance of stone architraves to transverse strain was overcome much later (Etruscans), thanks to the invention of the vault arch. With the invention of baked clay and during the Age of Metals, new techniques for an easier control of the shape became available. It should be noted that shape control, on a more sophisticated level, is still an objective of contemporary technology: consider the tolerance limits of modern machine tools, the ultra-miniaturization of the electronic circuits, the nanotechnologies.

Figure 2. Mosaic From the Mausoleum of Galla Placidia (386-452 A.C.) Ravenna, Italy (Photo credit accademiaravenna.net).

Wood accounts for many tools: the bow, the fist complex tool invented by man (30,000 years ago), the boats, and the wheel (IV millennium), whose importance cannot be under estimated. A first explanation of the mechanical properties (harness of the stone) can be given, as being due to the strong chemical bonds between the atoms of the macrocrystals composing the stone; the cleavage (obsidian) can be assigned to the amorphous structure. The low thermal conductivity of furs allows the introduction of Fourier’s law. The colour of mosaics (see for example Figure 2) allows the introduction to the interaction with light of materials: this can be dealt more extensively in the section on glass. THE NEOLITHIC REVOLUTION Pottery At least 10,000 years ago, in particular regions of the Earth, man learned to cultivate plants and to tame and rear animals. The small communities of hunters turned gradually into communities of farmers and breeders, and the first villages were built. With the advent of Neolithic, man, thanks to a new technique, invented a new material, baked clay. Some early examples date back to the IX millennium; the analysis of the remains of a jar of 7000 years ago (North Iran, see for example Figure 3, right) shows that it was used to

contain wine. Pottery was obtained by heating a mixture of clay and water to a sufficiently high temperature. Since the mixture can be easily molded by hand, the problem of shape control is solved. Further developments in the manufactory of pottery date back to the IV millennium, when the potter’s wheel was invented; thanks to this new fool, the artisan could work quickly and make objects with regular shapes and thinner walls.

Figure 3. Pottery wheel (left) and a Neolithic Pot from Susa, Iran (right, Louvre Museum).

The potter’s wheel is the progenitor of the modern lathe used in mechanical workshops (see Figure 3, left). Here and in the following the interconnections between materials technology and science and other techniques should be stressed. Fire played a key role. Men had known fire for half a million years, as testified by remains of ancient hearths. However, the first time it was used for technical purposes was for the baking of clay; this process is now known as sintering. Sintering changes the structure of the natural material, modifying the bonds among atoms and their arrangement in space, and producing a partial welding of the solid particles of the mixture; it is the most ancient process for transformation of matter. The role of fire and in general of furnaces to obtain high temperatures for new or better materials can be stressed; this shall be better illustrated with the later medieval developments.

Presumably the first baking was done in open furnaces. Later, two other types of furnaces were built, vertical and horizontal; the first type is the ancestor of modern blast furnaces. Higher temperatures were achieved by the Chinese (VII-IV century B.C.), who were able to make compact ceramics known as porcelain, made of white clay and kaolin. Important developments took place mainly during the last decades of the XX Century, because of the need for new materials resistant to high temperatures (refractoriness), to chemically hostile environments (chemically inert) and to strong mechanical stress. This is the reason why compounds of nitrogen, carbon and silicon have been studied extensively. Besides their structural properties, today ceramic materials have acquired interest for their magnetic properties (ferrites), electrical properties (piezoelectric, superionics, superconductors, etc.). THE AGES OF METALS Metals are widespread on Earth, but few metals can be found in their native state: gold, silver, copper, (platinum); these are the first metals that man learned to use (V millennium or earlier). Gold was used to make decorative articles and jewels. Later small bars of an alloy of gold and silver were made into coins and were exchanged in trading. Traces of the importance of gold can be found in myths and legends: Golden Apples in the garden of Hesperedis, the Golden Fleece won by Jason, King Midas condemned to turn into gold anything he touched, the Golden Calf (Exodus 32:1), etc. During the Middle Age generations of alchemists worked to obtain the “philosophers stone” capable of turning mercury, or lead, into gold. Gold, chemically stable but rare, had no other

De re metallica by Georgius Agricola, released in the year 1556, is a book cataloguing the state of the art of mining, refining, and smelting metals, that remained the authoritative text on mining for 180 years after its publication. In Figure 5 is a picture from this fundamental book.

