Chemistry Of Engineering Materials PDF

CHEMISTRY OF ENGINEERING MATERIALS After studying this chapter you should be able to: Describe and compare the composition, structure, classes, properties and performance of the engineering materials; Determine the types of bonds found in the engineering materials and their applications in na...

CHEMISTRY OF ENGINEERING MATERIALS After studying this chapter you should be able to: Describe and compare the composition, structure, classes, properties and performance of the engineering materials; Determine the types of bonds found in the engineering materials and their applications in nanotechnology. Why is it important to study chemistry of engineering materials? ▪To make any engineered device, structure or product, engineers need the right materials. ▪It is important for all architects and engineers to understand the chemistry of building materials so that they understand better the chemical processes involved and there will be more accurate results and long-lasting outcomes in any undertaking.  Engineers work with metals, ceramics, and plastics to create new materials. Engineers develop, process, and test materials used to create a range of products, from computer chips and aircraft wings to golf clubs and biomedical devices.  ENGINEERING MATERIALS ENGINEERING MATERIAL is defined as a component of inanimate stuff that an engineer may make use of in the course of his professional duties (used to produce products according to the needs and demand of society). Engineering Materials are used as raw material for any sort of construction or manufacturing in an organized way of engineering application.  MECHANICAL ENGINEERING MATERIALS Mechanical engineers look for materials that can withstand high temperatures so that gas turbines, jet engines, and other machinery can function more effectively, as well as materials that can withstand wear so that bearing materials may be manufactured. What materials are used in the automobiles? There are different types of materials used to design a car, and these materials determine the durability, design, and sometimes the speed of the vehicle. Cars are made of steel, plastic, aluminum, rubber, glass, fiberglass, lead, copper, titanium, magnesium  CIVIL ENGINEERING MATERIALS Civil Engineering deals with constructing, designing, and maintaining a physical environment. Civil Engineering construction works like bridges, dams, houses, roads, pavements are carried out with raw materials like stone, chips, cement, clay, paint, bars, etc.  Categories of Construction Materials CONCRETE WOOD METAL MASONRY GLASS  ELECTRICAL ENGINEERING MATERIALS Electrical engineers look for materials that will allow electrical equipment or machines to run at a quicker pace while minimizing the amount of power that is lost in the process, Examples of such items are electric machines, transformers, switchgear and control gear, measuring instruments, protective devices, wiring systems, and current-using equipment.  ELECTRICAL ENGINEERING MATERIALS The materials in use in electrical engineering can be divided into four important categories, according to their use: Materials used to conduct electricity, Materials used to insulate, Materials used to strengthen magnetic fields, Materials used to make supports, casings, and other mechanical parts, and co-inforcement  Properties of Engineering Materials Atomic structure Properties are influenced by Electromagnetic structure (Bonding characteristics) Both these aspects are essentially governed by properties of electrons including sharing of electrons.  Materials can be classified Based on state (phase) a given material can be Gas, Liquid or Solid (Based on the thermodynamic variables: Pressure, Temperature,…). ✔ Intermediate/coexistent states are also possible ✔ Kinetic variables can also affect how a material behaves: e.g. at high strain rates some materials may behave as solids and as a liquid at low strain rates Based on Structure (arrangement of atoms/molecules/ions) materials can be ▪ Crystalline ✔ Quasi- crystalline or Amorphous Intermediate states (say between crystalline and amorphous; i.e. partly crystalline) are also possible. ✔ Liquid Crystals are between Liquids and Crystals.  ▪ Similarly Solid Electrolytes (also known as fast ion conductors and superionic conductors) are also between crystals and liquids. These materials have a sub lattice which is ‘molten’ and the ions in this sub lattice are highly mobile (these materials are similar to liquid electrolytes in this sense).  Crystalline Materials can be single crystals polycrystalline Single crystal or monocrystalline solid is any solid object in which an orderly three-dimensional arrangement of the atoms, ions, or molecules is repeated throughout the entire volume. The crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries. Certain minerals, such as quartz and the gemstones, often occur as single crystals; Synthetic single crystals, especially silicon and gallium arsenide, are used in solid-state electronic devices such as integrated circuits and light-emitting diodes methylammonium lead iodide perovskite (MAPI) crystal Quartz/silica SiO2 A high-purity (99.999 %) Tantalum single crystal  CRYSTAL STRUCTURE is atomic arrangement in solids. A CRYSTAL is defined as an orderly array of atoms in space. POLYMORPHISM is the ability of solid material to exist in more than one form or crystal structure.  