Metals Structure.pdf

UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE Week 6: Structure and Applications of Metals I. Introduction The crystal structure of a material directly affects their properties. For example, gold and silver...

UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE Week 6: Structure and Applications of Metals I. Introduction The crystal structure of a material directly affects their properties. For example, gold and silver which share a common crystal structure are much less brittle than the metals beryllium and magnesium which possess a different crystal structure. Also, crystalline, and non-crystalline materials of the same composition can possess significantly differing properties. II. Objectives By the end of this lesson, you should be able to: 1. Outline the contributions to material processing made by the Egyptians. 2. Differentiate melting and smelting. 3. Distinguish between single crystals and polycrystalline materials, polymorphism and allotropy, and isotropy and anisotropy with respect to material properties. 4. Identify the differences in atomic/molecular structure between crystalline and non-crystalline materials. 5. Sketch unit cells for different crystal structures and the orthogonal crystal systems III. Egyptians and Material Processing Copper (Chalcolithic) and Bronze Ages In the Neolithic Age, which was the period at the end of the Stone Age, the Egyptians were experiencing increasing population along with extensive food production capabilities, several communities in similar stages of development, and an extensive trade network with other civilizations. As the Egyptians entered the Copper and Bronze Ages, their technological advancements in gold, copper, and bronze processing were aided by their access to key natural resources. Figure 6.1 from the British Museum shows known natural resources of ancient Egypt. Figure 6. 1 Natural resources of ancient Egypt. (Credit: The British Museum) MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 40 UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE Egyptian Gold Processing It is not surprising that gold was the first metal processed by the Egyptians. Very few metals are found in their native state, i.e., not bound to other elements in a compound such as a mineral. Copper is very rarely found in nature as an element and iron is typically only found as an element in some meteorites. Iron from meteorites was extremely rare in Egypt and was known as metal from the gods. Gold, however, is routinely found in nature as an element unlike copper and iron, and most other metallic elements. Gold, although rare, can be found as flakes or nuggets. As shown in Figure 6.2 from an ancient Egyptian tomb, the Egyptians used charcoal and blow pipes to reach the temperatures needed to melt Figure 6. 2 Ancient tomb illustration depicting gold processing. (Credit: Scielo) The molten gold was poured into molds to form jewelry and other items. In addition, the Egyptians were able to hammer gold into very thin (5 µm) leaves. Gold is a malleable material. Malleability is a er compressive stress, i.e., to form a thin sheet by hammering or rolling. A malleable material is also a ductile material, closely related but not exactly possessing the same definition in material science. Figure 6. 3 Gold leaf. (Credit: Eckhard Pecher, Wikimedia Commons) The Egyptians believed gold to be a divine material which held magical powers. Electrum is an alloy of gold which is approximately 80% gold mixed with 20% silver. An alloy is a mixture of metals or a mixture of a metal with small amounts of non-metals. MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 41 UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE Egyptian Copper Processing Native copper occurs in a very limited supply, so the start of the Copper Age is marked by the discovery of smelting copper from its ores which allows for a ready supply of copper. The two basic naturally occurring copper (II) carbonate minerals are pictured in Figure 6.4. Figure 6. 4 (a) Malachite (Credit: JJ Harrison, Wikimedia Commons) (b) Azurite (Credit: Eric Hunt via Wikimedia Commons) Copper is a very malleable material, unlike flint, which at the beginning of the Copper Age was the dominant weapon and tool material. Although copper is soft it does have a significant advantage over flint. It can be repaired. Native Americans used native copper beginning circa 6000 BCE. As mentioned, the supply of native copper is very limited, and its supply was easily exhausted. Copper ores, on the other hand, were readily available. However, to extract the copper from copper ores smelting was required. What is smelting? Smelting is a process that uses heat and chemistry to drive off other elements such as gases or slag, leaving behind only the metal. Typically, ores are impure and require a flux to separate the metal from the slag. Flux is an additive used to change the impurities from a form that is inseparable from the metal to a form that is separable. For example, adding iron ore as a flux during the smelting of copper can transform the impurity solid silicon dioxide into an iron-silicon oxide. Unlike the solid silicon dioxide which remains in the liquid copper, the iron-silicon oxide floats to the top and can be skimmed off. Smelting is different than melting in that in melting you must be able to raise the temperature to the melting point of the material. The Egyptians did not have the ability to reach the temperatures needed to melt the copper minerals outright. How Did Egyptians Discover that Malachite and Azurite Contain Copper? It is unknown exactly how the Egyptians discovered that malachite and azurite contain copper. Here are a couple of possibilities. 