04 Introduction to Materials:

Transcription

1 A. K. M. B. Rashid Professor, Department of MME BUET, Dhaka 04 Introduction to Materials: Life Cycle, Classification and Properties of Materials Topics to Cover Source of materials Life cycle of materials Recycling of materials and the green technology Classification of materials and their distinguishing features References: 1. Shackelford. Introduction to Materials Science for Engineers 2. Callister & Rethwisch. Materials Science and Engineering: An Introduction, 9 th Ed, Ch01, pp.5-14.

2 Sources of Materials Primary sources (natural resources) Minerals obtained by mining, drilling or digging in the earth inorganic, naturally occurring, crystalline solid of definite composition Rocks matter of which the earth s crust is comprised tends to be mixtures of two or more minerals need not to be crystalline nor of a fixed composition Secondary sources Industrial scrap damaged/defective products e.g., foundry returns, glass culets Products after use recycling e.g., steel scrap, old aluminium containers, plastic bottles Fossil fuels coal, oil or natural gas from the decomposition of organic materials (i.e., plants and animals) 3/32 Life Cycle of Materials From Cradle to the Grave Extraction, Refining and Processing Basic Materials Metals, Powders, Papers, Cement, Chemical, Fibres Manufacturing Process Raw Materials ore, coal, sand, rock, oil, wood recycle Engineering Materials Single Crystals, Alloys, Ceramics, Plastics, Composites Mine, Drill, Harvest Product Design, Manufacture, Assembly The Earth reuse Products Dispose Waste Performance, Service, Use 4/32

3 Energy Considerations The earth s materials are in a closed system, not an infinite reservoir Each step in the materials cycle consumes energy In order of increasing energy consumption: Reduce amount of material used Reuse existing material Recycle existing material scrap recovery these options also conserve raw materials Produce new material from natural resources 5/32 Environmental considerations Each step in the materials cycle produces byproducts Solid waste: litter; landfills Liquid waste: water pollution Gaseous waste: air pollution A mud lake Health impact Control of toxic materials (Pb in solders; Cr; volatile organics; ) Plastic debris Rivers to sea 6/32

4 Recycle of Materials Disposal and recycling are important stages in materials cycle where materials science and engineering plays a significant role. The green technology Use of materials that can be produced with lower environmental impact and be recycled easily The issues of recyclability and disposability are important when new materials are being designed and synthesized. During materials selection processes, the ultimate disposition of the materials employed should be an important criterion. Design the product so that different materials used can be separated easily Use production techniques that reduce environmental impact by consuming less energy and produce fewer byproducts Establish processes to recycle or reuse components and materials 7/32 From environmental perspective, ideal material should be either totally recyclable or completely biodegradable. Recyclable: a material, after having completed its life cycle in one component, could be re-processed, re-enter the materials cycle, and then be re-used in another component a process that could be repeated an indefinite number of times. Completely biodegradable: by interactions with the environment (natural chemicals, micro organisms, oxygen, heat, sunlight, etc.), material deteriorates and returns to virtually the same state in which it existed prior to the initial processing. Engineering materials exhibit varying degrees of recyclability and biodegradability. 8/32

5 What materials are recycled? Metals Lead (lead batteries) Aluminum (aluminum cans) Iron/steel (scrap metals) Gold, silver, platinum (contacts in electronic devices) Glasses Food containers Rubber and plastics (mainly thermoplastics) Plastic containers and bottles Tires Synthetic textile fibers Papers Newspapers, cardboard boxes, etc. 9/32 Example 1: Recycling aluminum Energy needed to re-melt 1 kg of Al cans Energy needed to extract 1 kg of Al from Al 2 O 3 Assumptions: Cans are pure Al Start at RT (298 K) Re-melt at T m of Al Input: T m,al = 933 K, DH F = J mol 1 c P,Al = 900 J kg 1 K 1 AW Al = g mol 1 Assumptions: T = 298 K 100% efficient process Input: G (given in reactions) AW Al = g mol 1 1. Energy needed to raise Al temperature from RT to MP = Sensible heat = m c P DT 2. Energy needed to melt Al = Latent heat of fusion = DH F 1 kg 900 J kg K 933 K 298 K Al 2 O 3 2Al O 2 ; G = T J G = J = 1590 KJ (per 2 mol Al) = 1590 KJ g 1 kg mol 1000 g = kj kg J mol x 1000 g kg g mol = 961 kj kg ~30 as much energy required for recycling! 10/32