CRYSTALLINE MATERIAL In a crystalline structure , the atoms are arranged in three dimensional array called a lattice. The lattice has a regular repeating configuration in all directions. Single Unit lattice atom Cell  POLY CRYSTALS Most engineering materials are poly crystals. Picture on the right shows a Nb-Hf-W plate with an electron beam weld Each "grain" is a single crystal. 1 If grains are randomly oriented, mm overall component properties are not directional. Grain sizes typ. range from 1 nm to 2 cm (i.e., from a few to millions of atomic layers).  AMORPHOUS MATERIAL The material has no regular arrangement of their molecules. Materials like glass and paraffin are examples of amorphous material. These materials have properties of solids. They have definite volume and shape and diffuse slowly.  CRYSTAL STRUCTURE IN METALS Majority of metals falls in either of the following crystal structure BCC (BODY CENTERED CUBIC) FCC (FACE CENTERED CUBIC) HCP (HEXAGONAL CLOSE PACKED)  CRYSTAL STRUCTURE IN METALS BCC (BODY CENTERED CUBIC) Examples:α-iron, Mo, W, V, Ta, Cr, Na, K BCC (BODY CENTERED CUBIC)  BCC (BODY CENTERED CUBIC) In this structure, there are 8 corner atoms and one atom at in the interior i.e. in the center of the unit cell with no atom on face.  FCC (FACE CENTERED CUBIC) Examples:γ-iron, Cu,Au,Ag,Al,Pb, Ni, Pt FCC (FACE CENTERED CUBIC)  FCC (FACE CENTERED CUBIC) In this structure, there are 8 corner atoms and 6 atoms at center of the face and interior atom HCP (HEXAGONAL CLOSE PACKED) Examples: Mg,Zn,Be,Cd,Co,Zr,Ti  HCP (HEXAGONAL CLOSE PACKED) For HCP structure , there are 12 corner atoms, 2 atoms at the centers of the above two faces and 3 atoms in the interior of the unit cell.  AMORPHOUS MATERIAL Amorphous solid is any non-crystalline solid in which the atoms and molecules are not organized in a definite lattice pattern. These materials have properties of solids. They have definite volume and shape and diffuse slowly. Such solids include Plastics, Glass, Rubber, Metallic glass, Polymers, Fused silica, Pitch tar, paraffin and gel.  AMORPHOUS MATERIAL The difference between crystalline and amorphous materials is primarily determined by the degree of ordering. Amorphous materials have no sharp melting point and lack definite structure. The amorphous solids have a wide range of melting and have no characteristic shape. They are flammable.  PHYSICAL PROPERTIES OF MATERIALS DENSITY DENSITY of a substance is its MASS PER UNIT VOLUME. where Ρ IS THE DENSITY, m IS THE MASS, AND V IS THE VOLUME. MELTING POINT The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. The melting point of a substance depends (usually slightly) on pressure and is usually specified at standard pressure.  PHYSICAL PROPERTIES OF MATERIALS SPECIFIC HEAT is energy required to change the temperature of an object by 1 degree C. The SI unit of heat capacity is Joule per Kelvin. Metals have lower specific heat capacity than plastics. Therefore they require less heat to reach a particular temperature than plastics. THERMAL EXPANSION is the tendency of matter to change in volume in response to a change in temperature, through heat transfer.  PHYSICAL PROPERTIES OF MATERIALS THERMAL CONDUCTIVITY It is the property of a material to conduct heat. Often denoted k, λ, or κ. In SI units, thermal conductivity is measured in watts per meter kelvin (W/(m·K)) High energy generation rates within electronics or turbines require the use of materials with high thermal conductivity such as Cu, Al, and Ag.  PHYSICAL PROPERTIES OF MATERIALS Materials with low thermal conductance, such as polystyrene and alumina, are used in building construction or in furnaces to slow the flow of heat, i.e. for insulation purposes. Low thermal conductivity refers to a material's inability to conduct heat efficiently. Materials with low thermal conductivity are good insulators. They tend to prevent heat transfer and have fewer free electrons.  PHYSICAL PROPERTIES OF MATERIALS Polystyrene's thermal resistance capacity is well suited for the walls and roofs of buildings and it is proven to be efficient in maintaining the indoor temperature. AL2O3 is an electrical insulator but has a relatively high thermal conductivity (30 Wm−1k−1) for a ceramic material. Alumina (Al2O3) is a widely used material for highly insulating films due to its very low electrical conductivity, even at high temperatures.  PROPERTIES OF MATERIALS Based on the Band Structure The band structure represents the energy levels of solids, and it is often used to determine whether a material is a conductor, semiconductor, or insulator. It can also be used to determine whether the material has direct or indirect band gaps and the valence bands and conduction bands (VB and CB).  PROPERTIES OF MATERIALS Based on the Band Structure Metals carry electricity with the aid of valence electrons, according to the band theory of metals. The same-energy atomic orbitals of metals combine to produce molecular orbitals near energy to one another to form a band. Metals conduct electricity because only a very small amount of energy is required to excite an electron from a filled level to an empty one, where it is free to migrate rapidly throughout the crystal in response to an applied electric field.  PROPERTIES OF MATERIALS Based on the Band Structure Metalloids have the physical properties of metals, but their chemical properties are closer to those of nonmetals. Semimetals tend to make excellent semiconductors, although most of the elements themselves are not technically semiconducting. The metalloids are a unique group of elements that share properties of both metals and nonmetals. They're also called semimetals because of the shared properties of these elements along the dividing line between metals and nonmetals.