Non-metals Technology Lecture Notes PDF

NON-METALS TECHNOLOGY LECTURE 4 Major Classes of Materials Today’s Topics……… Ceramics Polymers and Composite materials  What Are Ceramics? comes from the Greece word keramicos, which means burnt stuff broadly classed as inorganic non metallic materials Usually a compound, or a...

NON-METALS TECHNOLOGY LECTURE 4 Major Classes of Materials Today’s Topics……… Ceramics Polymers and Composite materials  What Are Ceramics? comes from the Greece word keramicos, which means burnt stuff broadly classed as inorganic non metallic materials Usually a compound, or a combination of compounds, between metallic and nonmetallic elements (mainly, O, N, C, B) always composed of more than one element (Al2O3, SiO2, NaCl, SiC, etc.) bonds are either totally ionic, or combination of ionic and covalent Common properties High melting point and high refractoriness (except glass) Generally electrical and thermal insulators Generally hard and strong with low plasticity Low fracture toughness (brittle) Chemically inert Many ceramics have low cost (bricks) Wide range of appearance Ceramic Structure More than one type of atoms (cations, anions). Complex structures, based on BCC, FCC, and HCP. Structures are named based on the first mineral that is discovered to have the structure. (e.g., rocksalt structure) Have low packing density Silicate structures Based on SiO44- tetrahedron Si-O bonding is largely covalent, but overall SiO4 block has charge of -4. Various silicate structures are formed by different ways of arranging SiO44- blocks. - vertex (ring) - edge (chain) - face (sheet) Defects in Ceramic Structure Like metals, defects such as vacancies and substitutional atoms are present. Slip is difficult in polycrystalline ceramics, so defects have little effect on strength. But, defects have significant influence on electric properties. Classification of Ceramics based on COMPOSITION Silicate Ceramics: presence of glassy phase in a porous structure - clay ceramics (with mullite – 3Al2O3.2SiO2) - silica ceramics (with cordierite 2MgO.2Al2O3. 2SiO2) Oxide Ceramics: dominant crystalline phase, with small glassy phase - single oxide (Al2O3), modified oxide (zirconia toughened alumina) - mixed oxide (mullite, BaTiO3) Non-oxide Ceramics: - carbon, SiC, BN, TiB2, sialon Glass-ceramics: partially crystallized glass - SiO2-Li2O, etc. Ceramic Fabrication Methods What is a Polymer ? Polymer is a large molecule consisting of repeated chemical units (‘mers’) joined together, like beads on a string. Usually contain 5 or more monomers, and some may contain 100s or 1000s of monomers in each chain. High molecular weight (M); e.g., polyethylene (PE)  Molecular forces in polymers 1. Intramolecular forces Forces between atoms in one chain generally covalent bonds (strong) 2. Intermolecular forces Forces between two chains: - van der Waals forces (PE) - hydrogen bridges (PS) (stronger) Can become very strong as M increases 3. Entanglements (physical) Note: In the crystalline state, the van der Waals bonds are important. In the rubbery amorphous state, the entanglements are important. Hydrocarbon Molecules Most polymers are organic, and formed from hydrocarbon molecules Each C atom has four e- that participate in bonds, each H atom has one bonding e- Polymer Molecules Polymer molecular shape Polymer molecular structure Polymer Crystallinity Classification of Polymers Polymer Processing Polymer Forming  Polymer Joining Cementing with a solution of the same polymer in a volatile solvent. The solvent softens the surface, and the dissolved polymer molecules bond them together Monomer-cementing, where surfaces are coated with monomer which polymerize onto the pre-existing polymer chains, creating a bond. Use of epoxy additives and various snap fasteners; must be designed to distribute the fastening load uniformly over a wide area to avoid fracture. Can be friction-welded by bringing the rotating parts into contact; frictional heat melts the surfaces which are held under static load until they re-solidify. Joining can sometimes be avoided by integral design, in which coupled components are molded into a single unit. Reference: MCE 131 Lecture Notes by A.K.M.B. Rashid, Department of MME, BUET, Dhaka Classification of Materials (Non-metals Technology)  Classification of Materials Solid materials have been conveniently grouped into three basic classifications: 1. metals, 2. ceramics, 3. polymers. In addition, there are the composites, combinations of two or more of the above three basic material classes. Another classification is advanced materials—those used in high-technology applications—viz. semiconductors, biomaterials, smart materials, and nanoengineered materials.  