1 - Nature of Materials.pdf

E N G G 4 1 2 : 1 M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G Chapter Nature of Materials Intended Learn...

E N G G 4 1 2 : 1 M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G Chapter Nature of Materials Intended Learning Outcomes After studying this chapter, you should be able to do the following: 1. Determine the fundamental concepts in Materials Science and Engineering. 2. Cite the criteria that are important in the material selection process. 3. Cite the four components that are involved in the design, production and utilization of materials and briefly describe the interrelationships between these components. 4. Enumerate the classification of materials and note the differences between them. 5. Briefly describe ionic, covalent, metallic and van der Waals bonds. This chapter primarily presents the fundamental concepts in Materials Science and Engineering. The discussion involves the material selection process, the types of engineering materials and chemical bonds specifically citing the differences between them. In this chapter you will learn about the material structure, how structure dictates properties and how processing can change structure. This will help you to use materials properly and realize new design opportunities with materials. FUNDAMENTAL CONCEPTS What is materials science? It involves investigating the relationships that exist between the structures and properties of materials. What about materials engineering? On the basis of these structure–property correlations, designing or engineering the structure of a material to produce a predetermined set of properties. Materials Development Materials are probably more deep-seated in our culture than most of us realize. Transportation, housing, clothing, communication, recreation, and food production—virtually every segment of our everyday lives is influenced to one degree or another by materials. Historically, the development and advancement of societies have been intimately tied to the members’ ability to produce and manipulate materials to fill their needs. In fact, early civilizations Module No. 1 – Nature of Materials 1 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G have been designated by the level of their materials development (Stone Age, Bronze Age, Iron Age). 1. Stone Age (beginning life – 3000 BC) - using naturally occuring materials with only changes in shape 2. Bronze Age (3000 BC – 1200 BC) – Copper and Tin Alloy - Ability to modify materials by refining (using heat), chemical modifications (alloying) and mechanical deformation (cold working) 3. Iron Age (1200 BC – Present) - Casting and alloying weren’t perfected until 16th century Mastery of Steel (Iron alloy) technology enables Industrial Revolution in the 18th and 19th century Ability to heat treat at high temperature, control microstructure at different length scale and ability to design specific microstructures for specific properties 4. Plastic Age (1940 – Present) - Discovery of polymers, and the ability to synthesize and process polymers. 5. Silicon Age (1950 - Present) - Commercialization of silicon technology (integrated circuits, electronic devices, etc…) leads to the information age, which gives boost to human productivity - Ability to control alloying accurately, ability to make thin films. 6. Future Nanotechnology - Synthesis and characterizations of nanomaterials and nanostructure Biotechnology - biomimetics and biomaterials Energy/Environmental - Next generation energy conversion Information Technology - Materials informatics Four Components of Materials Science When utilizing a material, one needs to understand that the structure, properties, processing, and performance of the material are interrelated. This is represented by the materials science tetrahedron shown in the figure below. If one alters the processing, there is a direct connection with the structure, properties, and performance of the material. Adjusting any one of the factors will have varying degrees of impact on the other three factors. Characterization is the heart of the tetrahedron, signifying its role in monitoring the four components. Module No. 1 – Nature of Materials 2 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G Material Science Tetrahedron Module No. 1 – Nature of Materials 3 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G 1.1 TYPES OF ENGINEERING MATERIALS Engineering materials refers to the group of materials that are used in the construction of manmade structures and components. The primary function of an engineering material is to withstand applied loading without breaking and without exhibiting excessive deflection. For example, the computer or the pen we use, are manufactured through controlled engineering processes. These gadgets make use of materials like HDPE, PP, Pb-Silica glass, copper, aluminum, tin, etc. in their fabrication. Civil construction works like bridges, dams, houses, roads, pavements