1. Egyptians used malachite as a pigment and cosmetic, including as a distinctive eyeliner. While a normal open fire would not reach the temperatures required to melt bulk malachite, in powder form it is possible that accidentally putting Malachite powder on the coals of the fire could produce small balls of copper. MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 42 UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE 2. A more likely possibility centers around the Egyptians using malachite as a pottery glaze. Small balls of copper could have been formed in the pottery kiln during firing, and then noticed by kiln workers after cooling. Egyptian Copper Smelting Process Figure 6. 5 Egyptian use of foot bellows. (Credit: The British Museum) The Egyptian copper smelting process raise the temperature of the fire, through the usage of foot bellows. Malachite and azurite were used as a source ore for the copper, charcoal was used as the reducing agent to separate oxygen from the copper, bone, wood, or flint, as a tool or weapon, is that when damaged it can be repaired. However, like most pure metals, i.e., metals with a low level of impurities, copper is soft. It turns out that intentionally or unintentionally adding another soft metal in small amounts can make the host material stronger and harder. This is a process known as alloying, which we will be discussing further in the next lesson. Egyptian Smelting of Tin L harder metal. Figure 6. 6 Cassiterite (Credit: Carles Millan, Wikimedia Commons) MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 43 UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE It is not known how exactly the Egyptians discovered the smelting of tin. In some ways, it is a bit surprising. Cassiterite, SnO2, the mineral used as the ore for extracting tin, is extremely difficult to find and not particularly noteworthy, i.e., it does not stand out in the field. It is hard and, like gold, has a high specific gravity. Having a high specific gravity means that flakes or nuggets of cassiterite, like gold, would settle to the bottom of a slurry if panning for gold. So, while it is difficult to find sources of cassiterite it might have been possible to backtrack upstream by finding cassiterite flakes downstream of sources. While it might be counterintuitive to think that the Egyptians added an even softer metal, tin, to copper to make it harder, it is possible that the Egyptians thought that whatever made cassiterite hard would be transferred to the copper. The smelting of tin is very similar to the smelting of copper. Charcoal is also used as the reducing agent. Tin, unlike copper, is too soft for practical purposes. However, when 10% tin, it can produce a much harder metal than unalloyed copper or tin. Please proceed to the next section to learn more about this new harder metal, bronze. Egyptian Bronze Processing Figure 6. 7 Swords of the Bronze Age. (Credit: Dbachmann, Wikimedia Commons) Bronze is an alloy of copper and tin. Tin is a slightly bigger atom than copper. In bronze, typically 5 10% is tin and the rest is copper. The slightly larger tin atoms replace copper atoms in the copper crystalline structure as shown in Figure 6.8. Although copper and tin are both soft metals and not ideal for tools or weapons, the combination that produces bronze is much harder than copper or tin. As we will learn later, this is due to the larger tin atoms making it harder for rows of copper atoms to move. This results in bronze being harder. Figure 6. 8 Tin atoms forcing copper atoms together and restricting their movement. (Credit:"Earth, Air, Fire, and Water: Elements of Materials Science," 2nd Edition, by P.R. Howell.) MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 44  UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE In the practice of producing bronze, the Egyptians placed tin with copper ingots into clay crucibles. The clay crucibles were lowered into a charcoal fire which could exceed 1100 °C by using blowing air using foot bellows. The Egyptians would then stir, remove the slag, and pour the melt into a mold. Why Did it Take So Long Between the Bronze Age and the Iron Age? The beginning of the Bronze Age occurred around 3500 BCE and the beginning of the Iron Age began around 1000 BCE. Why did it take 2000 years for bronze to be replaced