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Research in Globalization
From our earlier studies, we know that different possible arrangements of particles resulting in ... more From our earlier studies, we know that different possible arrangements of particles resulting in several types of structures. The correlation between the nature of interactions within the constituent particles and several properties of solids were also being explored. We were overall talking about crystal structure of solids as orderly arranged and considering it as a perfect form. By bringing all the atoms together to try to form a perfect crystal, we lower the total potential energy of the atoms as much as possible for that particular structure. But nothing is perfect in this world. Everybody has some imperfection and so are the crystals. One solid has large number of crystals and defects in crystals happen during crystallization process. If the crystallization is very fast it will become amorphous itself and if it is very slow it will be almost perfect crystal which is very rare. So for very good quality of crystals, the crystallization should occur with very, very slow speed. Even if you do with a very slow speed some defects will be occurs. This defect takes place with irregularity in arrangement. Slightly deviation from ideal arrangement will be observed.
In chapter three we have discussed that there are three states of matter; solids, liquids and gas... more In chapter three we have discussed that there are three states of matter; solids, liquids and gases. In the same chapter under section 3.3, we tried to mention water as an example exists in three state forms; ice (solid), water (liquid) and vapor (gas). If you see in this case the same matter is in three forms and the difference is only temperature. Based on the pressure and temperature, a matter exists in various phases. Liquids and gases are called fluids because of their ability to flow. The fluidity in both of these states is due to the fact that the molecules are free to move around.
Thermodynamics involves work and heat. It is a branch of physics that deals with heat and tempera... more Thermodynamics involves work and heat. It is a branch of physics that deals with heat and temperature. It began in the 19th century with the efforts of engineers to increase the efficiency of steam engines, but it has become the general theory of the macroscopic behavior of matter at equilibrium. In another language it is a macroscopic science. What is macroscopic? "Macro" means something which is big. So macroscopic is basically deals with bulk systems. Therefore, thermodynamics never talk about very small properties of molecules or atoms. It talks only about systems as a whole. It will not talk about the behavior or properties of each molecule or atoms which constitute an object. So, macroscopic restriction is basically specified by macroscopic variables or quantities which can be directly sense or measured such as volume and temperature.
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By Gizachew Berhanu of which qualify as engineering materials. Therefore, the word 'materials' he... more By Gizachew Berhanu of which qualify as engineering materials. Therefore, the word 'materials' here does not refer to all matter in the Universe. If this were so, it would include all the physical sciences and the life sciences-from astronomy to zoology! By including the word 'inanimate' in the definition, we can exclude the life sciences from our purview. We then have to be more specific and define materials as that part of inanimate matter which is useful to the engineer in the practice of his profession. In the currently understood sense of the term, materials refer only to solid materials, even though it is possible to quote a number of examples of liquid and gaseous materials such as sulphuric-acid and steam, which are useful to the engineer. 1.3 Historical Development of materials. All of us live in a world of dynamic change, and materials are no exception. The advancement of civilization has historically depended on the improvement of materials to work with. Transportation, housing, clothing, communication, recreation, and food production virtually every segment of our everyday lives is influenced to one degree or another by materials [1]. The development and advancement of societies have been intimately tied to the members' ability to produce and manipulate materials to fill their needs. Prehistoric humans were restricted to naturally accessible materials such as stone, wood, bones, skin and fur [1]. Over time, they discovered techniques for producing materials that had properties superior to those of the natural ones; these new materials included pottery and various metals. Furthermore, it was discovered that the properties of a material could be altered by heat treatments (annealing) and by the addition of other (carbon to steel) substances. Early civilizations have been designated by the level of their materials development moved from the materials Stone Age into Bronze Age then Iron Age to present information age. Note that this advance did not take place uniformly everywhere. In our country Ethiopia, agriculture comprises a large part of our present economy. The production and processing of materials into finished goods constitutes a large part of present economy in developed countries. Engineers design most manufactured products and the processing systems required for their production. Since products require materials, engineers should be knowledgeable about the internal structure and properties of materials so that they can choose the most suitable ones for each application and develop the best processing methods. Research and development engineers create new materials or modify the properties of existing ones. Design engineers use existing, modified, or new materials to design and create new products and systems. Sometimes design engineers have a problem in their design that requires a new material to be created by research scientists and engineers. For example, engineers designing a high-speed civil transport will have to develop new high-temperature materials that will withstand temperatures as high as 1800℃[3]. Research is currently underway to develop new ceramic-matrix composites, refractory intermetallic compounds, and single-crystal superalloys for this and other similar applications [2]. 