Figure 4. Danaë and the shower gold. From a Boeotian red-figure bell-shaped crater (450-425 A.C.). Louvre Museum.

practical use until recent times, when it found applications in electronics. Like gold and silver, native metallic copper can be found in nature in small quantities. Small objects made of native copper appear in Neolithic settlements, VIII-VII Millennium. The analysis of their microstructure shows that the metal was subjected to cold working for shaping and hardening. Most metals are part of non-metallic compounds in rocks. This is due to the fact that they are highly reactive and combine chemically with nonmetallic elements like oxygen, carbon, silicon to form oxides, carbonates, silicates, etc. The Copper Age The birth of the Copper Age is marked by the discovery that the metal could be obtained from its minerals. Cu is more commonly found in the form of oxides, carbonates, sulphates. Metallic copper can be obtained from minerals by reduction, namely by heating with charcoal; the melted metal can be poured into refractory containers (crucibles) of a given shape: due to this discovery, tools made of Cu were more commonly used during the III Millennium. Copper mines have been found back to the V Millennium.

Figure 5. Medieval mine (from “De re matallica” by Gorgius Agricola, 1556)

Much later the technical evolution of mineral extraction played a role in a quite different field: in the 18th Century A.C. the need for a better technique for draining water from the bottom of deep coal mines lead Thomas Newcomen in 1712 (Dartmuouth, 1664 – Londra, 1729) to develop a steam engine; however it had low efficiency and low power (about 4 kW). The goal of obtaining a more powerful and efficient engine was achieved by James Watt in 1769, with the introduction of a separate steam condenser.

During the last two Centuries, Cu has acquired a great importance in electrical applications; in fact Cu is a good conductor of electricity. Conductors of low resistivity are advantageous because they cause minor heat dissipation when electrical current passes through. In line with this, one can introduce the first elements on the electrical properties of materials, such as Ohm’s law and the Joule effect. The Bronze Age A new metallurgy development almost simultaneously with that of Cu; it was based upon alloys of copper and small quantities of other elements, arsenic and tin. These alloys have mechanical properties superior to those of pure copper, and have a lower melting temperature. The alloy usually referred to as bronze is made of copper and tin. Its name has been coined to denote the first period of human history: the Bronze Age. The spread of bronze metallurgy gave new impulse to trading; expeditions aimed at acquiring tin could last several years. Today bronze alloys, which also contain lead are employed because of their low friction property; special springs can be made by adding silicon; resistance to corrosion by sea water can be achieved by adding manganese. The Iron Age In the few most ancient finds of iron (IV Millennium) the metal is of meteoric origin; however meteorites are quite rare. The actual Iron Age began towards the end of the II Millennium, presumably thanks to the Hittite blacksmiths. The Hittites were an Endo-European people who, towards the end of the II Millennium, settled in the region of contemporary Turkey; they ruled for almost a millennium and the collapse of their Empire resulted in the dispersing of their skilful blacksmiths, hence the spread of iron metallurgy. Iron was produced from minerals, mainly hematite and magnetite, heated in furnaces fuelled by charcoal, these furnaces, instead of giving molten metal, yielded a spongy, solid matter (bloom),

containing iron as iron carbide (Fe 3C), pieces of Carbon and other impurities, in order to expel the impurities and reduce the content of carbon, the bloom was treated in forges by repeated heating and hammering the desired shape of iron objects was obtained by blacksmiths in their forge by hot working and cold working the connection with the mythology, the Olympic god of metallurgy, Hephaestus (see Figure 6), son of Zeus and Hera, and the first metallurgist of the Bible, Tubal Cain, show the importance attributed to iron.

Figure 6. Hephaestus’s Forge, Diego Velasquez, 1630. Prado Museum.