by iron? Looking around us we see structural steel and concrete seemingly everywhere in our modern cities. However, the processing of iron is not a trivial process. Due to limitations in furnace designs, i.e., the maximum obtainable temperatures, the availability and quality of iron varied greatly. Throughout history there have been legendary quality swords, i.e., Damascus and Samurai to name just a couple. These swords were produced using time-intensive and, many times, ritualistic processes. These blades were produced in areas known in the modern day as Iran, Japan, and China. Most of the iron used in weapons during the Iron Age, i.e., Roman swords, was a low- density iron sponge-like material. This sponge-like iron was then pounded to shape, densify, and remove impurities. Bronze was superior to the iron produced commonly, so why did iron ultimately replace bronze? Bronze weapons were indeed of higher quality than the common iron weapons typically produced. However, tin, which is required to produce bronze, is not abundantly available. Consequently, bronze weapons were the weapons utilized by nobles, royalty, pharaohs, etc. The common foot soldier was not going to possess bronze weapons; there were not enough to go around. Unlike tin, iron ore is readily available. So, although inferior to bronze, an army of hundreds or thousands could be equipped with iron weapons, which was not practical with bronze weapons. So, the ability to produce large numbers of iron weapons overcame the advantages of bronze. Eventually, time and further development allowed to produce these so-called legendary swords which supplanted bronze Industrial Revolution, that advancements in furnace design and process control enabled the reliable and massive production of the iron alloy known as steel. IV. Structure and Application of Metals When you mention crystal to most people, they think of fine glassware. Metal is not the first thing that comes to mind. But, in fact, most metals are crystalline, and it is rather difficult to make non- crystalline metals. Crystalline materials have their atoms arranged in a periodic, ordered 3D array. Typically, all the metals, many ceramics, and some polymers are crystalline. Non-crystalline materials have atoms with no periodic arrangement, i.e., a random order. Non-crystalline material can result when you have complex structures, or you rapidly cool from the liquid state to the solid state. Amorphous material is another name for non-crystalline material. Why do metals form crystals? It turns out that the lowest energy for metal atoms occurs when the box, you know that if you put the pieces in the box in an ordered fashion you can fit much more in the MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 45 UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE box than if you just throw things into the box in a disorderly fashion. So, for metals, ordered structures tend to be nearer the minimum energy and are more stable. In addition, since metallic bonds are nondirectional it is much simpler for metal atoms to densely pack than it is for ceramics and polymers. So how do metal atoms pack together? In the next section, we will look at one of the ways that metal atoms pack together. All metals, a major fraction of ceramics, and certain polymers acquire crystalline form when solidify, i.e. in solid state atoms self-organize to form crystals. Crystals possess a long-range order of atomic arrangement through repeated periodicity at regular intervals in three dimensions of space. When the solid is not crystalline, it is called amorphous. Examples of crystalline solids are metals, diamond and other precious stones, ice, graphite. Examples of amorphous solids are glass, amorphous carbon (a-C), amorphous Si, most plastics. Crystal Structures There is very large number of different crystal structures all having long-range atomic order; these vary from relatively simple structures for metals to exceedingly complex structures for ceramics and some polymers. To discuss crystalline structures, it is useful to consider atoms as being hard spheres, with well- defined radii. In this scheme, the shortest distance between two like atoms is one diameter. In this context, use of terms lattice and unit cell will be handy. Lattice is used to represent a three-dimensional periodic array of points coinciding with atom positions. Unit cell is smallest repeatable entity that can be used to completely represent a crystal structure. Thus, it can be considered that a unit cell is the building block of the crystal structure and defines the crystal structure by virtue of its geometry and the atom positions within. Figure 6. 