6 Example 2: Recycling of plastic containers and bottles Replacing the 760,000 tons of cans wasted in 2001 produced: 55,613 tons of SOx 19,476 tons of NOx } Acid rain and smog 5.5 million tons of CO 2 84,532 tons of CO 1,025 tons total fluorides } Greenhouse gases 15,828 tons of PM (particulate matter) respiratory distress 482 tons of VOC s (Volatile Organic Compounds) 2,776 tons of organics Carcinogens } (that cause cancer) 2.7 million tons of toxic mud wastes and other residues 11/32 Classification of Materials based on composition Metals and Alloys Ceramics, Glasses, and Glass-ceramics Polymers (plastics) - Thermoplastics and Thermosets Semiconductors Composite Materials 12/32

7 Metals and Alloys Distinguishing features Relatively strong & stiff Malleable & ductile Resistant to shock & fracture: tough Moderate melting point High density Excellent conductors of heat & electricity Shiny but opaque Examples Elements on the left side of the Periodic Table Pure metal elements (Al, Cu, Fe, Zn) Alloys (e.g., Bronze, Brass, Steels) Intermetallic compounds (e.g. Ni 3 Al) Applications Electrical wiring Structures: buildings, bridges Automobiles: body, chassis, springs, engine block Airplanes: engine components, fuselage, landing gear assembly Trains: rails, engine components, body, wheels Machine tools: drill bits, hammers, screwdrivers, saw blades Shape memory materials Super alloys (turbine blades) Magnets 13/32 Several uses of steel and pressed aluminium 14/32

8 Ceramics and Glasses Distinguishing features Composed of metals and non-metals Stronger & harder than metals Low malleability & ductility Low resistant to fracture: brittle High melting point: high refractoriness Lower density than most metals Electrical & thermal insulators Can be transparent (single crystals) Example Applications Single oxides (SiO 2, Al 2 O 3, Fe 2 O 3, MgO, etc.) Mixed-metal oxides (BaTiO 3, MgAl 2 O 4, YBa 2 Cu 3 O 7-x, etc.) Nitrides (Si 3 N 4, TiN, AlN, GaN, BN) Carbides (SiC, WC, TiC) Silicate glasses (soda-lime, borosilicate, Pyrex) Whiteware (e.g. porcelains) Structural or engineering ceramics (high-temperature, load bearing) Electrical ceramics (capacitors, insulators, transducers) Abrasives (emery paper, grinding wheel) Thermal insulation and coatings Glasses (e.g. soda-lime glass, crystal glass, optical fibres) Chemically bonded ceramics (e.g. cement and concrete) Bioceramics (artificial bone joints) Magnetic materials (audio/video tapes, hard disks) 15/32 Examples of ceramic and glass materials ranging from household products to high performance engineering ceramics and bio-ceramics. 16/32

9 Polymers Organic materials, either natural or synthetic in nature Derived from two Greek words: poly means many mer means part (single hydrocarbon molecules) Long chained molecules composed of many mer s bonded together by a process called polymerisation Example: Polyethylene - (C 2 H 4 ) n - n = Elements commonly associated with polymers: H (polyethylene) N (nylon) O (acrylic) F (PTFE or Teflon) Si (silicone), etc. 17/32 Distinguishing features Organic materials, composed primarily hydrocarbons Usually not strong but very ductile Low melting point Low density Poor conductor of electricity & heat Can be transparent Examples Polyethylene (PE) Polystyrene (PS) Polyurethane (PU) Polyvinylchloride (PVC) Nylon Rubbers Perspex (PMMA) Applications Adhesives and glues Containers Mouldable products (computer casings, telephone handsets) Clothing and upholstery material (vinyl, polyester, nylon) Water-resistant coatings (latex) Biodegradable products Biomaterials (organic/inorganic interfaces) Liquid crystals Low-friction materials (teflon) Synthetic oils and greases Gaskets and O-rings (rubber) Soaps and surfactants 18/32

10 Polymers or commercially called plastics needs no introduction 19/32 Semiconductors Similar to polymers, semiconductors have great (but invisible ) social impact. Technology has revolutionized society, but solid state electronics is revolutionizing the technology itself. These small groups of elements and compounds possess electrical conductivity intermediate between metals and insulators. 20/32