Metals Materials in this group are composed of one or more metallic elements (such as iron, aluminum, copper, titanium, gold, and nickel), and often also nonmetallic elements (for example, carbon) in relatively small amounts. Atoms in metals and their alloys are arranged in a very orderly manner. With regard to mechanical characteristics, these materials are relatively stiff and strong, yet are ductile (i.e., capable of large amounts of deformation without fracture), and are resistant to fracture, which accounts for their widespread use in structural applications. Metallic materials have large numbers of nonlocalized electrons; that is, these electrons are not bound to particular atoms. Many properties of metals are directly attributable to these electrons. For example, metals are extremely good conductors of electricity and heat, and are not transparent to visible light; a polished metal surface has a lustrous appearance. In addition, some of the metals (viz., Fe, Co, and Ni) have desirable magnetic properties.  Metals Figure 1: Examples of some objects made of metals and metal alloys which include silverware (fork and knife), scissors, coins, a gear, a wedding ring, and a nut and bolt.  Ceramics Ceramics are compounds between metallic and nonmetallic elements; they are most frequently oxides, nitrides, and carbides. For example, some of the common ceramic materials include aluminum oxide (or alumina, Al2O3), silicon dioxide (or silica, SiO2), silicon carbide (SiC), silicon nitride (Si3N4), and, in addition, what some refer to as the traditional ceramics—those composed of clay minerals (i.e., porcelain), as well as cement, and glass. With regard to mechanical behavior, ceramic materials are relatively stiff and strong—stiffnesses and strengths are comparable to those of the metals. In addition, ceramics are typically very hard.  Ceramics Compressive strengths of ceramics can be as much as 10 times their tensile strengths. On the other hand, they are extremely brittle (lack ductility), and are highly susceptible to fracture. These materials are typically insulative to the passage of heat and electricity (i.e., have low electrical conductivities), and are more resistant to high temperatures and harsh environments than metals and polymers. With regard to optical characteristics, ceramics may be transparent, translucent, or opaque, and some of the oxide ceramics (e.g., Fe3O4) exhibit magnetic behavior.  Ceramics Figure 2: Examples of some objects made of ceramics (scissors, a china tea cup, a building brick, a floor tile, and a glass vase.  Composites A composite is composed of two (or more) individual materials, which come from the categories of metals, ceramics, and polymers. The design goal of a composite is to achieve a combination of properties that is not displayed by any single material, and also to incorporate the best characteristics of each of the component materials. A large number of composite types exist that are represented by different combinations of metals, ceramics, and polymers. Furthermore, some naturally-occurring materials are also considered to be composites—for example, wood and bone. There are also a lot of synthetic (or man- made) composites.  Composites One of the most common and familiar composites is fiberglass, in which small glass fibers are embedded within a polymeric material (normally an epoxy or polyester). The glass fibers are relatively strong and stiff (but also brittle), whereas the polymer is ductile (but also weak and flexible). Thus, the resulting fiberglass is relatively stiff, strong, flexible, and ductile. In addition, it has a low density. Another of these technologically important materials is the “carbon fiber-reinforced polymer” (or “CFRP”) composite—carbon fibers that are embedded within a polymer. These materials are stiffer and stronger than the glass fiber-reinforced materials, yet they are more expensive. The CFRP composites are used in some aircraft and aerospace applications, as well as high-tech sporting equipment (e.g., bicycles, golf clubs, tennis rackets, and skis/snowboards).  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.  Advanced Materials Furthermore, they may be of all material types (e.g., metals, ceramics, polymers), and are normally expensive. Advanced materials include semiconductors, biomaterials, and what we may term “materials of the future” (that is, smart materials and nanoengineered materials). The properties and applications of a number of these advanced materials includes materials that are used for lasers, integrated circuits, magnetic information storage, liquid crystal displays (LCDs), and fiber optics.  