are carried out with raw materials like stone, chips, cement, clay, paint, bars, etc. Everything we use in our daily life can be tailored to use for specific cases. This can be done efficiently if we know the property of each material beforehand. Hence, materials have been extensively tested for their properties and classified into broad groups. From this grouping one can know about the gross property of any group of material. The major classifications of engineering materials include metals, polymers, ceramics, and composites. Materials are classified as: 1. Metallic-those material that exhibit electrical and thermal conductivity Play a most significant role in the industrial operations with which the engineer is concerned 2. Non-metallic-include wood, stone, brick, cement, resins (plastics), rubber, leather, ceramics and so forth Module No. 1 – Nature of Materials 4 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G Metals- normally combinations of metallic element Quite strong, yet deformable which account for their extensive use in structural applications forms cations and ionic bonds with non-metals have a crystalline structure in which the atoms are arranged in orderly manner relatively strong and ductile at room temperature and maintain good strength even at high temperature Ferrous-include steel, cast iron, wrought iron, malleable cast iron and iron-base metal Non-ferrous include all other metals and their combination such as copper, tin, zinc, aluminum, magnesium and titanium Ceramics - compounds between the non-metallic and non-metallic elements chemically bounded together Most frequently oxides, nitrides, and carbides Composed of clay minerals, cement, and glass Can be crystalline and non-crystalline but some consists of mixture of both Advantages in engineering application include light weight, high strength and hardness, good heat and wear resistance, reduces friction and insulative properties Typically, insulative to the passage of electricity and heat and are more resistant to high temperature and harsh environment than polymers and metal Hard bu not brittle Use ceramic tile for the space shuttle comes from the Greek word "κεραμικός" (keramikos), "of pottery" or "for pottery", from "κέραμος" (keramos), "potter's clay, tile, pottery"which is said to derive from the Indo-European word *cheros (unattested), meaning heat. Figure 1. Example of Ceramics Module No. 1 – Nature of Materials 5 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G Polymers - include familiar plastics and rubber materials Chemically based on carbon, hydrogen and another non-metallic element Low density and may be extremely flexible The word polymer is derived from the Greek words πολύ- - poly- meaning "many"; and μέρος - meros meaning "part". Polymeric material is non-crystalline but some consists of mixture of crystalline and non-crystalline The strength and ductility of materials vary greatly Some of materials are good insulator and are used for electrical insulation application A variety of other natural polymers exist, such as cellulose, which is the main constituent of wood and paper. The list of synthetic polymers includes synthetic rubber, Bakelite, neoprene, nylon, PVC, polystyrene, polyethylene, polypropylene, polyacrylonitrile, PVB, silicone, and many more. Synthetic polymer materials such as nylon, polyethylene, Teflon, and silicone have formed the basis for a burgeoning polymer industry Composite materials Mixture of two or more materials Consists of selective filler or reinforcing material and a compatible resin binder to obtain specific and properties desired Fiberglass is a familiar example (properly known as fiber-reinforced polymer (FRP) or glass-reinforced plastic) (acquire strength from the glass and flexibility from the polymer Designed to display a combination of the best characteristics of each of the component materials Plywood is a commonly encountered composite material Semiconductor materials Solid or liquid material which is able to conduct electricity at room temperature more readily than an insulator but less easily than a metal Have electrical properties that are intermediate between the electrical conductors and insulator At low temperatures, pure semiconductors behave like insulator The common semi-conductors include chemical elements and compounds such as silicon, germanium, selenium, gallium, arsenide, zinc selenide and lead telluride This means conductivity roughly in the range of 103 to 10−8siemens per centimeter. Are the foundation of modern electronics, including radio, computers, telephones, and many other devices Such devices include transistors, solar cells, many kinds of diodes including the light-emitting diode, the silicon-controlled rectifier, and digital and analog integrated circuits. Silicon is used to create most semiconductors commercially. Dozens of other materials are used, including germanium, gallium arsenide, and silicon carbide. Module No. 1 – Nature