Cold working, also known as work hardening is the strengthening of a metal or an alloy by plastic deformation. This strengthening occurs because of dislocations movements and dislocations generation within the crystal structure, interact with one another, and serve as pinning points or obstacles that significantly impede their motion. Because dislocation motion is hindered, plastic deformation cannot occur at normal stresses. This leads to an increase in the yield strength and a decrease in ductility of the material. Yield strength is increased in a cold-worked material. Simple pictures of perfect crystal lattices and of lattices containing linear imperfections (dislocations) can be

proposed in order to explain the mechanical properties of materials Because of its higher mechanical resistance, iron, gradually, replaced in many uses stone and bronze. Iron tools like hoes, pick-axes, swords, sickles and plugs, that enabled a deeper tillage of the soil, spread progressively; as a consequence, farming expanded over larger areas and the population grew. The transition however was slow, because of the complexity of the iron metallurgy. While bronze objects can be easily obtained via melting and pouring into crucibles of the desired shape, iron articles require a different technique. In fact, pure

iron melts above 1500°C, an such high temperature was achieved only much later, in medieval furnaces. An evidence of the difficulty of the transition from previously known metals to iron can be found in the Iliad (VII Century B.C.): there are about three hundred references to copper and only about twenty to iron. Iron articles appear most frequently from the VII Century onward; most of the archaeological finds are in bad condition, due to the fact that iron undergoes corrosion (rust).

Corrosion is the gradual destruction of materials (usually metals) by chemical reaction with their environment. The word commonly means oxidation of metals in reactions with an oxidant such as oxygen. Rusting, the formation of iron oxides is a well-known example of electrochemical corrosion. Many structural metals and alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can concentrate locally to form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface. Because corrosion occurs on exposed surfaces and is a diffusion-controlled process, methods to reduce the activity of the exposed surface, such as passivation and chromate conversion, can increase a material’s corrosion resistance. Some metals are more intrinsically resistant to corrosion than others. The materials most resistant to corrosion are those for which corrosion is thermodynamically unfavourable. Moreover some metals have naturally slow reaction kinetics, even though their corrosion is thermodynamically favourable. These include metals as zinc, magnesium, and cadmium. There are various ways of protecting metals from corrosion. (Oxidation: plating, painting, and the application of enamel are the most common anti-corrosion treatments.) In 1998, the total annual direct cost of corrosion in the U.S. was ca. $276 billion (ca. 3.2% of the US gross domestic product). Considerable improvements in iron metallurgy were made when new techniques were discovered: steelmaking (or cementation) and tempering. Towards the middle of the II Millennium blacksmiths realized that iron tools heated by red hot charcoal were harder than wrought iron. Today we know that this is due to the small amount of carbon that penetrates the outer layer of the iron and transforms it into steel.

Swords with steel blades were already manufactured at the beginning of the I Millennium. Quenching, which produces a harder but more fragile steel, was discovered later. Large scale use of the Roman Empire; the Romans made further progress; the “gladium”, a short and solid sword, was superior to the bronze sword of their enemies.

Iron-Carbon alloys are not homogeneous, but their microstructure changes according to the temperature to which they are heated and the rate of cooling. The mechanical properties depend strongly upon their microstructure. The analysis of the tools by means of optical and scanning electron microscope has provided information on the ancient metallurgical techniques. THE REVIVAL OF IRON METALLURGY importance in the industrial revolution is well known. During the second half of the 15th Early Middle Ages Century the bankers made large investments for the exploitation of ore deposits, in order to Towards the year 1000, there was a cultural establish a large scale steel industry. and economic revival in Europe. The production of iron also increased, probably There was a breakthrough in iron metallurgy also to satisfy the needs of larger armies, and, at the end of the 18th Century when coke, later on, after the invention of gunpowder, for having low sulphur content, was used; also the production of fire-arms. The growing need the invention of pudding, where melted cast of cast iron and steel necessitated bigger iron is stirred using long iron bars in the furnaces capable of reaching higher presence of hematite and iron oxide, and temperatures (complete melting of the cast subjected to strong air flows came about. iron). This, in turn, led to the construction of During this process decarburization takes big bellows for blowing more air. Human place and the iron thus obtained is sufficiently energy was not sufficient to move the pure and easily manageable. This step marks bellows, hence the energy of the running the beginning of the second Iron Age; the water through a waterwheel was exploited. amount of iron produced grew enormously. The complete melting of cast iron was one of Iron was widely employed also in the the greatest achievements of the Middle Ages, construction industry and in the great iron as well illustrated by Vinnoccio Biringuccio works; the first great iron bridge, over the in 1540. Figure 7 shows a picture from the river Severn, was built in 1781 and required famous book of Vinnoccio Biringuccio. 400 tons of cast iron. Napoleonic wars and, later, the development of railways, stimulated the production of larger and larger quantities of cast iron and steel. Curious indirect consequences:  After 1800, goose quills are replaced by steel pen-nibs;  Rail travels stimulated the development of personal watches and their extensive use. Figure 7. Bellows in the blacksmith’s workshop. (Vinnoccio Biringuccio, 1540).