9 A unit cell is the smallest repeating portion of a crystal lattice Important properties of the unit cells are: The type of atoms and their radii R. Cell dimensions (Lattice spacing a, b and c) in terms of R a*, b*, c* - - angle in reciprocal lattice n, number of atoms per unit cell. For an atom that is shared with m adjacent unit cells, we only count a fraction of the atom, 1/m. MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 46 UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE CN, the coordination number, which is the number of closest neighbors to which an atom is bonded. APF, the atomic packing factor, which is the fraction of the volume of the cell actually occupied by the hard spheres. APF = Sum of atomic volumes/Volume of cell. Simple Cubic Crystal Structure Start by taking four atoms and arranging them in a square. Then take four more atoms and arrange them in a square. Then put the first square on the second square to form a cube with eight atoms, one at each corner. This structure is the simple cubic crystal structure. It turns out that only the metal Polonium (Po) has this crystal structure. The reason this crystal structure is so rare is that packing atoms in this way does not lead to a very high packing density. Figure 6. 10 Simple cubic crystal structure. (Credit: Callister) Body Centered Cubic Structure (BCC) Let's take our simple cubic crystal structure of eight atoms from the last section and insert another atom in the center of the cube. This new structure, shown in Figure 6.11, is referred to as body-centered cubic since it has an atom centered in the body of the cube. Some examples of metals that possess this Figure 6. 11 Body-Centered Cubic Structure (Credit: Callister & Rethwisch 5e) MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 47 UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE Face Centered Cubic Structure (FCC) If, instead of starting with a square, we start with a triangle and continue to add atoms, packing as tightly as we can, we will end up with a layer of atoms as shown in Figure 6.12. Figure 6. 12 First layer of hexagonal structure (Credit: Callister & Rethwisch 5e) Now let us put an atom on top of that first layer over one of the 'B' positions and let it rest down into one of the valleys. We can now place two more atoms in nearby 'B' positions so that each will rest in their own valley in such a way that all three atoms will touch and form a triangle. Now let us add more atoms to the second layer, packing them in as tightly as possible. These two layers are shown in Figure 6.13. If you look closely, you should be able to see that the second layer only covers half of the valleys produced by the first layer. The 'C' valleys are left uncovered. In fact, half of the valleys of the second layer lineup with the unoccupied 'C' valleys of the first layer. Figure 6. 13 First and second layer of hexagonal structure. (Credit: Callister & Rethwisch 5e) put a third layer where the atoms are placed where the unoccupied valleys of the first two layers lineup, the 'C' valleys. It is a little difficult to visualize, but if one of the top layer atoms is one corner of our cube and that corner is pointing out then we obtain the cube shown in Figure 6.14. Figure 6. 14 Complete three-layer hexagonal structure. (Credit: Callister & Rethwisch 5e) MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 48 UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE This crystal structure is known as face-centered cubic and has atoms at each corner of the cube and six atoms at each face of the cube as shown in Figure 6.15. This structure has the atoms packed as tightly as theoretically possible. Metals that possess face-centered cubic structure include copper, aluminum, silver, and gold. Figure 6. 15 Face centered cubic (fcc) structure (Credit: Callister & Rethwisch 5e) Hexagonal Close Packed Crystal Structure (HCP) If you look at Figure 6.15, you might think that hexagon close-packed crystal structure is more complicated than face-centered cubic crystal structure. In fact, it is a simpler structure. Think back FCC where we constructed first one layer of atoms and then a second layer of atoms for face-centered cubic structure. Now, for hexagonal close-packed crystal structure, we do not construct a third layer. Instead, the third layer is simply the first layer repeated, the fourth layer is the second layer repeated, and so on and so on as shown in Figure 6.16. Figure 6. 16 Hexagonal close-packed structure. (Credit: Callister & Rethwisch 5e) It turns out that face-centered cubic and hexagonal close-packed crystal structures pack atoms equally tightly. Some metals with hexagonal close-packed crystal structures include cobalt, cadmium, zinc, hase of titanium. A more typical representation of the hexagonal close-packed structure is shown in Figure 6.17. In this representation a hexagon on the top and on the bottom sandwich a triangle in between the two hexagons. MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 49 UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE Figure 6. 17 Hexagonal close-packed structure unit cell. (Credit: Callister & Rethwisch 5e) Common Crystal Structures and Their Properties Table 6. 