of Materials 6 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G Biomaterial Employed in components into the human body for replacement of diseased or damage body parts These materials that does not produce toxic substances and must be compatible with body tissues All the above materials can be used as biomaterials can generally be produced either in nature or synthesized in the laboratory using a variety of chemical approaches utilizing metallic components or ceramics Biomaterials are used in: Joint replacements Bone plates Bone cement Artificial ligaments and tendons Dental implants for tooth fixation Blood vessel prostheses Heart valves Skin repair devices (artificial tissue) Cochlear replacements Contact lenses Breast implants Nanoengineered Materials materials of which a single unit is sized (in at least one dimension) between 1 and 1000 nanometers (10−9 meter) but is usually 1—100 nm. Materials with structure at the nanoscale often have unique optical, electronic, or mechanical properties. to develop mechanical, electrical, magnetic, and other properties that are not otherwise possible. We call this the “bottom-up” approach, and the study of the properties of these materials is termed “nanotechnology”; the “nano” prefix denotes that the dimensions of these structural entities are on the order of a nanometer (10 - 9 m)—as a rule, less than 100 nanometers (equivalent to approximately 500 atom diameters) One example of a material of this type is the carbon nanotube. In the future we will undoubtedly find that increasingly more of our technological advances will utilize these nanoengineered materials. 1.2 ENGINEERING MATERIALS COMPOSITION Atomic Structure Each atom consists of a very small nucleus composed of protons and neutrons, which is encircled by moving electrons. Both electrons and protons are electrically charged, the charge magnitude being1.60 x10 -19 C, which is negative in sign for electrons and positive for protons; neutrons are electrically neutral. Masses for these subatomic particles are infinitesimally small; protons and neutrons have approximately the same mass, 1.67 x 10 -27 kg, which is significantly larger than that of an electron, 9.11 x10 -31 kg. Module No. 1 – Nature of Materials 7 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G Each chemical element is characterized by the number of protons in the nucleus, or the atomic number (Z).1 For an electrically neutral or complete atom, the atomic number also equals the number of electrons. This atomic number ranges in integral units from 1 for hydrogen to 92 for uranium, the highest of the naturally occurring elements. The atomic mass (A) of a specific atom may be expressed as the sum of the masses of protons and neutrons within the nucleus. Although the number of protons is the same for all atoms of a given element, the number of neutrons (N) may be variable. Thus, atoms of some elements have two or more different atomic masses, which are called isotopes. The atomic weight of an element corresponds to the weighted average of the atomic masses of the atom’s naturally occurring isotopes. The atomic mass unit (amu) may be used for computations of atomic weight. A scale has been established whereby 1 amu is defined as 1/12 of the atomic mass of the most common isotope of carbon, carbon 12 (12C) (A = 12.00000). Within this scheme, the masses of protons and neutrons are slightly greater than unity. The atomic weight of an element or the molecular weight of a compound may be specified on the basis of amu per atom (molecule) or mass per mole of material. In one mole of a substance there are 6.023 x 10 23 atoms or molecules. These two atomic weight schemes are related through the following equation: 1 amu/atom (or molecule) = 1 g/mol For example, the atomic weight of iron is 55.85 amu/atom, or 55.85 g/mol. Sometimes use of amu per atom or molecule is convenient; on other occasions g (or kg)/mol is preferred. 1.3 CHEMICAL BONDING Primary Interatomic Bonds 1. Ionic Bonding Ionic bonding is perhaps the easiest to describe and visualize. It is always found in compounds that are composed of both metallic and nonmetallic elements, elements that are situated at the horizontal extremities of the periodic table. Atoms of a metallic element easily give up their valence electrons to the nonmetallic atoms. In the process all the atoms acquire stable or inert gas configurations and, in addition, an electrical charge; that is, they become ions. Sodium chloride (NaCl) is the classic ionic material. A sodium atom can assume the electron structure of neon (and a net single positive charge) by a transfer of its one valence 3s electron to a chlorine atom. After such a transfer, the chlorine ion has a net negative charge and an electron configuration identical to that of argon. In sodium chloride, all the sodium and chlorine exist as ions. This type of bonding is illustrated schematically in Figure 2. Module No. 1 – Nature of Materials 8 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G Figure 2 Schematic representation of ionic bonding in sodium chloride (NaCl). Ionic bonding is termed nondirectional; that is, the magnitude of the bond is equal in all directions around an ion. It follows that for ionic materials to be stable, all positive ions must have as nearest neighbors negatively charged ions in a three-dimensional scheme, and vice versa. The predominant bonding in ceramic materials is ionic. 