11 Distinguishing features Made primarily from metalloids Regular arrangement of atoms (crystals) Intermediate conductivity of electricity Extremely controlled chemical purity Opaque to visible light Shiny appearance Some have good plasticity, but others are fairly brittle Some have an electrical response to light Applications Computer CPUs Electrical components (transistors, diodes, etc.) Solid-state lasers Light-emitting diodes (LEDs) Flat panel displays Solar cells Radiation detectors Micro-electro-mechanical devices (MEMS) Examples Elemental semiconductor (Si, Ge, Sn) Compound semiconductor (GaAs, CdS, ZnO) 21/32 (a) Micro-Electrical-Mechanical Systems (MEMS) (b) Si wafer for computer chip devices 22/32

12 Composites Distinguishing features Physical mixture of two or more different materials (e.g., metal/ceramic, ceramic/polymer, polymer/polymer) Superior properties to that of either of the constituents Properties depend on amount and distribution of each material The entire Periodic Table is involved (except noble gases) Applications Sports equipment (golf club shafts, tennis rackets, bicycle frames) Aerospace materials (Space shuttle, heat shields) Thermal insulation Concrete "Smart" materials (for sensing and responding) Brake materials 23/32 Examples Particulate composites (cermets, duralumin) Laminate composites (golf club shafts, tennis rackets) Fiber reinforced composites (e.g. fiberglass) Wood (cellulose-fibre-reinforced lignin) Concrete (aggregate composite of cement, rock and sand) Polymer matrix composites (PMC) (glass fibres in a polymer: GFRP, CFRP) Metal matrix composites (MMCs) (SiC in aluminium, ) Ceramic matrix composites (CMCs) (zirconia toughened alumina, cermets (Ag in Alumina)) 24/32

13 Polymer composite materials, reinforcing glass fibers in a polymer matrix 25/32 Classification of Materials based on structure Amorphous material shows no long-range periodic arrangement. Crystalline material is a material comprised of one or many crystals. In each crystal, atoms or ions show a long-range periodic arrangement. Single crystal is a crystalline material that is made of only one crystal (there are no grain boundaries). Polycrystalline material is a material comprised of many crystals (as opposed to a single-crystal material that has only one crystal). 26/32

14 Classification of Materials based on function Aerospace C-C composites, SiO 2, Amorphous Silicon, Aluminium alloys, Superalloys Biomedical Hydroxyapatite (HA), Ti-alloys, Stainless Steel, Shape-memory alloys, Al 2 O 3, Plastics, PZT Electronic materials Si, GaAs, Ge, BaTiO 3, PZT, YBa 2 Cu 3 O 7-x, Al, Cu, W, Conducting polymers Energy technology & environmental technology UO 2, Ni-Cd, LiCoO 2, ZrO 2, Amorphous Silicon Magnetic materials Fe, Fe-Si, NiZn and MnZn ferrites, Co-Pt-Ta-Cr, g-fe 2 O 3 Optical materials SiO 2, GaAs, Glasses, Al 2 O 3, YAG, ITO Smart materials PZT, Ni-Ti shape-memory alloys, MR fluids, Polymer gels Structural Steels, Aluminium alloys, Concrete, Fibreglass, Plastics, Wood 27/32 Comparison of Properties of Materials Density Elastic Modulus 28/32

15 Strength Resistance to Fracture 29/32 Electrical Conductivity 30/32

16 TABLE 1-2 Strength-to-weight ratio of various materials Strength Density Strength-to-weight Material (lb/in 2 ) (lb/in 3 ) ratio (in) Polyethylene 1, x 10 6 Pure aluminium 6, x 10 6 Alumina (Al 2 O 3 ) 30, x 10 6 Epoxy 15, x 10 6 Heat-treated alloy steels 240, x 10 6 Heat-treated aluminium alloys 86, x 10 6 Carbon-carbon composite 60, x 10 6 Heat-treated titanium alloys 170, x 10 6 Kevlar-epoxy composite 65, x 10 6 Carbon-epoxy composite 80, x /32 Increasing temperature normally reduces the strength of a material. Polymers are suitable only at low temperatures. Some composites, special alloys, and ceramics, have excellent properties at high temperatures. 32/32

17 Next Class 05 Atomic Bonding and Materials Properties