Introduction to materials science and engineering

1. Introduction to materials science and engineering Lesson 1 SAWSAN DIAA SHUBBER

3. What is materials science and engineering? MSE is the field concerned with inventing new materials and improving previously known materials by developing a deeper understanding of the microstructure-composition-synthesis-processing relationships. Composition: the chemical make-up of a material. Structure: description of the arrangement of atoms.

4. Synthesis: how materials are made from naturally occurring or a man-made chemicals. processing : how materials are shaped into useful components to cause changes in the properties of different materials.

5. Classification of materials Copper, Steel,gold}}1-Metals and alloys. 2-Polymers(plastics). 3-Ceramics, glasses, and glass-ceramic. 4-Composite materials. 5- Semiconductors.

6. Metals Most of the elements in the Periodic Table (in the pure state) are metallic in nature. Aluminum, copper, and iron are examples. The metallic bond involves a mobile "gas" of electrons. This gas of negatively charged electrons binds together the positively charged atomic cores. The electron gas is also responsible for the electrical conductivities and optical absorption that are characteristic of metals.

8. Polymers Polymers are high molecular weight solids that are an important part of everyday life. An example is polyethylene (C2H4)n, where n is the "degree of polymerization," a number of around 1,000 (representing the fact that polyethylene is composed of a large number of ethylene molecules bound together by covalent bonding). All polymers are composed of a relatively small number of elements in the Periodic Table (primarily carbon and hydrogen and a few other "nonmetallic" elements such as nitrogen and fluorine)

9. Each covalent bond involves electron sharing between adjacent atoms, with the result that polymers do not have "free" electrons for electrical conduction and are electrical insulators. The use of polymeric insulation for electrical wiring is a practical example of this. The lack of free electrons endows some polymers with optical transparency ("clear plastic" wrap is an excellent example).

11. Ceramics The word ceramic is derived from the Greek word (keramikos, "having to do with pottery"). The term covers inorganic non-metallic materials whose formation is due to the action of heat. Up until the 1950s or so, the most important of these were the traditional clays, made into pottery, bricks, tiles and the like, along with cements and glass. A composite material of ceramic and metal is known as cermet. Historically, ceramic products have been hard, porous and brittle. The study of ceramics consists to a large extent of methods to mitigate these problems, and accentuate the strengths of the materials, as well as to offer up unusual uses for these material

13. Ceramics We can define ceramics by what they are not: They are nonmetallic and inorganic. Ceramics are chemical combinations of at least one metallic element and at least one nonmetallic one. A simple example is aluminum oxide (Al2O3). Such chemical combinations represent, in fact, a fundamental tendency in nature. For example, metals tend to combine chemically with nonmetallic elements in their environments. The rusting of iron is a familiar and costly example. It is also interesting to note that the melting point of aluminum is 660°C, whereas the melting point of aluminum oxide is 2,020°C. The chemical stability associated with the ionic bonds between aluminum and oxygen (involving electron transfer from aluminum to oxygen to produce Al3+ and O2− ions) makes ceramics temperature-resistant and chemically inert.

14. The category of ceramics is often broadened to "ceramics and glasses" because of the wide use of silicate glasses, distinctive materials that are chemically similar to ceramics. Silicon dioxide, SiO2, is a ceramic compound and the basis of a large family of silicate ceramics. Clay minerals and the many clayware ceramics are the most traditional examples. SiO2 is readily obtained in relatively pure form in common sand deposits. (These deposits, and the presence of SiO2 in many geological minerals, are the reason that silicon and oxygen together account for roughly 75 percent of the elements in Earth's crust.)

15. Upon heating, many of these silicate materials can be melted and, after cooling, retain the liquid like structure of the melt. Common window and container glass is made in this way, with a typical composition, by weight, of (roughly): 75 percent SiO2, 15 percent Na2O, and 10 percent CaO. Thus, ceramics and glasses are of one category (combinations of ionically bonded positive and negative ions). Their differences are at the atomic scale. Ceramics are crystalline substances, in which the ions are arranged in a regular and repeating order. Glasses are noncrystalline substances, in which the ions are situated in irregular, liquid like fashion.

