LECTURE 4.2

LECTURE OUTLINE Weekly Reading Weekly Reading Prototype Practice Quiz 4: Feedback Prototype Practice Quiz 4: Feedback The Chalcolithic and Bronze Ages The Chalcolithic and Bronze Ages

PROLOGUE TO PART D: THE MATERIALS SCIENCE TETRAHEDRON I: STRUCTURE The Prologue to Part D begins by introducing the structural hierarchy of materials, from the sub-atomic level (in the picometer to nanometer range) through the microstructural level (in the nanometer to micrometer to millimeter range) to the macroscopic (in the millimeter "and up" range). The various levels of structure are illustrated with respect to silica, a ubiquitous ceramic that we shall encounter throughout the text. Perhaps the most important aspect of the Prologue is the discussion concerning the "molecule" and the "monomer." Sometimes, it is easy to trivialize science in general textbooks, but in the Prologue, a serious discussion on the use of the terms "molecule" and "monomer" is given.

CHAPTER XII: WORKING MODELS OF THE ATOM This chapter presents a brief account of the atomic models that will be used throughout the remainder of the text. Two particular models are described: the Rutherford-Bohr model and the hard-sphere model. The Rutherford-Bohr model describes an atom in terms of a heavy nucleus, which is surrounded by electrons that are confined to a series of "shells." Rules for the occupancy of these shells are presented. The hard-sphere model is the simplest of all mental images of the atom. It is represented as a nanometer-scale billiard ball. The hard sphere has a characteristic radius, and this radius may be used to develop representational pictures of the packing of atoms in a solid or a liquid. The reader is also introduced to the "Lewis-Dot" notation, an invaluable tool for "electronic" bookkeeping.

CHAPTER XIII: THE THREE (?) STATES OF MATTER This chapter uses the hard-sphere model of the previous chapter to illustrate the arrangements of atoms in a solid, a liquid, and a gas—the three "conventional" states of matter. However, it is also argued that for many materials not all three conventional states are necessarily possible. It is also argued that there are other states of matter, including the "glassy state" and the "rubbery or plastic state." Because the concept of entropy is important when discussing the propensity for solids to be stable at low temperatures and gasses to be stable at high temperatures, the "influence" of entropy in the emergence of "order" is described. It is argued that the appearance of complex life forms does not violate the second law of thermodynamics—that the entropy of the universe must increase! A thought experiment is used to predict the occurrence of a crystalline solid when cooling rates from the liquid state are sufficiently slow, and of a glassy solid when the cooling rates are above some critical rate.

Prototype Practice Quiz 4: Feedback

QUIZ AVERAGE: 61%

Q23. Figures 2 and 3 are hardness plots for a series of tin bronzes—alloys of copper (Cu) and tin (Sn), Figure 2)—and for a series of arsenical bronzes— alloys of copper (Cu) and arsenic (As), Figure 3. For each alloy, there are two sets of data, one set is for “annealed” bronzes, the other for bronzes that were cold worked by something such as hammering. Which of the following alloys, and in what condition, would be the hardest? A Cu-3%Sn alloy, annealed a Cu-3%As alloy, annealed a Cu-3%Sn alloy, cold-rolled a Cu-1%As alloy, cold-rolled

A Cu-3%Sn alloy, annealed a Cu-3%As alloy, annealed a Cu-3%Sn alloy, cold-rolled a Cu-1%As alloy, cold-rolled

Q32. Like any large civilized nation, Ancient Egypt relied heavily on imported goods. For example, timber was imported from Lebanon. Figure 5 is a sketch map of the Middle East. Locate the approximate position of Lebanon in Figure 5. A B C D E