1 Common crystal structures and their properties. Unit Cell n CN a/R APF Simple Cubic 1 6 2 0.52 Body Centered Cubic 2 8 0.68 Face-Centered Cubic 4 12 0.74 Hexagonal Close Packed 6 12 0.74 Crystal Systems Most solids are crystalline in nature. A crystal is a substance in which the particles are arranged in an orderly, repeating, three-dimensional pattern. Particles of a solid crystal may be ions, atoms, or molecules, depending on the type of substance. The three-dimensional arrangement of a solid crystal is referred to as the crystal lattice. Different arrangements of the particles within a crystal cause them to adopt several different shapes. Crystals are classified into general categories based on their shapes. A crystal is defined by its faces, which intersect with one another at specific angles, which are characteristic of the given substance. The seven crystal systems are shown below, along with an example of each. The edge lengths of a crystal are represented by the letters a , b , and c. The angles at which the faces intersect are represented by the faces and in the number of edges of equal length on each face. MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 50 UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE Table 6. 2 The Seven Crystal Systems Crystal System Diagram Example Cubic Pyrite Tetragonal Wulfenite Orthorhombic Aragonite Monoclinic Azurite Rhombohedral Calcite Triclinic Microcline Hexagonal 120° Beryl MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 51  UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE V. Crystalline and Non-crystalline materials Single Crystals: Crystals can be single crystals where the whole solid is one crystal. Then it has a regular geometric structure with flat faces. Polycrystalline Materials: A solid can be composed of many crystalline grains, not aligned with each other. It is called polycrystalline. The grains can be aligned with respect to each other. Where they meet is called a grain boundary. Non-Crystalline Solids: In amorphous solids, there is no long-range order. But amorphous does not mean random, since the distance between atoms cannot be smaller than the size of the hard spheres. Also, in many cases there is some form of short-range order. For instance, the tetragonal order of crystalline SiO2 (quartz) is still apparent in amorphous SiO2 (silica glass). VI. Miller Indices It is understood that properties of materials depend on their crystal structure, and many of these properties are directional in nature. For example: elastic modulus of BCC iron is greater parallel to the body diagonal than it is to the cube edge. Thus, it is necessary to characterize the crystal to identify specific directions and planes. Specific methods are employed to define crystal directions and crystal planes. Methodology to define crystallographic directions in cubic crystal: 1. a vector of convenient length is placed parallel to the required direction. 2. the length of the vector projection on each of three axes are measured in unit cell dimensions. 3. these three numbers are made to smallest integer values, known as indices, by multiplying or dividing by a common factor. 4. the three indices are enclosed in square brackets, [uvw]. A family of directions is represented by. Methodology to define crystallographic planes in cubic crystal: 1. determine the intercepts of the plane along the crystallographic axes, in terms of unit cell dimensions. If plane is passing through origin, there is a need to construct a plane parallel to original plane. 2. take the reciprocals of these intercept numbers. 3. clear fractions. 4. reduce to set of smallest integers. 5. The three indices are enclosed in parenthesis, (hkl). A family of planes is represented by {hkl}. Example: If the x-, y-, and z- intercepts of a plane are 2, 1, and 3. The Miller indices are calculated as: 1. take reciprocals: 1/2, 1/1, 1/3. 2. clear fractions (multiply by 6): 3, 6, 2. 3. reduce to lowest terms (already there). Miller indices of the plane are (362). MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 52 UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE Figure 6.18 depicts Miller indices for number of directions and planes in a cubic crystal. Figure 6. 18 Miller indices in a cubic crystal. Some useful conventions of Miller notation: If a plane is parallel to an axis, its intercept is at infinity and its Miller index will be zero. If a plane has negative intercept, the negative number is denoted by a bar above the number. Never alter negative numbers. For example, do not divide -1, -1, -1 by -1 to get 1,1,1. This implies symmetry that the crystal may not have! The crystal directions of a family are not necessarily parallel to each other. Similarly, not all planes of a family are parallel to each other. By changing signs of all indices of a direction, we obtain opposite direction. Similarly, by changing all signs of a plane, a plane at same distance in other side of the origin can be obtained. Multiplying or dividing a Miller index by constant has no effect on the orientation of the plane. The smaller the Miller index, more nearly parallel the plane to that axis, and vice versa. When the integers used in the Miller