The need of big quantities of wood to feed the furnaces, in some regions of Europe, crated an environmental crisis due to the extensive deforestation. The subsequent need of coal made it necessary to dig deeper mines; thus, the water from the bottom of the mine had to be drained; it lead, in the 18 th century, to the invention of the steam engine, whose

Main development Century

during

the

XVIII

1664-1665 – Robert Boyle, one of the founders of modern chemistry, and Robert Hooke, physics and inventor, open the way to the structural analysis of steel. 1733 – René-Antoine Ferchault de Réaumur publishes a first systematic treatise: examining the fracture surfaces with microscope, finds that steel consists of small

grains and identifies the role of impurities in different types of iron-carbon alloys.

occur, and the influence of thermal processing on the size of grains and hardness.

1773 – chemical analysis shows the role played by carbon in cast iron and steel. Since the, the role of chemistry in steel industry becomes increasingly important.

1878 – Thomas process, similar to the Bessemer one, but more efficient in removing the content of phosphorous. Its adoption in Germany gives a strong impetus to the heavy industry.

1776 – John Wilkinson replaces bellows with steam engines to obtain higher air flows and to reach higher temperatures 1784 – puddle iron. Main developments Century and later

during

the

XIX

1821 – Bertiez achieves the chromium-steel alloy 1822 – Michael Faraday obtains chromium and nickel alloys; they will be widely used towards the end of the century. 1825 – first railways Stockton-Darlington; the Liverpool_ Manchester will be built 5 years later. 1855 – patent of the Bassemer process: the first industrial process for the massproduction of steel from molten pig iron; the key principle is removal of impurities from the iron by oxidation with air being blown through the molten iron; the oxidation also raises the temperature of the iron mass and keeps it molten. 1860 – Achievement of the tungsten steel alloy, a hard alloy used for rapid cutting tools (R. F. Mushet) 1864 – Martin-Siemens (or open earth) process, in which the excess carbon and other impurities are burnt out of pig iron (high carbon content, 3,5 – 4,5%) to produce steel; its main advantages were that it didn’t expose the steel to excessive nitrogen, which would cause the steel to become brittle. 1864-1866 – Thanks to the introduction of the metallographic (reflective) microscope, the microstructure and the properties of steel are investigated in greater detail (H. C. Sorby). 1870 – Dmitrij Konstantinovič černov identifies the critical point, i.e. the temperatures at which the phase changes

1879 – Adolf Martens publishes his first work on the microstructure of iron and steel; martensite, a metastable phase of steel. Is named for him. 1878-1890 – development of the electric furnace. 1887 – R. A. Hatfield patents the steel with high content of manganese, an alloy nonmagnetic and resistant t to wear. 1888 – Henri Louis Le Châtelier perfects the coupling of platinum with a platinumrhodium alloys that gives rise to the thermoelectric pyrometer and adapt an optic pyrometer for industrial use; that made high temperatures measurements possible. 1889 – Josiah Willard Gibbs announces his rule of phases that, later, will make it easier to better identify the phases of the Fe-C alloys. 1904 – Development of vanadium steel, that later shall be extensively employed by Ford in engines. 1934 – the dislocation model is proposed in order to interpret the mechanical properties of solids, in particular the plastic deformation GLASS The most ancient uses of glass, other than for the manufacturing of glass articles, were the coating of other materials for decorative purpose (glazing). Glazzed pearls were already manufactured before the IV Millennium; it took one more Millennium for the working technique to develop to the point that hollow objects could be made. Instructions on how prepare glass, carved on clay tables, have been found in the great library of Niniveh, the capital of the Assyrian Empire.