CRETE TURKEY CYPRUS LEBANON IRAQ AFGHANISTAN/ PAKISTAN ISRAEL/ JORDAN/ SAUDI ARABIA/ EGYPT SUDAN

Q33. An indigenous people on the Wayward Islands have been using a copper-13% aluminum bronze for millennia (both copper and aluminum were readily available on Wayward). However, the available resources of aluminum on Wayward are decreasing rapidly and so a new aluminum bronze, with a lower aluminum content, must be designed. The new alloy must have approximately the same hardness as the 13% aluminum bronze. Figure 6 is a plot of the hardness of a series of aluminum bronzes. Which of the following alloys should be chosen? 7% Al 10%Al 3%Al 5%Al 9%Al

The answer is 7%Al. For an alloy containing 13% aluminum, the hardness (or strength) of the alloy is about 400N/mm 2, which is given by the perpendiculars to the curve on Figure 6. Because the lower content aluminum alloy must also have a “hardness” of 400N/mm 2, the lower aluminum content is given by the second intersection of the bold horizontal line with the curve on Figure 6. Dropping a perpendicular from this second intersection yields approximately 7%Al.

Q34. Historically, the native Wayward islanders have produced their aluminum bronzes in sand casts. Sand casting yields a fairly slow cooling rate and has served the islanders well for millennia. Because of an acute shortage of aluminum, the islanders are experimenting with chill casting, in which the molten bronze is poured into a water-cooled copper mold. The more rapid cooling rate increases the strength/hardness of their bronzes. The object is to replace a Cu-14%Al sand cast alloy with a chill cast alloy of the lowest possible aluminum content but of approximately the same strength/hardness. Figure 7a and b are strength/hardness plots of the sand cast and chill cast alloys, respectively. Which of the following aluminum levels meets the design criterion for a chill casting? 4%Al 2%Al 6%Al 8%Al 10%Al

The answer is 4%Al. The rationale is as follows. The strength/hardness of the Cu-14%Al alloy is approximately 250N/mm 2 (Figure 7a). When we plot this value as a straight line on Figure 7b, it intersects the curve at 4%Al. Hence, a chill cast Cu-4%Al alloy has the same strength/hardness as a sand cast Cu-14% alloy.

Lesson 04: HISTORY OF MATERIALS The Chalcolithic and Bronze Ages

OUTLINE Natural Resources of Egypt Natural Resources of Egypt The Melting of Gold The Melting of Gold The Smelting of Copper The Smelting of Copper The Casting of a Bronze Door The Casting of a Bronze Door The Production of Egyptian Faience The Production of Egyptian Faience

NATURAL RESOURCES AVAILABLE TO EGYPT

MELTING GOLD IN THE OLD KINGDOM, I

MELTING GOLD IN THE OLD KINGDOM (II)

A GOLDSMITH’S SHOP IN THE NEW KINGDOM (I)

A GOLDSMITH’S SHOP IN THE NEW KINGDOM (II)

THE DIFFUSION OF COPPER METALLURGY THROUGHOUT EUROPE AND THE MIDDLE EAST

NATIVE COPPER FROM MICHIGAN’S UPPER PENNINSULA

MALACHITE: A GREEN COPPER CARBONATE

COPPER SMELTING AT TIMNA IN THE THIRD MILLENNIUM BC (I)

COPPER SMELTING AT TIMNA IN THE THIRD MILLENNIUM BC (II)

THE PROCESSING OF BRONZE AND THE CASTING OF A BRONZE DOOR (I)

THE PROCESSING OF BRONZE AND THE CASTING OF A BRONZE DOOR (II)

THE PROCESSING OF BRONZE AND THE CASTING OF A BRONZE DOOR (III)

THE PROCESSING OF BRONZE AND THE CASTING OF A BRONZE DOOR (IV)

THE EFFECT OF ADDING TIN TO COPPER

THE HARDNESSES OF TIN AND ARSENICAL BRONZES (I)

THE HARDNESSES OF TIN AND ARSENICAL BRONZES (II)

PROCESSING OF EGYPTIAN FAIENCE (I)

EGYPTIAN FAIENCE