Semiconductors Semiconductors have electrical properties that are intermediate between the electrical conductors (viz. metals and metal alloys) and insulators (viz. ceramics and polymers). Furthermore, the electrical characteristics of these materials are extremely sensitive to the presence of minute concentrations of impurity atoms, for which the concentrations may be controlled over very small spatial regions. Semiconductors have made possible the advent of integrated circuitry that has totally revolutionized the electronics and computer industries (not to mention our lives) over the past three decades.  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, some of the biomaterials that are utilized in artificial hip replacements  Materials of the Future - Smart Materials Smart (or intelligent) materials are a group of new and state-of- the-art 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 (that performs a responsive and adaptive function). Actuators may be called upon to change shape, position, natural frequency, or mechanical characteristics in response to changes in temperature, electric fields, and/or magnetic fields.  Advanced Materials Four types of materials are commonly used for actuators: shape memory alloys, piezoelectric ceramics, magnetostrictive materials, and electrorheological/magnetorheological fluids. Shape memory alloys are metals that, after having been deformed, revert back to their original shapes when temperature is changed. Piezoelectric ceramics expand and contract in response to an applied electric field (or voltage); conversely, they also generate an electric field when their dimensions are altered. The behavior of magnetostrictive materials is analogous to that of the piezoelectrics, except that they are responsive to magnetic fields.  Smart Materials Also, electrorheological and magnetorheological fluids are liquids that experience dramatic changes in viscosity upon the application of electric and magnetic fields, respectively. Materials/devices employed as sensors include optical fibers, piezoelectric materials (including some polymers), and microelectromechanical devices (MEMS). For example, one type of smart system is used in helicopters to reduce aerodynamic cockpit noise that is created by the rotating rotor blades. Piezoelectric sensors inserted into the blades monitor blade stresses and deformations; feedback signals from these sensors are fed into a computer-controlled adaptive device, which generates noise-canceling antinoise.  Smart Materials Four types of materials are commonly used for actuators: shape memory alloys, piezoelectric ceramics, magnetostrictive materials, and electrorheological/magnetorheological fluids. Shape memory alloys are metals that, after having been deformed, revert back to their original shapes when temperature is changed. Piezoelectric ceramics expand and contract in response to an applied electric field (or voltage); conversely, they also generate an electric field when their dimensions are altered. The behavior of magnetostrictive materials is analogous to that of the piezoelectrics, except that they are responsive to magnetic fields. Also, electrorheological and magnetorheological fluids are liquids that experience dramatic changes in viscosity upon the application of electric and magnetic fields, respectively. Materials/devices employed as sensors include optical fibers, piezoelectric materials (including some polymers), and microelectromechanical devices (MEMS). For example, one type of smart system is used in helicopters to reduce aerodynamic cockpit noise that is created by the rotating rotor blades. Piezoelectric sensors inserted into the blades monitor blade stresses and deformations; feedback signals from these sensors are fed into a computer-controlled adaptive device, which generates noise-canceling antinoise.  Nanoengineered Materials Until very recent times the general procedure utilized by scientists to understand the chemistry and physics of materials has been to begin by studying large and complex structures, and then to investigate the fundamental building blocks of these structures that are smaller and simpler. This approach is sometimes termed “topdown” science. However, with the advent of scanning probe microscopes, which permit observation of individual atoms and molecules, it has become possible to manipulate and move atoms and molecules to form new structures and, thus, design new materials that are built from simple atomic-level constituents (i.e., “materials by design”).  Nanoengineered Materials This ability to carefully arrange atoms provides opportunities 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. Thank You!!!