17. In defining the previous three materials (metals, polymers, and ceramics/glasses), we found that each category conveniently related to one of the primary types of chemical bonding: metallic, covalent, and ionic, respectively. To be precise, atomic bonding is seldom "pure." There is generally some covalent nature (electron sharing) to the ionic bonding in ceramics and glasses. The bonding between the adjacent atoms in large polymeric molecules is highly covalent, but the bonding between molecules is often "secondary." For example, there are weak attractions between adjacent polyethylene molecules that involve polarization, not electron transfer or sharing. This weak secondary bonding is the primary reason that commercial "plastics" are characteristically weak and deformable in comparison to metals and ceramics/glasses.

18. Among the materials available for modern structural applications, a fourth category is generally included—namely, "composites." Composite materials are defined as microscopic-scale combinations of individual materials belonging to the previous three categories (metals, polymers, ceramics/glasses). A good example is fiberglass, a composite of glass fibers (a few micrometers in diameter) embedded in a polymer matrix. Over the past several decades, fiberglass products have become commonplace. The advantage of composites is that they display the best properties of each component, producing products superior to products made of a single component. In the case of fiber-glass, the high strength of the small diameter glass fibers is combined with the flexibility of the polymer matrix.

19. Although most engineered materials can be put into one of the four categories described above, a sorting of the same materials based on electrical conductivity rather than atomic bonding demands an additional, fifth category. We noted above that metals are typically good electrical conductors and that polymers and ceramics/glasses are typically electrical insulators. Composites tend to have properties that are averages of those of their individual components.

20. As an example, fiberglass is an electrical insulator because both glass fibers and the polymer matrix tend to be insulators. Since the middle of the twentieth century, "semiconductors," with intermediate levels of electrical conductivity, have played an increasingly critical role in modern technology. The primary example is elemental silicon, which, as noted above, is a central component of modern, solid-state electronics.

21. Silicon is in column IVA of the Periodic Table. Its neighbor in column IVA, germanium, is also a semiconductor and also widely used in electronic devices. Chemical compounds of the elements near column IVA often display semiconduction—for example, gallium arsenide (GaAs), which is used as a high temperature rectifier and a laser material. The chemical bonding in the various elemental and compound semiconductors is generally strongly covalent.

28. ADVANCED MATERIALS Materials that are utilized in high-technology (or high-tech) applications are sometimes termed advanced materials. By high technology we mean a device or product that operates or functions using relatively intricate and sophisticated principles; examples include electronic equipment (camcorders, CD/DVD players, etc.), computers, fiber-optic systems, spacecraft, aircraft, and military rocketry. These advanced materials are typically traditional materials whose properties have been enhanced, and, also newly developed, high-performance materials. Furthermore, they may be of all material types (e.g., metals, ceramics, polymers), and are normally expensive.

29. Materials of the Future Smart (or intelligent) materials are a group of new materials now being developed that will have a significant influence on many of our technologies. The adjective “smart” implies that these materials are able to sense changes in their environments and then respond to these changes in predetermined manners—traits that are also found in living organisms. In addition, this “smart” concept is being extended to rather sophisticated systems that consist of both smart and traditional materials. Components of a smart material (or system) include some type of sensor (that detects an input signal), and an actuator .

30. Smart materials

31. Biomaterials Biomaterials are employed in components implanted into the human body for replacement of diseased or damaged body parts. These materials must not produce toxic substances and must be compatible with body tissues (i.e., must not cause adverse biological reactions). All of the above materials—metals, ceramics, polymers, composites, and semiconductors—may be used as biomaterials. For example, are utilized in artificial hip replacement .

32. Nanoengineered Materials the “nano” prefix denotes that the dimensions of these structural entities are on the order of a nanometer (109 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.