Normal glass is obtained by heating a mixture of silica sand (SiO2) and other substances, such as calcium oxide, sodium oxide, and various carbonates, up the melting point. Pure silica has a higher melting point. Pure silica has a higher melting point than the mixture. When the melt cools, it becomes gradually more viscous, and then solidifies into a rigid material. Thus, there is no characteristic critical temperature for the liquid-solid transition. The resulting amorphous solid is transparent, provided that the original mixture contains no impurities. Colored glass is obtained when small quantities of other substances are added. Beautiful vases made of colored glass have been found in Egyptian tombs of the XVIII dynasty (1580-1369 B.C.), see for example Lilyquist. They were obtained by shaping the glass around a core of chalk or sand that was removed after the baking process. Glass is an amorphous solid: it has a noncrystalline structure, i.e. its atoms are not orderly arranged in space. The difference between the liquid-solid transition and the glassy transition can also be shown. More generally, one could also explain the phase transitions. The technique of glass blowing was an important step forward that made it possible to work large containers with thin walls and different shapes. Apparently this technique was discovered in Syria during the first century B.C. During this same period glass started to be used for windows in roman buildings. The glass art did not make substantial progresses for many centuries. It developed mainly in Venice. Processing techniques were considered State secrets and the authorities of the Republic could order the death sentence for the craftsman and their family if they went abroad to export their know-how! The optical properties of materials, colour, reflectivity, transparency can be illustrated

trough classical images of mirrors, vases, mosaics, windows. This allows the introduction of the properties of light: spectrum of the radiation (wavelength/frequency, absorption, reflection diffusion, refraction and the role of lattice impurities. Glass and Science Important innovations appeared when advanced techniques for the polishing of the surfaces of compact glass were developed. Grinding and polishing of transparent glass lead to the production of lenses for spectacles; later, 17th Century, lenses for microscopes and telescopes were also made. These developments opened up unimaginable possibilities for the study of the sky and of the microscopic world. These technical developments, including also Newton’s prism for the refraction of light, played a key role in the revolution science. Recently, thanks to the achievements in chemistry and physics and under the pressure of industry, many different types of special glass have been produced. Shatterproof glass was an achievement of the thirties; another important step (1959) was the technique to obtain optimum quality flat surfaces: melted glass is allowed to solidify while floating on a bath of melted tin. The most impressive development was surely that of transparency. It is of the greatest importance in optical fibers for telecommunications, used as waveguides to transmit light pulses across large distances with a low level of attenuation and at higher bandwidths data rates than copper cables Guiding of light by internal reflection, the principle that makes fiber optics possible, was first demonstrated in Paris in the early 1840s. The crucial attenuation limit of 20dB/km was first achieved in 1870, by researchers working for the American glass maker Corning Glass Works, now Corning Incorporated. Today, thousands of types of glass are produced.

MAGNETIC MATERIALS The properties of magnets have always generated astonishment. Apparently Thales of Miletus, the first philosopher and scientist of western civilization (6th Century B.C.), already knew of a natural magnet, now called magnetite. Thales, as well as the successive philosophers, believed that magnets have a soul, and this idea stood for about two millennia. Other views, closer to the modern concepts of the magnetic field, explained the effect in terms of an invisible fluid emitted by the magnet. The Latin poet Titus Lucretius Caro (1th Century B.C.) wrote: “Sing me now, oh Muse, the reason of such an extraordinary effect. Explain me why the magnet strongly attracts and so passionately embraces the rough iron”. In the following poet describes the capacity of magnets to attract small iron rings and form a chain (magnetic induction), and attempts an atomistic explanation. During the entire Middle Age there was little progress. Several qualitative explanations were proposed during the 12th and 13th Centuries, Pierre de Mericourt, namely Petrus Peregrinus, in 1269 wrote the Epistula de Magnete (in this treatise there is also a design for a perpetual motion mechanism!). However, strange legends were circulating. In “the Arabian nights” there is the description of a black mountain that caused the wrecking of the ships that came too close, because the mountain attracted and pulled out the iron nails. The first descriptions of the use of magnetic bars, i.e. the compass as a means to find the way during the navigation, date back to the 13th Century in Western countries; Chinese knew it at least two centuries before. The Italian “Repubbliche Marinare” employed the compass during that period. This, and the invention of the vertical stern rudder (made possible also by the progress of iron metallurgy), put Europe on course for the great geographical conquests. First systematic studies