2. Covalent Bonding In covalent bonding, stable electron configurations are assumed by the sharing of electrons between adjacent atoms. Two atoms that are covalently bonded will each contribute at least one electron to the bond, and the shared electrons may be considered to belong to both atoms. Covalent bonding is schematically illustrated in Figure 3 for a molecule of methane. The carbon atom has four valence electrons, whereas each of the four hydrogen atoms has a single valence electron. Each hydrogen atom can acquire a helium electron configuration (two 1s valence electrons) when the carbon atom shares with it one electron. The carbon now has four additional shared electrons, one from each hydrogen, for a total of eight valence electrons, and the electron structure of neon. The covalent bond is directional; that is, it is between specific atoms and may exist only in the direction between one atom and another that participates in the electron sharing. Figure 3 Schematic representation of covalent bonding in a molecule of methane (CH4) Module No. 1 – Nature of Materials 9 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G Many nonmetallic elemental molecules as well as molecules (H 2, Cl2, F2, etc.) containing dissimilar atoms, such as CH4, H2O, HNO3, and HF, are covalently bonded. Furthermore, this type of bonding is found in elemental solids such as diamond (carbon), silicon, and germanium and other solid compounds composed of elements that are located on the right-hand side of the periodic table, such as gallium arsenide (GaAs), indium antimonide (InSb), and silicon carbide (SiC). 3. Metallic Bonding Metallic bonding, the final primary bonding type, is found in metals and their alloys. A relatively simple model has been proposed that very nearly approximates the bonding scheme. Metallic materials have one, two, or at most, three valence electrons. With this model, these valence electrons are not bound to any particular atom in the solid and are more or less free to drift throughout the entire metal. They may be thought of as belonging to the metal as a whole, or forming a “sea of electrons” or an “electron cloud.” The remaining nonvalenced electrons and atomic nuclei form what are called ion cores, which possess a net positive charge equal in magnitude to the total valence electron charge per atom. Figure 4 is a schematic illustration of metallic bonding. The free electrons shield the positively charged ion cores from mutually repulsive electrostatic forces, which they would otherwise exert upon one another; consequently, the metallic bond is nondirectional in character. In addition, these free electrons act as a “glue” to hold the ion cores together. Bonding energies and melting temperatures for several metals are listed in Table 1. Bonding may be weak or strong; energies range from 68 kJ/mol (0.7 eV/atom) for mercury to 850 kJ/mol (8.8 eV/atom) for tungsten. Their respective melting temperatures are -39 and 3410 0C( -38 and 6170 oF) Metallic bonding is found in the periodic table for Group IA and IIA elements and, in fact, for all elemental metals. Some general behaviors of the various material types (i.e., metals, ceramics, polymers) may be explained by bonding type. For example, metals are good conductors of both electricity and heat, as a consequence of their free electrons. By way of contrast, ionically and covalently bonded materials are typically electrical and thermal insulators, due to the absence of large numbers of free electrons. Figure 4 Schematic illustration of metallic bonding. Module No. 1 – Nature of Materials 10 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G SECONDARY BONDING OR VAN DER WAALS BONDING Secondary, van der Waals, or physical bonds are weak in comparison to the primary or chemical ones; bonding energies are typically on the order of only 10 kJ/mol (0.1 eV/atom). Secondary bonding exists between virtually all atoms or molecules, but its presence may be obscured if any of the three primary bonding types is present. Secondary bonding is evidenced for the inert gases, which have stable electron structures, and, in addition, between molecules in molecular structures that are covalently bonded. Secondary bonding forces arise from atomic or molecular dipoles. In essence, an electric dipole exists whenever there is some separation of positive and negative portions of an atom or molecule. The bonding results from the coulombic attraction between the positive end of one dipole and the negative