indices contain more than one digit, the indices must be separated by commas. E.g.: (3,10,13) By changing the signs of all the indices of (a) a direction, we obtain opposite direction, and (b) a plane, we obtain a plane located at the same distance on the other side of the origin. More conventions applicable to cubic crystals only: [uvw] is normal to (hkl) if u = h, v = k, and w = l. E.g.: (111). Inter-planar distance between family of planes {hkl} is given by: [uvw] is parallel to (hkl) if hu + kv + lw = 0. Two planes (h1k1l1) and (h2k2l2) are normal if h1h2 + k1k2 + l1l2=0. Two directions (u1v1w1) and (u2v2w2) are normal if u1u2 + v1v2 + w1w2=0 MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 53  UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE Angle between two planes is given by: The same equation applies for two directions. Why Miller indices are calculated in that way? Using reciprocals spares us the complication of infinite intercepts. Formulas involving Miller indices are very similar to related formulas from analytical geometry. Specifying dimensions in unit cell terms means that the same label can be applied to any plane with a similar stacking pattern, regardless of the crystal class of the crystal. Plane (111) always steps the same way regardless of crystal system. Miller-Bravis indices Though Miller indices can describe all possible planes through any crystal, Miller-Bravis indices are used in hexagonal crystal systems. This is because they reveal hexagonal symmetry more clearly. Although partially redundant, they are used exclusively for hexagonal systems. Direction indices are obtained as above where first three indices are representative of projections of the direction over three co-planar axes in the plane called basal plane while the last index denotes the projection over the axis perpendicular to the basal plane. Miller-Bravis indices for a plane are denoted as [uvtw], where t = -(u+v) In the same procedure, planes in a hexagonal crystal are denoted by (hkil), where i = (h+k). VII. Anisotropy been agreed that many of the materials properties depend on the crystal structure. However, crystals are not symmetric in all directions, or not the crystal planes same with respect to atomic density/packing. Different directions in the crystal have different packing. For instance, atoms along the edge of FCC crystals are more separated than along its face diagonal. This causes properties to be different in different directions. This directionality of properties is termed as Anisotropy. Substances in which measured properties are independent of direction in which they are measured are called isotropic. Though, in polycrystalline materials, the crystallographic orientations of individual grains are random, specimen may behave isotropically. MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 54  UNIVERSITY OF NUEVA CACERES COLLEGE OF ENGINEERING AND ARCHITECTURE VIII. Reading Assignment Read: Chapter 3 of Materials Science and Engineering 9th Ed., by William D. Callister Jr. and David G. Rethwisch. Answer the following guide questions. Submit your answers in pdf form. Late submission will not be accepted. 1. What contributions did the Egyptians make in the development of materials processing? 2. What is the difference between melting and smelting? 3. How do single crystal and polycrystalline material differ in grain structure? 4. How do crystal and polycrystalline materials differ in their atomic/molecular structure? 5. What is the difference between an amorphous and crystalline material? 6. What is the difference between crystal structure and a crystal system? 7. How does the crystal system affect the characteristics of a metal? 8. Give 5 metals for each type of crystal system. 9. Give 5 characteristics of a metal in BCC, FCC, HCP, and SCC. 10. What is the difference between atomic structure and crystal structure? IX. Summary This lesson was concerned primarily the structure of materials was discussed beginning with how metal atoms arrange to form solids. Within this framework, concepts of single crystal (highly ordered), polycrystalline (many unaligned regions of crystalline material), and non-crystalline (little to no order, also known as amorphous) materials were introduced. For crystalline solids, the notion of crystal structure was presented, and specified in terms of a unit cell. X. Citations and Attributions -education.psu.edu/matse81/) by Dr. Ronald Redwing, licensed by Penn State's College of Earth and Mineral Sciences (http:// e- education.psu.edu/oer/), Creative Commons license (cc By-NC-SA 4.0), https://creativecommons.org/licenses/by-nc-sa/4.0/, accessed July 2020 Materials Science (https://nptel.ac.in/courses/112/108/112108150/) by Prof. Satish V. Kailas, licensed by The National Programme on Technology Enhanced Learning (NPTEL) (https://nptel.ac.in/index.html), Creative Commons license (cc By-NC-SA 4.0), https://creativecommons.org/licenses/by-nc-sa/4.0/, accessed July 2020 MATERIALS SCIENCE AND ENGINEERING V.1.0 BY: DE VERA 55