The first scientific treatise, the De Magnete, was published by William Gilbert (Colchester 1544 – London 1603), the English personal physician of Queen Elizabeth. During 18 years of experiments he turned the confused knowledge of his times into a set of verified data. Gilbert realized that the Earth is a huge magnet whose poles are located near the geographic poles; he is therefore considered the father of geomagnetism. Gilbert had also the task of demonstrating that the widespread belief that the diamond could magnetize an iron needle was not true. His contemporary Giovanni Battista Porta wrote: “It is common opinion among sailors that onion and garlic are in contrast with magnets, and helmsmen are forbidden to eat them to prevent upsetting of the pole indicator. However, when I tried all these things, I found them untrue”. Further development Magnetic materials were more extensively used due to the development of electricity, after the invention, by Alessandro Volta (Como 1745 – Como 1827) of the “pile”. The availability of direct currents and of the magnetic field generated by these currents (Hans Christian Oersted, 1819) made it easier to magnetize materials and lead to the knowledge of the hysteresis loops. The new needs of the electric industry required new magnetic materials with properties different from those of the permanent magnets already known; for instance, for the transformers, materials of high permeability, capable of conveying the flux of the magnetic field, and of low coercivity, i.e. being easily demagnetized. More recently other material have been developed, for magnetic recording, for microwave devices, computer memories, etc. Basic steps in recent history of magnetic materials Pierre Curie (Paris, 1859-1906) studied ferromagnetism, paramagnetism, and diamagnetism for his doctoral dissertation and discovered the effect of temperature on

paramagnetism, which is now known as Curie’s law. He also discovered that ferromagnetic substances exhibited a critical temperature transition (curie point.), above which the substance loses its ferromagnetic behavior. 1897 – Charles-Eduard Guillaume (Nobel Prize) discovers an alloy (invar) consisting of 64% of iron and 36% of nickel, that exhibits nearly no thermal expansion; invar enables very accurate physical measurements to be performed. 1898 – It is discovered that manganese, when mixed with Cu and Sn gives a ferromagnetic alloy with properties similar to those of nickel. 1898 – Fe-Si alloy, largely employed in transformers. 1905 – Paul Langevin (Paris, 1872 – 1946) develops the atomic theory of paramagnetism. 1907 – Pierre-Ernest Weiss (Mulhouse, 1865 – Lion, 1940) proposes a theory of ferromagnetism based on the “molecular field”, and of the magnetic domains. 1911 – Heike Kamerlingh Onnes (Groningaen, 1853 – Leyden, 1926) discovers the superconductivity. 1912 – It is discovered that manganese, when mixed with Cu and Sn, gives a ferromagnetic alloy with properties similar to those of nickel. 1912 – It is discovered the high magnetization of the Fe-Co alloy. 1916 – Patented, with the name of Permalloy, a Ni 78%, Fe 22% alloy by a very high magnetic susceptibility. 1925 – George Eugene Uhlenbeck (1900, Batavia – 1988, Boulder) and Samuel Abraham Goudsmit (The Hague, 1902 – Reno, 1978) formulate the hypothesis that the electron has an intrinsic angular momentum (spin) and an associated magnetic momentum. 1928 – Werner Karl Heisenberg (Würzburg, 1901 – Munich, 1976) explains ferromagnetism by means of the exchange

interaction, a characteristic quantum mechanics.

concept

of

1932 – Felix Bloch (Zurich, 1905-1983) proposes a model to describe the structure and properties of the boundaries of the magnetic domains (Bloch walls). 1933 – beginning of the studies on soft ferrites. 1935- iron oxides deposited on wires for the magnetic recording. 1936 – Fe-Al-Co-Ni (alnico) alloy for permanent magnets. 1950 – barium ferrite, the basic component of ceramic permanent magnets. RECENT BASIC STEPS IN TECHNIQUES THAT ARE RELEVANT TO THE PRODUCTION OF NEW MATERIALS, AND TO THE STUDY OF THEIR PROPERTIES 1912 – X-ray diffraction enables the study of the crystalline structures; later it will be used also to determine the phases of the Fe-C alloys. 1945 – The first neutron diffraction experiments were carried out by Ernest O. Wollan; he was joined shortly thereafter by Clifford Shull, and together they established the basic principles of the technique, and applied it successfully to many different materials. 1931- German physics Ernst Ruska and the electrical engineer Max Knoll constructed the prototype transmission electron microscope (TEM). An electron microscope uses accelerated electrons as a source of illumination. Because the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, the electron microscope has a higher resolving power than a light microscope. 1937 – Manfred von Ardenne pioneered the scanning electron microscope (SEM). The SEM produce images by probing the specimen with a focused electron beam that is