4 By Gizachew Berhanu We must remember that materials usage and engineering designs are constantly changing. This change continues to accelerate. No one can predict the long-term future advances in material design and usage. Many years ago, many people would not have believed that someday computers would become a common household item similar to a telephone, television or a refrigerator. And today, we still find it hard to believe that someday space travel will be commercialized and we may even colonize Mars. Nevertheless, science and engineering push and transform our most unachievable dreams to reality. The search for new materials goes on continuously. More recently, the field of nonomaterials has attracted a great deal of attention from scientists and engineers all over the world. Novel structural, chemical, and mechanical properties of nonomaterial have opened new and exciting possibilities in the application of these materials to a variety of engineering and medical problems [3]. In many cases what was impossible yesterday is a reality today! 1.4 What is Materials Science and Engineering? The word 'science' in the phrase refers to the physical sciences, in particular to chemistry and physics. As we confine ourselves mainly to solids in materials science, the subject is related to solid state chemistry and solid state physics. Materials science is primarily concerned with the search for basic knowledge about the internal structure, properties, and processing of materials. The word 'engineering' indicates that the engineering usefulness of the matter under study is always kept in mind, irrespective of whether the basic laws of science can be applied rigorously or not. Materials engineering is mainly concerned with the use of fundamental and applied knowledge of materials so that the materials can be converted into products needed or desired by society. The term materials science and engineering combines both materials science and materials engineering and is the subject matter of this text. In general, Materials science and Engineering is an interdisciplinary field of science and engineering that studies and manipulates the composition and structure of materials across length scales to control materials properties through synthesis and processing [2]. The term composition means the chemical make-up of a material. The term structure means a description of the arrangement of atoms, as seen in chapter 4 in detail. The term property refers to a material trait in terms of the kind and magnitude of response to a specific imposed stimulus. Definitions of properties are made independent of material shape and size unless the size of the material is extremely small. Important properties of solid materials may be grouped into six different categories: 1) Mechanical properties:-refers to deformation to an applied load or force; examples include elastic modulus (stiffness), strength, and toughness. 2) Electrical properties:-For electrical properties, such as electrical conductivity and dielectric constant, the stimulus is an electric field. 3) Thermal properties:-The thermal behavior of solids can be represented in terms of heat capacity and thermal conductivity. 4) Magnetic properties:-demonstrate the response of a material to the application of a magnetic field. By Gizachew Berhanu 2. Ceramics: Ceramics can be defined as inorganic crystalline materials. These types of materials are generally compounds between metallic and nonmetallic elements and include compounds such as oxides, nitrides, and carbides [1]. Typically they are insulating and resistant to high temperatures and harsh environments. Beach sand and rocks are examples of naturally occurring ceramics. Traditional ceramics are used to make bricks, tableware, toilets, bathroom sinks, refractories (heat-resistant material), and abrasives. Advanced ceramics are materials made by refining naturally occurring ceramics and other special processes [5]. Advanced ceramics are used in substrates that house computer chips, sensors, capacitors, wireless communications, inductors, and electrical insulation. Some ceramics are used as barrier coatings to protect metallic substrates in turbine engines. In general, due to the presence of porosity (small holes), ceramics do not conduct heat well; they must be heated to very high temperatures before melting. Ceramics are strong and hard, but also very brittle. Glasses and Glass-Ceramics: A glass is defined by ASTM as "an inorganic product of fusion which has been cooled to rigid condition without crystallization" [6]. Glass is an amorphous material, often, but not always, derived from a molten liquid. The term "amorphous" refers to materials that do not have a regular, periodic arrangement of atoms. Amorphous materials will be discussed in Chapter 4. The fiber optics industry is founded on optical fibers based on high purity silica glass. Glasses are also used in houses, cars, computer and television screens, and hundreds of other applications. Glasses can be thermally treated (tempered) to make them stronger. Forming glasses and nucleating (forming) small crystals within them by a special thermal process creates materials that are known as glass-ceramics [6]. a) If no metals, it is difficult to have such kind of renaissance dam b) If no metal, no SINOTRUCK Fig 1.5 roles of metals and alloys in real world 9 By Gizachew Berhanu Fig 1.6 applications of glasses, glass-ceramic and ceramics materials 3. Polymers: Polymers are typically organic materials based upon carbon and hydrogen. They are very large molecular structures. Usually they are low density and are not stable at high temperatures. They are produced using a process known as polymerization. Polymeric materials include rubber and many types of adhesives. Polymers typically are good electrical and thermal insulators although there are exceptions such as the semiconducting polymers. They are typically not suitable for use at high temperatures [1]. Many polymers have very good resistance to corrosive chemicals. Polymers are used in many applications, including electronic devices. 4. Semiconductors: Semiconductors have electrical properties intermediate between metallic conductors and ceramic insulators. Electrical properties are strongly dependent upon small amounts of impurities. Silicon, germanium, and gallium arsenide-based semiconductors such as those used in computers and electronics are part of a broader class of materials known as electronic materials which have enabled the information age [2]. In some semiconductors, the level of conductivity can be controlled to enable electronic devices such as transistors, diodes, etc., that are used to build integrated...
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