region of an adjacent one. Dipole interactions occur between induced dipoles, between induced dipoles and polar molecules (which have permanent dipoles), and between polar molecules. Hydrogen bonding, a special type of secondary bonding, is found to exist between some molecules that have hydrogen as one of the constituents. These bonding mechanisms are now discussed briefly. Module No. 1 – Nature of Materials 11 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G Fluctuating Induced Dipole Bonds A dipole may be created or induced in an atom or molecule that is normally electrically symmetric; that is, the overall spatial distribution of the electrons is symmetric with respect to the positively charged nucleus. All atoms are experiencing constant vibrational motion that can cause instantaneous and short-lived distortions of this electrical symmetry for some of the atoms or molecules, and the creation of small electric dipoles, One of these dipoles can in turn produce a displacement of the electron distribution of an adjacent molecule or atom, which induces the second one also to become a dipole that is then weakly attracted or bonded to the first; this is one type of van der Waals bonding. These attractive forces may exist between large numbers of atoms or molecules, which forces are temporary and fluctuate with time. The liquefaction and, in some cases, the solidification of the inert gases and other electrically neutral and symmetric molecules such as H2 and Cl2 are realized because of this type of bonding. Melting and boiling temperatures are extremely low in materials for which induced dipole bonding predominates; of all possible intermolecular bonds, these are the weakest. Bonding energies and melting temperatures for argon and chlorine are also tabulated in Table 1. Table 1 Bonding Energies and Melting Temperatures for Various Substances Source: Callister (2007) Module No. 1 – Nature of Materials 12 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G Polar Molecule-Induced Dipole Bonds Permanent dipole moments exist in some molecules by virtue of an asymmetrical arrangement of positively and negatively charged regions; such molecules are termed polar molecules. Polar molecules can also induce dipoles in adjacent nonpolar molecules, and a bond will form as a result of attractive forces between the two molecules. Furthermore, the magnitude of this bond will be greater than for fluctuating induced dipoles Permanent Dipole Bonds Van der Waals forces will also exist between adjacent polar molecules. The associated bonding energies are significantly greater than for bonds involving induced dipoles. The strongest secondary bonding type, the hydrogen bond, is a special case of polar molecule bonding. It occurs between molecules in which hydrogen is covalently bonded to fluorine (as in HF), oxygen (as in H2O) and nitrogen (as in NH3). For each H—F, H—O, or H—N bond, the single hydrogen electron is shared with the other atom. Thus, the hydrogen end of the bond is essentially a positively charged bare proton that is unscreened by any electrons. This highly positively charged end of the molecule is capable of a strong attractive force with the negative end of an adjacent molecule. In essence, this single proton forms a bridge between two negatively charged atoms. The magnitude of the hydrogen bond is generally greater than that of the other types of secondary bonds and may be as high as 51 kJ/mol (0.52 eV/molecule), as shown in Table 1. Melting and boiling temperatures for hydrogen fluoride and water are abnormally high in light of their low molecular weights, as a consequence of hydrogen bonding. Module No. 1 – Nature of Materials 13 E N G G 4 1 2 : M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G REFERENCES Materials Science and Engineering: An Introduction, 10th Edition by William D. Callister Jr and David G. Rethwisch http://www.philadelphia.edu.jo/academics/haldabbas/uploads/ch01.pdf https://www.e-education.psu.edu/matse81/node/2094 https://mechanicalc.com/reference/engineering-materials https://www.the-warren.org/ALevelRevision/engineering/Materialclasses.html https://sengerandu.wordpress.com/tutorials/physical-metallurgy/engineering-materials/ https://weldguru.com/ferrous-metals/ https://unitedaluminum.com/chemical-composition-and-properties-of-aluminum-alloys/ https://www.unifiedalloys.com/resources/nickel-chemical-composition-chart/ https://www.copper.org/publications/pub_list/pdf/a1360.pdf https://www.daido.co.jp/en/products/titanium/chemical.html https://www.britannica.com/science/plastic https://www.sciencedirect.com/topics/materials-science/thermoplastics https://design-technology.org/lesson4b.htm https://www.thomasnet.com/articles/plastics-rubber/thermoset-vs-thermoplastics/ https://www.britannica.com/science/elastomer/Intermolecular-association- thermoplasticelastomers https://www.britannica.com/topic/ceramic-composition-and-properties-103137 Module No. 1 – Nature of Materials 14