scanned across a rectangular area of the specimen; it produces images by detecting secondary electrons which are emitted from the surface due to excitation by the primary electron beam. 1960 – Molecular beam epitaxy (MBE) is a method of depositing epitaxial thin films. It was invented at Bell Telephone Laboratories by J. R. Arthur and Alfred Y. Cho and is widely used in the manufacture of semiconductor devices. 1960 – Metalorganic vapour phase (MOVPE), or metalorganic chemical vapour deposition (MOCVD), is a chemical vapour deposition method used to produce single or polycrystalline thin films; it is a competing deposition technology to MBE. 1981 – A scanning tunneling microscope (STM) is an instrument for imaging surfaces at the atomic level; it is based on the concept of quantum tunneling. Its development earned its inventors, Gerd Binnig and Heinrich Rohrer (at IBM Zürich), the Nobel Prize in 1986. Atomic force microscope (AFM) or scanning force microscope (SFM) is a very highresolution on the order of fractions of a nanometer. The precursor to the AFM, the scanning tunneling microscope, was development by Gerd Binnig and Heinrich Rohrer in the early 1980s.

THE CONCEPTUAL MATERIALS SCIENCE

BASIS

OF

The materials development, as shown in the chapter, for millennia has been due to empirical findings and to the skill of artisans. Nowadays, as in the past few decades, there was the transition from the empirical techniques to the real MS: the fundamental basis of the study of the properties and the development of materials lies in the developments of physics (quantum physics) and chemistry. The understanding of the properties of crystalline solids, starting from their structure on the atomic scale, is essential in MS. The building blocks of this great construction, solid state physics and inorganic chemistry, have gradually become clear during the past two centuries. The bricks are the electrons and the nuclei, while the bearing structures are the laws of classical, statistical and quantum physics and of chemistry (Figure 8). The construction is not complete, new phenomena provide further conceptual challenges. It is not linear; in some fields the empirical developments are sometimes as effective as those based on scientific grounds (Figure 8). Often new materials are invented with properties, which had not been predicted. The richness of the entire scenario is fascinating.

Figure 8. The building blocks of Materials Science (left). Empirical advances are often as effective as those based on scientific ground (right).

DISCUSSION AND RECOMMENDATIONS

traditional disciplines and/or the difficulty of finding good teachers and texts.

The more recent developments, only sketched here, could be treated more extensively. The scheme presented obviously is not exhaustive, it is no simply an example, an outline on how such an introductory course could be organized. For instance, no mention has been made to important classes of materials, such as organic polymers, fiber reinforced composites, semiconductors and superconductors. One could chose other examples of materials, according to the subjects that shall be treated more thoroughly in future courses, and could stress the basic physical and chemical concepts which are the sound backgrounds of material science and technology. We recommend making a large use of images, anecdotes and reference to parallel historical events, in order to make the course more interesting and stimulating.

Strategies for winning over the faculty who are not likely to be receptive to such a course are not easy; each teacher is usually fond of their own traditional teaching experience, and with good reasons. It could be stressed that there is a need to capture the interest of students by providing a soft approach to the subject of MS and Technology, and an historical approach offers this opportunity.

CONCLUSIONS With respect to the non-traditional proposal of this chapter, the teachers of MS and Technology could have two opposing reactions, Some would not accept it, although using reasonable arguments, such as the, need of devoting all the time of the course to the

Other teachers will show interest and willingness. In this latter case it is advisable to pay serious attention to find or to prepare good texts, suitable for the general planning of the whole curriculum. A typical, traditional teacher is a person specialized in their own field of research, and this provides the necessary background for giving a good and up-to date course. However, an effort for widening the specialized vision can be of advantage both for students and for teachers. Moreover, as commented above and shown as examples in the boxes, the historical approach can be used by the teacher also to introduce in a qualitative way some concepts and physical laws that make a bridge between the empirical developments and the modern MS.